抄録
In this study, we investigated how the movements of upper torso and upper extremity joints (shoulder, elbow, and wrist) contribute to a ball velocity during overhand throwing. Ten healthy young males threw a rubber baseball towards a target. At first, they performed overhand throwing with maximal effort. Then, they pitched a ball at 80%, 60%, 40% and 20% of the maximal ball velocity in this order. We recorded their throwing motions using three high-speed digital video cameras (200 fps), and calculated angular velocities of wrist palmar flexion, elbow extension, shoulder horizontal adduction, shoulder internal rotation, and upper torso left rotation from three-dimensional coordinate data obtained by the DLT (Direct Linear Transformation) method. Based on these data, we computed the relative contributions of joint movement to ball velocity using cross products between each joint angular velocity vector and relative position vector from each joint to the center of the ball. As relative ball velocity increased, the angular velocities of wrist palmar flexion, elbow extension, and upper torso left rotation at the moment of peak ball acceleration increased (F(4, 36)= 12.1, p < 0.001 ; F(1.4, 12.6)= 28.0, p < 0.001 ; F(1.7, 15.2)= 46.6, p < 0.001, respectively), but the contribution of the angular velocity to ball velocity only increased in upper torso left rotation (F(4, 36)= 6.5, p < 0.001). At instance of ball release, although angular velocity of wrist palmar flexion, elbow extension, shoulder internal rotation, and upper torso left rotation increased with increasing relative ball velocity (F(1.5, 13.4)= 12.3 ; p < 0.01 ; F(1.5, 13.2)= 19.8, p < 0.001; F(1.4, 12.6)= 28.0, p < 0.001; F(4, 36)= 4.9, p < 0.01, respectively), the contribution of the angular velocity to ball velocity only increased in shoulder internal rotation (F(2.0, 17.5)= 7.1, p < 0.01). These results suggest that the human body mainly modulates angular velocities of upper torso left rotation and shoulder internal rotation to control ball velocity during overhand throwing.
