Comparison of pectoralis major and serratus anterior activity during scapular protraction with and without reciprocal inhibition in healthy individuals

Abstract

Background Sufficient scapular stability is essential for optimal upper-extremity function, with the serratus anterior (SA) playing a key role in both open and closed-chain exercises. However, compensatory pectoralis major (PM) overactivation often interferes with selective SA activation during the scapular protraction. This study compares muscle recruitment patterns between reciprocal inhibition (RI) and no-RI conditions. Objective The purpose of this study was to investigate the effects of a non-elastic band on the muscle activity of the PM and SA, as well as the SA/PM activity ratio, by comparing the RI condition and the no-RI condition during the scapular protraction. Methods Twenty healthy individuals performed the scapular protraction shoulder flexion under randomized no-RI and RI conditions. In the RI condition, isometric horizontal abduction resistance was applied via a non-elastic band to induce reciprocal inhibition of the PM. Surface EMG recorded SA and PM activities, analyzed using paired t-tests. Results SA activity showed no significant difference between the no-RI and RI conditions. In contrast, PM activity decreased significantly under the RI condition compared to the no-RI condition (p < 0.05). Consequently, the SA/PM ratio significantly increased, indicating that the RI protocol effectively suppressed compensatory PM activation while functional SA contribution was preserved (p < 0.05). Conclusion The scapular protraction under the RI condition might be an effective strategy for suppressing compensatory PM activation and increasing the SA/PM activity ratio. These findings suggest that this modified protocol might be a valuable clinical intervention for promoting selective scapular muscle balance.