Study of shoulder injuries on swinging motion of arm

Volleyball spikers and baseball pitchers often injure the end of long head tendon. The tendon is attached to the upper side of the scapula. Because a shoulder joint is a very shallow dimple, the restriction of the lateral movement is performed by mainly the tendons around the joint. Hence it is imagined that the lateral force may cause the shoulder injuries. In this study, the volleyball spiking motion and baseball throwing motion are recorded by high speed video cameras, and the motions of the arm are analyzed as the mechanical links system. In order to calculate the generated force at the shoulder joint, the acceleration is derived from the obtained video image. The generated force is calculated and is resolved into the longitudinal (direction from the shoulder to the threat) and the lateral components. An affection by the lateral force at the joint is discussed in this paper.