Elbow injuries are very common in baseball pitchers. Curveballs are thought to increase this risk, particularly if the athlete begins this pitch at an early age. The purpose of this study is to identify the differences of the upperarm motion between fastball (FB) and curveball (CB) baseball pitches. Three dimensional (3-D) high-speed cinematography was used to record FB and CB 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 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. Seven joint angle changes corresponding to all these degrees of freedom were obtained throughout the pitching motion.
　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 both FB and CB pitching in baseball. There was no difference in the changes of joint angles of the shoulder and elbow between FB and CB pitches. However, there was a significant difference in the motion of supination / pronation of the forearm and dorsal flexion / palmar flexion of the wrist prior to the ball release ; the forearm was largely supinated by 20~25 degrees in the CB compared to the FB, while the wrist was dorsi-flexed by 5~10 degrees in the FB com-pared to the CB.

DESCENTE SPORTS SCIENCE Vol.12/THE DESCENTE AND ISHIMOTO MEMORIAL FOUNDATION FOR THE PROMOTION SPORTS SCIENCE