Contraction mode and intensity effects on elbow antagonist muscle co-activation

Agonist muscle contraction mode and intensity effects on antagonist co-activation was examined between men and women.

Fifteen healthy young men (mean ± standard deviation age = 24.9 ± 4.2 years, body mass index = 23.17 ± 2.34) and 15 women (mean ± standard deviation age = 21.8 ± 2.3 years, body mass index = 24.16 ± 2.91) performed five isokinetic concentric and eccentric maximal-effort elbow flexor/extensor contractions to establish their peak torque. Participants then performed a series of randomly ordered sub-maximal (10-90% of peak torque, 10% increments) elbow flexor contractions over two separate experimental sessions. All sub-maximal elbow flexor contractions were concentric during the first session, while eccentric contractions were performed during the second session. Antagonist co-activation was quantified as the elbow extensor surface electromyogram (EMG) magnitude during all flexor contractions, normalized to its' respective MVC level, when acting as an agonist.

The results demonstrated significant contraction intensity (p < 0.001), gender (p < 0.001) and contraction mode (p < 0.001) main effects, indicating that co-activation: (1) increased from 10-90% MVC (5.40% to 12.01%), (2) was greater in women than men (12.06% vs 3.68%), and (3) was greater during concentric than eccentric contractions (9.82% vs 5.92%), without correcting for skinfold thickness. A significant gender by contraction intensity interaction demonstrated that women displayed greater increases in co-activation, as compared to the men, across 10-90% MVC. Following correction for skinfold thickness, the gender difference was not found to be statistically significant.

The major findings demonstrated that antagonist muscle co-activation demonstrated a dependency on contraction intensity and mode; however, a gender difference was not observed when corrected for skinfold thickness.