Sex differences in soleus muscle H‐reflex and V‐wave excitability
Gonçalo V. Mendonça, Pedro Pezarat‐Correia, André D. Gonçalves, Miguel Gomes, Joana M. Correia, Carolina Vila‐Chã
Abstract
New Findings What is the central question of this study? How do H‐reflex and V‐wave excitability compare between men and women engaging in similar levels of physical activity? What is the main finding and its importance? H‐reflex excitability is lower in women than in men because of their greater level of antagonist co‐activation during sustained plantar flexion isometric exercise. In addition, supraspinal drive is similar between men and women independently of their differences in H‐reflex excitability and antagonist muscle co‐activation. Abstract We compared H‐reflex and V‐wave excitability between men and women engaging in similar levels of physical activity. We also explored whether differences in antagonist muscle co‐activation between sexes might partially explain sexual dimorphism in the excitability of the H‐reflex and V‐wave. Fifty‐seven young participants were included (29 men: 21.7 ± 2.3 years; 28 women: 22.4 ± 3.3 years). Soleus M‐ and H‐recruitment curves were constructed on a tonic background muscle activation. V‐waves were elicited during maximal voluntary contraction (MVC). Besides being stronger than women, men achieved greater H max /M max values and presented a steeper slope of the ascending limb of the H‐reflex recruitment curve ( P < 0.05). The current intensity required to elicit H max was lower for men ( P < 0.05). The co‐activation of the tibialis anterior muscle during the sustained plantar flexions was greater in women (ratio between tibialis and soleus normalized EMG: 20.5 vs . 8.3%, P < 0.05). Covariance analysis showed that sexual dimorphism in H‐reflex excitability was dissipated when controlling for antagonist co‐activation. V‐wave normalized amplitude was similar between sexes even after controlling for the effects of H max /M max and antagonist co‐activation as covariates. Thus, women exhibit lower H‐reflex excitability than men and this is dependent on their higher level of antagonist muscle co‐activation. While sex differences in antagonist co‐activation persist during MVCs, this is not the case for V‐wave normalized amplitude. Thus, although the efficacy of the transmission between Ia afferent fibres to α‐motoneurons is lower in women because of a greater level of antagonist co‐activation, our findings are consistent with similar supraspinal drive between sexes.