A three-dimensional comparative study of the motions between speed throw and distance throw in the university baseball players

Abstract

The purpose of this study was to investigate the differences of the motions between the speed throw and the distance throw, using a three-dimensional(3D) motion analysis. Twenty-four male university baseball players were the subjects of this study. They were asked to throw a ball (mass 0.144kg) horizontally as fast as possible (speed throw: ST), and as far as possible (distance throw: DT). These motions were filmed by two high-speed video cameras. 3D landmark coordinates of the subiects and the ball were calculated by the DLT method. The following kinematic parameters were computed: angle of release, the component velocities of the ball, the 3D angles for the backward/forward lean, right/left lean of the upper torso, and the twist of the torso and those for the abduction/adduction, horizontal flexion/extension, internal/external rotation at the shoulder joint, and the flexion/extension at the elbow joint of the throwing arm. The sequential data were normalized with the time from the stride foot contact to the ball release, and then averaged. Angle of release was significantly larger in the DT than in the ST. Significant difference was not found between the resultant velocity of the ST and the DT. Vertical velocity of the ball was significantly larger in the DT than in the ST during the latter half of the acceleration phase. On the other hand, horizontal velocity of the ball was significantly larger in the ST than in the DT. The backward lean and the left lean angles of the upper torso were also significantly larger in the DT than in the ST throughout the all sequences analyzed. Ranges of these angular displacements between the stride foot contact and the release, however, had no significant difference between the ST and the DT. The shoulder adduction angle was also significantly larger in the DT than in the ST during the latter half of the acceleration phase. These results indicate that the differences in the release parameters between the ST and the DT were caused not only by the throwing arm motions but also by the motions of the upper torso. It has been suggested that the motions to upward and left ward of the upper torso helps to achieve longer throwing distance in the DT, and that forward lean of the upper torso possibly contributes to achieve larger horizontal ball velocity at the release in the ST.