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

Non-invasive neuromodulation in reducing the risk of falls and fear of falling in community-dwelling older adults: systematic review

Introduction

Neuromodulation is a non-invasive technique that allows for the modulation of cortical excitability and can produce changes in neuronal plasticity. Its application has recently been associated with the improvement of the motor pattern in older adults individuals with sequelae from neurological conditions.

Objective

To highlight the effects of non-invasive neuromodulation on the risk of falls and fear of falling in community-dwelling older adults.

Methods

Systematic review conducted in accordance with the items of the Cochrane Handbook for Systematic Reviews of Interventions. Searches were carried out in electronic databases: CENTRAL, Clinical Trials, LILACS, PEDro, PubMed, Web of Science, between 13/06/2020 and 20/09/2023, including all indexed texts without language and publication date restrictions, randomized controlled clinical trials, which presented as their main outcome non-invasive neuromodulation for reducing the fear of falling and risk of falls in the older adults, regardless of gender.

Results

An extensive search identified 9 eligible studies for qualitative synthesis from 8,168 potential articles. Rigorous filtering through automated tools, title/abstract screening, and full-text evaluation ensured a focused and relevant selection for further analysis. Most studies (80%) used transcranial direct current electrical stimulation as an intervention, over the motor cortex or cerebellum area, with anodal current and monopolar electrode placement. The intensity ranged from 1.2 mA to 2 mA, with a duration of 20 min (80%). The profile of the research participants was predominantly individuals over 65 years old (80%), with a high risk of falls (60%) and a minority reporting a fear of falling (40%). The outcomes were favorable for the use of neuromodulation for the risk of falls in the older adults, through improvements in static and dynamic balance.

Conclusion

The results may have limited applicability to direct outcomes related to the risk of falls, in addition to evidence regarding the difference or lack thereof in applicability between genders, fallers and non-fallers, as well as older adults individuals with low and high fear of falling.

Systematic review registration

The protocol for this review was registered in the International Prospective Register of Systematic Reviews (PROSPERO) to obtain the identification of ongoing research (ID: 222429).

Chronic Functional Adaptations Induced by the Application of Transcranial Direct Current Stimulation Combined with Exercise Programs: A Systematic Review of Randomized Controlled Trials

The present systematic review aimed to determine the chronic effects of the combination of transcranial direct current stimulation (tDCS) and exercise on motor function and performance outcomes. We performed a systematic literature review in the databases MEDLINE and Web of Science. Only randomized control trials that measured the chronic effect of combining exercise (comprising gross motor tasks) with tDCS during at least five sessions and measured any type of motor function or performance outcome were included. A total of 22 interventions met the inclusion criteria. Only outcomes related to motor function or performance were collected. Studies were divided into three groups: (a) healthy population (n = 4), (b) neurological disorder population (n = 14), and (c) musculoskeletal disorder population (n = 4). The studies exhibited considerable variability in terms of tDCS protocols, exercise programs, and outcome measures. Chronic use of tDCS in combination with strength training does not enhance motor function in healthy adults. In neurological disorders, the results suggest no additive effect if the exercise program includes the movements pretending to be improved (i.e., tested). However, although evidence is scarce, tDCS may enhance exercise-induced adaptations in musculoskeletal conditions characterized by pain as a limiting factor of motor function.

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

BACKGROUND

Despite reporting the positive effects of transcranial direct current stimulation (tDCS) on endurance performance, very few studies have investigated its efficacy in anaerobic short all-out activities. Moreover, there is still no consensus on which brain areas could provide the most favorable effects on different performance modalities. Accordingly, this study aimed to investigate the effects of anodal tDCS (a-tDCS) targeting the primary motor cortex (M1) or left dorsolateral prefrontal cortex (DLPFC) on physical performance, psychophysiological responses, and cognitive function in repeated all-out cycling.

METHODS

In this randomized, crossover, and double-blind study, 15 healthy physically active men underwent a-tDCS targeting M1 or the left DLPFC or sham tDCS in separate days before performing three bouts of all-out 30s cycling anaerobic test. a-tDCS was applied using 2 mA for 20 min. Peak power, mean power, fatigue index, and EMG of the quadriceps muscles were measured during each bout. Heart rate, perceived exertion, affective valence, and arousal were recorded two minutes after each bout. Color-word Stroop test and choice reaction time were measured at baseline and after the whole anaerobic test.

RESULTS

Neither tDCS montage significantly changed peak power, mean power, fatigue index, heart rate, affective valence, arousal, and choice reaction time (p> 0.05). a-tDCS over DLPFC significantly lowered RPE of the first bout (compared to sham; p=0.048, Δ=-12.5%) and third bout compared to the M1 (p=0.047, Δ=-12.38%) and sham (p=0.003, Δ=-10.5%), increased EMG of the Vastus Lateralis muscle during the second (p=0.016, Δ= +40.3%) and third bout (p=0.016, Δ= +42.1%) compared to sham, and improved the score of color-word Stroop test after the repeated all-out task (p=0.04, Δ= +147%). The qualitative affective response (valence and arousal) was also higher under the M1 and DLPFC compared to the sham.

CONCLUSION

We concluded that tDCS targeting M1 or DLPFC does not improve repeated anaerobic performance. However, the positive effect of DLPFC montage on RPE, EMG, qualitative affective responses, and cognitive function is promising and paves the path for future research using different tDCS montages to see any possible effects on anaerobic performance.

TRIAL REGISTRATION

This study was approved by the Ethics Committee of Razi University (IR.RAZI.REC.1400.023) and registered in the Iranian Registry of Clinical Trials (IRCT id: IRCT20210617051606N5; Registration Date: 04/02/2022).

Anodal Transcranial Direct Current Stimulation over the Right Dorsolateral Prefrontal Cortex Boosts Decision Making and Functional Impulsivity in Female Sports Referees

We investigated the effect of anodal transcranial direct current stimulation (tDCS) over the right dorsolateral prefrontal cortex (rDLPFC) on the sensitive decision making of female team sports referees. Twenty-four female referees voluntarily participated in this randomized, double-blind, crossover, and sham-controlled study. In three different sessions, participants received either anodal (a-tDCS; anode (+) over F4, cathode (-) over the supraorbital region (SO)), cathodal (c-tDCS; -F4/+SO), or sham tDCS (sh-tDCS) in a randomized and counterbalanced order. a-tDCS and c-tDCS were applied with 2 mA for 20 min. In sh-tDCS, the current was turned off after 30 s. Before and after tDCS, participants performed the computerized Iowa Gambling Task (IGT) and Go/No Go impulsivity (IMP) tests. Only a-tDCS improved IGT and IMP scores from pre to post. The delta (Δ = post-pre) analysis showed a significantly higher ΔIGT in a-tDCS compared to c-tDCS (p = 0.02). The ΔIMP was also significantly higher in a-tDCS compared to sh-tDCS (p = 0.01). Finally, the reaction time decreased significantly more in a-tDCS (p = 0.02) and sh-tDCS (p = 0.03) than in c-tDCS. The results suggest that the a-tDCS improved factors related to sensitive decision making in female team sports referees. a-tDCS might be used as an ergogenic aid to enhance decision performance in female team sports referees.

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

BACKGROUND

Transcranial direct current stimulation (tDCS) has been shown to have positive effects on exercise performance and cognitive function in the normal ambient condition. Hypoxia is deemed a stressful situation with detrimental effects on physiological, psychological, cognitive, and perceptual responses of the body. Nevertheless, no study has evaluated the efficacy of tDCS for counteracting the negative effects of hypoxic conditions on exercise performance and cognition so far. Hence, in the present study, we investigated the effects of anodal tDCS on endurance performance, cognitive function, and perceptual responses in hypoxia.

PARTICIPANTS AND METHODS

Fourteen endurance-trained males participated in five experimental sessions. After familiarization and measuring peak power output in hypoxia, in the first and second sessions, through the 3rd to 5th sessions, participants performed a cycling endurance task until exhaustion after 30 min hypoxic exposure at resting position followed by 20 min of anodal stimulation of the motor cortex (M1), left dorsolateral prefrontal cortex (DLPFC), or sham-tDCS. Color-word Stroop test and choice reaction time were measured at baseline and after exhaustion. Time to exhaustion, heart rate, saturated O₂, EMG amplitude of the vastus lateralis, vastus medialis, and rectus femoris muscles, RPE, affective response, and felt arousal were also measured during the task under hypoxia.

RESULTS

The results showed a longer time to exhaustion (+ 30.96%, p₌0.036), lower RPE (- 10.23%, p ₌ 0.045) and higher EMG amplitude of the vastus medialis muscle (+ 37.24%, p₌0.003), affective response (+ 260%, p₌0.035) and felt arousal (+ 28.9%, p₌0.029) in the DLPFC tDCS compared to sham. The choice reaction time was shorter in DLPFC tDCS compared to sham (- 17.55%, p₌0.029), and no differences were seen in the color-word Stroop test among the conditions under hypoxia. M1 tDCS resulted in no significant effect for any outcome measure.

CONCLUSIONS

We concluded that, as a novel finding, anodal stimulation of the left DLPFC might provide an ergogenic aid for endurance performance and cognitive function under the hypoxic condition probably via increasing neural drive to the working muscles, lowering RPE, and increasing perceptual responses.

Transcranial Direct Current Stimulation Combined With or Without Caffeine: Effects on Training Volume and Pain Perception

Purpose: This study aimed to investigate the acute effects of tDCS combined with caffeine intake on training volume and pain perception in the bench press in resistance-trained males. The correlation between training volume and pain perception was also assessed in all interventions. Methods: Sixteen healthy males (age = 25.2 ± 4.7 years, body mass = 82.8 ± 9.1 kg, and height = 178.3 ± 5.7 cm), advanced in RT, were randomized and counterbalanced for the following experimental conditions: Sham tDCS with placebo intake (Sham+Pla), Sham tDCS with caffeine intake (Sham+Caff), anodal tDCS with placebo intake (a-tDCS+Pla), and anodal tDCS with caffeine intake (a-tDCS+Caff). The caffeine or placebo ingestion (both with 5 mg.kg^-1) occurred 40 minutes before the tDCS sessions. The tDCS was applied over the left DLPFC for 20 minutes, with a 2 mA current intensity. After the tDCS sessions, participants performed the bench press with an 80% of 1RM load, where training volume and pain perception were measured. Results: Training volume was higher in the 1^st and 2^nd sets in both a-tDCS+Caff and Sham+Caff conditions, compared to the Sham+Pla condition (P < .05). Both a-tDCS+Caff and a-tDCS+Pla showed an increased pain perception during the third set compared to the first set. Also, no correlation was found between the number of repetitions and pain perception in any condition (P > .05). Conclusion: This research revealed that caffeine intake alone could be used as an ergogenic aid during resistance training programs in resistance-trained males.

Effects of single session transcranial direct current stimulation on aerobic performance and one arm pull-down explosive force of professional rock climbers

Objective: To explore the effects of single-session transcranial direct current stimulation (tDCS) on aerobic performance and explosive force in the one-arm pull-down of long-term trained rock climbers. Method: Twenty athletes (twelve male and eight female) from the Rock Climbing Team of Hunan province (Hunan, China) were selected for a randomized double-blind crossover study. After baseline tests, All subjects visited laboratories twice to randomly receive either sham or a-tDCS at a current intensity of 2 mA for 20 min. The two visits were more than 72 h apart. Immediately after each stimulation, subjects completed a 9-min 3-level-load aerobic test and a one-arm pull-down test. Results: Differences in the heart rate immediately after 9-min incremental aerobic exercises revealed no statistical significance between each group (p > 0.05). However, the decrease in heart rate per unit time after exercise after real stimulation was significantly better than before stimulation (p < 0.05), and no statistical significance was observed between after sham stimulation and before stimulation (p > 0.05). One-arm pull-down explosive force on both sides after real stimulation was improved by a-tDCS compared with before stimulation, but with no significant difference (p > 0.05). Real stimulation was significantly improved, compared with sham stimulation on the right side (p < 0.05). Conclusion: Single-session tDCS could potentially benefit sports performance in professional athletes.

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".

Effects of Mental Fatigue on Strength Endurance: A Systematic Review and Meta-Analysis

The purpose of the present systematic review and meta-analysis was to explore the effects of mental fatigue on upper and lower body strength endurance. Searches for studies were performed in the PubMed/MEDLINE and Web of Science databases. We included studies that compared the effects of a demanding cognitive task (set to induce mental fatigue) with a control condition on strength endurance in dynamic resistance exercise (i.e., expressed as the number of performed repetitions at a given load). The data reported in the included studies were pooled in a random-effects meta-analysis of standardized mean differences. Seven studies were included in the review. We found that mental fatigue significantly reduced the number of performed repetitions for upper body exercises (standardized mean difference: -0.41; 95% confidence interval [-0.70, -0.12]; p = .006; I2 = 0%). Mental fatigue also significantly reduced the number of performed repetitions in the analysis for lower body exercises (standardized mean difference: -0.39; 95% confidence interval [-0.75, -0.04]; p = .03; I2 = 0%). Our results showed that performing a demanding cognitive task-which induces mental fatigue-impairs strength endurance performance. Collectively, our findings suggest that exposure to cognitive tasks that may induce mental fatigue should be minimized before strength endurance-based resistance exercise sessions.

Effects of Preceding Transcranial Direct Current Stimulation on Movement Velocity and EMG Signal during the Back Squat Exercise

This study aimed to evaluate the effects of preceding anodal transcranial direct stimulation (a-tDCS) over the dorsolateral prefrontal cortex (DLPFC) during the back squat exercise on movement velocity and surface electromyographic (sEMG) activity. Thirteen healthy, well-trained, male firefighters (34.72 ± 3.33 years; 178 ± 7.61 cm; 76.85 ± 11.21 kg; 26.8 ± 4.2 kg·m−2; back squat 1-repetition maximum 141.5 ± 16.3 kg) completed this randomised double-blinded sham-controlled crossover study. After familiarisation and basal measurements, participants attended the laboratory on two occasions separated by 72 h to receive either Sham or a-tDCS (current intensity of 2 mA for 20 min). Immediately after stimulation, participants completed three sets of 12 repetitions (70% of 1-RM) with three minutes of recovery between sets monitored with a linear position transducer. The sEMG of the rectus femoris (RF) and vastus lateralis (VL) of both legs were recorded. No significant differences were observed between a-tDCS and Sham interventions on mean concentric velocity at any set (p > 0.05). Velocity loss and effort index were significantly higher (p < 0.05) in set 3 compared to set 1 only in the a-tDCS group. The right-leg RM and right-leg VL elicited the greatest muscle activation during set 1 after a-tDCS and Sham, respectively (p < 0.05). Our results revealed that a-tDCS over the DLPFC might impact movement velocity or fatigue tolerance in well-trained individuals. Notwithstanding, significant differences in dominant-leg muscle activity were found both in a-tDCS and Sham.

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 Influence of Transcranial Direct Current Stimulation on Shooting Performance in Elite Deaflympic Athletes: A Case Series

Transcranial direct current stimulation (tDCS) has been shown to improve motor learning in numerous studies. However, only a few of these studies have been conducted on elite-level performers or in complex motor tasks that have been practiced extensively. The purpose was to determine the influence of tDCS applied to the dorsolateral prefrontal cortex (DLPFC) on motor learning over multiple days on 10-m air rifle shooting performance in elite Deaflympic athletes. Two male and two female elite Deaflympic athletes (World, European, and National medalists) participated in this case series. The study utilized a randomized, double-blind, SHAM-controlled, cross-over design. Anodal tDCS or SHAM stimulation was applied to the left DLPFC for 25 min with a current strength of 2 mA concurrent with three days of standard shooting practice sessions. Shooting performance was quantified as the points and the endpoint error. Separate 2 Condition (DLPFC-tDCS, SHAM) × 3 Day (1,2,3) within-subjects ANOVAs revealed no significant main effects or interactions for either points or endpoint error. These results indicate that DLPFC-tDCS applied over multiple days does not improve shooting performance in elite athletes. Different stimulation parameters or very long-term (weeks/months) application of tDCS may be needed to improve motor learning in elite athletes.

Transcranial Direct Current Stimulation Enhances Exercise Performance: A Mini Review of the Underlying Mechanisms

Exercise performance (EP) is affected by a combination of factors including physical, physiological, and psychological factors. This includes factors such as peripheral, central, and mental fatigue, external peripheral factors such as pain and temperature, and psychological factors such as motivation and self-confidence. During the last century, numerous studies from different fields of research were carried out to improve EP by modifying these factors. During the last two decades, the focus of research has been mainly moved toward the brain as a dynamic ever-changing organ and the ways changes in this organ may lead to improvements in physical performance. Development of centrally-acting performance modifiers such as level of motivation or sleep deprivation and the emergence of novel non-invasive brain stimulation (NIBS) techniques such as transcranial magnetic stimulation (TMS) and transcranial direct current stimulation (tDCS) are the key motives behind this move. This article includes three sections. Section Introduction provides an overview of the mechanisms behind the reduction of EP. The main focus of the Effects of tDCS on EP section is to provide a brief description of the effects of tDCS on maximal and submaximal types of exercise and finally, the section Mechanisms Behind the Effects of tDCS on EP provides description of the mechanisms behind the effects of tDCS on EP.

Anodal Transcranial Direct Current Stimulation Does Not Affect Velocity Loss During a Typical Resistance Exercise Session

Purpose: This study investigated the effects of transcranial direct current stimulation (tDCS) on velocity loss in a typical resistance exercise session. Methods: Twelve recreationally resistance-trained males (age = 24.8 ± 3.0 years, body mass = 78.9 ± 13.6 kg, and height = 174.3 ± 7.3 cm) completed two experimental trials in a counterbalanced crossover design: anodal tDCS and sham conditions. The stimuli were applied over the left dorsolateral prefrontal cortex for 20 minutes, using a 2 mA current intensity in anodal tDCS and a 1-minute active stimulus in the sham condition. After stimulation, subjects performed three sets of the bench press at a 70% of 1 maximum repetition intensity and 1 min of inter-set rest. The velocity loss was calculated as the relative difference between the fastest repetition velocity (usually first) and the velocity of the last repetition of each set and averaged over all three sets. Results: The results found no interaction between conditions and sets (P = .122), and no effect for conditions (P = .323) or sets (P = .364) for the velocity loss in each set. Also, no differences were found between the average velocity loss of the three sets in the anodal tDCS (-25.0 ± 4.7%) and sham condition (-23.3 ± 6.4%; P = .323). Conclusion: Anodal tDCS does not affect movement velocity in a typical strength training protocol in recreationally trained subjects.

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.

The role of the neural stimulus in regulating skeletal muscle hypertrophy

Resistance training is frequently performed with the goal of stimulating muscle hypertrophy. Due to the key roles motor unit recruitment and mechanical tension play to induce muscle growth, when programming, the manipulation of the training variables is oriented to provoke the correct stimulus. Although it is known that the nervous system is responsible for the control of motor units and active muscle force, muscle hypertrophy researchers and trainers tend to only focus on the adaptations of the musculotendinous unit and not in the nervous system behaviour. To better guide resistance exercise prescription for muscle hypertrophy and aiming to delve into the mechanisms that maximize this goal, this review provides evidence-based considerations for possible effects of neural behaviour on muscle growth when programming resistance training, and future neurophysiological measurement that should be tested when training to increase muscle mass. Combined information from the neural and muscular structures will allow to understand the exact adaptations of the muscle in response to a given input (neural drive to the muscle). Changes at different levels of the nervous system will affect the control of motor units and mechanical forces during resistance training, thus impacting the potential hypertrophic adaptations. Additionally, this article addresses how neural adaptations and fatigue accumulation that occur when resistance training may influence the hypertrophic response and propose neurophysiological assessments that may improve our understanding of resistance training variables that impact on muscular adaptations.

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.

Acute effect of high-definition and conventional tDCS on exercise performance and psychophysiological responses in endurance athletes: a randomized controlled trial

Transcranial direct current stimulation (tDCS) has been used aiming to boost exercise performance and inconsistent findings have been reported. One possible explanation is related to the limitations of the so-called "conventional" tDCS, which uses large rectangular electrodes, resulting in a diffuse electric field. A new tDCS technique called high-definition tDCS (HD-tDCS) has been recently developed. HD-tDCS uses small ring electrodes and produces improved focality and greater magnitude of its aftereffects. This study tested whether HD-tDCS would improve exercise performance to a greater extent than conventional tDCS. Twelve endurance athletes (29.4 ± 7.3 years; 60.15 ± 5.09 ml kg^-1 min^-1) were enrolled in this single-center, randomized, crossover, and sham-controlled trial. To test reliability, participants performed two time to exhaustion (TTE) tests (control conditions) on a cycle simulator with 80% of peak power until volitional exhaustion. Next, they randomly received HD-tDCS (2.4 mA), conventional (2.0 mA), or active sham tDCS (2.0 mA) over the motor cortex for 20-min before performing the TTE test. TTE, heart rate (HR), associative thoughts, peripheral (lower limbs), and whole-body ratings of perceived exertion (RPE) were recorded every minute. Outcome measures were reliable. There was no difference in TTE between HD-tDCS (853.1 ± 288.6 s), simulated conventional (827.8 ± 278.7 s), sham (794.3 ± 271.2 s), or control conditions (TTE1 = 751.1 ± 261.6 s or TTE2 = 770.8 ± 250.6 s) [F_{(1.95; 21.4)} = 1.537; P = 0.24; η²p = 0.123]. There was no effect on peripheral or whole-body RPE and associative thoughts (P > 0.05). No serious adverse effect was reported. A single session of neither HD-tDCS nor conventional tDCS changed exercise performance and psychophysiological responses in athletes, suggesting that a ceiling effect may exist.

Acute effects of transcranial direct current stimulation on cycling and running performance. A systematic review and meta-analysis

Transcranial direct current stimulation (tDCS) has been proven to induce positive effects on athletic performance. The present study aimed to analyse the effect of anodal-tDCS on endurance (time to exhaustion [TTE] or endurance time trial [ETT]) and sprint performance during cycling and running tasks. We performed a systematic literature review in the databases Medline (via PubMed), SPORTDiscus and Science Direct. We included only randomised controlled trials conducted with healthy individuals in which an anodal-tDCS protocol was applied prior to cycling or running tests. The effect of anodal-tDCS (experimental condition) was compared against sham stimulation (control condition). A total of 15 interventions from 13 studies were included. The sub-group analysis revealed a positive effect of anodal-tDCS on TTE (standardised mean differences [SMD] = 0.37; 90% confidence interval [CI] = 0.13, 0.61; p = 0.01), but not on ETT (SMD = 0.00; 90% CI = -0.29, 0.30; p = 1.00) or sprint performance (SMD = 0.19; 90% CI = -0.23, 0.60; p = 0.46). The current meta-analysis suggests that the effect of anodal-tDCS on whole-body dynamic exercises (running and cycling) could be task dependent. Specifically, anodal-tDCS enhance running and cycling time to exhaustion performance during TTE tasks but not ETT or sprint tasks. The increase in cortical excitability induced by anodal-tDCS may lead to lower ratings of perceived exertion by reducing the input required to perform the physical task. Task should be taken into account, because it is probably influencing the result obtained by anodal-tDCS.