Effect of Friction between Fingertips and Ball on Muscle Activity of Forearm Muscle Groups during Fastball Pitching in Baseball.

Abstract

In this study, pitching experiments were conducted with two pitchers (pitcher A and pitcher B) under different friction conditions between the fingertips and the ball to investigate the effects of friction conditions between the fingertips and the ball on pitching performance, upper limb motion, and forearm muscle activity during pitching. The results showed that, for pitcher A, the ball speed and ball spin rate decreased and the pitch control of the ball decreased under the water-applied condition compared to the rosin powder-applied condition. In the water-applied condition, pitcher A performed upper limb movements to reduce his hand velocity and increase the pitching radius, which resulted in the reduced centrifugal force in the acceleration period. Furthermore, the muscle synergy patterns changed between the water- and rosin powder-applied conditions in pitcher A. In pitcher B, the ball spin rate decreased in the water-applied condition compared to the rosin powder-applied condition, but there was no change in pitch velocity and pitch control. The centrifugal force exerted on the hand during the acceleration phase did not change under the water-applied condition compared to the rosin powder-applied condition, and there was no effect on the muscle synergy patterns in pitcher B. However, the muscle activity of the shallow finger flexors and ulnar carpal extensors increased in the water-applied condition, suggesting that the pitcher B were trying to suppress slippage by increasing their grip on the ball.