CONSORT checklist.

<div><p>Transcranial direct current stimulation (tDCS), a non-invasive brain stimulation technique, has been shown to increase exercise performance in strength and cycling studies but its effects on running endurance remain unclear. The objectives of this randomized sham-controlled crossover trial were to assess tDCS efficacy on submaximal treadmill running time to exhaustion (TTE). Forty-five healthy male runners aged between 18 and 32 years (mean maximal oxygen consumption: 46.6 mL/min/kg) performed two constant-load tests at 90% of their maximal aerobic speed preceded by 20 minutes of active or sham multichannel (5 anodes, 3 cathodes) tDCS applied over the bilateral motor cortex with a total intensity of 4 mA. Ratings of perceived exertion (RPE), blood lactate, VO<sub>2,</sub> and heart rate were monitored every five minutes until volitional exhaustion. The median [IQR] TTE was similar following active (12.2 [10.5, 16.1] minutes) or sham (12.5 [10.2, 15.1] minutes) tDCS (p = 0.96). Likewise, there were no significant differences between active and sham conditions for RPE, blood lactate, final VO<sub>2</sub>, and final heart rate (all p ≥0.05). No difference in TTE was found when stratifying groups according to their VO<sub>2</sub>max (i.e., VO<sub>2</sub>max ≥ 45 mL/min/Kg, p = 0.53; VO<sub>2</sub>max < 45 mL/min/Kg, p = 0.45) but there was a trend for a significant correlation between VO<sub>2</sub>max and change in TTE (p = 0.06). TDCS applied over the bilateral motor cortex did not improve endurance performance in a large sample of trained runners. Characterization of individual tDCS responsiveness deserves further consideration. In our experimental conditions, tDCS had no ergogenic effect on endurance running performance.</p><p><b>Trial registration</b>: Clinical trial registration: <a href="https://clinicaltrials.gov/ct2/show/NCT04005846" target="_blank">NCT04005846</a>.</p></div>