Abstract
Our aim was to investigate the kinetics of hitting motions when batters hit balls pitched at different speeds (SLOW: 75-80 km/h, MEDIUM: 100-105 km/h, and FAST: 125-130 km/h). Baseballs pitched at different speeds were hit by 29 university baseball players. Three-dimensional kinematic data of swing motions and ground reaction forces of both feet were measured using a Vicon 612 (VICON MOTION SYSTEMS) with 2 force platforms. Joint forces and joint torques acting on lower limbs and torso were calculated. We also calculated the values of torque of the hip joint about the long axis of the lower torso. Our results indicated that when the ball was pitched at a high speed (FAST: 125-130 km/h), the batters required less movement time from the stride foot contact to the appearance of maximum velocity of center of gravity thus causing less impulse toward pitcher direction. The values of hip flexion torque of the stride leg and hip abduction torque of the pivot leg had a greater effect on torso rotation during hitting a ball pitched at a high speed.
