The influence of transcranial direct current stimulation on pain affect and endurance exercise

Abstract

Introduction: Transcranial direct current stimulation (tDCS) is a non-invasive form of electrical brain stimulation that has been offered as a novel method to enhance endurance exercise performance. While the underlying mechanisms for these performance enhancing effects remain unclear, one explanation relates to a reduction in pain experienced during exercise. Research examining this explanation however, has failed to consider the widely recognised motivational-affective component of the pain experience. Objectives: The present study aimed to determine whether pain experienced during exercise involves an affective component, and whether a reduction in pain affect may account for the performance-enhancing effects of tDCS. Methods: Healthy, pain-free individuals (n = 23), including 11 males and 12 females aged 18–39 years, were recruited for participation in a randomised, placebo-controlled, participant blinded, repeated measures design study. Participants attended two testing sessions separated by at least five days. In each session, participants received either active (2 mA, 20 min) or sham (placebo control) tDCS delivered to the left dorsolateral prefrontal cortex (DLPFC). Participants then completed an endurance exercise task comprised of a sustained isometric contraction of the leg extensors performed to exhaustion at an intensity corresponding to 25% of their maximal voluntary contraction. During this task, participants provided ratings of pain intensity and pain unpleasantness at 20 s intervals. Results: Ratings of pain intensity (p < .001) and pain affect (p < .001) increased throughout the endurance exercise task. However, the tDCS intervention did not enhance endurance exercise performance (p > .05), nor manipulate perceptions of pain affect (p > .05). Conclusions: While the endurance exercise task induced pain affect, tDCS over the left DLPFC was not effective in reducing this component of the pain experience, nor enhancing exercise performance.