Journal of Bodywork & Movement Therapies 37 (2024) 57–62

Contents lists available at ScienceDirect

Journal of Bodywork & Movement Therapies
journal homepage: www.elsevier.com/jbmt

Shoulder kinetic during pitching in baseball players with
scapular dyskinesis
Atsushi Ueda a, *, Aoi Matsumura b, Takafumi Shinkuma c, Takeshi Oki c, Yasuo Nakamura daDepartment of Rehabilitation Sciences, Faculty of Allied Health Sciences, Kansai University of Welfare Sciences, Japan
TAKE PHYSICAL CONDITIONING Inc., Japanc
Department of Orthopaedic Surgery, Hankai Hospital, Japand
Department of Health and Sports Science, Doshisha University, Japanb

A R T I C L E I N F O

A B S T R A C T

Handling Editor: Dr Jerrilyn Cambron

Introduction: Shoulder injuries in baseball players cause excessive shoulder load during pitching and scapular
dyskinesis (SD). However, the characteristics of pitching kinetics in the shoulder joint with SD are unclear. This
study aimed to investigate the effect of SD on pitching kinetics in the shoulder joint of baseball players.
Method: Seventy-two college and independent league baseball players participated in the study. The pitchingmotion was measured using an 18–camera motion-capture system. SD was classified into four types (I–IV) using
the scapular dyskinesis test (SDT). The pitching kinetics data were analyzed.
Results: The agreement of SD in this study was 56/72 (77.8%). SD were classified into 31 abnormal group (type
I–III) and 25 control group (type IV). Three participants with measurement failure during the pitching motion
analysis were excluded from the analysis. The abnormal group showed a larger maximum value of the gleno­
humeral normalized anterior joint force than the control group.
Conclusions: These results suggest that an increase in GH anterior force during pitching causes an excessive in­crease in external rotation of the GH with an insufficient posterior tilt of the scapula with SD. Therefore, baseballpitching with SD may involve shoulder injuries owing to excessive shoulder load during pitching.

1. Introduction
Shoulder injuries in baseball players are common upper-extremity
injuries (Burkhart et al., 2003c; Fares et al., 2020; Wasserman et al.,2019). Previous studies have reported that shoulder injury rates among
all injuries in college and professional baseball players are the highest at
21% and 27%, respectively (Fares et al., 2020; Wasserman et al., 2019).
Shoulder injuries in baseball players are a factor in pitching motion due
to the large range of motion and high throwing velocity, which causes anincrease in the mechanical stress placed on the shoulder joint (Burkhart
et al., 2003a). Furthermore, repetitive throwing motions ofoverhead-throwing athletes with shoulder dysfunctions cause patho­
logical alterations to the shoulder joint (Burkhart et al., 2003b).
Therefore, to prevent shoulder injuries in baseball players, clinicians
should consider the relationship between shoulder function and pitchingbiomechanics.
Shoulder biomechanics during the late cocking phase of the baseballpitching cause from 158◦ to 178◦ of shoulder external rotation(Aguinaldo and Chambers 2009; Fleisig et al., 2006; Nissen et al., 2007;
Sabick et al., 2004) and an increase in the shoulder anterior force(Fleisig et al., 1995). As a result, an excessive shoulder external rotation
and an increase in shoulder anterior joint force during pitching areassociated with throwing-related shoulder injuries, such as superior
labrum anterior to posterior (SLAP) lesions (Kuhn et al., 2003), anterior
shoulder instability (Mihata et al., 2004), rotator cuff injury (Fleisig
et al., 1995), and internal impingement (Mihata et al., 2012). Moreover,baseball players with abnormal scapular motion develop shoulder in­juries due to excessive shoulder loading during pitching (Burkhart et al.,2003b).
Scapular dyskinesis (SD) is a primary factor in shoulder disorders(Kibler et al., 2013). Defined as an abnormal scapular static position andmotion (Kibler et al., 2013), SD is classified into four types: type I,
inferior prominence of the scapula; type II, medial border prominence ofthe scapula; type III, excessive scapular elevation and upward rotation;and type IV, normal scapular motion (without SD) (Kibler et al., 2002).
In regards to SD and shoulder injuries, SD involves the development of* Corresponding author. 3–11–1 Asahigaoka, Kashiwara–shi, Osaka-fu, 582–00026, Japan
E-mail address: at-ueda@tamateyama.ac.jp (A. Ueda).
https://doi.org/10.1016/j.jbmt.2023.11.012
Received 1 October 2022; Received in revised form 22 September 2023; Accepted 11 November 2023
Available online 17 November 2023
1360-8592/© 2023 Published by Elsevier Ltd.

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Journal of Bodywork & Movement Therapies 37 (2024) 57–62

various shoulder injuries, such as rotator cuff injuries, subacromial
impingement, glenohumeral (GH) joint instability (Burkhart et al.,2003b; Hickey et al., 2018). Regarding SD and abnormal scapular mo­tion during shoulder movement, SD types I and II involve abnormal
scapular motion with excessive scapular internal rotation and insuffi­
cient scapular posterior tilt (Huang et al., 2015; Park et al., 2013),
respectively. Abnormal scapular motion can cause excessive shoulder
motion and mechanical stress during the pitching motion (hyper angu­
lation), resulting in pathological alterations of the shoulder joint (Bur­khart et al., 2003b). However, there is a lack of evidence regarding therelationship between abnormal scapular motion and pitchingbiomechanics.
The current study found that SD type I (decreased scapular posteriortilt) increased external rotation of the glenohumeral joint (GH) anddecreased posterior tilt of the scapulothoracic at the maximum shoulder
external rotation (MER) during the pitching motion compared to acontrol group without SD (Ueda et al., 2021). As a result, we havementioned that baseball players with SD may have experienced an in­crease in mechanical load on the shoulder joint, resulting in an increasein GH motion and a decrease in scapular motion during the pitching
movement (Ueda et al., 2021). However, previous studies have notclarified whether SD is associated with shoulder load during the pitchingmotion. The relationship between SD with scapular malposition,
abnormal motion, and shoulder load during the pitching motion may
help in understanding the pathological mechanism of throwing-relatedshoulder injuries. Hence, the hypothesis was that baseball pitchingwith SD would increase shoulder loading during pitching motion. The
current study aimed to investigate the characteristics of shoulder ki­
netics during baseball pitching in SD.

previous studies (Ueda et al., 2021). Shoulder movement speed during
the SDT was set at 3 s for raising and 3 s for lowering. Two physicaltherapists with >6 years of experience in musculoskeletal disorderrehabilitation assessed SD. Only those deemed to have SD by both
physiotherapists were included in the study. Exclusion criteria
comprised discrepancies in SD assessment between the physical thera­
pists and those with shoulder joint symptoms during SDT. The evalua­tion criteria for SD are classified into types I–IV) (Kibler et al., 2002).
Our participants were assigned to abnormal (SD types I‒III) and control(normal; SD type IV) as described (Uhl et al., 2009).
2.3. Biomechanical analysis
Baseball pitching was measured using an 18–camera motion capturesystem (Mac3D; Motion Analysis, Rohnert Park, California, USA). Fif­ty–six reflective markers were affixed to the entire body. The pitchingpractice was conducted for approximately 10 min. The pitching task for
all participants was performed as a straight throw on a flat floor (Ueda
et al., 2021).
The scapular kinematics during baseball pitching was measured
using the acromion marker cluster (AMC) method described in the au­thor’s previous studies (Matsumura et al., 2019; Ueda et al., 2021).
Previous studies have reported that measurement of scapular motion
during a pitching motion using a magnetic sensor, the intraclass corre­
lation coefficient (ICC) (standard error of measurement: SEM) of thescapula angle during the pitching motion at the maximum shoulder
external rotation and ball release periods were 0.91–0.85 (2.2–4.0◦ ) and
0.89–0.93 (3.1–4.5◦ ), respectively (Meyer et al., 2008).
The coordinate systems are the global coordinate system (ΣCa) andlocal coordinate systems of the thorax (ΣTh), scapula (ΣS), upper arm(ΣU), forearm (ΣFa), and hand (ΣH). The coordinate systems werereferenced using the method described by the International Society ofBiomechanics (Wu et al., 2005). In comparison to the author’s previous
study, kinematic parameters during the pitching motion were calculated
for external (+)/internal (− ) rotation of the thoracohumeral joint (ΣUrelative to ΣTh: TH) and scapulohumeral joint (ΣU relative to ΣS: GH),and posterior (+)/anterior (− ) tilt of the scapulothoracic joint (Σsrelative to ΣTh: ST), respectively (Wu et al., 2005). To calculate eachjoint angle, rotational sequences proposed by the International Societyof Biomechanics were used (Wu et al., 2005).
The joint force and moment during the pitching motion were
calculated using an inverse dynamic analysis. The joint force andmoment applied to the joints on the throwing side were calculated fromthe distal to proximal direction (from hand to shoulder) using the
Newton-Euler method (Fleisig et al., 1995). Additionally, the joint force
and moment in the shoulder joint were calculated as those of the TH and
GH joints, respectively. With regard to the kinetic parameters, normal­
ized data were also calculated using the values of body weight (kg) ×
gravitational acceleration (mg/s2) for joint force and height (m) andbody weight (kg) × gravitational acceleration (mg/s2) for joint moment.
The joint forces GH and TH were defined as anterior (+)/posterior (− ),superior (+)/(− ), and proximal (+)/distal (− ), respectively. The joint
moments of GH and TH were defined as horizontal abduction (+)/hor­
izontal adduction (− ) and external rotation (+)/internal rotation (− ).
The joint moments of GH and TH were defined as horizontal abduction(+)/horizontal adduction (− ) and external rotation (+)/internal rota­tion (− ).

2. Methods
2.1. ParticipantsParticipants in the kinetic analysis during a baseball pitching motion
included 72 asymptomatic healthy baseball players (66 college baseballplayers and 6 baseball players in an independent league in Japan),including participants in our previous study (kinematic analysis) (Ueda
et al., 2021). A power analysis was performed to determine the sample
size using G*power (version 3.1.9.4, Kiel University, Germany). The
sample size of our study was estimated to be 23 participants per group(Cohen’s D > 0.8). The current study fulfilled the sample size require­ment by adding five participants from the authors’ previous study (Ueda
et al., 2021) to analyze kinetic data during baseball pitching. Addi­
tionally, to be up to date the sample data in this study, all data wererecalculated. Patients with shoulder pain during various shoulder mo­
tions during the last three months were excluded from our study. The
current study was approved by the ethics committee of Doshisha Uni­
versity. All participants provided written informed consent.
Demographic data are shown in Table 1. Bilateral shoulder internaland external rotation range of motion (ROM) and maximum ball ve­
locity during the pitching motion were also measured. Passive internaland external rotation at 90◦ abduction of the shoulder was measured
using a goniometer (Awan et al., 2002). Differences in the shoulder in­
ternal range of motion between throwing and non-throwing sides werealso calculated to assess glenohumeral internal rotation deficits (GIRD),
then throwing and nonthrowing >15◦ was determined based on GIRD
assessment (Maenhout et al., 2012). The maximum ball speed during
pitching was measured using a radar gun (Ueda et al., 2021).

2.4. Data analysis
A pitching trial of the fastest pitching was performed to analyze thedata (Oliver & Weimar 2015). Pitching phases were defined as the stride
foot contact (SFC), MER, and ball release (BR) periods (Ueda et al.,2021), respectively. The joint angles of the GH and TH were obtained foreach period (SFC, MER, and BR). The maximum values of the ST angle,
joint moment, and joint force were calculated using SFC and BR. The

2.2. Scapular dyskinesis classification
SD was assessed using the scapular dyskinesis test (SDT) (Kawasaki
et al., 2012; Kibler et al., 2002). The SDT method in this study was
performed with bilateral shoulder flexion and abduction with 2–kg
weights for three cycles using the measurement method described in58

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Journal of Bodywork & Movement Therapies 37 (2024) 57–62

pitching cycle was normalized to 100% using SFC and BR. MATLAB
R2020a (MathWorks, MA, USA) was used for analysis.
All statistical analyses were performed using IBM SPSS Statistics
version 27 (IBM Corp., Armonk, NY, USA). Inter–rater reliability for SDT
was assessed using the kappa coefficient. Demographic data, kinematics(joint angle), and kinetic parameters (joint force and moment) during
baseball pitching between the abnormal and control groups werecompared using independent sample t-tests to determine differences indemographic data, kinematics, and kinetic parameters. The significancelevel was set at 5%. Moreover, the effect size (Cohen’s D) was calculatedusing G*power (version 3.1.9.4, Kiel University, Germany).
3. Results
Fig. 1 shows a flowchart of the recruitment process. The results ofthis study are presented in Table 1–4 and Fig. 2. The agreement of SD inthis study was 56/72 (77.8%). The kappa coefficient for the inter–rater
reliability of our SD assessment was 0.73.
The abnormal (SD type I) and control groups respectively comprised
28 and 25 of 56 participants. The abnormal group comprised 13, seven,four and four participants with isolated type I, types I + II, type I + III,and III, respectively. Twenty-four (42.8%), 7 (12.5%), and 8 (14.3%) of
56 participants had SD types I, II and III. None of the participants
experienced pain during SDT or pitching motion measurements. Threeparticipants in the abnormal group with missing markers or increased
noise during the pitching motion analysis were excluded. We finallyanalyzed 53 (abnormal, n = 28; control, n = 25) participants.
There were no statistically significant differences in the demographic
data of the participants between the two groups (Table 1). The incidenceof GIRD in the abnormal and control groups was 15 and 16 participants,
respectively.
Regarding the kinematic parameters of the GH during the pitchingmotion, the GH external rotation angle at the MER in the abnormalgroup was approximately 9◦ larger than that in the control group (p =0.01, D = 0.75). There were no statistically significant differences in theother GH angles at the MER between the groups (Table 2). The
maximum posterior tilt of the ST in the abnormal group from SFC and
MER was approximately 6◦ smaller than that in the control group (p =Fig. 2. Temporal changes in glenohumeral joint force (anterior/posterior force)and scapulothoracic and glenohumeral kinematics during baseball pitching in
the abnormal and control groups (black line: abnormal group; gray line: control
group). The pitching cycle during each period shows the average value between
the scapular dyskinesis type (I -IV). Stride foot contact (SFC); maximum
external rotation (MER); ball release (BR). Joint force; GH humeral orientation
with respect to the scapula: anterior (+)/posterior (− ). Joint angles; GH, gle­
nohumeral joint: external rotation (+)/internal rotation (− ). ST, scap­
ulothoracic joint: posterior tilt (+)/anterior tilt (− ).

0.02, D = − 0.70) (Table 2). Regarding the kinetic parameters of GH
during the pitching motion, the abnormal group had a significantly
larger maximum value (from SFC to MER) of normalized GH anterior
joint force than the control group (p < 0.01; D = 0.74). There were no
significant differences in other kinetic parameters (Table 4). The timingof the maximum value of the GH anterior force, ST posterior tilt angle,
and GH external rotation angle were 46%, 63%, and 77% for theabnormal group, and 46%, 64%, and 77%, respectively, for the control
group during the pitching cycle (Fig. 1) (see Table 3).
4. Discussion
The current study aimed to clarify the kinetic alteration of theshoulder joint while players with SD pitched baseballs. The maximum
GH anterior force from SFC to MER while pitching was significantly
larger in the abnormal group than in the control group; Moreover, a GH
external rotation at the MER was 9◦ higher and the maximum value of ST
posterior tilt was decrease by 6◦ the abnormal group compared with thecontrol group. These kinematic data obtained while pitching weresimilar to our previous findings (Ueda et al., 2021) and results partially
supported our hypotheses.
Shoulder (TH) joint forces and moments during baseball pitching in

Fig. 1. The flowchart of the recruitment process.
59

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Journal of Bodywork & Movement Therapies 37 (2024) 57–62

Table 1
Demographic data in the two groups.a.

Table 3
Shoulder joint kinetics during pitching in the two groups.a.

Abnormalgroup

Control
group

（n =
28）

（n =
25）

Age, years

20.5 ± 1.4

.34

0.28

Height,cm

.69

0.12

Weight, kg

174.9 ±
5.6
74.2 ± 7.4

.79

0.14

Body mass index, kg/m2

24.2 ± 2.0

.71

0.11

Competition history, years

12.4 ± 2.1

20.1 ±
1.4
175.6 ±
5.7
75.3 ±
8.0
24.4 ±
1.7
11.8 ±
2.7

.38

0.25

34.5 ±
12.6
51.5 ±
14.1− 17.0 ±
11.4
16

.49

0.20

.42

0.23

.73

0.11

112.0 ±
9.7
100.2 ±
8.1
11.8 ±
9.1
31.0 ±
2.3

.33

0.23

.81

0.06

.17

0.10

.72

0.09

Shoulder internal rotation range of motion, deg
Throwing side
32.2 ±
10.8
Non-throwing side
48.4 ±
12.3
Difference（throwing side − 15.6 ±non-throwing side）
14.7
Glenohumeral internal rotation
15
deficit, nd
Shoulder external rotation range of motion, deg
Throwing side109.8 ±
9.7
Non-throwing side
101.0 ±
7.8
Difference（throwing side 8.5 ± 8.8
non-throwing side）
ball velocity, m/s
31.2 ± 1.9

Pvalueb

Effectsizec

Kinetic parameters

Maximum joint force
Glenohumeral joint
anterior（+）/posterior（-）, N
superior（+）/inferior（-）,
N
proximal（+）/distal（-）,
N
Humeralthoracic joint
anterior（+）/posterior（-）, N
superior（+）/inferior（-）,
N
proximal（+）/distal（-）,
N
Maximum joint moment
Glenohumeral joint
horizontal abduction（+）/horizontal adduction（-）, N/mexternal rotation（+）/internal rotation（-）,
N/mHumeralthoracic joint
horizontal abduction（+）/horizontal adduction（-）, N/mexternal rotation（+）/internal rotation（-）,
N/maMean ± standard deviation.
Values less than 0.05 were consided statistically significant.
cCohen’s d effect size.
bAbnormalgroup

Controlgroup（n = 28）（n =25）

Maximum shoulder external rotation period
Glenohumeral joint
external rotation
140 ± 11（+）/internal rotation（-）, deg
Humeralthoracic joint
external rotation
160 ± 9（+）/internal rotation（-）, deg
Maximum value
Scaplothoracic joint
posterior tilt（+）/anterior
25 ± 9tilt（-）, deg

Controlgroup

Pvalueb

Effectsizec（n = 28）（n =25）

361 ± 69324 ± 64

.06

0.56

168 ± 66

152 ± 64

.39

0.25

640 ± 141

658 ±
184

.68

0.11

342 ± 70322 ± 73

.32

0.28

174 ± 50169 ± 54

.73

0.10

628 ± 148

635 ±
168

.88

0.04

81 ± 1978 ± 16.55

0.17− 39 ± 11− 40 ± 14

.85

0.08

63 ± 1463 ± 14.86

0.00− 63 ± 17− 60 ± 16.48− 0.18aMean ± standard deviation.
Values less than 0.05 were consided statistically significant.
cCohen’s d effect size.
b

Table 2
Shoulder joint kinematics during pitching in the two groups.a.
Joint angle

Abnormalgroup

Pvalueb

Effectsizec

131 ± 13

.01

0.75

156 ± 9.130.44

31 ± 8.02− 0.70angle (external rotation and horizontal internal rotation) and angularvelocity (internal rotation) during baseball pitching in Japanese in­dividuals are greater than those in Americans, resulting in greater me­
chanical stress on the shoulder joint. Takagi et al. (2014) reported thatan increase in the shoulder horizontal abduction angle at the MER
during pitching motion is related to an increase in the shoulder anterior
force. The findings of these previous studies suggest that an increase inshoulder joint load during the pitching motion is associated not onlywith body size and ball velocity, but also with an increase in shoulder
motion during the pitching movement (Oi et al., 2019).
The maximum normalized GH anterior force and GH external rota­tion at the MER was increased, and the ST posterior tilt peak wasdecreased while pitching in the abnormal, compared with the control
group. This finding suggested that the incidence of SD type I with adecreased posterior scapular tilt was the highest among SD types in theabnormal group and that this caused kinetic changes while pitching.
Fleisig et al. (1995) reported that the shoulder anterior force (TH joint)
at the MER during pitching motion produced approximately 310 N(approximately 3 kg). An increase in shoulder anterior force during thepitching motion is caused by a variety of throwing-related shoulder in­juries (Burkhart et al., 2003b; Fleisig et al., 1995; Takagi et al., 2014)
due to increased anterior translation of the humeral head during
pitching. Previous studies using cadavers have reported that maximum
shoulder external rotation with an insufficient scapular posterior tilt
increases the anterior shear force in the GH joint (Mueller et al., 2013).
Therefore, researchers in previous studies have described that SD with
scapular malposition and abnormal motion, such as a decreased poste­rior tilt (SD type I) are associated with the development of various
shoulder injuries, such as anterior shoulder instability, rotator cuff dis­ease, and SLAP lesions (Burkhart et al., 2003b; Fu et al., 2020). Thea

Mean ± standard deviation.
Values less than 0.05 were consided statistically significant.
cCohen’s d effect size.
bthis study were smaller than those reported in previous studies (Fleisig
et al., 1995; Oi et al., 2019; Pappas et al., 1985). The average values ofbody size (height and weight) and ball velocity in this study were lower
than those reported in previous studies. Previous studies have reported
that increases in the joint force and joint moment during pitching mo­tion are associated with body size (height and weight) and ball velocity(Oi et al., 2019; Okoroha et al., 2018; Slowik et al., 2019). Therefore, thedecrease in body size and ball velocity in our study may have reduced
joint forces and moments during the pitching motion compared withprevious studies. However, Oi et al. (2019) reported that the shoulder
60

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Journal of Bodywork & Movement Therapies 37 (2024) 57–62

P
valueb

Effectsizec

all baseball pitchers studies had less than average glenohumeral internalrotation deficits (<10◦ ± 2◦ ) (Borsa et al., 2008). Therefore, we inferredthat our kinematic data were obtained with GIRD. We did not generalize
baseball pitchers with below average glenohumeral internal rotation
deficits (GIRD) (<10◦ ± 2◦ ). Therefore, future studies will requirebiomechanical analyses to control the influence of GIRD.

0.44 ±
0.07
0.20 ±
0.08
0.88 ±
0.20

<.01

0.74

5. Conclusions

.26

0.35

.87

0.00

0.43 ±
0.08
0.23 ±
0.06
0.85 ±
0.18

.12

0.50

.47

0.15

.87

0.05

0.063 ±
0.011

0.060 ±
0.008

.26

0.31

− 0.031 ±0.007− 0.033± 0.009.95

0.25

0.050 ±
0.009

0.048 ±
0.008

.52

0.23

− 0.049 ±0.009− 0.046± 0.009.21

0.33

Table 4
Normalized data of shoulder joint kinetics during pitching in the two groups.a.
Kinetic parameters

Maximum joint force
Glenohumeral joint
anterior（+）/posterior（-）, N/kg
superior（+）/inferior（-）,
N/kg
proximal（+）/distal（-）,
N/kg
Humeralthoracic joint
anterior（+）/posterior（-）, N/kg
superior（+）/inferior（-）,
N/kg
proximal（+）/distal（-）,
N/kg
Maximum joint moment
Glenohumeral joint
horizontal abduction（+）/horizontal adduction（-）, N/m/height × kg
external rotation（+）/internal rotation（-）,
N/m/height × kg
Humeralthoracic joint
horizontal abduction（+）/horizontal adduction（-）, N/m/height × kg
external rotation（+）/internal rotation（-）,
N/m/height × kg

Abnormalgroup

Controlgroup（n = 28）(n = 25）

0.50 ± 0.09
0.23 ± 0.12
0.88 ± 0.17
0.47 ± 0.08
0.24 ± 0.07
0.86 ± 0.19

The current study aimed to clarify the characteristics of shoulder
load during baseball pitching with SD type I. Results showed that the
maximum GH anterior force during the baseball pitching late cocking
phase (from SFC to MER) in the abnormal group (SD type I) was
significantly larger than that in the control group. These results suggestthat an increase in GH anterior shear force during pitching due toexcessive GH external rotation with insufficient ST posterior tilt motion
with SD may cause shoulder injuries.
Clinical relevance● A simple assessment using the scapular dyskinesis test can predict
increases in anterior shear forces at the glenohumeral joint during
pitching.
● To minimize shoulder load during pitching, clinicians should
consider the scapular exercise program for scapular dyskinesis.
● Our findings provide a basis for understanding occurrence mecha­
nisms of shoulder injuries with overhead athletes.
CRediT authorship contribution statement
Atsushi Ueda: Conceptualization, Data curation, Formal analysis,
Methodology, Validation, Visualization, Writing – original draft,
Writing – review & editing. Aoi Matsumura: Methodology. Takafumi
Shinkuma: Validation, Visualization. Takeshi Oki: Validation, Writing– review & editing. Yasuo Nakamura: Resources, Software,Supervision.

aMean ± standard deviation.
Values less than 0.05 were consided statistically significant.
cCohen’s d effect size.
bfindings of the present and previous studies have suggested that an
excessive increase in GH external rotation with reduced scapular pos­terior tilt while pitching in baseball players with SD can increase the GH
anterior shear force at the MER during the pitching motion (Ueda et al.,2021).
Our results suggested that a simple assessment using the SDT can
indirectly judge increased anterior shear force with excessive the GH
external rotation during pitching. The current findings suggested that
decreasing the GH anterior force during pitching baseballs is crucial forsuppressing excessive external rotation with a sufficient posterior tilt of
the scapula is also important for SD (Ueda et al., 2021). As a result,clinicians should fully consider training programs for baseball playerswith SD. Hence, our findings should provide fundamental knowledge
that will help to prevent shoulder injuries and rehabilitation for over­head athletes with SD.
There were several limitations to the current study. First, there may
be scapular motion measurement errors due to skin motion artifact of
AMC on the scapula and other marker during the dynamic pitchingmotion (Oliver & Weimar 2015; Ueda et al., 2021). Second, the kinetic
parameters (joint force and moment) of the GH and TH joints in thisstudy were the resultant force and moment, whereas the contribution ofeach of the factors generating forces, such as various muscle contrac­
tions and extension of the ligament and joint capsule, could not be
separately evaluated (Takagi et al., 2014). Third, the results of thiscross-sectional study could not clarify the relationship between kinetic
alterations, SD, and shoulder injuries. In the future, clarifying the lon­
gitudinal relationship between SD and shoulder injuries in baseballplayers is needed. We could not control the influence of GIRD on scap­
ular static position and kinematic changes (Ellenbecker and Cools 2010;
Thomas et al., 2010). Compared with the non-throwing side, GIRD in thethrowing side (abnormal vs. control) was 15.6◦ ± 14.7◦ vs. 17.0◦ ± 11.4◦

Declaration of competing interest
There is no know conflict of interest associated with this paper.
Acknowledgments
This study was supported by the Athlete Care Association (Japan).
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