RELATIONSHIP BETWEEN FORCES EXERTED ON THE BALL BY THE FINGERS AND BACKSPIN OF THE BALL DURING BASEBALL PITCHING

Abstract

The purpose of this study was to investigate how the fingers generate the force to rotate the ball, with high-speed 3D videography. Velocities of the ball and finger joints, angles of finger joints, backspin rate, and forces exerted on the ball were calculated for fourteen varsity baseball players. Subjects were divided into two groups, i.e. G1 with large backspin rate and G2 with less backspin rate. There were differences in the patterns of joint angles of the proximal and distal interphalangeal joints, the direction of forces and the position of fingers relative to the ball between G1 and G2. A typical subject from G1 developed the FNOR (the force from the finger tip to the center of ball) downward to resist centrifugal force and FTAN (perpendicular to FTAN) forward to accelerate the ball, while a typical subject from G2 exerted these forces in the reversed manner to G1. It seemed that the difference in force application resulted from the difference in the position of the fingertips on the ball.