投球動作における上肢筋の筋電図学的研究

抄録

Ball sizes and weights used in a variety of sports and patterns of throwing vary according to the purposes of the given sports. In this study we intended to analyze the mechanics of throwing when the subject threw a ball horizontally at maximum speed. Procedure: EMG of the upper arm muscles such as extensor carpi radialis, flexor carpi ulnaris, biceps brachii triceps brachii, deltoideus, trapezius, teres major and pectoralis major, was recorded by the standard surface electrodes. Angular movements of the wrist and the elbow joints recorded by an electrogolliometer. The moment of release of the ball was determined with the electric switch. The subject was a healthy trained man (31 years of age). The balls used in this study well shown in Tab.1. Throwing patterns were three basic ones such as over-hand, side-hand, and under-hand. Results: All recordings of EMG, electrogoniograms and moment of release are shown in Fig.2, 3, and 4. The results obtained are as follows; 1) A form of throwing was generally divided into three phases, those were, back swing, throw and follow through. The time intervals of those three were around 0.2-0.5 sec, 0.3-0.45 sec and 0.2-0.35 sec, respectively (Tab.2). 2) A clear difference was found in EMG recordings between throwing a ball which was small enough to be grasped and throwing the other which is too large. 3) There was a definite difference in EMG recordings between over-hand throw and underhand throw. 4) During the phase of follow-through, action potentials of all muscles involving both extensors and flexors became great. The reason could be found in avoiding jerk of the arm and shoulder. 5) Except under-hand throw, sudden dorsal flexion of wrist was seen immediately after the release of ball. This showed that the subject threw the ball horizontally at maximum speed, and that the flatter the arc in which his hand travels, the greater the possibility of accuracy.