Shoulder adaptations among pitchers and position players over the course of a competitive baseball season

Abstract

Objective: To determine if throwing arm shoulder range of motion (ROM) and scapular kinematic differences exist between baseball pitchers and position players over the course of a baseball season.

Design: Prospective cohort.

Setting: Professional baseball athletic training room.

Participants: Sixteen asymptomatic professional baseball pitchers and 16 position players.

Independent variables: Preseason glenohumeral (GH) posterior tightness and scapular position.

Main outcome measures: Throwing arm GH horizontal adduction ROM and GH internal rotation bilateral asymmetry ROM, as well as bilateral differences in forward scapular posture and throwing arm scapular upward rotation at rest, 60, 90, and 120 degrees of humeral elevation were measured. These measurements were taken before and at the conclusion of a 140-game baseball season.

Results: Analyses of covariances showed no significant differences in GH horizontal adduction or internal rotation asymmetry ROM between groups over the course of the season. However, the pitchers developed significantly less scapular upward rotation at 60 degrees (P = 0.007) and 90 degrees (P = 0.006) of humeral elevation compared with the position players during the season. Forward scapular posture (P = 0.23) and scapular upward rotation at 0 degrees (P = 0.93) and 120 degrees (P = 0.29) of humeral elevation were not significantly different between groups.

Conclusions: These results suggest that baseball position players develop more scapular upward rotation over the course of a competitive season than pitchers. This discrepancy may increase the pitchers' risk of injury and may partially explain their higher incidence of shoulder injury compared with position players. Therefore, pitchers may benefit from strengthening exercises and stretches aimed at increasing scapular upward rotation throughout the competitive baseball season.