Discussion
hypoxia, cognitive improvements
HYPOXIA, VASODILATION
The main results of the present study were that (1) ‘DC + a-tDCS’ resulted in longer TTE in hypoxia than ‘WC + a-tDCS’ and ‘WC + sh-tDCS’ conditions, (2) with greater EMG activity of the VM muscle, and (3) improved cognitive performance during and after TTE. These results suggest the possibility of a synergistic effect between DC and a-tDCSFirst, it is important to note that despite performing the modified incongruent Stroop task for 30 min in hypoxia, cognitive performance was unchanged over time On the other hand, DC + a-tDCS improved cognitive performance during and after TTE in hypoxia. This is partially in line with previous studies showing cognitive improvements at rest with either DCThe improved cognitive performance with DC + a-tDCS might be due to increased blood flow and oxygenation to the brainWe found improved endurance performance (i.e., longer TTE) in hypoxia with DC + a-tDCS. This is also a novel finding of the present study. It should be noted that only DC + a-tDCS improved cognitive and endurance performance. Thus, we propose that this could be a synergistic effect since neither DC alone (DC + sh-tDCS) nor tDCS alone (WC + a-tDCS) improved cognitive or endurance performance. Despite previous studies have shown that a-tDCS targeting M1 or DLPFC separately improved endurance performance in cyclingOne possible mechanism for this synergistic effect is that the possible vascular effect of DC supplementation (i.e., vasodilation) allowed for the neuromodulatory effect of a-tDCS to take place. Theoretically, a tDCS-induced increase in corticospinal excitability and the change in the use of motor units can lead to an improvement in TTEWe found an increased EMG of the VM muscle under both DC + a-tDCS and DC + sh-tDCS compared to WC + sh-tDCS, but no difference in EMG of the RF and VL. Few studies analyzed the effect of tDCS on EMG during an endurance task, which limits comparisons. Vitor-Costa et al.On other hand, there was no change in HR, SpOThe interpretation and generalization of the findings of the present study should be made with caution since the participants were endurance-trained male cyclists. In addition, the lack of a measure of brain activity (e.g., EEG, fNIRS), corticospinal excitability, muscle, and brain blood flow, and oxygenation does not allow us to fully understand the mechanisms involved in the present findings. Future studies should consider these limitations and also expand the present findings, for instance, to higher levels of hypoxia. On the other hand, the strengths of the present study include a large array of outcome variables assessed and a complex experimental design testing the isolated and combined effects of DC and tDCS on cognitive and endurance performance in hypoxia and its related physiological and psychophysiological responses in professional athletes. From a practical perspective, if consistently replicated, the present findings indicate that athletes and coaches can use DC supplementation and tDCS to boost endurance performance in hypoxia.The present study showed a possible acute synergistic effect of a-tDCS targeting concurrently M1 and left DLPFC along with the consumption of dark chocolate on improving whole-body endurance performance after prior cognitive effort, with greater EMG of VM muscle, cognitive performance during and after endurance TTE under hypoxia, despite unchanged HR, SpO