The influence of shoulder abduction and external rotation on throwing arm kinetics in professional baseball pitchers

Background The relationships between shoulder abduction and external rotation with peak kinetic values at the shoulder and elbow in professional baseball pitchers are not well established. Methods Professional pitchers ( n = 322) threw 8–12 fastballs under 3D motion analysis (480 Hz). Pitchers were stratified into quartiles by shoulder abduction and external rotation at distinct timepoints. Regression analyses were performed to quantify associations between shoulder position and kinetics. Results Shoulder abduction remained relatively consistent throughout the pitch (foot contact–ball release: 85.5 ± 11.1–90.7 ± 8.4°); shoulder external rotation increased dramatically (foot contact–ball release: 30.8 ± 24.6–165.2 ± 9.7°). For every 10° increase in maximum shoulder rotation, shoulder superior force increased by 2.3% body weight ( p < 0.01), shoulder distraction force increased by 5.9% body weight ( p < 0.01), and ball velocity increased by 0.60 m/s ( p < 0.01). Shoulder abduction was significantly associated with shoulder superior force at all timepoints but not with ball velocity ( p > 0.05). For every 10° increase in shoulder abduction at ball release, shoulder superior force increased by 3.7% body weight ( p < 0.01) and shoulder distraction force increased by 11.7% body weight ( p < 0.01). Conclusion Increased shoulder abduction at ball release and increased maximum shoulder external rotation were associated with greater superior and distraction forces in the shoulder. Pitchers can consider decreasing shoulder abduction at later stages of the pitch to around 80° in order to minimize shoulder superior force, with no impact on ball velocity.

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Correlation of Shoulder and Elbow Kinetics With Ball Velocity in Collegiate Baseball Pitchers

Journal of Athletic Training ◽

10.4085/1062-6040-50.1.06 ◽

2015 ◽

Vol 50 (6) ◽

pp. 629-633 ◽

Cited By ~ 17

Author(s):

Eric G. Post ◽

Kevin G. Laudner ◽

Todd A. McLoda ◽

Regan Wong ◽

Keith Meister

Keyword(s):

External Rotation ◽

Pearson Correlation ◽

Anatomical Landmarks ◽

Positive Correlation ◽

Weak Positive Correlation ◽

Ball Velocity ◽

Collegiate Baseball ◽

Shoulder External Rotation ◽

Baseball Pitchers ◽

Distraction Force

Context Throwing a baseball is a dynamic and violent act that places large magnitudes of stress on the shoulder and elbow. Specific injuries at the elbow and glenohumeral joints have been linked to several kinetic variables throughout the throwing motion. However, very little research has directly examined the relationship between these kinetic variables and ball velocity. Objective To examine the correlation of peak ball velocity with elbow-valgus torque, shoulder external-rotation torque, and shoulder-distraction force in a group of collegiate baseball pitchers. Design Cross-sectional study. Setting Motion-analysis laboratory. Patients or Other Participants Sixty-seven asymptomatic National Collegiate Athletic Association Division I baseball pitchers (age = 19.5 ± 1.2 years, height = 186.2 ± 5.7 cm, mass = 86.7 ± 7.0 kg; 48 right handed, 19 left handed). Main Outcome Measure(s) We measured peak ball velocity using a radar gun and shoulder and elbow kinetics of the throwing arm using 8 electronically synchronized, high-speed digital cameras. We placed 26 reflective markers on anatomical landmarks of each participant to track 3-dimensional coordinate data. The average data from the 3 highest-velocity fastballs thrown for strikes were used for data analysis. We calculated a Pearson correlation coefficient to determine the associations between ball velocity and peak elbow-valgus torque, shoulder-distraction force, and shoulder external-rotation torque (P < .05). Results A weak positive correlation was found between ball velocity and shoulder-distraction force (r = 0.257; 95% confidence interval [CI] = 0.02, 0.47; r2 = 0.066; P = .018). However, no significant correlations were noted between ball velocity and elbow-valgus torque (r = 0.199; 95% CI = −0.043, 0.419; r2 = 0.040; P = .053) or shoulder external-rotation torque (r = 0.097; 95% CI = −0.147, 0.329; r2 = 0.009; P = .217). Conclusions Although a weak positive correlation was present between ball velocity and shoulder-distraction force, no significant association was seen between ball velocity and elbow-valgus torque or shoulder external-rotation torque. Therefore, other factors, such as improper pitching mechanics, may contribute more to increases in joint kinetics than peak ball velocity.

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Biomechanics of the Shoulder in Youth Baseball Pitchers

The American Journal of Sports Medicine ◽

10.1177/0363546505275347 ◽

2005 ◽

Vol 33 (11) ◽

pp. 1716-1722 ◽

Cited By ~ 147

Author(s):

Michelle B. Sabick ◽

Young-Kyu Kim ◽

Michael R. Torry ◽

Michael A. Keirns ◽

Richard J. Hawkins

Keyword(s):

Body Weight ◽

External Rotation ◽

Pitching Motion ◽

Little League ◽

Youth Baseball ◽

Shoulder External Rotation ◽

Baseball Pitchers ◽

Force Components ◽

Simulated Game ◽

Distraction Force

Background The effects of repetitive throwing on the shoulders of developing athletes are not well understood because of the paucity of data describing the biomechanics of youth pitchers and the plasticity of the developing skeleton. Hypothesis The direction and magnitude of the stresses that exist at the proximal humeral physis during the fastball pitching motion are consistent with the development of proximal humeral epiphysiolysis (Little League shoulder) and/or humeral retrotorsion. Study Design Descriptive laboratory study. Methods A total of 14 elite youth baseball pitchers (mean age, 12.1 ± 0.4 years) were filmed from the front and dominant side while throwing fastballs in a simulated game. The net force and torque acting on the humerus throughout the throwing motion were calculated using standard biomechanical techniques. Results The external rotation torque about the long axis of the humerus reached a peak value of 17.7 ± 3.5 N.m (2.7% ± 0.3% body weight × height) just before maximum shoulder external rotation. A shoulder distraction force of 214.7 ± 47.2 N (49.8% ± 8.3% body weight) occurred at, or just after, ball release. Conclusion Shear stress arising from the high torque late in the arm-cocking phase is large enough to lead to deformation of the weak proximal humeral epiphyseal cartilage, causing either humeral retrotorsion or proximal humeral epiphysiolysis over time. The stresses generated by the external rotation torque are much greater than those caused by distraction forces generated during the pitching motion of youth baseball pitchers. Clinical Relevance The motion of throwing fastballs by youth baseball pitchers results in force components consistent with proposed mechanisms for 2 clinical entities.

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Increased Shoulder Distraction Force and Shoulder Horizontal Abduction in Professional Baseball Pitchers With Discordant Torso Rotation Order

The American Journal of Sports Medicine ◽

10.1177/03635465211041381 ◽

2021 ◽

pp. 036354652110413

Author(s):

Joseph E. Manzi ◽

Brittany Dowling ◽

Joshua S. Dines ◽

Alexander Richardson ◽

Kathryn L. McElheny ◽

...

Keyword(s):

Upper Extremity ◽

Internal Rotation ◽

External Rotation ◽

Rotation Velocity ◽

Mean Difference ◽

Professional Baseball ◽

Pelvic Rotation ◽

Shoulder External Rotation ◽

Baseball Pitchers ◽

Distraction Force

Background: Inefficient energy transfer from the pelvis and trunk has been shown to increase compensation at the level of the shoulder. Kinetic chain sequencing of the core segments is underexamined in professional baseball pitchers, especially as it relates to changes in upper extremity kinetics. Purpose: To evaluate elbow and shoulder kinetics in a cohort of professional pitchers differentiated by instances of discordant pelvic to upper torso sequencing during the pitch. Study Design: Descriptive laboratory study. Methods: 285 professional baseball pitchers were evaluated using 3D motion capture (480 Hz). Pitchers were divided into “chronological” and “discordant” groups based on whether maximum pelvic rotation velocity occurred before (chronological) or after (discordant) maximum upper torso rotation velocity during the pitch motion. Pelvic, upper torso, and shoulder kinematic parameters, shoulder distraction force, shoulder internal rotation torque, and pitch efficiency (PE) were compared between groups. Results: Pitchers with discordant torso sequencing (n = 30; 110 pitches) had greater shoulder horizontal adduction at maximum external rotation (mean difference, 3.6°; 95% CI, −5.2° to −2.0°; t = −4.5; P < .001) and greater maximum shoulder external rotation (mean difference, 3.7°; 95% CI, 5.7° to 1.5°; t = −3.5; P < .001) than chronological pitchers (n = 255; 2974 pitches). PE did not differ between groups ( P = .856), whereas ball velocity was significantly faster in the discordant group (mean difference, 0.6 m/s; 95% CI, −1.1 to −0.3 m/s; t = −3.3; P = .0012). Chronological pitchers had significantly reduced shoulder distraction force (mean difference, −4.7% body weight (BW); 95% CI, −7.9% to −1.5% BW; t = −2.9; P = .004) with no difference in shoulder internal rotation torque ( P = .160). These kinematic and kinetic differences were not observed when accounting for interpitcher variability. Conclusion: Between pitchers, those who had a discordant pelvic to upper torso sequence experienced significantly greater shoulder distraction forces, potentially compensating by increasing maximum shoulder external rotation and horizontal abduction. Achieving maximal pelvic rotation velocity before maximal rotation velocity may be advantageous in preventing compensation at the upper extremity and excessive throwing arm loading. Clinical Relevance: Identifying risk factors for increased upper extremity forces has potential implications in injury prevention. Specifically, mitigating shoulder distraction forces may be beneficial in reducing risk of injury.

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Differences Among Overhand, 3-Quarter, and Sidearm Pitching Biomechanics in Professional Baseball Players

Journal of Applied Biomechanics ◽

10.1123/jab.2017-0211 ◽

2018 ◽

Vol 34 (5) ◽

pp. 377-385 ◽

Cited By ~ 9

Author(s):

Rafael F. Escamilla ◽

Jonathan S. Slowik ◽

Alek Z. Diffendaffer ◽

Glenn S. Fleisig

Keyword(s):

Sagittal Plane ◽

External Rotation ◽

Elbow Flexion ◽

Professional Baseball ◽

Shoulder Abduction ◽

Ball Release ◽

Peak Knee ◽

Knee Height ◽

Shoulder External Rotation ◽

Analysis System

The purpose of this study was to assess biomechanical differences among overhand, 3-quarter, and sidearm arm slot professional baseball pitchers. It was hypothesized that kinematic and kinetic differences would be found among the 3 groups, with sidearm pitchers demonstrating greater movement along the transverse plane and overhead pitchers demonstrating greater movement along the sagittal plane. Based upon arm slot angle at ball release, 30 overhand, 156 three-quarter, and 21 sidearm pitchers were tested using a 240-Hz motion analysis system, and 37 kinematic and kinetic parameters were calculated. One-way analyses of variance (α = .01) was employed to assess differences among groups. The comparisons showed the sidearm group had less shoulder anterior force, whereas the overhand group had the least elbow flexion torque. At ball release, trunk contralateral tilt and shoulder abduction were greatest for the overhand group and least for sidearm group. Additionally, the sidearm group demonstrated the lowest peak knee height, most closed foot angle, greatest pelvis angular velocity, and shoulder external rotation. The overhand group had the greatest elbow flexion at foot contact and greatest trunk forward tilt at ball release. The greater elbow flexion torque and shoulder external rotation exhibited by sidearm pitchers may increase their risk of labral injury. Conversely, the lower shoulder anterior force in sidearm pitchers may indicate lower stress on shoulder joint capsule and rotator cuff.

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Baseball Pitchers’ Kinematic Sequences and Their Relationship to Elbow and Shoulder Torque Production

Orthopaedic Journal of Sports Medicine ◽

10.1177/2325967119s00429 ◽

2019 ◽

Vol 7 (7_suppl5) ◽

pp. 2325967119S0042

Author(s):

Donna Moxley Scarborough ◽

Shannon E. Linderman ◽

Javier E. Sanchez ◽

Eric M. Berkson

Keyword(s):

Upper Extremity ◽

External Rotation ◽

Kinetic Chain ◽

Joint Torques ◽

Ball Velocity ◽

Collegiate Baseball ◽

Angular Velocities ◽

Shoulder External Rotation ◽

Baseball Pitchers ◽

The Ideal

Objectives: Ball velocity is generated during the overhead baseball pitch via efficient force transmission up the kinetic chain, from the lower body up and outward to the throwing hand. The kinematic sequence, or the sequential timing pattern of peak angular velocities of body segments during a pitch, provides insight to segment position and motion control that drives the kinetic chain (Putnam CA, 1993). Previous publications report an ideal kinematic sequence (KS) where the timing of each body segment’s peak angular velocity occurs in a proximal-to-distal (PDS) pattern resulting in greater ball velocity and reduction in throwing arm injury risk (Fortenbaugh D, et.al, 2009). A recent study revealed that baseball pitchers perform a variety of KSs (Scarborough DM et.al, 2018). There is no known investigation of the relationship of kinematic sequences and throwing arm joint torques. The purpose of this study was to 1) identify the number of different KSs performed by each pitcher and 2) compare elbow valgus and shoulder external rotation (ER) and extension (Ext) torques between the 3 primary KSs performed during the fastball pitch. Methods: Fourteen collegiate baseball pitchers (20.57 ± 1.91 yr) underwent 3D biomechanical pitch analysis using 20 motion-capture Vicon MX™ cameras (360 Hz). A total of 119 fastball pitches with an average of 8.5 ± 2.71 pitches per player were analyzed. Elbow valgus and shoulder external rotation and extension torques were calculated. The timing of peak angular velocities for the pelvis, trunk, arm, forearm and hand body segments were recorded to generate each pitch’s KS. KSs were then divided into groups based on similarities to the ideal PDS pattern. ANCOVA statistical analyses were performed to compare joint torques across these KS groups with ball velocity as a covariate. Results: A total of 13 different KSs were observed across the 14 pitchers resulting in an average of 3 ± 1.41 different KSs per pitcher. Three different primary KS groups were identified: (1) PDS group: with a KS closest to the ideal PDS pattern (2) the Altered Distal Upper Extremity segment: with the forearm peaking after the hand (the most common group) and (3) Altered Proximal Upper Extremity segment order with the arm segment peaking after the hand (2nd most common). Across these three primary KS patterns, statistically significant differences were noted for elbow valgus torque [F(62,2) = 8.785, ɳ2 = .221, p < 0.00], shoulder external rotation (ER) torque [F(62,2) = 14.127, ɳ2 = .313, p < 0.00] and shoulder extension (Ext) torque [F(62,2) = 13.237, ɳ2 = .299, p < 0.00] (Figure 1). Conclusion: Our findings demonstrate that collegiate baseball pitchers performed an average of 3 different kinematic sequence patterns during fastball pitching. This is the first study to demonstrate a relationship between KSs and elbow and shoulder torque production. As anticipated, the PDS KSs produced the least torque across the elbow and shoulder joints. Alterations in Distal Upper Extremity KS was most common and generated the greatest shoulder Ext torques. Alterations in the Proximal Upper Extremity KS demonstrated the greatest elbow valgus and shoulder ER. Further study of the influence of kinematic sequence on joint torques in the baseball pitch may provide insight into pitching injuries and injury avoidance programs.

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The relationship between range of motion and muscle strength of the shoulder joint in professional baseball pitchers

10.31083/jomh.2021.030 ◽

2021 ◽

Keyword(s):

Body Weight ◽

Range Of Motion ◽

Shoulder Joint ◽

External Rotation ◽

Linear Regression Analysis ◽

Isometric Strength ◽

Professional Baseball ◽

Baseball Pitchers ◽

Baseball Team ◽

The Relationship

Background and objective: This study aimed to assess the relationship between range of motion (ROM) and isometric strength of the shoulder joint, adjusted for humeral head retroversion angle (HHRA), in professional baseball pitchers. Material and Methods: A total of 18 pitchers from a professional baseball team were included in this study. The isometric strength of internal rotation (IR) and external rotation (ER) were measured using an isokinetic device at 85◦ and 30◦ ER, and at 25◦ IR. A linear regression analysis was then performed. Results: The HHRA of the dominant arm was approximately 7◦ greater than that of the non-dominant arm (P < 0.001). As the IR ROM increased by 1◦, the IR isometric strength at 25◦ IR was signiﬁcantly increased by 0.448% body weight (P < 0.05). However, as the ROM of IR increased, the IR isometric strength at 85◦ and 30◦ ER was not signiﬁcant (P > 0.05), and as the ROM of ER increased, the IR and ER isometric strength were not signiﬁcant (P > 0.05). Conclusions: Thus, the increase of IR ROM in professional baseball pitchers was associated with an increase in isometric strength at 25◦ IR, after adjustments were made for HHRA.

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Biomechanical Differences Between Japanese and American Professional Baseball Pitchers

Orthopaedic Journal of Sports Medicine ◽

10.1177/2325967119825625 ◽

2019 ◽

Vol 7 (2) ◽

pp. 232596711982562 ◽

Cited By ~ 2

Author(s):

Takanori Oi ◽

Shinichi Yoshiya ◽

Jon Slowik ◽

Alek Diffendaffer ◽

Yohei Takagi ◽

...

Keyword(s):

Knee Flexion ◽

The United States ◽

Abduction Angle ◽

Professional Baseball ◽

Shoulder Abduction ◽

Elbow Injury ◽

Risk Of Injury ◽

Ball Release ◽

Increased Risk ◽

Baseball Pitchers

Background: Although baseball injuries are common in both Japan and the United States, the majority of pitching injuries in Japanese players occur at the shoulder, whereas most pitching injuries in American players occur at the elbow. A biomechanical comparison between Japanese and American pitchers may help to identify the different injury mechanisms. Hypothesis: Japanese pitchers produce greater shoulder kinetics whereas American pitchers generate greater elbow kinetics. Also, kinematic differences will be found between the 2 groups, including longer stride and greater lead knee flexion for Japanese pitchers. Study Design: Descriptive laboratory study. Methods: Biomechanical data for 19 Japanese professional baseball pitchers and an age-matched group of 19 American professional baseball pitchers were collected by use of a 3-dimensional, automated, high-speed optical motion capture system. Anthropometric, kinetic, and kinematic data for both groups were compared by use of t tests ( P < .05). Results: American pitchers were taller and heavier and generated greater ball velocity (38.1 ± 1.6 vs 34.7 ± 1.1 m/s; P < .001) than their Japanese counterparts. Most elbow and shoulder kinetic parameters, including elbow varus torque (99 ± 17 vs 86 ± 17 N·m; P = .018), were greater for American pitchers. However, when normalized by bodyweight and height, shoulder horizontal adduction torque was greater for Japanese pitchers (6.8% ± 1.0% vs 5.8% ± 1.1%; P = .005). Japanese pitchers had longer stride (86% ± 5% vs 82% ± 6% of height; P = .023), greater shoulder abduction at ball release (101° ± 8° vs 94° ± 9°; P = .014), and greater knee flexion after ball release (39° ± 18° vs 28° ± 14°; P = .039). Japanese pitchers also demonstrated greater shoulder internal rotation velocity, elbow flexion, and elbow extension velocity. Conclusion: Greater elbow varus torque may predispose American pitchers to greater risk of elbow injury. Japanese pitchers may have increased risk of shoulder injury due to greater normalized horizontal adduction torque and greater abduction angle. Japanese pitchers may be able to reduce their shoulder torque and risk of injury by shortening their stride, reducing their lead knee flexion, and decreasing their throwing arm abduction. Clinical Relevance: Understanding anthropometric, kinetic, and kinematic differences between pitchers from the 2 countries may be of value to clinicians and coaches working to maximize performance of the pitchers while minimizing the risk of injury.

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Electromyographic Analysis and Phase Definition of the Overhead Football Throw

The American Journal of Sports Medicine ◽

10.1177/03635465020300061401 ◽

2002 ◽

Vol 30 (6) ◽

pp. 837-844 ◽

Cited By ~ 52

Author(s):

Bryan T. Kelly ◽

Sherry I. Backus ◽

Russell F. Warren ◽

Riley J. Williams

Keyword(s):

Internal Rotation ◽

Motion Analysis ◽

Muscle Activation ◽

External Rotation ◽

Shoulder Abduction ◽

Activation Patterns ◽

Muscle Activation Patterns ◽

Ball Release ◽

Shoulder External Rotation ◽

Electromyographic Analysis

Background The phases of the football throw need definition so that muscle activation patterns during the overhead football throw can be fully described. Hypothesis Electromyographic analysis of shoulder musculature can better define muscle activation patterns during the football throw. Study Design Descriptive anatomic study. Methods Videos of 20 elite-level quarterbacks were reviewed to define phases of the overhead football throw; 14 recreational male athletes underwent electromyography and motion analysis testing. Results Four sequential phases of the football throw were consistently observed. Early cocking (49% ± 11% of throw) was initiated at rear foot plant and continued to maximal shoulder abduction and internal rotation. Late cocking (20% ± 6%) started at maximal shoulder abduction and internal rotation and ended with maximal shoulder external rotation. The acceleration phase (15% ± 4%) began with maximal shoulder external rotation and ended with ball release. Follow-through (16% ± 5%) was defined as the phase from ball release to maximal horizontal adduction (across the body). Conclusion The four phases demonstrated little variation in motion analysis and electromyographic activation between subjects and were associated with muscle activation patterns consistent with upper extremity movements. Clinical Relevance A clearer understanding of muscle activation patterns may help to explain patterns of muscle injury and improve rehabilitation protocols in football-throwing athletes.

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The Relationship between Scapular Upward Rotation and Shoulder Internal and External Rotation Isokinetic Strength in Professional Baseball Pitchers

Healthcare ◽

10.3390/healthcare9060759 ◽

2021 ◽

Vol 9 (6) ◽

pp. 759

Author(s):

Byung Gon Kim ◽

Seung Kil Lim ◽

Sunga Kong

Keyword(s):

External Rotation ◽

Professional Baseball ◽

Isokinetic Strength ◽

Strength Ratio ◽

Shoulder Injury ◽

Isokinetic Dynamometer ◽

Normal Range ◽

History Of ◽

Baseball Pitchers ◽

The Relationship

This study aims to assess the relationship between scapular upward rotation (SUR) across varying humeral-elevation angles (HEAs) and shoulder isokinetic strength and ratio in professional baseball pitchers. The subjects were professional baseball pitchers (n = 16) without a history of shoulder injury in the last six months. The subject’s SUR angles were measured with the humerus elevated at HEAs of 0° (at rest), 60°, 90°, and 120° to the scapular plane. Shoulder isokinetic strength was evaluated for shoulder internal rotation (IR) and external rotation (ER) strength (PT%BW and TW%BW), and the ER/IR strength ratios were determined at 60, 120 and 180°/s using an isokinetic dynamometer. The SUR angle at an HEA of 0° was positively correlated with IR strength at 120°/s (r = 0.535) and 180°/s (r = 0.522). The SUR angle at an HEA of 60° was negatively correlated with the ER/IR strength ratios at 60°/s (r = −0.505) and 120°/s (r = −0.500). The SUR angle at an HEA of 90° was negatively correlated with the ER/IR strength ratios at 60°/s (r = −0.574; r = −0.554) and 120°/s (r = −0.521; r = −0.589) as well as with ER strength at 180°/s (r = −0.591, r = −0.556). The SUR angle at an HEA of 120° was negatively correlated with ER strength at 60°/s (r = −0.558), 120°/s (r = −0.504; r = −0.524), and 180°/s (r = −0.543) and the ER/IR strength ratio at 60°/s (r = −0.517). In this study, we found that the ratio of isokinetic strength between ER and IR became closer to the normal range on increasing the SUR angle. In particular, an HEA of 90°, which resembles the pitching motion, showed a clear relationship between SUR, shoulder ER, and the ratio of ER/IR isokinetic strength in professional baseball pitchers.

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Isokinetic Strength Profile of Shoulder Internal and External Rotators of Adolescent Volleyball Players

Orthopaedic Journal of Sports Medicine ◽

10.1177/2325967114s00276 ◽

2014 ◽

Vol 2 (11_suppl3) ◽

pp. 2325967114S0027

Author(s):

Gulcan Harput ◽

Hande Guney ◽

Fatma Filiz Colakoglu ◽

Gul Baltacı

Keyword(s):

Body Weight ◽

Repeated Measures ◽

External Rotation ◽

Isometric Strength ◽

Shoulder Abduction ◽

Strength Testing ◽

Muscle Testing ◽

Volleyball Players ◽

External Rotator ◽

Limb Dominance

Objectives: The aim of this study was to investigate the effects of limb dominance and gender on isometric, eccentric and concentric strength of the shoulder internal and external rotator muscles in adolescent volleyball players. Methods: Forty adolescent volleyball players [Male: 23( Age: 15.5±1.4 yrs, Body weight: 72±10.2 kg, Height: 184.4±7.6 cm, BMI: 20.9±2.6 kg/m2), Female: ( Age: 16.7±0.9 yrs, Body weight: 60.7±8.2 kg, Height: 172.5±5.3 cm, BMI: 20.4±2.3 kg/m2) participated in this study. Isomed 2000 isokinetic dynamometer was used to measure muscle strength testing. Isometric strength testing of shoulder internal and external rotator muscles were performed at 90 ° shoulder abduction and external rotation position. In the same position, concentric and eccentric muscle testing was performed at 90°/s angular velocity. Strength outcomes were recorded as Nm/kg. 2-way repeated measures of ANOVA was used for statistical analysis. Results: Dominance by gender interaction was not found significant for internal rotator (IR) and external rotator (ER) muscles' strength (IR: F(1,72)=2.87, p=0.06, ER: F(1,72)=1.98, p=0.15). There was a significant strength by dominance interaction for internal rotator muscles (F(2,72)=18.52, p<0.001). Isometric strength was greater in dominant limb (p<0.001)while concentric strength was found greater in non-dominant limb(p=0.006). Eccentric strength was found similar for limbs (p=0.18). IR muscles showed greater strength during eccentric (1.03±0.05), concentric (0.76±0.03) and isometric test (0.69±0.03), respectively. On the other hand, external rotators showed greater strength during eccentric (0.49±0.4), isometric (0.40±0.3) and concentric test (0.36±0.3), respectively. There was no significant gender effect on the strength (IR: F(2,72)=0.31, p=0.73, ER: F(2,72)=0.42, p=0.66). Conclusion: The strength of shoulder internal and external rotator muscles do not differ according to gender in adolescent volleyball players. Limb dominance has an effect on the strength of internal rotator muscles while it has no effect on the strength of external rotators. Both muscle groups show greater strength during eccentric testing.

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