打点高の異なる野球ティー打撃動作における左右各手のキネティクス的分析

抄録

The purpose of this study was to clarify the kinetic features of each hand under conditions of different hitting-point heights (high, middle, and low) in the baseball tee-batting. Twenty-three collegiate male baseball players’ motion were captured by VICON-MX system (12-camera, 250Hz), and kinetic data at each hand were collected by using an instrumented bat equipped with 28 strain gauges (1000Hz). Three kinds of tee-batting heights were set for each subject based on the upper and lower limits of the strike zone according to the baseball rule. A moving bat coordinate system was defined to compare the characteristics of kinetic variables with respect to the different hitting-point heights. The vertical displacements of the ball hitting-point on the bat were dominated mainly with translational movement of the bat. The mechanical works of the vertical component of the bat longitudinal force of each hand show positive and greater values under low height condition than those under other conditions during down swing phase. The negative works done by the moment of each hand about the bat longitudinal inclination axis also show a similar tendency of the works of the bat longitudinal force at each swing phase. In addition, the peak values of coupled force about the bat inclination axis were observed in the latter half of down swing phase, and the component of coupled force was greater values under high condition than those other condition. These results indicate that the bat longitudinal force is a great contributor to adjust the translational movement of bat in the vertical direction, and the coupled forces and the moment about the bat inclination axis control the rotational movement of bat.