Effects of Transcranial Direct Current Stimulation (tDCS) in Paracanoe Athletes: A Randomized Sham-Controlled Crossover Trial

Background Transcranial direct current stimulation (tDCS) over the dorsolateral prefrontal cortex has been investigated as a non-invasive strategy to modulate cognitive performance and autonomic regulation in sport, but evidence in Paralympic athletes remains scarce. This study evaluated the acute effects of anodal tDCS over the left dorsolateral prefrontal cortex on cognitive performance and cardiovascular autonomic modulation in para-canoeing athletes. Methods This pilot, randomized, sham-controlled, single-blind, within-subject crossover trial included eight male para-canoeing athletes (35.4 ± 5.4 years). In randomized order, separated by a seven-day washout, each participant received one session of anodal tDCS (anode at F3, cathode at Fp2; 2 mA; 20 minutes) and one sham session. Cognitive performance was assessed with the Stroop Test (eight athletes) and cardiac autonomic modulation with heart rate variability indices (five athletes with adequate signal quality). Differences between conditions and time points were estimated with the percentile bootstrap (10,000 resamples; 95% confidence intervals), with simulation-based power projection for larger samples. Results In the anodal condition, correct responses on the color Stroop increased from pre- to post-intervention (mean pre-minus-post difference − 7.63; 95% confidence interval − 15.50 to − 1.75). After the intervention, markers of relative sympathetic modulation of heart rate variability (absolute low-frequency power, its natural logarithm, and the ratio of low- to high-frequency power) were higher in the anodal than in the sham condition. In the sham condition, heart rate increased and the R–R interval decreased from pre- to post-intervention. Conclusions In this pilot sample, anodal tDCS over the left dorsolateral prefrontal cortex was associated with improved Stroop accuracy and a sympathetic shift in cardiac autonomic modulation, a promising signal that requires confirmation in a larger, independent sample before any applied recommendation. Trial registration: Brazilian Clinical Trials Registry (ReBEC), RBR-47g8ts7, registered on 18 May 2026 (retrospectively registered).