Preliminary evidence that anodal transcranial direct current stimulation enhances time to task failure of a sustained submaximal contraction.

Petra S Williams,Richard L Hoffman,Brian C Clark,François Hug

doi:10.1371/journal.pone.0081418

Petra S Williams, Richard L Hoffman + Show 2 more

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https://doi.org/10.1371/journal.pone.0081418

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Journal: PloS one	Publication Date: Dec 9, 2013
Citations: 104	License type: CC BY 3.0

Affiliation: Ohio University, Northern Arizona University

Abstract

The purpose of this study was to determine whether anodal transcranial direct current stimulation (tDCS) delivered while performing a sustained submaximal contraction would increase time to task failure (TTF) compared to sham stimulation. Healthy volunteers (n = 18) performed two fatiguing contractions at 20% of maximum strength with the elbow flexors on separate occasions. During fatigue task performance, either anodal or sham stimulation was delivered to the motor cortex for up to 20 minutes. Transcranial magnetic stimulation (TMS) was used to assess changes in cortical excitability during stimulation. There was no systematic effect of the anodal tDCS stimulation on TTF for the entire subject set (n = 18; p = 0.64). Accordingly, a posteriori subjects were divided into two tDCS-time groups: Full-Time (n = 8), where TTF occurred prior to the termination of tDCS, and Part-Time (n = 10), where TTF extended after tDCS terminated. The TTF for the Full-Time group was 31% longer with anodal tDCS compared to sham (p = 0.04), whereas TTF for the Part-Time group did not differ (p = 0.81). Therefore, the remainder of our analysis addressed the Full-Time group. With anodal tDCS, the amount of muscle fatigue was 6% greater at task failure (p = 0.05) and the amount of time the Full-Time group performed the task at an RPE between 8–10 (“very hard”) increased by 38% (p = 0.04) compared to sham. There was no difference in measures of cortical excitability between stimulation conditions (p = 0.90). That the targeted delivery of anodal tDCS during task performance both increased TTF and the amount of muscle fatigue in a subset of subjects suggests that augmenting cortical excitability with tDCS enhanced descending drive to the spinal motorpool to recruit more motor units. The results also suggest that the application of tDCS during performance of fatiguing activity has the potential to bolster the capacity to exercise under conditions required to derive benefits due to overload.

Highlights

In healthy individuals, fatigue is both a physical and perceptual experience that is a normal and expected physiologic reaction to sustained and intense activity [1,2,3]
There was no systematic effect of the anodal transcranial direct current stimulation (tDCS) stimulation for altering the to task failure (TTF) for the entire subject set (n = 18; p = 0.64 ES = 0.01) (Figure 4)
An analysis of these sub-groups indicated that the Full-Time group exhibited a 31% longer TTF with anodal tDCS stimulation when compared to the sham stimulation condition (16.4862.87 min vs. 13.1361.34 minutes, p = 0.04, ES = 0.47) (Figure 5B)

Summary

Introduction

Fatigue is both a physical and perceptual experience that is a normal and expected physiologic reaction to sustained and intense activity [1,2,3]. In order to sustain task performance, the amount of excitatory descending drive from supraspinal regions increases to compensate for the reduced excitability of the spinal region [2,4,11,16,17]. Despite the compensatory mechanisms from supraspinal inputs, task failure remains inevitable [14,15,18].

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