Anodal transcranial direct current stimulation does not influence the neural adjustments associated with fatiguing contractions in a hand muscle

PurposeThe objective of the current study was to investigate the mechanisms responsible for the briefer time to failure of a submaximal contraction (C2) when performed 60min after a similar contraction (C1), and the influence of anodal transcranial direct current stimulation (a-tDCS) applied over the motor cortex on these mechanisms.MethodsIn two sessions, ten adults sustained two isometric contractions (35% of maximum) to failure with the abductor pollicis brevis (APB). Before C2, either a-tDCS or sham stimulation was applied over the motor cortex. Fatigue-related changes in Hoffmann (H) and long-latency (LLR) reflexes, motor-evoked potential (MEP) induced by transcranial magnetic stimulation and associated silent period (SP), maximal motor wave (M-max), voluntary activation (VA), electromyographic (EMG) activity and peak force (PT3) evoked by a 3 pulse-train (100Hz) were investigated.ResultsThe results indicate that regardless of session, the time to failure was briefer (-13%, p<0.05) for C2 than C1, with no a-tDCS effect. During C1, MEP amplitude, SP duration and LLR amplitude increased, H-reflex amplitude did not change, and M-max, VA and PT3 decreased (p<0.05). Except for EMG activity that was greater during C2 than C1 (p<0.001), all variables were similar in C1 and C2 (p>0.05), and recovered their initial values after the 60-min rest, except PT3.ConclusionsThe results of the current study indicate that a-tDCS did not influence corticospinal excitability and time to failure of C2 when performed with the APB. These observations may reflect a peripheral origin of the briefer C2 time to failure in the APB.