Gender differences in muscle fatigue of the biceps brachii and influences of female menstrual cycle in electromyography variables

Several studies report gender differences in response to fatigue. Most results suggest that females have higher muscle endurance than males. Possible explanations lie on differences in muscle mass, substrate utilization, muscle morphology and neuromuscular activation. One relevant aspect not always considered is the hormonal fluctuations during the female menstrual cycle. The present work observed eighteen healthy and untrained adults (eight males, 26.9 ± 4.0 yr and ten females, 24.0 ± 2.8 yr) performing fatiguing isometric contractions to evaluate both the influence of menstrual cycle and gender differences in fatigability. Surface electromyographic signals were recorded from the biceps brachii using a linear electrode array of eight electrodes during 90 seconds at 40% of maximal voluntary contraction. Root mean square (RMS), mean frequency (MNF) the conduction velocity (CV) values were estimated using windows of 0.5 seconds. Female subjects showed overall lower fatigability, demonstrated by the lower mean CV decrease (1.494) compared to males (1.787). However, in periods of high decreases in hormones concentrations in females (the end of both the follicular and luteal phases), higher CV decreases were observed (1.921 and 2.183). These results indicate the need of considering the effects of hormonal fluctuations in females when observing gender effects on muscle fatigue.