The Effects of Transcranial Direct Current Stimulation (tDCS) on Fatigue During Maximal Intensity Exercise

Abstract

Transcranial Direct Current Stimulation (tDCS) of the brain has been shown to have profound effects on many physiological and psychological processes, including effects on the autonomic nervous system and fatigue. PURPOSE: The purpose of this study was to investigate the effects tDCS on parasympathetic and sympathetic nervous system modulation and their influence on a maximum effort fatiguing exercise protocol. METHODS: Twenty recreationally active subjects (10 male; 10 female) volunteered to participate in this study. Each individual visited the lab on four occasions. The first visit was a familiarization visit. Visits two through four consisted of a sham treatment, an anodal parasympathetic stimulation treatment, and an anodal sympathetic stimulation treatment, in random order. The subjects sat in a dark, quiet environment for 30-min while receiving the appropriate stimulation. The anode was placed on the T3 area, equidistant between the ear and the CZ point, while the cathode was placed on the contralateral side of the skull, just supraorbital. Following stimulation, the subject completed 50 maximum intensity isokinetic (Biodex medical Systems, Inc., Shirley, New York) leg extensions at an angular velocity of 180°s-1, followed my passive flexion. Autonomic modulation was quantified using time and frequency domain indices of heart rate variability. The data were analyzed using 1x3 repeated measures ANOVAs. RESULTS: For the heart rate variability data there were no significant effects for high frequency power (F1.8,33.2 = 0.80, p = 0.44, Eta2 = 0.04), low frequency power (F1.9,35.4 = 0.98, p = 0.38, Eta2 = 0.05), inter-beat interval (F1.8,35.0 = 0.58, p = 0.55, Eta2 = 0.03), root mean square of successive differences (F2.0,38.0 = 1.32, p = 0.28, Eta2 = 0.07), variance (F2.0,38.0 = 1.69, p = 0.20, Eta2 = 0.08), or SD-1 (F2.0,38.0 = 1.32, p = 0.28, Eta2 = 0.07). Likewise, there was no significant effect of tDCS on mean torque (F2.0,37.5 = 0.73, p = 0.49, Eta2 = 0.04) or peak torque (F2.0,38.0 = 0.22, p = 0.80, Eta2 = 0.01). CONCLUSION: In contrast to previously published studies, the results of this study showed no effects of tDCS on cardiovascular autonomic modulation or fatigue during high intensity exercise. Discrepancies between these results and other studies may be due to differences in stimulation protocol, brain area of stimulation, and/or exercise modality.