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 ( = 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 ( < 0.01), shoulder distraction force increased by 5.9% body weight ( < 0.01), and ball velocity increased by 0.60 m/s ( < 0.01). Shoulder abduction was significantly associated with shoulder superior force at all timepoints but not with ball velocity ( > 0.05). For every 10° increase in shoulder abduction at ball release, shoulder superior force increased by 3.7% body weight ( < 0.01) and shoulder distraction force increased by 11.7% body weight ( < 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.