It has been reported that the repetitive throwing activity leads the dominant shoulder joint to have characteristic features. However, it is unclear if these features are related to the onset of throwing shoulder pain. The purpose of this study was to clarify the features of shoulder associated with throwing shoulder pain in high school baseball players. We examined the range of motion, laxity and muscle strength of both shoulders in 57 baseball players in high school. Regarding to the range of motion, flexion, external rotation and internal rotation at 90 degrees of abduction were measured. The strength in the following muscles was measured with a hand-dynamometer (MICRO FET): the abductor at 45 degrees of scaption, the external and internal rotators at the hanging arm. In addition, the laxity in the shoulder was evaluated with the load and shift test. Fifty-seven players were divided into three groups according to their throwing shoulder pain; group N consisted of 26players with no shoulder pain, group P consisted of 9 players with throwing shoulder pain at the examination, group NP consisted of 22 players with throwing shoulder pain in the past. The statistical analysis was done using a one-way ANOVA. The external rotation and range of rotation (external and internal rotation) of the throwing shoulder in group P was significantly less than those in the other two groups. There was no significant differences in the range of flexion andinternal rotation, the laxity andthe strength of the shoulder among the three groups. The decrease of external rotation in the dominant side might cause throwing shoulder pain in high school baseball players.
