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

Experimental studies showed improvement in physical performance following acute application of transcranial direct current stimulation (tDCS). This study examined the neuromuscular and neural response to a single training session (Part 1) and after a 3-week resistance training (Part 2) performed with the knee extensors, preceded by tDCS over the primary motor cortex. Twenty-four participants (age, 30 ± 7 years; stature, 172 ± 8 cm; mass, 72 ± 15 kg) were randomly allocated to perform either resistance training with anodal tDCS (a-tDCS), or by a placebo tDCS (Sham). Resistance training consisted of 3 × 10 isometric contractions of 3 s at 75% MVC. Measures of neuromuscular function (MVC, voluntary activation and potentiated twitch force), corticospinal excitability, and short and long cortical inhibition were assessed. Acute tDCS did not affect neuromuscular and neural responses to a single training session (all ps ≥ 0.10). Conversely, after the 3-week training program, MVC increased in both groups (p < 0.01), with a greater increase observed for a-tDCS vs. Sham (⁓6%, p = 0.04). Additionally, increased voluntary activation (⁓2%, p = 0.04) and corticospinal excitability (⁓22%, p = 0.04), accompanied with shorter silent period (-13%, p = 0.04) was found following a-tDCS vs. Sham. The potentiated twitch force and measures of short and long cortical inhibition did not change after training programme (all ps ≥ 0.29). Pre-training administration of tDCS only resulted in greater neuromuscular adaptations following 3-weeks of resistance training. These results provide new evidence that tDCS facilitates adaptations to resistance training in healthy individuals.