Bilateral extracephalic transcranial direct current stimulation improves endurance performance in healthy individuals

Abstract

Background: Transcranial direct current stimulation (tDCS) has been used to enhance endurance performance but its precise mechanisms and effects remain unknown.

Objective: To investigate the effect of bilateral tDCS on neuromuscular function and performance during a cycling time to task failure (TTF) test.

Methods: Twelve participants in randomized order received a placebo tDCS (SHAM) or real tDCS with two cathodes (CATHODAL) or two anodes (ANODAL) over bilateral motor cortices and the opposite electrode pair over the ipsilateral shoulders. Each session lasted 10 min and current was set at 2 mA. Neuromuscular assessment was performed before and after tDCS and was followed by a cycling time to task failure (TTF) test. Heart rate (HR), ratings of perceived exertion (RPE), leg muscle pain (PAIN) and blood lactate accumulation (ΔB[La^-]) in response to the cycling TTF test were measured.

Results: Corticospinal excitability increased in the ANODAL condition (P < 0.001) while none of the other neuromuscular parameters showed any change. Neuromuscular parameters did not change in the SHAM and CATHODAL conditions. TTF was significantly longer in the ANODAL (P = 0.003) compared to CATHODAL and SHAM conditions (12.61 ± 4.65 min; 10.61 ± 4.34 min; 10.21 ± 3.47 min respectively), with significantly lower RPE and higher ΔB[La^-] (P < 0.001). No differences between conditions were found for HR (P = 0.803) and PAIN during the cycling TTF test (P = 0.305).

Conclusion: Our findings demonstrate that tDCS with the anode over both motor cortices using a bilateral extracephalic reference improves endurance performance.

Keywords: Endurance performance; Fatigue; Perception of effort; tDCS.

Fig. 1.

Overall view of transcranial direct current stimulation (tDCS) montages and phases of the experimental protocol. Panel A. Schematic illustration showing placement of electrodes. The montage for ANODAL condition and for CATHODAL condition are respectively illustrated on the left and right side of the panel. Anodal electrode (A) and cathodal electrode (C). Panel B. Maximal muscular wave (M-wave); motor evoked potential (MEP); maximal voluntary contraction (MVC); transcranial direct current stimulation (tDCS); cycling time to task failure (TTF) test.

Fig. 2.

Effects of transcranial direct current stimulation (tDCS) on performance and perceptual/physiological responses during the cycling TTF test. Panel A shows time to task failure (TTF) in different conditions; Panel B shows blood lactate accumulation (ΔB[La⁻]) in different conditions; Panel C, D and E show respectively time courses of rating of perceived exertion(RPE), leg muscle pain (PAIN) and heart rate (HR) during the TTF test. *Denotes significant main effect of condition (P < 0.05); §Denotes significant difference from CATHODAL and SHAM (P < 0.05); Data are presented as mean ± SD (n = 12).

Fig. 3.

Neuromuscular function before and after transcranial direct current stimulation (tDCS). Panel A shows maximal voluntary contraction (MVC) torque; Panel B shows voluntary activation level (VAL); Panel C shows peak torque of the doublet (Doublet). Data are presented as mean ± SD (n = 12).

Fig. 4.

Corticospinal response before and after transcranial direct current stimulation (tDCS). Panel A shows motor evoked potential area (MEP_area) and muscular wave (M_wave) MEP_area/M-wave ratio. Panel B shows MEP peak to peak amplitude (MEP_amp). Panel C shows MEP peak to peak duration (MEP_dur); Panel D shows MEP cortical silent period (CSP); §Denotes significant difference from CATHODAL and SHAM (P < 0.05); †Denotes significant condition × time interaction (P < 0.05). Data are presented as mean ± SD (n = 12).