Selective Activation of the Infraspinatus during Various Shoulder External Rotation Exercises

Abstract

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 ablebodied 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 repeatedmeasures 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.

Isolated Activation of the Infraspinatus Muscle in Four Manual Muscle Testing Positions

“…To maximize the EMG ratio, high infraspinatus activity and low surrounding muscle (middle trapezius, upper trapezius, and posterior deltoid) activity are required. Our results are consistent with those of several previous studies, which reported that SWE is an effective exercise position to isolate the activity of the infraspinatus muscle while minimizing surrounding muscle activity 6,11,14 . There are several possible explanations for our results.…”

“…shoulder external rotation to strengthen the infraspinatus muscle isolately 2,11 . Adducted shoulder position isolates the infraspinatus from the posterior deltoid, and side-lying external rotation exercise may be the most effective maneuver to increase infraspinatus activity in isolation 5,6 .…”

Differences in Muscle Activities of the Infraspinatus and Posterior Deltoid during Shoulder External Rotation in Open Kinetic Chain and Closed Kinetic Chain Exercises

“…Reinold et al4 ) found that shoulder external rotation in the side-lying position elicits the greatest electromyographic (EMG) activity in the infraspinatus. Findings by Kim et al6 ) show that shoulder external rotation while sitting maximizes the contribution of the infraspinatus, compared to the shoulder abduction with external rotation in the prone position, shoulder external rotation with abduction while sitting, and shoulder external rotation while side-lying.…”

The effect of exercise types for rotator cuff repair patients on activities of shoulder muscles and upper limb disability

“…There are limits to performing activities of daily living and keeping maximum contraction of the muscles, and inputs such as proprioception and visual feedback become damaged11 ) . When rotator cuff injury patients perform humeral external rotation, their movement differs from a normal person’s external rotation, and special measures are needed for this12, 13 ) . Therefore, this study prescribed open kinetic chain exercise (OKCE) and closed kinetic chain exercise (CKCE) for humeral external rotation, to recover muscle endurance and weak muscle strength, at six weeks after rotator cuff repair.…”