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

Abstract

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. 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. Descriptive laboratory study. 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. Four variables were included in the significant model (<i>F</i>_4,39 = 147.51; <i>P</i> < .001) and explained peak shoulder distraction force (<i>R</i>² = 0.944; adjusted <i>R</i>² = 0.938; SE = 0.036): increased peak elbow distraction force (<i>t</i> = 19.90; <i>P</i> < .001) and extension moment (<i>t</i> = 3.63; <i>P</i> = .001), as well as decreased elbow flexion velocity (<i>t</i> = -2.37; <i>P</i> = .023) and trunk flexion at foot contact of the pitch (<i>t</i> = -3.00; <i>P</i> = .005). 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. Variables associated with peak throwing shoulder distraction force provide information regarding injury mechanism and coachable cues that might reduce shoulder injury risk among pitchers.