ウインドミル投法の筋電図的分析 : 競技レベルによる相違とボール速度の変化を中心にして

Abstract

Two groups consisting of five and three adult males, who are skilled and unskilled in the windmill pitch, respectively, were selected as the subjects, and the electromyographic difference in the pitching originated in the skill level and ball velocity was studied using of EMG's and VTR's. 1) Between the initial velocity of ball (Y) and maximum angular velocity (X) of the angle between horizontal and the line connecting shoulder and wrist, the relationships found for the skilled subjects were y=0.020x - 1.28 (r=.913, p&lt.001) and the unskilled y= 0.015x + 0.73(r=.867, p&lt.01), respectively. 2) The unskilled had no significant correlation between the horizontal maximum velocity of the wrist and maximum angular velocity of the angle between the forearm and brachium, and this finding suggests that they can not use their elbow joint for pitching. 3) Between the initial velocity of the ball and horizontal maximum velocity of the wrist just before releasing the ball, a significant correlation was found for both the skilled (r=.634,p&lt.05) and the unskilled (r=.754, p&lt.05). 4) Between the initial velocity of the ball and snap ratio, a significant correlation was seen for both these groups, skilled (r=.852, p&lt.001) and unskilled (r=.759, p&lt.05), and had comparable regression coefficients. 5) The skilled subjects' pitching consisted of some motion characteristics; a great step length, trunk twisting in the throwing direction, adduction of the shoulder joint, extension and pronation of the elbow joint, and flexion of the wrist joint, while the unskilled showed a small step length, flexion of shoulder joint with a touch of abduction, and the flexion of the wrist joint. 6) The pitching, especially the velocity of ball, was dependent on the skill level even among the skilled subjects. This fact appeared to result from the magnitude of the rotation speed of the upperlimb, the transfer of kinetic energy to the ball via applying the upper portion of forearm on the trunk at the end of forward swing phase, efficiency of the snap motion, and the translational velocity of the center of body's gravity. 7) It was thought that among the skilled, the ball velocity was controlled by the rotation speed of the upperlimb and the strength of the trunk twist. In comparison, the unskilled controlled the velocity by delaying the timing for increasing the rotation speed of the upperlimb and the change in the strength of the backward kick. 8) The unskilled subjects had poor ability for exhibiting stable performance, which was caused by the rotation speed of the shoulder joint and uncertain snap motion fluctuated ball-releasing point.