The Influence of Bilateral Dual Source Transcranial Direct Current Stimulation on the Progression of Muscle Fatigue

Transcranial direct current stimulation (tDCS) applied unilaterally to the primary motor cortex (M1) can significantly prolong the time to task failure (TTF) of a fatiguing contraction. The primary purpose of the study was to examine the influence of bilateral dual source tDCS (dstDCS) applied over the left and right M1s (ds-tDCS) on the TTF of a precision grip task. This was accomplished through the utilization of a double-blind, randomized, SHAM-controlled, within-subjects design. Fourteen participants completed two experiments (ds-tDCS and SHAM stimulation conditions) with a seven-day washout period between sessions. Each experiment involved the performance of a sustained isometric fatiguing contraction using a precision grip (index finger and thumb) of the right hand while either ds-tDCS or SHAM stimulation was applied to the left and right M1 by two separate stimulation devices. Participants were directed to match a target force equivalent to 15% of the maximum voluntary contraction (MVC) force for as long as possible (TTF). The main findings were that both the TTF and the percentage decline in MVC force were not significantly different between the ds-tDCS and SHAM stimulation conditions. In addition, the force error, standard deviation (SD) of force, and EMG activity was not significantly different between the ds-tDCS and SHAM stimulation conditions. These findings suggest that ds-tDCS does not reduce the rate of progression of muscle fatigue in a sustained submaximal isometric contraction of hand muscles.