Torso kinematic patterns associated with throwing shoulder joint loading and ball velocity in Little League pitchers.

The purpose of this study was to investigate the associations between kinematic patterns of the torso segment and shoulder joint loading as well as pitching performance in youth pitchers. Twenty-four Little League pitchers threw fastballs while motion capture and force plate data were collected and ball speed was measured with a radar gun. Three-dimensional torso segment kinematics (absolute angles and angular velocities) and shoulder net joint moments (NJM) and forces were calculated. The time-series kinematic data were used as inputs to a principal components analysis to extract torso movement patterns. Associations between torso movement patterns and discrete peak shoulder NJM, compressive force, and ball speed were investigated with nonparametric correlations. Torso segment motion patterns related to forward flexion, lateral flexion (away from pitching arm), and axial rotation and rotational velocities were associated with shoulder joint kinetics and ball speed. In addition, excessive axial (transverse plane) torso rotation at ball release correlated positively with shoulder joint loads but not ball speed, which may indicate the prospect for decreasing joint kinetics while maintaining pitching performance through targeted interventions. These results provide a deeper understanding about the interrelationships between torso kinematic patterns, shoulder kinetics, and pitching performance.