Transcranial Direct Current Stimulation and Sports Performance

Effects of physical training combined with transcranial direct current stimulation on maximal strength and lower limb explosive strength in healthy adults

Objective

The purpose of this systematic review and meta-analysis was to investigates whether transcranial direct current stimulation applied during physical training increases muscle strength in comparison with sham tDCS combined with physical training.

Methods

Randomized controlled trials of the effects of tDCS combined physical training intervention on muscle strength and cortical excitability were collected by searching Web of Science, Pubmed, EBSCO, CNKI. The retrieval date ends in April 2024. 11 randomized controlled trials are finally included. The total sample size of the study is 338. The experimental group was subjected to tDCS combined with physical training intervention, and the control group was physical training combined with sham tDCS intervention.

Results

There is a significant increase in maximal strength (SMD = 0.38; 95% CI: 0.09, 0.67; p = 0.01) and lower limb explosive strength (MD = 2.90; 95% CI: 1.06, 4.74; p = 0.002) when physical training was performed with tDCS, but not following physical training combined with sham tDCS. Subgroup analysis of the subject population showed an increase in muscle strength in those with training experience following tDCS combined with physical training (SMD = 0.39; 95% CI: 0.08, 0.70; p = 0.01), but not for those without training experience (SMD = 0.29; 95% CI: -0.06, 0.63; p = 0.10). Motor evoked potential (MEP) wave amplitude increased significantly following physical training with tDCS (SMD = 0.71; 95% CI: 0.18, 1.24; p = 0.008), but was not different between groups (SMD = 0.16; 95% CI: -0.33, 0.65; p = 0.52).

Conclusions

tDCS combined with physical training intervention can improve muscle strength, lower limb explosive strength and cerebral cortex excitability. Compared to tDCS combined with training of small muscle groups, tDCS combined with training of large muscle groups was more effective in improving muscle strength. Muscle strength was more likely to improve after tDCS combined with physical training in people with physical training experience compared with people without physical training experience. The combination of tDCS with physical training intervention and the sham-tDCS with physical training intervention both increased cortical excitability.

Systematic Review Registration

https://www.crd.york.ac.uk/, PROSPERO, identifier (CRD42024550454).

Transcranial electrical stimulation for procedural learning and rehabilitation

Procedural learning is the acquisition of motor and non-motor skills through a gradual process that increases with practice. Impairments in procedural learning have been consistently demonstrated in neurodevelopmental, neurodegenerative, and neuropsychiatric disorders. Considering that noninvasive brain stimulation modulates brain activity and boosts neuroplastic mechanisms, we reviewed the effects of coupling transcranial direct current stimulation (tDCS) with training methods for motor and non-motor procedural learning to explore tDCS potential use as a tool for enhancing implicit learning in healthy and clinical populations. The review covers tDCS effects over i. motor procedural learning, from basic to complex activities; ii. non-motor procedural learning; iii. procedural rehabilitation in several clinical populations. We conclude that targeting the primary motor cortex and prefrontal areas seems the most promising for motor and non-motor procedural learning, respectively. For procedural rehabilitation, the use of tDCS is yet at an early stage but some effectiveness has been reported for implicit motor and memory learning. Still, systematic comparisons of stimulation parameters and target areas are recommended for maximising the effectiveness of tDCS and its robustness for procedural rehabilitation.

[An efficient and practical electrode optimization method for transcranial electrical stimulation]

Transcranial electrical stimulation (TES) is a non-invasive neuromodulation technique with great potential. Electrode optimization methods based on simulation models of individual TES field could provide personalized stimulation parameters according to individual variations in head tissue structure, significantly enhancing the stimulation accuracy of TES. However, the existing electrode optimization methods suffer from prolonged computation times (typically exceeding 1 d) and limitations such as disregarding the restricted number of output channels from the stimulator, further impeding their clinical applicability. Hence, this paper proposes an efficient and practical electrode optimization method. The proposed method simultaneously optimizes both the intensity and focality of TES within the target brain area while constraining the number of electrodes used, and it achieves faster computational speed. Compared to commonly used electrode optimization methods, the proposed method significantly reduces computation time by 85.9% while maintaining optimization effectiveness. Moreover, our method considered the number of available channels for the stimulator to distribute the current across multiple electrodes, further improving the tolerability of TES. The electrode optimization method proposed in this paper has the characteristics of high efficiency and easy operation, potentially providing valuable supporting data and references for the implementation of individualized TES.

Auditory Noise Facilitates Lower Visual Reaction Times in Humans

Noise is commonly seen as a disturbance but can influence any system it interacts with. This influence may not always be desirable, but sometimes it can improve the system's performance. For example, stochastic resonance is a phenomenon where adding the right amount of noise to a weak signal makes it easier to detect. This is known as sub-threshold detection. This sub-threshold detection's natural fingerprint is the fact that the threshold values follow an inverse U-shaped curve as the noise intensity increases. The minimum threshold value is the point of maximum sensitivity and represents the optimal point that divides the dynamics in two. Below that point, we can find the beneficial noise branch, where the noise can facilitate better detection. Above that point, the common detrimental noise concept can be found: adding noise hinders signal detection. The nervous system controls the movements and bodily functions in the human body. By reducing the sensory thresholds, we can improve the balance of these functions. Additionally, researchers have wondered if noise could be applied to different senses or motor mechanisms to enhance our abilities. In this work, noise is used to improve human reaction times. We tested the hypothesis that visual reaction times decrease significantly when the subject's perception is in the beneficial noise branch and closer to the optimal point than outside of this condition. Auditory noise was introduced in 101 human subjects using an interface capable of searching for the right amount of noise to place the subject in the beneficial noise branch close to the optimal point. When comparing the results, the reaction times decreased when the subjects were at the optimal point compared to when the subjects were outside of such conditions. These results reveal the possibility of using this approach to enhance human performance in tasks requiring faster reaction times, such as sports.

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.

HD-tDCS induced changes in resting-state functional connectivity: Insights from EF modeling

BACKGROUND

High-definition transcranial direct current stimulation (HD-tDCS) holds promise for therapeutic use in psychiatric disorders. One obstacle for the implementation into clinical practice is response variability. One way to tackle this obstacle is the use of Individualized head models.

OBJECTIVE

This study investigated the variability of HD-tDCS induced electric fields (EFs) and its impact on resting-state functional connectivity (rsFC) during different time windows.

METHODS

In this randomized, double-blind, and sham controlled study, seventy healthy males underwent 20 min of 1.5 mA HD-tDCS on the right inferior frontal gyrus (rIFG) while undergoing resting-state functional magnetic resonance imaging (rs-fMRI). Individual head models and EF simulations were created from anatomical images. The effects of HD-tDCS on rsFC were assessed using a seed-to-voxel analysis. A subgroup analysis explored the relationship between EF magnitude and rsFC during different stimulation time windows.

RESULTS

Results highlighted significant variability in HD-tDCS-induced EFs. Compared to the sham group, the active group showed increased rsFC between the rIFG and the left prefrontal cortex, during and after stimulation. During active stimulation, EF magnitude correlated positively with rsFC between the rIFG and the left hippocampus initially, and negatively during the subsequent period.

CONCLUSION

This study indicated an HD-tDCS induced increase of rsFC between left and right prefrontal areas. Furthermore, an interaction between the magnitude and the duration of HD-tDCS on rsFC was observed. Due to the high EF variability that was apparent, these findings highlight the need for individualized HD-tDCS protocols and the creation of head models to optimize effects and reduce response heterogeneity.

Effects of Tai Chi combined with tDCS on cognitive function in patients with MCI: a randomized controlled trial

Background

Mild cognitive impairment (MCI) is a critical stage of dementia. Previous reviews have suggested that physical exercise combined with non-invasive brain stimulation is more beneficial for improving cognitive function. However, no targeted studies have confirmed the effect of Tai Chi combined with transcranial direct current stimulation (tDCS) on the improvement of cognitive function in patients with MCI. Thus, this randomized trial was conducted to assess the effect of Tai Chi combined with tDCS on the cognitive performance of patients with MCI.

Methods

From April 2018 to February 2020, a randomized, single-blind clinical trial was conducted, involving 180 participants with MCI who were divided into four intervention groups: Tai Chi combined with tDCS (TCT), Tai Chi combined with sham tDCS (TCS), walking combined with tDCS (WAT), and walking combined with sham tDCS (WAS). All participants were assessed at baseline and 12 weeks for global cognitive function, memory, attention, and executive function.

Results

At baseline, there were no significant differences in age, gender, education duration, body mass index, or the Baker Depression Inventory among the four groups (P ≥ 0.05). After 12 weeks of intervention, the TCT group showed greater improvements in MOCA scores, memory quotient scores, and digit-symbol coding task reaction time compared to the TCS, WAS, and WAT groups (P < 0.05). The TCT group also had a shorter Stroop test color reaction time compared to the WAS and WAT groups (P < 0.05), a higher increase in Auditory Verbal Learning Test-immediate recall than the TCS and WAT groups (P < 0.05), a shorter visual reaction time than the TCS group (P < 0.05), and a shorter sustained attention time compared to the WAT group (P < 0.05).

Conclusion

Tai Chi combined with tDCS effectively improves global cognitive performance, memory, execution function, and attention in patients with MCI. These findings suggest the potential clinical use of Tai Chi combined with tDCS as a physical exercise combined with a non-invasive brain stimulation intervention to improve cognitive function in older adults with MCI.

Clinical trial registration

ChiCTR1800015629.

An Operational Approach for Optimizing Transcranial Direct Current Stimulation

Transcranial direct current stimulation (tDCS) is a non-invasive brain stimulation technique that has been utilized for treating brain disorders and improving cognitive function. In order to achieve targeted tDCS, many optimization methods of montages and electric currents have been proposed. However, these methods have some limitations. Most of them were proposed for single-objective optimization (focality or intensity) and have no constrain with the number of electrodes (Most devices only have less than 8 electrodes currently). In this study, we proposed an operational optimization approach for well-targeted tDCS, which aims to optimize for two objectives of electric field (EF) intensity and focality with constraints on the number of electrodes. Compared with traditional tDCS in our cohort (10 subjects), our method significantly improves the EF focality. When compared to commonly used 4×1 high-definition tDCS (HD-tDCS), our method can achieve higher EF intensity in the target region with less than 8 electrodes. Our method can balance the two objectives of EF and shorten optimization time, which is convenient for practical application.

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.

Effect of Transcranial Pulsed Current Stimulation on Fatigue Delay after Medium-Intensity Training

The purpose of this study was to investigate the effect of transcranial pulsed current stimulation (tPCS) on fatigue delay after medium-intensity training. Materials and Methods: Ninety healthy college athletes were randomly divided into an experimental group (n = 45) and control group (n = 45). The experimental group received medium-intensity training for a week. After each training, the experimental group received true stimulation of tPCS (continuous 15 min 1.5 mA current intensity stimulation). The control group received sham stimulation. The physiological and biochemical indicators of participants were tested before and after the experiment, and finally 30 participants in each group were included for data analysis. Results: In the experimental group, creatine kinase (CK), cortisol (C), time-domain heart rate variability indices root mean square of the successive differences (RMSSD), standard deviation of normal R-R intervals (SDNN), and frequency domain indicator low frequency (LF) all increased slowly after the intervention. Among these, CK, C, and SDNN values were significantly lower than those in the control group (p < 0.05). Testosterone (T), T/C, and heart rate variability frequency domain indicator high frequency (HF) in the experimental group decreased slowly after the intervention, and the HF value was significantly lower than that in the control group (p < 0.05). The changes in all of the indicators in the experimental group were smaller than those in the control group. Conclusion: The application of tPCS after medium-intensity training enhanced the adaptability to training and had a significant effect on the maintenance of physiological state. The application of tPCS can significantly promote the recovery of autonomic nervous system function, enhance the regulation of parasympathetic nerves, and delay the occurrence of fatigue.

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 over the orbital prefrontal cortex maintains endurance performance in mentally fatigued swimmers

BACKGROUND

Using anodal transcranial direct current stimulation (a-tDCS) on frontal brain areas might be a promising strategy to mitigates mental fatigue and maintain endurance performance swimmers.

OBJECTIVE

The objective was to analyze the effect of a-tDCS over the orbital prefrontal cortex (oPFC) on endurance performance of mentally fatigued female amateur swimmer.

METHODS

Nineteen female amateur swimmers participated in this study. In two experimental visits, the swimmers completed the 3-min all-out tethered swimming after performing a 30-min Stroop test with a-tDCS or placebo (Sham) stimulation over the left-oPFC. The brain stimulation conditions (i.e., a-tDCS and Sham) were performed in a double-blinded and counterbalanced order.

RESULTS

It was found lower critical force, mean force, force minimum, fatigue index, and aerobic impulse for Sham than a-tDCS (p < 0.05). There was no main effect of condition for peak force (p >  0.05).

CONCLUSION

We concluded that a-tDCS applied over the left-oPFC in female amateur swimmers mentally fatigued maintained endurance performance. From a practical point of view, the use of a-tDCS should be considered to counteract harmful cognitive effects and maintain endurance performance during competitive race events.

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.

Repeated Use of Transcranial Direct Current Stimulation Over the Dorsolateral Prefrontal Cortex Before Training Changes Visual Search and Improves Decision-Making Response Time in Soccer Athletes

The study aimed to analyze the effect of anodal transcranial direct current stimulation (a-tDCS) over the left dorsolateral prefrontal cortex on soccer athletes’ decision making and visual search behavior. It was a single-blind, randomized, and experimental investigation. The 23 soccer athletes were pair-matched according to decision-making skill and then randomized into two groups: a-tDCS and sham. The decision making (during small-sided game and screen task) and visual search behavior were measured before and after the 8-week intervention. Only the a-tDCS group reduced response time in the decision-making screen task (p < .05). The a-tDCS group showed a higher number of fixations than sham group (p < .05) during the small-sided game. The a-tDCS group showed a lower duration of fixation than sham group (p < .05) during the small-sided game. Our results indicated that using a-tDCS over left dorsolateral prefrontal cortex changed visual search behavior and improved the response time of decision-making skill.

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.

Anodal tDCS accelerates on-line learning of dart throwing

Transcranial direct current stimulation (tDCS) has been shown to enhance or block online learning of motor skills, depending on the current direction. However, most research on the use of tDCS has been limited to the study of relatively simple motor tasks. The purpose of the present study was to examine the influence of anodal (a-tDCS) and cathodal (c-tDCS) direct current stimulation on the online learning during a single session of dart throwing. Fifty-eight young adults were randomized to a-tDCS, c-tDCS, or SHAM groups and completed a pre-test block of dart throws, a 20-minute practice block of throws while receiving their stimulation condition, and a post-test block of dart throws. The results showed that a-tDCS accelerated the skill learning of dart throwing more than SHAM and c-tDCS conditions. The SHAM and c-tDCS conditions were not different. We conclude that a-tDCS may have a positive effect in a single training session which would be ideal in a recreational game environment where repeated practice is not common.

Transcranial Direct Current Stimulation Reduces the Negative Impact of Mental Fatigue on Swimming Performance

The issue of using transcranial direct current stimulation (tDCS) to improve sport performance has recently been a topic of interest for researchers. The purpose of this study was to examine the effect of tDCS over left dorsolateral prefrontal cortex (DLPFC) on mental fatigue and physical performance in professional swimmers. Fifteen professional swimmers were randomly assigned in a single-blinded, randomized, counterbalanced order to sham, anodal and cathodal stimulation conditions. Mental fatigue was induced by using a 60-min modified Stroop color-word task. Subjective ratings of mental fatigue were measured before and after the stroop task. The results showed that only anodal tDCS of the left DLPFC reduces adverse effects of mental fatigue in 50-meter swimming performance, whereas cathodal stimulation had no significant effect.

Effects of Bilateral Transcranial Direct Current Stimulation on Simultaneous Bimanual Handgrip Strength

Although the effects of transcranial direct current stimulation (tDCS) on contralateral unimanual movement have been well reported, its effects on coordinated multi-limb movements remain unclear. Because multi-limb coordination is often performed in daily activities and sports, clarifying the effects of tDCS on multi-limb coordination may have valuable implications. However, considering the neural crosstalk involved in bimanual movements, including the transcallosal pathway and ipsilateral motor pathway, the extent of tDCS-induced improvement may differ between unimanual and bimanual movement. We examined how tDCS affects simultaneous bimanual maximal voluntary contraction (MVC) by testing the effects of tDCS of the bilateral primary motor cortex (M1) on unimanual and bimanual handgrip strength. Twenty-one right-handed healthy adults underwent three bilateral tDCS protocols ("RaLc," with an anode on right M1 and a cathode on left M1, "RcLa," with an anode on left M1 and a cathode on right M1, and "Sham") in a randomized order. A 1.5 mA current was applied for 15 min during tDCS. Participants then performed maximal unimanual and bimanual handgrip tests. Bimanual handgrip force was higher in both hands in the RcLa condition than in the Sham condition. Similarly, unimanual handgrip force was higher in the RcLa condition than in the Sham condition. Stimulus responses were asymmetrical and were not observed in the RaLc condition. Our findings demonstrate that RcLa tDCS leads to neuromodulation that can produce greater unimanual and bimanual handgrip strength. This result provides basic evidence that tDCS may be useful in sports, particularly those involving bilateral coordination of upper limb movement.

Transcranial direct current stimulation for auditory verbal hallucinations: a systematic review of clinical trials

Transcranial direct current stimulation (tDCS) has been reportedly beneficial for different neurodegenerative disorders. tDCS has been reported as a potential adjunctive or alternative treatment for auditory verbal hallucination (AVH). This study aims to review the effects of tDCS on AVH in patients with schizophrenia through combining the evidence from randomized clinical trials (RCTs). The databases of PsycINFO (2000-2019), PubMed (2000-2019), EMBASE (2000-2019), CINAHL (2000-2019), Web of Science (2000-2019), and Scopus (2000-2019) were systematically searched. The clinical trials with RCT design were selected for final analysis. A total of nine RCTs were eligible and included in the review. Nine RCTs were included in the final analysis. Among them, six RCTs reported a significant reduction of AVH after repeated sessions of tDCS, whereas three RCTs did not show any advantage of active tDCS over sham tDCS. The current studies showed an overall decrease of approximately 28% of AVH after active tDCS and 10% after sham tDCS. The tDCS protocols targeting the sensorimotor frontal-parietal network showed greater treatment effects compared with the protocols targeting other regions. In this regard, cathodal tDCS over the left temporoparietal area showed inhibitory effects on AVHs. The most effective tDCS protocol on AVHs was twice-daily sessions (2 mA, 20-minute duration) over 5 consecutive days (10 sessions) with the anode over the left dorsolateral prefrontal cortex and the cathode over the left temporal area. Some patient-specific and disease-specific factors such as young age, nonsmoking status, and higher frequencies of AVHs seemed to be the predictors of treatment response. Taken together, the results of tDCS as an alternative treatment option for AVH show controversy among current literatures, since not all studies were positive. However, the studies targeting the same site of the brain showed that the tDCS could be a promising treatment option to reduce AVH. Further RCTs, with larger sample sizes, should be conducted to reach a conclusion on the efficacy of tDCS for AVH and to develop an effective therapeutic protocol for clinical setting.

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.

Future Portrait of the Athletic Brain: Mechanistic Understanding of Human Sport Performance Via Animal Neurophysiology of Motor Behavior

Sport performances are often showcases of skilled motor control. Efforts to understand the neural processes subserving such movements may teach us about general principles of behavior, similarly to how studies on neurological patients have guided early work in cognitive neuroscience. While investigations on non-human animal models offer valuable information on the neural dynamics of skilled motor control that is still difficult to obtain from humans, sport sciences have paid relatively little attention to these mechanisms. Similarly, knowledge emerging from the study of sport performance could inspire innovative experiments in animal neurophysiology, but the latter has been only partially applied. Here, we advocate that fostering interactions between these two seemingly distant fields, i.e., animal neurophysiology and sport sciences, may lead to mutual benefits. For instance, recording and manipulating the activity from neurons of behaving animals offer a unique viewpoint on the computations for motor control, with potentially untapped relevance for motor skills development in athletes. To stimulate such transdisciplinary dialog, in the present article, we also discuss steps for the reverse translation of sport sciences findings to animal models and the evaluation of comparability between animal models of a given sport and athletes. In the final section of the article, we envision that some approaches developed for animal neurophysiology could translate to sport sciences anytime soon (e.g., advanced tracking methods) or in the future (e.g., novel brain stimulation techniques) and could be used to monitor and manipulate motor skills, with implications for human performance extending well beyond sport.

Unskilled shooters improve both accuracy and grouping shot having as reference skilled shooters cortical area: An EEG and tDCS study

Transcranial direct current stimulation (tDCS) has been used as a non-invasive method for enhanced motor and cognitive abilities. However, no previous study has investigated if the tDCS application in unskilled shooters on cortical sites, selected based on the cortical activity of skilled shooters, improves the accuracy and shot grouping. Sixty participants were selected, which included 10 skilled shooters and 50 unskilled shooters. After we identified the right dorsolateral prefrontal cortex (DLPFC) as the area with the highest activity in skilled shooters, we applied anodal tDCS over the right DLPFC in the unskilled shooters under two conditions: sham-tDCS (placebo) and real-tDCS (anodal tDCS). We also analyzed electroencephalography. Our results indicated that anodal tDCS application enhanced the shot accuracy (p = 0.001). Furthermore, the beta power in the EEG recording was higher in the left DLPFC, left and right parietal cortex (p = 0,001) after applying anodal tDCS, while the low-gamma power was higher in the right DLPFC in sham-tDCS (p = 0.001) and right parietal cortex after anodal-tDCS (p = 0.001). Our findings indicate that anodal tDCS can improve accuracy and shot grouping when applied over the unskilled shooters' right DLPFC. Furthermore, beta and low-gamma bands are influenced by anodal tDCS over the right DLPFC, which may be predictive of skill improvement.

Citizen Neuroscience: Brain-Computer Interface Researcher Perspectives on Do-It-Yourself Brain Research

Devices that record from and stimulate the brain are currently available for consumer use. The increasing sophistication and resolution of these devices provide consumers with the opportunity to engage in do-it-yourself brain research and contribute to neuroscience knowledge. The rise of do-it-yourself (DIY) neuroscience may provide an enriched fund of neural data for researchers, but also raises difficult questions about data quality, standards, and the boundaries of scientific practice. We administered an online survey to brain-computer interface (BCI) researchers to gather their perspectives on DIY brain research. While BCI researcher concerns about data quality and reproducibility were high, the possibility of expert validation of data generated by citizen neuroscientists mitigated concerns. We discuss survey results in the context of an established ethical framework for citizen science, and describe the potential of constructive collaboration between citizens and researchers to both increase data collection and advance understanding of how the brain operates outside the confines of the lab.

Transient Amplitude Modulation of Alpha-Band Oscillations by Short-Time Intermittent Closed-Loop tACS

Non-invasive brain stimulation (NIBS) techniques such as transcranial alternating current stimulation (tACS) have recently become extensively utilized due to their potential to modulate ongoing neuronal oscillatory activity and consequently to induce cortical plasticity relevant for various cognitive functions. However, the neurophysiological basis for stimulation effects as well as their inter-individual differences is not yet understood. In the present study, we used a closed-loop electroencephalography-tACS(EEG-tACS) protocol to examine the modulation of alpha oscillations generated in occipito-parietal areas. In particular, we investigated the effects of a repeated short-time intermittent stimulation protocol (1 s in every trial) applied over the visual cortex (Cz and Oz) and adjusted according to the phase and frequency of visual alpha oscillations on the amplitude of these oscillations. Based on previous findings, we expected higher increases in alpha amplitudes for tACS applied in-phase with ongoing oscillations as compared to an application in anti-phase and this modulation to be present in low-alpha amplitude states of the visual system (eyes opened, EO) but not high (eyes closed, EC). Contrary to our expectations, we found a transient suppression of alpha power in inter-individually derived spatially specific parieto-occipital components obtained via the estimation of spatial filters by using the common spatial patterns approach. The amplitude modulation was independent of the phase relationship between the tACS signal and alpha oscillations, and the state of the visual system manipulated via closed- and open-eye conditions. It was also absent in conventionally analyzed single-channel and multi-channel data from an average parieto-occipital region. The fact that the tACS modulation of oscillations was phase-independent suggests that mechanisms driving the effects of tACS may not be explained by entrainment alone, but rather require neuroplastic changes or transient disruption of neural oscillations. Our study also supports the notion that the response to tACS is subject-specific, where the modulatory effects are shaped by the interplay between the stimulation and different alpha generators. This favors stimulation protocols as well as analysis regimes exploiting inter-individual differences, such as spatial filters to reveal otherwise hidden stimulation effects and, thereby, comprehensively induce and study the effects and underlying mechanisms of tACS.

Ergogenic Effects of Bihemispheric Transcranial Direct Current Stimulation on Fitness: a Randomized Cross-over Trial

Several types of routines and methods have been experimented to gain neuromuscular advantages, in terms of exercise performance, in athletes and fitness enthusiasts. The aim of the present study was to evaluate the impact of biemispheric transcranial direct current stimulation on physical fitness indicators of healthy, physically active, men. In a randomized, single-blinded, crossover fashion, seventeen subjects (age: 30.9 ± 6.5 years, BMI: 24.8±3.1 kg/m2) underwent either stimulation or sham, prior to: vertical jump, sit & reach, and endurance running tests. Mixed repeated measures anova revealed a large main effect of stimulation for any of the three physical fitness measures. Stimulation determined increases of lower limb power (+ 5%), sit & reach amplitude (+ 9%) and endurance running capacity (+ 12%) with respect to sham condition (0.16<ηp2 < 0.41; p<0.05). Ratings-of-perceived-exertion, recorded at the end of each test session, did not change across all performances. However, in the stimulated-endurance protocol, an average lower rate-of-perceived-exertion at iso-time was inferred. A portable transcranial direct current stimulation headset could be a valuable ergogenic resource for individuals seeking to improve physical fitness in daily life or in athletic training.

Non-Invasive Brain Stimulation: Augmenting the Training and Performance Potential in Esports Players

During the last two decades, esports, a highly competitive sporting activity, has gained increasing popularity. Both performance and competition in esports require players to have fine motor skills and physical and cognitive abilities in controlling and manipulating digital activities in a virtual environment. While strategies for building and improving skills and abilities are crucial for successful gaming performance, few effective training approaches exist in the fast-growing area of competitive esports. In this paper, we describe a non-invasive brain stimulation (NIBS) approach and highlight the relevance and potential areas for research while being cognizant of various technical, safety, and ethical issues related to NIBS when applied to esports.

Multitasking and Time Pressure in the Operating Room: Impact on Surgeons' Brain Function

OBJECTIVE

To assess the impact of multitasking and time pressure on surgeons' brain function during laparoscopic suturing.

SUMMARY BACKGROUND DATA

Recent neuroimaging evidence suggests that deterioration in surgical performance under time pressure is associated with deactivation of the prefrontal cortex (PFC), an area important for executive functions. However, the effect of multitasking on operator brain function remains unknown.

METHODS

Twenty-nine surgical residents performed an intracorporeal suturing task under four conditions: 1) self-paced suturing, 2) time-pressured suturing, 3) self-paced suturing plus decision-making, and 4) time-pressured suturing plus decision-making. Subjective workload was quantified using the Surgical Task Load Index. Technical skill was objectively assessed using task progression scores, error scores, leak volumes, and knot tensile strengths. PFC activation was measured using optical neuroimaging.

RESULTS

Compared with self-paced suturing, subjective workload (au) was significantly greater in time-pressured suturing (146.0 vs 196.0, P < 0.001), suturing with decision-making (146.0 vs 182.0, P < 0.001), and time-pressured suturing with decision-making (146.0 vs 227.0, P < 0.001). Technical performance during combined suturing and decision-making tasks was inferior to suturing alone under time pressure or self-paced conditions (P < 0.001). Significant dorsolateral PFC (DLPFC) activations were observed during self-paced suturing, and ventrolateral PFC (VLPFC) deactivations were identified during time-pressured suturing. However, suturing in conjunction with decision-making resulted in significant deactivation across both the VLPFC and DLPFC (P < 0.05). Random effects regression analysis confirmed decision-making predicts VLPFC and DLPFC deactivation (z = -2.62, P < 0.05).

CONCLUSIONS

Performance degradation during high workload conditions is associated with deactivation of prefrontal regions important for attentional control, working memory, and cognitive flexibility, particularly during tasks involving simultaneous motor and cognitive engagement.

Effect of transcranial direct current stimulation on sports performance for two profiles of athletes (power and endurance) (COMPETE): a protocol for a randomised, crossover, double blind, controlled exploratory trial

BACKGROUND

Transcranial direct current stimulation (tDCS) is promising for improving motor and cognitive performance. Nevertheless, its mechanisms of action are unclear and need to be better characterised according to the stimulated brain area and the type of exercise performed.

METHODS/DESIGN

This is a double-blind crossover study, organised into two parts: the first is to assess the effects of tDCS on explosive performance (jump task) and the second is to assess the effects on endurance performance (cycling time trial task). Participants, who are recreationally active or athletes (parkour practitioners, cyclists), will receive two active tDCS sessions (over the left dorsolateral prefrontal cortex and right motor cortex) and one sham tDCS session (part A), or two sequences (one active and one sham) of two daily tDCS sessions over 5 days (part B). Motor and cognitive performance will be compared before and after tDCS sessions (part A), and before and after the first session, after the last session and at day 12 and day 30 of each tDCS sequence (part B).

DISCUSSION

This study investigates the acute and repeated effects of tDCS on the motor and cognitive performance of healthy subjects. It will try to evaluate if tDCS could be considered as a neuroenhancement technology according to the physical task investigated (endurance versus explosive).

TRIAL REGISTRATION

ClinicalTrials.gov, NCT03937115. Registered on 3 May 2019; retrospectively registered.

Anodal transcranial direct current stimulation reduces motor slowing in athletes and non-athletes

Background

Motor fatigability describes a phenomenon that occurs when exhaustive exercise or physically demanding tasks are executed over an extended period of time. Concerning fast repetitive movements, it is noticeable by a reduction in movement speed (motor slowing, MoSlo) and occurs due to both central and peripheral factors. The aim of the present study was to examine the presence of MoSlo during hand- (HTT) and foot-tapping tasks (FTT) comparing trained football (FB) and handball players (HB) and non-athletes (NA). Furthermore, we were interested in how far anodal transcranial direct current stimulation (tDCS) might be capable of modulating MoSlo as compared to sham.

Methods

A total number of 46 participants were enrolled in a sham-controlled, double-blinded, cross-over study. HTT and FTT were performed before, during, after as well as 30 min after 20 min of tDCS over the leg area of the primary motor cortex (M1).

Results

We could demonstrate that MoSlo during HTT and FTT is a general phenomenon that is observed independent of the type of sports and/or training status. Furthermore, we were able to show a tDCS-induced reduction in MoSlo specifically during FTT in both trained athletes and NA. No such effects could be observed for HTT, indicating local specificity of tDCS-induced effects on a behavioral level.

Conclusion

We could demonstrate that tDCS is capable of reducing motor fatigability during fast repetitive movements. These findings are of pivotal interest for many sports where fatigability resistance is a limiting factor in maintaining repetitive movement patterns.

Neurostimulation, doping, and the spirit of sport

There is increasing interest in using neuro-stimulation devices to achieve an ergogenic effect in elite athletes. Although the World Anti-Doping Authority (WADA) does not currently prohibit neuro-stimulation techniques, a number of researchers have called on WADA to consider its position on this issue. Focusing on trans-cranial direct current stimulation (tDCS) as a case study of an imminent so-called ‘neuro-doping’ intervention, we argue that the emerging evidence suggests that tDCS may meet WADA’s own criteria (pertaining to safety, performance-enhancing effect, and incompatibility with the ‘spirit of sport’) for a method’s inclusion on its list of prohibited substances and methods. We begin by surveying WADA’s general approach to doping, and highlight important limitations to the current evidence base regarding the performance-enhancing effect of pharmacological doping substances. We then review the current evidence base for the safety and efficacy of tDCS, and argue that despite significant shortcomings, there may be sufficient evidence for WADA to consider prohibiting tDCS, in light of the comparable flaws in the evidence base for pharmacological doping substances. In the second half of the paper, we argue that the question of whether WADA ought to ban tDCS turns significantly on the question of whether it is compatible with the ‘spirit of sport’ criterion. We critique some of the previously published positions on this, and advocate our own sport-specific and application-specific approach. Despite these arguments, we finally conclude by suggesting that tDCS ought to be monitored rather than prohibited due to compelling non-ideal considerations.

Combined and Isolated Effects of Acute Exercise and Brain Stimulation on Executive Function in Healthy Young Adults

Abstract: Acute cognitive enhancement has been sought by healthy young individuals to improve academic and professional performance. Among several methods, physical exercise interventions and transcranial direct current brain stimulation (tDCS) have shown promise in impacting executive functions. Here, we observed a set of new findings about the causal effect of acute aerobic exercise and tDCS across three facets of executive function: Inhibition (as measured by a flanker task) was selectively impacted by acute aerobic exercise but not tDCS, whereas working memory (as measured by an n-back task) was impacted by both acute aerobic exercise and tDCS, with effects emerging on distinct processing components for each manipulation. Sustained attention (as measured by the Mackworth clock task), on the other hand, was not impacted by acute aerobic exercise or tDCS. Interestingly, no effects of combining acute aerobic exercise and tDCS emerged. We argue that understanding the unique and combined contributions of these cognitive enhancement techniques can not only contribute to a deeper mechanistic explanation in healthy individuals but also inform future research with clinical and aging populations.

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.

The Impact of Transcranial Direct Current Stimulation on Upper-Limb Motor Performance in Healthy Adults: A Systematic Review and Meta-Analysis

Background: Transcranial direct current stimulation (tDCS) has previously been reported to improve facets of upper limb motor performance such as accuracy and strength. However, the magnitude of motor performance improvement has not been reviewed by contemporaneous systematic review or meta-analysis of sham vs. active tDCS.

Objective: To systematically review and meta-analyse the existing evidence regarding the benefits of tDCS on upper limb motor performance in healthy adults.

Methods: A systematic search was conducted to obtain relevant articles from three databases (MEDLINE, EMBASE, and PsycINFO) yielding 3,200 abstracts. Following independent assessment by two reviewers, a total of 86 articles were included for review, of which 37 were deemed suitable for meta-analysis.

Results: Meta-analyses were performed for four outcome measures, namely: reaction time (RT), execution time (ET), time to task failure (TTF), and force. Further qualitative review was performed for accuracy and error. Statistically significant improvements in RT (effect size −0.01; 95% CI −0.02 to 0.001, p = 0.03) and ET (effect size −0.03; 95% CI −0.05 to −0.01, p = 0.017) were demonstrated compared to sham. In exercise tasks, increased force (effect size 0.10; 95% CI 0.08 to 0.13, p < 0.001) and a trend towards improved TTF was also observed.

Conclusions: This meta-analysis provides evidence attesting to the impact of tDCS on upper limb motor performance in healthy adults. Improved performance is demonstrable in reaction time, task completion time, elbow flexion tasks and accuracy. Considerable heterogeneity exists amongst the literature, further confirming the need for a standardised approach to reporting tDCS studies.

The Effect of Cerebellar Transcranial Direct Current Stimulation on Motor Learning: A Systematic Review of Randomized Controlled Trials

Background: Cerebellar transcranial direct current stimulation (ctDCS) appears to modulate motor performance in both adaptation and motor skill tasks; however, whether the gains are long-lasting is unclear.

Objectives: This systematic review aims to evaluate the effect of ctDCS with respect to different time scales of motor learning.

Methods: Ten electronic databases (CINAHL, MEDLINE, SPORT Discus, Scopus, Web of Science, Cochrane via OVID, Evidence-Based Reviews (EBM) via OVID, AMED: Allied and Complementary Medicine, PsycINFO, and PEDro) were systematically searched. Studies evaluating the effect of ctDCS compared to sham ctDCS on motor learning in healthy individuals were selected and reviewed. Two authors independently reviewed the quality of the included studies using the revised Cochrane's risk-of-bias tool. The results were extracted with respect to the time scale in which changes in motor performance were evaluated.

Results: Seventeen randomized controlled trials met the eligibility criteria of which 65% of the studies had a “high” risk-of-bias, and 35% had “some concerns.” These studies included data from 629 healthy participants. Of the studies that evaluated the effect of anodal ctDCS during and immediately after the stimulation, four found enhanced, three found impaired, and ten found no effect on gains in motor performance. Of the studies that evaluated the effect of anodal ctDCS after a break of 24 h or more, seven found enhanced, two found impaired, and one found no effect on gains in motor performance. Of the studies that evaluated the effect of cathodal ctDCS across a range of time scales, five found impaired, one found enhanced, and five found no effect on gains in motor performance.

Conclusions: In healthy individuals, anodal ctDCS appears to improve short to longer-term motor skill learning, whereas it appears to have no effect on gains in motor performance during and immediate after the stimulation. ctDCS may have potential to improve motor performance beyond the training period. The challenge of the motor task and its characteristics, and the stimulation parameters are likely to influence the effect of ctDCS on motor learning.

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.

Effects of transcranial direct current stimulation (tDCS) on balance improvement: a systematic review and meta-analysis

Background: Transcranial direct current stimulation (tDCS) has emerged as a promising therapeutic tool to improve balance and optimize rehabilitation strategies. However, current literature shows the methodological heterogeneity of tDCS protocols and results, hindering any clear conclusions about the effects of tDCS on postural control. Objective: Evaluate the effectiveness of tDCS on postural control, and identify the most beneficial target brain areas and the effect on different populations. Methods: Two independent reviewers selected randomized tDCS clinical-trials studies from PubMed, Scopus, Web of Science, and reference lists of retrieved articles published between 1998 and 2017. Most frequently reported centre of pressure (COP) variables were selected for meta-analysis. Other postural control outcomes were discussed in the review. Results: Thirty studies were included in the systematic review, and 11 were submitted to a meta-analysis. A reduction of COP displacement area has been significantly achieved by tDCS, evidencing an improvement in balance control. Individuals with cerebral palsy (CP) and healthy young adults are mostly affected by stimulation. The analysis of the impact of tDCS over different brain areas revealed a significant effect after primary motor cortex (M1) stimulation, however, with no clear results after cerebellar stimulation due to divergent results among studies. Conclusions: tDCS appears to improve balance control, more evident in healthy and CP subjects. Effects are observed when primary MI is stimulated. Cerebellar stimulation should be better investigated.

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.

Transcranial Direct Current Stimulation of motor cortex enhances running performance

Transcranial direct current stimulation (tDCS) is a technique used to modulate neuronal excitability through non-invasive brain stimulation that can enhance exercise performance. We hypothesize that tDCS would improve submaximal running time to exhaustion (TTE) and delay the increase in the rating of perceived exertion (RPE) over time. We also hypothesize that tDCS would not lead to difference in cardiorespiratory responses. We employed a randomized, single-blinded, and counterbalanced design in which 10 trained men participated. After receiving either 20 min of 1.98 mA anodal tDCS applied over the primary motor cortex (M1) or sham-operated control on separate days, participants completed a constant-load test involving running at a speed equivalent to 80% of their own maximum oxygen consumption (VO2max). During this constant-load test, RPE, heart rate (HR), VO2, pulmonary ventilation (VE), respiratory exchange ratio (RER), and ventilatory threshold (VT) were continuously monitored. TTE was recorded at the end of the test. TTEs were significantly longer in the tDCS than in the sham conditions (21.18 ± 7.13 min; 18.44 ± 6.32 min; p = 0.011). For TTE, no significant differences were found in RPE between conditions at isotime. In addition, no significant differences in HR, VO2, VE, RER, and VT were found during TTE between the two stimulation conditions at any time point. These results indicate that the application of tDCS does not induce a change of the exercise performance-related index; however, it can affect the increase of the exercise duration due to the stimuli in the M1 area.

A Review of Acute Aerobic Exercise and Transcranial Direct Current Stimulation Effects on Cognitive Functions and Their Potential Synergies

Today, several pharmaceutic and non-pharmaceutic approaches exist to treat psychiatric and neurological diseases. Because of the lack of treatment procedures that are medication free and without severe side effects, transcranial direct current stimulation (tDCS) and aerobic exercise (AE) have been tested to explore the potential for initiating and modulating neuroplasticity in the human brain. Both tDCS and AE could support cognition and behavior in the clinical and non-clinical context to improve the recovery process within neurological or psychiatric conditions or to increase performance. As these techniques still lack meaningful effects, although they provide multiple beneficial opportunities within disease and health applications, there is emerging interest to find improved tDCS and AE protocols. Since multimodal approaches could provoke synergetic effects, a few recent studies have begun to combine tDCS and AE within different settings such as in cognitive training in health or for treatment purposes within clinical settings, all of which show superior effects compared to single technique applications. The beneficial outcomes of both techniques depend on several parameters and the understanding of neural mechanisms that are not yet fully understood. Recent studies have begun to directly combine tDCS and AE within one session, although their interactions on the behavioral, neurophysiological and neurochemical levels are entirely unclear. Therefore, this review: (a) provides an overview of acute behavioral, neurophysiological, and neurochemical effects that both techniques provoke within only one single application in isolation; (b) gives an overview regarding the mechanistic pathways; and (c) discusses potential interactions and synergies between tDCS and AE that might be provoked when directly combining both techniques. From this literature review focusing primarily on the cognitive domain in term of specific executive functions (EFs; inhibition, updating, and switching), it is concluded that a direct combination of tDCS and AE provides multiple beneficial opportunities for synergistic effects. A combination could be useful within non-clinical settings in health and for treating several psychiatric and neurologic conditions. However, there is a lack of research and there are several possibly interacting moderating parameters that must be considered and more importantly must be systematically investigated in the future.

Effect of transcranial direct current stimulation on exercise performance: A systematic review and meta-analysis

BACKGROUND

Transcranial direct current stimulation (tDCS) has been used to improve exercise performance, though the protocols used, and results found are mixed.

OBJECTIVE

We aimed to analyze the effect of tDCS on improving exercise performance.

METHODS

A systematic search was performed on the following databases, until December 2017: PubMed/MEDLINE, Embase, Web of Science, SCOPUS, and SportDiscus. Full-text articles that used tDCS for exercise performance improvement in adults were included. We compared the effect of anodal (anode near nominal target) and cathodal (cathode near nominal target) tDCS to a sham/control condition on the outcome measure (performance in isometric, isokinetic or dynamic strength exercise and whole-body exercise).

RESULTS

22 studies (393 participants) were included in the qualitative synthesis and 11 studies (236 participants) in the meta-analysis. The primary motor cortex (M1) was the main nominal tDCS target (n = 16; 72.5%). A significant effect favoring anodal tDCS (a-tDCS) applied before exercise over M1 was found on cycling time to exhaustion (mean difference = 93.41 s; 95%CI = 27.39 s-159.43 s) but this result was strongly influenced by one study (weight = 84%), no effect was found for cathodal tDCS (c-tDCS). No significant effect was found for a-tDCS applied on M1 before or during exercise on isometric muscle strength of the upper or lower limbs. Studies regarding a-tDCS over M1 on isokinetic muscle strength presented mixed results. Individual results of studies using a-tDCS applied over the prefrontal and motor cortices either before or during dynamic muscle strength testing showed positive results, but performing meta-analysis was not possible.

CONCLUSION

For the protocols tested, a-tDCS but not c-tDCS vs. sham over M1 improved exercise performance in cycling only. However, this result was driven by a single study, which when removed was no longer significant. Further well-controlled studies with larger sample sizes and broader exploration of the tDCS montages and doses are warranted.

Endurance Performance is Influenced by Perceptions of Pain and Temperature: Theory, Applications and Safety Considerations

Models of endurance performance now recognise input from the brain, including an athlete's ability to cope with various non-pleasurable perceptions during exercise, such as pain and temperature. Exercise training can reduce perceptions of both pain and temperature over time, partly explaining why athletes generally have a higher pain tolerance, despite a similar pain threshold, compared with active controls. Several strategies with varying efficacy may ameliorate the perceptions of pain (e.g. acetaminophen, transcranial direct current stimulation and transcutaneous electrical stimulation) and temperature (e.g. menthol beverages, topical menthol products and other cooling strategies, especially those targeting the head) during exercise to improve athletic performance. This review describes both the theory and practical applications of these interventions in the endurance sport setting, as well as the potentially harmful health consequences of their use.

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.

Studying brain activity in sports performance: Contributions and issues

Understanding the interactions between brain activity and behavior comprehensively in achieving optimal exercise performance in sports is still lacking. The existent research in this area has been limited by the constraints of sports environments and the robustness of the most suitable non-invasive functional neuroimaging methods (electroencephalography, EEG and functional near-infrared spectroscopy, fNIRS) to motion artifacts and noise. However, recent advances in brain mapping technology should improve the capabilities of the future brain imaging devices to assess and monitor the level of adaptive cognitive-motor performance during exercise in sports environments. The purpose of this position manuscript is to discuss the contributions and issues in behavioral neuroscience related to brain activity measured during exercise and in various sports. A first part aims to give an overview of EEG and fNIRS neuroimaging methods assessing electrophysiological activity and hemodynamic responses of the acute and chronic relation of physical exercise on the human brain. Then, methodological issues, such as the reliability of brain data during physical exertion, key limitations and possible prospects of fNIRS and EEG methods are provided. While the use of such methods in sports environments remains scarce and limited to controlled cycling task, new generation of wearable, whole-scalp EEG and fNIRS technologies could open up a range of new applications in sports sciences for providing neuroimaging-based biomarkers (hemodynamic and/or neural electrical signals) to various types of exercise and innovative training.