Anodal tDCS improves neuromuscular adaptations to short-term resistance training of the knee extensors in healthy individuals

Experimental studies show improvement in physical performance following acute application of transcranial direct current stimulation (tDCS). This study examined the neuromuscular and neural responses to a single training session (Part 1) and following a 3 wk resistance training program (Part 2) performed with the knee extensors, preceded by tDCS over the primary motor cortex. Twenty-four participants (age, 30 +/- 7 yr; stature, 172 +/- 8 cm; mass, 72 +/- 15 kg) were randomly allocated to perform either resistance training with anodal tDCS (a-tDCS) or a placebo tDCS (Sham). Resistance training consisted of 3 x 10 isometric contractions of 3 s at 75% maximal voluntary contraction (MVC). Measures of neuromuscular function (MVC, voluntary activation, and potentiated twitch force), corticospinal excitability, along with short and long cortical inhibition were assessed. Acute tDCS did not affect neuromuscular and neural responses to a single training session (all P >= 0.10). Conversely, after the 3 wk training program, MVC increased in both groups (P < 0.01) with a greater increase observed for a-tDCS vs. Sham (similar to 6%, P = 0.04). Additionally, increased voluntary activation (similar to 2%, P = 0.04) and corticospinal excitability (similar to 22%, P = 0.04), accompanied by a shorter silent period (-13%, P = 0.04) were found after a-tDCS vs. Sham. The potentiated twitch force and measures of short and long cortical inhibition did not change after the training program (all P >= 0.29). Pretraining administration of tDCS only resulted in greater neuromuscular adaptations following 3 wk of resistance training. These results provide new evidence that tDCS facilitates adaptations to resistance training in healthy individuals. NEW & NOTEWORTHY The initial increase in maximal strength during resistance training is attributed to neural adaptations. Acute administration of transcranial direct current stimulation (tDCS) has been shown to improve motor function and neural adaptations in healthy and clinical populations. This study measured the neuromuscular and neural response to acute (single training session) and short-term (3 wk) resistance training with tDCS. Greater neuromuscular and neural adaptations were only found following 3 wk of resistance training.