Anodal tDCS over the left DLPFC but not M1 increases muscle activity and improves psychophysiological responses, cognitive function, and endurance performance in normobaric hypoxia: a randomized controlled trial

Abstract

Background Transcranial direct current stimulation (tDCS) has been shown to have positive effects on exercise performance and cognitive function in the normal ambient condition. Hypoxia is deemed a stressful situation with detrimental effects on physiological, psychological, cognitive, and perceptual responses of the body. Nevertheless, no study has evaluated the efficacy of tDCS for counteracting the negative effects of hypoxic conditions on exercise performance and cognition so far. Hence, in the present study, we investigated the effects of anodal tDCS on endurance performance, cognitive function, and perceptual responses in hypoxia. Participants and methods Fourteen endurance-trained males participated in five experimental sessions. After familiarization and measuring peak power output in hypoxia, in the first and second sessions, through the 3rd to 5th sessions, participants performed a cycling endurance task until exhaustion after 30 min hypoxic exposure at resting position followed by 20 min of anodal stimulation of the motor cortex (M1), left dorsolateral prefrontal cortex (DLPFC), or sham-tDCS. Color-word Stroop test and choice reaction time were measured at baseline and after exhaustion. Time to exhaustion, heart rate, saturated O2, EMG amplitude of the vastus lateralis, vastus medialis, and rectus femoris muscles, RPE, affective response, and felt arousal were also measured during the task under hypoxia. Results The results showed a longer time to exhaustion (+ 30.96%, p=0.036), lower RPE (− 10.23%, p = 0.045) and higher EMG amplitude of the vastus medialis muscle (+ 37.24%, p=0.003), affective response (+ 260%, p=0.035) and felt arousal (+ 28.9%, p=0.029) in the DLPFC tDCS compared to sham. The choice reaction time was shorter in DLPFC tDCS compared to sham (− 17.55%, p=0.029), and no differences were seen in the color-word Stroop test among the conditions under hypoxia. M1 tDCS resulted in no significant effect for any outcome measure. Conclusions We concluded that, as a novel finding, anodal stimulation of the left DLPFC might provide an ergogenic aid for endurance performance and cognitive function under the hypoxic condition probably via increasing neural drive to the working muscles, lowering RPE, and increasing perceptual responses.

Effect of tDCS targeting the M1 or left DLPFC on physical performance, psychophysiological responses, and cognitive function in repeated all-out cycling: a randomized controlled trial

“…In M1 and DLPFC conditions, the electric current was gradually ramped up for 30 s, maintained at 2 mA for 20 min, and then progressively ramped down for 30 s. For the sham condition, the DLPFC montage was used but the 2-mA current was maintained active only for 30 s and then was ramped down for 30 s. This sham tDCS procedure has been shown to effectively blind participants [ 30 , 37 – 39 ]. Moreover, to avoid creating expectations effects [ 40 , 41 ], participants were not informed that there would be a sham stimulation condition [ 30 ].…”

“…To assess participants’ blinding effectiveness, participants completed a questionnaire that lists the sensations and level of intensity experienced during the stimulation after each experimental session [ 46 ]. This questionnaire has been used in previous studies involving tDCS and exercise performance [ 30 , 47 ]. Itching, pain, burning, warmth/heat, pitching, metallic/iron taste, fatigue, and other sensations (open questions) were all listed on the questionnaire.…”

“…The Stroop test is a standard and valid test for measuring inhibitory control which is considered an important factor in regulating strenuous physical tasks by inhibiting unpleasant sensations during exercise [ 18 ]. It has previously been used in other studies with a similar design [ 18 , 22 , 30 , 60 ]. The standardized version of the paper-based color-word Stroop test revised by Golden (1975), consisting of 3 cards listing 100 items each presented in a “5 (columns) × 20 (rows)” matrix was used in the present study.…”

“…The effect of tDCS may depend on the stimulation parameters such as the nominal target, electrode position, current intensity, density, duration, and timing of application. However, to the best of our knowledge, very few studies have compared the effect of tDCS montage on exercise performance [ 30 ], and no study was performed on repeated anaerobic maximal exercise performance. Moreover, most of the previous studies have investigated the effect of tDCS on sprint-interval performance (repeated sprints with ≤ 10 s in duration) [ 22 – 24 ] in which the phosphagen system is the main energy source [ 26 ] while there is also no study investigating the efficacy of tDCS in sporting activities that require speed endurance or speed strength in which repeated sprints with longer duration (15 to 90 s) must be performed.…”

“…Hence, we aimed to investigate the effects of anodal tDCS over M1 and DLPFC on anaerobic performance in repeated all-out anaerobic exercise, physiological, psychophysiological, and cognitive responses. We hypothesized that both tDCS montages targeting M1 and DLPFC (a) would improve repeated anaerobic performance; (b) increase the electromyographic (EMG) amplitude of the tight muscles; (c) decrease RPE; (d) increase the affective responses; and (e) improve the cognitive performance in repeated all-out cycling task [ 18 , 30 , 32 – 35 ].…”