Biomechanics Related to Increased Softball Pitcher Shoulder Stress: Implications for Injury Prevention

BACKGROUND: Softball pitchers exhibit high throwing shoulder distraction force, which is a theorized mechanism of throwing shoulder overuse injury. Windmill pitching involves a variety of highly individualistic pitching styles, and certain kinematics preceding ball release likely influence the amount of shoulder stress that a pitcher accrues. PURPOSE: To examine the association of trunk and throwing arm kinematics, kinetics, and timing variables with peak throwing shoulder distraction force in high school softball pitchers. STUDY DESIGN: Descriptive laboratory study. METHODS: A total of 37 high school pitchers (mean ± SD; height, 1.71 ± 0.06 m; weight, 75.53 ± 16.12 kg; age, 16 ± 2 years) threw 10 fastball pitches at regulation distance (43 ft [13.1 m]) and with maximum effort. Kinematic data were collected at 240 Hz using an electromagnetic motion capture system synced with motion analysis software. The 3 fastest pitches were averaged and analyzed. Kinematic, kinetic, and timing variables were entered into a stepwise linear regression analysis. RESULTS: Four variables were included in the significant model (F(4,39) = 147.51; P < .001) and explained peak shoulder distraction force (R(2) = 0.944; adjusted R(2) = 0.938; SE = 0.036): increased peak elbow distraction force (t = 19.90; P < .001) and extension moment (t = 3.63; P = .001), as well as decreased elbow flexion velocity (t = −2.37; P = .023) and trunk flexion at foot contact of the pitch (t = −3.00; P = .005). CONCLUSION: Elbow kinetics and angular velocity, as well as trunk positioning at foot contact, are associated with peak throwing shoulder distraction force in high school softball pitchers. CLINICAL RELEVANCE: Variables associated with peak throwing shoulder distraction force provide information regarding injury mechanism and coachable cues that might reduce shoulder injury risk among pitchers.