A Single Anodal Transcranial Direct Current Stimulation Session to Enhance Sport-Specific Performance in Trained Individuals? A Systematic Review and Meta-Analysis

BackgroundTranscranial direct current stimulation (tDCS) has emerged as a promising and feasible method to improve motor performance in healthy and clinical populations. However, the potential of tDCS to enhance sport-specific motor performance in athletes remains elusive. ObjectiveWe aimed at analyzing the acute effects of a single anodal tDCS session on sport-specific motor performance changes in athletes compared to sham. MethodsA systematic review and meta-analysis was conducted in the electronic databases PubMed, Web of Science, and SPORTDiscus with publication dates through April 2022. The meta-analysis was performed using an inverse variance method and a random-effects model. Additionally, two subgroup analyses were conducted (1) depending on the stimulated brain areas (i.e., primary motor cortex (M1), temporal cortex (TC), prefrontal cortex (PFC), cerebellum (CB)), and (2) studies clustered in subgroups according to different sports performance domains (endurance, strength, and visuomotor skill). ResultsA total number of 18 studies enrolling a sample size of 245 athletes were deemed eligible for inclusion. Across all included studies, a significant moderate standardized mean difference (SMD) favoring anodal tDCS to enhance sport-specific motor performance could be observed (SMD = 0.27, 95%CI [0.10, 0.44], p = 0.002). Subgroup analysis depending on cortical target areas of tDCS indicated non-significant moderate to high SMD in favor of anodal tDCS compared to sham for M1 (SMD = 0.24, 95%CI [-0.01, 0.49], p = 0.06), TC (SMD = 0.40, 95%CI [-0.10, 0.89], p = 0.12), PFC (SMD = 0.23, 95%CI [-0.04, 0.50], p = 0.09) and CB (SMD = 0.89, 95%CI [-0.15, 1.94], p = 0.09). Performance domain subgroup analysis revealed non-significant moderate SMD favoring anodal tDCS compared to sham: endurance domain (SMD = 0.23, 95%CI [-0.01, 0.47], p = 0.06), strength domain (SMD = 0.44, 95%CI [-0.14, 1.01], p = 0.14, Chi2 = 0.31) and visuomotor skill domain (SMD = 0.30, 95%CI [-0.03, 0.62], p = 0.07). ConclusionA single anodal tDCS session leads to performance enhancement in athletes in sport-specific motor tasks. Although no conclusions can be drawn regarding the modes of action as a function of performance domain or stimulation site, these results imply intriguing possibilities concerning sports performance enhancement. Furthermore, this study highlights the need to investigate tDCS applications under real-life conditions rather than in highly controlled laboratory settings to uncover the true potential of non-invasive brain stimulation as a performance enhancement not only in sports but also in the context of prevention or rehabilitation of neurological diseases.