Elbow extension-trunk rotation ratio during early acceleration is associated with biomechanical efficiency in...

Trunk-arm coordination influences throwing-arm torques in baseball pitching, yet quantitative descriptions of coordinated trunk-arm motion are lacking. This study described trunk-arm coordination during pitching using joint excursion ratios and clarified the relationships between joint excursion ratios and biomechanical efficiency. 18 Division III college baseball pitchers underwent markerless motion capture, from which four joint excursion ratios and throwing-arm torques were calculated. Pearson coefficients described associations between joint excursion ratios and throwing-arm torques normalised by height, mass, and ball velocity. Multivariable linear regression models predicting raw throwing-arm torques and containing mass and each significantly correlated joint excursion ratios as predictors were compared to univariable models containing mass alone. Significant associations were observed between elbow extension/trunk rotation (EETR) ratio and normalised peak elbow (r = -0.47, p = 0.045) and peak shoulder (r = -0.51, p = 0.025) torques. Addition of EETR ratio explained 16% greater variance in raw shoulder external rotation torque/ball velocity and 13% greater variance in raw elbow valgus torque/ball velocity than mass alone. This study suggests EETR ratio during the first half of the acceleration phase is associated with biomechanical efficiency.