The Efficacy of Transcranial Direct Current Stimulation to Enhance Endurance Exercise Performance

In the last two decades, non-invasive brain stimulation techniques such as transcranial direct current stimulation (tDCS) have been proposed to increase endurance capacity within exhaustive exercise trials. Consequently, interest in the use of tDCS has spread throughout research, commercial and public communities. Despite the promising findings of an ergogenic effect detailed within exhaustive exercise, the mechanisms of action underlying tDCS are uncertain and the efficacy of tDCS to enhance self-paced performance is inconclusive. Therefore, this thesis explored the efficacy of tDCS to enhance endurance exercise performance. The first experimental chapter (chapter 2) demonstrated that anodal tDCS applied to the dorsolateral prefrontal cortex (DLPFC) in a bilateral montage had no significant effect on 15 minute cycling TT performance. Study two explored the effect of tDCS delivered to the DLPFC in an extracephalic montage on cycling TT performance. An extracephalic montage is suggested to avoid the complications associated with the cathodal electrode seen in cephalic and bilateral montages. This study also demonstrated that tDCS had no significant effect on TT performance. Study three explored the effect of anodal tDCS applied through the Halo Sport Neurostimulation system on physiological adaptation to endurance training. This study demonstrated that tDCS applied to the motor cortex (M1) during 6 weeks of high intensity interval training did not augment the training response to a greater extent than the sham group. Finally, study four investigated the capability of the Halo Sport Neurostimulation System to induce changes in corticospinal excitability. The results demonstrated that this device had no effect on the corticospinal excitability of the M1 when delivered at rest and during submaximal exercise. The present thesis demonstrates that the acute and chronic applications of conventional tDCS are not viable methods of enhancing endurance performance or increasing the physiological adaptations to training. Therefore, the use of tDCS to enhance performance of recreationally active participants cannot be recommended.