ANGULAR MOMENTUM TRANSFERS IN BASEBALL PITCHING

Abstract

This study calculated the angular momentum acquired from the ground and its transfers between body segments during a baseball pitch. Seven Division I baseball pitchers were filmed with three high-speed video cameras while they threw maximum effort fastballs from a regulation mound. From the video data, three-dimensional locations of select body landmarks and joint centers were calculated. These three-dimensional data, along with data obtained from anthropomorphic models, were used to calculate angular momentum about three orthogonal axes that translated with each subject’s center of mass during the baseball pitch. A fourth axis was defined post hoc, aligned with the angular momentum vector of the right arm-and-ball at the time of release. The angular momentum of each segment group was projected onto this axis during the entire trial. A composite trial of the seven subjects was generated. Angular momentum values about the projection axis were small until approximately 0.200 s before the onset of double-support. After this instant, the system experienced a large influx of angular momentum, so that by the beginning of double-support the pitcher had already acquired about three quarters of the angular momentum that he would have at release (210  73 mm  s-1 out of 278  30 mm  s-1). During double-support the remaining quarter of angular momentum was generated. Additionally, during the later part of double-support the angular momentum associated with motions of the right leg, trunk-and-head, and left arm was transferred to the right arm-and-ball, thereby contributing to its velocity and to the velocity of the ball at release.