野球打撃動作における下胴角速度生成メカニズム

抄録

Previous studies, which calculate dynamic contributions of the whole-body joint torques to the generation of bat head speed by using the equation of motion for whole-body with bat system, showed that the motion-dependent term is the largest contributor to the generation of the bat head speed at the ball impact, and also showed that joint torques of the upper limb joints and the torso joint are the main contributors to the head speed with consideration of the generating factors of the motion-dependent term. These results do not tell us the roles of the lower limb joints in the bat head speed generating mechanism. So in order to quantify the roles of the lower limb joints in the mechanism, we quantify the dynamic contributions of the whole-body joint torques to the generation of forward/backward rotational motion of the lower trunk segment during baseball batting motion. Five collegiate baseball players participated in this experiment. They performed hitting a teed ball as strong as possible. Kinetic data of each hand and each foot were obtained by using an instrumented bat equipped with 28 strain gauges and 3 force platforms, respectively. From the results, the flexion/extension torque of both hip joints showed the largest contribution to the forward angular velocity of the lower trunk segment against the large negative contribution due to the torso joint torque. This result indicates that these hip joint torques play an important role to exert large rotational torque at the torso joint, and these hip joint torques show indirect contributions to the bat head speed.