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Welcome to today’s webinar
Isokinetic Dynamometry for assessment of muscle strength and
joint function.
Presented by Bill Baltzopoulos
Professor of Biomechanics
Head of the Research Institute for Sport & Exercise Sciences (RISES)
Liverpool John Moores University
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About today’s webinar
Today’s webinar is being produced jointly by BASES and Human
Kinetics.
It is scheduled to last for about an hour and will be recorded and
made available for download and playback. You will receive an
email containing a link to the recording when it is available.
You can submit questions by typing them into the question box
located in the lower right corner of your screen and click “send.”
Bill will answer as many as possible during a Q&A session at the
end.
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About today’s presenter
Bill Baltzopoulos is a BASES accredited biomechanist (research) and
has served as Chair of the Biomechanics section and representative
to the Education & Training Committee. His main interests include the
structure and function of the musculoskeletal system and the
measurement and modelling of joint and muscle function during
different activities, including isokinetic dynamometry, training and
rehabilitation exercises and various sports. He is one of the main
author of the various BASES guidelines related to muscle strength
and isokinetic dynamometry and the organizer of the BASES
workshops in these areas. He is also the lead author of the recent
BASES expert position statement on assessment of muscle strength
with isokinetic dynamometry.
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Measurement of Static and Dynamic Muscle Strength
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Force-Length-Velocity relationship
Lieber (1992)
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Human Movement - joint rotation:
Moment=F r
r
F
Moment (Nm) =Muscle Force (N) X Moment Arm (m)
Since muscle force depends on muscle length and muscle
velocity, moments are affected by joint angle and angular velocity
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F
d
M r
M=rxF=r·F·sinq=d·F
Joint Rotation: Muscle Moment (Nm)
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d
M
M=F x d
F
Joint Rotation: Muscle Moment (Nm)
Joint Moment (Nm) =MuscleForce (N) X Moment Arm (m)
M=F x d
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Strength is the maximum joint moment at different joint
angles and angular velocities measured with
Isokinetic dynamometers
Moment (Nm)
Very useful for measurement of muscle strength
because of the ability to measure the
strength-muscle length-velocity relationship
Signorile & Applegate (2000)
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Isokinetic Dynamometry: A bit of history…
Thistle, H. G. et al. (1967). Isokinetic contractions: a new concept of
resistive exercise, Archives of Physical Medicine Rehabilitation, 6, 279-282
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Isokinetic Dynamometry: Single Joint Testing
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Isokinetic Dynamometry:
Control of Angular Velocity
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Feedback system to maintain the velocity
constant and equal to the required test ang.velocity
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Moment of Force: M=r x F
F
r
+-
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1. Read Ang. Velocity
2. Compare ang. velocity to target ang.velocity
If Ang. Velocity < Target decrease Resistive Moment
If Ang. Velocity > Target increase Resistive Moment
3. Apply Resistive Moment
0
10
20
30
40
50
60
70
80
0.00 0.05 0.01 0.15 0.20 0.25 0.30 0.35 0.40 0.45Time (s)
Mo
men
t (N
m)
Feedback loop for control of angular velocity
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Application of Resistive Moment
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Isokinetic Dynamometry: Constant Joint Angular Velocity
(not constant muscle contraction linear velocity)
but how is the resistive moment related to the joint (sum of all muscle) moment?
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Newton’s Laws of Motion (2D)
Second Law (Rotational Movement):
ΣΜ=Ια
Isokinetic or Isometric:α=0
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Mj=MD+Mw
Fq
W
FD
Fh
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With Isokinetic Dynamometres we can measure total
Joint Moments only (not muscle moments or forces)
Fq
W
FD
Fh
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M
Strength Measurements:
With Dynamometres we can measure
total Joint Moments only (not muscle forces)
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M
Strength Measurements:
With Dynamometres we can measure
total Joint Moments only
(not individual muscle forces)
(not individual muscle moments)
The Total Joint Moment is the Sum of All Muscle Moments
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Brunel University London
O'Brien et al. (2010). J Biomech
Growth affects tendon mechanical properties
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Achilles tendon stiffness
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Brunel University London
Musculoskeletal system plasticity:The importance of tendon and muscle health across the life-span
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Strength requirements in different sports
Strength-limited sports
Strength-related sports
Strength-independent sports ( Wrigley 2000)
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Strength requirements in different sports
Performance Criterion
Strength
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Isokinetic Dynamometry:
Very useful for measurement of sport-specific strength
because of the ability to measure the
strength-muscle length-velocity relationship
Signorile & Applegate (2000)
Long Distance Long Middle Distance
Short Middle Distance Sprinters
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d
M
M=F*d
F
Joint Rotation: Muscle Moment (Nm)
The Total Joint Moment is the Sum of All Muscle Moments
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Mj=MD+Mw
Fq
W
FD
Fh
Very important that
all moments are
measured relative
to the same axis of
rotation i.e. must
have perfect
alignment of joint
and dynamometer
axes of rotation
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Misalignment of joint and dynamometer axes of rotation due to
compliance/deformation of soft tissue, seat, attachment & straps
and shifting of the knee joint axis with knee motion
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Effects of misalignement of axes of rotation
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Errors between measured and resultant joint
moments when using isokinetic dynamometers
due to axes misalignment
• Herzog (1988): Single subject ~ 2%
• Kaufman et al. (1995): 10-13%
• Arampatzis et al (2004): Isometric 7.3% (range: 1-17%)
Arampatzis et al. (2004).
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• Herzog (1988): Single subject ~ 2%
• Kaufman et al. (1995): 10-13%
• Arampatzis et al (2004): Isometric 7.3% (range: 1-17%)
Errors between measured and resultant joint
moments when using isokinetic dynamometers
due to axes misalignment
All previous studies used external cameras and skin
markers to identify knee joint centre/axis of rotation
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Measurement of knee joint kinematics during
contraction using X-Ray video fluoroscopy
Isometric
Isokinetic Concentric 30 & 60 deg/s
Isokinetic Eccentric 60 deg/s
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“Isometric” Knee Extension
@ 90 deg knee flexion angle
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Calculation of the actual joint moment
WSF
WD
FD
PD
PK
dWD
dWSF
dDdK
PF
φ
FS
WSF
WD
FD
PD
PK
dWD
dWSF
dDdK
PF
φ
FS
K
D
•d
d
Mj= MD K
D
•d
d
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0
20
40
60
80
100
120
140
160
180
200
30 40 50 60 70 80
Knee Angle (deg)
Mo
me
nt
(Nm
)
Dynamometer Moment
Resultant Joint Moment
-5
0
5
10
15
20
30 40 50 60 70 80
Knee Angle(deg)
ΔΜknee(%
Mmax)
Errors between measured and resultant joint moments when
using isokinetic dynamometers due to axes misalignment
Isokinetic Concentric Knee extension @ 30 deg/s
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Errors between measured and resultant joint moments when
using isokinetic dynamometers due to axes misalignment
Isometric Knee extension
0 20 40 60 80 100
-25
-20
-15
-10
-5
0
5
10
Mj-M
D (
Mm
ax)
%MVC
c
0 20 40 60 80 100
0
20
40
60
80
100
120
140
160
180
200
*
*
*
*
Mo
men
t (N
m)
%MVC
MD
Mj
c
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Axes misalignment problems
• The joint moment error due to axes misalignment cannot be neglected if the true joint moments need to be determined
• Implications for measurement of dynamic joint function for strength and rehabilitation assessment
• Align axes of rotation:
– accurately
– under contraction conditions
– near the position of expected maximum joint moment
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Axes of rotation alignement
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Axes of rotation alignement
Define ROM for safe axes of rotation alignment
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Axes of rotation alignement
Define ROM for safe axes of rotation alignment
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Accurate alignment of dynamometer & joint
axes of rotation
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5 simple steps for valid and reliable isokinetic
measurements
Step No 1:
Align axes of rotation:
• accurately
• under contraction conditions
• near the position of expected maximum joint
moment
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Important Issues during Isokinetic Dynamometry
Stabilisation
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Important Issues in Strength Measurement :
Stabilisation problems
&
Effects on Activation
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Stabilisation problems:
Effects on Activation?
0
50
100
150
200
250
300
350
400
450
Seated No
Stablilisation
Seated Normal
Stabilisation
Supine No
Stabilisation
Supine Normal
Stabilisation
Supine Manual
Pelvis Stabilisation
Condition
KE
Jo
int
Mo
men
t
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5 simple steps for valid and reliable isokinetic
measurements
Step No 2:
Stabilise properly all segments involved in the production
of joint movement
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Joint moment at different joint positions and angular
velocities measured with Isokinetic dynamometers
Moment (Nm)
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Moment (Nm)
0
10
20
30
40
50
60
70
80
0.00 0.05 0.01 0.15 0.20 0.25 0.30 0.35 0.40 0.45
Time (s)
Mo
men
t (N
m)
Moment (Nm)
Joint moment during concentric knee extension @ 300 deg/s
What is the maximum knee extension moment @ 300 deg/s?
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0
1 0 0
2 0 0
3 0 0
4 0 0
Test Velocity 300 deg/s
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0
10
20
30
40
50
60
70
80
0
50
100
150
200
250
0
1 0 0
2 0 0
3 0 0
4 0 0
60 deg/s 180 deg/s
300 deg/s
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0
10
20
30
40
50
60
70
80
0.00 0.05 0.01 0.15 0.20 0.25 0.30 0.35 0.40 0.45
Time (s)
Mo
men
t (N
m)
0
1
2
3
4
5
6
7
Velo
cit
y (
rad
/s)
Moment (Nm)
Velocity (rad/s)
At high joint velocities the isokinetic (constant velocity)
movement is very limited or non-existent
The peak dynamometer moment may not be recorded in
isokinetic conditions and at the preset or target velocity
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At high joint velocities the isokinetic (constant velocity)
movement is very limited or non-existent!!
0
10
20
30
40
50
60
70
80
0.00 0.05 0.01 0.15 0.20 0.25 0.30 0.35 0.40 0.45
Time (s)
Mo
men
t (N
m)
0
1
2
3
4
5
6
7
Velo
cit
y (
rad
/s)
Moment (Nm)
Velocity (rad/s)
X X
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System 4:
Windowing function to exclude non-isokinetic conditions
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System 4:
Windowing function to exclude non-isokinetic conditions
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5 simple steps for valid and reliable isokinetic
measurements
Step No 3:
Monitor Angular Velocity throughout the ROM and
exclude non-isokinetic data from the analysis
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Important Issues during Isokinetic Dynamometry
Adjacent joint position affects muscle length in
two-joint muscles and therefore moment in the
tested joint
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Important Issues in Isokinetic Dynamometry
Adjacent joint position affects muscle length in two-joint
muscles and therefore moment in the tested joint (knee
extension or flexion in this example)
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Isometric force in supine & seated positions
Supine Seated
150
175
200
225
250
275
300
325
350
Isom
etri
c M
VC
(Nm
)
Maffiuletti & Lepers (2003)
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Important Issues in Isokinetic Dynamometry
Yang & Lieska (1992) Tq ~ Tq
Th < Th
Hopkins et al. (1993) Tq < Tq
Th < Th
Worrell et al. (1989) Tq < Tq
Th < Th
Black et al. (1993) Tq ~ Tq
Th < Th
Supine Seated
Pavol & Grabiner (2000) Tq < Tq
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Important Issues in Isokinetic Dynamometry:
Knee Flexion
Ankle joint position and gastrocnemius muscle
length effects on knee flexion moment
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Miller et al. (1996) Th < Th
Croce et al. (2000) Th < Th
Miller et al. (1997) Th < Th
Important Issues in Isokinetic Dynamometry:
Knee Flexion
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5 simple steps for valid and reliable isokinetic
measurements
Step No 4:
Plan positioning of adjacent segments and joints
appropriately and control properly
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5 simple steps for valid and reliable isokinetic
measurements
Step No 5:
Record all test settings, subject positioning and
stabilisation accurately
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• Axes of Rotation Alignment
• Isokinetic (constant ang. velocity) Phase
• Stabilisation
• Positioning
• Recording of Test Settings
5 simple steps for valid and reliable isokinetic
measurements
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Isokinetic dynamometers are excellent tools and very
useful for measuring static & dynamic joint function…
…but users must ensure that some important principles
are not violated by following some simple practical steps
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Requirements for reduction of measurement
variability in isokinetic dynamometry
(Best Practice):
• Align axes of rotation:
• accurately
• under contraction conditions
• near the position of expected maximum joint
moment
• Calculate and monitor angular velocity independently and
use isokinetic data only
• Stabilise segments and reduce extraneous movement
• Position and control second joint when biarticular muscles
are involved
• Record all test settings and subject positioning
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References
Baltzopoulos, V. et al. (2012) Measurement of Muscle Strength using Dynamometry. Expert
Statement of the British Association of Sports Sciences, The Sport and Exercise Scientist,
http://www.bases.org.uk/About/BASES-Expert-Statements/Measurement-of-Muscle.
Baltzopoulos, V. and Maganaris C. (2009). Biomechanics of Human Movement. In R. Maughan
(ed.) Olympic Textbook of Science in Sport, International Olympic Committee Medical
Commission, pp 215-229, Wiley-Blackwell, Oxford.
Baltzopoulos, V. (2008). Isokinetic Dynamometry. In C.J. Payton & R. M. Bartlett (ed.)
Biomechanical Evaluation of Movement in Sport and Exercise, pp 103-128, Routledge,
London. ISBN-13: 978-0415434690
Baltzopoulos, V. and N. Gleeson (2008). Volume 2, Chapter 1: Skeletal muscle function. In
Kinanthropometry and Exercise Physiology Laboratory Manual, 3rd edition (edited by R. Eston
and T. Reilly), pp 3-40, London: Routledge. ISBN-10: 0415437237
Baltzopoulos, V. and N. Gleeson (2001). Volume 2, Chapter 1: Skeletal muscle function. In
Kinanthropometry and Exercise Physiology Laboratory Manual, 2nd edition (edited by R.
Eston and T. Reilly), pp 7-36. London: E. and FN. Spon.
Baltzopoulos, V. and Kellis, E. (1997). Isokinetic strength during childhood and adolescence. In
Paediatric Anaerobic Performance (edited by E. van Praagh), pp 225-240, Champaign, Illinois:
Human Kinetic
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Thank You
Any Questions?
We have already received a high number of questions
and we will now try and answer as many as possible in
the time remaining.
Any that remain unanswered will be forwarded to Bill
and he’ll try and email you a reply in due course.
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Thank you for joining us
Thank you to everyone for joining us today and thanks also to Bill
for what I’m sure you will agree was a fascinating and informative
presentation.
Please take a few moments when your webinar window closes to
complete a short survey on today’s webinar – we appreciate your
feedback as it helps us continually improve our webinars.
We will email everyone a link to the recording of today’s
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or colleagues.
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Join us again
Join us on Wednesday 16th March, 2016 at 10.am GMT, for the
next BASES webinar.
“The importance of well-developed physical qualities for rugby
players”, presented by Dr Rich Johnston.
You will automatically receive an invitation to this webinar.
Alternatively you can find details on the Human Kinetics website at
www.humankinetics.com
Thanks for joining us and enjoy the rest of your day.