Relationships between throwing mechanics and shoulder distraction in collegiate baseball pitchers.

A distraction force occurs at the shoulder joint in all throwing motions. At the professional level, the relationship between this force and pitching mechanics has been explained. Three-dimensional, high-speed (240 Hz) video data were collected on fastballs from 48 collegiate baseball pitchers. Kinematic parameters related to pitching mechanics and resultant kinetics on the throwing arm elbow and shoulder joints were calculated. Multiple linear regression analysis was used to investigate the relationships between shoulder distraction and pitching mechanics. Shoulder distraction stress averaged 81% body weight for the collegiate pitchers. The mean ball velocity was 81 mph. Ten parameters of pitching mechanics accounted for 89% of the variance in shoulder distraction. Two of the variables (maximum shoulder abduction torque and elbow angle at release) previously shown to affect shoulder distraction in professional baseball pitchers appear to be important for collegiate pitchers as well. These data provide a scientific basis for clinicians, athletes, and coaches to establish methods to reduce distraction force at the shoulder joint through modification of pitching mechanics.