Effects of Non-throwing Arm on Trunk and Throwing Arm Movements in Baseball Pitching

概要

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The purpose of this study was to investigate the effects of non-throwing arm on trunk and throwing arm movements in baseball pitching. Ten right-handed collegiate baseball players were asked to throw baseballs under two conditions, the normal and the restricted conditions. Under the restricted condition, non-throwing arm was fixed to the trunk by a rubber band. Their motions were analyzed by three-dimensional high-speed motion analysis and compared between two conditions. Under the restricted condition, upper torso rotated more counterclockwise and trunk twist angle decreased, at the instant of stride foot contact on the ground. It might be because the moment of inertia of upper torso and upper extremities along the trunk axis was smaller without non-throwing arm movement. Additionally, the maximum angular velocities of shoulder internal rotation and elbow extension as well as pitched ball velocity were lower under the restricted condition. When trunk twist, which stretches trunk rotator musculature, is small, the energy exerted by the musculature and transferred to throwing arm would decrease. Therefore, non-throwing arm in baseball pitching motion is considered to contribute to enhance pitched ball velocity by controlling the moment of inertia of upper torso and upper extremities along the trunk axis.