Journal of Medical and Biological Engineering, 30(3): 177-180 177
Different Limb Kinematic Patterns during Pitching Movement
Between Amateur and Professional Baseball Players
Lan-Yuen Guo1,* Wei-Yin Lin1 Yu-Jung Tsai1 Yi-You Hou1,2
Chih-Chang Chen3 Chich-Haung Yang4 Chu-Chung Huang3 Yi-Hsien Liu5
1Department of Sports Medicine, College of Medicine, Kaohsiung Medical University, Kaohsiung 807, Taiwan, ROC 2Department of Medical Information Management, Kaohsiung Medical University, Kaohsiung 807, Taiwan, ROC
3Human Computer Interaction Technology Center, Industrial Technology Research Institute South, Tainan 734, Taiwan, ROC 4Department of Physical Therapy, Tzu-Chi College of Technology, Hualien 970, Taiwan, ROC
5Department of Electrical Engineering, National Sun Yat-Sen University, Kaohsiung 804, Taiwan, ROC
Received 5 Feb 2009; Accepted 27 Nov 2009
Abstract
Recent studies focused on the biomechanics of the pitching have exclusively studied professionals, whereas there
is little information on amateur pitchers. Notably, amateur pitchers with improper techniques may result in suboptimal
performance and can potentially lead to injury. The present study was aimed to compare the kinematics of the upper
extremity during the action of baseball pitching between amateur and professional players. Eighteen subjects (including
8 amateur with 0.9 years mean pitching period, and 10 professional pitchers with 6.7 years mean pitching period) were
recruited. Ten kinematic parameters for different instances and phases of pitching cycle were calculated to examine
differences between professionals and amateurs. Our results showed four of the ten kinematic parameters with
significant difference between these two groups. The parameters included elbow flexion and stride length at foot contact
phase, maximum shoulder external rotation at arm cocking phase and knee flexion at ball release phase. The findings
suggest that correct pitching movement may assist in increasing ball velocity and potentially prevent injury.
Keywords: Baseball, Pitching, Kinematics, Amateur, Professional
1. Introduction
Baseball is a common sport in Taiwan, which is generally
played starting in childhood. However, amateur pitchers with
improper techniques can often sustain injuries, especially
children who have just started pitching. Thus, it is logical to
speculate that in order to avoid injuries, the best strategy is to
ensure proper pitching mechanics [1]. Despite the complicated
nature of pitching, accurate pitching motion is associated with
greater pitching velocity and reduced sport injury risk [2].
Previous studies indicated differences between professional
pitchers by analyzing some of the best pitchers’ throws [3].
However, there is little information comparing the motion
pattern of body segments between professional and amateur
pitchers, although researchers have verified that the
biomechanical variables have a high repeatability among
professional pitchers.
Professional players show consistent motion pattern of
* Corresponding author: Lan-Yuen Guo
Tel: +886-7-3121101 ext. 2737 ext. 11; Fax: +886-7-3138359
E-mail: [email protected]
upper extremity and trunk during pitching movement. Escamilla
et al. studied several biomechanical variables, including
shoulder external and internal rotation, shoulder abduction,
shoulder horizontal adduction, elbow flexion and external
rotation, among baseball pitchers during the 1996 Olympic
games [4]. That study found all good performers had high
similarity in pitching motion and most pitchers adopted
overhead pitching to reach greater velocity. Overhead pitching
motion of professional pitchers can be divided into six phases:
wind-up, stride, arm cocking, arm acceleration, arm deceleration
and follow-through [5]. Skillful pitching in a joint motion is
characterized by activation from proximal to distal joints for
greater energy output. In the acceleration phase, the pitchers
extend the elbow in a second; the motion produced is not only
by the elbow joint, but also the other joint components, such as
shoulder girdle rotation, combined together.
Although biomechanical characteristics of professional
pitching have been well documented [6-8], there is little
information that compares the characteristics of pitching
mechanics between professional and amateur pitchers. The
purpose of this study was to compare the kinematic patterns of
upper extremity during baseball pitching movement between
amateur and professional players. We hypothesized that there
J. Med. Biol. Eng., Vol. 30. No. 3 2010 178
are significant differences in upper limb kinematics between
these two groups in a pitching task.
2. Methods
Eighteen subjects without any neuromuscular disease or
history of major musculoskeletal injury participated in this
study. These participants were categorized into 8 amateur and
10 professional-level pitchers, age ranged from 15 to 24 years.
The professional-level pitchers had received specialist training,
and came from the same high school’s team. On the contrary,
the eight amateur pitchers had not received the specialist
training. The mean heights and mean weights are shown in
Table 1. For the professional group, mean duration of pitching
experience was 6.7 years and for amateur pitchers was 0.9
years. Each participant was examined in an indoor laboratory.
Basic anthropometric information was obtained, including age,
height, weight, and physical training information prior to data
collection.
Table 1. Basic data among professionals and amateurs.
Parameter Professional
mean (SD)
Amateur
mean (SD) p-value
Age (years) 17.2 (3.0) 19.4 (1.2) 0.08
Height (cm) 181.3 (8.6) 172.5 (7.2) 0.04*
Mass (kg) 78.4 (14.5) 70.5 (10.2) 0.21
Pitching period (years) 6.7 (2.8) 0.9 (0.3) 0.00**
*Significant (p < 0.05); **Significant (p < 0.01)
All subjects were instructed to stretch and warm up before
formal data collection about pitching. There were 42 reflective
markers attached to bony landmarks on each subject (Figure 1).
Six-cameras (Qualisys ProReflex, Sweden) with 120 Hz
automatic digitizing system (Qualisys, Gothenberg, Sweden)
were used to capture the movement of those reflective markers.
Qualisys Track Manager (QTM) and Visual3D (C-Motion,
Inc., Germantown, MD, USA) were used to analyze the
movement data for determining three-dimensional coordinates
for each segment. Initially, subjects faced forward and stood on
a flat surface. Approximately 474.5 cm in front of the subject,
we placed a soft pad that consisted of cotton to absorb the
shock produced by the pitch ball. The pad size was about
140 cm by 192 cm. The averages of 3 fastball pitching
movements and 3 static anatomy positions were collected for
each subject. The professional players were requested to pitch
with straight ball. According to one reference [9], a ratio
(sample frequency)/(cut-off frequency) of 12 was effective at
rejecting noise and passing data. Therefore, marker position
data were filtered with a 10 Hz low-pass filter for the sample
frequency 120 Hz in this study.
We calculated 10 kinematic parameters (Table 2) for
different instances and phases of the pitching cycle (Figure 2),
including shoulder external rotation, shoulder abduction, elbow
flexion, knee flexion and stride length, which (was defined as a
distance between different heel markers shown as percentage of
the subject’s height). We used independent t-test to examine
differences in upper extremity and trunk kinematics between
amateur and professional players. A previous study had
Figure 1. The reflective marker set.
Table 2. Kinematic parameters of pitching phase.
Phases or
instants
Instant of
wind-up
Instant of
front foot contact
Arm
cocking phase
Arm
acceleration phase
Instant of
ball release
Parameters
Knee flexion
Elbow flexion
Maximum
elbow
flexion
Average
shoulder
abduction
Knee flexion
Shoulder external
rotation
Maximum
shoulder external
rotation
Elbow flexion
Knee flexion
Stride
length/height
(%)
Wind-upStrideArm
cocking
Arm
acceleration
Arm
deceleration
Follow-
through
Knee upFoot contactMax ERReleaseMax IR
Figure 2. The six phases of pitching motion.
reported the time of foot contact at 40%, maximum shoulder
external rotation at 80% and ball release at 100% of the pitch
cycle [10]. The height and common of significant level were
represented by p < 0.01 and p < 0.05, respectively.
3. Results
Kinematic parameters on different phases of the pitching
cycle were analyzed for each pitcher. Across the different
phases of the pitching cycle, we found that 4 of 10 kinematic
parameters showed significant differences between professional
and amateur pitchers (Table 3). Although amateur pitchers
showed no significant difference in knee flexion compared to
professional pitchers during the wind-up phase, front foot
contact phase, elbow flexion, and stride length were
significantly different between professional and amateur
pitchers (Table 3, Figure 3). Professional pitchers had greater
stride length and reduced elbow flexion in front of foot contact
phase when compared with the amateur group.
During the arm cocking phase, maximum shoulder
external rotation showed significant difference between the
professional and amateur group (Table 3, Figure 3). The
Limb Kinematic comparisons of Baseball Players 179
Table 3. Kinematic difference between professionals and amateurs.
Parameter Professional mean (SD) Amateur mean (SD) p-value
Wind-up
Knee flexion 85.2 (24.6) 73.3 (36.1) 0.42
Front foot contact
Elbow flexion 63.6 (26.5) 98.4 (16.0) 0.01*
Shoulder external rotation 83.9 (17.3) 74.0 (70.5) 0.71
Knee flexion 39.0 (14.3) 25.0 (16.3) 0.07
Stride length/height (%) 70.5 (3.9) 56.8 (7.8) 0.00**
Arm cocking
Maximum elbow flexion 91.2 (19.7) 108.6 (16.5) 0.06
Maximum shoulder external rotation 155.1 (23.2) 114.9 (51.3) 0.04*
Arm acceleration
Average shoulder abduction 72.2 (8.6) 57.9 (21.8) 0.07
Instant of ball release
Knee flexion 44.3 (8.8) 21.6 (14.9) 0.00**
Elbow flexion 45.5 (38.2) 27.0 (19.1) 0.20
*Significant (p < 0.05); **Significant (p < 0.01)
0 20 40 60 80 100
0
10
20
30
40
50
60
70
80
Join
t an
gle
(d
egre
es)
Pitching cycle (%)
Amateur
Professional
Knee flexion
(a)
0 20 40 60 80 1000
20
40
60
80
100
120
Join
t an
gle
(d
egre
es)
Pitching cycle (%)
AmateurProfessional
Elbow flexion
(b)
0 20 40 60 80 100
-120
-100
-80
-60
-40
-20
0
20
40
60
80
100
Join
t an
gle
(deg
rees
)
Pitching cycle (%)
Amateur
Professional
Shoulder rotation
(c)
Figure 3. Limb kinematic patterns of (a) knee joint, (b) elbow joint and (c) shoulder joint during pitching movement between amateur and
professional baseball players.
professional group showed greater shoulder external rotation
than amateur pitchers. At the instant the ball was released, we
found that professional pitchers showed significantly greater
knee flexion compared to amateur pitchers (Table 3, Figure 3).
4. Discussion
Upper extremity biomechanics of skilled baseball pitchers
have been well documented [6-8] and demonstrate that
biomechanical variables show high repeatability among those
good performers. Professional pitchers have specific motion
patterns. Most professional pitchers use overhead pitching, as
sidearm pitching that releases the ball at 3 o’clock by right-handed
pitchers, or 9 o’clock by left-handed pitchers, can lead to more
arm injuries than overhead pitchers [11] and shorten the career of
pitchers. Overhead pitching is a common and complicated way to
produce higher velocity throws. In our study, most professional
pitchers (87% among all pitchers) used pitching over their
shoulder to throw the ball. However, movement of amateur
pitchers is typically similar to sidearm, regardless of no standard
sidearm patterns. The higher standard deviation of kinematic
variables in the amateur group indicates that they do not have a
specific pitching motion pattern compared with the professional
group. Amateur pitchers may not have learnt proper pitching
mechanics; hence, in the long-term, amateur pitchers may waste
energy and increase the risk of injury.
There is lack of data in relation to the kinematic difference
between professional and amateur pitchers. In our study, we
found four significant differences among ten kinematic
parameters between professionals and amateurs. During
wind-up phase through to stride foot contact phase,
professional pitchers showed greater knee flexion than amateur
pitchers. Larger knee flexion during this period may be related
to two factors. First, the wind-up phase and stride foot contact
phase were influenced by their balance condition. The amateur
group may have weaker muscle strength than professional
pitchers, and therefore may not have enough balance ability for
a greater knee flexion range. Second, the short stride length
may be related to smaller knee flexion. We found that the
amateur group had significantly shorter stride length than the
professional group, and this may be related to a smaller knee
flexion during the wind-up phase. However, Dun et al.
compared motion differences between junior professional
pitchers and senior professional pitchers [12], and found that
older pitchers displayed more narrow stride length, more trunk
rotation, and less shoulder external rotation in cocking phase.
They also found compensatory movements to increase the ball
velocity, and this was consistent with other studies [13-17]. The
stride phase plays a critical role for the young pitcher, who uses
the time to store energy for the successive phases of movement
[5]. Therefore, stride length can be an indicator of
performances for pitchers.
J. Med. Biol. Eng., Vol. 30. No. 3 2010 180
In the present study, shoulder external rotation of
professional pitchers during arm cocking phase was
significantly larger than that of the amateur group. Professional
pitchers may take advantage of the elastic energy of shoulder
muscles to produce larger forces to throw the ball. Possible
advantages of pre-stretching the anterior shoulder muscle
during the early phase may assist to store elastic energy in these
tissues for the subsequence of the pitch. Hence, pitchers can
produce a quicker and more powerful shoulder rotation by
using elastic energy. Escamilla et al. inferred that the greater
external rotation of shoulder may induce longer time for the
arm to lag behind the body during the cocking phase and arm
acceleration phase [4]. Fleisig et al. stated that pitcher
mechanics did not change significantly with professional level
[3]. Even though maximum shoulder external rotation at arm
cocking phase is not an important factor to evaluate the
outstanding level at professional level, it may assist players and
coaches to distinguish between amateur and professional
pitchers. Our study showed that the elbow flexion of
professional pitchers was approximately 40 degree at ball
release, and this is similar to that reported in the above
literature. However, elbow flexion of amateur pitchers was
similar to that of professional pitchers. Knee flexion at the
onset of ball release is significantly different between
professional and amateur pitchers. Amateurs with a small knee
flexion may be related to earlier ball release. Hence, knee
flexion at ball release may be another indicator that
differentiates performances for pitchers.
Pitching injury most commonly occurs in the upper limbs,
such as the shoulder and elbow joints. Evidence suggests that
the probabilities of shoulder and elbow injury increase with
increases in pitching duration, wherein the faster the pitching
velocity, the higher the injury probability. Thus, our study
focused on pitching movements during different phases and
analyzed the kinematics of the shoulder and the elbow joints,
i.e. the shoulder external rotation and the elbow flexion. Our
study demonstrated significant differences in elbow flexion
between the two groups in the front foot contact phase. There
was also significant difference in shoulder external rotation in
the arm cocking phase. Our study showed that the elbow
flexion and the shoulder external rotation influenced pitching
performance. Although there is no direct evidence that proves
the relationship between the two factors, Olsen et al. [2]
showed a strong relationship between injury probability and the
pitching period, practice time and the number of pitches. When
a pitcher mostly depends on shoulder external rotation and
elbow flexion, it increases the injury probability at the same
time. In summary, amateur pitchers have reduced number of
pitchers and thus have lower injury probability theoretically.
Nevertheless, the amateur pitches do not have correct pitching
skill and training methods with them, so they may demonstrate
a greater potential to sustain a sports injury.
In summary, four kinematic differences of the upper
extremity were found among amateur and professional players.
These variables could be used to examine whether amateur
pitchers can perform the proper pitching mechanics shown by
professionals for producing faster velocity ball and preventing
pitching-related injuries. However, ball velocity and accuracy
are also relative to good baseball pitching performance. The
lack of those parameters is the limitation of this research. In the
future, the difference of ball velocity and accuracy between
amateur pitchers and professionals will be added.
References
[1] J. R. Andrews and G. S. Fleisig, “Preventing throwing injuries,” J.
Orthop. Sports Phys. Ther., 27: 187-188, 1998.
[2] S. J. Olsen II, G. S. Fleisig, S. Dun, J. Loftice and J. R. Andrews,
“Risk factors for shoulder and elbow injuries in adolescent
baseball pitchers,” Am. J. Sports Med., 34: 905-912, 2006.
[3] G. S. Fleisig, S. W. Barrentine, N. Zheng, R. F. Escamilla and J.
R. Andrews, “Kinematic and kinetic comparison of baseball
pitching among various levels of development,” J. Biomech., 32:
1371-1375, 1999.
[4] R. F. Escamilla, G. S. Fleisiq, N. Zheng, S. W. Barrentine and J.
R. Andrews, “Kinematic comparisons of 1996 Olympic baseball
pitchers,” J. Sports Sci., 19: 665-676, 2001.
[5] G. S. Fleisig, S. W. Barrentine, R. F. Escamilla and J. R. Andrews,
“Biomechanics of overhand throwing with implications for
injuries,” Sports Med., 21: 421-437, 1996.
[6] M. B. Sabick, M. R. Torry, Y. K. Kim and R. J. Hawkins,
“Humeral torque in professional baseball pitchers,” Am. J. Sports
Med., 32: 892-898, 2004.
[7] S. W. Barrentine, R. F. Escamilla and G. S. Fleisig, “Kinematic
analysis of the wrist and forarm during baseball pitching,” J.
Biomech., 14: 24-39, 1998.
[8] D. F. Stodden, G. S. Fleisig, S. P. McLean and J. R. Andrews,
“Relationship of biomechanical factors to baseball pitching
velocity: within pitcher variation,” J. Appl. Biomech., 21: 44-56,
2005.
[9] D. A. Winter (Ed.), Biomechanics and Motor Control of Human
Movement, New York: Wiley, 1990.
[10] D. W. Keeley, T. Hackett, M. Keirns, M. B. Sabick and M. R.
Torry, “A biomechanical analysis of youth pitching mechanics,” J.
Pediatr. Orthop., 28: 452-459, 2008.
[11] J. A. Albright, P. Jokl, R. Shaw and J. P. Albright, “Clinical study
of baseball pitchers: correlation of injury to the throwing arm
with method of delivery,” Am. J. Sports Med., 6: 15-21, 1978.
[12] S. Dun, S. F. Glenn, J. Loftice, D. Kinqsley and J. R. Andrews,
“The relationship between age and baseball pitching kinematics
in professional baseball pitchers,” J. Biomech., 40: 265-270,
2007.
[13] T. S. Ellenbecker, E. P. Roetert, D. S. Bailie, D. J. Davies and S.
W. Brown, “Glenohumeral joint total rotation range of motion in
elite tennis players and baseball pitchers,” Med. Sci. Sports
Exerc., 34: 2052-2056, 2002.
[14] K. M. Reagan, K. Meister, M. B. Horodyski, D. W. Werner, C.
Carruthers and K. Wilk, “Humeral retroversion and its
relationship to glenohumeral rotation in the shoulder of college
baseball players,” Am. J. Sports Med., 30: 354-360, 2002.
[15] H. C. Crockett, L. B. Gross, K. E. Wilk, M. L. Schwartz, J. Reed,
J. O’Mara, M. T. Reilly, J. R. Dugas, K. Meister, S. Lyman and J.
R. Andrews, “Osseous adaptation and range of motion at the
glenohumeral joint in professional baseball pitchers,” Am. J.
Sports Med., 30: 20-26, 2002.
[16] K. Meister, T. Day, M. Horodyski, T. W. Kaminski, M. P. Wasik
and S. Tillman, “Rotational motion changes in the glenohumeral
joint of the adolescent/little league baseball player,” Am. J.
Sports Med., 33: 693-698, 2005.
[17] G. Baltaci, R. Johnson and H. Kohl 3rd, “Shoulder range of
motion characteristics in collegiate baseball players,” J. Sports
Med. Phys. Fit., 41: 236-242, 2001.