THROWING ARM MOTION TO DETERMINE SPIN AXIS OF PITCHED BASEBALL

Abstract

The purpose of the present study was to investigate a throwing arm kinematics to determine the direction of spin axis of pitched baseball. The baseball was filmed immediately after ball release using a high-speed video camera (250 Hz). The direction of the spin axis and the spin rate were calculated based on the positional changes of the marks on the ball. The throwing motion was recorded with 3-D motion analysis system (Vicon), and angles of wrist flexion/extension, radial/ulnar deviation, and forearm pronation/supination were calculated as kinematic parameters. The direction of the hand segment in global reference frame was also obtained. The spin axis direction significantly correlated with the hand direction, while, there were no special relationship between the spin axis of the ball and joint angular kinematics obtained in this study. It follows from what has been reported that pitched ball trajectory is associated with attitude of the hand when a ball was released from the fingertip.