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: yuen@kmu.edu.tw

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.

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