Selective activation of the infraspinatus muscle

Abstract

Context: To improve selective infraspinatus muscle strength and endurance, researchers have recommended selective shoulder external-rotation exercise during rehabilitation or athletic conditioning programs. Although selective strengthening of the infraspinatus muscle is recommended for therapy and training, limited information is available to help clinicians design a selective strengthening program.

Objective: To determine the most effective of 4 shoulder external-rotation exercises for selectively stimulating infraspinatus muscle activity while minimizing the use of the middle trapezius and posterior deltoid muscles.

Design: Cross-sectional study.

Setting: University research laboratory.

Patients or other participants: A total of 30 healthy participants (24 men, 6 women; age = 22.6 ± 1.7 years, height = 176.2 ± 4.5 cm, mass = 65.6 ± 7.4 kg) from a university population.

Intervention(s): The participants were instructed to perform 4 exercises: (1) prone horizontal abduction with external rotation (PER), (2) side-lying wiper exercise (SWE), (3) side-lying external rotation (SER), and (4) standing external-rotation exercise (STER).

Main outcome measure(s): Surface electromyography signals were recorded from the infraspinatus, middle trapezius, and posterior deltoid muscles. Differences among the exercise positions were tested using a 1-way repeated-measures analysis of variance with Bonferroni adjustment.

Results: The infraspinatus muscle activity was greater in the SWE (55.98% ± 18.79%) than in the PER (46.14% ± 15.65%), SER (43.38% ± 22.26%), and STER (26.11% ± 15.00%) (F3,87 = 19.97, P < .001). Furthermore, the SWE elicited the least amount of activity in the middle trapezius muscle (F3,87 = 20.15, P < .001). Posterior deltoid muscle activity was similar in the SWE and SER but less than that measured in the PER and STER (F3,87 = 25.10, P < .001).

Conclusions: The SWE was superior to the PER, SER, and STER in maximizing infraspinatus activity with the least amount of middle trapezius and posterior deltoid activity. These findings may help clinicians design effective exercise programs.

Figures

Figure 1.

Four types of exercise. A, Prone external-rotation exercise. B, Side-lying wiper exercise. C, Side-lying external-rotation exercise. D, Standing external-rotation exercise.

Figure 2.

Comparison of the muscle activity among 4 different exercises. A, Infraspinatus. B, Middle trapezius. C, Posterior deltoid. a Indicates difference between exercise positions. Abbreviations: PER, prone external-rotation exercise; SER, side-lying external-rotation exercise; STER, standing external-rotation exercise; SWE, side-lying wiper exercise.