A Mechanism for Power Output of the Upper Limbs During Overhead Throw with Stretch-Shortening Cycle

抄録

The purpose of this study was to investigate the effect of the stretch-shortening cycle (SSC) on power output in overhead throwing and on the behavior of shoulder extensor muscles by means of kinematics, kinetics and EMG. Thirteen healthy men performed two kinds of medicine ball throw; concentric throw (CT) without SSC and rebound throw (RT) with SSC. All throws were videotaped using a high-speed camera. Kinematics and kinetics such as joint angle, joint torque and joint torque power of the upper limbs were calculated utilizing the inverse dynamics approach. The EMG activities of trapezius, latissimus dorsi, deltoid, pectoralis major and triceps brachii muscles were recorded using surface electrodes. Mean ball power in RT was significantly higher than that in CT. There was a significant correlation between augmentation of mean ball power and that of mean shoulder joint torque power in RT compared with CT. The EMG activities of pectoralis major and triceps brachii muscles showed nearly no activity during the shoulder flexion phase. These results suggest that although enhancement of power by overhead throwing using upper limb muscles was mainly caused by the enhancement of shoulder joint torque power, the shoulder extensor muscles are not eccentrically contracted but passively stretched during shoulder flexion phase in throwing. This finding contradicts a previously proposed mechanism of power enhancement in SSC.