Selective Activation of the Infraspinatus during Various Shoulder External Rotation Exercises

抄録

[Purpose] To investigate the selective activation of the infraspinatus muscle while minimizing the use of the posterior deltoid muscles during common shoulder external rotation exercises. [Subjects] Thirty-two able-bodied volunteers (18 males, 14 females; aged 22 to 31 years, mean ± SD, 24.7 ± 3.3 years) were recruited for this study. [Methods] The participants were instructed to perform four exercises: side-lying external rotation; prone abduction with external rotation; sitting external rotation, and sitting with abduction and external rotation exercise. The EMG signal amplitude was measured during each exercise. Surface EMG signals were recorded from the infraspinatus and posterior deltoid muscles. Differences among the exercises were tested using one-way repeated-measures analysis of variance. [Results] EMG activities of the infraspinatus and posterior deltoid muscles in prone abduction with external rotation were significantly higher than in the other exercises. The EMG ratio (infraspinatus/posterior deltoid) was significantly higher in sitting external rotation than in the other exercises. [Conclusion] Based on these findings, sitting with external rotation should be used to minimize posterior deltoid activation and selectively stimulate infraspinatus muscle activity during shoulder external rotation exercise.