ABSTRACT
Objective To investigate the activities of infraspinatus (IS) and posterior deltoid (PD) under shoulder external rotation at open kinetic chain (OKC) and closed kinetic chain (CKC) exercise with shoulder abduction 0° and 90° to determine the optimal external rotation rehabilitation exercise.Methods From April to June, 2018, 19 healthy adults finished the movement of 0° OKC, 0° CKC, 90° OKC and 90°CKC. The root mean square (RMS) of IS and PD was recorded with surface electromyography (sEMG), then the standardized RMS (RMS％), ratio of IS/PD and onset time of activation were calculated.Results RMS％ of PD was the minimal at 90° CKC, and was less than that of 0° CKC (P ＜ 0.05). IS/PD was the most at90° CKC, and was more than that of 90° OKC (P ＜ 0.05). The onset time of IS was the earliest in 90° CKC, and earlier than that of 90° OKC (P ＜ 0.05) and 0°OKC (P ＜ 0.05). The onset time of PD was the latest in 0° CKC, and latter than that of 90° OKC (P ＜ 0.05).Conclusion 90°CKC activates IS mostly and earliest, which can be used in early rehabilitation for rotator cuff injury.