Limited Total Arc Glenohumeral Rotation and Shoulder Biomechanics During Baseball Pitching

Context: Upper extremity injuries in baseball pitchers cause significant time loss from competing and decreased quality of life. Although shoulder range of motion (ROM) is reported as a key factor to prevent potential injury, it remains unclear how limited glenohumeral ROM affects pitching biomechanics which may contribute to upper extremity injuries. Objective: To investigate how pitchers with decreased total arc glenohumeral ROM of the throwing arm differed in upper extremity pitching kinematics and kinetics as well as ball velocity compared with pitchers with greater levels of glenohumeral ROM. Design: Cross-sectional study. Setting: Laboratory. Patients or other participants: Fifty-seven baseball pitchers (ages 18-24) were divided into either control (>= 160 degrees total arc) or lower ROM (<160 degrees total arc) groups. Main outcome measure(s): The mean glenohumeral ROM deficits, pitching kinematic and kinetic outcomes, and ball velocity were compared between groups. Results: The control group demonstrated significantly less deficit in total arc ROM between arms than the lower ROM (control: -1.5 degrees +/- 10.0 degrees; lower ROM: -12.4 degrees +/- 13.9 degrees; P < .001). While the lower ROM group displayed less maximal shoulder external rotation (ER) while pitching, the control group had significantly less difference in ROM between maximal shoulder ER while pitching and clinically measured ER (lower ROM: 64.4 degrees +/- 12.1 degrees; control: 55.8 degrees +/- 16.6 degrees; P = .025). The control group had significantly faster ball velocity than the lower ROM group (control: 85.0 +/- 4.3 mph; lower ROM: 82.4 +/- 4.8 mph; P = .024). Conclusion: Pitchers with decreased total arc glenohumeral ROM (<160 degrees total arc) may undergo overstretching toward ER in the shoulder during the late cocking phase. Pitchers with higher total arc ROM can pitch the same or faster ball without increasing loading in the upper extremity. Total arc glenohumeral ROM measurement can be a clinical screening tool to monitor shoulder condition over the time, and pitchers with limited total arc ROM might be at higher risk of shoulder injury.