Effects of Transcranial Direct Current Stimulation on Exercise Tolerance and Related Psychophysiological Responses

During fatiguing exercise, a myriad of peripheral and central physiological perturbations occur in the brain and in the central nervous system, which impair the capability to produce force or power through muscle contractions. The capacity to tolerate such conditions is a determinant factor for exercise capacity in healthy and clinical populations, which in turn impacts physical performance . Transcranial direct current stimulation (tDCS), which involves the transmission of a weak electrical current through the scalp for several minutes, is a form of non-invasive brain stimulation that aims to alter the level of cortical excitability of the stimulated area. It has been proposed as an ergogenic tool to counteract central fatigue mechanisms and alter the physiological responses and perceived exertion of healthy individuals during different types of exercise, including ones requiring whole-body dynamic contractions. Conflicting results emerge from the literature, often due to a lack of tDCS and exercise protocol standardization. Furthermore, a precise cause-effect relationship and the related mechanisms have yet to emerge. Therefore, two studies were conducted in this dissertation. In Study 1, twelve participants were enrolled and visited the laboratory on four experimental trials after a preliminary visit for cardiorespiratory and anthropometrics assessments. They performed, in a randomized and counterbalanced order, two constant work-rate cycling in the heavy domain (Δ15%) and two in the severe domain (Δ75%) following a 20-minute of either anodal (2 mA) or sham primary motor cortex (M1) tDCS session. No significant differences in exercise tolerance and related psychophysiological responses were found between real and sham conditions. In Study 2, a similar design was employed to assess differences in exercise tolerance and related psychophysiological responses, especially the rate of perceived exertion, during constant work-rate cycling in the heavy domain (Δ25%), following a 10-minute 1 mA of either anodal, cathodal, or sham tDCS of the supplementary motor area (SMA). No significant differences in all studied parameters were found between the conditions. The findings suggest that one session of M1 or SMA tDCS stimulation is incapable of affecting exercise tolerance and related psychophysiological responses during exercise involving dynamic contraction of large muscle mass in young, healthy, active males. More studies are needed to compare different protocols and investigate the neurophysiological rationale for exercise capacity enhancement through tDCS.