投球動作解析システムによるＴＯＰポジションの運動学的解析

Abstract

Baseball pitching involves a complicated and rapid movement that has been investigated to prevent injuries and to improve the pitching performance. It is difficult to assess the pitching motion with high accuracy and a high sampling rate, due to the limitations of preexistent camera systems. The current camera system, however, has enough capacity to measure pitching motions with high accuracy and a high sampling rate.We have been diagnosing shoulder joint injuries caused by pitching. The patients (N = 939) felt pain during the pitching sequence as follows: top position (32.5%), maximum external rotation (27.2%), and ball release (14.5%). Hence the top position is one of the most important postures to investigate the mechanisms of shoulder joint injury in pitchers. There have been no studies that focused on the top position, however.The main purpose of this study was to develop a system to assess the pitching motion accurately. Another purpose was to estimate the instant of the top position and evaluate the kinematics of the shoulder and elbow joints.Pitching movement was assessed using a motion capture system (ProReflex MCU500, Qualisys Inc., Sweden) in a studio that has an official pitcher’s mound and home base. This system can record the positions of reflective markers at 500 Hz using seven CCD cameras. Thirty-two markers were mounted on the joints and body landmarks of each subject. Two markers were mounted on the ball. The pitching motions of eleven subjects were assessed, after a period for warm up. Kinematics parameters were calculated using three-axis gyroscopic Euler angle.The instant of the top position was observed for all subjects before the lead foot touched the ground. The interval from the top position to ball release was 0.242 ± 0.0438 [s] (n = 11). The subjects were divided into two groups by the type of posture at the instant of the top position, as follows: internal rotation group (n = 5), 11.8 ± 6.08 degrees, and external rotation group (n = 6), 38.1 ± 19.97. Other kinematics parameters at the top position were adduction of the shoulder at 74.2 ± 19.84 degrees, horizontal adduction of the shoulder at 37.3 ± 14.10 degrees, and extension of the elbow at 92.1 ± 21.63 degrees. The timing and posture of the estimated top position were almost the same as those of the conventional top position.From the top position to lead foot contact on the pitching sequence, there were three patterns of elbow leading. The three patterns did not depend upon experience. We interpreted them as individual variations.