ABSTRACT
To analyze the relationship of cause and effect between the onset of throwing disorders of the shoulder and decreased muscle strength, two studies were conducted at a baseball field. In study 1, shoulder joint muscle strength was measured when pain developed during practice and the relationship between pain onset and muscle strength was investigated. Decreased muscle strength was noted at the time of pain onset in 8.1% of players. Study 2 was a prospective study in which the relationship between changes in shoulder joint muscle strength from the start of pitching at the beginning of the season to one month later when competitive games began, and shoulder pain that appeared at the beginning of competitive games was analyzed. Based on the results, the possibility of shoulder joint muscle strength being a predictive factor for the onset of throwing disorders of the shoulder was investigated. However the pain group had greater muscle strength than the normal group at the beginning of the season. On the baseball field, the players’ throwing motions and joint function change daily, making it difficult to determine the reason for onset of disorders and injuries. These results suggest that onset of pain at the start of competitive games cannot be predicted from muscle strength at the beginning of the season.