Anodal HD-tDCS attenuates forearm muscle fatigue via enhanced beta-band corticomuscular coherence

This study aims to investigate the fatigue-attenuating effects of anodal high-definition transcranial direct current stimulation (HD-tDCS) on the forearm flexor muscles during isometric contractions and clarify whether these effects are mediated by enhanced corticomuscular coherence (CMC) in beta and gamma frequency bands.

Twenty healthy young male participants underwent anodal HD-tDCS intervention on the contralateral motor cortex (left hemisphere) of the forearm flexor muscles at 2 mA for 20 min, prior to performing a 30% maximal voluntary contraction (MVC) isometric endurance task. This study employed a crossover sham-controlled design, with participants receiving either anodal stimulation (HD-tDCS) or sham stimulation prior to the task. During the task, electroencephalography (EEG) and surface electromyography (sEMG) of the forearm flexor muscles signals were recorded. CMC areas in EEG beta and gamma bands, as well as the frequency of the maximal peak of the coherence (Cohmax) in the beta and gamma bands, were calculated.

The time to failure (TTF) was significantly greater in the anodal HD-tDCS group compared to the baseline and sham groups (P < 0.05). Subjective perception of fatigue assessed by the Borg Rating of Perceived Exertion (RPE) was also significantly lower in the anodal HD-tDCS group compared to the baseline and sham groups (P < 0.05). The anodal HD-tDCS group exhibited significantly higher beta-band (13-30 Hz) CMC during fatigue compared to both the baseline and sham groups (P < 0.05), especially in terms of the frequency of Cohmax in the beta band. There were no significant differences in gamma-band (31-50 Hz) CMC. Correlation analysis showed that TTF was negatively correlated with RPE (r=-0.58, P = 0.0073) and positively correlated with beta-band CMC area (r = 0.54, P = 0.015).

Anodal HD-tDCS applied to the contralateral motor cortex (M1) can effectively prolong the TTF of the forearm flexor muscles and reduce perception of fatigue. This may be attributed to the enhancement of synchronized activity between the brain and muscles induced by anodal HD-tDCS, resulting in improved muscle function.