EFFECTS OF TRANSCRANIAL DIRECT CURRENT STIMULATION OVER THE SUPPLEMENTARY MOTOR AREA ON EXERCISE TOLERANCE AND PSYCHOPHYSIOLOGICAL RESPONSES TO HEAVY-INTENSITY EXERCISE

INTRODUCTION: Transcranial direct current stimulation (tDCS) has emerged as a minimally invasive form of cortical stimulation that may modulate psychophysiological responses to exercise and enhance exercise performance. While some studies have reported increased exercise tolerance during large-muscle mass dynamic exercise, overall findings remain inconsistent. The reasons for these discrepancies among tDCS studies are unclear but may, in part, be attributed to variations in electrode montage and placement. We therefore hypothesised that an electrode montage targeting the supplementary motor area (SMA) — a key region implicated in the effort perception, which is a potential factor influencing the ergogenic effects of tDCS — could, in contrast to conventional placements over the primary motor cortex, lead to a reduced perception of effort and, arguably, influence exercise tolerance during heavy-intensity cycling exercise. METHODS: Twelve healthy, recreationally active men (mean age: 25 ± 2 years, V̇O₂peak: 42.9 ± 3.6 mL∙kg⁻¹∙min⁻¹) participated in the study. All volunteers were required to visit the laboratory on four separate occasions. On Day 1, they performed a ramp-incremental exercise test on an electronically braked cycle ergometer to determine the gas exchange threshold (GET), V̇O₂peak, and peak power output (POpeak). On Days 2–4, participants completed a heavy-intensity exercise bout to exhaustion at a workload corresponding to 25% of the difference between the GET and POpeak attained during the ramp exercise test. Each test was conducted following the administration, in a randomised crossover design, of 10 minutes of brain stimulation using either sham tDCS, anodal tDCS, or cathodal tDCS (current intensity: 1 mA). Perceived exertion was recorded every 2 minutes during the exercise tests. Pulmonary gas exchange and ventilation, central haemodynamics, and electromyographic activity responses were continuously monitored. RESULTS: There were no significant differences in pulmonary gas exchange and ventilation, central haemodynamics, electromyographic activity, or perceived exertion between sham, anodal, and cathodal tDCS during heavy-intensity exercise bouts (P > 0.05). The tolerable duration of heavy-intensity exercise was also unaffected by the tDCS conditions, with values of 30.8 ± 7.8 minutes, 31.2 ± 11.4 minutes, and 30.8 ± 12.0 minutes for sham, anodal, and cathodal tDCS, respectively (P > 0.05). CONCLUSION: The present findings suggest that a single session of brain stimulation applied over the SMA region does not significantly alter psychophysiological responses to heavy-intensity exercise or enhance exercise tolerance in healthy, recreationally active men. These results indicate that this simple, non-invasive neuromodulatory technique is ineffective during fatiguing, high-intensity activities involving large muscle mass. However, further research is required to explore alternative brain stimulation protocols and exercise modalities.