J Shoulder Elbow Surg (2022) 31, 2611–2619

www.elsevier.com/locate/ymse

The relationship between scapular position andglenohumeral rotational range of motion in highschool baseball players
Takashi Higuchi, PhD, PTa,*, Yasuaki Tanaka, MSc, PTb, Yuji Kanazawa, PhD, PTc,
Moemi Matsuo, PhD, OTd, Shigeki Yokoyama, PhD, PT, JSPO-ATea

Department of Physical Therapy, Osaka University of Human Sciences, Settsu, Osaka, Japan
Department of Rehabilitation, Saiseikai Nagasaki Hospital, Nagasaki, Nagasaki, Japanc
Faculty of Health and Medical Sciences, Hokuriku University, Kanazawa, Ishikawa, JapandFaculty of Rehabilitation Sciences, Nishi Kyushu University, Kanzaki, Saga, Japane
Department of Physical Therapy, Kyoto Tachibana University, Kyoto, Japanb

Background: Past research indicated that scapular malposition is related to the glenohumeral internal rotation deficit (GIRD). However,there is no research examining the effect of throwing-related pain on this relationship. This study investigated the relationship between
scapular position and range of motion (ROM) and compared the difference in this relationship between with and without throwingrelated pain.
Methods: Forty male baseball players in high school were recruited for this study. The existence and degree of throwing-related pain
were obtained from a questionnaire. Participants were divided into 2 groups according to the presence or absence of the pain. Glenohumeral internal and external rotation ROM (abduction internal rotation angle and abduction external rotation angle [ABER], respectively) were measured using a digital inclinometer. The pectoralis minor muscle length was measured using a vernier caliper and scapula
index, which indicated the scapular position, measured using a measuring tape. All these measurements were taken on both dominant
and nondominant sides. The GIRD and total motion arc (TMA) deficit were calculated from the ROM measurements. Groups werecompared using a mixed-model analysis of variance.
Results: There was a significant interaction between group and ABER dominance. Other variables were not seen as the interaction effect. There was a significant positive correlation between the scapula index and TMA (r ¼ 0.47, P ¼ .02) and a negative correlation
between the scapula index and GIRD (r ¼ 0.65, P < .01) in the dominant side of the pain group. In addition, in the nondominantside of the pain group, the scapula index and ABER were significantly correlated (r ¼ 0.43, P ¼ .04).
Conclusions: The results of this study indicate that the scapular position is associated with the glenohumeral ROM in high school baseball players. In addition, this study demonstrated that the scapular internally rotated position was correlated with the GIRD and TMA
deficit in high school baseball players who had throwing-related pain. On the other hand, the scapular externally rotated position wascorrelated with increased ABER, mainly in the pain-free baseball players or on the nondominant side. These results indicated that thescapular position might affect the glenohumeral rotational ROM in high school baseball players.

The ethics committee of Kyoto Tachibana University has approved thisstudy (approval no. 15-04).

*Reprint requests: Takashi Higuchi, PhD, PT, Department of Physical
Therapy, Osaka University of Human Sciences, 1-4-1, Shojaku, Settsu,
Osaka 566-8501, Japan.
E-mail address: t.higuchi1124@gmail.com (T. Higuchi).

1058-2746/$ - see front matter Ó 2022 Journal of Shoulder and Elbow Surgery Board of Trustees. All rights reserved.
https://doi.org/10.1016/j.jse.2022.05.023

2612

T. Higuchi et al.

Level of evidence: Level III; Case-Control Design; Epidemology StudyÓ 2022 Journal of Shoulder and Elbow Surgery Board of Trustees. All rights reserved.
Keywords: Scapular position; glenohumeral range of motion; high school; baseball players

The shoulder joint is the most susceptible to throwing
injuries,12,25,42 such as rotator cuff tear, biceps tendinitis,
labrum tear, or internal impingement,7,8,43,48 for baseballplayers. Throwing injuries cause a decrease in throwing
performance (lack of control, reduction of ball velocity,etc.), withdrawal, or retirement from baseball.1,15 Therefore, clarifying the causes of throwing injuries is essential
for effective prevention or treatment of these injuries.
The throwing motion is one of the body’s fastest andmost stressful activities, especially in the upper extremity.
The maximum humeral internal rotation (IR) velocity inthe acceleration phase of the throwing motion reaches
approximately 7000 -8000 per second,14,16 followed byadaptive changes in soft tissue, such as microtrauma andthickening, which occur at the posterior portion of theshoulder. Thomas et al44 reported that collegiate baseballplayers had thicker posterior shoulder capsules on thedominant side of their body compared with the nondominant side, and the thickness was associated with glenohumeral internal rotation deficit (GIRD). Therefore, theseadaptive changes, such as posterior glenohumeral joint
capsule thickness and/or decreased flexibility,6,44 arethought to cause GIRD.8,32,47 Another adaptive change isthe uniformness of the scapular position between thedominant and nondominant sides of the body, and this iscommon in overhead athletes.13,38,44 Oyama et al38 reported that healthy college-aged overhead athletes, consisting of baseball pitchers, volleyball players, and tennis
players, had more scapular internally rotated, anterior tilted, and protraction positions on the dominant sidecompared with the nondominant side. Hodgins et al21 reported that the tightness of the pectoralis minor muscle is a
cause of the scapular position change. Therefore, each
adaptive change has a reason. However, the scapula has afunction as a stable base for the upper extremity;26 therefore, the scapular position change could affect the glenohumeral joint function.
Itami et al23 reported that increased scapular IR position
decreased glenohumeral external rotation range of motion(ROM) because of internal impingement and increased
elbow valgus load to compensate for the decreased ROM
simulating the acceleration phase of throwing motion.
Furthermore, Mihata et al33 reported that increased scapular
IR position increases glenohumeral contact pressure. These
2 studies are cadaveric, but increases in scapular IR position may restrict glenohumeral rotation ROM and cause
throwing-related shoulder and elbow injuries.
Previous research has highlighted the relationship between scapular position and glenohumeral ROM. Laudner

et al30 found the relationship between scapular forward
posture and glenohumeral horizontal abduction ROM in 40
professional baseball players. It concluded that posterior
shoulder tightness (PST) might partially predict excessive
forward scapular posture. The relationship between thescapular anterior tilt angle in static posture and glenohumeral IR ROM has been documented.1 Ribeiro andPascoal40 reported that this anterior scapular tilt is observed
more in overhead players on the dominant side whenengaging in active IR motion of the glenohumeral joint
with the arm abducted. However, subjects of this researchwere healthy, as those who had shoulder pain or throwingrelated pain were excluded.
In addition, to our knowledge, there is no research
regarding the relationship between the degree of scapular
IR and glenohumeral ROM. The increase of scapular IR is
one of the adaptive changes with repetitive ball throwing.
Then the degree of scapular IR change could affect the
glenohumeral ROM as the anterior scapular tilt does. This
study investigated the relationship between the scapular
position and glenohumeral ROM and examined the differences between with and without throwing-related pain. This
study hypothesizes that (1) IR ROM and total motion arc(TMA) are restricted in the pain group, and (2) glenohumeral rotation ROM and TMA are restricted along withincreased scapular IR position.

Materials and methods
Research design
We used a case-control study design to assess the relationshipbetween the scapular position and glenohumeral ROM andexamined the differences between with and without throwingrelated pain. This study was conducted during the winter offseasonof the school in which there is no baseball game because it isbelieved that the game has effects such as ROM restriction andtightness of the muscles on the players. Those effects haveresulted in the accuracy of the test, such as glenohumeral ROM,
pectoralis minor muscle length, and scapula index.

Participants
An a priori power analysis was calculated using G*Power 3.1.9.7
software. Parameters for power estimates are as follows: a ¼ 0.05,
1  b ¼ 0.8; the size effect was determined by group means andstandard deviations from the first 3 participants’ data in bothgroups. An estimate of sample size for the scapula index was 20 inboth groups. Forty male high school baseball players wereRelationship between scapular position and ROM

2613

Figure 1 Measurement of the scapula index. (A) Measurement of the distance between the sternal notch and the coracoid process. (B)Measurement of the distance between the posterolateral corner of the acromion and the thoracic spine.
recruited for this study. The inclusion criteria were male highschool baseball players with more than 3 years of playing experience. Exclusion criteria consisted of a record of shoulder or
elbow surgery. Before testing, a customized self-administeredquestionnaire regarding the player’s age, height, weight, throwing
side (dominant side), duration of baseball playing experience,playing position (pitcher, catcher, infielder, outfielder), andthrowing-related pain on the dominant side of the shoulder or
elbow at the measurement was completed. The visual analog scale(VAS) was used to determine the degree of throwing-related pain.
Participants who had the pain of at least 1 mm of VAS wereallocated to the pain group. Twenty-three players (age: 16.4  0.6
years, height: 170.5  5.3 cm, weight: 67.6  8.0 kg) had athrowing-related pain (pain group), and 17 players (age:16.2  0.6 years, height: 170.6  6.0 cm, weight: 69.2  8.2 kg)
had no pain during ball throwing (pain-free group). The paingroup consisted of 12 shoulders and 11 elbow pain participants.

Measurements
In this study, all measurements were taken before the daily
practice of baseball to minimize the effect of the ball throw. The
measurement consists of glenohumeral ROM, pectoralis minor
muscle length, and scapular position.

Pectoralis minor muscle length
The pectoralis minor muscle length was defined as the difference
between the sternocostal joint of rib 4 (Rib 4) and the CP (Rib 4-CP
distance).4 The validity of this measurement was examined using
fresh cadavers and validly revealed the muscle length. Palpation wasused to denote Rib 4 and CP. To identify Rib 4, the first sternocostal
joint was denoted. Rib 4 was then determined by moving downalong the joints individually. Palpation was also used to identify the
CP. The distance between Rib 4 and CP, which demonstrated thepectoralis minor muscle length, was measured using a verniercaliper (Shinwa Rules) with an accuracy of 0.01 mm.41
The landmarks were palpated and affirmed before the values
were obtained to reduce skin movement. Participants were told to
sit in a chair without a backrest and preserve a natural but
unrounded body position with their upper extremities relaxed.
Participants were instructed to sit on a chair without a backrestand maintain a neutral and not too upright or rounded posture with
their upper extremities relaxed. The participants were also
instructed not to breathe deeply and fix their gaze on a point infront to prevent measurement errors. The foot position was notstandardized during the measurements, but all the participants
took the sitting position with their hips and knees flexed at 90 . No
participants took any abnormal foot positions that affected themeasurements. Readings were performed once by a physiotherapist. The intraclass correlation coefficient and standard error ofmean values were 0.93 and 0.2 cm, respectively.

Glenohumeral range of motion
The glenohumeral ROM was evaluated in a supine position withthe subject’s shoulder abducted at 90 , elbow flexed at 90 , andforearm in a neutral position. A researcher then held the participant’s shoulder, placing the thumb on the coracoid process (CP)and the other 4 fingers on the posterior surface of the scapula. In
contrast, the other hand secured the participant’s wrist and rotatedthe shoulder internally and externally. During the measurements, 1
more researcher fixed a digital inclinometer with an accuracy of
0.1 (Shinwa Rules, Sanjo, Japan) to the participant’s forearm toassess the glenohumeral abduction IR angle (ABIR) and abduction
ER angle (ABER). Two physiotherapists performed this measurement for both the dominant and nondominant sides once. The
sum of the ABIR and ABER was defined as the TMA. The
dominant ABIR was subtracted from the nondominant ABIR todetermine the GIRD. The test-retest reliability was preliminarily
performed. As a result, 17 healthy shoulders were measured threetimes in 1 day; the ABIR’s intraclass correlation coefficient (1.3)
and standard error of mean values were 0.98 and 3.9 , respectively, whereas the ABERs were 0.97 and 4.4 , respectively.

Scapular position
An investigator calculated the length from the participant’s sternal
notch (SN) to the CP (SN-CP distance) while he or she was seatedin a neutral sitting position on a chair without a backrest. The spanfrom the posterolateral corner of the acromion (PLA) to thethoracic spine (TS) at the same level was measured to define the
PLA-TS distance. The SN-CP and PLA-TS distances were
measured using a tape rule (Figure 1). The scapula index, indicating the scapular position due to pectoralis minor tightness, wascalculated using the following equation: scapula index ¼ (SN CP distance/PLA  TS distance)  100. The scapula index
measures the scapular internally/externally rotated position, which
was first proposed by Borstad.3 The scapula index help measure
the scapular position because it is correlated with scapular IR as
measured using a 3-dimensional motion capture system. In thismeasurement, a higher value means the scapula is at a more
externally rotated position and vice versa.

2614
Table I

T. Higuchi et al.
Participant demographics

Age (yr)
Height (cm)Weight (kg)Throwing pain (mm)Body site (number)
Playing experience (yr)Position (number)
Pitcher
Catcher
Infielder
Outfielder

Pain group (n ¼ 23)

Pain-free group (n ¼ 17*)

P value (95% CI)

16.4  0.6
170.5  5.3
67.6  8.0
35.4  28.0
Shoulder: 12
Elbow: 11
7.8  1.8

16.2  0.6
170.6  6.0
69.2  8.2.38 (0.6 to 0.2)
.94 (3.5 to 3.8).55 (3.7 to 6.8)<.01 (L47.6 to L23.3)

6
3
7
7

0

7.8  2.2

.92 (1.3 to 1.2)
50
8
695% CI, 95% confidence interval.
Age, height, weight, throwing pain, and playing experience were expressed as mean  standard deviation.
Bold values indicate statistical significance.
* Two players in the pain-free group play pitcher and infielder.

Data analysis
ABIR, ABER, TMA, Rib4-CP distance, and scapula index were
examined using a 2-factor mixed-model analysis of variance in the 2groups (pain and pain-free groups). Within-subject factor was thedominance of the participants. A statistically significant interaction
effect was examined by comparing a simple main effect of the groupfactor with the dominance factor. Demographic data and GIRD
were compared using the unpaired t-test between 2 groups. The
Pearson correlation coefficient was used to examine the relationshipbetween each group’s scapula index, pectoralis minor muscle
length, and ROM. All statistical analysis was carried out using SPSS
v.20.0 (IBM, Armonk, NY, USA) at a 5% level of error.

Results
Demographic data of participants in both groups are given
in Table I. There were no significant differences in age,height, and playing experience between the 2 groups. The
mean VAS score of throwing-related pain was 35.4  28.0
in the pain group, and 23 participants (57.5%) had
throwing-related pain. There was a significant interaction
between group and dominance for ABER regarding eachvariable. Comparison of the simple main effect by groupdemonstrated a significant difference in ABER (df ¼ 1;
F ¼ 6.28; P ¼ .02). The pain group had a significantly
lower ABER than the pain-free group (Table II). In the
ABIR, TMA, Rib4-CP distance, and scapula index, interaction effects were not seen, and there was a significant
main effect for the dominance.
There was a significant positive correlation between thescapula index and TMA (r ¼ 0.47, P ¼ .02) and a negative
correlation between the scapula index and GIRD
(r ¼ 0.65, P < .01) in the dominant side of the pain group(Table III). In the nondominant side of the pain group, thescapula index and ABER were significantly correlated

Table II Comparison of each variable between pain groupand pain-free group
df F
P
Pain
ratio value group(n ¼ 23)
ABIR*
Dominant
Nondominant
ABER*,yDominant
1 6.28 .02z
Nondominant 1 0.26 .62
TMA
Dominant
Nondominant
GIRD
38
.71
Rib4-CP*
Dominant
NondominantScapula index*
Dominant
Nondominant

Pain-freegroup(n ¼ 17)26.9  9.1
34.8  6.7

27.1  8.7
36.1  10.6

115.6  9.4
108.1  9.8

122.8  8.3
109.6  7.5

142.6  14.1 150.0  10.4
142.9  10.9 145.7  11.6
7.9  9.6
9.0  9.1
17.6  1.2
18.2  1.4

17.7  1.4
18.1  1.4

60.6  3.0
62.6  4.9

59.1  3.2
61.2  3.4

ABIR, abduction internal rotation angle; ABER, abduction externalrotation angle; TMA, total motion arc; GIRD, glenohumeral internalrotation deficit; Rib4-CP, distance from the sternocostal joint of rib 4
to the coracoid process; df, degree of freedom.
Data are expressed as mean  standard deviation.
The degree of freedom, F ratio, and P value were not calculated
because there was no statistically significant interaction effect in
ABIR, TMA, Rib4-CP, and scapula index.
GIRD was compared using the unpaired t-test.
Bold values indicate statistical significance.
* Indicates a statistically significant main effect for dominance.
y
Indicates a statistically significant main effect for the group.
z
Indicates a statistically significant difference between groups.
Results are from the mixed-model analysis of variance due to a statistically significant interaction effect between group and dominance.

(r ¼ 0.43, P ¼ .04) (Table IV). There was no significant
correlation between the scapula index and ROM on theRelationship between scapular position and ROM
Table III

2615

Correlation matrix between each variable on the dominant side of the pain group

ABER
GIRD
TMA
Rib4-CP
Scapular index

ABIR

ABER

GIRD

TMA

Rib4-CP

0.167 (.447)
L0.746* (<.01)
0.754* (<.01)
0.529 (<.01)
0.326 (.130)

0.26 (.230)
0.773* (<.01)
0.253 (.245)
0.396 (.062)

0.653* (<.01)0.649* (<.01)0.649* (<.01)

0.509y (.013)
0.473y (.023)

0.334 (.119)

ABER, abduction external rotation angle; GIRD, glenohumeral internal rotation deficit; TMA, total motion arc; Rib4-CP, distance from the sternocostal
joint of rib 4 to the coracoid process; ABIR, abduction internal rotation angle.
Data are presented as r value (P value).
Bold values indicate statistical significance.
* P < .01.
y
P < .05.

Table IV

Correlation matrix between each variable on the nondominant side of the pain group

ABER
GIRD
TMA
Rib4-CP
Scapular index

ABIR

ABER

GIRD

TMA

Rib4-CP0.169 (.442)
0.422* (.045)
0.460* (.027)
0.359 (.093)
0.364 (.088)

0.373 (.080)
0.798y (<.01)
0.189 (.388)
0.428* (.041)

0.078 (.724)
L0.652y (<.01)0.627y (<.01)0.050 (.822)
0.163 (.457)

0.560y (<.01)

ABER, abduction external rotation angle; GIRD, glenohumeral internal rotation deficit; TMA, total motion arc; Rib4-CP, distance from the sternocostal
joint of rib 4 to the coracoid process; ABIR, abduction internal rotation angle.
Data are presented as r value (P value).
Bold values indicate statistical significance.
* P < .05.
yP < .01.

dominant side in the pain-free group (Table V). However, atrend of nonsignificant correlation between the scapula
index and ABER was seen on the nondominant side(r ¼ 0.48, P ¼ .05) (Table VI).

Discussion
The main findings of this study are as follows: (1) the
scapular internally rotated position is associated with GIRD
and TMA deficit in the pain group, (2) this association is
not seen in the pain-free group, and (3) ABER is significantly decreased in the pain group compared with that in
the pain-free group.
The scapula index had been proposed to indicate thescapular internally/externally rotated position, wherein agreater degree of the scapula index indicates that thescapula is at a more externally rotated position. Therefore,
the results of this study suggest that the scapular internallyrotated position is associated with GIRD and TMA deficit
in baseball players who have throwing-related shoulder or
elbow pain. The increased scapular internal rotated positionor anteriorly tilted position is associated with the glenohumeral ABIR deficit.27,49 Ribeiro and Pascoal40 reported a
relationship between the scapular anterior tilted positionand decreased glenohumeral ROM when the subjects were

instructed to move their arm actively. Borich et al2 reported
that the throwing athletes who have the GIRD had asignificantly greater scapular anterior tilt during active arm
movement than athletes who have no IR ROM deficit.
Many researchers had thought that PST or GIRD is a causeof scapular malposition. However, Kibler26 described thatthe scapula is a stable base for the upper extremity, and it ispossible to assume that the scapular positional change
could affect glenohumeral ROM. Itami et al23 reported that
increased scapular internally rotated position significantly
decreased glenohumeral rotational ROM because of internal impingement occurrence. Past research reported that the
glenohumeral ROM deficit, such as GIRD or TMA deficit,
is thought to cause throwing injuries. Therefore, the resultof this study suggests that the scapular internally rotatedposition could be a cause of GIRD or TMA deficit, leading
to throwing injuries.
Scapula index and ABER were significantly correlatedwith the nondominant side of the pain group. In addition,
the exact relationship trend was observed on the dominantside of the pain group and the nondominant side of thepain-free group, although not significant (P ¼ .06 and .05,
respectively). In this study, a rolled towel was not placed
under the participants’ arms during the measurement of
ROM to obtain an adequate glenohumeral horizontal
abduction position.28 Therefore, glenohumeral horizontal

2616
Table V

T. Higuchi et al.
Correlation matrix between each variable on the dominant side of the pain-free group

ABER
GIRD
TMA
Rib4-CP
Scapular index

ABIR

ABER

GIRD

TMA

Rib4-CP0.25 (.33)
0.29 (.27)
0.63* (<.01)0.23 (.39)
0.24 (.35)

0.16 (.55)
0.59y (.01)
0.49y (.04)
0.17 (.51)

0.11 (.67)
0.15 (.56)
0.14 (.59)

0.21 (.43)
0.05 (.85)

0.734* (<.01)

ABER, abduction external rotation angle; GIRD, glenohumeral internal rotation deficit; TMA, total motion arc; Rib4-CP, distance from the sternocostal
joint of rib 4 to the coracoid process; ABIR, abduction internal rotation angle.
Data are presented as r value (P value).
Bold values indicate statistical significance.
* P < .01.
y
P < .05.

Table VI

Correlation matrix between each variable on the nondominant side of the pain-free group

ABER
GIRD
TMA
Rib4-CP
Scapular index

ABIR

ABER

GIRD

TMA

Rib4-CP0.21 (.42)
0.62* (<.01)
0.78* (<.01)
0.10 (.71)
0.27 (.29)

0.28 (.28)
0.45 (.06)
0.32 (.22)
0.48 (.054)

0.39 (.13)
0.14 (.59)
0.02 (.95)

0.29 (.26)
0.06 (.82)

0.37 (.15)

ABER, abduction external rotation angle; GIRD, glenohumeral internal rotation deficit; TMA, total motion arc; Rib4-CP, distance from the sternocostal
joint of rib 4 to the coracoid process; ABIR, abduction internal rotation angle.
Data are presented as r value (P value).
Bold values indicate statistical significance.
* P < .01.

abduction is increased relatively when the participant has amore scapular internally rotated position during ABER
measurement. Cieminski et al11 reported that glenohumeral
ROM was restricted when horizontal abduction of the
glenohumeral joint increased. They concluded that it iscaused by increased soft tissue tension surrounding the
glenohumeral joint. Soft tissues surrounding the glenohumeral joint, such as ligaments or joint capsules, restrict
the glenohumeral movement.5,29,34 Higuchi et al19 reported
that stretching the pectoralis minor muscle increases the
ABIR, scapular externally rotated, and posteriorly tilted
positions. In addition, the degree of the scapular externallyrotated position change and the extent of the ABIR increase
were significantly correlated. Therefore, increasing thescapular externally rotated position would be a useful option to improve the GIRD and/or TMA deficit for theprevention or treatment of throwing injuries.
There was no significant correlation between the scapular internally rotated position and glenohumeral ROM in
the pain-free group, although there is a significant correlation in the pain group. One possible explanation for thisdifference is that baseball players with glenohumeral ROM,
which is susceptible to the scapular position, may be prone
to throwing injuries. Tyler et al46 reported that the preseason supraspinatus weakness is associated with increased
shoulder or elbow injury risk in high school baseballplayers. Furthermore, Byram et al9 reported that the preseason glenohumeral external rotation muscle strength andsupraspinatus weakness are associated with throwingrelated injury requiring surgical intervention. These reports suggest that the weakness of the shoulder muscles is a
cause of throwing injuries. Huston and Wojtys22 reported
that collegiate athletes had significantly lower joint laxity
than noncollegiate athletes. Lower ABER in the pain groupobtained in this study may partially indicate the tightness ofthe shoulder muscles. It may be possible that the participants in the pain group had less muscle strength surrounding the shoulder, leading to much severe muscle
tightness induced by repetitive throwing motion. The
tightness increases depending on the scapular position to
the glenohumeral ROM. However, this study did not evaluate muscle strength and joint laxity, and the theory
mentioned above is just speculation. Moreover, the reason
why the relationship between the scapular internally rotatedposition and ABER was seen only for the pain group remains unclear. Further research is needed to determine
which factor increases the dependence on the scapular
position for the glenohumeral ROM.
In this study, ABER was significantly reduced in thepain group compared with the pain-free group. It has beenreported that decreased ABER is associated with shoulder
and elbow injuries in baseball players.10,18,35 SufficientRelationship between scapular position and ROM
ABER for throwing motion is necessary to create IR velocity20,31 because the maximum IR velocity in the acceleration phase of throwing reaches more than 7000 -8000
per second.14,16 Furthermore, sufficient ABER decreased
elbow valgus stress during throwing motion.39 Excess IR
force for the glenohumeral joint, which is thought to cause
throwing-related pain, would be created to compensate forthe decreased ABER during throwing. Therefore, interventions aiming to increase the ABER would be beneficial to prevent or treat throwing injuries.
Garrison et al17 compared high school and collegiate
baseball players with and without ulnar collateral ligament
tear and reported that players without ulnar collateral ligament tear have 119.7  11.8 in ER ROM and20.9  6.1 in IR ROM in their dominant shoulder. These
results are similar to this study, and it is suggested that theresults in this study would be a normative value in highschool baseball players. Regarding the scapular position,
Borstad3 reported that the scapula index with the shorterand longer pectoralis minor muscle is 61.3  0.9 and65.5  1.2, respectively. In this study, the scapula index in
the dominant shoulder was 60.6  3.0 in the pain group and59.1  3.2 in the pain-free group. The results of the scapula
index in this study are also similar to the values of Borstad’s3 study. Although a normative value of the scapula
index is not established yet, the scapula index obtained inthis study would not be considered an outlier.
Several limitations exist in this study. First, the participants of this study were recruited from a local high school
baseball team. Therefore, the results of this study do not
apply to other sports or age groups. Participants of thisstudy had approximately 7-8 years of baseball experience.
This means they started their baseball career when they
were around 8 years old. In addition, they have beenpracticing baseball for 6 days per week. This duration andfrequency of exposure to baseball are typical for Japanese
baseball players; therefore, the results of this study would
not differ from general Japanese high school baseballplayers. Second, the scapular position was defined only by
the scapula index. Anterior/posterior tilting and upward/
downward rotation of the scapular position were notmeasured in this study. However, whether these movements
negatively affect the glenohumeral joint is controversial.
Muraki et al36 reported that the increased scapular anterior
tilt did not increase the subacromial contact pressure duringhumeral elevation. Karduna et al24 reported that theincreased scapular upward rotation decreased the subacromial space. Increased subacromial contact pressure or
reduced subacromial space is thought to cause shoulder
injuries. Therefore, the results of these studies suggested
that the impact of the scapular anterior/posterior tilt and
upward/downward rotation for shoulder injuries may be
more restrictive than is commonly believed. Third, PST andretrotorsion of the humeral head, which are thought toaffect the glenohumeral ROM,37,45 were not measured.
Therefore, how much the scapular IR position affects ROM

2617
in the dominant side of the baseball players is unclear.
Finally, participants were divided by their complaints ofthrowing-related pain. Further prospective studies withlarge sample sizes and detecting the cause of throwingrelated pain are warranted to address the effect of scapular function on throwing injuries.

Conclusion
This study examined the relationship between thescapular position and glenohumeral ROM and comparedthis relationship with and without throwing-related pain.
Scapular IR position correlated with GIRD and TMA
deficit in the players who had throwing-related pain. In
addition, the same trend of this correlation was seen inplayers without throwing-related pain, although it was
not statistically significant. These results suggest that the
glenohumeral ROM would be much more susceptible torestriction with increased scapular IR position, especially in throwing-related pain players. The restriction of
the glenohumeral ROM is thought to be a cause ofthrowing injuries. It is believed that increasing thescapular external rotation position would be necessary to
prevent and treat throwing injuries.

Disclaimers:
Funding: No funding was disclosed by the authors.
Conflicts of interest: The author, their immediate family,
and any research foundation with which they are affiliated have not received any financial payments or otherbenefits from any commercial entity related to the subject of this article.

Acknowledgment
The authors would like to thank Enago for the English
language review.

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