Angular Movement Characteristics Of The Upper Trunk And Hips In Skilled Baseball Pitching

Abstract

The overarm throw is one of the fundamental skills in many sport activities which generate high end-point speed. In order to quantify the substantial role of body rotation during overarm throwing, a two segment model was developed which can be used to determine the orientations of the upper trunk and hips from the three-dimensional landmark coordinate data of subjects. Also, three rotation angles were defined by choosing a Cardan angle system which had the following advantages: (1) they are independent components so they can be used as generalized coordinates in both kinematic and kinetic analysis; (2) they closely correspond to common anatomical description of the counterclockwise/clockwise rotation about the longitudinal axis of the body, medial/lateral rotation and anterior/posterior rotation. High speed (250 frame/second) three-dimensional film data was collected for three professional baseball pitchers. They were instructed to make a maximum effort while pitching. Five trials were analyzed for each subject. Although the counterclockwise rotation, lateral rotation and anterior rotation of the upper trunk and hips showed significantly different time history patterns among the subjects, there were also certain similar movement characteristics as follows: the lateral rotation of the upper trunk and the anterior rotation of both upper trunk and hips had much smaller peak velocities compared to that of counterclockwise rotation. The lateral rotation of the upper trunk contributed to the ball speed mainly during a short period from the beginning of ball acceleration to the start of elbow extension. The anterior rotation of the upper trunk and hips contributed to the ball speed from the beginning of ball acceleration to the time of ball release. After the instant of stride foot contact, the hip counterclockwise rotation was the major contributor to ball velocity during the period from the beginning of ball deceleration to the start of ball acceleration. The trunk counterclockwise rotation contributed to ball speed considerably during the period from the start of ball acceleration to the start of humerus internal rotation. After the start of elbow extension body rotation began to decelerated, which confirmed a proximal-to-distal sequence kinematically in pitching. The contribution of the entire body rotation to the ball speed was about 50 percent before the start of elbow extension, 30 percent at the start of humerus internal rotation, and less than 10 percent at the instant of ball release.