i A thesis Submitted for the degree Doctor of Philosophy by Anthony Blazevich, BSc (Hons) School of Exercise Science and Sport Management Southern Cross University, Lismore, Australia 2000. EFFECT OF MOVEMENT PATTERN AND VELOCITY OF STRENGTH TRAINING EXERCISES ON TRAINING ADAPTATIONS DURING CONCURRENT RESISTANCE AND SPRINT/JUMP TRAINING
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Effect of Movement Pattern and Velocity of Strength Training
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i
A thesis Submitted for the degree
Doctor of Philosophy
by
Anthony Blazevich, BSc (Hons)
School of Exercise Science and Sport Management
Southern Cross University, Lismore, Australia
2000.
EFFECT OF MOVEMENT PATTERN AND
VELOCITY OF STRENGTH TRAINING
EXERCISES ON TRAINING ADAPTATIONS
DURING CONCURRENT RESISTANCE AND
SPRINT/JUMP TRAINING
ii
DECLARATION
The work presented in this thesis is the original work of the author except where
acknowledged in the text. I hereby declare that I have not submitted this material
either in whole or in part for a degree at this or any other institution.
____________________ _________________
Anthony Blazevich.
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ACKNOWLEDGMENTS
I’d first of all like to acknowledge my supervisors Dr. Robert Newton and Assoc.
Prof. Roger Bronks who gave me the freedom to pursue my research interests
while keeping a firm watch over me. Their belief in my ability has given me the
confidence to complete my this thesis.
Assoc. Prof. Greg Wilson who brought me to Southern Cross University and
ensured that I remembered exactly what I was wanted to research and was not
only my first PhD supervisor, but also helped me through many tough times.
My fellow postgraduates, Nick Gill, Anthony Giorgi, Tony Shield, Adam
Bryant, Nathan Deans and Phil Smith who all at some point or another helped
me with my research and put up with my whingeing.
The School of Exercise Science and Sport Management for providing me with
the opportunity to develop my knowledge in the Sport Science field, and for
providing the funding for my research. Also, the American Society of
Biomechanics whose Student Grant-in-Aid progam jointly funded my research.
Mr. Terry Woods for having faith in my teaching and researching ability and
allowing me to teach while completing the final stages of my Thesis.
My parents, Ron and Yvonne, and my brother Michael for letting me know that
it wasn’t just OK, but obligatory for me to fulfil my ambition to become the best
sports scientist I could be even though I’d have to live as a student for many
years.
To all of the subjects, and my friends in Lismore, who so graciously gave their
time and effort to help me. Many of my subjects offered their time and support for
little personal reward, I will never forget that.
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To my genuine support staff Carol Hayllar, Sharee Mulcahy, Carol Hartmann,
Tiffeny Byrnes, Rob Baglin and Mark Fisher. They not only provided support
essential for me to complete my work, but to kept me sane when I was bordering
on insanity.
A final mention must also be made to two people who have been there for me
through both the tough times and the good, who provided inspiration and support
when I needed it, who counselled me when I was down, and were unselfishly
happy for me when I achieved. First, Nick Gill who was there from the beginning
to not only help me be the scientist I am today, but the person I am as well. No
one has accompanied me through more of a metamorphosis than him. And
second, Jen Goward for her care and constant belief in my ability, and also for
putting up with my constant mood swings.
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PUBLICATIONS/PRESENTATIONS FROM THESIS
Blazevich, A.J. & Gill, N. (2001). Reliability and validity of two isometric squattests. Journal of Strength and Conditioning Research. In Press.
Conference Presentations
Blazevich, A.J.*, Newton, R.U. & Bronks, R. (2000). Podium Presentation -Movement specificity of muscle architectural changes after concurrent sprint/jumpand resistance training. The 2nd International Conference on Weightlifting andStrength Training, Ipoh Malaysia, 2000.
Blazevich, A.J.*, Bronks, R. & Newton, R.J. (2000). Movement specificity ofmuscle architectural changes after concurrent sprint/jump and resistancetraining.2000 Pre-Olympic Congress, Brisbane Australia, 2000.
Blazevich, A.J.*, Newton, R.U., Sharman, M., Bronks, R. & Gill, N. (2000).Specificity of Strength training exercises to the vertical jump and 20 m sprint tests.Australian and New Zealand Society of Biomechanics Conference, Gold CoastAustralia, 2000.
Blazevich, A.J.*, Newton, R.U., Bronks, R. & Gill, N. (1999). Influence ofmovement pattern of resistance training on athletic performance during concurrentresistance and task training. IOC World Congress in Sports Science, SydneyAustralia, 1999.
Blazevich, A.J.*, Newton, R.U., Sharman, M., Bronks, R. & Gill, N. (1999).Specificity of strength training exercises to the sprint run and vertical jump tests.IOC World Congress in Sports Science, Sydney Australia, 1999.
CONFERENCE PRESENTATIONS........................................................................................................ V
TTAABBLLEE OOFF CCOONNTTEENNTTSS............................................................................................................................. II
2.2 EFFECT OF RESISTANCE TRAINING MOVEMENT PATTERN ON TASK PERFORMANCE ............. 14
2.2.1 Body position ................................................................................................................................... 14
2.2.2 Joint angles and muscle lengths ......................................................................................................... 16
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2.2.3 Unilateral versus bilateral specificity ................................................................................................. 23
2.2.4 Type of contraction ........................................................................................................................... 25
2.2.5 Type of pre-contraction ..................................................................................................................... 26
4.2.3 Data analysis..................................................................................................................................... 93
4.4.4 Future research ................................................................................................................................. 99
5.2.3 Determination of testing loads ......................................................................................................... 104
5.2.4 Test contractions............................................................................................................................. 105
5.2.5 Data analysis................................................................................................................................... 105
6.2.3 Data Analysis ................................................................................................................................. 118
7.2.5 Data analysis................................................................................................................................... 146
yrs, height = 1.81 ± 0.09 m, weight = 96.3 ± 10.0 kg) performed a standard warm-
up including five minutes of stationary cycling at a self-selected workload and
three to five trials each of a VJ, BJ, SQ with a load of 60% of bodyweight and FHS
with no load added to the sled (the FHS is described later). After reflective
markers were placed on joint centres of the head, trunk and limbs, subjects
performed three maximal trials of single- and double-leg vertical and standing
broad jumps with their arms in different positions, squat lifts and jump-squats with
different loads, and single- and double-leg FHS with different loads. The
movements were recorded by a high-speed video system (200 Hz) and data sets
relating to joint movement (joint angular displacement, velocity and acceleration)
were calculated after digitising joint markers using Peak Motus software (Peak
Performance Technologies, USA).
For all exercises studied, the timing of joint angle changes was the same during
the descending phase with hip, knee and ankle joints flexing (dorsiflexion at the
ankle) simultaneously. However, joint extension during the ascending phase was
different between the tasks. Joint extension occurred sequentially for the VJ, BJ
and JSQ exercises with hip extension preceding both knee and ankle
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(plantarflexion) extension. For the slower squat lifts (SQ) joint extensions
occurred simultaneously. The FHS was performed differently to these however in
that hip and knee extension occurred simultaneously with ankle plantarflexion
delayed. The use of an arm swing during VJ and BJ exercises caused the hip
angle to become smaller (more closed) at the end of the transition phase possibly
allowing greater use of the larger hamstring, gluteal and erector muscles. VJ’s
performed without arm swing exhibited the same joint changes as the JSQ
exercise but there were differences in hip joint range of motion between the two
exercises when the arms used.
From these results it was concluded that the joint angle changes of subjects
performing the VJ without arm swing were similar to that of the JSQ. The two
tasks are also performed bilaterally and in a vertical body position, thus their
movement patterns can be considered comparable. However the movement
patterns of the BJ and FHS were dissimilar with the timing of joint angle changes
being different. Joint angle changes for the FHS were then compared to
published data for the acceleration phase of sprint running (Jacobs & Ingen
Schenau, 1992). There was good agreement in the timing and magnitude of joint
angle changes for these two tasks. Given both exercises are performed with the
body in a semi-prone position and the FHS can be performed unilaterally, the
movement patterns of these two exercises could also be considered comparable.
xvi
STUDY TWO: RELIABILITY AND VALIDITY OF TWO ISOMETRIC SQUAT
AND FORWARD HACK SQUAT TESTS
Given the results of Study One, the FHS and SQ exercises were chosen for use in
training and testing in this thesis. However, performing 1-RM tests for the
purposes of assessing performance or designating training loads can be a long
process. It would therefore be ideal to use simpler isometric tests for these
purposes. The aim of this study was first to examine the reliability of isometric
squat (ISQ) and isometric forward hack squat (IFHS) tests to determine if
repeated measures on the same subjects yielded reliable results, and second to
examine the relationship between isometric and dynamic measures of strength to
assess validity. Fourteen male subjects (age range = 19 – 26 yrs) performed
maximal ISQ and IFHS tests on two occasions and 1-RM SQ and FHS tests on
one occasion. The two tests were found to be highly reliable (ICCISQ = 0.97 and
ICCIFHS = 1.00). There was a strong relationship between average ISQ and 1-RM
squat performance, and between IFHS and 1-RM FHS performance (rSQ = 0.77,
rFHS = 0.76; p<0.01) but a weak relationship between squat and FHS test
performances (r<0.55). There was also no difference between observed 1-RM
values and those predicted by our regression equations. Errors in predicting 1-
RM performance were in the order of 8.5% (SEE = 13.8 kg) and 7.3% (SEE =
19.4 kg) for ISQ and IFHS respectively. Correlations between isometric and 1-RM
tests were not of sufficient size to indicate high validity of the isometric tests.
Together the results of the present study suggest that ISQ and IFHS tests could
detect small differences in multi-joint isometric strength between subjects, or
performance changes over time, and that the scores in the isometric tests are well
related to 1-RM performance. However, there was a small error when predicting
1-RM performance from isometric performance so these tests probably cannot
discriminate between small changes in dynamic strength. The weak relationship
between squat and FHS test performance can be attributed to differences in the
movement patterns of the tests.
xvii
STUDY THREE: RELIABILITY OF UNILATERAL AND BILATERAL
FORWARD HACK SQUAT TESTS
The purpose of this study was to examine the reliability of complex, dynamic
unilateral and bilateral FHS tests and determine whether the loads lifted during the
tests affected their reliability. Eleven active, male subjects (age = 20.5 ± 1.1 yrs)
performed two maximal repetitions of a FHS at each of two loads (loads equal to
40% and 70% of maximal isometric force were added to the sled of the machine)
in both uni- and bilateral conditions. Reliability of both uni- and bilateral tasks was
high (ICC = 0.90 and 0.95 respectively) when the heavier load was lifted (70% of
isometric maximum). However, when the load was lighter (40% of isometric
maximum) reliability was low (ICC = 0.70 and 0.64 for unilateral and bilateral trials
respectively). Thus, while the laterality of movement did not affect task reliability,
the load lifted did. The most likely explanation for this result is that the greater
load promotes greater kinaesthetic feedback from muscle spindles, golgi tendon
organs and pacinian corpuscles to the spinocerebellum. In addition, subjects
displayed a bilateral deficit; a phenomenon that has been shown in past research.
This result indicates that the uni- and bilateral tests were measuring different
entities. Thus, testing should be performed according to the type of strength that
must be measured (unilateral or bilateral).
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STUDY FOUR: PERFORMANCE RELATIONSHIPS BETWEEN VERTICAL
JUMP, SPRINT RUNNING AND STRENGTH TRAINING EXERCISES:
IMPLICATIONS FOR MOVEMENT SPECIFICITY
The results from Study One suggested that two pairs of tasks, 1) JSQ and VJ
(with arms crossed over the chest), and 2) FHS and acceleration phase of a sprint
run, were comparable in their movement patterns. The purpose of this study was
to investigate the relationship between subjects’ performances in tests of these
exercises to determine whether movement pattern alone determined performance
similarities between tasks. Thirty-one active subjects including 23 men and eight
women who volunteered from the University population (age range = 18 - 26 yrs)
performed sprint run (20 m), VJ, SQ and FHS tests. Relationships between
subjects’ performances were investigated by both correlation and components
analysis.
Subjects who performed well in the SQ and JSQ tests did not necessarily perform
well in the VJ tests relative to other subjects. However, the FHS and sprint tests,
and the ISQ and VJ tests, were significantly correlated (r = 0.51 – 0.73; p<0.01).
The components (from factor analysis) associated with the VJ and SQ tests, and
the FHS and sprint tests, were different; components could be described by the
force-velocity characteristics of the test exercises. The FHS and sprint tests were
however more similar based on the components under which they were placed.
The FHS may therefore be considered functionally similar to the acceleration
phase of a sprint run when tested under the conditions presented here.
Furthermore, as subjects who performed well in the ISQ also performed well in the
VJ, the two tasks must have some functional similarity. The ISQ requires high
muscle forces over small ranges of motion for optimum performance while high
forces at the eccentric/concentric (downward/upward) transition point in the VJ is
also important. Therefore, the movement pattern and ‘neuromuscular intent’ of
the exercises, but not necessarily their velocity, may have contributed to their
movement specificity. The results have implications for our understanding of
movement specificity.
xix
STUDY FIVE: NEUROMUSCULAR AND PERFORMANCE ADAPTATIONS
TO SHORT-TERM CONCURRENT RESISTANCE AND SPRINT/JUMP
TRAINING.
Given that, for most athletes, resistance training forms only part of a total training
program, it is important that adaptations to resistance training (RT) are described
when task training is performed concurrently. The purpose of this study was first
to determine whether changes in VJ and sprint running test performances after a
period of concurrent resistance- and sprint/jump training were related to the
movement pattern of RT exercises in well-trained subjects. From the results of
studies one and two, and given the known specificity of adaptations to resistance
training, one might expect that subjects who perform JSQ training would improve
their VJ, while subjects who perform FHS training would improve their sprint, more
than other subjects. A second purpose was to examine changes in the
neuromuscular system when the RT was performed concurrently with VJ and
sprint/jump training.
30 active individuals volunteered from the University population (Age range = 18 –
26 yrs). Of the 30 subjects, 23 (eight women & 15 men) completed the study with
approximately equal numbers of subjects in each of three training groups
(described below). Subjects participated in four weeks of resistance- and
sprint/jump training (familiarisation) prior to a second five-week (specific) training
phase.
Following the four-week familiarisation phase, subjects were divided into three
Familiarisation(4 weeks)
Pre-test Specific training (5 weeks)Four groups: SQ, FHS & SJ
Post-test
Overview of training and testing. A familiarisation phase preceded the five-week‘specific’ training phase. Testing was performed before and after the specific trainingphase.
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training groups with male and female subjects distributed equally among the
groups. These groups were labelled squat (SQ), forward hack squat (FHS) and
sprint/jump (SJ) based on their training. All groups performed at least two
sprint/jump sessions per week with SQ and FHS groups also performing two
weight training sessions and SJ two additional sprint/jump sessions each week.
Before and after the five-week specific training phase, subjects performed 20 m
sprint, VJ, SQ, FHS and isokinetic leg extension tests. In addition to these
performance tests, muscle thickness, pennation and fascicle length were
measured at two regions of both the vastus lateralis (VL) and rectus femoris (RF)
muscles and EMG was recorded from leg musculature during performance of VJ
and sprint tasks.
After training, subjects significantly increased their 10 m sprint (p<0.05), single-
and double-leg isometric FHS force (p<0.01), force during a double-leg FHS at
40% of isometric maximum, and force during a squat at 30% of isometric
maximum (p<0.05). However, there were no significant differences between the
training groups. This suggests that the five-weeks of training was sufficient to
cause performance changes, but that the training did not result in inter-group
differences. There was also no difference in isokinetic knee extension torque at
either 30o.s-1 or 180o.s-1 but there was a trend toward SQ subjects producing their
torque at a more closed knee angle compared to FHS (ES = 0.71) and SJ (ES =
0.90) subjects. Thus there was a trend toward angle-specific torque changes with
the angle of peak torque decreasing for SQ subjects but increasing for FHS
subjects.
Muscle architectural changes were different between the training groups. In
general, subjects who performed resistance training (SQ and FHS) showed
greater pennation and shorter fascicle lengths (used as an estimate of fibre
length) in VL, while the opposite was true for SJ subjects. For RF, pennation
increased at the distal region in FHS and SQ subjects (p<0.05), but there were no
changes at the proximal region and no significant changes in fascicle length in any
group. Thus for the uni-articular VL architectural adaptations occurred in line with
xxi
those hypothesised. The lack of change in RF might be related to its biarticular
action, muscle length changes are not as great in many multi-joint movements so
the stimulus for adaptation would have been small (Jacobs et al., 1993). There
were significant increases in muscle thickness of both VL and RF although these
changes were not significantly different between the groups. Therefore the
different training regimes performed by the subjects did not differently affect their
muscle thickness.
Changes in normalised EMG during the acceleration phase of running were
inconsistent between subjects. SQ and FHS subjects (results were pooled for
these subjects to increase statistical power) exhibited greater gluteus maximus
activation during the recovery part of the stride and greater biceps femoris, vastus
lateralis and rectus femoris activity immediately prior to foot-ground contact. Such
changes may not be conducive to efficient running. There were few changes for
SJ subjects. For VJ, decreased activity of rectus femoris in the descending phase
and increased gluteus maximus in the transition phase in SQ and FHS subjects
were hypothesised to aid jump efficiency and power. Again there were few
changes in the EMG of SJ subjects. Thus RT appeared to influence EMG and
therefore possibly inter-muscular coordination, particularly in SQ and FHS
subjects. There were however no significant changes in muscle co-contraction
during the sprint or changes in muscle onset times (i.e. time at which muscle
activity significantly increased) during the VJ.
The results of this study suggest that VJ, sprint and strength changes to short-
term concurrent training are not as specific to training as when RT is performed
alone. There were no significant differences in changes in strength, VJ and sprint
performance, and few changes in isokinetic test variables between the groups.
There were however significant changes in muscle architecture that appeared
related to the training performed by subjects. Furthermore, although the EMG
recordings do not provide conclusive evidence that inter-muscular coordination
changed with training, some changes were seen. It appears that, at least in the
short term, similar gains in strength and speed can be attained by different training
xxii
regimes. However there were significant muscular, and evidence for neural,
adaptations to the training. Thus, perhaps in the long-term, the movement pattern
of training exercises and the proportion of low-velocity strength training in a
regime might affect athletic performance and this should be followed up in future
training studies.
1
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2
1.1 INTRODUCTION
Resistance training (RT) is an important component of training for athletes who
require speed, power or strength to successfully compete in their sport. For
example, many sprint runners perform resistance exercises concurrently with their
running training to improve their speed and maximal power. However, which
resistance training exercises elicit optimum improvements in task performance is
yet to be determined (the term ‘task’ refers to the movement which is the focus for
improvement, for example a sporting movement such as running or jumping).
Evidence suggests that adaptations to training are movement-specific, thus some
authors predict that RT exercises best improve movements when they are similar
to the training exercise (Abernethy et al., 1994; Lindh, 1979; Rutherford et al.,
1986; Thépaut-Mathieu et al., 1988).
Movement specificity encompasses both movement pattern- and velocity-specific
adaptations to training. That is, an exercise may mimic or replicate the ranges of
motion, body positions and types of contraction of a movement (i.e. movement
pattern) and/or mimic the velocity of a movement. Thus, movement-specific
adaptations refer to the neuromuscular and performance adaptations to an
exercise of a specific movement pattern and velocity.
With respect to movement pattern specificity, it has been shown that adaptations
to RT depend on several ‘factors’. These include the body position adopted
(Raasch & Morehouse, 1957; Wilson et al., 1996), the muscle lengths and joint
angles through which work is performed (Kitai & Sale, 1989), whether training is
performed unilaterally or bilaterally (Tanaguchi, 1997) and the types of
contractions and precontractions used (e.g. eccentric, concentric, isometric, rapid
pre-stretch, etc.; Hortobágyi et al., 1996; 2000) during training. The mechanisms
responsible for such training effects are unclear. Evidence from research
investigating a neural basis for movement pattern specificity is contradictory in its
conclusions (i.e. changes in muscle co-contraction and timing of muscle
3
recruitment, e.g. Weir et al., 1994, 1995b) while little research has examined
muscular changes such as sarcomere length-tension characteristics (Koh, 1995).
From a more practical standpoint, research investigating movement pattern-
specific adaptations to RT has proffered as many questions as it has answered.
For example, it is unclear how similar movement patterns of a task must be to a
resistance exercise for optimum improvement, whether the movement patterns of
resistance exercises must be similar to the sporting task when both resistance-
and task training are being performed concurrently in a training regime, and
whether it is necessary to consider all factors of movement pattern specificity for
optimal improvements in sporting performance. Moreover, most studies
investigating movement pattern-specific adaptations to RT have used untrained or
‘active’ subjects (e.g. Delecluse et al., 1995; Narici et al., 1989; Sleivert et al.,
1995; Young & Bilby, 1993). Given that the propensity for adaptation of well-
trained or elite athletes could be different to that of untrained individuals (Häkkinen
et al., 1987) the results of research using untrained subjects may not predict the
adaptation process of well-trained athletes. Thus, research involving well-trained
subjects is necessary to establish the necessity for movement pattern-specific
resistance training when task training is performed concurrently. It is also
necessary to determine whether some ‘factors’ affecting movement pattern-
related adaptations are more important than other factors.
With respect to the velocity specificity of adaptations to RT, results of studies
investigating responses to isokinetic training suggest that strength increases are
greater at, and perhaps below, the movement velocities of the training exercises
(Caiozzo et al., 1981; Petersen et al., 1989). When an isotonic (isoinertial)
training mode is used, subjects who trained using higher-velocity movements
tended to perform better in tasks requiring higher movement speeds (Wilson et al.,
1993). These velocity-specific adaptations have been considered a reflection of
many neuromuscular changes. Changes in the nervous system are thought to
include increases in total muscle recruitment (Häkkinen and Komi, 1983, 1985,
1986; Häkkinen et al., 1985b), an increase in the firing frequency of motor units
4
(Behm & Sale, 1993b), a selective activation of fast-twitch fibres (Grimby &
Hannerz, 1977; Nardone et al., 1989) which may be more likely during the
performance of complex movements (Behm & Sale, 1993b), and the selective
recruitment of muscles containing a high fast-twitch fibre content (Duchateau et
1991; Voigt et al., 1995), broad jump (Robertson & Fleming, 1987), sprint run
(Mann & Herman, 1985; Mero & Komi, 1987; Simonsen et al., 1985) and
acceleration phase of a sprint run (Jacobs & Ingen Schenau, 1992; Mero &
Komi, 1990). Also, common resistance training tasks such as the squat lift
have also been well described (McCaw & Melrose, 1999; McLaughlin et al.,
1977; Ninos et al., 1997; Wretengeng et al., 1996). Nonetheless, few
researchers have compared and contrasted the movement patterns of athletic
tasks with movement patterns of resistance exercises (e.g. Canavan et al.
[1996] compared the Olympic clean movement to the vertical jump).
Furthermore, little attempt has been made to describe RT exercises that may
have similar movement patterns to athletic tasks by performing well-controlled
kinematic studies.
The first purpose of this study was to describe and compare the movement
patterns of athletic subjects performing vertical jump (VJ), standing broad
jump (BJ), squat lift (SQ) and jump-squat (JSQ) tasks. The term ‘movement
pattern’ will be used to describe only the timing and magnitude of joint angle
changes (with reference to angular velocities and accelerations) during a
movement. Thus no reference to body position or other factors describing a
movement pattern will be considered in this definition. A second purpose was
to compare the movement patterns of a new exercise, named the forward
hack squat (FHS), and the acceleration phase of a sprint run. Running
acceleration is essential to the performance of many sports so resistance
training exercises that can improve running performance would benefit many
athletes. The FHS was designed in an attempt to augment sprint running
improvements. The acceleration phase of a sprint run was chosen rather than
the maximum velocity phase since 1) the beginning of the acceleration phase
is easy to pinpoint considering it occurs when the subject’s velocity is zero; 2)
resistance training exercises that mimic the movement pattern of the
acceleration phase should be easier to design than those for the maximum
velocity phase; 3) many sports require participants to accelerate rapidly, but
57
not necessarily attain maximum speed; and 4) the acceleration phase of a
sprint run is more often used as a test of dynamic performance in research
studies. Due to space limitations in our laboratory, we were unable to
videotape and complete a kinematic analysis of sprint running. As such, the
kinematics of the FHS was compared to sprint running data published by
Jacobs and Ingen Schenau (1992). This was the only study found to provide
an extensive description of the early acceleration phase of sprinting (second
stance phase) rather than the maximum velocity phase or ‘block’ (starting)
phase. Subjects in that study were seven well-trained male sprint runners
(100 m time = 10.6 ± 0.2 s). Given the subjects in the present thesis were not
elite runners, it cannot be assumed that they would use the same technique in
the acceleration phase as those of Jacobs & Ingen Schenau (1992).
However, they were of similar height and age (see ‘3.2.1 Subjects’).
3.2 METHODS
3.2.1 Subjects
Eight male subjects (age = 25.1 ± [SD] 2.5 yrs, height = 1.81 ± 0.09 m, weight
= 96.3 ± 10.0 kg) volunteered for the study. This subject number was chosen
in order to gain a broad description of movement patterns for the chosen
tasks; many biomechanical analyses have used fewer than eight subjects
(e.g. Bobbert & Van Soest, 1994; Bobbert et al., 1996; Mero & Komi, 1987,
1994; Robertson & Fleming, 1987; Simonsen et al., 1985). The height and
age of subjects were similar to those presented in Jacobs and Ingen Schenau
(1992; age 23 ± 2 yrs, height = 1.84 ± 0.06 m) and would allow good
comparison of resistance training movement patterns to the acceleration
phase of the sprint run as described by those authors. All subjects had
performed regular, heavy weight training at least three times a week for at
least one year prior to participation in the study. They also regularly
participated in sports involving jumping and running. Prior to participation,
58
subjects were briefed on the study, read and signed statements of
Informed Consent and performed at least three familiarisation trials of each
test exercise. The study was approved by the Southern Cross University
Human Experimentation Ethics Committee (see Appendix A).
3.2.2 Overview
Subjects performed a standard warm-up including five minutes of stationary
cycling at a self-selected workload and three to five trials each of a VJ, BJ, SQ
with a load of 60% of bodyweight and FHS with no load added to the sled (the
FHS exercise is described later). Reflective markers were placed on the body
landmarks (see Table 3.1). Subjects then performed three maximal trials of
single- and double-leg VJ and BJ with their arms in different positions, SQ and
JSQ with different loads, and single- and double-leg FHS with different loads.
Subjects rated their performance in each trial and poor trials (i.e. those in
which the subject failed to perform maximally or considered himself
unbalanced) were repeated. The order of exercises was the same for all
subjects. To minimise fatigue subjects rested for one minute between trials of
the same task and three minutes between sets of different tasks. The
movements were recorded by a high-speed video camera (200 Hz) and data
sets relating to joint movement (joint angular displacement, velocity and
acceleration) were calculated after digitising joint markers using Peak Motus
software.
3.2.3 Videography
3.2.3.1 Body landmarks
59
After the standard warm-up, reflective markers (2 cm diameter) were
placed on landmarks on the subjects’ head, arms, trunk and legs (Table 3.1).
All markers were placed on the right side of the body and subjects performed
all movements with their right side to the camera. For SQ and JSQ, the 7th
cervical vertebra (C7) was obscured from view. Therefore, a rigid extension
was placed on the weightlifting bar that allowed an accurate estimation of C7
position. Calculation of C7 position by this method is described in detail later.
3.2.3.2 Camera set-up and video recording
A high-speed video camera (Peak HSC-200, Peak Technologies, Inc. USA)
operating at 200 Hz was placed 12 m from the subject and a one-metre scale
rod was placed at the subject’s feet for later calculation of the scaling factor.
A 1000 W lamp was placed adjacent to the camera and shone on the subject
to increase the contrast of the reflective markers relative to the background
(Burgess-Limerick et al., 1993). The camera was 1.8 m off the ground and
recorded the sagittal view to clearly capture the subject’s head (TMJ; Table
3.1) marker during the squat lift when weights on the bar often obscured it.
The distant camera positioning (12 m) was used to minimise parallax error
created by the high placement of the camera. Camera settings are described
Table 3.1. Landmark names and marker positions forreflective markers.
Landmark Marker PositionHead Temporomandibular joint (TMJ)Neck 7th Cervical vertebra (C7)Shoulder Glenohumeral jointElbow Elbow axisWrist Ulnar styloidAnterior pelvis Anterior superior iliac spinePosterior pelvis Posterior superior iliac spineHip Greater trochanterKnee Femoral condyleAnkle Lateral malleolusHeel Lateral posterior calcaneusToe Metatarsal head II
60
in Table 3.2. These settings allowed high resolution of markers and
optimum field of view for capturing the movements. Once the video was set
up for each subject, the camera was not moved or adjusted for the duration of
testing.
Prior to each task being performed, subjects were viewed at 50 Hz on a
Gateway EV 700 Monitor (Gateway, USA) to ensure the subject was in full
view of the camera. The frame rate was then increased to 200 Hz and the
images of tasks recorded on videotape (Panasonic XD Pro S-VHS,
Panasonic, Japan). Recording began two seconds prior to each movement
and ended two seconds after completion. Video images were recorded by a
Panasonic AG 5700 videocassette recorder (Panasonic, Japan) for later
analysis.
3.2.4 Description of movement tasks
3.2.4.1 Vertical jumps
Subjects performed three trials of a single-leg jump with arm swing and three
trials of four different double-leg countermovement vertical jumps. The hand
positions were varied across trials; the VJ techniques are described in Table
3.3. Changing the hand positions was expected to alter the distance of the
body’s centre of mass from the hip joint and possibly change the movement
pattern adopted by the subjects. It would then be possible to compare the
movement patterns used in performing these different jumps to the movement
Table 3.2. Camera settings during dataacquisition.
Characteristic Camera settingFrame rate 200 HzShutter speed 1/1000 sAperture 2.8 f-stopsFocal length 3×Distance (d) 12 m
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pattern used to perform the squat exercises.
On instruction the subjects performed the designated jump for maximum
height; a countermovement was allowed prior to the upward. Subjects
descended until their internal knee angle was approximately 100o (± 10o).
Jumps were practiced prior to testing however no mechanical device was
used to ensure the correct knee angle was adopted. Trials where the knee
angle varied by more than 10o from the requested angle were disqualified
from later analysis.
3.2.4.2 Broad jumps
One version of a single-leg BJ and three versions of the double-leg BJ were
performed. The jumps are described in Table 3.4. Subjects performed three
trials of each jump for maximum horizontal distance. No other stipulation was
made regarding the jump’s performance so the subjects performed the jumps
naturally.
Table 3.3. Description of vertical jump techniques. The jumps were performed in the orderpresented here.
Jump DescriptionSingle-leg with arm swing Jump was performed unilaterally. The arms were free to
swing during the jump.Double-leg with arm swing Jump was performed bilaterally. The arms were free to swing
during the jump.Double-leg with hands onhead
Jump was performed bilaterally. The hands were placed onthe head and the elbows faced forward to stop the TMJmarker being obscured.
Double-leg with armsacross chest.
Jump was performed bilaterally. The arms were crossed overthe chest with hands on opposite shoulders. The right wristwas supinated to ensure the wrist marker was visible duringthe jump.
Double-leg with hands onhips
Jump was performed bilaterally. Hands were placed on thehips at the level of the Iliac crest so that the pelvic/hip markerswere not obscured.
62
3.2.4.3 Free-weight barbell squat lift
Subjects performed three squat lifts at each of three weights. First, weights
were placed on a 20 kg Olympic weightlifting bar such that the combined load
equalled 60% of bodyweight. With the loaded bar resting across the
shoulders level with the 7th cervical vertebra (C7), subjects squatted until the
internal knee angle was approximately 100o before moving back to the
starting position. Pilot testing showed that subjects often perform
countermovement jumps to a 100o knee angle. As such, movement
instructions for the SQ and VJ movements were the same. Subjects had
practiced lowering the weight to a knee angle of 100o during the warm-up and
lifts were disqualified from analysis if the knee angle was not within 10o of the
stipulated angle. The subjects were also asked to perform the movement in a
total of two to four seconds with equal time devoted to the downward and
upward phases. After three trials, they repeated the efforts with loads equal
to 100% and 140% of bodyweight. It was hypothesised that changing the
weight lifted would change the movement pattern used for the task since the
centre of mass of the weight-body system would be higher at the higher loads.
Table 3.4. Description of broad jump techniques. The jumps were performed in the orderpresented here.
Jump DescriptionSingle-leg with arm swing Jump was performed unilaterally. The arms were free to
swing during the jump.Double-leg with arm swing Jump was performed bilaterally. The arms were free to swing
during the jump.Double-leg with armsacross chest.
Jump was performed bilaterally. The arms were crossed overthe chest with hands on opposite shoulders. The right wristwas supinated to ensure the wrist marker was visible duringthe jump.
Double-leg with hands inhips
Jump was performed bilaterally. Hands were placed on thehips at the level of the Iliac crest so that the pelvic/hip markerswere not obscured.
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3.2.4.4 Jump-squat
Three repetitions of a JSQ were performed with a load equal to 60% of
bodyweight. Thus comparisons were possible between JSQ and SQ
movement patterns since both were performed with a load of 60% of
bodyweight. The JSQ was performed similarly to SQ except subjects
performed the concentric phase of the movement with maximal effort. As
such the subject’s feet left the ground during the upward phase. As for VJ,
subjects were asked to descend until the internal knee angle was 100o and
jump for maximum height. Trials where the knee angle varied by more than
10o from the requested angle were disqualified from later analysis.
3.2.4.5 Forward hack squat (FHS)
The FHS was performed in a semi-prone position by lowering and raising a
weight placed on a sled that moves on rails. The exercise was called the
‘forward hack squat’ because the direction of the movement of the weight is
similar to the semi-supine hack squat exercise performed by many weight
trainers. The double-leg FHS is shown in Figure 3.1 and the single-leg
variation is shown in Figure 3.2. Subjects performed five different FHS tasks
including double-leg FHS with 60%, 100% and 140% of bodyweight added to
the 74 kg sled and single-leg FHS with no weight and 50% of bodyweight
added to the sled. Despite the different movement characteristics of SQ and
FHS exercises, pilot testing in our laboratory showed that forces produced at
loads of 60%, 100% and 140% of bodyweight were similar for the SQ and
FHS exercises.
64
Subjects lowered the weight until their internal knee angle was 100o and then
lifted the weight back to the starting position. A 100o knee angle was chosen
since research by Jacobs and Ingen Schenau (1992) showed this to be the
smallest knee angle achieved during the acceleration phase of a sprint run,
and subjects moved to this knee angle during the VJ and SQ exercises. Thus
more accurate comparisons could be made between the FHS, SQ, VJ and
sprint movements. While the eccentric phase was completed in one to two
seconds (so that the contribution of the stretch-shorten cycle to the movement
was consistent across trials) the concentric phase was always performed in
less than one second. For the single-leg FHS (Figure 3.2), the ‘free’ leg was
extended straight backwards during the eccentric phase but became flexed at
the hip and knee during the concentric phase.
Figure 3.1a. The forward hack squat (FHS)
exercise was performed in a semi-prone
position by first lowering a sled (onto which
weights were placed) until the internal knee
angle was approximately 100o. The sled is
placed on rollers and moves along a central
rail. Notice that the internal hip angle is less
than 90o in this position.
Figure 3.1b. After lowering the sled it was
then moved back to the starting position in
preparation for the next repetition.
65
3.2.5 Analysis of video data
The video recordings of each trial were replayed and captured as digital video
by a computer and marker positions digitised using Peak Motus software
(Peak Performance Technologies, USA). Spatial models were designed as
described below and a calibration factor was calculated by the software after
digitisation of the scale rod. Calibration was performed for every movement
for every subject since the subjects’ positions at the beginning of the
movement could not be held perfectly constant. The digitised data was
scaled according to the calibration factor and filtered to remove high
frequency noise before missing data was interpolated and new data sets
formed (see below). From the new data sets, angular displacement, velocity
and acceleration were calculated and compared between tasks.
3.2.5.1 Spatial model
A spatial model was designed to describe the body landmarks, body
segments and joint angles. Body landmarks corresponding to the marker
Figure 3.2. The single-leg forward hack squat was performed as per the double-leg
version except that the ‘free’ leg is extended behind the body in the descending phase and
then flexed (as seen here) in the ascending phase. As such, the movements of the legs
are more similar to those in the acceleration phase of sprint run.
66
placements described above were defined. From these, body segments
and joint angle definitions were described as shown in Tables 3.5 and 3.6
respectively. For the squat lift and jump-squat tasks, the C7, wrist, elbow and
shoulder markers were obscured by the weights added to the bar. In the
spatial model for the squat lifts, these markers were not described, but were
labelled and designated as a ‘virtual point’. The positions of these markers
were estimated by an alternate method (see below).
3.2.5.2 Calculation of virtual point position
A 40 cm inflexible extension was placed on the centre of the bar and
protruding perpendicularly from it. Two reflective markers of 1.5 cm diameter
were set 29.2 cm (proximal marker) and 38 cm (distal marker) from the outer
border of the bar on the side opposite to the extension (see Figure 3.3). The
Table 3.6. Joint angle definitions.
Joint angle DefinitionPelvis-thigh Angle calculated clockwise from pelvis segment to thigh segment. Hip
flexion decreases the angle.
Hip Vector from the knee to greater trochanter to C7. Hip flexion decreasesthe angle.
Knee Anatomical 180o angle between the greater trochanter, knee and ankle.Knee flexion increases the angle.
Ankle Anatomical 90o angle calculated clockwise from the foot segment to the legsegment. Dorsiflexion decreases the angle.
Table 3.5. Body segment definitions.
Segment label Proximal marker Distal markerHead/neck C7 Temporomandibular joint (TMJ)Trunk C7 Greater trochanterUpper arm Shoulder ElbowForearm Elbow WristPelvis Anterior superior iliac spine Posterior superior iliac spineThigh Greater trochanter Knee
Leg (shank) Knee Ankle
Foot Heel Toe
67
markers formed a straight line and the bar rested on the C7 vertebra (the
position of the bar was checked prior to all SQ and JSQ trials) so that a ‘virtual
point’ could be calculated that was situated on the line made by the markers
and at a distance of a certain number of multiples of the distance between the
two markers. These markers were digitised, their raw coordinates exported to
a spreadsheet and the coordinates of the virtual point calculated. The x-
where ydist is the vertical distance (distance in the y plane) from the bar to the
distal bar extension marker, yprox is the vertical distance from the bar to the
A
Reflective markers placed 29.3 cm and 38cm from the opposite surface of the weightbar (point A).
Bar extension (40 cm long).
Figure 3.3. A bar extension was placed on the weight bar. Reflective markers placed onthe bar were later digitised. The position of C7, shoulder, elbow and wrist landmarkswere calculated by equations (1) and (2) and imported into the original filtered data setsas ‘virtual’ point data.
68
proximal bar extension marker, and 3.32 represents the multiples of the
distance between the two markers as described above and shown in Figure
3.3. Once the x- and y-coordinates of the virtual point were calculated, the
data were imported back into the trial data. A moving stick figure was created
from the raw data and the movement of the virtual point inspected to ensure
its correct calculation. The virtual data were used for the coordinate positions
of the C7, shoulder, elbow and wrist markers. While the bar rested across the
shoulders and was placed adjacent to the C7 vertebra, and the wrist marker
was in close proximity to the bar, the elbow was approximately 10 - 15 cm
from the bar. The distance from the elbow to the bar was minimised by
subjects placing their hands wide on the bar, however some error would have
occurred when using the virtual data as a description of the location of the
elbow joint. The error was consistent across all SQ and JSQ trials since the
subject’s hand positions were held constant.
3.2.5.3 Digitisation procedure
After the spatial model was described a 0.05 s segment of video sequence
containing the scaling rod was captured. The scaling rod was manually
digitised and a calibration factor calculated by the software. Subsequently, a
three second segment of video of the same movement, encapsulating one
subject performing one task, was captured and cropped approximately 0.1 s
(equal to 20 frames) either side of the start and end points of the movement.
Landmarks were digitised using the auto-tracking facility with parabolic
automatic point prediction. The automatic digitisation procedure was watched
carefully to ensure marker confusion did not occur and markers were not
digitised when invisible (i.e. markers positions were not guessed when
obscured from view). Gaps in the raw position data that resulted from these
periods of marker obscurity were filled by mathematical interpolation (Peak
Motus, Peak Performance Technologies, USA) when the period of marker
obscurity lasted less than one-sixth of movement time. Trials were discarded
from analysis if gaps longer than one-sixth of movement time were found for
any marker.
69
Raw data sets (including virtual point data) for all tasks were filtered using a
4th order, zero-lag Butterworth filter with a 6 Hz cut-off frequency. A cut-off
frequency of 6 Hz was chosen since the movement frequencies of human
subjects rarely exceed this value. A cut-off frequency of 6 Hz has been used
previously when analysing human lifting techniques (Burgess-Limerick et al.,
1993; Kromodihardjo & Mital, 1987) and similar cut-off frequencies have been
used in the analysis of high-speed movements (Gregor et al., 1985; Vint &
Hinrichs, 1996; Voigt et al., 1995). The filtered, raw coordinates were scaled
using the previously determined scaling factor and calculations of joint angular
displacements, velocities and accelerations performed.
3.2.6 Statistical Analysis
Means and standard deviations were calculated for joint angle, angular
velocity and angular acceleration data sets from the eight subjects. To
compare movements two methods were used. First, the times to complete
16%, 33%, 50%, 66% and 84% of a movement were calculated and graphed
against movement time (normalised to 100% of movement time). For this
analysis, the first and second phases of a movement were calculated
separately such that mid-movement occurred at 50%. Then 16% and 33% of
movement were calculated at 33% and 66% of the first (descending) phase.
66% and 84% of movement were calculated at 33% and 66% of the second
(ascending) phase. For example, if the knee angle for a movement moved
through a range of motion of 60o during the descending phase (i.e. 0 – 60o of
knee flexion) and then 70o (60 – -10o) during the ascending phase of a
movement, then 16%, 33%, 50%, 66% and 84% of the total movement
occurred at 20o, 40o, 60o (during knee flexion), 46.2o and 23.1o (during knee
extension).
The second method used to compare movements was by statistical analysis.
There are several methods that can be used to compare curves, however
70
none are without fault. For simplicity, curves were broken into sections
representing 5% of movement time and compared using paired t-tests (since
the same subjects performed all movements). This method has been used
previously in research investigating the sprint run (Weimann & Tidow, 1995).
Due to the large number of t-tests, the Bonferroni-corrected alpha level was
reduced to 0.0025 (for an overall alpha level of 0.05) making significant
differences very difficult to detect and the statistical analysis overly
conservative. In such instances (i.e. where the universal null hypothesis is not
of interest) Bonferroni correction is not warranted as important information
may be lost after analysis (Perneger, 1998). Thus Bonferroni correction was
not performed.
3.3 RESULTS
3.3.1 General Movement Descriptions
The movement patterns of subjects performing SQ, FHS, VJ and BJ tasks are
shown in Figures 3.4 – 3.7. Only one version of each exercise will be
described here, a comparison of different versions of each exercise will follow.
In these figures a decrease in angle of the hip and ankle joints represents joint
flexion, while an increase in knee joint angle represents joint flexion. This is
because the internal hip and ankle angles, but the external knee angle, are
shown to minimise overlap of hip and knee graphs and improve clarity.
Nonetheless, for all joints (hip, knee and ankle) an increase in angular velocity
or acceleration is shown as a positive inflection in the graph.
3.3.1.1 Squat lift
The movement pattern of a SQ performed with a load equal to bodyweight
resting across the shoulders is shown in Figure 3.4. The general movement
patterns for squats with loads of 60% and 140% were similar and therefore
71
will not be presented here. From the starting (standing) position the hip, knee
and ankle joints flexed simultaneously and the body moved to a squatting
position. The angular acceleration of the joints was small throughout this
descending phase. At the transition from descending to ascending phases
the hip and knee angles (mean ± SD) were 92 ± 9o and 98 ± 7o (82o internal
knee angle) respectively. Ankle dorsiflexion was greatest at –30 ± 6o at this
transition point. Almost as a mirror image of the descending phase, the
ascending phase was also characterised by simultaneous extension of the
hip, knee and ankle joints and no rapid accelerations. The body finished in
the original, upright position.
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Figure 3.4. Movement pattern of the squat liftexercise. The exercise is characterised bysimultaneous movements of the hip, knee andankle joints. The angular velocities of these jointsmirrored each other although higher angularvelocities occurred at the knee because of itslarger range of motion. Error bars representstandard deviation.
Figure 3.5. Movement pattern of the forwardhack squat (FHS) exercise. While similar to thesquat lift, ankle plantarflexion occurred after hipand knee extension. Thus the FHS appears ahybrid of push-like and throw-like movementpatterns. Error bars represent standard deviation.
72
3.3.1.2 Forward Hack squat
The movement pattern for a bilateral FHS with a weight equal to bodyweight
placed on the sled of the machine is shown in Figure 3.5. The different
movement pattern adopted during FHS compared to SQ was expected given
the constraints of the FHS machine. Similar to SQ the hip, knee and ankle
joints flexed simultaneously. However while the hip angle reached a minimum
of 102 ± 13o (i.e. only slightly more open than during SQ) the smallest knee
angle was 81 ± 7o (99o internal knee angle), 17o more closed than for SQ.
Therefore, compared to SQ, the movement pattern of FHS is one where hip
flexion is greater than knee flexion in the descending phase of the movement.
The ankle range of motion was also different. While identical minimum ankle
angles were achieved during both SQ and FHS tasks (the minimum ankle
angle for FHS was 30 ± 6o), ankle plantarflexion occurred much later in the
FHS movement. The different timing of ankle angle changes can be observed
clearly in the angular velocity and acceleration graphs. The increase in
angular velocity and acceleration occurred after the peak in hip and knee
angular velocity and acceleration. Therefore, while movement about the hip
and knee joints occurred simultaneously, movement at the ankle was delayed.
3.3.1.3 Vertical jump
The movement pattern for a VJ with arms placed across the chest (VJ ac) is
shown in Figure 3.6. Unlike the RT exercises, a larger proportion of the
movement time was devoted to the descending phase of the movement as a
consequence of the high vertical velocity of the centre of gravity achieved
during the ascending phase. The magnitude of joint angle changes however
were similar to those of SQ (the smallest hip, knee and ankle angles were 98
± 10o, 97 ± 9o and 33 ± 4o respectively). Possibly the most striking difference
between the VJ and resistance exercises was the timing of joint angle
73
changes. In the VJ, the hip angular velocity increased before the knee and
ankle (middle graph, Figure 3.6) although all joints reached their peak angular
velocity at the same time (immediately prior to toe-off). Thus the VJ
movement pattern exhibited sequential extension of joints from proximal to
distal consistent with a throw-like movement.
3.3.1.4 Broad jump
The movement pattern for a BJ with arms placed across the chest (BJ ac) is
presented in Figure 3.7. Similar to the VJ, angular accelerations and
velocities were far higher than for the resistance exercises, however the
Time (0.5% intervals)
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Figure 3.6. Movement pattern of the verticaljump. The exercise was characterised by largeaccelerations of the hip, knee and ankle joints.The angular velocities of these joints reached theirmaxima simultaneously. Error bars representstandard deviation.
Figure 3.7. Movement pattern of the broad jump.The hip extended early in the ascending phase toreach a higher angular velocity than the knee andankle joints. Error bars represent standarddeviation.
74
changes in joint angles were unlike any other movement described thus
far. The hip angle rapidly closed during the descending phase, followed later
by the knee then ankle joints. The smallest hip angle was 85 ± 20o in the
transition from descending to ascending phases. While this is smaller than for
other movements it was highly variable. The knee and ankle angles later
closed to 82 ± 14o (98o internal knee angle) and -36 ± 7o respectively. The
ascending phase began with rapid extension of the hip joint (see middle and
bottom graphs, Figure 3.7) before the lagging knee and ankle joints extended.
Unlike all other movements, the highest angular velocities occurred at the hip,
rather than the knee. Thus, while the BJ was similar to the VJ in that joint
extensions occurred sequentially, the BJ movement pattern was very different
to the other movements described previously.
3.3.2 Comparisons of Task Movement Patterns
Comparisons between tasks are shown in Figures 3.8 – 3.13. Each
movement is divided into the phases previously described. For example, the
16% bin on the x-axis represents that part of the movement where subjects
were 16% of their way through the total movement, or 33% of their way into
the descending phase. The 50% mark represents the transition period
between descending and ascending phases. The 84% mark represents that
part of the movement where subjects were 84% of their way through the total
movement, or 66% of their way through the ascending phase. The phase of
movement is plotted against the total movement time (y-axis). As such, these
are displacement versus time graphs. A steep gradient suggests that the
subjects were moving slowly (i.e. they took more time to move through the
movement phases). In contrast, a flatter gradient suggests that subjects were
moving more quickly in that part of the movement (that is, they moved
considerable distance in little time). Error bars were omitted to improve
clarity. Further statistical comparisons will be presented later.
75
3.3.2.1 Squat lift comparisons (SQ versus JSQ)
The movement pattern of JSQ differed from the traditional squat lifts (SQ +
60% and SQ + 140%; squat with a load of bodyweight is not shown) in that
the descending phase was performed slower than the ascending phase (see
Figure 3.8). Also, while the relative timing of hip angle changes was similar to
the traditional squats, both knee and ankle joint extension was delayed. That
is, the JSQ knee and ankle curves rise early suggesting relatively slower
movement, then flatten toward the end of the movement suggesting more
rapid joint angle changes. The size of this effect was greater for the ankle
than the knee suggesting a sequential extension of joints from hip to ankle.
Thus the movement pattern of the JSQ was different to the traditional squat
lifts.
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Figure 3.8. Comparison of the jump-squat (JSQ),and squat lifts with 60% (SQ + 60%) and 140%(SQ + 140%) of bodyweight across the shoulders.
Figure 3.9. Comparison of single-leg forwardhack squat (FHS 1L) and forward hack squatswith 60% (FHS + 60%) and 100% (FHS + BW) ofbodyweight added to the sled.
Hip
76
While there was little difference between either of the traditional squat lifts, the
ascending phase of the heavier lift (SQ + 140%) was slower (ie the curve
steeper) than for the lighter squat lift. Such a result would be expected given
the extra force required to move the heavier load.
3.3.2.2 Forward hack squat comparisons
Movement pattern differences between the FHS movements were perhaps
more numerous than for SQ (see Figure 3.9). The single-leg FHS differed to
the lighter FHS (FHS + 60%) in that the ascending phase was longer (ie the
curve was flatter between 50% and 100% of the movement) and
plantarflexion tended to occur more consistently rather than undergoing rapid
acceleration later in the movement. The single-leg FHS also differed to the
heavier FHS (FHS + BW) in that plantarflexion was more consistent. As such,
the single-leg FHS exhibited a very distinct push-like pattern of movement.
There were differences between the two double-leg FHS movements with
knee and ankle motion being slightly delayed early in the descending phase at
the lighter weight (FHS + 60%). There were however no significant
differences between the two tasks in the ascending phase.
3.3.2.3 Vertical jump comparisons
There were few differences between the movement patterns of the vertical
jumps where arms were not free to swing (i.e. on head, chest or hips),
therefore only the VJ with arms across chest and with arm swing are shown in
Figure 3.10. The two movements differed in that hip extension was delayed
at the transition phase and occurred rapidly later in the ascending phase in VJ
with arm swing (VJ wa). There was also a small difference at the ankle with
extension occurring later and more rapidly when the arms were free to swing.
77
Thus, although there were no differences at the knee, there were
differences in the timing of hip extension between the two VJ techniques.
3.3.2.4 Broad jump comparisons
There was little difference between those BJ where arms were (broad jumps
with arm swing; BJ wa) and were not (broad jump with arms across chest; BJ
ac) used. However, like VJ, hip extension was delayed early in the ascending
phase and more rapid toward the end when the arms were free to swing
(Figure 3.11). There were differences however between the double-leg and
single-leg (single leg broad jump; BJ 1L) jumps. Movements at the hip, knee
and ankle joints were more consistent in their changes for the single-leg jump
rather than showing periods of slower and more rapid change.
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60%
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100%
VJ ac
VJ wa
0%
20%
40%
60%
80%
100%
16% 33% 50% 66% 84%
Hip
Knee
Ankle
% T
otal
Mov
emen
t Tim
e
Phase of Movement
% T
otal
Mov
emen
t Tim
e
0%
20%
40%
60%
80%
100%
0%
20%
40%
60%
80%
100%
Bj 1LBj acBj wa
0%
20%
40%
60%
80%
100%
16% 33% 50% 66% 84%
Phase of Movement
Ankle
Knee
Hip
Figure 3.10. Comparison of vertical jumps witharms across the chest (VJ ac) and with arm swing(VJ wa).
Figure 3.11. Comparison of single-leg broadjump (BJ 1L), broad jump with arms across thechest (BJ ac) and broad jump with arm swing (BJwa).
78
3.3.2.5 Vertical jump versus jump-squat
Given the similar magnitudes of joint angle changes between VJac (VJ with
arms across chest) and JSQ, the two tasks were compared for their timing of
joint angle changes. As shown in Figure 3.12, there was little difference
between the movement patterns of the two tasks although relative velocity of
the joint angle changes during the descending phase of the JSQ was slightly
different. This may have been expected given the joint angles of the two
tasks differed slightly at the start of movement causing joint angle changes in
the JSQ to be slightly smaller than for VJac. There was no difference in the
timing of joint angle changes in their ascending phases.
3.3.2.6 Broad jump versus forward hack squat
As the body position during ascending phases of FHS and BJ were similar,
the timing of joint angle changes were compared (see Figure 3.13). There
appeared to be no similarity between the two movements. Their descending
phases were likely to exhibit different movement patterns given that the body
position during the descending phase of a FHS was semi-prone whereas the
body was upright during the BJ. However differences, although minimal at the
ankle, also existed during the ascending phase where the body position and
goal (direction of movement) of the tasks were similar. The FHS cannot
therefore be considered similar to BJ.
79
3.3.2.7 Similarities between squat lift and vertical jump tasks
Given the apparent similarity between different vertical jumps and between VJ
and SQ/JSQ, these movements were further analysed. The joint angle
changes for the VJ with arm swing and with arms across the chest are shown
in Figure 3.14. The significant effect of arm swing on hip range of motion can
be seen with differences (not corrected for experiment-wise error rate)
between the tasks occurring throughout the movement.
0%
20%
40%
60%
80%
100%
0%
20%
40%
60%
80%
100%
16% 33% 50% 66% 84%
0%
20%
40%
60%
80%
100%
FHS + BW
BJ ac
Phase of Movement
Ankle
Knee
% T
otal
Mov
emen
t Tim
e
Hip
Phase of Movement
% T
otal
Mov
emen
t Tim
e
0%
20%
40%
60%
80%
100%
0%
20%
40%
60%
80%
100%
VJ acJSQ
0%
20%
40%
60%
80%
100%
16% 33% 50% 66% 84%
Ankle
Hip
Knee
Figure 3.13. Comparison of forward hack squatwith a load equal to bodyweight added to the sled(FHS + BW) and broad jump with arms across thechest (BJ ac).
Figure 3.12. Comparison of the vertical jump witharms across chest (VJ ac) and jump-squat (JSQ).
80
Both of these jumping styles were compared to the SQ and JSQ. There were
large differences between the VJ with arm swing and all of the squat tasks.
However there was little difference between movement patterns for VJac and
JSQ (Figure 3.15). Other vertical jumps without arms swing (i.e. with hands
on head and with hands on hips) were not as similar as VJac. The main
differences between VJac and JSQ were at the beginning of the movement
(see Figure 3.15). The hip and knee joints were more flexed during a JSQ
possibly due to the load lifted. However, as the movement proceeded the
plots of the joint angles merge. Indeed there was little difference in the joint
angles of hip, knee and ankle between the movements both at the transition
from descending to ascending phases, and during the entire ascending
phase. Differences in the ascending phase were limited only to the point
immediately before toe-off where extension of the hip and ankle joints was
more complete during the VJ. Thus, subjects adopted similar movement
patterns for the performance of JSQ and VJac.
Figure 3.14. Comparison of vertical jumps with arm swing (VJwa) and vertical jumps witharms across chest (VJ ac). Both the timing and magnitude of hip joint angle changes weredifferent between the two tasks (* indicates p<0.05). There was little difference at the kneeand ankle joints although the vertical jump with arms across the chest was characterised byslightly less plantarflexion at the end of the ascending phase (# indicates p<0.05). Error barswere omitted to aid readability but standard deviations were similar to those in Figure3.7.
-50
0
50
100
150
200
0 20 40 60 80 100
Percent of Movement Time (%)
Join
t Ang
les
(deg
rees
)Hip angle VJwa
Knee angle VJwa
Ankle angle VJwa
Hip angle VJ ac
Knee angle VJ ac
Ankle angle VJ ac
*
#
*
*
81
3.3.2.8 Similarities between the forward hack squat and acceleration
phase of sprint running
Given the dissimilarity of FHS and BJ movement patterns, the timing and
magnitude of joint angle changes for the concentric phase of a FHS were
compared to those of the acceleration phase of a sprint run described by
Jacobs and Ingen Schenau (1992). While the data for the sprint run were not
available, some comparisons could be made to the joint angle curves
presented by the authors (Figure 3.16). There appeared to be good
agreement in the joint angle curves for the hip and knee joints. Both tasks
were characterised by smaller joint angle changes early in the concentric
phase but more rapid changes later. Further, the joint angular velocity curves
(curves for the sprint run are not presented here) were similar in that the
-50
0
50
100
150
200
0 20 40 60 80 100
Percent of Movement Time (%)
Join
t Ang
les
(deg
rees
)
Hip angle JSQ
Knee angle JSQ
Ankle angle JSQ
Hip angle VJ ac
Knee angle VJ ac
Ankle angle VJ ac
*
*
+
#
#
Figure 3.15. Comparison of the jump-squat (JSQ) and vertical jump with arms across chest (VJ ac).While there is a small but significant difference in joint angles at the start of the movements, their timingof joint angle changes, and magnitude of joint angles at the point of transition from descending toascending phases are almost identical. Subjects starting from a more upright position in the JSQ couldmake the two tasks more similar. * - hip angles significantly different, + - knee angles significantlydifferent, # - ankle angles significantly different (p<0.05). Error bars were omitted to aid readability, butstandard deviations were similar to those presented in figures 3.5 and 3.7.
82
greatest angular velocities occurred at the knee joint. The hip and knee
joints attained their maximum angular velocity simultaneously with the
maximum at the ankle occurring marginally later. Greater differences were
seen in the range of motion of the ankle with plantarflexion being greater at
the start and end of the concentric phase in the sprint run. In order to perform
the FHS more similar to the sprint run, subjects could have plantarflexed more
at these points during the movement.
Joint angles during a Forward Hack Squat with weight
1
1.5
2
2.5
3
3.5
Hip
Ang
le (
radi
ans)
1
1.5
2
2.5
3
3.5
Kne
e A
ngle
(ra
dian
s)
1
1.5
2
2.5
3
3.5
0 20 40 60 80 100
Percent of Push-off Time (%)
Ank
le A
ngle
(ra
dian
s)
Joint angles during a sprint push-off. Adapted from Jacobs and Ingen Shenau,
1992.
1
1.5
2
2.5
3
3.5
Hip
Ang
le (
radi
ans)
1
1.5
2
2.5
3
3.5
Kne
e A
ngle
(ra
dian
s)
1
1.5
2
2.5
3
3.5
180 160 140 120 100 80 60 40 20 0
Time (ms)
Ank
le a
ngle
(ra
dian
s)
Figure 3.16. Comparison of joint angle changes for the forward hack squat (FHS) andacceleration phase of a sprint run (adapted from Jacobs & Ingen Schenau, 1992). Anglesare presented in radians as per Jacobs & Ingen Schenau (1 radian = 57.3o). Hip and kneepatterns were very similar while the ankle angle differed largely at the start and end of thepushing phase.
83
3.4 DISCUSSION
The purpose of this study was to compare the movement patterns of subjects
performing VJ and BJ to their movement patterns during the squat lift (SQ and
JSQ) and FHS exercises. This discussion will not directly compare the
movement patterns of these tasks to those described in previous studies, but
focus on comparing the movements presented here with the aim of finding
resistance exercises that are similar in movement pattern to the VJ and BJ,
and the acceleration phase of the sprint run.
The VJ is performed bilaterally and in an upright position and was therefore
first compared to the SQ. During the descending phase of the VJ, joint angle
changes occurred simultaneously with flexion of the hip, knee and shoulder
joints. However these joints opened sequentially (from hip to ankle) during
the upward phase. Nonetheless, the angular velocities of these joints
reached their maxima simultaneously immediately prior to toe-off. Such a
movement pattern has been previously reported for the vertical jump (Bobbert
et al., 1986; Pandy & Zajac, 1991; Voigt et al., 1995).
Since two different styles of VJ were analysed, one where the arms were free
to swing (vertical jump with arm swing; VJwa) and the other where the arms
were held stationary (in fact three versions of the latter were also compared),
variations of the VJ were examined. Most notably, the two jumping styles
differed in that the hip angle of VJwa was smaller (more closed) at the
transition from descending to ascending phases. While its effect has not been
directly examined in the literature, the increase in range of motion of the hip
would possibly cause an increase in hip extensor moment. Some authors
have suggested that the increased hip moment, or rather the increase in joint
power from this, would be transferred by biarticular muscles to the ankle
culminating in an increase in ankle plantarflexor moment and an increase in
jump height (Bobbert & Ingen Schenau, 1988, 1992; Van Soest et al., 1993).
84
SQ was often performed by simultaneous flexion of the hip, knee and ankle
joints during the descending phase and then simultaneous extension during
ascent. The timing of joint angle changes was therefore different to either of
the two VJ styles. Although there was a difference in the hip angle at
transition from descending to ascending phases between VJ and SQ, there
was little difference between the magnitude of joint angle changes. However,
it cannot be concluded that the movement patterns adopted during VJ and SQ
tasks were the same.
There was little difference between movement patterns of JSQ and VJac.
Since the jump-squat is performed with a maximal ascending phase, the JSQ
and VJac had the same sequence of joint angle changes (i.e. hip before knee
before ankle). Furthermore, as illustrated in Figure 16, there was little
difference in joint angles at the transition from descending to ascending
phases. Probably the greatest difference between the two tasks was at the
movement’s beginning where joints were more closed during the JSQ. This
was likely a result of subjects squatting slightly under the load of the barbell
prior to the jump. Nonetheless, VJac could be considered very similar to the
JSQ since they were both performed bilaterally, in an upright body position
and the magnitude and timing of joint angle changes were very similar. How
the movement pattern of subjects performing the JSQ would change if heavier
loads were used is unclear from the present research.
The BJ is performed bilaterally from an upright position although the
ascending phase has a large horizontal component. In contrast to previous
research (Robertson & Fleming, 1997), the hip, knee and ankle joints
extended sequentially during the ascending phase. However, as reported
previously, the change in hip joint angle (and possibly contribution to total
torque) was far greater than the change at the knee (Robertson & Fleming,
1997) although the knee angular velocity was very high (Aguado et al., 1997).
As it is difficult to perform the SQ with such a movement pattern the FHS was
analysed and subjects’ movement patterns compared to those for the BJ.
85
BJ’s performed with arm swing were different to those without in that the
hip angle was lesser at the transition from descending to ascending phases.
The movement pattern of the double-leg BJ exhibited a sequential pattern
rather than they’re being simultaneous joint angle changes. These
characteristics are the same for the FHS so it was compared to the BJ.
The double-leg FHS was characterised by simultaneous extension of hip and
knee joints, but delayed ankle extension making it a hybrid of the throw-like
and push-like movement patterns often used to describe movements. The
single-leg FHS was characterised by simultaneous extension of the hip and
knee joints but a slower and more consistent change at the ankle joint. The
magnitude of joint angle changes were however not different between one-
and double-leg versions. The movement patterns of the FHS and BJ were
therefore not the same. Also, the magnitude of joint angle changes between
the FHS and BJ was very different. Thus, despite the two tasks being similar
in their laterality (i.e. both tasks can be performed unilaterally or bilaterally)
and the body position adopted during the ascending phase, the timing and
magnitude of joint angle changes were very different. The movement pattern
that characterised the FHS was therefore different to the BJ.
Given the dissimilarity of the FHS and BJ, the FHS was compared to the
acceleration phase of a sprint run. Due to space limitations in our laboratory,
the sprint run could not be kinematically analysed. Therefore the movement
pattern of the FHS was compared to the previously published data of Jacobs
and Ingen Schenau (1992). Qualitative comparison on the timing and
magnitude of joint angle changes for the two tasks showed that their
movement patterns were more similar than to the VJ or BJ. The greatest
difference between the two tasks was at the end of the push-off phase of both
movements where the sprint run is characterised by more prominent ankle
plantarflexion. Nonetheless, subjects in the present study performed the FHS
task without any instruction as to the level of plantarflexion required.
Plantarflexion at the end of the movement could probably be increased
86
significantly by these subjects without affecting the movement pattern of
the hip and knee joints.
The hip and knee joints extend simultaneously early in the push-off phase of
sprinting presumably to rotate the body forward before more rapid and
sequential extension of all three joints occurs later in the movement (Jacobs &
Ingen Schenau, 1992). A similar timing of joint angle changes was seen in
the ascending phase of the FHS. Further, the time at which the maximum
angular velocity of the joints occurred was also identical. Given therefore that
the timing and magnitude of joint angle changes were similar (and could be
made more similar with greater plantarflexion late in the pushing phase of the
FHS), both tasks can be performed unilaterally and the body is semi-prone in
the pushing phase of both movements, the movement pattern adopted for the
FHS and acceleration phase of sprint running appear very similar. Research
using the same subjects performing both tasks is necessary to more precisely
examine similarities and differences between the two movements.
In conclusion, the movement patterns of different exercises changed as the
constraints of the exercises (i.e. use of arm swing, load lifted, laterality, etc.)
were changed. This increased the number of movement patterns that could
be compared in order to find resistance exercises that could be considered
similar to VJ, BJ, and the acceleration phase of sprint running. Indeed, the
JSQ was very similar to the VJ without arm swing (especially when the arms
were crossed over the chest), although the effect of lifting greater JSQ loads
was not addressed in this study. Also, within the confines of the research
performed, one might conclude that the movement patterns of the FHS and
acceleration phase of a sprint run are also very similar. Given the movement
pattern specific adaptations to RT, the newly developed FHS exercise may be
a superior training exercise than SQ, JSQ or VJ to enhance sprint running
acceleration.
87
CCHHAAPPTTEERR 44:: SSTTUUDDYY TTWWOO
88
RELIABILITY AND VALIDITY OF ISOMETRIC
SQUAT AND FORWARD HACK SQUAT TESTS
4.1 INTRODUCTION
Research studies investigating adaptations to weight training often
incorporate the barbell squat as a dominant training exercise (Baker et al.,
1994; Delecluse et al., 1995; Häkkinen & Komi, 1983; Häkkinen et al., 1985a;
Thorstensson et al., 1976; Willoughby, 1993; Young & Bilby, 1993).
Nonetheless, despite research suggesting that the mode (contraction type:
isometric, concentric, eccentric) and movement pattern of strength tests
should be similar to those of the training exercises (for reviews see:
Abernethy et al. [1995] and Morrissey et al. [1995]), relatively few studies use
the 1-RM (one repetition maximum) squat test to determine strength changes
after training (Thorstensson et al., 1976; Willoughby, 1993; Young & Bilby,
1993). Instead, strength changes after squat lift training are often examined
by isometric tests (Häkkinen & Komi, 1983; Häkkinen et al., 1985a, 1987;
Young & Bilby, 1993) which may be preferred for their high test-retest
reliability (Agre et al., 1987; Bemben et al., 1992; Young & Bilby, 1993),
relatively simple administration and reduced risk of injury.
The relationship between dynamic strength increases and isometric strength
is not strong (Baker et al., 1994; Sale et al., 1992). For example, Sale et al.
(1992) found that isometric knee extension strength did not increase after a
19 weeks of leg press training despite muscle hypertrophy occurring over the
training period. Such results are possibly due to the different contraction
modes of training and testing exercises. However, the weak relationship
between changes in the isometric and dynamic tests may also be related to
their different movement patterns. A large body of evidence suggests that
89
adaptations to resistance training are specific to the movement pattern of
the training exercises (Abernethy & Jürimäe, 1996; Rutherford & Jones, 1986;
Thepau-Mathieu et al., 1988; Wilson et al., 1996). Thus, if isometric tests of
strength are to be used in preference to dynamic tests, or to assist in the
provision of training loads, it may be important that the body position adopted
in the isometric test be identical to the training exercise.
Given the SQ is commonly used in studies investigating adaptations to
resistance training, an isometric squat test (ISQ; figure 4.1A) might be a
useful alternative to the 1-RM squat. However, the movement pattern of SQ
is not similar to movements performed in many sports. The isometric FHS
(IFHS; Figure 4.1B) may be used since it allows isometric testing with a
movement pattern similar to sprint running (see Study One).
The purpose of this study was first to examine the reliability of both the ISQ
and IFHS tests to determine if repeated measures on the same subjects
AB
Figure 4.1. Subject position for both the isometric squat (ISQ; A) and forward hack squat
(IFHS; B) tests.
90
yielded reliable results, and second to examine the relationship between
isometric and 1-RM measures of strength. The ISQ test was performed with a
knee angle of 90o and the IFHS test with a hip angle of 90o so that the
subjects were in the lowest position of the movement. It was hypothesised
that the isometric force would be best related to dynamic 1-RM at this position
since it is here that the lifts are most difficult. This study is important in the
context of the thesis since a training study will be conducted. If isometric tests
can be used to predict 1-RM, training loads can be set with minimal effort or
injury risk and an indication of changes in subjects’ 1-RM strength could be
gained.
4.2 METHODS
4.2.1 Subjects
Fourteen athletic males (Age range = 19 – 26 yrs) volunteered to participate in
the study. All played competitive sport at a recreational or representative
level and had at least six months of weight training experience. The research
was approved by the Southern Cross University Human Ethics Committee
and subjects signed a statement of informed consent. They were able to
withdraw from the study at any time.
4.2.2 Testing
Subjects performed ISQ and IFHS tests on two occasions at the same time of
day one week apart. Subjects also performed a 1-RM squat or FHS test on
different testing days so that after two weeks each subject had performed
both the 1-RM squat and FHS tests once. The order of testing was
randomised between subjects to prevent order effects although isometric tests
were always performed before 1-RM tests. All tests followed a warm-up
91
including five minutes of moderate intensity running, ten minutes of
stretching and several warm-up repetitions of squat and FHS exercises at
increasing intensity.
4.2.2.1 Isometric squat (ISQ)
Subjects squatted until the internal knee angle was 90o with a 20 kg bar
resting across the shoulders. While in this position, the hip angle was
measured and recorded. Subjects then moved to a Smith Machine (a squat
rack designed to allow the bar to move only in the vertical plane) and squatted
with its bar across their shoulders until their hip and knee angles were
identical to the barbell squat. Metal stops were then placed on top of the bar
to prevent its upward movement. Once bar height was established, subjects
performed two warm-up trials of the isometric squat, one at 60% and one at
80% of their perceived maximum exertion (Figure 4.1). They then performed
three maximal isometric efforts lasting four seconds with three minutes rest
separating each trial. Hip and knee angles were checked prior to each effort
and loud verbal encouragement was given to increase subject motivation.
Force produced during the squat was recorded by a force platform (Kistler
Instrumenté, Switzerland) on which the subject’s feet were placed during each
isometric effort. The position of the feet was recorded for subsequent efforts.
Force was sampled at 1000 Hz and stored on computer (IBM compatible 486
DX) for subsequent analysis.
4.2.2.2 Isometric forward hack squat (IFHS)
The rails along which the sled moves were adjusted to an angle of 39o to the
horizontal. Subjects placed two feet on the foot platform such that the body
formed a straight line from the head to the ankle while in the standing position.
They then lowered the weight until the internal hip angle was 90o and the
92
internal knee angle was 110o (Figure 4.1B). This approximated the hip and
knee angles during push-off in the acceleration phase of sprint running
(Jacobs & Ingen Schenau, 1992). A metal peg was used to hold the machine
in this position for the subsequent maximal isometric contractions. Subjects
then lifted the sled slowly until the metal peg stopped its upward movement
and hip and knee angles were checked to ensure they were at 90o and 110o
respectively before the subjects provided two warm-up (60% and 80% of
perceived maximum) and three maximal isometric contractions lasting four
seconds. Three minutes rest separated each maximal effort. Force produced
during the isometric contraction was sampled at 100 Hz by a load cell (Output
= 1.9231 mV/V, hysteresis <0.02%, Model LPS-2KG, Scale Components Pty.
Ltd., Australia) placed parallel to the direction of sled movement. The signal
was fed into a personal computer (IBM compatible 486 DX) and data stored
for later analysis using a custom program written using AMLAB software
(Chatanooga, Inc., USA).
4.2.2.3 1-RM squat
1-RM squat strength (free-weight) was tested by subjects lifting increasingly
heavy weights until a weight could not be lifted. Subjects placed their feet
with the same stance as for the ISQ test and stood with a loaded barbell
across the shoulders. Subjects then squatted until their internal knee angle
was 90o before lifting the weight back to the standing position. The smallest
increment in weight between lifts was 5 kg. At least three minutes separated
each trial.
4.2.2.4 1-RM forward hack squat (FHS)
The position of the subjects’ feet and body, and of the rails on which the sled
moved, were identical to the IFHS. Each FHS trial required the subject to
lower the weight until their internal knee angle was 110o before lifting the
93
weight back to the standing position. Subjects attempted to lift
incrementally heavier weights until a weight could not be lifted. At least three
minutes separated each attempt and the smallest increase in weight between
successive lifts was 10 kg.
4.2.3 Data analysis
Change in the mean between testing session one and two, typical error (i.e.
variance of the change in performance between the two testing sessions),
Pearson’s Product Moment Correlations and Intraclass Correlation
Coefficients (ICC’s) were calculated as outlined by Hopkins (2000). After
curve-fitting procedures were used to ascertain the linear relationships
between the data (SPSS v10.0, SPSS Inc.), validity statistics including
Pearson’s correlations and linear regression equations with standard error’s of
the estimates were calculated. For reliability and validity statistics, 95%
Confidence intervals (95% CI) were calculated for relevant data. Finally,
paired t-tests with Bonferroni correction were used to compare observed and
predicted (from regression equations) 1-RM test scores to examine
differences between data sets. Alpha was set at 0.1 to reduce the likelihood
of type II error (finding no difference between observed and predicted values
when a difference existed).
4.3 RESULTS
4.3.1 Reliability of ISQ and IFHS
Reliability statistics for ISQ and IFHS are presented in Table 4.1. For ISQ,
there was a small and non-significant increase in force produced in the
second testing session (26.9 N or 0.9% of 2321 N). The reliability of the test
was very high with ICC = 0.97 and typical error of only 69 N. For IFHS, there
94
was a small and non-significant decrease in the force produced in the
second testing session (26.9 N or 1.2% of 2335 N). The test-retest reliability
of the test was also very high with an ICC = 1.00 and typical error only 30 N.
Thus, the two isometric tests were very reliable.
FHS Mean LCI UCI Squat Mean LCI UCI
∆ mean (N) -21.0 -62.7 20.7 ∆ mean 26.9 -42.0 95.9
There was a significant relationship between the average ISQ (average of
testing week one and testing week two) and 1-RM squat performance, and
average IFHS and 1-RM FHS performance (see Table 4.2). There was
however a poor correlation between subject performances in ISQ and IFHS
tests and only a moderate correlation between 1-RM squat and FHS test
performances. Therefore subjects who performed well in the isometric tests
also performed well in the dynamic tests but subjects who performed well in
the squat tests did not necessarily perform well in the FHS tests.
Table 4.1. Reliability statistics for ISQ and IFHS. Both tests show high reliability. ∆ mean –change in the mean from test week 1 to test week 2, ICC – Intraclass Correlation Coefficient,LCI – lower limit of confidence interval (95%), UCI – upper limit of confidence interval (95%).
Table 4.2. Pearson’s correlations for test performances. Thesquat lift was highly correlated with the ISQ. FHS was highlycorrelated with the IFHS. Lower correlations were foundbetween squat and FHS.
95
Test comparisons r R2 p-value
ISQ versus squat 0.77 0.61 <0.01
IFHS versus FHS 0.76 0.59 <0.01
ISQ versus IFHS 0.47 0.23 >0.1
Squat versus FHS 0.55 0.30 >0.05
Force produced during isometric contractions was converted to weight in
kilograms and compared to individual’s 1-RM lifts. On average, ISQ lifts were
147% of those on the 1-RM and IFHS lifts were only 89% of the 1-RM. Linear
regression equations to predict 1-RM performance from isometric
performance are presented in Figure 4.2. The standard error of the estimate
for ISQ was 13.8 kg (95% CI = 10.9 – 18.6 kg) and for IFHS was 19.4 kg
(95% CI = 15.4 – 26.2 kg). These standard errors represent 8.5% and 7.3%
of the average performance in 1-RM squat and FHS respectively. There was
no significant difference between predicted and obtained values for the data
presented here.
96
4.4 DISCUSSION
4.4.1 Reliability and validity
The results of the present study suggest that the reliability of both the
isometric squat (ISQ) and isometric forward hack squat (IFHS) tests are very
high (ICC = 0.97 & 1.00 respectively). These intra-class correlation
y = 0.0432x + 163.85
R2 = 0.5747
0
100
200
300
400
0 1000 2000 3000 4000
Average Isometric FHS (N)
1-R
M F
HS
(kg
)
y = 0.0356x + 78.67
R2 = 0.5856
0
100
200
300
400
0 1000 2000 3000 4000
Average Isometric Squat (N)
1-R
M S
qu
at (
kg)
Figure 4.2. Scatterplots of isometric versus 1-RM test performance. The linear regressionequations and R2 values are indicated on the graphs. Almost 60% of the variation in 1-RMperformance can be accounted for by isometric test scores.
97
coefficients are similar to those previously reported for isometric (0.85 –
0.99 [Agre et al., 1987; Bemben et al., 1992; Viitasalo et al., 1981; Wilson et
al., 1993]) and 1-RM tests (0.92 – 0.98 [Henessey & Watson, 1994; Hoeger et
al., 1990; Hortobágyi et al., 1989; Sale, 1991]). The difference in mean
performance (shift in the mean) between repeated test occasions was less
than 1.5% of the average performance. For the subjects tested here
therefore, there was little or no difference between performances at each
testing occasion despite the complex multi-joint coordination required to
perform the present tests. This suggests that the isometric tests used in the
present study would be able to detect small changes in isometric strength
between subjects or after some form of intervention.
There was also a strong relationship between subject scores in the isometric
tests and the associated 1-RM tests (rsquat = 0.77, rFHS = 0.76; p<0.01) with
over 60% of the variation in 1-RM tests explained by subject’s isometric
performances. Thus, subject scores in the isometric tests were strongly
related to their 1-RM scores. Furthermore, there was no significant difference
between values predicted by regression equations and those obtained by
testing of subjects’ 1-RM. Isometric measures could then be considered good
indicators of dynamic performance.
Nonetheless, the correlations obtained here were less than 0.8 and could not
be considered indicative of high validity. R2 values for the correlations
between isometric and 1-RM tests suggest that up to 40% of the variance in
1-RM performance could be explained by factors other than isometric
performance (see Table 4.2). Furthermore, while the standard errors of the
estimates for the relationships between the isometric and 1-RM tests were
small (SEEsquat = 13.8 kg, SEEFHS = 19.4 kg), they still represent 8.5% and
7.3% of the average 1-RM score for the squat and FHS respectively. Thus
there is some error in predicting 1-RM performance from isometric
performance using the tests presented here. While performance in the
isometric tests could be used as a good indication of a subject’s 1-RM
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performance, and this performance could be predicted well from the
regression equations, precise estimates of 1-RM performance were not
possible.
4.4.2 Movement specificity
Of importance also is the weak relationship between subjects’ performances
in the squat and FHS tests. Those subjects who performed well in the squat
tests did not necessarily perform well in the FHS tests (risometric = 0.47, r1-RM =
0.55). Given the tests involve the same contraction modes (either isometric
[isometric tests] or an eccentric phase followed immediately by a concentric
phase [1-RM tests]), differences between test performances could be
attributed to their different movement patterns. The principle of movement
specificity has been shown extensively by past research (Abernethy &
Jürimäe, 1996; Baker et al., 1994; Blazevich & Gill, 2001; Blazevich et al.,
2000; Morrissey et al., 1995; Wilson et al., 1996). In the present study, high
force production in one posture was not always complemented by high force
production in the alternative posture suggesting an effect of movement pattern
on test performance.
4.4.3 Practical applications
The isometric squat and FHS tests were highly reliable and a strong
relationship existed between isometric and 1-RM performance. The ISQ and
IFHS tests could therefore be used to assess dynamic strength changes with
training. Given their high reliability, they could certainly be used to examine
changes in isometric strength between subjects, or after intervention.
However, the validity of the tests was moderate (r<0.8) and the number of
subjects tested here reasonably small. Caution should then be exercised
when trying to predict a subject’s precise 1-RM from isometric measures.
Furthermore, if the isometric tests were to be used to estimate changes in 1-
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RM strength following intervention, the number of subjects would have to
be larger than if a 1-RM test was used. The increase in subject number would
equal 1/R2 (Hopkins, 2000), which for the ISQ test is 1/0.59, or 1.7, times the
subject number. Increasing subject numbers would increase the power of the
tests to nullify the loss of power caused by the moderate relationship between
the test types (lower validity of the isometric measures). Finally, subjects who
produced high forces in one posture (e.g. squat) did not necessarily produce
high forces in the other posture (e.g. FHS). Therefore, to best detect
performance changes with training, or differences between subjects, that test
which best matches the training movement patterns should be used.
4.4.4 Future research
Given the moderate validity of the isometric tests for estimating 1-RM
performance, some modifications could be made to the tests to improve their
validity. One change might be to vary the joint angles at which the test is
performed. In the present study, joint angles were chosen such that muscle
lengths were long and the forces relatively low. However, Sale (1991)
suggested that test variability was reduced when measurements were taken
at the strongest point in the range of motion. Moreover, Murphy et al. (1995)
found that the elbow angle in a bench press-specific isometric test affected
the relationship between isometric and 1-RM strength. The authors indicated
that tests should be performed at the joint angle at which peak forces were
provided. Thus, changing the joint angles adopted for the present isometric
tests may improve their validity.
Future research should also examine the relationship between these isometric
tests and their associated 1-RM tests by investigating the relationship
between changes in isometric and 1-RM strength after a period of resistance
training. While a highly reliable and valid isometric test should measure
performance similarly to its comparable dynamic test, this is not always the
case. Baker et al. (1994) found that a 27% improvement in 1-RM squat and
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9% improvement in isometric leg extension force after squat training were
unrelated (r = 0.16, p>0.05). This was despite significant correlations (r =
0.57 – 0.61) between the variables pre- and post-training which would have
indicated moderate validity. Such results are possibly due to the different
contraction modes between training and testing exercises. Nonetheless, the
low relationship between changes in the isometric and dynamic tests may be
related to their different movement pattern. The movement patterns of the
isometric tests used in the present study were similar to their 1-RM
counterparts, thus minimizing the differences between tests. However, it is
still unclear whether changes in ISQ and IFHS test performance would be
related to 1-RM squat and FHS test performance after a period of resistance
training.
4.4.5 Conclusion
The isometric squat and forward hack squat tests were highly reliable (>0.97)
and would therefore be able to detect small differences in multi-joint isometric
strength between subjects, or performance changes over time. They are well
related to their 1-RM counterparts (SQ and FHS) with significant correlations
found between the test pairs (p<0.01). However, validity correlations were
only moderate (rsquat = 0.77, rFHS = 0.76). Therefore it is unclear whether
these tests can discriminate small changes in dynamic strength. Although 1-
RM strength can be estimated well from the regression equations, precise
estimates of 1-RM strength were not possible. Future research should
examine the relationship between changes in 1-RM and isometric
performance after a period of training to determine whether movement-
specific isometric exercises such as those presented here can be used to
detect small changes in dynamic performance.
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RELIABILITY OF UNILATERAL AND
BILATERAL FORWARD HACK SQUAT TESTS
5.1 INTRODUCTION
Much research has investigated differences in force production between uni-
and bilateral movements. For example, Secher et al. (1976, 1978) reported
that maximal, voluntary, isometric strength of the leg extensors was greater
(115% and 123% for 1976 and 1978 studies respectively) under bilateral
conditions. More recently, Häkkinen et al. (1996) and Tanaguchi (1997)
showed that bilateral strength increased more in subjects who trained
bilaterally while unilateral strength improved most in subjects who trained
unilaterally. These specific changes appeared similar for different exercise
tasks (hand grip strength, leg extensor power and arm extensor power;
Tanaguchi, 1997). Such evidence has lead researchers to suggest that
adaptations to uni- and bilateral training are dissimilar. Also, the maximum
voluntary force that can be produced by a limb depends on whether a
unilateral or bilateral task is used in testing.
Given the laterality specificity of performance, testing of performance changes
after bilateral training should probably be done using bilateral tests. Also,
unilateral changes should be assessed by unilateral tests. However, while
bilateral testing protocols are common, and reliability and validity studies have
supported their use as testing tools (e.g. Arnold & Perrin, 1993; Rahmani et
al., 2000; Steiner et al., 1993; Wilhite et al., 1992), it is unclear if unilateral
tests show the same reliability. Unilateral pushing tasks are less commonly
performed and balance during unilateral tasks may be more difficult to
maintain. The reliability of unilateral tasks could therefore be lower than
bilateral tasks.
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To the author’s knowledge, no research has compared the reliability of
unilateral and bilateral tests. Inspection of research that has included both
unilateral and bilateral testing has either shown that variability of
performances were similar between the two types of tasks (Häkkinen et al.,
1996; Howard & Enoka, 1991) or that perhaps bilateral tasks showed more
variability (Tanaguchi, 1997). Furthermore, variability of jump height, work,
joint torque and joint power values appeared similar for one- and two-legged
jumps (Van Soest et al., 1985). Thus, while no research has specifically
tested the hypothesis, it appears likely that uni- and bilateral tests of
performance would be equally reliable.
The purpose of the present study was to examine the reliability of test
performances in the dynamic forward hack squat task. The forward hack
squat was chosen as the test exercise since no reliability studies have been
performed for dynamic contractions and, given its novelty, subjects would be
unlikely to be accustomed to its movement pattern. While the reliability of
isometric FHS has been previously shown (Study Two), the reliability of
dynamic squats has not. As an adjunct, reliability will be measured with two
different loads placed on the machine to determine whether the load lifted (or
the velocity of the movement) affects the test’s reliability.
5.2 METHODS
5.2.1 Subjects
Eleven active, male subjects volunteered for the study (Age = 20.5 ± 1.1 yrs).
Subjects signed statements of Informed Consent and were free to discontinue
the study at any time. The research was approved by the Southern Cross
University Human Research Ethics Committee prior to the commencement of
testing.
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5.2.2 Protocol
Subjects participated in two identical testing sessions separated by one week.
In each session, testing was preceded by a five minute cycle at a self-
selected workload and two sets of two-legged forward hack squats with a self-
selected weight (equal to approximately 50% and 100% of bodyweight).
Cycle workload and weight lifted in the forward hack squat were recorded for
the first session and repeated in the second session.
5.2.3 Determination of testing loads
After warm-up, subjects performed two maximal, bilateral isometric
contractions lasting three seconds with hip and knee angles of 90o and 100o
(internal angle) followed by two unilateral contractions using the subjects’
preferred legs. The rails of the forward hack squat machine were aligned at
49o to the horizontal. Bilateral contractions were always performed before
unilateral contractions. Force produced by the subjects during the isometric
contractions was measured by a load cell placed in series with the movement
direction of the weighted sled (Output = 1.9231 mV/V, hysteresis <0.02%,
Model LPS-2KG, Scale Components Pty. Ltd., Australia). Force was sampled
at 100 Hz and the data fed into a personal computer (IBM compatible 486 DX)
and stored using a custom program written using AMLAB software
(Chatanooga, Inc., USA).
Weights equal to 40 and 70% of maximum isometric force were then
calculated using the following equation:
Weight = x * (y/100) - 74.6 kg
cos 41o / 9.81
where y is the percent required of the isometric maximum (equal to 40 or 70),
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x is isometric maximum force in Newtons, cos 41o is used to calculate the
vertical component of the total isometric force, 9.81 (m.s-1) is a gravity
constant that is used to convert Newtons (N) to kilograms, and 74.6 kg is the
vertical component of the weight of the sled apparatus which forms part of the
total weight of the lifted system. The kilogram amount was then added to the
sled to the nearest five kilograms and maximal dynamic contractions
performed.
5.2.4 Test contractions
Subjects performed two maximal, dynamic contractions at both the 40% and
70% loads (i.e. two one-legged trials at both 40% and 70%, and two two-
legged at both 40% and 70%). The order of contractions was randomised
between subjects to minimise order effects. The weight was lowered in a
controlled eccentric phase lasting one to two seconds and then raised as
rapidly as possible. A spring mechanism prevented the sled from moving out
of the subject's reach at the top of the movement and allowed a safe, maximal
push to the limit of the subject's range of motion. Subjects were asked to hit
the spring at the top of the movement as hard as possible. All subjects were
allowed several familiarisation trials to gain confidence in the spring
mechanism prior to the recorded trials. Thus there was no deceleration of the
weight prior to hitting the spring. One minute of rest was allowed between
trials of a lift and five minutes of rest was allowed between different types of
lift. During dynamic trials, the force transducer again recorded force.
5.2.5 Data analysis
Reliability statistics including the difference in the mean force between the two
trials and the intra-class correlation coefficients were calculated by the
methods of Hopkins (2000). 95% confidence intervals (CI) were also
calculated to show the variation in reliability statistics. Finally, the bilateral
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deficit was calculated similarly to that proposed by Howard & Enoka (1991)
except that instead of forces produced in left leg and right leg trials being
added and compared to the bilateral condition, the force produced in the
single leg condition was doubled. This would cause slight overestimation of
the bilateral deficit since often one leg is stronger than the other is and, in
general, subjects would have performed the trials with their strongest leg.
5.3 RESULTS
Mean (± SD) force production for the four conditions is presented in Table 5.1.
More force was produced during trials at the 70% load than at 40%.
Furthermore, more force was produced during bilateral trials. Interestingly,
force produced in the bilateral trials was less than double the force produced
during the unilateral trials. The subjects therefore exhibited a bilateral deficit
Results of the reliability tests are presented in Table 5.2. Intra-class
correlation coefficients were higher for trials at the 70% load than 40%. The
variability of the coefficients (indicated by the 95% CI) was also less for the
70% load. Therefore, reliability of trials at the heavier load was greater than
Table 5.1. Mean (±SD) force produced during each trial. More forcewas produced in trials at the 70% load and during bilateral trials.
1L – one-legged (unilateral), 2L – two-legged (bilateral)40% - 40% of isometric maximum added to machine70% - 70% of isometric maximum added to machine
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for the lighter load. There appeared to be no effect of laterality on task
The purpose of the present study was to examine the reliability of test
performances in the dynamic forward hack squat task. The forward hack
squat was chosen as the test exercise since no reliability studies have been
performed for dynamic contractions and, given its novelty, subjects would be
unlikely to be accustomed to its movement pattern. As an adjunct, reliability
was measured with two different loads placed on the machine to determine
whether the load lifted (or the velocity of the movement) affected the test’s
reliability. Results of the reliability tests suggest that there was no difference
in the reliability of unilateral and bilateral tests. The result is interesting given
that unilateral strength tasks are less commonly performed and balance
during unilateral tasks may be more difficult to maintain. One could consider
that complex motor tasks that are performed unilaterally would be more
difficult to learn than bilateral tasks. However the results of the present study
suggest that subjects were equally able to perform uni- and bilateral tasks
reliably.
Of interest was the finding that the reliability of tasks at the heavier (70%) load
was higher than tasks at the lighter (40%) load. The result suggests that
Table 5.2. Reliability statistics for force produced during dynamicforward hack squat trials. Reliability was greater for the heavier loadswith no difference between uni- and bilateral trials.
1L – one-legged (unilateral), 2L – two-legged (bilateral)40% - 40% of isometric maximum added to machine70% - 70% of isometric maximum added to machine
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something related to either the load lifted, or velocity of the movement,
affected reliability. The most likely explanation for this result is that the
greater load promotes greater kinaesthetic feedback from muscle, tendon and
joint proprioceptors. Particularly, muscle spindles, golgi tendon organs and
pacinian corpuscles could provide more feedback under the heavier loads.
Stretch or pressure stimulates proprioceptors. The greater the stretch or
pressure, the greater the feedback from these receptors. This information is
then received by the spinocerebellum which compares the information to the
signals sent from the cortical motor area (Sherwood, 1993). The
spinocerebellum then corrects deviations from the intended movement. Thus,
greater loads would allow more information from proprioceptors for the
spinocerebellum to correct movement.
Of final note is the result that the force produced during bilateral trials was
less than twice that produced in the unilateral trials. Thus the subjects in the
present study exhibited a bilateral deficit as has been reported in previous
studies (Häkkinen et al., 1996; Howard & Enoka, 1991; Tanaguchi, 1997).
The bilateral deficit was calculated similarly to that proposed by Howard &
Enoka (1991) except that instead of forces produced in left leg and right leg
trials being added and compared to the bilateral condition, the force produced
in the single leg condition was doubled. This would cause slight
overestimation of the bilateral deficit since often one leg is stronger than the
other is and, in general, subjects would have performed the trials with their
strongest leg. Nonetheless, the result provides further evidence that unilateral
and bilateral tests measure different entities and that testing should be
specific with respect to laterality. For example, strength tests measuring
changes in performance after unilateral training should be performed
unilaterally. This is especially true in light of the findings of the present study
that suggest the reliability of complex, unilateral tasks is as high as bilateral
tasks.
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PERFORMANCE RELATIONSHIPS
BETWEEN VERTICAL JUMP, SPRINT RUNNING
AND STRENGTH TRAINING EXERCISES:
IMPLICATIONS FOR MOVEMENT SPECIFICITY
6.1 INTRODUCTION
Based on the results of Study One it was concluded that the timing and
magnitude of hip, knee and ankle joint angle changes were similar for JSQ
and VJ (with arms crossed over the chest) tasks and for the FHS and the
acceleration phase of a sprint run. However, it is unclear whether subjects
who perform well in a JSQ or FHS test would also perform well in a VJ or
sprint run. The results of longitudinal studies indicate that adaptations to an
exercise stimulus are specific to the movement patterns of the training
exercises (Lindh, 1979; Martin et al., 1994; Rutherford et al., 1986; Thépaut-
Mathieu et al., 1988; Weir et al., 1994), even when the movement velocity of
the training exercise differs from the test exercise (Wilson et al., 1996; Young
& Bilby, 1993). As such, a subject could be expected to perform equally well
relative to other subjects in tests that require the same movement patterns,
even if the movement velocities of the tasks were dissimilar.
This creates somewhat of a paradox since the velocity specificity of
movement has also been extensively shown (Blazevich & Jenkins, 1997;
Caiozzo et al., 1981; Ewing et al., 1990). It is therefore unclear whether
adaptations to exercise are specific to the velocity of the training exercises, or
to some other closely related principle. It is possible that adaptations are
specific to the neuromuscular intent of the task rather than movement velocity
per se (Behm & Sale, 1993a). In the present thesis, the phrase
‘neuromuscular intent’ describes the ‘intended’ mode/s of muscular action.
111
That is, it describes the intention to provide concentric, eccentric or
isometric muscle contractions regardless of whether the muscles actually
lengthen or shorten and the actual mode and velocity of movement is not
considered. For example, the ‘neuromuscular intent’ during a VJ is to produce
high static muscle force, or to provide muscle stiffness in the squatting
position (transition between downward and upward phases), and then to
contract rapidly during the upward phase. Regardless, the entire movement
is regarded as high-velocity.
Examples of research indicating that neuromuscular intent, rather than
movement velocity, is an important factor in the adaptive process to
resistance training are limited. Adams et al. (1992) showed that a
combination of squat and plyometric training was superior to using only one
form of training to improve VJ performance. One could speculate that squat
training improved subject’s muscle strength and stiffness, while plyometric
training improved subject’s intermuscular coordination (Bobbert & Van Soest,
1994), use of the stretch-shorten cycle and high-velocity force production.
Therefore, training was optimum when exercises were specific to both
movement pattern and mode (neuromuscular intent). Further, Behm and
Sale (1993a) hypothesised that the ‘intent’ to perform rapid contractions was
important for velocity-specific adaptations to occur. Thus, while movement
pattern specificity is seen even with tasks of different velocities, the
neuromuscular intent of exercises might be important.
The purpose of this study therefore was to investigate the relationship
between subjects’ performances in JSQ and VJ tests, and the FHS and 20 m
sprint tests, to determine the extent to which subjectss performances in
certain tests were dependent on similarities in the movement pattern,
movement velocity and/or neuromuscular intent of the tests. It was
hypothesised that if movement pattern solely determined task similarity,
subjects would perform equally well (relative to other subjects) in JSQ and VJ
tests, and FHS and sprint tests. If both the movement pattern and
112
neuromuscular intent were important then not only should subject
performances in dynamic FHS tests and sprint tests be similar but so should
subject performances in ISQ and VJ tests. The VJ requires high levels of
muscle force for optimum use of the stretch-shorten cycle prior to the upward,
concentric, phase (Asmussen & Bonde-Petersen, 1974; Gollhofer et al., 1992)
and would therefore largely require the same neuromuscular intent as an ISQ
performed in a squating position. Finally, if movement velocity was important,
better relationships might exist between JSQ, VJ and sprint than ISQ tests.
6.2 METHODS
6.2.1 Subjects
Thirty-one athletic subjects including 23 men and eight women volunteered
from the University population (age range = 18 - 26 yrs). All subjects were
currently participating in organised sport (minimum of club-level) and had a
minimum of six months of resistance training experience. Both male and
female subjects were included in the study on grounds of equity however all
subjects had to perform a 20 m sprint in under 4 s and produce at least 1800
N in an isometric squat (knee angle 90o). Subjects had no recent injury or
medical conditions that would impede maximal performance and all subjects
read and signed statements of informed consent prior to participation. The
project was approved by the Southern Cross University Human Research
Ethics Committee prior to the commencement of testing.
6.2.2 Procedure
Following a standardised warm-up including ten minutes of low-impact
aerobic activity involving walking, running, subjects performed SQ, FHS, VJ
and 20 m sprint tests. Two minutes rest was allowed between successive test
trials while ten minutes of rest was allowed between the performance of
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different tests. The order of tests was randomised between subjects by
each of the first 24 subjects being given one of 24 possible testing orders.
The next seven subjects were randomly allocated a testing order such that no
more than two subjects had the same test order. Thus the influence of
fatigue/potentiation on performance was minimised.
6.2.2.1 20 m sprint
Subjects’ times to run 10 m and 20 m were recorded by infra-red electronic
timing lights (Swift Performance Equipment, Australia) while running on a
synthetic, indoor surface. All subjects performed four practice runs at
increasing speed starting at a 'fast jog' and culminating in a maximal run.
Each subject was then allowed three timed runs, although a fourth run was
allowed if subjects produced their best time on the third run. Each sprint was
started from a semi-squatting position with one foot placed in front of the other
to lower the body's centre of mass and permit a more optimum acceleration
than that gained from an upright start. However 'crouch' starts of the type
seen in competitive running were not permitted to prevent bias toward
experienced sprint runners. The toe of the front foot was placed 30 cm
behind a line that marked the start of the 20 m. In this way the subjects’
forward lean did not prematurely break the infra-red beam between the
starting gates and activate the electronic timing mechanism. Subjects had
performed eight sprint sessions over four weeks prior to testing to practice
acceleration technique and ensure optimum running performance.
Subjects started in their own time with no external command. Timing was
automatically started when the subject broke the beam between the first pair
of timing lights (at 0 m of the 20 m). All subjects wore standard jogging shoes
and no performance shoes (i.e. spiked shoes) were allowed. Subjects were
instructed to run maximally to pass through all of the timing gates in the
minimum time.
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6.2.2.2 Vertical Jump
Force and displacement were recorded for three maximal, double-leg VJ’s
with the subject’s arms folded across their chests. All had performed eight VJ
training sessions over four weeks prior to testing to practice jump technique
and ensure reliable jump performance. A cable position transducer with a
plastic-hybrid precision potentiometer (Model PT9101, accuracy ±0.10% full
stroke, Celesco Transducer Products, Inc., USA) measured displacement.
The cable was connected to a belt tightly secured around the subject’s waist
(Figure 6.1).
Voltage from the position transducer was sampled at 100 Hz using a personal
computer (IBM compatible, 486 DX) and stored on disc. Subsequently,
displacement was calculated using a scaling factor by a custom program.
The data were then smoothed with a fourth-order, zero-lag Butterworth filter
with a cut-off frequency of 10 Hz. Force was recorded using a Kistler Force
Platform (Type 9287, Kistler Instrumenté, Switzerland). Force data were
sampled at 1000 Hz using a personal computer (IBM compatible 486DX).
From force and displacement data maximum force, displacement, velocity,
Cable to transducer (above, not shown).
Belt to which cable was secured.
Figure 6.1. Body position for VJ showingcable (to position transducer) and belt.
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Figure 6.2. Position for isometric squat test. Hipangles were measured during a squat with a freebar. Knee angles were maintained at 90o.Subjects then descended to these angles duringthe free-weight squat lifts.
power, time to peak power, and rate of power development were calculated
on all jumps.
6.2.2.3 Squat lift
Subjects performed three squat lift tasks: an ISQ and JSQ’s at 30% and 60%
of isometric maximum. Results from Study Two showed that these loads
were equal to approximately 44% and 88% of dynamic 1-RM. First, subjects
were asked to squat with an unloaded bar to a 90o knee angle and their hip
angle was measured. They then squatted under a bar that was fixed and
immovable such that their hip and knee angles were the same as those
recorded during the unloaded squat. This position is shown in Figure 6.2.
Subjects were instructed to perform a maximal isometric squat against the bar
for three seconds during which time force was measured by a Kistler Force
Platform, sampled at 1000 Hz and stored on computer. The instruction was to
perform the squat ‘as hard as possible’ and the maximum force recorded was
taken as isometric squat strength.
The peak in force was converted from Newtons of force to kilograms of weight
by dividing by the gravity constant of 9.81 ms-2 and 30% and 60% of this load
116
calculated. Subjects then performed three squats (with a free bar) on the
force platform with these loads. The subjects were required to lower the
weight slowly to a 90o knee angle (practice repetitions allowed the subjects to
estimate this position and each trial was observed to ensure the knee angle
was very close to 90o at the bottom of the movement). The subject then
exerted maximum effort upward against the weighted bar which was lifted
rapidly such that subjects’ feet often left the ground. The squat could be best
described as a jump squat (JSQ). The maximum force recorded during the
concentric (upward) phase was taken as a measure of squat strength
(Schmidtbleicher & Buehrle, 1987). The same test was repeated for the 60%
load. Thus, force measures were obtained for the squat lift under isometric
conditions, and with two different dynamic loads. From the force data, peak
force and time to peak force were calculated.
6.2.2.4 Forward Hack Squat
Subjects performed three maximum efforts of a two-legged FHS. These
included a maximal IFHS and lifts at 40% and 70% of isometric maximum.
Results from Study Two showed that these loads were equal to approximately
36% and 62% of dynamic 1-RM. The subject placed two feet on the foot
platform such that the body formed a straight line from the head to the ankle
while in the standing position. The subjects then lowered the weight until the
internal hip angle was 90o and the internal knee angle was 110o (Figure 6.3).
This approximated the hip and knee angles during push-off in the acceleration
phase of sprint running (Jacobs & Ingen Schenau, 1992). A metal peg was
used to hold the machine in this position for subsequent maximal isometric
contractions. For these contractions, subjects lifted the sled slowly until the
metal peg stopped its upward movement and hip and knee angles were
checked to ensure they were at 90o and 110o respectively. Subjects then
provided a maximal isometric contraction (i.e. as hard as possible) while
maintaining the pre-determined hip and knee angles. The contractions lasted
three seconds. Force during each isometric contraction was sampled at 100
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Figure 6.3. Position for the isometricforward hack squat (FHS). The hipangle (angle between the C7 vertebra,greater trochanter and lateral condyle)was 90o and knee angle 110o.
Hz by a load cell placed in series with the movement direction of the weighted
sled (Output = 1.9231 mV/V, hysteresis <0.02%, Model LPS-2KG, Scale
Components Pty. Ltd., Australia). The signal was collected using a personal
computer (IBM compatible 486 DX) and data stored using a custom program
written using AMLAB software (Chatanooga, Inc., USA; see Appendix X).
To determine weights equal to 40% and 70% of maximum isometric force, the
vertical component of the force was calculated first. The following equation
was used:
Weight = x * (y/100) - 74.6 kg
cos 41o / 9.81
where y was the percent required of the isometric maximum (equal to 40 or
70), x was the previously determined isometric maximum force in Newtons,
cos 41o was used to calculate the vertical component of the total isometric
force, 9.81 (m.s-2) is the gravity constant used to convert Newtons (N) to
kilograms, and 74.6 kg is the vertical component of the weight of the sled
apparatus which forms part of the total weight of the lifted system. That is, the
vertical component of the total force provided during the isometric contraction
was calculated, a percentage of that weight determined (40% or 70%) then
the weight of the sled was subtracted to determine the actual weight to be
added to the sled. The kilogram amount was then placed on the sled to the
nearest five kilograms.
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Subsequently, the subject performed maximal, dynamic contractions at the
40% and 70% loads where the weight was lowered in a controlled eccentric
phase lasting one to two seconds and then raised as rapidly as possible. A
spring mechanism prevented the sled from moving out of the subject's reach
at the top of the movement and allowed a safe, maximal push to the limit of
the subject's range of motion. The subject was asked to hit the spring at the
top of the movement as hard as possible. All subjects were allowed several
familiarisation trials to gain confidence in the spring mechanism prior to the
recorded trials. Thus there was no deceleration of the weight prior to hitting
the spring. During dynamic trials, both force and displacement were
recorded. Displacement was measured by a cable position transducer (as
described previously) with the cable attached to the sled apparatus and data
was collected using an IBM compatible computer. From the force and
displacement recordings, maximum movement velocity, peak force and peak
power were calculated as measures of performance.
6.2.3 Data Analysis
After force and displacement data were collected during the SQ, FHS and VJ
tests, various performance variables were calculated, as mentioned above, by
a custom program. All variables were subject to Correlation and Components
Analysis (SPSS for Windows v10.0, SPSS Inc.). Numerous variables (related
to power, maximum movement velocity and time to peak force and power)
were highly inter-correlated and were listed under the same components in
the Component analysis. Such variables were eliminated from further
analysis since they provided no information in addition to that gained from
analysing displacement and force variables (from which they were calculated)
alone. As such, analysis of the results was limited to force measures for the
resistance tasks, as well as VJ height and sprint running time.
Pearson's product moment correlation coefficients were calculated to
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determine relationships among the performance variables. Alpha level was
set at 0.01 to decrease the likelihood of Type I error. Thus only highly
significant relationships were reported as such. The various components
associated with subject performances were also analysed by Components
Analysis using Principal Components extraction and Varimax rotation (SPSS
for Windows v10.0, SPSS Inc.).
6.3 RESULTS
Descriptive statistics for the variables analysed are presented in Table 6.1.
Results of the correlation analysis are presented in Table 6.2. Two-legged
FHS performance was significantly correlated with 10 m and 20 m sprint time
(r = -0.54 – -0.73, r2 = 0.29 – 0.53; p<0.01) such that subjects who ran faster
also performed better in FHS tests. Force produced during the SQ was also
correlated with 10m and 20 sprint time although the correlations were
consistently, but only slightly, lower (r = -0.51 – -0.67, r2 = 0.26 – 0.45; p<0.01;
compare correlations in Table 6.2). Indeed coefficients of determination
suggest that the proportion of the sprint times that can be accounted for by
squat performance was less than 45%. Force produced during the FHS
(isometric, 30% and 60%) were also significantly related to VJ height (r = 0.53
Table 6.1. Mean performance (±SD) forthose variables selected for analysis.
Performance Variable Mean (±SD)10 m sprint time (s) 1.89 (0.22)20 m sprint time (s) 3.28 (0.40)VJ height (m) 0.42 (0.10)FHS isom. (N) 1824 (487)FHS force 40% (N) 1182 (473)FHS force 70% (N) 2004 (586)Squat force isom. (N) 1709 (305)Squat force 30% (N) 1915 (397)Squat force 60% (N) 2294 (586)isom. – isometric30%, 40%, 60%, 70% - load lifted aspercent of isometric maximum.FHS – forward hack squat test
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– 0.71, r2 = 0.28 – 0.50; p<0.01) as was force produced during ISQ (r = 0.63,
r2 = 0.40; p<0.01) and squat with a load of 30% of isometric maximum (r =
0.55; r2 = 0.30; p<0.01). However force produced during a squat with 60% of
isometric maximum was not significantly correlated (Figure 6.4).
Strength Variable 10 m time 20 m time Vertical jump
FHS isom. -0.72 -0.73 0.56
FHS force 40% -0.54 -0.56 0.58
FHS force 70% -0.72 -0.71 0.68
Squat isom. -0.67 -0.51 0.63
Squat force 30% -0.50 -0.61 0.55
Squat force 60% -0.61 -0.67 (0.44)
isom. – isometric30%, 40%, 60%, 70% - load lifted as percent of isometric maximum.FHS – forward hack squat testAll correlations (non-bracketed) are significant, p<0.01.Bracketed correlation coefficients were not statistically significant.
0500
10001500200025003000350040004500
0 0.2 0.4 0.6 0.8
Vertical Jump Height (m)
Squ
at F
orce
(N
)
Squat forceisom.
Squat force60%
Linear (Squatforce 60%)
Linear (Squatforce isom.)
Figure 6.4. Scatterplots of isometric force produced during a squat (Squat force isom.)and force during a squat with a load of 60% of maximum isometric load (Squat force 60%)against VJ height. There is a higher correlation between ISQ force and jump height (r =0.63) than squat force at 60% of isometric maximum and jump height (r = 0.44).
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Results of the Components Analysis were that the variables could be
grouped according to four components (see Table 6.3). The components in
Table 6.3 have been ordered according to the movement velocities and loads
of the movements with Component 1 being the slowest movement velocity
and Component 2 the fastest. SQ and IFHS variables have not been grouped
with any of the high-speed movements suggesting that their force-velocity
characteristics were different. The results also show however that sprint time
was not grouped with any of the FHS variables despite subjects performing
well in the FHS also performing well in the sprint (i.e. they were highly
correlated).
Another interesting finding of the study was that there was a plateau in sprint
running performance at high strength levels. That is, sprint times did not
improve linearly with strength at the highest strength levels (Figure 6.5). This
would have reduced the correlation between FHS and sprint performances
and suggests that strength is not the most important factor in performance in
fast runners.
Table 6.3. Results of the Factor Analysis. The analysis has revealed four componentsthat could be related to the movement velocity (or load) of the test. Components arearranged according to their movement velocity (i.e. 1,3,4,2).
Component 1 3 4 2
Variables Squat isom.Squat force 30%Squat force 60%FHS isom.
FHS 70% FHS 40% 10 m time20 m timeVJ height
Movement velocity
Movementload
Very low
Very high
Low
High
Moderate
Moderate
High
Moderate83% of total variance can be explained by the four components.Minimum communality = 0.65.isom. – isometric force30%, 40%, 60%, 70% - load lifted as percent of isometric maximum.FHS – forward hack squat test
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6.4 DISCUSSION
Correlations between dynamic squat (which could be considered jump squats
since subjects’ feet invariably left the ground during the ascending phase) and
VJ performance were generally poor with the highest correlation being
between the ISQ and VJ (r = 0.63; p<0.01). Results of the component
analysis indicate also that their force-velocity characteristics were different
(Table 6.3). Therefore, although the results of Study One were that subjects
adopted similar movement patterns during the performance of VJ and JSQ
exercises, they were not well related functionally (r = 0.55; r2 = 0.3). A likely
reason for this discrepancy would be the different movement velocities
achieved and load lifted during performance of the tasks. The VJ is
performed at a high velocity and utilises the stretch-shorten cycle whereas the
squat lift is performed slower and with heavier loads. Indeed the lightest
dynamic squat was performed with a load equal to 30% of isometric maximum
(approximately 44% of dynamic 1-RM; Study Two). These loads are far
greater than for the VJ and the movement velocities achieved were therefore
0
500
1000
1500
2000
2500
3000
2.5 3 3.5 4 4.5
20 m Sprint Time (s)
FH
S F
orce
(N
)FHS isom.
FHS force 40%
Figure 6.5. Scatterplots of isometric force produced during a forward hack squat (FHSisom.) and force during a FHS with a load of 40% of maximum isometric load (FHS force40%) against 20 m sprint time. There is a plateau in sprint times at around 2.7 s.
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very different. Thus, movement pattern alone did not determine task
similarity.
There was however a significant correlation between ISQ force and VJ height
despite the contraction modes of the two tasks being different. The close
performance relationship might reflect the necessity for high muscle strength
(muscle stiffness) in the squatting position for performance of both tasks (i.e.
the intent to produce high muscle stiffness regardless of the actual mode of
contraction; neuromuscular intent). The countermovement jump relies largely
on the stretch-shorten cycle for power development (Gollhofer et al., 1992).
Pre-activation of muscles to attain high muscle forces has been shown to
enhance the storage and utilisation of elastic energy in stretch-shorten
movements (Asmussen & Bonde-Petersen, 1974; Gollhofer et al., 1992) thus
increasing their efficiency. Further, earlier activation of agonist muscles in a
movement allows more work to be done early in that movement (Bobbert et
al., 1996; Fukashiro et al., 1995; Voigt et al., 1995; Walshe et al., 1997;
Wilson et al., 1991). The ability to use the stretch-shorten cycle optimally in
vertical jumping is therefore contingent on being able to attain high levels of
muscle force/stiffness in the squatting position. Given the high correlation
between ISQ force and VJ height, it appears that task similarity depended on
both the movement pattern and intent to produce high muscle force/stiffness.
Correlations between isometric and dynamic FHS force and sprint running
time were generally high (r = 0.56 – 0.73; p<0.01). Therefore, subjects who
produced large forces in the FHS tests also performed well in the sprint test.
The plateau in 20 m sprint times at high FHS forces (Figure 6.4) would have
affected this correlation. Component analysis revealed that performances in
FHS and sprint tasks were described by different components. 10 m and 20
m sprint times were listed under component 2, generally representing high
velocity movements (see Table 6.3), whereas the dynamic FHS variables (i.e.
not the isometric variables) were listed under components 3 and 4, generally
representing moderate or slower-velocity movements. A conclusion that may
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be drawn from this is that while the sprint and FHS tests could not be
considered identical (given their different movement velocities), the similarity
in their movement patterns and force-velocity requirements were not as
different as for the isometric and dynamic squat and sprint/vertical jump tasks.
Since the weights used in FHS relative to 1-RM (36% and 62%) were lower
than for the squat (44% and 88%), the result was somewhat expected. Given
the movement patterns are the same (see Study One) and subjects who
performed well in FHS tests also performed well in the sprint tests, it appears
that movement specificity is determined both by the movement pattern and
neuromuscular intent, but not the velocity, of the tasks.
The results of this study offer some insight to the complex functioning of the
neuromuscular system. From Study One it was concluded that the movement
patterns of the JSQ and FHS exercises were similar to the VJ and sprint
(acceleration phase) respectively. Movement pattern-specific adaptations to
training have been shown repeatedly (Martin et al., 1994; Rutherford & Jones,
1986; Thépaut-Mathieu et al., 1988; Weir et al., 1994; Wilson et al., 1996),
even when training and testing exercises were performed at different
contraction velocities (Wilson et al., 1996; Young & Bilby, 1993). The results
of such research suggest that subjects should perform well in tests with the
same movement patterns. One would therefore conclude that, to at least
some degree, subjects who performed well in one resistance exercise would
also perform well in its related performance task. However, in this study,
subjects who performed well in the JSQ tests did not necessarily perform to
the same relative level in the VJ test.
These results may have been due to the resistance and performance (VJ and
sprint) tasks having different force-velocity characteristics (different
neuromuscular intent). The squat tests possibly required high dynamic
muscle strength while performance in the VJ tests depended on the efficiency
of the stretch-shorten cycle. The ISQ and VJ tests may have been more
functionally similar because of the high muscle force/stiffness required for
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their performance (same neuromuscular intent). The results of this study
also suggest that while there was some difference in the force-velocity
characteristics of the FHS and sprint tests, neuromuscular intent was the
same. Therefore, subjects were likely to produce comparable performances
in tasks that had similar movement patterns, and required similar
neuromuscular intent. The velocity of movement was not a major factor. The
next step toward understanding the effect of movement pattern, movement
velocity and neuromuscular intent on training adaptations is to perform
longitudinal research investigating adaptations to the different types of
training.
In summary, specificity of task performance in humans has previously been
shown to be related to the movement pattern of tasks even when the
velocities at which the tasks were performed were not the same (Wilson et al.,
1996; Young & Bilby, 1993). However, the results of this study suggest that
the neuromuscular intent of the tasks is also important. The results do not
indicate that the actual movement velocity of exercises is important since ISQ
force was well related to VJ performance. A longitudinal study would best test
the influence of movement pattern and neuromuscular intent on training
adaptations.
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CCHHAAPPTTEERR 77 –– SSTTUUDDYY FFIIVVEE
127
NEUROMUSCULAR AND PERFORMANCE
ADAPTATIONS TO SHORT-TERM CONCURRENT
RESISTANCE AND SPRINT/JUMP TRAINING
7.1 INTRODUCTION
Adaptations to RT appear specific to the movement patterns (Abernethy &
Jürimäe, 1996; Kitai & Sale, 1989; Weir et al., 1994; Wilson et al., 1996) and
velocities (Caiozzo et al., 1981; Delecluse et al., 1995) of the exercises used
in training. In studies investigating the movement-specific adaptations to
training, much of the specific adaptations have been ascribed to changes in
muscle recruitment strategies (Kitai & Sale, 1989; Weir et al., 1994) or in the
length-force characteristics of sarcomeres (Herring et al., 1984; Koh, 1995;
Van Eijden & Raadsheer, 1992). Velocity-specific adaptations have been
ascribed mostly to increases in type-II myosin heavy chain isoforms within
sarcomeres (Adams et al., 1993; Andersen et al., 1994), increases in the total
size or number of type II muscle fibres (Jansson et al., 1990; Mannion et al.,
1993) or an increase in the recruitment of motor units during muscle
contraction (Behm & Sale, 1993b; Cannon & Cafarelli, 1987; Häkkinen et al.,
1985 a,b; Häkkinen & Komi, 1985, 1986). Thus, specific adaptations to RT
occur in many different parts of the neuromuscular system. Despite this, little
research has examined movement-specific changes in muscle architecture, or
examined both muscular and neural changes simultaneously. Furthermore
longitudinal studies investigating movement pattern-specific effects have been
fraught with limitations (this will be discussed later).
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7.1.1 Muscle Architecture
Muscle architecture describes the size of a muscle in terms of the volume,
cross-sectional area or thickness, the angulation of its fibres relative to the
tendon [pennation) and the length of its fibres (measured as fascicle length)
after training. These factors have been shown to change with RT
(Henriksson-Larsén et al., 1992) however little research has investigated such
changes. With respect to muscle size, increases have been commonly
observed after periods of resistance-type training with much of this increase
being related to fibre size (Colliander & Tesch, 1990; Narici & Kayser, 1995;
Sale et al., 1992; Wang et al., 1993). Increases in muscle size in response to
training appear after several weeks (Moritani, 1993; Moritani & DeVries, 1979;
Narici et al., 1989) and certainly after changes have occurred at the
sarcomere (Heslinga et al., 1995; Williams, 1990) and in the nervous system
(DeVries, 1968; Narici et al., 1989; Sale, 1988). Since few changes have
been seen in the electromyogram of experienced weight trainers (Häkkinen et
al., 1987, 1991), increases in muscle size have been proposed as the major
determinant of muscle strength in well-trained athletes (Narici et al., 1989).
In addition to muscle size changes, changes in muscle pennation could affect
strength development. Increases in pennation possibly allow a greater
muscle mass to attach to a given area of tendon (Kawakami, 1993; Rutherford
& Jones, 1992). As such pennation should increase with the size of the
muscle. Research examining the relationship between muscle size and
pennation (Henriksson-Larsén et al., 1992; Kawakami et al., 1993, 1995;
Rutherford & Jones, 1992) has not conclusively shown whether the two
variables are (Kawakami et al., 1993, 1995; Rutherford & Jones, 1992 [cross-
sectional]) or are not (Henriksson-Larsén et al. 1992; Rutherford & Jones,
1992 [longitudinal]) related. Therefore it is still unclear whether pennation
changes occur in response to changes in muscle size.
Longer muscle fibres have been theoretically and experimentally shown to
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contract at higher velocities than shorter fibres (Burkholder et al., 1994;
Sacks & Roy, 1982; Wickiewicz et al., 1984). Since fibres are grouped into
fascicles, and the spaces between fascicles are visible in vivo using
ultrasound and computer aided techniques, fibre length is commonly
estimated by measuring the length of these fascicles (Fukunaga et al., 1997;
Kawakami et al., 1998). However no research had examined the relationship
between fascicle (fibre) length and human movement performance until Abe
et al. (1999) showed that fascicle length was greater in sprinters than long
distance runners, and Kumagai et al. (2000) showed a significant relationship
between fascicle length and sprint performance in 100 m sprinters. Still no
research has investigated changes in fascicle length (fibre length) in
controlled training studies using concurrent resistance and task training.
Therefore it is unclear whether fascicle length is altered in response to RT, or
concurrent resistance and task training.
7.1.2 Longitudinal Research
While some longitudinal studies have investigated neuromuscular changes
accompanying training, the exact neuromuscular adaptations that result from
training, and the populations to which the results can be related, are still
unclear. First, subjects in most training studies are not well-trained and
adaptations within their neuromuscular system may well be different to trained
individuals (Häkkinen et al., 1987; Narici et al., 1989). Second, the subjects in
such training studies have generally trained using isokinetic (Ewing et al.,
1990; Mannion et al., 1994; Narici et al., 1989) or isotonic (Abernethy &
Jürimäe, 1996; Petersen et al., 1989; Sale et al., 1992; Wilson et al., 1993,
1996) training modes without also performing additional, task-specific,
practice. A paucity of research has examined the effect of training movement
pattern or velocity when subjects performed both resistance- and task training
concurrently (Delecluse et al., 1995; Tanaka et al., 1993; Voigt & Klausen,
1990). Research that has examined adaptations to concurrent training
suggests that RT performed at high velocities (Delecluse et al., 1995) may be
130
more beneficial than that at lower velocities (Tanaka et al., 1993; Voigt &
Klausen, 1990) even when the movement patterns of the resistance and task
training exercises are similar (Tanaka et al., 1993). Third, while much
research has focussed on changes in the nervous system with training,
relatively few studies have investigated changes in muscle architecture after
RT (Henriksson-Larsén et al., 1992; Kawakami et al., 1993, 1995; Rutherford
& Jones, 1992). Moreover, none have examined changes in both the nervous
system and muscle architecture after a period of concurrent resistance and
task training.
Given that, for most athletes, RT forms only part of a total training program, it
is important that adaptations to RT are described when task training is
performed concurrently. The purpose of the present study was first to
determine if changes in VJ, sprint run and strength tests were related to the
movement pattern or velocity of multi-joint, dynamic RT exercises in well-
trained subjects, and second to examine changes in the nervous and
muscular systems when the RT was performed concurrently with VJ and
sprint training (i.e. task practice).
7.2 METHODS
7.2.1 Subjects
Thirty active individuals from the University population volunteered for the
study (Age range = 18 – 26 yrs). Given the magnitudes of changes in
performance shown in studies investigating movement-specific adaptations,
an effect size of at least 1.0 was expected. A priori power analysis revealed
that ten subjects were required in each group to be 80% confident (i.e. power
= 0.8) of finding differences significant at the 0.05 level (Table 8.3.13, Cohen,
1988). Of the 30 subjects, 23 (eight women & 15 men) completed the study
with the largest portion of withdrawals resulting from injury sustained outside
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the study. This would have affected the power of tests. Male and female
subjects have been used in many strength/sprint training studies (Esbjörnsson
Liljedahl et al., 1996; Herbert et al., 1998; Hortobàgyi et al., 2000; Mannion et
al., 1994; Smith & Rutherford, 1995). Given the difficulty in recruiting athletic
subjects for the present study, both men and women were included to
increase subject numbers. All subjects had participated in sport at the
recreational or representative level, had a minimum of three months of weight
training experience, could produce a force equal to twice their bodyweight
during an isometric squat lift, had no recent injuries or medical conditions that
would prevent maximal exertion. All subjects read and signed statements of
informed consent prior to participation in the study. The research was
approved by the Southern Cross University Human Ethics Committee
(Appendix B).
7.2.2 Protocol
Subjects participated in four weeks of resistance- and sprint/jump training
(familiarisation) prior to a second five-week (specific) training phase (Figure
7.1). During the four-week familiarisation phase, subjects performed two
sprint/jump sessions per week with each session involving one hour of
supervised training in sprint running and vertical jumping technique. The
purpose of such training was three-fold: 1) to ensure all subjects had
experience with sprint and jump technique so that ‘learning’ of the tasks was
minimal during the subsequent ‘specific’ training phase, 2) to improve the
reliability (decrease the variability) of the subjects’ performances, and 3) to
ensure subjects were training regularly prior to the first testing occasion.
In addition to the sprint/jump training, subjects also performed two supervised
weight training sessions per week. Each session involved performing three
sets of ten repetitions of reclined leg-press, deadlift, leg extension, leg curl
and standing calf raise exercises. If greater than 12 or less than eight
repetitions were performed in a set, the weight was adjusted for subsequent
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sets. The purpose of such training was to ensure all subjects were performing
weight training consistently prior to the study and that all subjects were
competent lifters. Attendance at training sessions was monitored and
subjects who did not perform a minimum of six sprint/jump and six RT
sessions over the four-week period were excluded from the study. Given that
all subjects had been performing RT, and training involving sprinting and
jumping, prior to the study those subjects recruited for the specific training
phase could be considered well-trained.
Following the four-week familiarisation phase, subjects were divided into three
training groups with male and female subjects distributed equally among the
groups. These groups were named squat (SQ), forward hack squat (FHS)
and sprint/jump (SJ) based on their training (see over). Briefly, all groups
performed at least two sprint/jump sessions per week with SQ and FHS also
performing two weight training sessions and SJ two additional sprint/jump
sessions (i.e. four sessions) each week. By the end of the study the SQ, FHS
and SJ groups contained eight, seven and eight subjects respectively (each
group contained at least two females, thus male/female ratios were similar
between the groups).
After the four-week familiarisation phase, but before the five-week specific
training phase, subjects performed 20 m sprint, vertical jump, squat lift,
forward hack squat and isokinetic leg extension tests (pre-test). On a
separate day, EMG was collected from leg musculature during performance of
vertical jump and sprint tasks. Collecting EMG on a separate day would have
minimised the effects of fatigue on the EMG recordings. Muscle thickness,
Familiarisation
(4 weeks)
Pre-test Specific training (5 weeks)
Four groups: SQ, FHS & SJ
Post-test
Figure 7.1. Overview of training and testing. A familiarisation phase preceded the 5-week ‘specific’ training phase to ensure all subjects were currently training. Testingwas performed before and after the specific training phase.
133
pennation and fascicle length were also measured at two regions of both
the vastus lateralis and rectus femoris muscles (see over). The tests were
repeated after the five-week specific training phase (post-test). Three days of
rest separated the last training session of each phase from the testing.
7.2.3 Testing
7.2.3.1 20 m sprint
Times to sprint 10 m and 20 m were recorded using the same protocol
described previously (see Study Four). Briefly, subjects performed three
maximal sprints from a standing start. Electronic timing gates at 0, 10 and 20
m recorded time. The best running time to the 10 m and 20 m marks were
taken as that subject’s performances.
7.2.3.2 Vertical Jump
Subjects performed single- and double-leg vertical jumps using the same
protocol as described previously (see Study Four). Briefly, subjects
performed countermovement jumps with arms crossed over the chest. Jump
height was measured by a cable position transducer; the cable was
connected to a belt secured around the subject’s waist. The greatest jump
height recorded in three trials for both one- (subject’s preferred leg) and two-
legged jumps was taken as a measure of jump performance.
7.2.3.3 Squat lift
Subjects performed dynamic, free-weight squat lifts (minimum internal knee
angle was 90o) and isometric squats as described previously (see Study
Four). The descending phase of the squat lift was performed at a moderate
speed (1-2 s) but the ascending phase was performed maximally. In most
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instances the subject’s feet left the force platform at the end of the
movement and is best termed a ‘jump squat’ (JSQ). The maximum force
produced during the squat lift was taken as a measure of performance.
Testing maximum isometric strength rather than 1-RM strength would have
improved subject safety while allowing good measurement of subjects’ task-
specific strength. Testing of the relationship between dynamic and isometric
squat maximums suggested that weights of 30% and 60% of isometric
maximum correspond to weights of 44% and 88% of dynamic maximum (see
Study Two). Thus force produced during these efforts may indicate the
subjects’ ability to lift lighter and heavier loads rapidly.
7.2.3.4 Forward hack squat
Subjects performed both isometric and dynamic single- and double-leg FHS
as described previously (see Study Four). For the dynamic FHS, subjects
lowered the sled (including weights) at a moderate speed (1-2 s downward
phase) but performed the concentric phase at maximum velocity. A metal
stop was placed such that a spring attached to the sled contacted the stop at
the top of the movement, but before the subjects’ feet left the foot platform.
Therefore, subjects could provide maximum force throughout the concentric
phase without concern for injury. The maximum force produced during FHS
lifts (disregarding the force produced during impact of the sled with the metal
stop) was taken as a measure of performance. The minimum internal hip
angle was 90o and the internal knee angle was 110o. This approximated the
hip and knee angles during push-off in the acceleration phase of sprint
running (Jacobs & Ingen Schenau, 1992). Testing of the relationship between
dynamic and isometric forward hack squat maximums suggested that weights
of 40% and 70% of isometric maximum correspond to weights of 35% and
62% of dynamic maximum (see Study Two).
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7.2.3.5 Isokinetic knee extensor torque
Concentric, isokinetic knee extensor torque of each subject’s right leg was
tested at joint angular velocities of 30o.s-1 and 180o.s-1 using a KinCom
Isokinetic Dynamometer (Chatanooga Inc., USA). Subjects sat with a hip
angle of 90o and were secured by straps across the chest and waist. Gravity
correction of the subject’s limb was performed and anatomical references
defined. To define the anatomical reference, joint angle was measured during
a maximal knee extension contraction and this angle entered into the
computer. Often, angles are defined under passive conditions and the joint
angle during contraction can be different to that measured by the
dynamometer. In our case, the joint angle measured by the dynamometer
was very close to the joint angle actually achieved during the maximal
contractions. During testing, subjects performed two sets of four repetitions of
isokinetic knee extension and flexion at an angular velocity of 180o.s-1, then
three maximal repetitions of knee extension and flexion at 30o.s-1.
Only force data collected during knee extension was used for analysis. From
this, the maximum torque produced at both speeds was calculated, as was
the angle at which the maximum torque was produced at 30o.s-1. The angle of
maximum torque at 180o.s-1 was not used for analysis since torque at this
speed was highly variable both within and between subjects. The knee joint
angle during the concentric movement phase ranged from an external angle
of 95o (knee flexed) to 10o (knee extended) however only data collected from
knee extension between the angles of 80o and 20o was used for analysis. As
such, torque peaks associated with the impact of the tibia against the force
transducer early in the concentric phase were not included in the analysis.
7.2.3.6 Muscle Size and Architecture
While in a supine position subject’s knees were flexed to 90o and supported
136
by the researcher. After applying hypoallergenic, water-soluble
transmission gel to the skin, a qualified sonographer used an 8 MHz linear
ultrasound transducer (Acuson 8L5, California, USA) to scan the surface of
the thigh to locate the muscle-tendon junction at the distal end of the rectus
femoris muscle (RF d). The point was clearly identified since the muscle
appears dark, but the tendon light, on the computer screen (see Figure 7.2).
The areas of transition from muscle to tendon appeared small (approximately
one centimetre). The transducer was then moved two centimetres proximally
where muscle thickness (distance between the superficial and deep borders
of the muscle) was calculated from a transverse section by an Acuson
Sequoia 512 system (Acuson, California, USA) after the muscle was manually
traced on the image screen. The distance to this point was measured on a
line from the joint cleft at the lateral condyle of the femur to the palpable
centre of the greater trochanter (Figure 7.3). The scanning head was then
rotated to view a longitudinal section of the muscle where the aponeurosis of
the muscle and fascicles attached to it were clearly visible. A photograph
(computer-aided transparency) of the ultrasound image was taken for
subsequent pennation measurement. The scanning head was then moved
proximally and muscle thickness measured at regular intervals along the
Figure 7.2. The muscle-tendon junction of rectus femoris was determined by moving thescanning head (ultrasound) distally along the thigh. Diagram A shows the dark centre of rectusfemoris and the white connective tissue that surrounds it (circled). The muscle-tendon junctionwas defined as the point at which the whole of the muscle became white. A longitudinal section(Diagram B) where the rectus femoris can been seen to taper from dark muscle to whiteconnective tissue can verify this.
A B
Rectus femoristapers
137
muscle. At a point where the muscle thickness was deemed greatest, the
measures were repeated. This point was named RF p (proximal rectus
femoris). Measures of muscle thickness and pennation after the five weeks of
training were taken as close as possible to these sights after measuring the
distances from the lateral condyle. Repeatability of the measures was
practiced prior to testing to ensure reliability and has been demonstrated
previously (Giorgi et al., 1999). The reliability of the sonographer has been
determined previously (Ostrowski et al., 1997).
For the vastus lateralis muscle, measures were taken with the subject
remaining in a supine position with the knee flexed to 90o. Measures of
muscle thickness and photographs for pennation assessment were taken two
centimetres from the most distal muscle point (VL d – distal vastus lateralis)
and at the point of greatest muscle thickness (VL p – proximal vastus
lateralis). Again, the distances to these points were measured from the lateral
condyle.
Figure 7.3. Muscle thickness, pennationand fascicle length estimates weremade at two sites of the rectus femorisand vastus lateralis muscle usingultrasound. These sites are shown inthe diagram and described in the text.
RF – Rectus femorisVL – Vastus lateralis
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Pennation measurement
The angles of three fascicles were measured manually three times on the
photograph transparency of the ultrasound image by a goniometer and the
angle for each fascicle taken as the median of the three recordings. The
fascicle angle was measured at the fascicle-aponeurosis junction. As such
slight fascicle curvature was not accounted for (Kawakami et al., 1993). The
mean of the median angle of the three fibre bundles was considered the
muscle pennation angle. The bundles chosen were contained within two
centimetres of each other in the muscle. Reliability of pennation
measurement has been shown (Kawakami et al., 1993; Henriksson-Larsen et
al., 1992) and reliability of our pennation measurements has also been shown
(Blazevich & Giorgi, 2001).
Estimation of fascicle length
Fascicle length (FL) at each region on the two muscles was estimated as the
length of the hypotenuse of a triangle with an angle equal to the pennation
angle (θ) and the side opposite to this angle equal to the muscle thickness (T).
Therefore, FL=T/sinθ. Fascicle length is commonly estimated by this method
(Henriksson-Larsén et al., 1992; Kawakami et al., 1995; Kumagai et al.,
2000). Nonetheless, more recently digital measures have been used where
the fascicle length is measured after tracing it from ultrasound photographs.
We have compared the two methods, the results are presented in Appendix
F). Briefly, mathematical estimation is less reliable than the digital method
making significant changes in fascicle length harder to detect. Given the
results in Appendix F, we predict an error of up to five millimetres may be
expected in the present study using the mathematical method. Digital
techniques were not available for use in this study.
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5.2.3.7 Electromyographic (EMG) analysis
EMG recordings of five muscles of the right leg (gluteus maximus, biceps
femoris [long head], psoas major, rectus femoris and vastus lateralis) were
analysed for contraction/co-contraction patterns after subjects performed both
two-legged vertical jumps and sprint runs. After hair removal and light
abrasion with sandpaper to decrease skin resistance, stainless steel, bipolar,
pre-amplified surface electrodes (inter-electrode distance = 20 mm) were
placed over the muscle belly’s of the five muscles (see Table 7.1). The
recording electrodes were oriented parallel to the predicted line of muscle
fibres. The leads from the electrodes were attached to 6 m extension leads to
allow the subjects to move over a 12 m distance. Subjects then performed
two maximal vertical jumps and two maximal sprints over 8 m such that the
right leg contacted the ground on at least three occasions. A video camera
operating at 50 Hz (shutter speed 1/1000 s) captured the movement on tape
and EMG data collection commenced immediately as the subjects were
instructed to perform the jump or sprint. A light-emitting diode placed in the
camera’s view was illuminated at the same time so the EMG could be
synchronised to the movement. During the movements, raw EMG signals
sampled at 1000 Hz were amplified and collected using A/D conversion
(DT01EZ; Data Translation, USA) by personal computer (386 DX IBM-
compatible). High frequency noise was reduced by a 500 Hz anti-alias filter
and low frequency noise (particularly that caused by movements of the long
electrode cables) was minimised by passing the raw signals through a 10 Hz
high-pass filter. The data was then stored for subsequent analysis.
The VJ was analysed as two parts, the first being the descending or eccentric
phase and the second being the ascending or concentric phase. The sprint
run was likewise divided into two parts, the first being from first contact of the
foot with the ground (foot-ground contact; right foot) to the first contact of the
contralateral (left) foot with the ground, and the second being from
contralateral foot-ground contact to foot-ground contact of the first (right) foot.
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For all subjects, the stride analysis started from the first contact of the right
foot after the subjects had left the starting position. To determine the sections
of EMG used for analysis, the video was analysed for event times. The
associated EMG was then rectified and then averaged in bins of 5% of
movement time. The two phases of each movement were analysed
separately so that the first 50% of the EMG output related to the first
movement phase while the second 50% related to the second movement
phase. Thus, the different phases of the movements were time-normalised.
The EMG data were analysed by two methods. First, EMG recorded during
each 5% period were normalised to the greatest EMG recorded in any 5% bin
for a particular muscle in that movement. Thus an indication of the magnitude
of EMG detected during the movements was obtained. Second, muscle co-
contraction patterns were calculated for the sprint run and muscle activity
onset times calculated for the VJ. A ten-point moving average (1% of
movement time) was applied to the rectified data before determining muscle
burst onset (on) and offset (off) times. Each muscle was analysed separately
and deemed ‘on’ when ten consecutive samples of EMG exceeded a
threshold of 15% of the maximum amplitude of EMG collected for the duration
Table 7.1. Details of electrode placements on the five thigh muscles.
Muscle Electrode placement
Gluteus maximus (GL) Centre of the palpable part of the muscle with the electrodealigned diagonally downwards in line with the fibres
Biceps femoris (BF) A point 50% of the distance from the gluteal fold to the poplitealcrease on a line drawn vertically up the thigh from the palpabletendon on the lateral aspect of the lower, posterior thigh.Subjects flexed the knee to cause contraction of the muscle toensure electrode placement on the belly of the muscle. Theelectrode was aligned parallel to the femur.
Vastus lateralis (VL) A point 50% of the distance from the lateral border of the patellato the greater trochanter and on the line joining these landmarks.The electrode was aligned such that the long axis of the electrodeconfiguration passed through the patella’s centre.
Rectus femoris (RF) A point 50% of the distance from the most medial palpable pointof the inferior superior iliac spine to the middle of the superiorborder of the patella and aligned parallel to the femur (thus thecomplex pennation of RF was not accounted for).
Psoas major (HF; hipflexor
Immediately below the inguinal fold and 2 cm medial to theanterior superior iliac spine. Aligned parallel to the femur.
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of the task. A 15% threshold was selected after trialing thresholds ranging
from 5% to 30% and comparing the on and off times derived manually. The
muscle was deemed ‘off’ when the EMG amplitude diminished to less than
15% of the maximum normalised EMG for ten consecutive samples. On and
off times were checked manually after analysis to reduce the risk of identifying
the muscle as ‘on’ when the muscle was relatively inactive (type I error). This
method of determineing on/off times has been previously presented (Steele &
Brown, 1999).
Muscle co-contraction changes (sprint run) for two pairs of muscles (GL/HF
and VL/BF) were evaluated. The analysis was run for three separate data
sets. First, the percent of movement time in which both muscles were active
in the first and second phases of the movements (i.e. foot-ground contact and
recovery phases for running, and descending and ascending phases of the
vertical jump) was calculated. Two further data sets were calculated, one
where co-contraction patterns were normalised to the average time in which
the muscles were labeled ‘on’ (average of percent time in which one muscle
was ‘on’ and the percent time the second muscle was ‘on’), and a second
where co-contraction patterns were normalised to the ‘on’ time of the muscle
that was active longest during the movement.
Specific terms have been used to describe certain phases of the sprint
running movement. These include:
Acceleration phase of the sprint run – Considered as that part of a sprint run
beginning at the movement’s onset and ending when maximal (or near-
maximal) speed is reached. In the present study, the term refers more to the
early part of this phase when the body has a distinct forward lean. Jacobs &
Ingen Schenau (1992) described this phase by examining sprint runners from
the second to the fourth step of a sprint run from a stationary start.
Foot-ground contact phase – occurs when the foot first strikes the ground and
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ends when the foot leaves the ground.
Recovery phase – describes that part of the running stride from when the foot
leaves the ground to when the foot once again makes contact with the
ground.
Toe-off – refers to the precise moment when the foot leaves the ground (ie
between foot-ground contact and recovery phases).
7.2.4 Training
7.2.4.1 Training groups
Squat (SQ) training
Subjects in the squat (SQ) group used the free-weight squat lift as their
dominant training exercise during the specific training phase (supplemenatry
exercises are described later). The squat lift required subjects to lower their
body to a sitting or squatting position with a knee angle of 90o with a weighted
bar rested across the shoulders then lift the weight back up to the starting
position. Subjects were guided to the correct knee angle by a supervisor
during each squat. Training was performed two times per week. In the first
session of each week (heavy day), subjects performed three warm up sets of
the squat lift (see Appendix D for details) followed by three sets of six squats
with weights equal to 50% - 80% of their pre-determined isometric maximum
force (described earlier). Three minutes rest separated sets. Weights were
increased when subjects could perform more than six repetitions in a set. The
weight lifted throughout the five weeks of training increased from 50 – 60% to
70% - 80%. In some instances, subjects lifted up to 90% of their
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predetermined isometric maximum in sessions toward the end of the
training period. In the second session of each week (light day), subjects lifted
weights equal to 30 – 50% of their isometric maximum for three sets of six
repetitions. No subjects were allowed to lift more than 50% of their
predetermined isometric maximum regardless of strength gains. In both
sessions, the ascending (concentric) phase of the squat was performed at
maximum velocity such that the subjects’ feet left the ground. Thus, the squat
could be considered a jump-squat. The loads were different between
sessions to provide a different movement stimulus (Wilson et al., 1993) and
prevent subjects becoming accustomed to the training. Typical training
sessions for heavy and light days are presented in Appendix D.
In addition to the squat lift training, SQ subjects also performed two sets of ten
repetitions of a back extension exercise, three sets of eight repetitions of a leg
curl (knee flexion) and two sets of eight standing calf raises. All sets were
performed with a weight that allowed movement failure within the allotted
number of repetitions on the heavy day, but could be performed with greater
movement speed and without failure on the light day. Subjects were also
encouraged to perform two sets of abdominal crunches and spend 15 minutes
stretching the major lower limb muscles after training. In addition to the
weight training, SQ subjects also performed two sprint/jump sessions per
week (see over).
Forward hack squat (FHS) training
Training performed by the forward hack squat (FHS) group differed to SQ only
in the exercise used as the dominant lift in weight training. FHS used the one-
legged FHS exercise as their dominant training exercise during the specific
training phase (Figure 7.4). Thus, in contrast to SQ, training was performed
unilaterally since sprint running is performed unilaterally and some research
(Häkkinen et al., 1996; Rube & Secher, 1990; Tanaguchi, 1997) has shown
that adaptations to RT can be specific to the laterality of training exercises.
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Within each session, legs were trained alternately with one set being
performed with the right leg and the next with the left. Training was performed
twice a week (same as SQ). In both sessions, the concentric (upward) phase
of the FHS was performed at maximum velocity such that the sled on which
the weights were placed was moved forcefully into a spring at the top of the
movement. The spring height was set individually for each subject. Typical
training sessions for heavy and light days are presented in Appendix D.
Sprint/jump (SJ) training
Subjects in the sprint/jump (SJ) group did not perform weight training during
the five-week specific training phase. Instead, SJ subjects participated in four
sprint/jump sessions. Thus, the total number of training sessions performed
by all training groups was the same.
7.2.4.2 Sprint and jump training
SQ and FHS subjects performed two sprint/jump training sessions per week
while the sprint/jump (SJ) group performed four sessions per week. The
Figure 7.4. Single-leg forward hack squat. These diagrams show clearly the body position andlaterality of the task. The ‘free’ leg can also be seen flexing while the ‘working’ leg extends.This movement was performed in an attempt to better simulate the acceleration phase of sprintrunning.
145
sessions typically lasted one hour and consisted of a ten minute warm-up,
five minutes stretching, 35 min of sprint and jump training and another ten
minutes of stretching at the end of the session. The sprint/jump sessions
were divided into a sprint component and jump component. During the sprint
component, subjects predominantly practiced running over distances up to 30
m using the techniques previously taught to them. A qualified sprint coach
who was unaware as to the group allocation of subjects supervised all
sessions for each group. Subjects often ran up to 20 sprints in a session with
training volume increasing over the nine weeks of training (four-week
familiarisation and five-week specific training phases). The jump component
typically consisted of both one- and two-legged jumps in sets of three to five
repetitions. Subjects practiced jumping with different countermovement
distances in order to find their optimum knee bend. Subjects were also
expected to perform the jumps maximally and ensure complete extension of
the hip, knee and ankle joints at take-off.
Sessions typically consisted of 20 jumps separated by rest. The training load
was increased over the nine weeks of training. The intensity of the runs and
jumps was always maximal, however the volume of work increased. In the
first week of training, two sets of three sprint runs were separated by two
minutes of rest. Two sets of three vertical jumps were also performed with
one minute of rest separating sets. By the end of the study, four sets of four
sprints with two minutes rest were performed with four sets of four vertical
jumps. For SJ subjects, sprint sessions could not be performed on four
consecutive days. Sprint training may, for example, be performed on
Monday, Tuesday, Thursday and Saturday. For SQ and FHS subjects sprint
sessions were performed on different days to the RT and one rest day
separated the four sessions. For example, sprint sessions may have been
performed on Monday and Thursday with RT sessions being performed on
Tuesday and Friday.
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7.2.5 Data analysis
After satisfying the assumptions of homogeneity of variance (Lavene’s test),
sphericity (Mauchly’s test) and normal distribution of data (Kolmogorov-
Smirnov test), performance changes with training (sprint run, VJ, SQ and
FHS) were analysed using Repeated Measures ANOVA (SPSS v10.0, SPSS
Inc) with ‘group’ as the between subjects factor and ‘time’ (pre- to post-
training) as the within subjects factor. When significant group effects were
revealed, Tukey’s HSD post-hoc analysis was used to determine differences
between the three groups. For all analyses, significance was set at an alpha
level of p<0.05, unless otherwise stated.
Analyses of muscle thickness, pennation and fascicle length were performed
separately. For each measurement site, Repeated Measures ANOVA
examined significant effects of group and time. Interaction effects were
further analysed by one-way ANOVA of difference scores (ie. pre- to post-
training changes). Bonferroni post-hoc analysis tested for significant
differences. In the event of non-homogeneous distribution of data,
Tamhane’s T2 post-hoc analysis was used. Tamhane’s T2 post-hoc analysis
does not assume equal variances. To examine the relationships between
muscle thickness, pennation and fascicle length at each site on the muscles,
Pearson’s Product Moment correlation coefficients were computed on the
difference scores (absolute variable changes from pre- to post-training). In
order to control for type 1 error, significance was set at p<0.01.
Changes in isokinetic knee extension torque produced during contractions at
two speeds were compared using Repeated Measures ANOVA with ‘training
group’ as a between-group factor. Differences in the torque produced at the
different speeds, and changes in the angle at which peak torque was
produced were analysed. Between group effects were further analysed by
Tukey’s HSD post-hoc test.
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Electromyogram data were analysed in two ways. First, changes (±95%
confidence intervals) in normalised EMG for each muscle were calculated for
each 5% of movement. Paired t-tests with Bonferroni correction were used to
assess differences between groups. Due to loss of data, only ten subjects
were included in the analysis. Four subjects had performed RT (SQ and FHS
subjects) while six performed only sprint and jump training (SJ subjects). As
such, comparisons were made only between weight-trainers and SJ subjects.
No comparison was made between SQ and FHS groups because the low
subject number and large number of t-tests performed would have made
significant results unlikely (Perneger, 1998). Therefore effect sizes were
calculated to provide a description of between-group differences without
concern for sample size. In order to control for type I error rate only effect
sizes greater than 1.0 (i.e. between-group differences were greater than the
pooled standard deviation) were deemed large and of statistical importance.
Changes in muscle co-contraction (sprint run) and muscle activity onset times
(VJ) for gluteus maximus and psoas major (GL/HF), and vastus lateralis and
biceps femoris (VL/BF) muscle pairs were compared between the groups
(again, comparisons were only made for ten subjects. As such, comparisons
were made between weight-trainers and SJ subjects) by Repeated Measures
ANOVA. ‘Group’ and ‘movement phase’ were submitted as between-group
factors.
For all Repeated Measures ANOVA’s, power analysis was also performed to
examine the likelihood that significant effects could be detected. When power
was low (power < 0.8) effect sizes were calculated on near-significant results
(p<0.1) to examine differences without concern for sample size. When
significant group effects were revealed, Tukey’s HSD post-hoc analysis was
used to determine differences between the three groups. For all analyses,
significance was set at an alpha level of p<0.05, unless otherwise stated.
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7.3 RESULTS
7.3.1 Performance Changes with Training
There were no differences between the groups’ performances either before or
after the training in any strength, VJ or sprint test. There was however an
effect of time (p< 0.01) such that, for many strength and performance
measures, subjects improved over the five weeks of training. Pre- and post-
training test performances of all subjects (pooled) are presented in Table 7.2.
Test Variable Pre-test 95% CI Post-test 95% CI Mean
Change
p-value
10 m sprint (s) 1.91 1.78-2.02 1.86 1.77-1.95 -0.05 <0.05
20 m sprint (s) 3.26 3.00-3.47 3.22 3.05-3.40 -0.04 NS
VJ 1L (m) 0.29 0.25-0.33 0.28 0.25-0.32 -0.01 NS
VJ 2L (m) 0.40 0.34-0.46 0.41 0.36-0.46 +0.01 NS
FHS 1L iso (N) 1186 1030-1342 1455 1256-1654 +269 <0.01
FHS 2L iso (N) 1817 1558-2077 2108 1827-2389 +291 <0.01
SQ 30% F (N) 1937 1729-2145 2048 1866-2230 +111 <0.05
SQ 60% F (N) 2327 2022-2632 2374 2126-2622 +47 NS
Table 7.2. Pre-training, post-training and change scores for sprint, VJ, FHS and Squat tests (allsubjects pooled). There was an increase in some strength measures and decrease in 10 msprint time (p<0.05). There were no between-group differences.
NS – Not statistically significantVJ – vertical jump, FHS – forward hack squat, SQ – squat.iso – isometric contraction30%, 40%, 60%, 70% - load as a percent of isometric maximumVelp – Peak movement velocity1L – single-leg2L – double-leg
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7.3.2 Isokinetic Knee Extension Torque
7.3.2.1 Angle of peak torque
Reliability of measures of the angle at which peak torque was produced (APT
– Angle of Peak Torque) were poor at 180o.s-1, but were good at 30o.s-1 (see
Table 7.3). Thus changes in APT were analysed only for the slow speed.
There was a near-significant (p<0.07) increase in APT (i.e. the knee angle
was closer to 90o) when all subject data was combined for all groups,
however there was no difference between the groups (see Table 7.4).
Statistical power was low for both main effect (Power = 0.44) and interaction
(Power = 0.39) analyses making it unlikely that significant effects would be
seen. Effect sizes (ES) were thus calculated to examine performance
changes without concern for subject sample size. The effect statistics
suggest that changes in APT may have differed between SQ and FHS (ES =
0.71) and SQ and SJ (ES = 0.90) groups with the knee angle for SQ subjects
being greater (more flexed) after training. Low subject numbers in the present
study may therefore have prevented significance being reached.
Angular Velocity Statistic Score Lower 95% CI Upper 95% CI
30o.s-1 Change in mean 0.61o -2.54 1.32
ICC 0.85 0.64 0.94
180o.s-1 Change in mean 1.18o -1.56 3.91
ICC 0.63 0.26 0.84
Table 7.3. Reliability statistics for angle of peak torque. Inter-repetition reliability for the slow(30o.s-1) movement was better than for the fast movement (180o.s-1).
Subjects produced more knee extension torque at 30o.s-1 than 180o.s-1 (246.7
± 62.6 Nm and 161.8 ± 45.1 Nm respectively; p<0.001) although there were
no significant between-group differences after training. Thus there were no
training-related changes in isokinetic knee extension torque at either
contraction velocity.
7.3.3 Muscle Size and Architecture
7.3.3.1 Muscle thickness
Mean muscle thickness for each training group at each test occasion is
presented in Table 7.5. There was an overall increase in muscle thickness
after training (p<0.05). However, the increase was not different between the
groups (see Figure 7.5). Thus, muscle thickness generally increased in both
muscles in response to training but the change was not related to the training
performed by the subjects. Given the low statistical power of the tests (power
< 0.6), effect sizes were calculated on near-significant results (p<0.1). At
VLd, muscle thickness of FHS subjects decreased relative to both SQ and SJ
(ES = 0.96 and 1.9 respectively). There was no apparent difference between
SQ and SJ. At VLp, muscle thickness of SQ and FHS increased more than
SJ (ES = 1.18 and 0.78 respectively). At RFd, muscle thickness of FHS and
SJ increased more than SQ (ES = 1.27 and 0.90 respectively). While there
Table 7.4. Angle of peak torque (0o = full extension) pre- and post-testing. There wereno differences between the groups.
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was a small difference between FHS and SJ (with muscle thickness of FHS
increasing more, ES = 0.43), the difference was small. There were no
apparent differences between the groups at RFp.
Table 7.5. Mean (±SD) pre- and post-test muscle thickness and change in thickness. Meanchange values are rounded to two significant figures and are not calculated from thepreviously-rounded pre- and post-test scores. There were no between-group differences inchanges in muscle thickness, however there was an overall increase in muscle thicknessacross all groups at each muscle site (p<0.05*) except VL d. VL d – vastus lateralis distal, VL p– vastus lateralis proximal, RF d – rectus femoris distal, RF p – rectus femoris proximal.
Muscle Pre-test
Mean (mm)SD
Post-test
Mean (mm)SD
Change*
Mean (mm)95%Confidence interval
SQ VL d 13.0 3.9 13.6 3.8 0.6 -0.4 – 1.6VL p 23.4 4.4 26.0 3.6 2.6 0.8 – 4.3RF d 13.4 2.3 13.6 3.2 0.2 -1.3 – 1.7RF p 24.0 2.6 25.9 2.2 2.4 0.7 – 4.2
FHS VL d 13.9 2.8 11.3 2.8 -2.6 -9.2 – 4.0VL p 20.0 0.8 22.3 1.4 2.3 0.1 – 4.5RF d 11.1 1.6 14.2 2.0 3.1 -0.6 – 6.8RF p 23.0 1.6 25.5 2.6 2.5 0.7 – 4.3
SJ VL d 11.0 0.6 12.4 2.0 1.3 -1.3 – 4.0VL p 21.0 2.1 21.6 1.7 0.7 -0.8 – 2.2RF d 11.4 1.0 13.8 2.8 2.3 -0.7 – 5.4RF p 20.8 3.3 25.0 4.1 4.2 0.9 – 7.5
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-10
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10
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e o
f th
ickn
ess
(mm
)
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Ch
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ickn
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(mm
) Proximal Vas tus Lateralis
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(mm
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Ch
ang
e o
f th
ickn
ess
(mm
)
Squat
FHS
Sprint/jump
Proximal Rectus Femoris
Distal Vastus Lateralis
Figure 7.5. Muscle thickness changes for all muscle sites. There was a significant increasein muscle thickness after training (p<0.05) but no difference between groups. Solid barsrepresent mean scores while error bars represent the 95% confidence intervals of thechange in muscle thickness.
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7.3.3.2 Muscle pennation
Mean pennation for each training group at each test occasion is presented in
Table 7.6. Statistically significant (p<0.05) changes in pennation were only
seen at VLd where pennation increased after SQ and FHS training but
decreased after SJ training (Figure 7.6). Given the low statistical power of the
tests (power < 0.6), effect sizes were calculated on near-significant results
(p<0.2). For both VL p and RF d, squat and FHS groups showed increases in
pennation while SJ decreased. At VL p effect sizes for the differences in
pennation change scores were 1.08 and 0.78 for SQ and FHS respectively
when compared to SJ. At RF d effect sizes were 0.98 and 1.45. Thus there
was a trend toward greater increases in pennation of muscles of SQ and FHS
subjects that should be followed up in future research.
Table 7.6. Mean (±SD) pre- and post-test muscle pennation and change in pennation. There wasa significant difference in the change in pennation between both the SQ and SJ, and FHS and SJfor VL d (p<0.05*). VL d – vastus lateralis distal, VL p – vastus lateralis proximal, RF d – rectusfemoris distal, RF p – rectus femoris proximal.
Muscle Pre-test
Mean (deg) SD
Post-test
Mean (deg) SD
Change
Mean (deg) Confidence interval
SQ VL d 8.3 1.8 8.8 0.8 0.5 -1.4 – 2.4VL p 9.9 2.2 11.4 1.6 1.5 -0.5 – 3.5RF d 4.1 1.1 5.4 1.0 1.3 -0.2 – 2.8RF p 10.9 3.1 10.1 1.7 -0.9 -4.5 – 2.6
FHS VL d 8.8 0.5 9.9 1.8 1.1 -1.4 – 3.7VL p 10.0 3.2 11.3 3.1 1.3 -1.7 – 4.2RF d 4.1 0.6 6.0 1.2 1.9 0.2 – 3.5RF p 8.3 3.6 9.0 2.1 0.8 -7.5 – 9.0
SJ VL d 9.9 0.7 6.8 0.8 -3.1* -4.0 - -2.2VL p 9.6 1.8 9.0 1.6 -0.6 -2.7 – 1.5RF d 5.4 1.4 5.2 2.6 -0.2 -4.4 – 4.0RF p 10.7 5.2 11.3 5.6 0.6 -0.8 – 2.0
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Figure 7.6. Change in muscle pennation for all muscle sites. At VL d, SQ and FHSincreased pennation while SJ decreased (p<0.05*). There were no other significantchanges. Solid bars represent mean changes in pennation while error bars represent 95%confidence intervals for the change in pennation.
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eg) Distal Vastus Lateralis
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deg
) Proximal Vastus Lateralis
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FHS
Sprint/jump
Proximal Rectus Femoris
*
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7.3.3.3 Fascicle length
Mean estimated fascicle length for each training group at each test occasion
is presented in Table 7.7. At VLd, fascicle lengths for SJ subjects increased
while there were no changes in SQ and FHS subjects. This was reflected in a
significant group × time interaction effect where fascicle lengths of SJ subjects
changed differently to both SQ and FHS subjects (p<0.05; Figure 7.7). At VL
p, there was a non-significant trend toward a group × time interaction (p=0.08;
ES = 4.33) such that again, SJ increased while FHS and SQ did not change.
Thus for vastus lateralis, fascicle length did not change for the SQ and FHS
groups, but increased significantly for SJ.
There were no differences between the groups’ fascicle length changes in the
rectus femoris although for the proximal part of this muscle, fascicle length
increased overall after training (p<0.05). Therefore, training group did not
influence fascicle length of the rectus femoris.
Table 7.7. Mean (±SD) pre- and post-test estimated fascicle length and change in fasciclelength. At VL d there was a significant difference in the change in fascicle length between SQand SJ, and FHS and SJ (p<0.05a). There was also a near significant difference between SQ andSJ for VL p (p=0.08b). Estimated fascicle length increased for RF p with no differences betweenthe groups. VL d – vastus lateralis distal, VL p – vastus lateralis proximal, RF d – rectus femorisdistal, RF p – rectus femoris proximal.
Muscle Pre-test
Mean (deg) SD
Post-test
Mean (deg) SD
Change
Mean (deg)95%Confidence interval
SQ VL d 92.2 28.0 88.5 17.1 -3. 7a -24.3 – 16.9VL p 140.0 29.1 133.0 16.2 -6.1b -37.9 – 24.7RF d 170.0 42.1 207.4 69.4 51.6 -53.0 – 128.2RF p 117.9 34.0 216.1 16.5 -6.6 44.3 – 152.2
FHS VL d 78.9 18.6 71.9 22.9 10.5a -31.6 – 19.5VL p 108.1 53.0 113.9 38.6 32.2 -20.0 – 41.0RF d 131.7 11.9 137.7 33.3 37.6 -63.7 – 65.0RF p 160.1 97.0 181.9 64.0 0.6 -180.3 – 240.6
SJ VL d 64.4 7.1 116.0 15.8 67.5a 31.3 – 71.8VL p 129.3 27.0 161.5 24.1 98.3b 9.9 – 54.6RF d 127.3 41.5 194.9 48.8 31.6 -73.1 – 208.2RF p 106.2 29.3 147.8 36.8 41.6 10.9 – 72.3
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Figure 7.7. Change in fascicle length for all muscle sites. Fascicle length increased for SJat VL d (distal vastus lateralis) while there was no change for SQ and FHS (interactioneffect: p<0.05*). There was also a near-significant difference in the change in fascicle lengthbetween SQ and SJ at VL p (p=0.08+). There were no group differences in fascicle lengthfor rectus femoris. Solid bars represent mean changes in fascicle length while error barsrepresent the 95% confidence intervals for the change in fascicle length.
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7.3.3.4 Relationship between muscle thickness, pennation and
fascicle length
There was no correlation between changes in muscle thickness and
pennation or between changes in thickness and fascicle length. However,
highly significant correlations were found between muscle pennation and
determination ranged from 0.67 to 0.85, therefore 67% - 85% of the variability
in fascicle length can be accounted for by changes in pennation, or vice
versa. Thus, while there was no relationship between muscle thickness and
pennation changes with training, there was a strong relationship between
pennation and fascicle length changes.
7.3.4 Electromyographic Changes
7.3.4.1 Changes in normalised EMG
Pre- to post-training changes in EMG amplitude (normalised to the greatest
EMG during the movement) were calculated for ten subjects. Of those, four
performed RT (SQ and FHS subjects) while six performed only sprint/jump
training (SJ). While low subject numbers likely yielded low statistical power,
Table 7.8. Results of correlation analysis on pennation and estimated fascicle lengthchanges after training. There was a strong relationship between pennation andfascicle length despite no relationship between thickness and either pennation orfascicle length.
data analysis was performed to determine trends that might have been
significant with a larger sample size. There were no differences between
those subjects who performed RT (SQ and SJ) and those who did not (SJ) in
the changes in normalised EMG during the sprint and VJ when univariate
tests were corrected for type I error rate (Bonferroni correction). Therefore,
effect sizes were calculated for 5% sections of movement to examine the
differences between groups without regard for sample size. A stringent effect
size of 1.0 was taken as a ‘large’ effect (Hopkins, 2000). In some cases
uncorrected p-values from t-tests performed on the data were used to indicate
parts of the movement where between-group differences were notable.
For running acceleration (see Figure 7.8) there was an increase in gluteus
maximus (GL) EMG in the weight-trained subjects from the point at which the
right foot left the ground to approximately the point at which the foot passed
under the body (45% - 70% of movement). No differences appeared for
biceps femoris (BF) although EMG for both groups decreased relative to pre-
training levels during foot-ground contact and then increased prior to foot-
ground contact. Thus BF may have been activated differently after training
regardless of the type of training performed by the subjects. Vastus lateralis
EMG of weight-trained subjects was greater from immediately after the right
foot left the ground to just prior to foot-ground contact (65% - 95% of
movement) suggesting greater muscle activity during the recovery phase of
the stride. For rectus femoris (RF), weight-trained subjects tended to increase
EMG prior to foot-ground contact (65 – 95% of movement) while there was no
change in SJ subjects. Finally, hip flexor (HF; psoas major) activity increased
in SJ subjects early in the foot-ground contact phase, and was elevated in
both groups around toe-off and early in the recovery phase. There was also a
marked decrease in HF activity immediately prior to foot-ground contact (90 –
100%) in weight-trained subjects. A t-test (not corrected for type I error rate)
found a significant difference between EMG changes in weight-trained and SJ
subjects in this part of the movement.
159
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Figure 7.8. Change (±95% CI) innormalised EMG for five thighmuscles during the accelerationphase of a sprint run. There wereno differences between weight-trained subjects (dark line) andsprint/jump subjects (light line) forany muscle. Foot-ground contactoccurred at 0% of movement, thefoot left the ground at 50% ofmovement and then contacted theground again at 100% ofmovement.
corrected) difference between subjects who performed RT and those that did
not (significant differences from 75 – 80% and 85 – 90% of movement).
Similarly complex changes were seen in BF with the EMG of SJ subjects
decreasing late in the descending phase (35 – 40% of movement) and the
EMG of weight-trained subjects decreasing early in the ascending phase (60
– 70% of movement). Generally though, both groups produced less EMG
after training either late in the descending or early in the ascending phase, but
more during the middle of the ascending phase. There were no between-
group differences in the change in EMG for VL or HF, although for RF the
weight-trained subjects showed less muscle activity early in the descending
phase (5 – 25% of movement) with the difference being significant by t-test
(uncorrected; 5 – 10% of movement).
7.3.4.2 Changes in muscle co-contraction (sprint run) and activity onset
times (vertical jump)
There were no differences between changes in the co-contraction patterns of
weight-trained and SJ subjects in either phase of the sprint run and VJ
movements. While the observed power of the tests was generally poor
(<0.50) no comparisons approached significance. Thus effect sizes were not
calculated to examine the magnitude of differences without consideration for
sample size.
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Figure 7.9. Change (±95% CI) innormalised EMG for five thighmuscles during the performance of avertical jump. There were nodifferences between weight-trainedsubjects (dark line) and sprint/jumpsubjects (light line) for any muscle.Forward rotation of the upper body(which signalled the beginning of thedescending phase of the jump)occurred at 0% of movement, thetransition from the descending toascending phase occurred at 50% ofmovement, while the toe left theground at the end of the jump at100% of movement.
Mathieu et al., 1988; Weir et al., 1995b). Unfortunately, no research has
examined the activation of compartments during maximal contractions to
determine if compartments that remain inactive during a particular task
become active at maximum.
8.2.4 Long-term adaptations?
Several processes could mediate longer-term improvements in strength.
First, the working muscle will be better able to cope with the loads imposed on
it such that eventually muscle damage and breakdown are of smaller
magnitude and protein synthesis can more dramatically outweigh it. As such,
increases in muscle size would be more rapid. This greater muscle
hypertrophy would lead to improved muscle strength. Also, the nervous
system would continue to adapt to the ‘new’ muscle state acquired from
training. Inter- and intra-muscular coordination would be enhanced so that
certain muscles within a group would be recruited before others thus
amplifying both angle-specific and body position- or posture-specific training
adaptations. Indeed one would ‘learn’ how to most effectively use the muscle
that has changed since training began. Importantly, by providing the muscle
with several stimuli (i.e. concurrent training) the adaptive process would be
more complex and clear changes would not be as readily seen. Such a result
was clearly observed in the present thesis. The processes outlined above
can be summarised as in Figure 8.1.
8.3 SUMMARY
Changes in neural pathways may not adequately predict early increases in
strength with RT. However many adaptations within the muscular system can
account for research observations well. These include changes in sarcomere
lengths and number, architectural changes and fibre hypertrophy (without total
muscle size increases). Neural adaptations may be secondary to these
199
muscular changes while long-term strength changes might be a result of
continued hypertrophy and more minor neural adaptations.
Visible hypertrophy
Fibre hypertrophyPennation & fibre length
Sarcomere adaptation
Inter- and intra-muscular coordination
Synchronisation/inhibitory reflex
0 1 2 3 4 5 6 7 8
Week of Training
0 1 2 3 4 5 6 7 8
Week of Training
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A
BFigure 8.1. Hypothesised time course of muscular (A) and neural (B) changes with resistance exercise.Many of the early changes (<2 weeks) might result from muscular adaptations with changes in thenervous system promptly following. Long-term (>6 weeks) adaptations might occur from considerablehypertrophy and continuing neural adaptation. Different muscles (i.e. different size, architecture, action,etc.) would respond differently, the model presented here is theoretical and may not be faithful to the timecourse f change.
B
A
200
CCHHAAPPTTEERR 99:: TTHHEESSIISS
SSUUMMMMAARRYY
201
9.1 SUMMARY
The first study examined the movement patterns of several resistance and
performance tasks in order to describe similarities between them. The results
were that the VJ without arm swing (particularly with arms placed across the
chest) was kinematically similar to the jump squat exercises. The traditional,
slower squat lift however was not similar largely because joint angle changes
occurred simultaneously rather than sequentially. Also, none of the broad
jump variations were similar to the FHS. Nonetheless the acceleration phase
of sprint running, as described by Jacobs and Ingen Schenau (1992) did
appear similar in both the magnitude and timing of joint angle changes to the
FHS. Given that the FHS is performed in a semi-prone position and can be
performed unilaterally, one could consider the pushing phases of these two
movements very similar. A kinematic study investigating the movement
patterns of subjects performing both tasks is required to more clearly establish
their similarity.
Although two groups of tasks (VJ with arms across the chest and jump-squat,
and the FHS and acceleration phase of a sprint run) were found to be
kinematically similar, it was unclear if they could be described as functionally
(kinetically) similar. That is, do subjects who perform well in a resistance task
also perform well in its related performance task? It is possible that for
optimum improvements in a performance task to occur, the resistance task
might have to be both kinematically and functionally similar. Results of Study
Four included a strong relationship existed between ISQ and VJ performance,
but not JSQ and VJ performance. This suggested that JSQ, while being
kinematically similar, was not functionally similar. The similarity between ISQ
and VJ may reflect their requirement for high muscle forces/stiffness at long
muscle lengths. In the VJ, high muscle forces/stiffness may be required for
optimum use of the stretch-shorten cycle. There was however a strong
relationship between the FHS and acceleration phase of a sprint run.
Furthermore, component analysis hinted at a similarity in their force-velocity
202
characteristics. As such the FHS and sprint tasks could be considered
both kinematically and functionally similar. Given the results of this fourth
study, it was deemed possible to test the effects of kinematic and functional
similarity on performance adaptations in the third study.
The purpose of the fifth study was to examine changes in SQ, FHS, sprint and
VJ performance after a short period of either concurrent resistance- and
sprint/jump training or sprint/jump training alone. Further, the effect of
movement pattern of RT exercises could be compared by two of the
resistance groups performing tasks with different movement patterns as their
dominant training exercise. After five weeks of training there was no
difference between the groups in squat, FHS, sprint or VJ performance.
Therefore, short duration, concurrent training appeared to have no significant
movement pattern- or velocity-specific effects in well-trained subjects. It was
also not possible therefore to determine if only kinematic similarity, or both
kinematic and functional similarity, was required between resistance and
performance tasks for optimum improvements in a task to occur. The low
statistical power resulting from low subject numbers may have affected
significant findings. However, if clear differences existed between groups,
these would have likely been detected since statistically significant
improvements in many of the resistance and task tests were found across the
groups after the five weeks of training.
Many factors affect the movement pattern-specific effect. Three of these were
examined in this fifth study: body position, joint angle and laterality. There
was no apparent effect of body position on training adaptations as there was
no difference between the resistance groups in their performance of the FHS
and squat tests. Although the magnitude and timing of joint angle changes
and laterality also differed between these two tasks, one would expect that if
body position affected performance then some differences between groups
would have been found given they trained with exercises that had different
body positions. On the other hand, a difference between the groups would
203
not have been conclusive evidence of an effect of body position given the
other factors that differed between the tasks.
With respect to joint angle changes, while the timing and magnitude of joint
angle changes differed between the SQ and FHS tasks, there were no
differences between the groups that trained with these tasks. Nonetheless,
there was some evidence (supported by high effect sizes) of between-group
differences in the angle at which peak torque was produced (APT) during slow
isokinetic knee extension. APT in subjects who performed SQ training was
produced at a more closed angle after training while there was no difference
in the angle for subjects who trained with the FHS. Given that the range of
motion through which the knee moved was greater for subjects who
performed the SQ training, the result provides some evidence for angle-
specific torque changes. If small changes in APT did occur between groups,
between-group differences in dynamic tests could possibly be expected after
longer training periods.
Effects of laterality of training were also investigated. There was no evidence
for laterality-specific adaptations as there were no differences in unilateral VJ,
unilateral FHS or unilateral isokinetic knee extension performance after
training. Again, the result might be due to the short training period and/or low
subject number. Alternatively the result might suggest that early adaptations
to concurrent strength and sprint/jump training are not specific to the laterality
of training exercises.
The effects of training velocity could be examined since one group performed
no RT and therefore performed only high-speed running and jumping
movements. There was strong evidence that muscle pennation of the vastus
lateralis muscle increased while fascicle length decreased in groups who
performed RT in addition to the sprint/jump training. Subjects who performed
no RT however showed no increase in pennation but longer fascicle lengths.
Such changes may have contributed to similar increases in muscle thickness
204
after training. The changes were certainly similar to those described
previously in the literature (Burkholder et al., 1994; Kawakami et al., 1995).
Nonetheless, these architectural changes, while theoretically important to the
shortening velocity of the muscle, did not manifest themselves by changes in
dynamic performance in this short-term study. There was no difference
between groups in the performance of the SQ, FHS, sprint or jump tests, nor
was there a difference in their improvements in isokinetic knee extensor
torque at any movement speed (30o.s-1 or 180o.s-1). The lack of significant
change in the knee extension test might be due to the training and testing
modes being different. However, the change in architectural characteristics of
muscle suggest that long-term training, even when resistance- and task
training are performed concurrently, might result in velocity-specific
performance changes. Given that changes occur rapidly however, athletes
who use resistance- and task training concurrently might be able to quickly
reverse any adverse architectural changes by performing only sprint-type
training.
Finally, the results of the EMG analyses were equivocal due to high inter-
individual variability and low statistical power. There was some evidence
however that changes in muscle activity of resistance-trained subjects may
have affected sprint running but improved VJ efficiency. However there was
no change in muscle co-contraction patterns in sprint running or in the muscle
activity onset times during VJ. There were also no changes in the muscle
activity patterns of sprint/jump subjects. As such, changes in the nervous
system may be highly individual, especially when resistance- and task training
are performed concurrently by well-trained subjects for short periods and
changes in the nervous system resulting from training may not be as
consistent as when RT is performed in isolation.
In conclusion, for the subjects tested here there was some evidence of
muscle architectural changes related to the velocity of training exercises.
However there were no differences between the groups in their performance
205
of SQ, FHS, sprint or VJ tests, and little or no change in joint angle-specific
torque at the knee or muscle activity patterns. Therefore, for short training
periods, changes resulting from concurrent training appear different to those
where RT is performed in isolation in that changes are not as abrupt or
consistent across subjects. Nonetheless, there is enough evidence to
suggest that differences between ‘specific’ and ‘non-specific’ training may be
significant after longer training periods.
9.2 FUTURE RESEARCH
There are many neuromuscular adaptations that can occur with RT and with
concurrent training. Certainly there is still much work needed to ascertain the
exact nature of these adaptations. This work been highlighted throughout the
thesis and will not be reiterated here. Some important research that must be
conducted however stems from limitations of Study Five. Namely:
1) changes in muscle activation need to be examined in greater detail,
2) more subjects are required to provide a more detailed and accurate
account of neuromuscular and performance changes,
3) training should be performed for longer (> 3 months) periods to allow
examination of both short- and long-term adaptations to the training.
4) Different concurrent training regimes need to be used in studies to assess
the effects of relative volumes and intensities of resistance- and task
training.
Such research, combined with more detailed research investigating singular
mechanisms would improve our knowledge of adaptations to concurrent
resistance- and speed training and help coaches and athletes plan their
training for optimum performance.
206
RREEFFEERREENNCCEESS
207
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APPENDIX A
ETHICS APPLICATION
BIOMECHANICAL AND CROSS-SECTIONAL ANALYSIS OF
FOUR RESISTANCE TRAINING EXERCISES
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Southern Cross University
Human Experimentation Ethics Committee
Proposed Project Using Experimental Procedures on HumanSubjects
INITIAL APPLICATION for approval for year 1997
1. Name of Project: Biomechanical and Cross-sectional Analysis of FourResistance Training Exercises
2. Name: Anthony Blazevich
Position: PhD Candidate
School: Exercise Science and Sport Management
Telephone Extension: 3231
3. Supervisor: Dr. Greg Wilson
4. Technicians associated with experiment:Mr. Robert BaglinMr. Mark Fisher
5. Funding - Have you received or applied for external funding of thisexperiment?
NO
6. Proposed date of commencement: September 15 1997.
7. Duration and estimated finishing date: October 31 1997.
8. Intended number of participants: 30 active male subjects, who haveexperience in weight training, will be voluntarily recruited from the Universityand local community.
9. Age range of participants: 18 - 30 yrs
10. Aim or purpose of the experiment: The purpose of the study is two-fold.The first purpose is to compare subject’s performances in several resistancetraining exercises with their performance in vertical jump, broad jump andsprint running tests. Resistance training exercises will include a reverse hacksquat (i.e. the subject performs a movement similar to a squat on a hacksquatmachine but faces the machine such that the body is prone but inclined to45o), barbell squat lift, Smith Machine squat lift and incline seated leg press
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(hereafter referred to as leg press). The second purpose is to describe thekinetics, kinematics and electromyogram (EMG) patterns of the fourresistance training exercises. The movement pattern and EMG will then becompared to that of the running acceleration phase of sprint running and thevertical jump as described in the literature.
11. Methodology of the proposed study (including the source ofparticipants and how they were selected), procedures (e.g. blood samples),and methods to be adopted:
Thirty experienced male and female weight trainers who also perform trainingwhich includes running (eg soccer, hockey or rugby players, recreationalathletes, etc.) will be recruited from the University population and local area.The subjects will perform maximal lifts with a load equal to 80% of maximumon the reverse hack squat, barbell squat, Smith Machine squat and leg pressexercises as well as performing vertical jump, broad jump and 20 m sprinttests over three days. The vertical jump tests will include both squat jumpswith (counter-movement jump, CMJ) and without (squat jump, SJ) a counter-movement (i.e. a noticeable dip of the body before the vertical jump).Subjects will be asked to perform a training session three days prior to thefirst testing day to become familiar with the resistance training exercises.Training will involve two sets of ten repetitions of each of the resistanceexercises at a weight which could be lifted only ten times in each set.
On the first day of testing, subjects will perform each resistance trainingexercise at incremental weights until a weight cannot be lifted after a thoroughwarm-up including 5 minutes of cycling and several submaximum lifts. Thus,a measure of each subject’s maximum lift (1 RM - one repetition maximum)will be determined. On the second day of testing - two days after thedetermination of 1RM’s - subjects will perform two maximal SJ’s, CMJ’s and20 m sprints from a standing start. A third repetition will be performed if thesecond trial is greater than the first. On the third day, maximum lifts with eachof the four resistance exercises with 80% of each subject’s 1 RM will beperformed. Force will be recorded on a force platform which will be positionedeither under the feet (for the squat lifts) or on face of the weighted sledge (forthe leg press). The force platform will register zero force when the subject isstanding on the platform with the weight taken on the shoulders (or, for the legpress, while the subject is supporting the weight). Two trials will be allowed,but a third trial will be allowed if the second lift is greater than the first.
To minimise fatigue, four minutes of passive rest will be allowed betweeneach 1 RM and 80% of 1 RM trial and between the 30 m sprints, while twominutes rest will be allowed between successive jumps. Ten minutes of restwill be allowed between each testing block (i.e. between 1 RM tests on eachresistance exercise, and between the jumps and sprints). Subjects will beallowed to perform low intensity cycle exercise or jogging to aid recoveryduring this period. The order of testing will be randomised for each subject oneach day. This should ensure that effects of fatigue or familiarisation do notresult in a bias towards any one test.
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During the testing period, ten male subjects will be randomly selected toparticipate in a biomechanical analysis of the resistance training movements.EMG data will be recorded from eight muscles (as described below) by bipolarsurface electrodes prior to a video analysis of the same movement.
(If there is insufficient space, an addendum should be attached)
12. Indicate any potential risk you can envisage to the participants andsafety precautions to be taken.
Subjects will be required to exert maximum effort during the testing sessionsand as such there is always the possibility that muscular strains can occur.However, only previously trained subjects are to be recruited as subjects andall subjects will be thoroughly warmed up prior to testing. Further, the testingwill be strictly supervised such that appropriate loads and techniques areemployed on all exercises. Dermal infection has also been reported afterplacement of EMG electrodes on the skin. To prevent infection, alcohol willbe applied to the skin prior to electrode placement and an antiseptic creamwill be applied to the skin after the electrodes have been removed.
13. Comment of any relevant ethical considerations, and attach theconsent form to be signed by participants, for approval.
The project is a standard cross-sectional and biomechanical study involvingtesting methods which are common practice and have been successfully andsafely performed by the investigator on a number of occasions.
A copy of the consent form to be signed by participants must be attached forapproval.
14. Comments (if thought necessary from Head of School e.g. onrelationship of this experiment to current practice in the discipline.
Signed Head of School: ________________________________
Date: ____________________
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15. Certification:
I, the person responsible, certify that the proposed experiment will confirmwith the general principles set out in the N.H. and M.R.C. “Statement onHuman Experimentation and Supplementary Notes (1987)”.
Biomechanical and Cross-sectional Analysis of Four Resistance TrainingExercises
You are invited to participate in a study designed to compare subject’sperformances in four resistance training exercises (reverse hack squat,barbell squat, Smith Machine squat and leg press) with their performance invertical jump, broad jump and sprint running tests, and to describe the kinetics(forces), kinematics (motions) and electromyogram (EMG) patterns of the fourresistance training exercises. The movement pattern and EMG will then becompared to that of the running acceleration phase of sprint running and thevertical jump as described in the literature.
PROCEDURES TO BE FOLLOWEDAll testing will be carried out in the Biomechanics and Rehabilitation ResearchLaboratories of the School of Exercise Science and Sport Management. Afterperforming a training session three days prior to the first testing day tobecome familiar with the resistance training exercises, subjects will undergothree days of testing. On the first day of testing, subjects will perform eachresistance training exercise (the reverse hack squat, barbell squat, SmithMachine squat and leg press) at incremental weights until a weight cannot belifted. Thus, a measure of each subject’s maximum lift (1 RM - one repetitionmaximum) will be determined. On the second day of testing, two days afterthe determination of 1RM’s, subjects will perform two maximal SJ’s, CMJ’sand 20 m sprints from a standing start. A third repetition will be performed ifthe second trial is greater than the first. On the third day, maximum lifts witheach of the four resistance with 80% of their 1RM will be performed. Forcewill be recorded on a force platform which will be positioned either under thefeet (for the squat lifts) or on face of the weighted sledge (for the leg press).The force platform will register zero force when the subject is standing on theplatform with the weight taken on the shoulders (or, for the leg press, whilethe subject is supporting the weight). Two trials will be allowed, but a thirdtrial will be allowed if the second lift is greater than the first..
During the testing period, ten male subjects will be randomly selected toparticipate in a biomechanical analysis of the resistance training movements.EMG data will be recorded from eight muscles (as described below) by bipolarsurface electrodes prior to a video analysis of the same movement.Participation in the biomechanical analysis is not dependent uponparticipation in the cross-sectional analysis.
The above are standard tests of lower body strength and power. Further, thebiomechanical analysis is similar to that performed in numerous previousstudies. To minimise fatigue during the three days of testing, four minutes ofpassive rest will be allowed between each 1 RM and 80% of 1 RM trial and
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between the 30 m sprints, while two minutes rest will be allowed betweensuccessive jumps. Ten minutes of rest will be allowed between each testingblock (i.e. between 1 RM tests on each resistance exercise, and between thejumps and sprints). Subjects will be allowed to perform low intensity cycleexercise or jogging to aid recovery during this period. The order of testing willbe randomised for each subject on each day. This should ensure that effectsof fatigue or familiarisation do not result in a bias towards any one test.
POSSIBLE SUBJECT DISCOMFORTS/RISKS
Subjects may experience some muscular soreness after the familiarisationand testing sessions. Further, the performance of maximal muscularcontractions, either during the testing or familiarisation sessions, has apotential to result in muscular strains. All necessary safe guards (includingproper warm-up and supervision) will be used to minimise such anoccurrence. Also, acute dermal infections have been reported after EMGelectrode use. To eliminate the chance of infection, an alcohol solution will beapplied to the skin prior to EMG electrode placement and an antiseptic creamwill be applied after EMG electrode removal.
SUBJECT BENEFITS
Subjects can benefit from participation in the study by:Having the opportunity to observe methods of experimental research in thisarea.Contributing to the advancement of science as a research participant.Obtaining information and advice on strength and power training.Being first to obtain the results and practical implications of the study.Having their lower body strength and power, and sprinting and jumpingabilities tested at no expense.
INVESTIGATOR RESPONSIBILITIES
Any information that is obtained in connection with this study and thatcan be identified with you will remain confidential and will be disclosed onlywith your permission.
If you decide to participate, you are free to withdraw your consent andto discontinue participation at any time without prejudice. However, priornotice of withdrawal would be appreciated.
If you have any questions, please contact Tony Blazevich on (H) 223 763 or(Uni) 203 231, at any time.
You will be given a copy of this form to keep.
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SUBJECT’S DECLARATION OF CONSENT
I _________________________________ , being over eighteen years of ageconsent to being a subject in the research project “Biomechanical and Cross-sectional Analysis of Four Resistance Training Exercises”.
I have been given a copy of a “Form of Disclosure and Informed Consent”document which I fully understand describing the procedures to be followedand the consequences and risks involved in my participation as a subject.
I have read the information above and any questions I have asked have beenanswered to my satisfaction. I agree to participate in this activity, realisingthat I may withdraw without prejudice at any time.
I agree that research data gathered from the study may be published providedmy name is not used.
NAME OF SUBJECT ______________________________
SIGNATURE OF SUBJECT _________________________DATE ____________
NAME OF WITNESS ______________________________
SIGNATURE OF WITNESS _________________________DATE ____________
SIGNATURE OF RESEARCHER _____________________DATE ____________
certifying that the terms of the form have been verbally explained to thesubject, that the subject appears to understand the terms prior to signing theform, and that proper arrangements have been made for an interpreter whereEnglish is not the subjects first language.
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APPENDIX B
ETHICS APPLICATION
INFLUENCE OF MOVEMENT PATTERN OF RESISTANCE
TRAINING EXERCISES ON VERTICAL JUMP AND SPRINT
RUNNING PERFORMANCE DURING CONCURRENT
RESISTANCE AND TASK TRAINING
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Southern Cross University
Human Experimentation Ethics Committee
Proposed Project Using Experimental Procedures on HumanSubjects
INITIAL APPLICATION for approval for year 1999
1. Name of Project: Influence of movement pattern of resistance trainingexercises on vertical jump and sprint running performance during concurrentresistance and task training
2. Name: Anthony Blazevich
Position: PhD Candidate
School: Exercise Science and Sport Management
Telephone Extension: 3231
3. Supervisor: Dr. Robert Newton
4. Technicians associated with experiment:Mr. Robert BaglinMr. Mark Fischer
5. Funding - Have you received or applied for external funding of thisexperiment?Submitted full version to American Society of Biomechanics Graduate StudentGrant-in-aid scheme.
6. Proposed date of commencement: March 21, 1999.
7. Duration and estimated finishing date: June 1, 1999.
8. Intended number of participants: 60 active male subjects will bevoluntarily recruited from the University and local community.
9. Age range of participants: 18 - 30 yrs
Aim or purpose of the experiment: The present investigation will examine theperformance changes of complex tasks (vertical jump and acceleration phaseof a sprint run) while task training is performed with resistance training (eitherthe squat lift or a new forward hack squat exercise). In addition, performancechanges after concurrent task and resistance training will be compared toperformance changes of subjects performing no resistance training but twice
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the number of task training sessions.
11. Methodology of the proposed study (including the source ofparticipants and how they were selected), procedures (e.g. blood samples),and methods to be adopted:
Experimental Design:Training will consist of a four-week familiarisation training phase in which allsubjects will perform sprint running (20 m) and vertical jump training twice aweek in addition to two resistance training sessions a week. The resistancetraining will consist of exercises that can be regarded as being non-specific tothe vertical jump and sprint running tasks. The familiarisation period willincorporate that period of training where substantial performanceimprovements in vertical jump and sprint running would occur. Thus, smallerimprovements are likely during the specific phase of training. The specificphase of training will last 6 weeks, short enough for minimal increases inhypertrophy to occur and for architectural (including sarcomere lengthchanges) and neural adaptations to be the most likely culprits for adaptation.During this phase of training, subjects will be organised into three traininggroups (2 experimental and 1 control), one group will dominantly use thesquat lift (or jump squat) and one group the one-legged forward hack squatduring their resistance training. Biomechanical analyses in our laboratoryhave compared and contrasted several versions of the vertical jump andsquat lift as well as examining the forward hack squat. Versions of theseexercises have been found that are very similar and could be deemedmovement pattern-specific. Other supplementary exercises will also beperformed during the training. Both of experimental groups will also performtwo vertical jump and sprint running sessions a week. The third, control,group will perform no resistance training but will participate in four verticaljump and sprint running sessions a week. Subjects will undergo a series oftests before and after this six-week specific training period.
Resistance TrainingDuring the ‘non-specific’ training phase, all subjects, including the controls,will perform resistance training twice a week with the dominant exercise beingthe leg press (incline). Other supplementary exercises will include the legextension, leg flexion (leg curl), deadlift and standing calf raise exercises.Four sets of leg press will be performed and two sets of all other exercises.Weights will be increased such that in week one, subjects will perform sets of12 repetitions and proceed to sets of 6 – 8 by the fourth week. Thus, allsubjects will perform general strengthening prior to the specific training phase.
During the ‘specific’ training phase, the two experimental groups will use their‘specific’ exercise as the dominant movement. Training will alternate suchthat the first session of each week is performed at weights of 80% of 1 RMwhile in the second session weights of 30% of 1 RM will be used. The ‘squat’group will perform the bilateral squat lift as their dominant exercise with all liftsbeing performed with a maximal concentric phase. As such, the exercisecould be likened to the jump squat since most subjects will leave the ground
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at the end of the concentric phase. The eccentric phase will always beperformed over a 1 – 2 s period. In the first week, the subjects will perform 3sets of 6 repetitions of the squat exercise after 2 warm-up sets at increasingweights. Training will progress to 4 sets of 8 repetitions by the end of thetraining period. Supplementary training will include 3 sets of 10 repetitions ofprone back extension, 3 sets of 10 repetitions of leg curl and 3 sets of 10repetitions of the standing calf raise exercise. The group using the forwardhack squat exercise (‘FHS’) will perform the task unilaterally in training. Thus,while each leg might perform those repetitions in which they are directlyinvolved, synergist and fixator musculature will be involved in all repetitions.As such, training will be adjusted accordingly. In the first week, the subjectswill perform 2 sets of 6 repetitions on each leg after 2 warm-up sets atincreasing weights. Training will progress to 3 sets of 8 repetitions by the endof the training period. As for the squat group, all movements will beperformed with a maximal concentric phase with the weight being stopped atthe top of its movement by a spring to prevent injury. Supplementary trainingwill be identical to the squat group. Weights used by both groups will beincreased over the training period as their performances in these lifts improve.
Vertical Jump and Sprint Running Training
Experimental subjects will perform two sessions, while the control group willperform four session, each week. After a thorough warm-up, subjects willperform sets of 20 m sprint and vertical jumps. In the first session each week,sprint training will be performed first while in the second session verticaljumps will be performed first. This should eliminate the effects of fatigue onlearning and performance. In the first week, subjects will perform sessionsinvolving 3 x 30 m sprints and 3 sets of 3 countermovement jumps with oneminute rest between sets. By the end of the full 10 weeks of training, trainingwill increase to 6 x 30 m sprints and 6 sets of 4 countermovement jumps with4 minutes rest between sprints and 2 minutes rest between sets of jumps. Allsubjects will be briefed on the fundamentals of sprint running and verticaljumping during the familiarisation period.
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Testing
Testing will be performed immediately prior and subsequent to the six weekspecific training phase with the test battery for each subject being spacedover several sessions to minimise fatigue.
1) Squat lift: squat lifts with a maximal concentric phase and an eccentricphase lasting 1 – 2 s will be performed on a force platform. Performancemeasures will include maximum force, time at which maximum force occurredand impulse during the concentric phase of the movement. In addition, bardisplacement will be registered by use of a flywheel instrument attached to thebar from which the concentric and eccentric phases can be discerned and barvelocity can be calculated. Subjects first perform a maximal isometric squatat the bottom position of a squat (individually determined at the point theirlowest point in a jump squat) and maximum force will be measured. Squat lifttesting will then be performed with weights equivAlént to 30% and 80% of thismaximum isometric force. By not performing lifts with maximum weight, therisk of injury should be dramatically reduced. Since the aim of the presentstudy is to investigate the effect of movement pattern, rather than velocity, oftraining exercises, testing after the 6 week training period will utilise thesesame weights, rather than a new weight that is congruent with subject’sstrength increases. Thus, subjects’ performances will be compared at a givenweight, similar to the vertical jump where weights are not changed aftertraining. Subjects will be allowed three attempts at each.2) Forward Hack Squat: after measuring subjects isometric force at thebottom of the forward hack squat movement, subjects will perform maximalone- and two-legged forward hack squats with a 1 – 2 s eccentric phase.Measures will be as per the squat lift. Subjects will be allowed three attemptsat each.3) Countermovement Vertical Jump: subjects will jump for maximumheight on a force platform. Ground reaction forces will be mearsured for eachjump from which body displacement will be estimated. Thus, problemsassociated with jump and reach tests will be eliminated. Subjects will performboth one- and two-legged trials; three repetitions will be performed of each.4) Sprint Test: 10 m and 20 m sprint times will be recorded during a 20 mmaximal sprint. Subjects will begin from a standing start with one foot in frontof the other but will be allowed to bend the knees to lower the body’s centre ofgravity. Subjects will be allowed three trials.5) Muscle Pennation and Thickness Tests: ultrasound will be used toimage the vastus lateralis and rectus femoris of subjects (10 subjects fromeach group only). For the rectus femoris, photographs will be taken at points20% and 50% of the distance from the tendomuscular junction (clearly visiblein most subjects) to its attachment at the hip. Thus measures of pennation,thickness and anatomical cross-sectional area will be taken at the midpointand at one end of the muscle. For vastus lateralis, photographs will be takenat 20% and 50% of the distance from the lateral condyle of the femur to thegreater trochanter.6) Electromyographic Analysis of the Vertical Jump and Sprint Run: Afterstandard skin preparation including hair removal, light abrasion with
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sandpaper and swabbing with disinfecting alcohol, 8 subjects from each ofthe three groups will perform two-legged vertical jumps and 10 m sprints withelectrodes placed on their gluteus maximus, vastus lateralis, biceps femoris(long head), illiopsoas and rectus femoris muscles. Timing of musclecontractions and level of cocontraction will subsequently be estimated. Allsubjects will be filmed to ascertain key events during each task; an LED willbe used to synchronise EMG and video data.7) Isokinetic Knee Extension: To examine changes in the torque-anglerelationship about the knee, subjects will perform slow (30o.s-1) and fast(300o.s-1) isokinetic knee extensions. An isometric pre-load force will beimposed prior to the movement to minimise force spikes at the onset ofmovement and provide more reliable force measures in the early part of themovement. Biomechanical analyses suggest that the angle through which theknee moves differs between the squat and FHS exercises making this jointideal for torque-angle testing.
Statistical Analysis
After testing for normality of the data, repeated measures ANOVA’s with twofactors (group and time) will examine differences in performance from pre- topost-training. An Alpha Level of 0.05 will be used to minimise type I error.Correlation coefficients will also be calculated to examine relationshipsbetween test performances, and between changes in test performances andchanges in physiological variables (eg muscle thickness, pennation, level ofco-contraction, joint-specific torque, etc.).
12. Indicate any potential risk you can envisage to the participants andsafety precautions to be taken.
Subjects will be required to exert maximum effort during the testing sessionsand as such there is always the possibility that muscular strains can occur.However, only previously trained subjects are to be recruited as subjects andall subjects will be thoroughly warmed up prior to testing. Further, the testingwill be strictly supervised such that appropriate loads and techniques areemployed on all exercises. Dermal infection has also been reported afterplacement of EMG electrodes on the skin. To prevent infection, alcohol willbe applied to the skin prior to electrode placement and an antiseptic creamwill be applied to the skin after the electrodes have been removed.
13. Comment of any relevant ethical considerations, and attach theconsent form to be signed by participants, for approval.
The project is a standard training study involving testing methods which arecommon practice and have been successfully and safely performed by theinvestigator on a number of occasions.
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14. Comments (if thought necessary from Head of School e.g. onrelationship of this experiment to current practice in the discipline.
Signed Head of School: ________________________________
Date: ____________________
15. Certification:
I, the person responsible, certify that the proposed experiment will confirmwith the general principles set out in the N.H. and M.R.C. “Statement onHuman Experimentation and Supplementary Notes (1987)”.
Influence of movement pattern of resistance training exercises on verticaljump and sprint running performance during concurrent resistance and tasktraining
You are invited to participate in a study designed to examine the performancechanges of complex tasks (vertical jump and acceleration phase of a sprintrun) while task training is performed with resistance training (either the squatlift or a new forward hack squat exercise). In addition, performance changesafter concurrent task and resistance training will be compared to performancechanges of subjects performing no resistance training but twice the number oftask training sessions.
PROCEDURES TO BE FOLLOWED
Experimental Design:Training will consist of a four-week familiarisation training phase in which allsubjects will perform sprint running (20 m) and vertical jump training twice aweek in addition to two resistance training sessions a week. The resistancetraining will consist of exercises that can be regarded as being non-specific tothe vertical jump and sprint running tasks. The familiarisation period willincorporate that period of training where substantial performanceimprovements in vertical jump and sprint running would occur. Thus, smallerimprovements are likely during the specific phase of training. The specificphase of training will last 6 weeks, short enough for minimal increases inhypertrophy to occur and for architectural (including sarcomere lengthchanges) and neural adaptations to be the most likely culprits for adaptation.During this phase of training, subjects will be organised into three traininggroups (2 experimental and 1 control), one group will dominantly use thesquat lift (or jump squat) and one group the one-legged forward hack squatduring their resistance training. Biomechanical analyses in our laboratoryhave compared and contrasted several versions of the vertical jump andsquat lift as well as examining the forward hack squat. Versions of theseexercises have been found that are very similar and could be deemedmovement pattern-specific. Other supplementary exercises will also beperformed during the training. Both of experimental groups will also performtwo vertical jump and sprint running sessions a week. The third, control,group will perform no resistance training but will participate in four verticaljump and sprint running sessions a week. Subjects will undergo a series oftests before and after this six-week specific training period.
Resistance TrainingDuring the ‘non-specific’ training phase, all subjects, including the controls,will perform resistance training twice a week with the dominant exercise being
265
the leg press (incline). Other supplementary exercises will include the legextension, leg flexion (leg curl), deadlift and standing calf raise exercises.Four sets of leg press will be performed and two sets of all other exercises.Weights will be increased such that in week one, subjects will perform sets of12 repetitions and proceed to sets of 6 – 8 by the fourth week. Thus, allsubjects will perform general strengthening prior to the specific training phase.
During the ‘specific’ training phase, the two experimental groups will use their‘specific’ exercise as the dominant movement. Training will alternate suchthat the first session of each week is performed at weights of 80% of 1 RMwhile in the second session weights of 30% of 1 RM will be used. The ‘squat’group will perform the bilateral squat lift as their dominant exercise with all liftsbeing performed with a maximal concentric phase. As such, the exercisecould be likened to the jump squat since most subjects will leave the groundat the end of the concentric phase. The eccentric phase will always beperformed over a 1 – 2 s period. In the first week, the subjects will perform 3sets of 6 repetitions of the squat exercise after 2 warm-up sets at increasingweights. Training will progress to 4 sets of 8 repetitions by the end of thetraining period. Supplementary training will include 3 sets of 10 repetitions ofprone back extension, 3 sets of 10 repetitions of leg curl and 3 sets of 10repetitions of the standing calf raise exercise. The group using the forwardhack squat exercise (‘FHS’) will perform the task unilaterally in training. Thus,while each leg might perform those repetitions in which they are directlyinvolved, synergist and fixator musculature will be involved in all repetitions.As such, training will be adjusted accordingly. In the first week, the subjectswill perform 2 sets of 6 repetitions on each leg after 2 warm-up sets atincreasing weights. Training will progress to 3 sets of 8 repetitions by the endof the training period. As for the squat group, all movements will beperformed with a maximal concentric phase with the weight being stopped atthe top of its movement by a spring to prevent injury. Supplementary trainingwill be identical to the squat group. Weights used by both groups will beincreased over the training period as their performances in these lifts improve.
Vertical Jump and Sprint Running Training
Experimental subjects will perform two sessions, while the control group willperform four session, each week. After a thorough warm-up, subjects willperform sets of 20 m sprint and vertical jumps. In the first session each week,sprint training will be performed first while in the second session verticaljumps will be performed first. This should eliminate the effects of fatigue onlearning and performance. In the first week, subjects will perform sessionsinvolving 3 x 30 m sprints and 3 sets of 3 countermovement jumps with oneminute rest between sets. By the end of the full 10 weeks of training, trainingwill increase to 6 x 30 m sprints and 6 sets of 4 countermovement jumps with4 minutes rest between sprints and 2 minutes rest between sets of jumps. Allsubjects will be briefed on the fundamentals of sprint running and verticaljumping during the familiarisation period.
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Testing
Testing will be performed immediately prior and subsequent to the six weekspecific training phase with the test battery for each subject being spacedover several sessions to minimise fatigue.
1) Squat lift: squat lifts with a maximal concentric phase and an eccentricphase lasting 1 – 2 s will be performed on a force platform. Performancemeasures will include maximum force, time at which maximum force occurredand impulse during the concentric phase of the movement. In addition, bardisplacement will be registered by use of a flywheel instrument attached to thebar from which the concentric and eccentric phases can be discerned and barvelocity can be calculated. Subjects first perform a maximal isometric squatat the bottom position of a squat (individually determined at the point theirlowest point in a jump squat) and maximum force will be measured. Squat lifttesting will then be performed with weights equivalent to 30% and 80% of thismaximum isometric force. Since the aim of the present study is to investigatethe effect of movement pattern, rather than velocity, of training exercises,testing after the 6 week training period will utilise these same weights, ratherthan a new weight that is congruent with subject’s strength increases. Thus,subjects’ performances will be compared at a given weight, similar to thevertical jump where weights are not changed after training. Subjects will beallowed three attempts at each.2) Forward Hack Squat: after measuring subjects isometric force at thebottom of the forward hack squat movement, subjects will perform maximalone- and two-legged forward hack squats with a 1 – 2 s eccentric phase.Measures will be as per the squat lift. Subjects will be allowed three attemptsat each.3) Countermovement Vertical Jump: subjects will jump for maximumheight on a force platform. Ground reaction forces will be measured for eachjump from which body displacement will be estimated. Thus, problemsassociated with jump and reach tests will be eliminated. Subjects will performboth one- and two-legged trials; three repetitions will be performed of each.4) Sprint Test: 10 m and 20 m sprint times will be recorded during a 20 mmaximal sprint. Subjects will begin from a standing start with one foot in frontof the other but will be allowed to bend the knees to lower the body’s centre ofgravity. Subjects will be allowed three trials.5) Muscle Pennation and Thickness Tests: ultrasound will be used toimage the vastus lateralis and rectus femoris of subjects (10 subjects fromeach group only). For the rectus femoris, photographs will be taken at points20% and 50% of the distance from the tendomuscular junction (clearly visiblein most subjects) to its attachment at the hip. Thus measures of pennation,thickness and anatomical cross-sectional area will be taken at the midpointand at one end of the muscle. For vastus lateralis, photographs will be takenat 20% and 50% of the distance from the lateral condyle of the femur to thegreater trochanter.6) Electromyographic Analysis of the Vertical Jump and Sprint Run: 8subjects from each of the three groups will perform two-legged vertical jumpsand 10 m sprints while electrodes are placed on the gluteus maximus, vastus
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lateralis, biceps femoris (long head), illiopsoas and rectus femoris muscles.Timing of muscle contractions and level of cocontraction will subsequently beestimated. All subjects will be filmed to ascertain key events during eachtask; an LED will be used to synchronise EMG and video data.7) Isokinetic Knee Extension: To examine changes in the torque-anglerelationship about the knee, subjects will perform slow (30o.s-1) and fast(300o.s-1) isokinetic knee extensions. An isometric pre-load force will beimposed prior to the movement to minimise force spikes at the onset ofmovement and provide more reliable force measures in the early part of themovement. Biomechanical analyses suggest that the angle through which theknee moves differs between the squat and FHS exercises making this jointideal for torque-angle testing.
POSSIBLE SUBJECT DISCOMFORTS/RISKS
Subjects may experience some muscular soreness after the familiarisationand testing sessions. Further, the performance of maximal muscularcontractions, either during the testing or training sessions, has a potential toresult in muscular strains. All necessary safe guards (including proper warm-up and supervision) will be used to minimise such an occurrence. Also, acutedermal infections have been reported after EMG electrode use. To eliminatethe chance of infection, an alcohol solution will be applied to the skin prior toEMG electrode placement and an antiseptic cream will be applied after EMGelectrode removal.
SUBJECT BENEFITS
Subjects can benefit from participation in the study by:Opportunity to improve speed and strength by taking part in a supervised,periodised training regime.Being tested on two occasions to determine level of training and rate ofimprovement.Free use of an air conditioned gym for training.Obtaining information and advice on strength and power training.Having the opportunity to observe methods of experimental research in thisarea.Contributing to the advancement of science as a research participant.Being first to obtain the results and practical implications of the study.
INVESTIGATOR RESPONSIBILITIES
Any information that is obtained in connection with this study and thatcan be identified with you will remain confidential and will be disclosed onlywith your permission.
If you decide to participate, you are free to withdraw your consent andto discontinue participation at any time without prejudice. However, priornotice of withdrawal would be appreciated.
If you have any questions, please contact Tony Blazevich on (H) 216 617 or
268
(Uni) 203 231, at any time.
You will be given a copy of this form to keep.
269
SUBJECT’S DECLARATION OF CONSENT
I _________________________________ , being over eighteen years of ageconsent to being a subject in the research project “Influence of movementpattern of resistance training exercises on vertical jump and sprint runningperformance during concurrent resistance and task training”.
I have been given a copy of a “Form of Disclosure and Informed Consent”document which I fully understand describing the procedures to be followedand the consequences and risks involved in my participation as a subject.
I have read the information above and any questions I have asked have beenanswered to my satisfaction. I agree to participate in this activity, realisingthat I may withdraw without prejudice at any time.
I agree that research data gathered from the study may be published providedmy name is not used.
NAME OF SUBJECT ______________________________
SIGNATURE OF SUBJECT _________________________DATE ____________
NAME OF WITNESS ______________________________
SIGNATURE OF WITNESS _________________________DATE ____________
SIGNATURE OF RESEARCHER _____________________DATE ____________
certifying that the terms of the form have been verbally explained to thesubject, that the subject appears to understand the terms prior to signing theform, and that proper arrangements have been made for an interpreter whereEnglish is not the subjects first language.
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APPENDIX C
STATEMENT OF INFORMED CONSENT
RELIABILITY AND VALIDITY OF ISOMETRIC SQUAT AND
FORWARD HACK SQUAT TESTS
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Southern Cross University
FORM OF DISCLOSURE AND INFORMED CONSENT
Reliability and validity of isometric squat and forward hack squattests.
You are invited to participate in a study designed to examine the reliability andvalidity of isometric squat and forward hack squat tests.
PROCEDURES TO BE FOLLOWED
Experimental Design:
Subjects will attend two 45-min testing sessions. Each session will involve 3isometric squat lifts, 3 isometric forward hack squat (FHS) lifts, and theperformance of 1 repetition maximum (1 RM) of either the squat or FHS.
Testing
Squat: Subjects will stand under an immoveable bar with a knee angleof 90o and the bar resting across the shoulders. When instructed, subjectswill push upward against the bar with maximal exertion. Force producedduring the push will be recorded by force platform.
FHS: Subjects will position themselves on the FHS machine with aknee angle of 90o and a hip angle of 110o. When instructed, the subjects willpush upward against shoulder pads that are immoveable. Force producedduring the push will be recorded by load cell.
1 RM squat: After warm up including several repetitions of submaximal squatlifts, subjects will perform single squat lifts with the weight being increasedincrementally until the weight cannot be lifted. Metal stops will prevent the barand weights from moving below a predetermined level to minimise injury risk.The maximum weight lifted will be taken as that subject’s 1 RM.
1 RM FHS: After warm up including several repetitions of submaximal FHSlifts, subjects will perform single FHS lifts with the weight being increasedincrementally until the weight cannot be lifted. Metal stops will prevent thesled and weights from moving below a predetermined level to minimise injuryrisk. The maximum weight lifted will be taken as that subject’s 1 RM.
Following the testing, reliability of the isometric lifts will be calculated, and therelationship between isometric and 1 RM strength will be determined.
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POSSIBLE SUBJECT DISCOMFORTS/RISKS
Subjects may experience some muscular soreness after the testing sessions.Further, the performance of maximal muscular contractions can potentiallyresult in muscular strains. All necessary safe guards (including proper warm-up and supervision) will be used to minimise such an occurrence.
SUBJECT BENEFITS
Subjects can benefit from participation in the study by:Obtaining information and advice on strength and power training.Having the opportunity to observe methods of experimental research in thisarea.Contributing to the advancement of science as a research participant.
INVESTIGATOR RESPONSIBILITIES
Any information that is obtained in connection with this study and thatcan be identified with you will remain confidential and will be disclosed onlywith your permission.
If you decide to participate, you are free to withdraw your consent andto discontinue participation at any time without prejudice. However, priornotice of withdrawal would be appreciated.
If you have any questions, please contact Tony Blazevich on (Uni) 66 203231, at any time.
You will be given a copy of this form to keep.
273
SUBJECT’S DECLARATION OF CONSENT
I _________________________________ , being over eighteen years of ageconsent to being a subject in the research project “Reliability and validity ofisometric squat and forward hack squat tests.”.
I have been given a copy of a “Form of Disclosure and Informed Consent”document that I fully understand describing the procedures to be followed andthe consequences and risks involved in my participation as a subject.
I have read the information above and any questions I have asked have beenanswered to my satisfaction. I agree to participate in this activity, realisingthat I may withdraw without prejudice at any time.
I agree that research data gathered from the study may be published providedmy name is not used.
NAME OF SUBJECT ______________________________
SIGNATURE OF SUBJECT _________________________DATE ____________
NAME OF WITNESS ______________________________
SIGNATURE OF WITNESS _________________________DATE ____________
SIGNATURE OF RESEARCHER _____________________DATE ____________
certifying that the terms of the form have been verbally explained to thesubject, that the subject appears to understand the terms prior to signing theform, and that proper arrangements have been made for an interpreter whereEnglish is not the subjects first language.
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APPENDIX D
TRAINING PROGRAMS
EXAMPLE RESISTANCE TRAINING PROGRAMS FOR SQ
(SQUAT) AND FHS (FORWARD HACK SQUAT) GROUPS
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Gym Training ProgramName: Person ATraining Group: SquatPredicted Maximum: 189.12 kg
Weights for Heavy Sessions should range from approximately:Week 1 85.96 – 107.46 kgWeek 5 128.95 – 150.44 kg
Weights for Explosive Sessions should range from approximately:Week 1 42.98 – 64.47 kgWeek 5 64.47 – 85.96 kg
Heavy day program:
Warm-up on squats bar only, 8 repsWarm-up on squats, 20% of max. predicted = 40 kg, 8 repsSet 1, 30 - 40% of max. predicted = 60 - 85 kg, 8 repsSet 2, use weight in range above (heavy) = 6 repsSet 3, use weight in range above = 6 repsSet 4, use weight in range above = 6 reps
2 sets of 10 repetitions of back extension (use weights if required)3 sets of 8 repetitions of leg curl (heavy and controlled)2 - 3 sets of 8 calf raises (heavy and controlled)
Light day program:
Warm-up on squats bar only, 8 repsWarm-up on squats, 20% of max. predicted = 40 kg, 8 repsSet 1, 30 - 40% of max. predicted = 60 - 85 kg, 8 repsSet 2, use weight in range above (light) = 6 repsSet 3, use weight in range above = 6 repsSet 4, use weight in range above = 6 reps
2 sets of 10 repetitions of back extension (use weights if required)3 sets of 8 repetitions of leg curl (slightly lighter and faster)2 - 3 sets of 8 calf raises (slightly lighter and faster, slow down, fastup)
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Gym Training ProgramName: Person BTraining Group: Forward Hack SquatPredicted Maximum: 103.65 kg
Weights for Heavy Sessions should range from approximately:Week 1 14.53 – 32.35 kgWeek 5 50.18 – 68.00 kg
Weights for Explosive Sessions should range from approximately:Week 1 0 kgWeek 5 0 – 14.5 kg
Heavy day program:
Warm-up on squats bar only, 8 repsWarm-up on squats, 20% of max. predicted = 0kg, 8 repsSet 1, 30 - 40% of max. predicted = 0 kg, 8 repsSet 2, use weight in range above (heavy) = 6 repsSet 3, use weight in range above = 6 reps
2 sets of 10 repetitions of back extension (use weights if required)3 sets of 8 repetitions of leg curl (heavy and controlled)2 - 3 sets of 8 calf raises (heavy and controlled)
Light day program:
Warm-up on squats bar only, 8 repsWarm-up on squats, 20% of max. predicted = 0 kg, 8 repsSet 1, 30 - 40% of max. predicted = 0 kg, 8 repsSet 2, use weight in range above (light) = 6 repsSet 3, use weight in range above = 6 reps
2 sets of 10 repetitions of back extension (use weights if required)3 sets of 8 repetitions of leg curl (slightly lighter and faster)2 - 3 sets of 8 calf raises (slightly lighter and faster, slow down, fastup)
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APPENDIX F
RELIABILITY STUDY
A COMPARISON OF DIGITAL CURVIMETER AND
MATHEMATICAL ESTIMATES OF FASCICLE LENGTH IN
CONTRACTING MUSCLE.
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ABSTRACT
Fascicle length can be measured in vivo by ultrasound techniques, although
two methods of estimating fascicle length are currently used: mathematical
estimation and curvimeter measurement. The purpose of this study was to
first to determine if significant differences exist between fascicle length
measures estimated by mathematical and curvimeter methods, and second to
examine the reliability of the mathematical procedure relative to the
curvimeter procedure. Photographs of up to nine sites on the gastrocnemius
medialis muscle of six subjects were taken using ultrasound imaging.
Photographs were taken in both relaxed and contracted (plantarflexion at 50%
of maximum) conditions and muscle thickness, pennation and fascicle length
subsequently measured. Differences between mathematical and curvimeter
estimates of fascicle length were examined by multilevel regression analysis.
There was no significant difference between fascicle length measures
estimated by the two methods, although differences were greater for the
relaxed and relaxed-contracted (change in fascicle length from relaxed to
contracted state) conditions compared to the contracted condition. Reliability
of single estimates were high for the curvimeter method (Intraclass
correlations [ICC’s] = 0.75 – 0.91) but low for mathematical estimation (ICC’s
= 0.39 – 0.60). Nonetheless, by averaging a number (N=9) of repeated
measurements on the subjects, reliability of the mathematical method was
increased significantly (ICC’s = 0.85 – 0.93). These results suggest that, for
the gastrocnemius medialis muscle, there was little difference between
fascicle length estimated by mathematical or curvimeter methods although the
reliability of mathematical estimates was very low, and statistical power would
be dramatically reduced. Nonetheless, reliability of a number of repeated
measurements was high and comparable to the curvimeter method.
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INTRODUCTION
Muscle contraction properties are strongly influenced by architectural
characteristics such as muscle size, pennation (fibre angle relative to the
tendon or aponeurosis) and fibre length. For example, muscles that are often
recruited to perform high force, low velocity contractions tend to have shorter
fibres and greater pennation while muscles recruited during rapid contractions
have longer fibres and lesser pennation (Burkholder et al., 1994; Kawakami et
al., 1995; Kumagai et al., 2000). Assessing inter-individual differences and
longitudinal changes in muscle architecture aids our understanding of the
muscular system. Moreover, knowledge of muscle architecture during
contraction is important for the development of realistic muscle models. Since
pennation and fibre length change during contraction, muscle models that
incorporate only architectural parameters of relaxed muscle are prone to
prediction errors. Therefore, knowledge of muscle architecture both at rest
and during contraction can allow researchers to better predict the functional
properties of human muscle.
Muscle architecture has been studied in both resting (Kumagai et al., 2000;
Van Eijden et al., 1997) and contracting (Herbert & Gandevia, 1995;
Kawakami et al., 1998; Narici et al., 1996) muscle. Such research has
examined how exercise affects architecture (Henriksson-Larsén et al., 1992;
Kawakami et al., 1993, 1995; Kumagai et al., 2000) and how architecture
changes during muscle contraction (Herbert & Gandevia, 1995; Narici et al.,
1996). While there are recognised methods of measuring muscle size and
pennation, methods for measuring fibre length are not consistent. The fibre
length of many human muscles is synonymous with the length of the fascicles
that encase fibre bundles. Since fascicles can be clearly visualised using
ultrasound imaging, fascicle length can be estimated from ultrasound
photographs.
Nonetheless, fascicle length can be estimated by two different methods. First,
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fascicle length can be estimated mathematically by the equation:
FL = MT/sin θ
where FL is the fascicle length, MT the muscle thickness, and θ the angle of
muscle pennation. Prediction of fibre length from fascicle length by this
method has been used extensively in past research (Henriksson-Larsén et
al., 1992; Kawakami et al., 1995; Kumagai et al., 2000). However, this
method incorrectly assumes that fascicles are linear within the muscle. More
recently, researchers have captured entire fascicles on ultrasound images
and used a digital curvimeter (Comcurve-8, Koizumi, Japan) to more directly
measure fascicle length (Fukunaga et al., 1997; Kawakami et al., 1998, 2000).
Here, the ultrasound images are printed onto calibrated recording film (SSZ-
305, Aloka) and the length of fascicles measured by a curvimeter. The
advantage of this method is that the curve of the fascicle is accounted for.
Thus, compared to mathematical estimation, it can be considered that the
measures of fascicle length by digital curvimeter are truer.
Unfortunately, digital curvimeter procedures have not been used in many
previous studies. Nonetheless, it is unclear how reliable current mathematical
estimation procedures are given fascicle curvature is not accounted for.
Furthermore, no research has compared fascicle length measures obtained
by the two methods. The purpose of the present study therefore was two-fold,
first to determine if a significant difference exists between fascicle length
values estimated by the two methods in both relaxed and contracted muscle,
and second to examine the reliability of the mathematical procedure relative to
the digital curvimeter procedure.
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METHODS
Measurement of Muscle Architecture
Previously published measures of fascicle length, fascicle angle (pennation)
and muscle thickness of the human gastrocnemius medialis (GM) (Kawakami
et al., 2000) were reanalysed to calculate mathematical estimates of fascicle
length. Methods used to measure muscle architecture are presented in
Kawakami et al. (2000), however a summary of the methods will be presented
here. B-mode ultrasonography was used to view images of GM in a two-
dimensional plane while six male subjects lay prone with their knee extended
and ankle at 90o. Each subject’s foot was firmly attached to an electric
dynamometer (Myoret, Asics) and the lower leg fixed to a test bench.
Measurements were taken for two conditions, with the gastrocnemius relaxed
and while performing isometric plantar flexion at a level of 50% of maximum
voluntary force. Plantar flexor torque was recorded from the output of the
dynamometer by a computer (PC-9801, NEC). It was assumed that there
was no muscle activity in the passive condition.
In both relaxed and contracted conditions, ultrasound images were obtained
from up to nine sites on GM. Longitudinal ultrasonic images of GM were
obtained at each site such that the echoes from interspaces of fascicles and
from the superficial and deep aponeuroses were visualised (Figure 1). The
ultrasonic images were then printed onto calibrated recording films (SSZ-305,
Aloka). The plane of the ultrasonogram was deemed parallel to the fascicles
since the fascicles could be followed from superficial to deep aponeurosis
(Kawakami et al., 1993). In the printed images, the length of the fascicles and
fascicle angles (pennation) were measured. Fascicle length was measured
by the use of a digital curvimeter (Comcurve-8, Koizumi) which allowed the
somewhat curved fascicles to be measured directly. Reliability of fascicle
length measures using the digital curvimeter has been previously established
(Fukunaga et al., 1997). Fascicle angle was measured with a protractor after
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a line was drawn tangentially to the fascicle at the contacting point onto the
aponeurosis. The angle made by the line and aponeurosis was measured as
the fascicle angle. At each point, muscle thickness was also measured.
Muscle thickness was defined as the distance from the junction of the adipose
and muscle boundaries to the internal aponeurosis. From measures of
muscle thickness and fascicle angle at each of the eight sites, fascicle length
was also mathematically estimated (FL = MT/sin θ, where FL is the fascicle
length, MT the muscle thickness, and θ the angle of muscle pennation).
Values for fascicle length using the two methods (digital curvimeter versus
mathematical estimation) were then compared.
A
B
Muscle/adiposeboundary
Fascicle
Aponeurosis
Musclethickness
Figure 1. Ultrasound photographs of gastrocnemius medialis under relaxed (A) andcontracted (B; 50% MVC) conditions. When contracted, muscle thickness and fasciclelength decrease compared to the relaxed state. Digital curvimeter estimates of fasciclelength are performed by tracing a fascicle from the aponeurosis to the muscle/adiposeboundary. For the mathematical method, fascicle length is estimated by the formula FL =MT/sin θ, where FL is the fascicle length, MT the muscle thickness, and θ the angle ofmuscle pennation (angle between the fascicle and aponeurosis).
B
A
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Data Analysis
Description of data
The change in fascicle length from the relaxed (A) to contracted (B) state was
designated ‘relaxed-contracted (C)’. There were eight repeated measures
(replicates) on two subjects and nine repeated measures (replicates) on the
other four subjects. Although Kawakami et al. (2000) found systematic
variation among these repeated measures, for present purposes they were
treated as randomly varying replicates. Corresponding to the curvimeter-
measured data (mFL; measured fascicle length), fascicle lengths were
estimated by the equation presented previously to construct a completely
parallel ‘estimated fascicle length’ (estFL) data set.
Data Analysis
Hierarchical (multilevel) linear regression models were fitted to the data.
(Goldstein, 1995; Hox, 1994; Snijders and Bosker, 1999). The residuals
about the fixed parts of the models (overall constant and any explanatory
factors) were modeled as varying randomly at the replicate within subject (e0ij)
and subject (u0j) levels. Restricted maximum likelihood estimates were
obtained to correct for the downward bias of maximum likelihood estimates of
variance components (Snijders and Bosker, 1999, p.56).
Three sets of three analyses (A1 to C3) were performed. For each of the sets
of relaxed (A), contracted (B) and relaxed-contracted (C) data, analyses were
performed on the measured lengths (A1,B1,C1), the estimated lengths
(A2,B2,C2) and the relationship between the measured and estimated lengths
(A3,B3,C3). The analyses A and B were variance components models in
which no explanatory variables (other than the overall intercepts) were fitted,
but in analyses C the measured values were regressed on the estimated
284
values. The purpose of the analyses A and B was to estimate the
reliabilities of the measured and estimated lengths, while the purpose of the
analyses C was to estimate the ‘predictability’ of measured from the estimated
lengths.
Three subsidiary analyses (two-level variance components models) - one
each for relaxed, contracted and relaxed-contracted muscle - were performed
on the measurement-estimate difference scores in order to estimate the
extent to which the estimates were high (overestimates) or low
(underestimates) relative to the digital curvimeter measurements.
Two measures of reliability were determined for variance components
(intercept only) models: the intraclass correlation coefficient (ICC = ρ1)
measuring the reliability of a single replicate and ρ2 measuring the reliability of
the mean of n level 1 units as a measure of a level 2 unit (mean of a number
of replicates as a measure of subject fascicle length). Measures of reliability
were calculated according to the formulae presented in Snijders and Bosker
(1999, pp.24-26; n=9 in the present analyses). Two measures of explained
variance are reported for models with explanatory variables: R12 and R2
2
measuring the proportional reductions in mean squared prediction errors at
levels 1 and 2 respectively due to the explanatory variables, calculated
according to the formulae presented in Snijders and Bosker (1999, pp.102-
103).
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RESULTS
Results are presented in Table 1. An explanation of abbreviations is provided
below the table. Due to the length of the table, it is presented at the end of
this paper.
Comparison of Measured and Estimated Fascicle Length
Error-bar plots showing the subjects means and 95% confidence intervals for
the measured and estimated fascicle length are presented in Figure 2. For
relaxed, contracted and relaxed-contracted muscle, estimated fascicle length
underestimated the digital curvimeter measurements. The average
underestimation ranged from 0.43mm (1.2%) for contracted muscle, through
1.02mm (1.8%) for relaxed muscle to 1.21 (3.2%) for relaxed-contracted
muscle. These difference estimates correspond closely to the absolute
differences in the sizes of the β0ij parameter estimates from the A1-A2, B1-B2,
and C1-C2 pairs of analyses, as reported in Table 1. In no case were the
underestimates significant. t-values (parameter estimate / standard error)
ranged from 0.51 for relaxed-contracted, 0.58 for contracted and 1.03 for
relaxed muscle.
Relationship between the Estimates and the Measurements
The analyses A3, B3 and C3 found highly significant relationships between
the estimates and the measurements for each of the relaxed, contracted and
relaxed-contracted muscle fascicle lengths (the β1 estimates from Table 1).
However, although highly significant, the effects were far smaller than might
be expected of the relationship between reliable estimates and their
corresponding measurements. At the replicate level, the proportional
reductions in the mean squared prediction errors R-squared measure range
from 0.18 for relaxed-contracted, through 0.20 for relaxed to 0.22 for
contracted muscle. At the subject level, the proportional reductions in mean
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squared prediction errors were slightly higher at 0.20, 0.21 and 0.23
respectively. These relatively small proportions of the total variation among
the measurements ‘explained by’ the estimated fascicle length values are due
mostly to the variability or unreliability of these estimates.
Variance Components and Reliability
The proportions of total variance for the measurements at the subject level –
Figure 2. Mean fascicle lengths (with 95%confidence intervals) for measured ("") andestimated (ï) relaxed, contracted andrelaxed-contracted fascicle lengths.Estimated fascicle lengths were generallyshorter (not significant) and more variablethan measured fascicle lengths.
287
the intraclass correlations (ICC’s) or reliabilities of measurement at the
subject level from a single, randomly selected replicate (ρ1’s) - range from
0.75 for relaxed-contracted, 0.90 for relaxed and 0.91 for contracted muscle.
Although 0.75 is somewhat lower than ideal, this would be an acceptable level
of measurement reliability for some research. In contrast, the proportions of
total variance for estimated fascicle length at the subject level range from 0.39
for relaxed-contracted, 0.48 for relaxed and 0.60 for contracted muscle.
Apart, perhaps, for the 0.60 estimate for contracted muscle, these are less
than acceptable levels of measurement reliability, with adverse effects on
statistical power and contributing to production of inconsistent findings in
research on small samples.
These reliability estimates might be lower than the values of reliability for true
replicates because the ‘replicates’ here were expected to vary systematically
to some degree (since measures were taken from different regions within the
muscle rather than at one site). Nonetheless, the unreliability of the estimates
relative to the measurements is clear in the comparisons of their respective
amounts of replicate variation: ie 57.1 to 5.4 for relaxed, 21.4 to 3.1 for
contracted and 59.7 to 11.2 for relaxed-contracted.
Whilst single estimates provide unacceptably low levels of measurement
reliability at the subject level (ICC’s = ρ1’s), the means of a number of
replicates (ρ2’s) possess quite acceptable reliabilities. These were calculated
on the basis of 9 replicates (the mode in the present data) and ranged from
0.85 for relaxed-contracted, through 0.89 for relaxed and to 0.93 for
contracted muscle.
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DISCUSSION
Average estimated fascicle length (estFL; mathematical method) was less
than measured fascicle length (mFL; curvimeter method) for all conditions
(relaxed, contracted and relaxed-contracted muscle) with differences ranging
from approximately 0.4 to 1.2 mm (1.2 – 3.2%). None of these differences
were statistically significant. Whether underestimation of this order is
substantively important will depend upon the context of the particular
research, but the small number of subjects and low statistical power would
have influenced its significance here. In the present study however, there
was no significant difference in fascicle length measures between the two
methods.
Nonetheless, differences between estFL and mFL were greater for relaxed
than contracted muscle. While small, the difference is likely to be related to
the length of fascicles in these muscle states. Fascicles are longer in relaxed
than contracted muscle. For a given relative difference in fascicle lengths
determined by the two methods, the absolute difference will be greater than in
contracted muscle. The difference between estFL and mFL was greatest
when fascicle length change from relaxed to contracted states was estimated
(1.2 mm or 3.2% of average fascicle length). When measures of fascicle
length in relaxed and contracted muscle were used to determine the change
in fascicle length, there was a summation effect culminating in greater
differences between the two methods. Thus, for the gastrocnemius medialis
muscle, there was no significant difference between fascicle length
determined by digital curvimeter and mathematical methods, although in
muscle with long fascicles the difference between the methods would be
greater and the difference between muscles might be significant.
There was also no statistically significant difference between the measured
fascicle lengths and those predicted from the regression of measured fascicle
lengths on estimated fascicle lengths for relaxed, contracted and relaxed-
289
contracted muscle. Nonetheless, for repeated measures at each section of
the muscle, the proportional reductions in the mean squared prediction errors
R-squared measures ranged from 0.18 for relaxed-contracted, through 0.20
for relaxed to 0.22 for contracted muscle. When measures at different sites of
the muscle were averaged for each subject, the proportional reductions in
mean squared prediction errors were slightly higher at 0.20, 0.21 and 0.23
respectively. While these relatively small proportions of the total variation
among the measurements ‘explained by’ estFL were due largely to the
variability or unreliability of these estimates (see below), approximately 80%
of the total variance was left unexplained. Thus, despite mFL being predicted
well by estFL in the present study, there were clearly other factors affecting
the prediction of mFL besides estFL variability.
Reliability of the Measures
The reliability of digital curvimeter measurements at the subject level from a
single, randomly selected replicate (ρ1’s) on the gastrocnemius was
calculated. ICC’s were 0.91. 0.90 and 0.75 for contracted, relaxed and
relaxed-contracted conditions respectively. These reliability estimates might
be lower than the values of reliability for true replicates because the
‘replicates’ here were expected to vary systematically to some degree (since
measures were taken from different regions within the muscle rather than at
one site). Nonetheless, ICC’s for fascicle length determined mathematically
were 0.60, 0.48 and 0.39 for contracted, relaxed and relaxed-contracted
conditions respectively. The unreliability of estFL relative to mFL was further
highlighted by the comparisons of their respective amounts of replicate
variation: ie 57.1 to 5.4 for relaxed, 21.4 to 3.1 for contracted and 59.7 to 11.2
for relaxed-contracted. Thus, again, variability of mathematical estimation
was far greater than for the curvimeter method. Such reliability is less than
acceptable and would adversely affect statistical power and contribute to
inconsistent findings in research on small samples.
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Increasing the Reliability of Mathematically Estimated Fascicle Lengths
Whilst single estimates provide unacceptably low levels of measurement
reliability at the subject level (ICC’s = ρ1’s), the means of a number of
replicates (ρ2’s) possessed quite acceptable reliabilities. ICC’s for the
average fascicle length of a subject ranged from 0.85 for relaxed-contracted,
through 0.89 for relaxed and to 0.93 for contracted muscle. This suggests a
remedy in terms of averaging repeated measurements on the same region of
muscle (replicates) within subjects and conditions. As Table 1 shows,
although reliabilities at the replicate level (ICC = ρ1) vary between only 0.39
and 0.60, the reliabilities of averages of 9 replicates as measures at the
subject level (ρ2) range between 0.85 and 0.93. The minimum number of
replicates (nmin) required to yield a desired level of reliability at the subject
level (ρ2) given the reliability of an estimate at the replicate level (ρ1) is given
by Snijders and Bosker (1999, p.144) as,
nmin = ρ2(1-ρ1) / ρ1 (1-ρ2)
Although the power of studies could be increased by increasing the sample
size at the subject level, it may generally be more efficient to increase the
reliability of measurements at the within-subject (replicates) level (i.e. take
repeated measurements on individual subjects). This raises the general
question of how best to allocate resources between the two levels so as to
maximise research efficiency: increase subject numbers or increase the
number of repeated measurements on each subject. Snijders and Bosker
(1993) and Mok (1995) address this issue, and Snijders, Bosker and
Guldemond offer free, downloadable software (PINT = ‘power in two-level
designs’ at http://stat.gamma.rug.nl/snijders/multilevel.htm. Thus, a
comprehensive discussion of the issue will not be presented here.
In summary, for the gastrocnemius medialis muscle, there was no significant
difference between mathematical and curvimeter measures of FL. The
291
mathematical method therefore provided a good estimation of fascicle
length in relaxed, contracted and relaxed-contracted conditions. Nonetheless,
there was a trend toward greater error in the mathematical method compared
to curvimeter measures (which were assumed to be accurate measures of FL)
in relaxed muscle where fascicles are long. This suggests that differences in
FL determined by the two methods would be greater for muscles with long
fascicles. The reliability of the mathematical method for measures of a single
muscle point was low. However, by taking the average of repeated measures
on subjects, reliability increased significantly. Thus researchers using
mathematical estimation of FL from muscle thickness and pennation
measurements should consider increasing the number of repeated measures
of individual subjects to improve reliability and increase statistical power.
2 15 0.20mFL: measured fascicle length (digital curvimeter)estFL: estimated fascicle length (mathematical method)r: relaxed muscle, c: contracted muscle1 Model A1: dependent variable = mFLr; independent variable = intercept only2 Model A2: dependent variable = estFLr; independent variable = intercept only3 Model A3: dependent variable = mFLr; independent variables = intercept, estFLr4 Model B1: dependent variable = mFLc; independent variable = intercept only5 Model B2: dependent variable = estFLc; independent variable = intercept only6 Model B3: dependent variable = mFLc; independent variables = intercept, estFLc7 Model C1: dependent variable = m∆FL; independent variable = intercept only8 Model C2: dependent variable = est∆FL; independent variable = intercept only9 Model C3: dependent variable = m∆FL; independent variables = intercept, est∆FL10 Variance components and their standard errors (SE)11 –2LL = minus 2 loglikelihood = deviance12 ICC = intraclass correlation coefficient = ρ1 = reliability of a single replicate13 ρ2 = reliability of mean of 9 replicates as measure of a subject
293
14 R12 = proportion of replicate variance explained
15 R22 = proportion of subject variance explained
Table 1. Results of the multilevel regression analysis for relaxed (A), contracted (B) andrelaxed-contracted (C) conditions. Fascicle length calculated by curvimeter (1) andmathematical (2) methods are indicated in the ‘β0ij = intercept’ row and are in the units ofmillimetres. For all contraction states, mathematical estimates were slightly, but notsignificantly, lower than curvimeter estimates. Variance of measures at one site on themuscle were higher for mathematical estimates [e0ij : Var(replicates)], although variancecalculated on the mean of repeated measures (ie at the subject level) was relatively similarbetween the methods [u0j : Var(subjects)]. Reliability of fascicle length estimates at individualsites using the mathematical method were low (ICC = ρ1) although reliability was improvedsubstantially when repeated measures were averaged (ρ2). Models A3, B3 and C3 show theprediction of measured fascicle length (mFL; curvimeter estimates) from estimated fasciclelength (estFL; mathematical estimates) with proportions of replicate and subject varianceexplained (R1
2 and R22 respectively). There was no statistically significant difference between
measured fascicle lengths and those predicted from estimated fascicle length although theproportion of variance explained was low.
Narici, M.V., Bonzoni, T., Hiltbrand, E., Fasel, J., Terrier, F., & Cerretelli, P.
(1996). In vivo human gastrocnemius architecture with changing joint angle at
rest and during graded isometric contraction. Journal of Physiology, 496.1:
287-297.
Snijders, T.A.B. & Bosker, R.J. (1993). Standard errors and sample sizes in
two-level research. Journal of Educational Statistics, 18, 3: 237-260.
Snijders, T.A.B. & Bosker, R.J. (1999). Multilevel Analysis: An Introduction to
Basic and Advanced Multilevel Modeling. London: Sage Publications Ltd.
Van Eijden, T.J.G.J., Korfage, J.A.M., & Brugman, P. (1997). Architecture of
the human jaw-closing and jaw-opening muscles. The Anatomical Record,
248: 464-474.
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APPENDIX G
FORWARD HACK SQUAT DATA COLLECTION SCHEMATIC
297
1
2
3
4
6
5
7
8
9
10
11
13
12
14
15
1618
17
299
Diagram(ICAM)
Description/definition
Setpoint: implements voltage reference, DC voltage – (1) 10 V, (2)0 V.Analog output: directs data stream to an output on an analogmodule, here it powers the load cell (3) or position transducer (4).Analog input: receives external signals, e.g. fromtransducers/potentiometers. (5) received force input, amplifier gain= 300 volts/volt, DC offset range = 127. (6) received position input,amplifier gain = 10 000 volts/volt, DC offset range = 127.Zero order hold: set to hold value in input data stream [force (7)or position (8)] until next trigger (see below).Subtraction: subtracts two input values (e.g. a raw input from aheld [see above] value).Multiplication: multiplies two input values.
Variable amplifier: amplifies input data stream by a specifiedvalue using a potentiometer while the system is running. (9)calibrate force, gain = 0.742 units/unit, (10) calibrate position, gain= 1.02 units/unit.Display trace: displays a moving trace of the values of a datastream. (11) force trace, (12) position trace.Numeric display: displays a value in numeric form.
Peak detector: measures the peak value of a signal, can be resetto a specified level (usually zero) before each data acquisitionperiod (trial). (13) detects peak force, resets to zero.Square wave generator: provides a square wave at frequencyproportional to the voltage at its input, allows setting to 0 V (as inthis case) to provide 0 Hz. (14) oscillator calibration = 10 Hz/unit,frequency with 0V input = 3 Hz, Peak to peak amplitude = 10 units,zero offset.Check box or trigger: triggers an event such as data collection orreset. (15) collect data.Pulse generator: outputs pulse of specified duration. Used here tocollect 400 samples of force and position data over a 4 s timeperiod.Variable set point: implements a floating point variable voltagereference, allows reference voltage to be altered while program isrunning. (16) set to ‘angle = 51 deg’.Function: converts X to Y. (17) convert degrees to radians, (18)cos function to calculate vertical component of force.