Short-Term Effects of Anodal Transcranial Direct Current Stimulation on Endurance and Maximal Force Production. A Systematic Review and Meta-Analysis.

Alix-Fages Alix-Fages,Romero-Arenas Romero-Arenas,Jerez-Martínez Jerez-Martínez,Márquez Márquez,Río-Rodriguez Río-Rodriguez,Fernandez-Del-Olmo Fernandez-Del-Olmo,Colomer-Poveda Colomer-Poveda,Castro-Alonso Castro-Alonso

doi:10.3390/jcm8040536

Abstract

The purpose of the present systematic review and meta-analysis was to explore the effects of transcranial direct current stimulation (tDCS) on endurance (i.e., time to task failure (TTF)) and maximal voluntary contraction (MVC). Furthermore, we aimed to analyze whether the duration of stimulation, the brain region targeted for stimulation, and the task performed could also influence motor performance. We performed a systematic literature review in the databases MEDLINE and Web of Science. The short-term effects of anodal tDCS and sham stimulation (placebo) were considered as experimental and control conditions, respectively. A total of 31 interventions were included (MVC = 13; TTF = 18). Analysis of the strength-related tDCS studies showed small improvements in the MVC (SMD = 0.19; 95% CI = −0.02, 0.41; p = 0.08). However, the results of the endurance-related interventions indicated a moderate effect on TTF performance (SMD = 0.26; 95% CI = 0.07, 0.45; p = 0.008). Furthermore, the sub-analysis showed that anodal tDCS over M1 and stimulation durations longer than 10 min produced the best results in terms of TTF performance enhancement. Additionally, the effects of anodal tDCS were larger during full body exercises (i.e., cycling) when compared to uniarticular tasks. In conclusion, the current meta-analysis indicated that anodal tDCS leads to small and moderate effects on MVC and TTF, respectively.

Highlights

Non-invasive brain stimulation paradigms have been receiving increased interest in recent years as tools for modulating cortical excitability and behaviour in a range of clinical settings and experimental conditions
The search strategy was composite by two main concepts, the first one referring to non-invasive brain stimulation techniques (i.e., “Transcranial direct current stimulation (tDCS)” OR “a-tDCS” OR “anodal-tDCS” OR “c-tDCS” OR “cathodal-tDCS” OR “transcranial direct current stimulation”) and the other one referring to the main performance outcomes focus of this review (i.e., “strength” OR “maximal voluntary contraction” OR “MVC” OR “one repetition maximum” OR “1RM” OR “endurance” OR “time to task failure” OR “resistance” OR “time limit” OR “time to exhaustion”)
The studies of Kan et al [13], Angius et al [20], Flood et al [24] and Angius et al [27] were included in both MVC and to task failure (TTF) analysis because they explored the effects of anodal tDCS on both strength- and endurance-related variables

Summary

Introduction

Non-invasive brain stimulation paradigms have been receiving increased interest in recent years as tools for modulating cortical excitability and behaviour in a range of clinical settings and experimental conditions. Transcranial direct current stimulation (tDCS) is a form of stimulation that holds particular promise in both of these settings as it is non-invasive, painless, well-tolerated [1] and safe [2]. This form of stimulation consists of delivering a constant and weak electrical current to the brain by placing two or more electrodes over the scalp [3]. Stimulation lasting for longer than nine minutes might induce significant after-effects on cortical excitability that could last up to 90 min [4,5] These effects are mainly due to changes in resting membrane potential of the targeted cells [1]. The effects of tDCS on cortical excitability are polarity specific, since anodal tDCS increases cortical excitability while cathodal tDCS produces the opposite effect [3]

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