Sex-related differences in motor unit yield, subcutaneous tissue thickness, and maximal force

Neurophysiological differences between sexes are well-documented; males generally exhibit greater maximal strength and a greater number of recorded motor units (motor unit yield) compared to females, especially in surface electromyography recordings. This disparity in motor unit yield has been attributed to greater subcutaneous tissue thickness in females, which can affect electromyography signal quality. This study aimed to evaluate sex-related differences in the number of recorded motor units and subcutaneous tissue thickness, and to investigate the relationships between recorded motor unit yield, and each of subcutaneous tissue thickness, and maximal voluntary contraction force. Participants (16 F, 15 M) performed isometric dorsiflexion contractions at 20%, 40%, 60%, 80%, and 100% of maximal voluntary contraction force. Subcutaneous tissue thickness was measured using ultrasound, concurrently with surface electromyography from the tibialis anterior. Results indicated no significant difference in the number of identified motor units between males and females at any contraction intensity (p ≥ 0.06). However, males demonstrated a higher maximal voluntary contraction (p < 0.001), and females exhibited greater subcutaneous tissue thickness (p < 0.001). No significant relationships between subcutaneous tissue thickness and motor unit yield, or between maximal voluntary contraction force and motor unit yield, were observed.