The ergogenic effect of transcranial direct current stimulation on cycling time to exhaustion task performance in physically active people

Resumen

Endurance exercise consisting of sustained whole-body dynamic exercise inevitably induces muscle fatigue, which leads to task failure. It is considered that the brain plays a key role during the regulation of endurance exercise performance. It is believed that exercise-induced muscle fatigue elicits a reduction in motor cortex excitability, spinal excitability, and the contractile capacity of the active muscle fibers. Therefore, an increased amount of descending drive from supraspinal regions is required to maintain task performance. Numerous investigations have conducted to identify the different method to decrease muscle fatigue during an endurance task. These studies have indicated that techniques that can increase motor cortex excitability could increase the time to task failure due to more efficient motor commands. Therefore, the main objective of this thesis was to investigate the ergogenic effect of transcranial direct current stimulation on endurance exercise performance in physically active people. In the first study, we performed a systematic review and meta-analysis to quantify the effect of a-tDCS on endurance (TTE and ETT) and sprint performance during cycling and running tasks. We found that the acute effect of a-tDCS increases TTE performance during endurance cycling and running (p = 0.04). The subgroup analysis revealed a positive effect of a-tDCS on TTE during cycling and running (p = 0.01), but not on ETT (p = 1.00) or sprint performance (p = 0.46). However, it should be noted that only four studies have investigated the ETT task, and two studies have investigated the sprint task. These results indicated that the task should be considered as it probably influences the results obtained by a-tDCS. Moreover, included studies results were inconsistent probably due to the influence of different tDCS parameters like stimulation duration, intensity, electrode montage, targeted brain area, and electrode size, which influence the excitability of the targeted brain area. In the second study, we conducted a crossover double-blind, randomized and placebo-controlled study design to investigate the effect of bilateral extracephalic tDCS applied over M1 during a constant-load cycling TTE task with 16 physically active people (3 women and 13 men). We found that bilateral extracephalic a-tDCS over M1 increases constant-load cycling TTE performance by 12% compared with sham condition (p = 0.04), but without changes among two experimental conditions in HR response (p = 0.12), RPE (p = 0.13), and exercise-induced muscle pain (p = 0.16). Overall, this thesis shows that tDCS can influence active peoples’ endurance TTE performance during cycling and running task. However, despite the influence of bilateral extracephalic tDCS over M1 on the increment in TTE, suggesting that no influence on variables including HR response, RPE, and exercise-induced muscle pain. Therefore, more studies are needed to understand the effect of tDCS on perceptual and physiological parameters during physical performance.