No effect of tDCS of the primary motor cortex on isometric exercise performance or perceived fatigue

Anodal transcranial direct current stimulation (tDCS) of the primary motor cortex has been reported to improve isometric exercise performance without changing corticospinal excitability. One possible cause for this may be the previous use of relatively high (2 mA) current intensities, which have inconsistent effects on corticospinal excitability. The present pre-registered study aimed to replicate previously reported ergogenic effects of 2 mA tDCS and examine whether 1 mA anodal tDCS both improved isometric exercise performance and perceived fatigue, and more reliably altered corticospinal excitability. On three separate occasions, participants performed a sustained submaximal isometric knee extension until failure after receiving either 1, 2 mA or sham anodal tDCS. Corticospinal excitability of the knee extensors was measured using transcranial magnetic stimulation immediately before and after tDCS. Rating of fatigue was recorded throughout the isometric exercise. Neither 1 nor 2 mA tDCS improved exercise performance, or reduced perceived fatigue, compared with sham stimulation. There was also no effect of tDCS on the corticospinal excitability of the knee extensors. We found no effect of tDCS on either exercise performance, perceived fatigue or corticospinal excitability. This study adds to the growing body of literature reporting no ergogenic effect of tDCS. Large pre-registered replications of previously reported effects are now required before tDCS can be considered an effective method to improve exercise performance.