Characterising sex‐related differences in lower‐ and higher‐threshold motor unit behaviour through high‐density surface electromyography

Abstract

AbstractEmerging questions in neuromuscular physiology revolve around whether males and females share similar neural control in diverse tasks across a broad range of intensities. In order to explore these features, high‐density electromyography was used to record the myoelectrical activity of biceps brachii during trapezoidal isometric contractions at 35% and 70% of maximal voluntary force (MVF) on 11 male and 13 female participants. Identified motor units were then classified as lower‐threshold (recruited at ≤30%MVF) and higher‐threshold (recruited at >30%MVF). The discharge rate, interspike interval variability, recruitment and derecruitment thresholds, and estimates of neural drive to motor neurons were assessed. Female lower‐threshold motor units showed higher neural drive (P < 0.001), accompanied by higher discharge rate at recruitment (P = 0.006), plateau (P = 0.001) and derecruitment (P = 0.001). On the other hand, male higher‐threshold motor units showed greater neural drive (P = 0.04), accompanied by higher discharge rate at recruitment (P = 0.005), plateau (P = 0.04) and derecruitment (P = 0.01). Motor unit discharge rate normalised by the recruitment threshold was significantly higher in female lower‐threshold motor units (P < 0.001), while no differences were observed in higher‐threshold motor units. Recruitment and derecruitment thresholds are higher in males across all intensities (P < 0.01). However, males and females have similar activation and deactivation strategies, as evidenced by similar recruitment‐to‐derecruitment ratios (P > 0.05). This study encompasses a broad intensity range to analyse motor unit sex‐related differences, highlighting higher neural drive and discharge rates in female lower‐threshold motor units, elevated recruitment and derecruitment thresholds in males, and convergences in activation and deactivation strategies.Highlights What is the central question of the study?Do male and female motor units behave similarly in low‐ and high‐intensity contractions? What is the main finding and its importance?Female motor units show higher discharge rates in low‐intensity tasks and lower discharge rates in high‐intensity tasks, with no differences in recruitment behaviour. A broader inter‐spike interval variability was also observed in females. These findings underline that there are sex‐specific differences concern the firing strategies based on task intensity.