Abstract
Many joint actions are involved in the throwing motion of a fastball pitch; therefore, two dimensional (2-D) procedures are insufficient for analyzing the throwing motion. In this study,three dimensional (3-D) high-speed cinematography was used to record fastball pitches of varsity baseball pitchers. Two small reference sticks were fixed on the hands and forearms of the throwing arm of the subjects to detect their movements.The direct linear transformation (DLT) method was used for 3-D space reconstruction from 2-D images filmed by two from 2-D images filmed by two phase-locked cameras (200 frames/s).The throwing arm has seven degrees of freedom of joint motion except in the fingers; three for the shoulder, one for the elbow, one for the radioulnar, and two for the wrist. Following seven joint angle changes corresponding to all these degrees of freedom were obtained throughout the pitching motion. 1) horizontal abduction/horizontal adduction angle at the shoulder joint, 2) abduction/adduction angle at the shoulder joint, 3) internal rotation/external rotation angle at the shoulder joint, 4) flexion/extension angle at the elbow joint, 5) pronation/supination angle at the radio-ulnar joint (forearm), 6) radial flexion/ulnar flexion angle at the wrist joint, 7) palmar flexion/dorsi flexion angle at the wrist joint. The results showed that horizontal adduction and internal rotation of the shoulder,extension of the elbow, pronation of the forearm, and palmar flexion of the wrist were the important joint actions for fastball pitching in baseball. Preliminary to these motions were motions in the opposite direction; e.g., horizontal abduction and external rotation of the shoulder,flexion of the elbow, supination of the forearm, and dorsi flexion of the wrist were detected.These motions in the opposite direction would be useful to extend the range of the motion in each joint angle. The results also appear to be connected to intrinsic muscle propertios, that greater power can be exerted during shortening of the muscle when it is stretched just before the shortening action.
