Introduction: Anodal transcranial direct current stimulation (a-tDCS) consists of a low-intensity electrical stimulation that can increase corticospinal excitability when applied over the motor cortex (3). Previous work reported that a-tDCS increased time to failure of a sustained submaximal isometric contraction of elbow flexors performed 60 min after a similar contraction (1). Furthermore, it has been shown that during this type of fatiguing contraction, corticospinal excitability changes differently between agonist and antagonist muscles during sustained contractions (2). The aim of this work was to study the effects of a-tDCS on time to failure in relation with changes in excitability of the corticospinal pathway of two agonist [biceps brachii (BB), brachioradialis (BRD)] and one antagonist triceps brachii (TB) muscles during a sustained isometric contraction performed with the elbow flexors. Methods: Eleven young adults performed 2 isometric contractions until failure at an intensity of 35% of maximal voluntary force separated by one hour in 2 separate sessions. During one session, a-tDCS was applied over the motor cortex for 10 min at the end of the rest period between the 2 fatiguing contractions whereas during the other session, sham stimulation was applied. Surface electromyogramme (EMG) was recorded for BB, BRD and TB during the first (C1) and second (C2) fatiguing contraction. Changes in corticospinal excitability during C1 and C2 were assessed by recording, in the same muscles, motor evoked potential (MEP) elicited by transcranial magnetic stimulation of the motor cortex. Results: Time to failure was briefer for C2 than C1 in both experimental sessions, but the reduction was less pronounced (p = 0.04) after a-tDCS (-14.4 ± 12.7%) than sham stimulation (-23.3 ± 11.9%). In contrast, changes in MEP amplitude and EMG activity in both agonist and antagonist muscles were similar between C1 and C2, and did not differ between sessions (p>0.05). Similarly co-activation did not change during the different contractions (p>0.05). Discussion: In agreement with previous work (1), time to failure of C2 was increased following a-tDCS. However, atDCS did not influence muscle activity (EMG) and corticospinal excitability (MEP) during C2, neither in agonist nor antagonist muscles. These results suggest that the effect of a-tDCS on time to task failure should rely on other neural structures than the corticospinal pathway or on cognitive functions involved during sustained isometric contractions.
© Copyright 2016 21st Annual Congress of the European College of Sport Science (ECSS), Vienna, 6. -9. July 2016. Veröffentlicht von University of Vienna. Alle Rechte vorbehalten.