Changes in the electromyographic activities of the infraspinatus and posterior deltoid according to abduction angles of the shoulder joint during shoulder external rotation in closed kinetic chain exercise

[Purpose] This study’s purpose was to identify abduction angles of the shoulder joint that can provide effective infraspinatus muscle exercises while minimizing the muscle activity of the posterior deltoid muscle. [Subjects and Methods] The subjects of this study were 15 healthy young students in their 20s. Subjects adopted a standing position and performed shoulder external abduction while pushing their hands against the wall. The current research was undertaken to compare the activity of the infraspinatus muscle and the posterior deltoid muscle at abduction angles of 45, 90 and 135° of the shoulder joint during closed kinetic chain exercises. [Results] A activity of the infraspinatus muscle showed no statistically significant differences. The activities of posterior deltoid muscle were greater at the angle of 45° than at 90 and 135°. [Conclusion] These results indicate that to strengthen the infraspinatus, shoulder external rotation exercises at abduction angles of the shoulder joint greater than 45° are more effective.