The Effect of Dual Source Premotor Cortex Transcranial Direct Current Stimulation on Muscle Fatigue in Hand Muscles

Single source transcranial direct current stimulation (tDCS) has been shown to increase the time to task failure (TTF) fatiguing contractions when applied to the dorsolateral prefrontal cortex (DLPFC) and to the primary motor cortex (M1). The primary purpose was to determine whether dual source tDCS delivered bilaterally over the premotor cortices (pmc-tDCS) could increase the TTF of a fatiguing contraction performed by hand muscles. A double-blind, randomized, SHAM-controlled, crossover design was used for this study with each participant performing two experimental sessions held on separate days a week apart. The only difference between the two sessions was the type of stimulation (pmc-tDCS or SHAM; counterbalanced) applied concurrent with the fatiguing contraction. In each experiment, the fatiguing contraction was performed by gripping a manipulandum with the index finger and thumb. This was accomplished by using a precision grip and matching an isometric target equal to 15% of the maximum voluntary contraction (MVC) for as long as possible until task failure. The main findings were: 1) both the TTF and the percentage decline in MVC force did not significantly differ between the pmc-tDCS and SHAM conditions; 2) the rates of increase in electromyographic (EMG) activity, force error, and standard deviation (SD) of force were not significantly different between the pre-tDCS and SHAM conditions; and 3) transfer of motor skill under fatigue was similar between the two stimulation conditions. Collectively, these results suggest that pmc-tDCS does not decrease the rate of muscle fatigue during a sustained isometric contraction of the muscles of the hand.