“There is significant scientific literature showing a physiological basis for using tDCS to boost motor leaning and so sport performance.”
Implicit motor learning is essential in the acquisition of new motor skills. The primary motor cortex has been found to be a key structure in the acquisition of new motor skills through repetition.
“Behavioral tDCS effects on motor sequence consolidation vary with the time point of stimulation: While anodal tDCS applied to the PMC during training on a serial reaction time task (SRTT)  attenuated stabilization of the learned motor sequence , a facilitating effect of tDCS applied after training was found when stimulation was carried out during rapid eye movement (REM) sleep but not in awake volunteers . The results led to the hypothesis that tDCS effects may vary with baseline cortical activation as shown for TMS  and point to the significance of the PMC for later stages of motor sequence consolidation particularly over-night.”
The results of this paper found that tdCS facilitated a particular motor skill rather than aided in acquisition.
Full Article: http://www.sciencedirect.com/science/article/pii/S0166432816305435