Simulating tDCS electrode placement to stimulate both M1 and SMA enhances motor performance and modulates cortical excitability depending on current flow direction

Introduction

The conventional method of placing transcranial direct current stimulation (tDCS) electrodes is just above the target brain area. However, this strategy for electrode placement often fails to improve motor function and modulate cortical excitability. We investigated the effects of optimized electrode placement to induce maximum electrical fields in the leg regions of both M1 and SMA, estimated by electric field simulations in the T1and T2-weighted MRI-based anatomical models, on motor performance and cortical excitability in healthy individuals.

Methods

A total of 36 healthy volunteers participated in this randomized, triple-blind, sham-controlled experiment. They were stratified by sex and were randomly assigned to one of three groups according to the stimulation paradigm, including tDCS with (1) anodal and cathodal electrodes positioned over FCz and POz, respectively, (A-P tDCS), (2) anodal and cathodal electrodes positioned over POz and FCz, respectively, (P-A tDCS), and (3) sham tDCS. The sit-to-stand training following tDCS (2 mA, 10 min) was conducted every 3 or 4 days over 3 weeks (5 sessions total).

Results

Compared to sham tDCS, A-P tDCS led to significant increases in the number of sit-to-stands after 3 weeks training, whereas P-A tDCS significantly increased knee flexor peak torques after 3 weeks training, and decreased short-interval intracortical inhibition (SICI) immediately after the first session of training and maintained it post-training.

Discussion

These results suggest that optimized electrode placement of the maximal EF estimated by electric field simulation enhances motor performance and modulates cortical excitability depending on the direction of current flow.

Does a single session of transcranial direct current stimulation enhance both physical and psychological performance in national- or international-level athletes? A systematic review

Some studies showed that a single session of transcranial direct current stimulation (tDCS) has the potential of modulating motor performance in healthy and athletes. To our knowledge, previously published systematic reviews have neither comprehensively investigated the effects of tDCS on athletic performance in both physical and psychological parameters nor investigated the effects of tDCS on high-level athletes. We examined all available research testing a single session of tDCS on strength, endurance, sport-specific performance, emotional states and cognitive performance for better application in competition and pre-competition trainings of national- or international-level athletes. A systematic search was conducted in PubMed, Web of Science, EBSCO, Embase, and Scopus up until to June 2023. Studies were eligible when participants had sports experience at a minimum of state and national level competitions, underwent a single session of tDCS without additional interventions, and received either sham tDCS or no interventions in the control groups. A total of 20 experimental studies (224 participants) were included from 18 articles. The results showed that a single tDCS session improved both physical and psychological parameters in 12 out of the 18 studies. Of these, six refer to the application of tDCS on the motor system (motor cortex, premotor cortex, cerebellum), five on dorsolateral prefrontal cortex and two on temporal cortex. The most sensitive to tDCS are strength, endurance, and emotional states, improved in 67%, 75%, and 75% of studies, respectively. Less than half of the studies showed improvement in sport-specific tasks (40%) and cognitive performance (33%). We suggest that tDCS is an effective tool that can be applied to competition and pre-competition training to improve athletic performance in national- or international-level athletes. Further research would explore various parameters (type of sports, brain regions, stimulation protocol, athlete level, and test tasks) and neural mechanistic studies in improving efficacy of tDCS interventions. Systematic Review Registration: https://www.crd.york.ac.uk/prospero/display_record.php?ID=CRD42022326989, identifier CRD42022326989.

The effect of warm-up with transcranial direct current stimulation on performance factors in collegiate golfers

PURPOSE

This study aimed to determine the effects of warm-up using transcranial direct current stimulation (tDCS) on performance factors in collegiate golfers and to provide a scientific basis for the effectiveness and methodology of tDCS. We sought to compare the effects of tDCS as an additional treatment during warm-up. tDCS is generally activated when a small electric current is applied to the motor cortex of the cerebral cortex, which has been reported to be helpful in improving motor function. Therefore, we sought to prove the effectiveness of combined warm-up exercise and tDCS.

METHODS

Twenty-two collegiate male golfers were divided into tDC- (tDCS; n=11) and sham-treated (sham; n=11) groups. To examine performance factors, the following were assessed following tDCS application: carry, clubhead speed (CHS), ball speed (BS) for driver performance, countermovement jump (CMJ) for lower extremity muscle power, global rating of change (GRC) for the subjective change in condition of the participants, and test of attentional interpersonal style (TAIS) for concentration.

RESULTS

This study showed that warm-up with tDCS had positive effects on carry (p=.004), CHS (p=.019), BS (p=.017) of driver performance, CMJ (p=.002), and GRC (p=.005), however, no significant effect on TAIS was found, which suggest that the effects of the warm-up with tDCS were significant for driver performances, CMJ, and GRC.

CONCLUSION

Future studies should independently validate the effectiveness of tDCS and apply it to different situations and timeframes, such as training and competitions, to provide new alternative strategies or performance improvement.

The impact of cerebellar transcranial direct current stimulation on isometric bench press performance in trained athletes

Athletic development centers on optimizing performance, including technical skills and fundamental motor abilities such as strength and speed. Parameters such as maximum contraction force and rate of force development, influence athletic success, although performance gains become harder to achieve as athletic abilities increase. Non-invasive transcranial direct current stimulation of the cerebellum (CB-tDCS) has been used successfully to increase force production in novices, although the potential effects in athletes remain unexplored. The present study examined the effects of CB-tDCS on maximum isometric voluntary contraction force (MVCiso) and isometric rate of force development (RFDiso) during a bench press task in well-trained athletes. 21 healthy, male, strength-trained athletes participated in a randomized, sham-controlled, double-blinded crossover design. Each participant completed the isometric bench press (iBP) task on two separate days, with at least 5 days between sessions, while receiving either CB-tDCS or sham stimulation. Electromyography (EMG) recordings of three muscles involved in iBP were acquired bilaterally to uncover differences in neuromuscular activation and agonist-antagonist co-contraction between conditions. Contrary to our hypothesis, no significant differences in MVCiso and RFDiso were observed between CB-tDCS and sham conditions. Furthermore, no tDCS-induced differences in neuromuscular activation or agonist-antagonist co-contraction were revealed. Here, we argue that the effects of CB-tDCS on force production appear to depend on the individual's training status. Future research should study individual differences in tDCS responses between athletes and novices, as well as the potential of high-definition tDCS for precise brain region targeting to potentially enhance motor performance in athletic populations.

Effects of bi-hemispheric anodal transcranial direct current stimulation on soccer player performance: a triple-blinded, controlled, and randomized study

The search for increased performance and physical performance are linked to the use of ergogenic resources. The vertical jump is one of the measures commonly used to evaluate the performance of lower limbs in athletes. Transcranial direct current stimulation (tDCS) is a non-invasive, safe, economically viable technique that can modulate cortical excitability, which can influence the increase in the performance of athletes in general. This study aimed to investigate whether the use of tDCS on the primary motor cortex (M1) improves the performance of soccer players. A cross-sectional study was conducted. Twenty-seven players were randomized into three groups: Active tDCS group (n = 9), Sham group (n = 9), and control group (n = 9). Stimulation was applied at 2 mA for 15 min using a cephalic mount. Visual Pain Scale (VAS) and Subjective Recovery Scale (SRS) were monitored before and after tDCS. In addition, the participants performed the Countermovement Jump (CMJ) before and after the stimulation intercalated with Heart Rate (HR) and Rating of Perceived Exertion (RPE CR-10). No differences were found in any of the performance variables analyzed (p > 0.05) nor in the responses of HR (p > 0.05), RPE (p > 0.05), VAS (p > 0.05), and SRS (p > 0.05) between groups. The tDCS in M1 did not change the performance of the vertical jump, and there was no improvement in the subjective scales. New studies should also be developed with different stimulus intensities in different cortical areas and sports modalities.

Evaluation of Transcranial Direct Current Stimulation in Motor Function and Neural Rehabilitation

ABSTRACT

Transcranial direct current stimulation (tDCS) is used in neuromodulation to regulate the excitability of the cerebral cortex and induce neural plasticity. It was initially used to rehabilitate patients with neurological diseases. However, with the increasing number of studies involving healthy individuals, this technology is currently used in the field of sports as well. The administration of tDCS to the cerebral cortex, especially over the primary motor cortex (M1), has been found to improve muscle strength, enhance endurance, and promote motor skills in humans. This study mainly summarizes the effects of tDCS on motor function, mainly involving motor promotion of tDCS in healthy athletes and nonathletes, and in patients diagnosed with neurological diseases. The tDCS is a promising and effective tool used to promote motor function by regulating cortical excitability. However, no consensus is available regarding individually appropriate models of tDCS.

The impact of bilateral anodal transcranial direct current stimulation of the premotor and cerebellar cortices on physiological and performance parameters of gymnastic athletes: a randomized, cross-over, sham-controlled study

Professional sports performance relies critically on the interaction between the brain and muscles during movement. Transcranial direct current stimulation (tDCS) is a noninvasive brain stimulation technique which modulates cortical excitability and can be used to improve motor performance in athletes. The present study aimed to investigate the effect of bilateral anodal tDCS (2 mA, 20 min) over the premotor cortex or cerebellum on motor and physiological functions and peak performance of professional gymnastics athletes. Seventeen professional gymnastics athletes participated in a randomized, sham-controlled, crossover study. In this study, we assessed the efficacy of two anodal tDCS protocols (2 mA, 20 min) with stimulation over the bilateral premotor cortex or cerebellum with the return electrodes placed over the opposite supraorbital areas. Power speed, strength coordination, endurance, static and dynamic strength, static and dynamic flexibility, and rating of perceived exertion were measured before and immediately after tDCS interventions (bilateral anodal tDCS over premotor cortices, anodal tDCS over the cerebellum, and sham tDCS). Additionally, physiological muscle performance parameters, including maximum voluntary isometric contraction (MVIC) of upper body muscles, were assessed during tDCS. Bilateral anodal tDCS over the premotor cortex, compared to anodal tDCS over the cerebellum and sham tDCS conditions, significantly improved power speed, strength coordination, and static and dynamic strength variables of professional gymnastics athletes. Furthermore, bilateral anodal tDCS over the cerebellum, compared to sham tDCS, significantly improved strength coordination. Moreover, bilateral premotor anodal tDCS significantly increased MVIC of all upper body muscles during stimulation, while anodal tDCS over the cerebellum increased MVIC in only some muscles. Bilateral anodal tDCS over the premotor cortex, and to a minor degree over the cerebellum, might be suited to improve some aspects of motor and physiological functions and peak performance levels of professional gymnastics athletes.Clinical Trial Registration ID: IRCT20180724040579N2.

Reduced isometric knee extensor force following anodal transcranial direct current stimulation of the ipsilateral motor cortex

BACKGROUND

The goal of this study was to determine if 10-min of anodal transcranial direct current stimulation (a-tDCS) to the motor cortex (M1) is capable of modulating quadriceps isometric maximal voluntary contraction (MVC) force or fatigue endurance contralateral or ipsilateral to the stimulation site.

METHODS

In a randomized, cross-over design, 16 (8 females) individuals underwent two sessions of a-tDCS and two sham tDCS (s-tDCS) sessions targeting the left M1 (all participants were right limb dominant), with testing of either the left (ipsilateral) or right (contralateral) quadriceps. Knee extensor (KE) MVC force was recorded prior to and following the a-tDCS and s-tDCS protocols. Additionally, a repetitive MVC fatiguing protocol (12 MVCs with work-rest ratio of 5:10-s) was completed following each tDCS protocol.

RESULTS

There was a significant interaction effect for stimulation condition x leg tested x time [F(1,60) = 7.156, p = 0.010, ηp2 = 0.11], which revealed a significant absolute KE MVC force reduction in the contralateral leg following s-tDCS (p < 0.001, d = 1.2) and in the ipsilateral leg following a-tDCS (p < 0.001, d = 1.09). A significant interaction effect for condition x leg tested [F(1,56) = 8.12, p = 0.006, ηp2 = 0.13], showed a significantly lower ipsilateral quadriceps (to tDCS) relative MVC force with a-tDCS, versus s-tDCS [t(15) = -3.07, p = 0.016, d = -0.77]. There was no significant difference between the relative contralateral quadriceps (to tDCS) MVC force for a-tDCS and s-tDCS. Although there was an overall significant [F(1,56) = 8.36, p < 0.001] 12.1% force decrease between the first and twelfth MVC repetitions, there were no significant main or interaction effects for fatigue index force.

CONCLUSION

a-tDCS may be ineffective at increasing maximal force or endurance and instead may be detrimental to quadriceps force production.

The influence of a single transcranial direct current stimulation session on physical fitness in healthy subjects: a systematic review

Physical fitness is of indisputable importance for both health, and sports. Currently, the brain is being increasingly recognized as a contributor to physical fitness. Hereby, transcranial direct current stimulation (tDCS), as an ergogenic aid, has gained scientific interest. The current PRISMA-adherent review aimed to examine the effect of tDCS on the three core components of physical fitness: muscle strength, -endurance and cardiopulmonary endurance. Randomized controlled- or cross-over trials evaluating the effect of a single tDCS session (vs. sham) in healthy individuals were included. Hereby, a wide array of tDCS-related factors (e.g., tDCS montage and dose) was taken into account. Thirty-five studies (540 participants) were included. Between-study heterogeneity in factors such as age, activity level, tDCS protocol, and outcome measures was large. The capacity of tDCS to improve physical fitness varied substantially across studies. Nevertheless, muscle endurance was most susceptible to improvements following anodal tDCS (AtDCS), with 69% of studies (n = 11) investigating this core component of physical fitness reporting positive effects. The primary motor cortex and dorsolateral prefrontal cortex were targeted the most, with positive results being reported on muscle and cardiopulmonary endurance. Finally, online tDCS seemed most beneficial, and no clear relationship between tDCS and dose-related parameters seemed present. These findings can contribute to optimizing tDCS interventions during the rehabilitation of patients with a variety of (chronic) diseases such as cardiovascular disease. Therefore, future studies should focus on further unraveling the potential of AtDCS on physical fitness and, more specifically, muscle endurance in both healthy subjects and patients suffering from (chronic) diseases. This study was registered in Prospero with the registration number CRD42021258529. "To enable PROSPERO to focus on COVID-19 registrations during the 2020 pandemic, this registration record was automatically published exactly as submitted. The PROSPERO team has not checked eligibility".

Single-session anodal transcranial direct current stimulation to enhance sport-specific performance in athletes: A systematic review and meta-analysis

BACKGROUND

Transcranial direct current stimulation (tDCS) has emerged as a promising and feasible method to improve motor performance in healthy and clinical populations. However, the potential of tDCS to enhance sport-specific motor performance in athletes remains elusive.

OBJECTIVE

We aimed at analyzing the acute effects of a single anodal tDCS session on sport-specific motor performance changes in athletes compared to sham.

METHODS

A systematic review and meta-analysis was conducted in the electronic databases PubMed, Web of Science, and SPORTDiscus. The meta-analysis was performed using an inverse variance method and a random-effects model. Additionally, two subgroup analyses were conducted (1) depending on the stimulated brain areas (primary motor cortex (M1), temporal cortex (TC), prefrontal cortex (PFC), cerebellum (CB)), and (2) studies clustered in subgroups according to different sports performance domains (endurance, strength, visuomotor skill).

RESULTS

A total number of 19 studies enrolling a sample size of 258 athletes were deemed eligible for inclusion. Across all included studies, a significant moderate standardized mean difference (SMD) favoring anodal tDCS to enhance sport-specific motor performance could be observed. Subgroup analysis depending on cortical target areas of tDCS indicated a significant moderate SMD in favor of anodal tDCS compared to sham for M1 stimulation.

CONCLUSION

A single anodal tDCS session can lead to performance enhancement in athletes in sport-specific motor tasks. Although no definitive conclusions can be drawn regarding the modes of action as a function of performance domain or stimulation site, these results imply intriguing possibilities concerning sports performance enhancement through anodal M1 stimulation.

Effects of Transcranial Direct Current Stimulation over the Primary Motor Cortex in Improving Postural Stability in Healthy Young Adults

Transcranial direct current stimulation (tDCS) over the primary motor cortex (M1) is of increasing interest to improve motor performance in healthy adults and patients with respective deficits. This study aimed to examine whether tDCS over M1 can improve static and dynamic postural stability in young healthy adults. Seventeen healthy participants (mean age = 25.14 ± 2.50 (standard deviation, SD) years) received sham and anodal tDCS (2 mA) over the vertex at the Cz electrode position for 15 min. Static and dynamic postural stability were evaluated before and immediately after tDCS. The center of pressure (COP) sway area (COPSA) and COP maximum displacements to medio-lateral (COPML) and antero-posterior directions (COPAP) were used to evaluate static postural stability. The anterior−posterior stability index (APSI), medial−lateral stability index (MLSI), vertical stability index (VSI), dynamic postural stability index (DPSI), and time to stabilization (TTS) in forward (FL), 45° anterior lateral (LL), and 45° anterior medial (ML) direction landing, as well as the Y-balance composite score (YBTCS) were used to assess dynamic postural stability. The results showed that the LL-TTS (p = 0.044), non-dominant leg COPSA (p = 0.015), and YBTCS (p < 0.0001) were significantly improved in the real stimulation as compared with the sham stimulation session, and anodal tDCS significantly changed dominant leg COPAP (p = 0.021), FL-APSI (p < 0.0001), FL-TTS (p = 0.008), ML-TTS (p = 0.002), non-dominant leg YBTCS (p < 0.0001), and dominant leg YBTCS (p = 0.014). There were no significant differences in all obtained balance values in the sham stimulation session, except for non-dominant leg YBTCS (p = 0.049). We conclude that anodal tDCS over M1 has an immediate improving effect on static postural stability and dynamic performance in young healthy adults. This makes tDCS a promising adjuvant rehabilitation treatment to enhance postural stability deficits in the future.

Transcranial Direct Current Stimulation Does Not Affect Sprint Performance or the Horizontal Force-Velocity Profile

Purpose: The aim of this study was to explore the effects of transcranial direct current stimulation (tDCS) on sprint performance and the horizontal force-velocity (F-v) profile. Method: Thirty-two healthy subjects (25 men and 7 women; age = 21.8 ± 2.4 years) completed three sessions separated by 1 week following a double-blinded crossover design. Each session consisted of two maximal sprints of 30 meters that were performed after applying ANODAL, CATHODAL or SHAM tDCS over the left dorsolateral prefrontal cortex (DLPFC) for 15 minutes at 2 mA. The 30-m time and the horizontal F-v profile variables (theoretical maximal force [F₀], theoretical maximal velocity, Fv slope, maximal power [Pmax], decrease in the ratio of horizontal-to-resultant force, and maximal ratio of horizontal-to-resultant force) were compared between the tDCS conditions. Results: No significant differences between the tDCS conditions were observed for any variable (p range = 0.061 to 0.842). The magnitude of the differences was negligible for most of the comparisons (effect size [ES] < 0.20) with the only exception of P_max and F₀ which were greater for the ANODAL compared to the SHAM condition (both ES = 0.20). Conclusions: The application of tDCS over the DLPFC is not effective to increase non-fatigued sprint performance.

The Effect of Anodal Transcranial Direct Current Stimulation on Quadriceps Maximal Voluntary Contraction, Corticospinal Excitability, and Voluntary Activation Levels

ABSTRACT

Kristiansen, M, Thomsen, MJ, Nørgaard, J, Aaes, J, Knudsen, D, and Voigt, M. The effect of anodal transcranial direct current stimulation on quadriceps maximal voluntary contraction, corticospinal excitability, and voluntary activation levels. J Strength Cond Res 36(6): 1540-1547, 2022-Anodal transcranial direct current stimulation (a-tDCS) has previously been shown to improve maximal isometric voluntary contraction (MVIC), possibly through an upregulation of corticospinal excitability. Because muscle strength is an essential part of the performance of many sports, any ergogenic effect of a-tDCS on this parameter could potentially increase performance outcomes. The purpose of this study was to investigate the effect of a-tDCS on MVIC, voluntary activation levels (VALs), and corticospinal excitability, assessed by eliciting motor-evoked potentials (MEPs), in untrained subjects. Thirteen subjects completed 2 test sessions in which they received either a-tDCS or sham stimulation for 3 consecutive intervals of 10 minutes, separated by 5-minute breaks. Before and after each stimulation session, transcranial magnetic stimulation was used to elicit MEPs, and femoral nerve stimulation was used to assess VAL by measuring twitch torque during an MVIC test and in a relaxed state. Two-way analyses of variance with statistical significance set at p ≤ 0.05 were used to test for differences. A significant main effect was identified, as the MVIC pre-test (271.2 ± 56.6 Nm) was on average 4.1% higher compared to the post-test (260.6 ± 61.4 Nm) (p = 0.05). No significant differences were found in MEP, MVIC, or VAL as a result of stimulation type or time. In healthy subjects, the potential for improvement in corticospinal excitability may be negligible, which may in turn explain the lack of improvements in MEP, MVIC, and VAL after a-tDCS. The small decrease in MVIC for both conditions and nonsignificant changes in MEP and VAL do not justify the use of a-tDCS in combination with sporting performance in which the intent is to increase maximal isometric strength performance in the quadriceps muscle of healthy subjects.

Non-invasive brain stimulation and neuroenhancement

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The available data frame with a wide parameter space of tES does not allow an overarching protocol recommendation.

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Established engineering risk-management procedures with regard to manufacturing should be followed.

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Consensus among experts is that tES for neuroenhancement is safe as long as tested protocols are followed.

Attempts to enhance human memory and learning ability have a long tradition in science. This topic has recently gained substantial attention because of the increasing percentage of older individuals worldwide and the predicted rise of age-associated cognitive decline in brain functions. Transcranial brain stimulation methods, such as transcranial magnetic (TMS) and transcranial electric (tES) stimulation, have been extensively used in an effort to improve cognitive functions in humans.

Here we summarize the available data on low-intensity tES for this purpose, in comparison to repetitive TMS and some pharmacological agents, such as caffeine and nicotine. There is no single area in the brain stimulation field in which only positive outcomes have been reported. For self-directed tES devices, how to restrict variability with regard to efficacy is an essential aspect of device design and function. As with any technique, reproducible outcomes depend on the equipment and how well this is matched to the experience and skill of the operator. For self-administered non-invasive brain stimulation, this requires device designs that rigorously incorporate human operator factors. The wide parameter space of non-invasive brain stimulation, including dose (e.g., duration, intensity (current density), number of repetitions), inclusion/exclusion (e.g., subject’s age), and homeostatic effects, administration of tasks before and during stimulation, and, most importantly, placebo or nocebo effects, have to be taken into account. The outcomes of stimulation are expected to depend on these parameters and should be strictly controlled. The consensus among experts is that low-intensity tES is safe as long as tested and accepted protocols (including, for example, dose, inclusion/exclusion) are followed and devices are used which follow established engineering risk-management procedures. Devices and protocols that allow stimulation outside these parameters cannot claim to be “safe” where they are applying stimulation beyond that examined in published studies that also investigated potential side effects.

Brain stimulation devices marketed for consumer use are distinct from medical devices because they do not make medical claims and are therefore not necessarily subject to the same level of regulation as medical devices (i.e., by government agencies tasked with regulating medical devices). Manufacturers must follow ethical and best practices in marketing tES stimulators, including not misleading users by referencing effects from human trials using devices and protocols not similar to theirs.

Transcranial Direct Current Stimulation (tDCS) Improves Back-Squat Performance in Intermediate Resistance-Training Men

Purpose: The purpose of this study was to evaluate the effects of anodal tDCS applied over the dorsolateral prefrontal cortex (DLPFC) on muscle endurance in the back-squat exercise. Methods: Eleven healthy males, intermediate in resistance training (RT), aged between 18 and 31 years (25.5 ± 4.4 years) were recruited. In the initial visits (1st and 2nd visits), participants performed a 1RM test to determine the load in the back-squat exercise. Following the two initials visits, participants attended the lab for the two experimental conditions (anodal tDCS and sham), which were completed a week apart, with sessions randomly counterbalanced. The stimulation was applied over the DLPFC for 20 minutes using a 2 mA current intensity. Immediately after the experimental conditions, participants completed three sets of maximum repetitions (80% of 1RM), with a 1-minute recovery interval between each set in the back-squat exercise. Muscle endurance was determined by the total number of repetitions and the number of repetitions in each set. Results: The total number of repetitions was higher in the anodal tDCS condition compared to sham condition (p ≤ .0001). Moreover, the number of repetitions performed in the first set was higher for anodal tDCS condition than in the sham condition (p ≤ .01). Conclusion: This study found improvement in back-squat exercise performance after the application of anodal tDCS. The effects of anodal tDCS applied over DLPFC may be a promising ergogenic resource on muscle endurance in the back-squat exercise.

Halo Sport Transcranial Direct Current Stimulation Improved Muscular Endurance Performance and Neuromuscular Efficiency During an Isometric Submaximal Fatiguing Elbow Flexion Task

The present study examined the effects of transcranial direct current stimulation (tDCS) using Halo Sport on the time to exhaustion (TTE) in relation with muscle activities and corticomuscular coupling of agonist and antagonist muscles during a sustained isometric fatiguing contraction performed with the elbow flexors. Twenty healthy male college students were randomly assigned to tDCS group and control group. The two group participants performed two experimental sessions which consisted of pre-fatigue isometric maximal voluntary contraction (MVC), sustained submaximal voluntary contractions (30% maximal torque) performed to exhaustion, and post-fatigue MVC with the right elbow flexor muscles. Sham stimulation (90 s) and tDCS (20 min) were applied for control and tDCS group participants 20 min prior to the second session test, respectively. MVC strength in pre- and post-fatigue test, TTE, electroencephalogram (EEG), and electromyography (EMG) of biceps brachii (BB) and triceps brachii (TB) were recorded during the tests. It was found that tDCS using the Halo Sport device significantly increased TTE and thus improved muscular endurance performance. The improvement may be partly related to the improvement of neuromuscular efficiency as reflected by decrease of antagonistic muscle coactivation activities, which may be related to cortical originated central processing mechanism of neuromuscular activities.

Transcranial Direct Current Stimulation Enhances Muscle Strength of Non-dominant Knee in Healthy Young Males

Transcranial direct current stimulation (tDCS) has been applied in training and competition, but its effects on physical performance remain largely unknown. This study aimed to observe the effect of tDCS on muscular strength and knee activation. Nineteen healthy young men were subjected to 20 min of real stimulation (2 mA) and sham stimulation (0 mA) over the primary motor cortex (M1) bilaterally on different days. The maximal voluntary contraction (MVC) of the knee extensors and flexors, and surface electromyography (sEMG) of the rectus femoris (RF) and biceps femoris (BF) were recorded before, immediately after, and 30 min after stimulation. MVC, rate of force development (RFD), and sEMG activity were analyzed before and after each condition. MVC of the non-dominant leg extensor and flexor was significantly higher immediately after real stimulation and 30 min after stimulation than before, and MVC of the non-dominant leg flexor was significantly higher 30 min after real stimulation than that after sham stimulation (P < 0.05). The RFD of the non-dominant leg extensor and flexor immediately after real stimulation was significantly higher than before stimulation, and the RFD of the non-dominant leg extensor immediately after real stimulation and 30 min after stimulation was significantly higher than that of sham stimulation (P < 0.05). EMG analysis showed the root mean square amplitude and mean power frequency (MPF) of the non-dominant BF and RF were significantly higher immediately after real stimulation and 30 min after stimulation than before stimulation, and the MPF of the non-dominant BF EMG was significantly higher 30 min after real stimulation than that after sham stimulation (P < 0.05). Bilateral tDCS of the M1 can significantly improve the muscle strength and explosive force of the non-dominant knee extensor and flexor, which might result from increased recruitment of motor units. This effect can last until 30 min after stimulation, but there is no significant effect on the dominant knee.

Transcranial direct current stimulation (tDCS) and sporting performance: A systematic review and meta-analysis of tDCS effects on physical endurance, muscular strength, and visuomotor skills

Transcranial direct current stimulation (tDCS) is a non-invasive brain stimulation technique that has been linked with a range of physiological and cognitive enhancements relevant to sporting performance. As a number of positive and null findings have been reported in the literature, the present meta-analysis sought to synthesise results across endurance, strength, and visuomotor skill domains to investigate if tDCS improves any aspect of sporting performance. Online database searches in August 2020 identified 43 full-text studies which examined the acute effects of tDCS compared to sham/control conditions on physical endurance, muscular strength, and visuomotor skills in healthy adults. Meta-analysis indicated a small overall effect favouring tDCS stimulation over sham/control (standardized mean difference (SMD)=0.25, CI95%[0.14;0.36]). Effects on strength (SMD=0.31, CI95%[0.10;0.51]) and visuomotor (SMD=0.29, CI95%[0.00;0.57]) tasks were larger than endurance performance (SMD=0.18, CI95%[0.00;0.37]). Meta-regressions indicated effect sizes were not related to stimulation parameters, but other factors such as genetics, gender, and experience may modulate tDCS effects. The results suggest tDCS has the potential to be used as an ergogenic aid in conjunction with a specified training regime.

Transcranial Direct Current Stimulation Does Not Improve Countermovement Jump Performance in Young Healthy Men

ABSTRACT

Romero-Arenas, S, Calderón-Nadal, G, Alix-Fages, C, Jerez-Martínez, A, Colomer-Poveda, D, and Márquez, G. Transcranial direct current stimulation does not improve countermovement jump performance in young healthy men. J Strength Cond Res 35(10): 2918-2921, 2021-The main purpose of this study was to report the effects of transcranial direct current stimulation (tDCS) on countermovement jump (CMJ) performance in young healthy men. Seventeen healthy male subjects volunteered for the study (age: 22.4 ± 2.6 years; body mass: 71.8 ± 8.7 kg; height: 174.6 ± 5.9 cm; and CMJ height: 36.8 ± 6.3 cm). After a familiarization session, subjects underwent 3 experimental conditions, 7 days apart, in a randomized, double-blinded crossover design: anodal, cathodal, and sham tDCS. The stimulation was applied over the dorsolateral prefrontal cortex for 15 minutes. During experimental sessions, subjects completed a warm-up and 3 CMJ trials separated by 1 minute before and after each of the 3 experimental conditions. Countermovement jump height and muscular peak power were extracted from the best CMJ in each moment. A 2-way repeated-measures analysis of variance with time and condition as factors were performed for CMJ height and muscular peak power. Effect size analysis was conducted using Cohen's d coefficient. The analysis did not show either significant main effects or interactions for both time and condition factors in the CMJ performance (p > 0.05). Furthermore, effect size was trivial for all conditions (d: 0.01-0.14) in CMJ height and muscular peak power. These findings suggest that tDCS may not be a valuable tool to improve vertical jump performance.

Effects of anodal transcranial direct current stimulation on implicit motor learning and language-related brain function: An fMRI study

AIM

Anodal transcranial direct current stimulation (tDCS) over the left dorsolateral prefrontal cortex (DLPFC) is known as a useful application for improving depressive symptoms or cognitive performance. Antidepressive effects by anodal tDCS over the left DLPFC are expected, but the neural mechanisms of these effects are still unclear. Further, in depression, reduced performance and left prefrontal hypofunction during the verbal fluency task (VFT) are generally known. However, few studies have examined the effect of tDCS on the language-related cerebral network. We aimed to investigate whether anodal tDCS at the left DLPFC affects cognitive performance and the neural basis of verbal fluency.

METHODS

Nineteen healthy volunteers participated in this study. The effects of tDCS on cognitive behavior and cerebral function were evaluated by (i) performance and accuracy of implicit/explicit motor learning task (serial reaction time task/sequential finger-tapping task), and (ii) cerebral activation while the subjects were performing the VFT by using a functional MRI protocol of a randomized sham-controlled, within-subjects crossover design.

RESULTS

Reaction times of the implicit motor learning task were significantly faster with tDCS in comparison with the sham. Further, language-related left prefrontal-parahippocampal-parietal activation was significantly less with tDCS compared with the sham. Significant correlation was observed between shortened response time in serial reaction time task and decreased cerebral activation during VFT with tDCS.

CONCLUSION

Anodal tDCS over the left DLPFC could improve cognitive behavior of implicit motor learning by improving brain function of the frontoparietal-parahippocampal region related to motor learning, as well as language-related regions.

Transcranial direct-current stimulation (tDCS) in the primary motor cortex and its effects on sensorimotor function: a quasi-experimental single-blind sham-controlled trial

The main aim was to assess the short-term effects of active-tDCS (a-tDCS) in the primary motor cortex (anodal stimulation-M1) on sensorimotor variables. These variables included discriminative sensation through the two-point discrimination (2-PD) test, tactile acuity threshold and pressure pain threshold (PPT), and electromyographic (EMG) activity compared with a sham-tDCS (s-tDCS) in healthy individuals. A total of 100 participants were included. Fifty of the participants received the a-tDCS application of 2 mA for 20 min, whereas the remaining fifty received the s-tDCS. The 2-PD and tactile acuity threshold in thenar eminence of the hand and in the dorsal part of the foot and also, PPT and EMG activity during maximal voluntary contraction in the biceps brachii and rectus femoris were assessed before and after the tDCS application. The a-tDCS intervention was not significantly superior to the s-tDCS in any variable. However, significant within-group pre- and post-intervention differences were found in the a-tDCS, such as the tactile acuity threshold in thenar eminence of the hand, with a small effect size (p = .012, d = 0.20) and in the PPT of the rectus femoris, also with a small effect size (p = .001, d =  - 0.17). Regarding EMG activity, a trend towards greater activity was observed in participants with a-tDCS compared with s-tDCS, which showed a trend towards decreased EMG activity. In fact, although no differences were found between the groups, within-group differences were statistically significant in the biceps brachii pre- and postintervention (p = .023, d =  - 0.16, and p = .002, d = 0.18, respectively), and also in the rectus femoris, only in the a-tDCS, with a small effect size (p = .011, d =  - 0.14). This study showed no significant between-group differences in sensorimotor outcomes. A single session of tDCS in isolation appears to produce immediate effects in healthy participants on sensorimotor function; however, these effects were very small.

Effectiveness of Unihemispheric Concurrent Dual-Site Stimulation over M1 and Dorsolateral Prefrontal Cortex Stimulation on Pain Processing: A Triple Blind Cross-Over Control Trial

BACKGROUND

Transcranial direct current stimulation (tDCS) of the motor cortex (M1) produces short-term inhibition of pain. Unihemispheric concurrent dual-site tDCS (UHCDS-tDCS) over the M1 and dorsolateral prefrontal cortex (DLPFC) has greater effects on cortical excitability than when applied alone, although its effect on pain is unknown. The aim of this study was to test if anodal UHCDS-tDCS over the M1 and DLPFC in healthy participants could potentiate conditioned pain modulation (CPM) and diminish pain temporal summation (TS).

METHODS

Thirty participants were randomized to receive a sequence of UHCDS-tDCS, M1-tDCS and sham-tDCS. A 20 min 0.1 mA/cm2 anodal or sham-tDCS intervention was applied to each participant during three test sessions, according to a triple-blind cross-over trial design. For the assessment of pain processing before and after tDCS intervention, the following tests were performed: tourniquet conditioned pain modulation (CPM), pressure pain temporal summation (TS), pressure pain thresholds (PPTs), pressure pain tolerance, mechanosensitivity and cold hyperalgesia. Motor function before and after tDCS intervention was assessed with a dynamometer to measure maximal isometric grip strength.

RESULTS

No statistically significant differences were found between groups for CPM, pressure pain TS, PPT, pressure pain tolerance, neural mechanosensitivity, cold hyperalgesia or grip strength (p > 0.05).

CONCLUSIONS

Neither UHCDS-tDCS nor M1-tDCS facilitated CPM or inhibited TS in healthy subjects following one intervention session.

Transcranial Stimulation Improves Volume and Perceived Exertion but does not Change Power

This study aimed to analyze the acute effect of anodal transcranial direct current stimulation (a-tDCS) over the primary motor cortex (M1) on the volume, perceived exertion, and neuromuscular performance measurements in trained and untrained adults. Twenty-four male adults (12 trained and 12 untrained) participated in this single-blind, randomized, and sham-controlled study. The participants performed three back squat repetitions using the 15RM load with maximal concentric velocity to assess neuromuscular performance before tDCS and 30-min after resistance exercise. Next, they were randomly assigned to a-tDCS over M1 or the sham condition. Participants performed ten sets of parallel back squat with 15RM load and repetitions sustained to momentary muscular failure. The total number of repetitions was higher (p<0.05) and perceived exertion was lower (p<0.05) after a-tDCS in both groups. Peak power, velocity, and force decreased in both groups after the RE session (p<0.05), but with a higher rate in untrained individuals (p<0.05). No significant effect was found for peak power, peak velocity, and peak force (p>0.05). This study suggests that using a-tDCS may improve the total volume of repetitions and perceived exertion in trained and untrained individuals.

Does anodal tDCS improve basketball performance? A randomized controlled trial

Shooting precision as well as dribbling and agility are crucial components of performance in basketball. We examined the effects of anodal tDCS over the dominant primary motor cortex in supporting these basketball specific abilities. Fifty-two sports students were enrolled in a double-blind, randomized, placebo-controlled, crossover trial with two interventions. Twenty minutes of anodal 1 mA tDCS/sham tDCS were applied over the primary motor cortex of the dominant hemisphere. Basketball shooting precision (basketball shooting accuracy test) and basketball specific dribbling and agility (Illinois ball-dribbling test) were tested prior and after each intervention. Basketball shooting precision and basketball specific dribbling and agility improved after real tDCS but not after sham tDCS. ANOVAs show significant intervention*time effects on both the shooting accuracy test (F_1,51= 5.6; P = 0.022) and on the Illinois ball-dribbling test (F_1,51 = 4.5; P = 0.038). Anodal 1 mA tDCS over the dominant primary motor cortex is effective in supporting short-term performance in basketball. However, the available data is insufficient for application of this novel method within the framework of conventional sports training.

Corticospinal and spinal adaptations to motor skill and resistance training: Potential mechanisms and implications for motor rehabilitation and athletic development

Optimal strategies for enhancing strength and improving motor skills are vital in athletic performance and clinical rehabilitation. Initial increases in strength and the acquisition of new motor skills have long been attributed to neurological adaptations. However, early increases in strength may be predominantly due to improvements in inter-muscular coordination rather than the force-generating capacity of the muscle. Despite the plethora of research investigating neurological adaptations from motor skill or resistance training in isolation, little effort has been made in consolidating this research to compare motor skill and resistance training adaptations. The findings of this review demonstrated that motor skill and resistance training adaptations show similar short-term mechanisms of adaptations, particularly at a cortical level. Increases in corticospinal excitability and a release in short-interval cortical inhibition occur as a result of the commencement of both resistance and motor skill training. Spinal changes show evidence of task-specific adaptations from the acquired motor skill, with an increase or decrease in spinal reflex excitability, dependant on the motor task. An increase in synaptic efficacy of the reticulospinal projections is likely to be a prominent mechanism for driving strength adaptations at the subcortical level, though more research is needed. Transcranial electric stimulation has been shown to increase corticospinal excitability and augment motor skill adaptations, but limited evidence exists for further enhancing strength adaptations from resistance training. Despite the logistical challenges, future work should compare the longitudinal adaptations between motor skill and resistance training to further optimise exercise programming.

Systematic Review of the Impact of Transcranial Direct Current Stimulation on the Neuromechanical Management of Foot and Ankle Physical Performance in Healthy Adults

Objective: This study aims to review existing literature regarding the effects of transcranial direct current stimulation (tDCS) on the physical performances of the foot and ankle of healthy adults and discuss the underlying neurophysiological mechanism through which cortical activities influence the neuromechanical management of the physical performances of the foot and ankle.

Methods: This systematic review has followed the recommendations of the Preferred Reporting Items for Systematic reviews and Meta-Analyses. A systematic search was performed on PubMed, EBSCO, and Web of Science. Studies were included according to the Participants, Intervention, Comparison, Outcomes, and Setting inclusion strategy. The risk of bias was assessed through the Cochrane Collaboration tool, and the quality of each study was evaluated through the Physiotherapy Evidence Database (PEDro) scale.

Results: The electronic search resulted in 145 studies. Only eight studies were included after screening. The studies performed well in terms of allocation, blinding effectiveness, and selective reporting. Besides, the PEDro scores of all the studies were over six, which indicated that the included studies have high quality. Seven studies reported that tDCS induced remarkable improvements in the physical performances of the foot and ankle, including foot sole vibratory and tactile threshold, toe pinch force, ankle choice reaction time, accuracy index of ankle tracking, and ankle range of motion, compared with sham.

Conclusion: The results in these studies demonstrate that tDCS is promising to help improve the physical performances of the foot and ankle. The possible underlying mechanisms are that tDCS can ultimately influence the neural circuitry responsible for the neuromechanical regulation of the foot and ankle and then improve their physical performances. However, the number of studies included was limited and their sample sizes were small; therefore, more researches are highly needed to confirm the findings of the current studies and explore the underlying neuromechanical effects of tDCS.

The Immediate Effects of Transcranial Direct Current Stimulation on Quadriceps Muscle Function in Individuals With a History of Anterior Cruciate Ligament Reconstruction: A Preliminary Investigation

CONTEXT

Altered quadriceps activation is common following anterior cruciate ligament reconstruction (ACLR), and can persist for years after surgery. These neural deficits are due, in part, to chronic central nervous system alterations. Transcranial direct current stimulation (tDCS) is a noninvasive modality, that is, believed to immediately increase motor neuron activity by stimulating the primary motor cortex, making it a promising modality to use improve outcomes in the ACLR population.

OBJECTIVE

To determine if a single treatment of tDCS would result in increased quadriceps activity and decreased levels of self-reported pain and dysfunction during exercise.

DESIGN

Randomized crossover design.

SETTING

Controlled laboratory.

PATIENTS

Ten participants with a history of ACLR (5 males/5 females, 22.9 [4.23] y, 176.57 [12.01] cm, 80.87 [16.86] kg, 68.1 [39.37] mo since ACLR).

INTERVENTIONS

Active tDCS and Sham tDCS.

MAIN OUTCOME MEASURES

Percentage of maximum electromyographic data of vastus medialis and lateralis, voluntary isometric strength, percentage of voluntary activation, and self-reported pain and symptom scores were measured. The 2 × 2 repeated-measures analysis of variance by limb were performed to explain the differences between time points (pre and post) and condition (tDCS and sham).

RESULTS

There was a significant time main effect for quadriceps percentage of maximum electromyographic of vastus medialis (F9,1 = 11.931, P = .01) and vastus lateralis (F9,1 = 9.132, P = .01), isometric strength (F9,1 = 5.343, P = .046), and subjective scores for pain (F9,1 = 15.499, P = .04) and symptoms (F9,1 = 15.499, P = .04). Quadriceps percentage of maximum electromyographic, isometric strength, and voluntary activation showed an immediate decline from pre to post regardless of tDCS condition. Subjective scores improved slightly after each condition.

CONCLUSIONS

One session of active tDCS did not have an immediate effect on quadriceps activity and subjective scores of pain and symptoms. To determine if tDCS is a valid modality for this patient population, a larger scale investigation with multiple treatments of active tDCS is warranted.

Transcranial Direct Current Stimulation: No Effect on Aerobic Performance, Heart Rate, or Rating of Perceived Exertion in a Progressive Taekwondo-Specific Test

PURPOSE

To investigate the effects of anodal transcranial direct current stimulation (a-tDCS) on the aerobic performance, heart rate (HR), and rating of perceived exertion (RPE) of highly trained taekwondo athletes.

METHODS

Twelve (8 men and 4 women) international/national-level athletes received a-tDCS or sham treatment over the M1 location in a randomized, single-blind crossover design. The stimulation was delivered at 1.5 mA for 15 min using an extracephalic bihemispheric montage. Athletes performed the progressive-specific taekwondo test 10 min after stimulation. HR was monitored continuously during the test, and RPE was registered at the end of each stage and at test cessation.

RESULTS

There were no significant differences between sham and a-tDCS in time to exhaustion (14.6 and 14.9, respectively, P = .53, effect size = 0.15) and peak kicking frequency (52 and 53.6, respectively, P = .53, effect size = 0.15) or in HR (P > .05) and RPE responses (P > .05).

CONCLUSIONS

Extracephalic bihemispheric a-tDCS over M1 did not influence the aerobic performance of taekwondo athletes or their psychophysiological responses, so athletes and staff should be cautious when using it in a direct-to-consumer manner.

Anodal transcranial direct current stimulation enhances strength training volume but not the force-velocity profile

PURPOSE

This study aimed to explore the acute effect of transcranial direct current stimulation (tDCS) on the force-velocity relationship, strength training volume, movement velocity, and ratings of perceived exertion.

METHODS

Fourteen healthy men (age 22.8 ± 3.0 years) were randomly stimulated over the dorsolateral prefrontal cortex with either ANODAL, CATHODAL or SHAM tDCS for 15 min at 2 mA. The one-repetition maximum (1RM) and force-velocity relationship parameters were evaluated during the bench press exercise before and after receiving the tDCS. Subsequently, participants completed a resistance training session consisting of sets of five repetitions with 1 min of inter-set rest against the 75%1RM until failure.

RESULTS

No significant changes were observed in the 1RM or in the force-velocity relationship parameters (p ≥ 0.377). The number of repetitions was higher for the ANODAL compared to the CATHODAL (p = 0.025; ES = 0.37) and SHAM (p = 0.009; ES = 0.47) conditions. The reductions of movement velocity across sets were lower for the ANODAL than for the CATHODAL and SHAM condition (p = 0.014). RPE values were lower for the ANODAL compared to the CATHODAL (p = 0.119; ES = 0.33) and SHAM (p = 0.150; ES = 0.44) conditions. No significant differences between the CATHODAL and SHAM conditions were observed for any variable.

CONCLUSION

The application of ANODAL tDCS before a resistance training session increased training volume, enabled the maintenance of higher movement velocities, and reduced RPE values. These results suggest that tDCS could be an effective method to enhance resistance-training performance.

Acute Effects of High-Definition Transcranial Direct Current Stimulation on Foot Muscle Strength, Passive Ankle Kinesthesia, and Static Balance: A Pilot Study

This study aimed to examine the effects of single-session anodal high-definition transcranial direct current stimulation (HD-tDCS) on the strength of intrinsic foot muscles, passive ankle kinesthesia, and static balance. Methods: In this double-blinded self-controlled study, 14 healthy younger adults were asked to complete assessments of foot muscle strength, passive ankle kinesthesia, and static balance before and after a 20-minute session of either HD-tDCS or sham stimulation (i.e., control) at two visits separated by one week. Two-way repeated-measures analysis of variance was used to examine the effects of HD-tDCS on metatarsophalangeal joint flexor strength, toe flexor strength, the passive kinesthesia threshold of ankle joint, and the average sway velocity of the center of gravity. Results: All participants completed all study procedures and no side effects nor risk events were reported. Blinding was shown to be successful, with an overall accuracy of 35.7% in the guess of stimulation type (p = 0.347). No main effects of intervention, time, or their interaction were observed for foot muscle strength (p > 0.05). The average percent change in first-toe flexor strength following anodal HD-tDCS was 12.8 ± 24.2%, with 11 out of 14 participants showing an increase in strength, while the change following sham stimulation was 0.7 ± 17.3%, with 8 out of 14 participants showing an increase in strength. A main effect of time on the passive kinesthesia threshold of ankle inversion, dorsiflexion, and anteroposterior and medial–lateral average sway velocity of the center of gravity in one-leg standing with eyes closed was observed; these outcomes were reduced from pre to post stimulation (p < 0.05). No significant differences were observed for other variables between the two stimulation types. Conclusion: The results of this pilot study suggested that single-session HD-tDCS may improve the flexor strength of the first toe, although no statistically significant differences were observed between the anodal HD-tDCS and sham procedure groups. Additionally, passive ankle kinesthesia and static standing balance performance were improved from pre to post stimulation, but no significant differences were observed between the HD-tDCS and sham procedure groups. This may be potentially due to ceiling effects in this healthy cohort of a small sample size. Nevertheless, these preliminary findings may provide critical knowledge of optimal stimulation parameters, effect size, and power estimation of HD-tDCS for future trials aiming to confirm and expand the findings of this pilot study.

Cerebellar Transcranial Direct Current Stimulation Improves Maximum Isometric Force Production during Isometric Barbell Squats

Maximum contraction force (MVC) is an important predictor of athletic performance as well as physical fitness throughout life. Many everyday life activities involve multi-joint or whole-body movements that are determined in part through optimized muscle strength. Transcranial direct current stimulation (tDCS) has been reported to enhance muscle strength parameters in single-joint movements after its application to motor cortical areas, although tDCS effects on MIVC in compound movements remain to be investigated. Here, we tested whether anodal tDCS and/or sham stimulation over primary motor cortex (M1) and cerebellum (CB) improves maximum isometric contraction force (MIVC) during isometric barbell squats (iBS). Our results provide novel evidence that CB stimulation enhances MIVC during iBS. Although this indicates that parameters relating to muscle strength can be modulated through anodal tDCS of the cerebellum, our results serve as an initial reference point and need to be extended. Therefore, further studies are necessary to expand knowledge in this area of research through the inclusion of different tDCS paradigms, for example investigating dynamic barbell squats, as well as testing other whole-body movements.

Neurodiagnostics in Sports: Investigating the Athlete's Brain to Augment Performance and Sport-Specific Skills

Enhancing performance levels of athletes during training and competition is a desired goal in sports. Quantifying training success is typically accompanied by performance diagnostics including the assessment of sports-relevant behavioral and physiological parameters. Even though optimal brain processing is a key factor for augmented motor performance and skill learning, neurodiagnostics is typically not implemented in performance diagnostics of athletes. We propose, that neurodiagnostics via non-invasive brain imaging techniques such as functional near-infrared spectroscopy (fNIRS) will offer novel perspectives to quantify training-induced neuroplasticity and its relation to motor behavior. A better understanding of such a brain-behavior relationship during the execution of sport-specific movements might help to guide training processes and to optimize training outcomes. Furthermore, targeted non-invasive brain stimulation such as transcranial direct current stimulation (tDCS) might help to further enhance training outcomes by modulating brain areas that show training-induced neuroplasticity. However, we strongly suggest that ethical aspects in the use of non-invasive brain stimulation during training and/or competition need to be addressed before neuromodulation can be considered as a performance enhancer in sports.

Effects on Volume Load and Ratings of Perceived Exertion in Individuals' Advanced Weight Training After Transcranial Direct Current Stimulation

Lattari, E, Rosa Filho, BJ, Fonseca Junior, SJ, Murillo-Rodriguez, E, Rocha, N, Machado, S, and Maranhão Neto, GA. Effects on volume load and ratings of perceived exertion in individuals' advanced weight training after transcranial direct current stimulation. J Strength Cond Res 34(1): 89-96, 2020-The aim of this study was investigate the effects of transcranial direct current stimulation (tDCS) on volume load and ratings of perceived exertion. Fifteen young healthy individuals, aged between 20 and 30 years in advanced strength training were recruited. Test and retest of the 10 maximum repetitions (10RM) were performed to determine the reliability of load used. Subjects performed 3 experimental conditions in a randomized, double-blinded crossover design: anodic stimulation (a-tDCS), cathodic stimulation (c-tDCS), and sham (2 mA for 20 minutes targeting the dorsolateral prefrontal cortex left). Immediately after the experimental conditions, subjects completed 1 set of maximum repetitions with 10RM load (volume load) and answered to OMNI-RES (poststimulation) (level of significance p ≤ 0.05). The volume load showed main effect for condition (F(2, 28) = 164.801; p < 0.001). In poststimulation, a-tDCS was greater than c-tDCS (p ≤ 0.001) and sham (p ≤ 0.001). For ratings of perceived exertion (OMNI-RES), the results showed main effect for condition (F(2, 28) = 9.768; p ≤ 0.05). In poststimulation, c-tDCS was greater than a-tDCS (p ≤ 0.05) and sham (p ≤ 0.05). We conclude that the use of a-tDCS may promote increase in volume load for the LP45 exercise. Moreover, higher volume loads are necessary to maximize muscle strength and anabolism.

Combining transcranial direct-current stimulation with gait training in patients with neurological disorders: a systematic review

BACKGROUND

Transcranial direct-current stimulation (tDCS) is an easy-to-apply, cheap, and safe technique capable of affecting cortical brain activity. However, its effectiveness has not been proven for many clinical applications.

OBJECTIVE

The aim of this systematic review was to determine whether the effect of different strategies for gait training in patients with neurological disorders can be enhanced by the combined application of tDCS compared to sham stimulation. Additionally, we attempted to record and analyze tDCS parameters to optimize its efficacy.

METHODS

A search in Pubmed, PEDro, and Cochrane databases was performed to find randomized clinical trials that combined tDCS with gait training. A chronological filter from 2010 to 2018 was applied and only studies with variables that quantified the gait function were included.

RESULTS

A total of 274 studies were found, of which 25 met the inclusion criteria. Of them, 17 were rejected based on exclusion criteria. Finally, 8 trials were evaluated that included 91 subjects with stroke, 57 suffering from Parkinson's disease, and 39 with spinal cord injury. Four of the eight assessed studies did not report improved outcomes for any of its variables compared to the placebo treatment.

CONCLUSIONS

There are no conclusive results that confirm that tDCS can enhance the effect of the different strategies for gait training. Further research for specific pathologies, with larger sample sizes and adequate follow-up periods, are required to optimize the existing protocols for applying tDCS.

Bi-hemispheric anodal transcranial direct current stimulation worsens taekwondo-related performance

Transcranial Direct Current Stimulation (tDCS) is a neuromodulatory technique that has been used as an ergogenic aid in exercise/sports performance. However, little is known about its effects on highly-trained subjects, as athletes. The present study aimed to verify the effects of bi-hemispheric anodal tDCS (a-tDCS) on the performance of taekwondo athletes. Additionally, we investigated the persistence of the effects of the a-tDCS one hour after it. Nineteen Taekwondo athletes received active or sham bi-hemispheric a-tDCS over the primary motor cortex (M1). a-tDCS was delivered at 1.5 mA for 15 min. Athletes performed Countermovement Jumps (CMJ) and the Frequency Speed of Kick Test (FSKT) immediately (Mo1) and one hour after stimulation (Mo2). The athletes also reported their session-rating of perceived exertion (session-RPE). The total number of kicks (TK) was higher in sham than in the active a-tDCS condition (p < 0.01). In addition, TK was higher at Mo2 than at Mo1 (p < 0.05). Similarly, the session-RPE was higher in the a-tDCS condition (p < 0.05) and was greater one-hour post-stimulation (p < 0.01). No differences were found for CMJ performance (p > 0.05). Thus, bi-hemispheric a-tDCS worsens performance of taekwondo athletes, and the effect remains present even 1 h after the stimulation.

Is tDCS an Adjunct Ergogenic Resource for Improving Muscular Strength and Endurance Performance? A Systematic Review

Exercise performance is influenced by many physical factors, such as muscle strength and endurance. Particularly in the physical fitness and sports performance contexts, there are many types of ergogenic aids to improve muscular strength and endurance performance, with non-athletes and even athletes using illegal drugs to reach the top. Thus, the development of innovative methods to aid in exercise performance is of great interest. One such method is transcranial direct current stimulation (tDCS). A systematic search was performed on the following databases, until January 2019; PubMed/MEDLINE, SCOPUS, and Pedro database. Studies on tDCS for muscular strength and endurance performance improvement in non-athletes and athletes adults were included. We compared the effect of anodal-tDCS (a-tDCS) to a sham/control condition on the outcomes muscular strength and endurance performance. We found 26 controlled trials. No trial mentions negative side effects of the intervention. The data show differences between the studies investigating muscle strength and the studies evaluating endurance, with regard to successful use of tDCS. Studies investigating the efficiency of tDCS on improving muscular strength demonstrate positive effects of a-tDCS in 66.7% of parameters tested. In contrast, in studies evaluating the effects of a-tDCS on improving endurance performance the a-tDCS revealed a significant improvement in only 50% of parameters assessed. The majority of the data shows consistently influence of a-tDCS on muscular strength, but not to endurance performance. The results of this systematic review suggest that a-tDCS can improve muscular strength, but not to endurance performance.

Effects of Transcranial Direct Current Stimulation of Primary Motor Cortex on Reaction Time and Tapping Performance: A Comparison Between Athletes and Non-athletes

Recent studies provided compelling evidence that physical activity leads to specific changes on a functional and structural level of brain organization. The observed neural adaptions are specific to the sport and manifested in those brain regions which are associated with neuronal processing of sport-specific skills. Techniques of non-invasive brain stimulation have been shown to induce neuroplastic changes and thereby also facilitate task performance. In the present study, we investigated the influence of transcranial direct current stimulation (tDCS) over the leg area of the primary motor cortex (M1) on simple reaction time tasks (RTT) and tapping tasks (TT) as a comparison between trained football (FB) and handball players (HB) and non-athletes (NA). We hypothesized that anodal tDCS over M1 (leg area) would lead to specific behavioral gains in RTT and TT performance of the lower extremity as compared to sham condition. On an exploratory level, we aimed at revealing if trained athletes would show stronger tDCS-induced behavioral gains as compared to NA, and, furthermore, if there are any differential effects between FB and HB. A total number of 46 participants were enrolled in a sham-controlled, double-blinded, cross-over study. A test block consisting of RTT and TT was performed before, during, after as well as 30 min after a 20-min tDCS application. Additionally, the specificity of tDCS-induced changes was examined by testing upper extremity using the same experimental design as a control condition. Our data showed no group- or sport-specific tDCS-induced effects (online and offline) on RTT and TT neither for lower nor upper extremities. These findings indicate that neither athletes nor NA seems to benefit from a brief period of tDCS application in speed-related motor tasks. However, more knowledge on neuronal processing of RTT and TT performance in trained athletes, the influence of tDCS parameters including stimulation sites, and the effect of inter-individual differences are required in order to draw a comprehensive picture of whether tDCS can help to enhance motor abilities on a high-performance level.

Short-Term Effects of Anodal Transcranial Direct Current Stimulation on Endurance and Maximal Force Production. A Systematic Review and Meta-Analysis

The purpose of the present systematic review and meta-analysis was to explore the effects of transcranial direct current stimulation (tDCS) on endurance (i.e., time to task failure (TTF)) and maximal voluntary contraction (MVC). Furthermore, we aimed to analyze whether the duration of stimulation, the brain region targeted for stimulation, and the task performed could also influence motor performance. We performed a systematic literature review in the databases MEDLINE and Web of Science. The short-term effects of anodal tDCS and sham stimulation (placebo) were considered as experimental and control conditions, respectively. A total of 31 interventions were included (MVC = 13; TTF = 18). Analysis of the strength-related tDCS studies showed small improvements in the MVC (SMD = 0.19; 95% CI = −0.02, 0.41; p = 0.08). However, the results of the endurance-related interventions indicated a moderate effect on TTF performance (SMD = 0.26; 95% CI = 0.07, 0.45; p = 0.008). Furthermore, the sub-analysis showed that anodal tDCS over M1 and stimulation durations longer than 10 min produced the best results in terms of TTF performance enhancement. Additionally, the effects of anodal tDCS were larger during full body exercises (i.e., cycling) when compared to uniarticular tasks. In conclusion, the current meta-analysis indicated that anodal tDCS leads to small and moderate effects on MVC and TTF, respectively.

Acute effects of single dose transcranial direct current stimulation on muscle strength: A systematic review and meta-analysis

Previous studies investigating the effects of transcranial direct current stimulation (tDCS) on muscle strength showed no consensus. Therefore, the purpose of this article was to systematically review the literature on the effects of single dose tDCS to improve muscle strength. A systematic literature search was conducted on PubMeb, ISI Web of Science, SciELO, and Scopus using search terms regarding tDCS and muscle strength. Studies were included in accordance with Population, Intervention, Comparison, Outcomes, and Setting (PICOS) including criteria. Healthy men and women, strength training practitioners or sedentary were selected. The acute effects of single dose anode stimulus of tDCS (a-tDCS) and the placebo stimulus of tDCS (sham) or no interventions were considered as an intervention and comparators, respectively. Measures related to muscle strength were analyzed. To conduct the analyses a weighted mean difference (WMD) and the standardized mean difference (SMD) were applied as appropriate. A total of 15 studies were included in this systematic review and 14 in meta-analysis. Regarding the maximal isometric voluntary contraction (MIVC), a small effect was seen between tDCS and Sham with significant difference between the conditions (SMD = 0.29; CI95% = 0.05 to 0.54; Z = 2.36; p = 0.02). The muscular endurance measured by the seconds sustaining a percentage of MIVC demonstrated a large effect between tDCS and Sham (WMD = 43.66; CI95% = 29.76 to 57.55; Z = 6.16; p < 0.001), showing an improvement in muscular endurance after exposure to tDCS. However, muscular endurance based on total work showed a trivial effect between tDCS and Sham with no significant difference (SMD = 0.22; CI95% = -0.11 to 0.54; Z = 1.32, p = 0.19). This study suggests that the use of tDCS may promote increase in maximal voluntary contraction and muscular endurance through isometric contractions.

The effects of transcranial direct current stimulation on objective and subjective indexes of exercise performance: A systematic review and meta-analysis

OBJECTIVE

To examine the effects of transcranial direct current stimulation (tDCS) on objective and subjective indexes of exercise performance.

DESIGN

Systematic review and meta-analysis.

DATA SOURCES

A systematic literature search of electronic databases (PubMed, Web of Science, Scopus, Google Scholar) and reference lists of included articles up to June 2018.

ELIGIBILITY CRITERIA

Published articles in journals or in repositories with raw data available, randomized sham-controlled trial comparing anodal stimulation with a sham condition providing data on objective (e.g. time to exhaustion or time-trial performance) or subjective (e.g. rate of perceived exertion) indexes of exercise performance.

RESULTS

The initial search provided 420 articles of which 31 were assessed for eligibility. Finally, the analysis of effect sizes comprised 24 studies with 386 participants. The analysis indicated that anodal tDCS had a small but positive effect on performance g = 0.34, 95% CI [0.12, 0.52], z = 3.24, p = .0012. Effects were not significantly moderated by type of outcome, electrode placement, muscles involved, number of sessions, or intensity and duration of the stimulation. Importantly, the funnel plot showed that, overall, effect sizes tended to be larger in studies with lower sample size and high standard error.

SUMMARY

The results suggest that tDCS may have a positive impact on exercise performance. However, the effect is probably small and most likely biased by low quality studies and the selective publication of significant results. Therefore, the current evidence does not provide strong support to the conclusion that tDCS is an effective means to improve exercise performance.

Brain stimulation and physical performance

Non-invasive brain stimulation techniques have been used for decades to study brain function and for the treatment of various neurological disease. These techniques involve the passage of electrical current or magnetic field in a controlled manner to a targeted brain area. Recently, experimental studies explored the application of transcranial direct current stimulation (tDCS) for the improvement of physical performance in healthy individuals. In this chapter we reviewed and analyzed the current scientific literature, highlighted methodological limitations and also suggested possible neurophysiological mechanisms. The chapter also provides some technical and theoretical research-based principles for future research, to promote a better understanding of potential and caveats of this emerging field. Finally, ethical and regulatory issues related to performance enhancement via non-invasive brain stimulation are also discussed.