A kinematics study on the characteristics of throwing movements in young children: comparison with the young children in the 1980s

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The purpose of this study was to clarify the difference between the present and the 1980s by comparing the throwing performance and throwing motion for young children from the viewpoint of kinematics. There were 29 children, 14 boys and 15 girls aged five years. Their tennis ball throwing motions were videotaped with two cameras for 3‒D motion analysis (120 fps). The kinematic variables computed were the release velocity, release angle of the ball, the joint angles of the upper and lower limb joint and the segment angles of the trunk. The throw distance and release parameters were not significantly different between boys and girls. A significant positive correlation was found between the throw distance, the initial projection velocity, the projection angle, the projection height and the projection height ratio in boys and between the throw distance and the projection angle, steps and step ratios in the girls. In boys, the maximum velocity appeared in order from the shoulder to the elbow, and from the wrist to the hand to the ball, from near the trunk to the end. In girls, the maximum velocity of the elbow appeared earlier than that of the shoulder. Theses tendency were similar to the characteristics of young children about 35 years ago. There was no significant difference between boys and girls in shoulder angle, hip angle and trunk twist during maximum backswing. Comparing this study with that of about 35 years ago, the initial projection velocity and projection height were significantly decreased in boys, and no significant decrease in all items were observed in girls.