The effects of transcranial direct current stimulation on objective and subjective measures of sports performance: a systematic review and meta-analysis.
Objective: To examine the effects of transcranial direct current stimulation (tDCS) on objective and subjective outcomes of sports performance.
Design: Systematic review and meta-analysis.
Data Sources: A systematic literature search of electronic databases (PubMed, WOS, Scopus, Google Scholar) and reference lists of included articles up to June 2018.
Eligibility Criteria: Randomized sham-controlled trial comparing anodal stimulation with a sham condition providing data on objective and subjective outcomes of sports performance.
Results: The analysis of effect sizes from 28 studies comprising 419 participants indicated that anodal tDCS had a small but positive effect on performance g = 0.27, 95% CI [0.05, 0.49], z = 2.40, p = 0.016. Effects were not moderated by type of outcome, electrode placement, muscles involved, number of sessions, or intensity and duration of the stimulation. Importantly, the funnel plot showed that, overall, effect sizes tended to be larger in smaller studies with a high standard error.
Summary/Conclusion: The results suggest that if tDCS has a positive impact on sports performance, the effect is probably small and most likely biased by low quality studies and the selective publication of significant results. Therefore, the current evidence does not provide strong support to the conclusion that tDCS is an effective means to improve performance.