Muscle Activity During Scapular Muscle Exercises With Multijoint Compound Movement: Analysis Using Fine-Wire and Surface Electrodes.

Abstract

Improvements in motor control of the scapular muscles are important for the prevention and rehabilitation of shoulder and elbow injuries in overhead athletes. To clarify scapular muscle activity during multijoint compound movement exercises using fine-wire and surface electrodes. Descriptive laboratory study. Sixteen healthy men performed 5 types of exercises (cat and dog, trunk rotation, A-exercise, T-exercise, and Y-exercise). Muscle activity was measured as percentage of maximum voluntary isometric contraction (%MVIC) by using fine-wire electrodes in the rhomboid major (Rhom) and using surface electrodes in the upper (UT), middle (MT), and lower (LT) trapezius and serratus anterior (SA) muscles. The Rhom/UT, MT/UT, LT/UT, and SA/UT muscle activity ratios were calculated. One-way analysis of variance was used to compare the %MVIC and muscle activity ratios between exercises. There was no significant difference in Rhom activity between the exercises (34.6-54.2%MVIC; P = .25). LT activity was significantly greater in the trunk rotation (58.0 ± 24.6%MVIC) and Y-exercise (63.2 ± 40.1%MVIC) than in the cat and dog scapular retraction (19.6 ± 9.3%MVIC) and A-exercise (28.2 ± 14.2%MVIC) (P < .05). SA activity was significantly greater in the cat and dog scapular protraction (26.7 ± 11.0%MVIC) and Y-exercise (25.6 ± 19.3%MVIC) than in the other exercises (P < .05). The SA/UT activity ratio in the cat and dog scapular protraction exercise (9.64 ± 8.48) was significantly higher than in the other exercises (P < .05). All the exercises were effective for activating the Rhom. The trunk rotation and Y-exercise were effective for activating the LT, and the cat and dog scapular protraction exercise was effective for activating the SA while suppressing the UT. These results enable exercise selection based on muscle activity characteristics (moderate [20%-50%MVIC] and high [>50%MVIC] levels contribute to muscle activation) to prevent and rehabilitate shoulder and elbow injuries.