Comparative study of the differences in shoulder muscle activation according to arm rotation angle.

BACKGROUND

Scapular muscle exercise is important for patients with shoulder disorders. Distal variance leads to changes in shoulder muscle activation. Here, we aimed to determine whether scapular muscle activation is affected by different arm rotation angles.

METHODS

Overall, 30 healthy men participated in this study. The subjects were asked to keep their arms at 120 degrees of shoulder flexion while holding a 1.0-kg dumbbell in palms down (pronation) and palms up (supination) positions. Electromyography was used to measure anterior, middle, posterior deltoid, serratus anterior, upper, and lower trapezius muscle activation during the task. The muscle activations of each shoulder were compared between the pronation and supination positions.

RESULTS

Anterior deltoid and serratus anterior activations were significantly higher in supination than in pronation (p < .05). Alternatively, posterior deltoid and lower trapezius muscles were significantly more activated in pronation than in supination (p < .05).

CONCLUSION

Scapular muscle activation changed with arm rotation angle. Arm rotation angle should be assessed to estimate scapular muscle activation during exercise and motion analysis in clinical practice.