Biomechanical Determinants of Elbow Varus Moment in Baseball Pitching: A Large-Scale Motion Capture Analysis

ABSTRACT Objective: Elbow varus moment is a risk factor for ulnar collateral ligament injury in baseball pitchers, yet how body mass, pitch speed, and age contribute to elbow loading remains understudied across levels. This study examined whether pitch speed, body mass, and age predict elbow varus moment during pitching, and characterized loading differences across levels. Methods: Three-dimensional motion capture and kinetic data from 411 fastball trials, contributed by 100 athletes across high school, college, independent league, and Minor League Baseball, were drawn from the publicly available OpenBiomechanics Project. Multiple linear regression identified predictors of elbow varus moment, with athlete-clustered robust standard errors applied to account for repeated trials per athlete. A one-way ANOVA compared loading across playing levels. Results: The regression model explained 49% of the variance in elbow varus moment, F(3, 407) = 130.4, p < .001. Body mass was the strongest independent predictor (β = .55, p < .001), followed by pitch speed (β = .33, p < .001); age showed no significant effect (β = −.04, p = .338). These patterns held after correcting for clustered trials and after removing an extreme high-loading case. Elbow varus moment rose steadily across levels, from 98.27 Nm in high school to 135.92 Nm in MiLB pitchers, F(3, 407) = 26.69, p < .001. Conclusion: Body mass, more than pitch speed, drove elbow loading, and loading climbed from amateur to professional competition. Pairing anthropometric monitoring with velocity-based tracking may strengthen elbow-injury-prevention and load-management strategies in rehabilitation at every level of play.