How to throw a rise ball using a windmill pitch in fastpitch softball : kinematics of the hand and fingers of the pitching arm

The purpose of this paper was to analyze the snap of the wrist joint of the pitching arm kinematically in windmill pitches of a rise ball in fastpitch softball, and to investigate the mechanism which explains how the increase of a backspin speed of the ball is brought about. Five male collegiate fastpitch softball pitchers participated in this study. Each subject pitched a rise ball 20 times in a laboratory. Their pitching motions and the motion of the ball were captured using eight high-speed cameras (500 fps), and the motions of the forearm, hand, fingers of the pitching arm and the ball were kinematically analyzed with the markers attached to their bodies and the ball. The angular velocities of the wrist palmar flexion of all subjects began to increase rapidly associated with the increases of the backspin speed of the ball and the linear speed of the fingertip of the middle finger when the forearm brushed the lateral side of the hip. The mean time period from the start of the brushing to the appearance of the maximum angular velocity of the wrist palmar flexion was at most 0.014 s among all subjects. The mean value of the maximum velocity of each subject was statistically larger than the mean maximum wrist palmar flexion velocity produced voluntarily by human subjects using only the muscles crossing the wrist joint (Jessop and Pain, 2016, p. 41). The mean maximum velocities of the four subjects in this study exceeded the latter maximum by 1.5 times at least, and the velocity of another subject also exceed-ed the latter maximum. The time period from the start of the brushing to the appearance of the maximum backspin speed of the ball in a pitch was at most 0.016 s in the pitches done by all subjects. In baseball throwing, the resultant joint force acting from the forearm to the hand of the throwing arm helps increase the mechanical energies of the hand and ball during the final phase of throwing motion (Miyanishi et al., 1997, pp. 59–63). In this phase, the larger the dorsiflexion angle of the wrist joint up to an angle of π/2 rad, the larger the rate of the increase of the mechanical energies due to the rotation of the hand (Ae, 2004, p. 439, equation (38)). The mean dorsiflexion angles shown by the subjects of this study at the start of brushing were at most about one-third of the maximum angles observed in the phase of baseball throwing (Barrentine et al., 1998, p. 30; Sakurai et al., 1993, p. 62; Solomito et al., 2014, p. 324). The mean linear speeds of the fingertip at the appearance of the maximum backspin speed were statistically larger than the speeds at the start of the brushing for three subjects. These results suggest that the snaps of the wrist joint in the rise ball pitches were not voluntarily brought about using the muscles but mainly from the impulsive force acting on the forearm caused by the brushing considering the recruitment of the nervous system, the rate of muscular activation, and the dorsiflexion angle of the wrist joint at the start of the brushing, and that the increases of the backspin speed of the ball after the start of the brushing for the three subjects were brought about by the snaps considering the in-crease of the backspin speed associated with the increase of the linear speed of the fingertip.