Effects of Transcranial Direct Current Stimulation on Upper Limb Muscle Strength and Endurance in Healthy Individuals: A Systematic Review and Meta-Analysis

Abstract

ObjectiveWhether transcranial direct current stimulation (tDCS) can improve upper limb muscle strength and endurance in healthy subjects is still controversial. This article reviews the relevant literature on the use of tDCS to improve upper limb muscle strength and endurance in healthy individuals.MethodsWe systematically searched the Cochrane Library, PubMed, EMBASE, and the Web of Science until September 4, 2021. Randomized parallel or crossover experimental studies on the effects of tDCS on upper limb muscle strength and endurance in healthy individuals were included. Review Manager 5.3 software was used to evaluate methodological quality and analyze the combined effect of the included literature.ResultsTwelve studies (189 participants) were included in the qualitative synthesis, and nine studies (146 participants) were included in the meta-analysis. Compared with the control group, the tDCS intervention had no significant effect on improving upper limb muscle strength [I2 = 0%, 95% CI (−0.79, 0.23), p = 0.98, MD = 0.01]. In this analysis, tDCS had a significant heterogeneity (I2 = 87%) in improving upper limb muscle endurance compared with the control group. After the subgroup analysis and the sensitivity analysis, the source of heterogeneity was excluded. The final results showed that tDCS had a significant effect on improving upper limb muscle endurance [I2 = 0%, 95% CI (1.91, 4.83), p < 0.00001, MD = 3.37].ConclusionstDCS has no significant effect on improvement of upper limb muscle strength, but has a significant effect on improving upper limb endurance performance (especially on the non-dominant side).

Zapping the brain to enhance sport performance? Evidence from an umbrella review of the effect of transcranial direct current stimulation on physical performance

“…While most of the meta-analyses only required that participants should be healthy adults, the works by Alves-Lobão et al (35) and Maudrich et al (10) constrained their reviews to studies with samples of athletes. Hu et al (37), on the contrary, selected tDCS interventions with untrained adults. Alves-Lobão et al (35) additionally restricted their search to articles from 2009 onwards.…”

“…The seven meta-analyses that evaluated the effect of tDCS using standardized effect sizes (i.e., (9, 37) used unstandardized mean differences) showed on average an effect of 0.44 (0.22 – 1.44). However, among these meta-analyses, the extremely disparate value of the review by Alves-Lobão and collaborators (35); 2022; g = 1.44) makes this work an outlier.…”

“…). The average centrality score (53.2, 95%CI[40.5, 65.8]) and the normalized closeness scores (1.14, 95%CI [0.96, 1.33]) of this group differ from the indices of the other three remaining meta-analyses(10,35,37; centrality score: 11, 24, and 10; normalized closeness score: 0.40, 0.62, and 0.39), as evidence of this distancing from the central group (Table1). The separation of these meta-analyses could be due to divergences in the inclusion criteria they used, especially regarding the selection of participants.…”

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

“…The idea of this study relates to the fundamental debate regarding the scope of applicability of tDCS, in other words, the ecological validity of tDCS. Concerning motor performance, tDCS is predominantly employed in patients or healthy participants with proven ability to enhance motor performance [5][6][7][8]. However, the question remains whether performance-enhancing effects are also detectable in trained athletes, particularly in sport-specific motor tasks.…”

“…tDCS has been successfully employed in healthy and clinical populations. Both cognitive and motor functions could be improved in healthy adults, and partially restored in patients suffering from Parkinson's disease or stroke (for a detailed description of these findings, please see the following reviews [5][6][7][8]).…”