Transcranial direct current stimulation to enhance athletic performance outcome in experienced bodybuilders
Transcranial direct current stimulation to enhance athletic performance outcome in experienced bodybuilders
Ali-Mohammad Kamali 0 1 2 3
Zahra Kheradmand Saadi 2 3
Seyedeh- Saeedeh Yahyavi 0 1 2 3
Asadollah Zarifkar 0 2 3
Hadi Aligholi 0 2 3
Mohammad NamiID 0 2 3
0 Department of Neuroscience, School of Advanced Medical Sciences and Technologies, Shiraz University of Medical Sciences , Shiraz , Iran , 2 DANA Brain Health Institute, Iranian Neuroscience Society-Fars Branch , Shiraz, Iran, 3 Neuroscience Laboratory, NSL (Brain , Cognition and Behavior), Department of Neuroscience, School of Advanced Medical Sciences and Technologies, Shiraz University of Medical Sciences , Shiraz , Iran
1 Student research committee, Shiraz University of Medical Sciences , Shiraz , Iran , 5 Department of Foreign Languages and Literature, Shiraz University , Shiraz , Iran , 6 Department of Physiology, School of Medicine Shiraz University of Medical Sciences Shiraz Iran, 7 Academy of Health , Senses Cultural Foundation, Sacramento, California , United States of America
2 Editor: Benjamin Thompson, University of Waterloo , CANADA
3 University of Medical Sciences under the grant No. 1396-01-74-14298
Data Availability Statement: All relevant data are
within the manuscript and its Supporting
Competing interests: The authors have declared
that no competing interests exist.
Transcranial direct current stimulation (tDCS) is currently under investigation as a promising
technique for enhancement of athletic performance through modulating cortical excitability.
Through consecutive randomization, 12 experienced bodybuilders were randomly assigned
to two arms receiving either sham or real tDCS over the primary motor cortex (leg area) and
left temporal cortex (T3) for 13 minutes in the first session. After 72 hours, both groups
received the inverse stimulation. After the brain stimulation, cerebral hemodynamic
response (using frontopolar hemoencephalography) was examined upon taking three
computer-based cognitive tasks i.e. reasoning, memory and verbal ability using the Cambridge
Brain Science-Cognitive Platform. Subsequently, the bodybuilders performed knee
extension exercise while performance indicators including one-repetition maximum (1RM),
muscular endurance (SEI), heart rate (ECG), motivation (VAS), surface electromyography over
quadriceps femoris muscle (sEMG) and perceived exertion (RPE) were evaluated. The real
tDCS vs. sham group showed decreased RPE and HR mean scores by 14.2% and 4.9%,
respectively. Regarding muscular strength, endurance, and electrical activity, the 1RM, SEI,
and sEMG factors improved by 4.4%, 16.9%, and % 5.8, respectively. Meanwhile,
compared to sham, real tDCS did not affect the athletes? motivation. Incidentally, it turned out
that subjects who underwent T3 anodal stimulation outperformed in memory (p = 0.02) and
verbal functions (0.02) as well as their corresponding frontopolar hemodynamic response
[(memory HEG (p = 0.001) and verbal HEG (p = 0.003)]. Our findings suggest that
simultaneous tDCS-induced excitation over the M1 leg area and left temporal area may potentially
improve the overall athletic performance in experienced bodybuilders (Trial registration:
IRCT20181104041543N1, Registered on 4 Nov. 2018, retrospectively registered).
In competitive sports, three principles including faster, higher, and stronger hold significant
importance in not only professional but also amateur athletes. Over recent years, there has
been an increasing interest in brain stimulation and neuromodulation to cross-link
neuroscience and athlete?s performance [
]. One of the brain stimulation methods is transcranial direct
current simulation (tDCS) which results in brain excitability changes through a weak direct
current. In 2013, Davis coined the word ?neurodoping? which is representative of using
advanced techniques for mental and physical enhancement of athletes [
]. The compelling
idea of incorporating neuroscience in sport as well as he relationship between industry and
science has led to the knowledge-based products for improving professional athletes?
performance (www.haloneuro.com) [
]. In fact, factors such as motor learning, muscular strength,
fatigue or even processing speed for specific motor skills may gain through non-invasive brain
stimulation methods [
tDCS transmits a weak current (1 to 2 mA) through surface electrodes over scalp typically
for the duration 5 to 20 minutes. This electrical current is transferred to brain tissue and affects
the excitability and neuronal activity of the brain. In other words, tDCS changes the action
potential threshold in neurons [
]. Anodal tDCS leads to depolarization in resting membrane
potential and axons of target neurons resulting in an increased neuronal firing rate and cortical
]. On the other hand, cathodal tDCS leads to decreased excitability through
]. Studies have indicated that the effect of at least 10 minutes brain
stimulation would last an hour after the intervention [
]. It is presumed that a similar plasticity
trend exists in glutamatergic neurons [
]. This tDCS-induced modulation is evident in fMRI
studies where anodal and cathodal stimulation increases and decreases blood oxygen
leveldependent (BOLD) response in targeted areas, respectively [
An earlier report indicated the positive effects of tDCS over the right motor cortex of
healthy subjects in increasing isometric endurance of left elbow, decreasing muscle fatigue,
and improving motivation and muscle synergy [
]. Similarl, another study showed the
effectiveness of anodal tDCS over the motor cortex for improving muscular endurance, decreasing
fatigue, and enhancing athletes? performance [
Moreover, anodal tCDS over the temporal cortex (TC) has been found to modulate the
activity of autonomic nervous system (ANS) and improve peak power output of trained
cyclists by reducing their perceived exertion (PE) and heart rate (HR) [
]. TC has been
associated with ANS- autonomic dysfunction during or after seizures and may result in cardiac and
pulmonary changes [
]. In another study, tDCS over the left temporal lobe, increased HR
variability which was indicative of improving parasympathetic modulation of HR [
]. It should
be noted that higher vagal modulation enhances the autonomic cardiac function where
physical fitness is attributed to cardiac vagal function during exercise [
]. Compared to
non-athletes, athletes have higher vagal modulation and their HR increase more slowly in a specific
motor task [
]. In case that tDCS can change brain areas associated with ANS and increase
vagal modulation, it can improve athletes? performance during training. Vagal modulation
changes can be assessed by HR changes before and after tDCS [
With respect to motor functions, an investigation showed that anodal tDCS over M1
improved the cycling performance and increased time to exhaustion; however, no significant
changes were reported for PE and HR factors [
In addition to the effectiveness of tDCS for muscular fatigue, a recent research
demonstrated the positive effect of dlPFC stimulation on implicit motor learning [
]. The study
which was done on 27 healthy individuals showed that cathodal stimulation of dlPFC
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compared to sham tDCS improved golf putting performance suggestive of enhanced implicit
motor learning. Nevertheless, the participants? verbal working memory was impaired.
Previously, modulation of motor cortex through the application of tDCS had been studied
] whereby anodal stimulation of the M1, premotor, or prefrontal cortices during a
reduction time task indicated the active role of M1 in implicit motor learning, while the stimulation
of other areas showed no specific effect on the same. In line with this study, another research
examined the effects of tDCS over M1 on motor skill acquisition and its long-term retention.
The findings showed that anodal tDCS group developed a better skill acquisition trend
compared to the sham group [
Given the importance of motivation in performance and physiological response of the
athletes, the efficacy of tDCS on motivational level of athletes has been addressed in some reports
In one of our research-team?s reports, anodal and cathodal tDCS over the left prefronral
and ipsilateral cerebellar cortices, respectively, in professional pistol shooters could improve
shooting task scores [
]. However, this emerging field requires more research to define the
effectiveness of tDCS on athletes in various sport field as well as the optimized protocols
including stimulation duration, electrode montage and stimulation amplitude for tDCS
application in sport.
Furthermore, most of the studies done till now have examined a small muscle mass such as
biceps brachialis. Thus, examining a rather big section of muscles can be of greater
significance. So far, there is no study addressing the effects of tDCS on weight lifting exercises.
Nevertheless, some studies have shown that tDCS cannot enhance motor functions. For
instance, one report indicated that stimulation of the right motor cortex (2mA) did not exert
any significant effect on the neuromuscular fatigue [
]. Another study showed that tDCS did
not improve muscular performance in an isometric exercise. The authors concluded that since
the muscle has already been reaching its maximal strength capacity, the intervention could not
further enhance the muscular strength [
]. Nevertheless, the majority of sports-related studies
into the motor cortex have shown the positive significant effects of tDCS [
That said, the present investigation was designed to examine the effects of anodal tDCS
over M1 leg area and TC on muscular power, short-term muscular endurance, subjective
fatigue perception, HR, cognitive functions, frontopolar hemodynamic response, and
motivation towards the lifting task. The study primarily hypothesized that our intervention vs. sham
condition would lead to an enhanced short-term muscular endurance, decreased subjective
fatigue perception, decreased post exercise HR, increased frontopolar hemodynamic response,
and motivation while cognitive functions are sustained or even improved.
Ethical approval and consent to participate
This was a factorial single-armed randomized trial in which subjects were assigned to sham or
true tDCS intervention through simple randomization in 1:1 ratio. Approval for this study was
obtained from the Shiraz University of Medical Sciences (SUMS) (No. 1396-01-74-14298).
Since the Iranian Registry of Clinical Trials (IRCT) registration process is time-consuming, in
some cases the university?s review board allows trial commencement based on the permission
granted by the institution. The first participant?s recruitment was then done based on the
ethical board approval (IR.SUMS.REC.1396.147 granted on 4th April 2017) and the permission
granted by the institutional review board committee at SUMS (1396-01-74-14298). The work
was also registered by IRCT under the code IRCT20181104041543N1 (granted on 23rd Dec
2018) and the registration timing was retrospective.
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Recruitment was done during the period of 4th April 2017-22nd October 2018.
The authors confirm that all ongoing and related trials for this intervention are registered.
Informed consent: The entire process including its rationale and objective, the participants?
role and safety consideration was explained to each candidate in plain language. The
participants were then asked to sign a written informed consent indicating that their data would
remain confidential and they may resign from the process on their discretion whenever during
the project. The consent was made in two identical copies of which the participants could
Sampling method, case selection: Case selection followed a cluster random sampling
method. The bodybuilding sport clubs were alphabetically sorted and randomly approached
within various district of the town. Candidates (experienced bodybuilders) who had at least 2
years of consistent bodybuilding exercise (minimum of three sessions per week lifting
workouts) were sequentially selected and debriefed about the project to get possibly enrolled.
After random selection of 6 bodybuilding gyms across the city of Shiraz and posting
announcement in the gyms, 12 experienced bodybuilders were randomly chosen from those
who volunteered to participate in the study.
With respect to sample size calculation, we referred to the earlier related reports [
] in which the sample size ranged from 8 To 16 The Kelsey and Fleiss sample size
calculation formula [
] was used (power 80 and ? = 0.05) whereby the minimum justifiable number
of 20 participants were decided to get enrolled. Based on earlier reports in the field of sport,
the specialized population namely bodybuilders limited the sample size of the study. Those
who enrolled in the study were males aging 18 to 40 with weight between 60 to 120 kg who
were regularly training weightlifting exercise (at least 3 times a week) not on doping drugs for
at least 3 months prior to enrollment. The participants were assured not to have psychological
or neurological disorders or a history of alcohol or drug use. In addition, the volunteers were
instructed to refrain from vigorous activities and the ingestion of beverages containing caffeine
and alcohol or of using tobacco for 24 h prior to each test.
Since subjects? performance was compared to their own sham-stimulation status, the use of
ordinary food supplements was excluded from our "red-flag" checklist. Meanwhile the use of
medicaments and specific supplements (within three months prior to enrollment) which were
indicated in the official list of the World Anti-doping Agency (2018) was considered as an
The above three-month time window was decided since majority of the doping listed agents
can hardly be traced in regular anti-doping test after such a period.
After all, the study design (within group self-comparison upon sham and true brain
stimulation) could potentially minimize the biasing effect.
Through a double-blind, counterbalanced design, a clinical neuroscientist who was blind to
session assignment used a random digit table to sequentially allocate subject to interventions.
Data were obtained over two sessions with the interval of 72 hours (Fig 1A). A researcher who
was blinded to data collection process randomly assigned the participants to sham and real
tDCS arms using consecutive randomization. Subjects were randomly submitted to 2 mA
sham or real tDCS over M1 and TC for 13 minutes in the first session. After 72 hours, the
group who received sham first, received real tDCS and the first real tDCS group received sham
in the second session. Since the participants were under maximum physical pressure during
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Fig 1. Study protocol, leg extension exercise involving quadriceps muscles, and the tDCS montages used for brain stimulation. (A) Participants were randomly
assigned to either sham or real tDCS at 2mA for 13 minutes over the first session. Then, they performed 3 tasks including reasoning, memory and verbal from
CBScognitive platform (see Methods section) with the intervals of 3 minutes? rest. CBS-CP and the HEG data were concurrently recorded while subjects carried out the
tasks. Later, they performed the leg extension exercise and their 1RM were recorded. With the interval of 3 minutes, the participants? perceived exertion was examined
and then, they performed the leg extension with 30% of their 1RM and their endurance level was recorded. Meanwhile, their heart rate during the exercise was also
recorded. After 72 hours, the real group received sham tDCS whereas sham group received real tDCS for 13 minutes and they performed the rest of the tasks similar to
the first session. (B) The examinees were supposed to choose a weight, bend the legs at a 90-degree angle and after extending the legs, move them back to the primary
position. To calculate the 1RM, the athletes were asked to perform the exercise for at least 6 to 12 times with the maximum weight. For the SEI, they were required to
bear 30% of their 1RM weight and perform the exercise as many times as they could. The sEMG sensors were attached to the midpoint of anterior superior iliac spine
and patella through chest leads with the ground on patella and the sEMG data were recorded during the 1RM exercise. The ECG sensors were attached to the upper
right portion of chest below collarbone and below left breast over lower rib-cage to obtain recording during the endurance exercise. (C) A 2 mA anodal tDCS pad
electrode was placed over the left temporal cortex (T3) and anodal tDCS over the Cz covering C1 and C2 (M1 leg area) for a course of 13 minutes. The size of the
electrodes is depicted in the Fig. The cathode electrodes for M1 and T3 were placed over the right and left shoulders, respectively.
PLOS ONE | https://doi.org/10.1371/journal.pone.0220363
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each testing session, a proper interval was required between the two sessions. The 72h
intermission was therefore considered to avoid the confounding effect of muscular fatigue.
Moreover, a day before the study (for both sessions), the participants were contacted via phone and
reminded to get some quality sleep and maintained their routine diet. In addition, they were
asked to avoid coffee, alcohol, and other exclusion criteria on the day of the study. In addition,
the study design (random true or sham stimulation in the first or second session) could reduce
the effect of inter-day variability in performance over the two different sessions. The Visual
Analogue Scale was used to measure the participants? fatigue on the study day to exclude those
with subjectively reported excessive fatigue.
It is shown that the effects of 13 minute 2mA stimulation on cortical excitability would
fade after 150 minutes [
]. Following the brain stimulation, to examine the participants?
cognitive performance, the bodybuilders were required to perform 3 tasks from the
computerized Cambridge Brain Sciences-Cognitive Platform (CBS-CP) with the intervals of 3
minutes between each task. Meanwhile, their prefrontal hemodynamic response was
evaluated using the hemoencephalography (HEG) setup upon performing the mentioned tasks.
The participants were then asked to warm up and perform the knee extension exercise for at
least 6 to 12 times with the maximum weight that they could bear with the Knee Extension
Machine in order to obtain their 1RM (Fig 1B). This exercise is considered as one of the
basic moves in weightlifting practice targeting the quadriceps femoris muscle. It should be
noted that only the practices in which the legs could bend at a 90-degree angle were
recorded as correct moves.
After 3 minutes rest, in order to assess the participants? exertion rate upon knee extension
exercise for obtaining 1RM, the bodybuilders were asked to fill the hr questionnaire .
Earlier reports have postulated a high correlation between RPE and blood as well as muscle
lactates which are biochemical indicators of heart and muscle exertion . Furthermore, to
assess the participants? motivation in continuing the exercises, a Visual Analogue Scale (VAS)
was used. After that, participants were asked to choose a weight equaling 30% of their 1RM
and perform the knee extension exercise as many times as they could. This time, multiplication
of the weight by the number of successive exercise was considered as the Short-term
Endurance Index (SEI). Moreover, the participants? HR during exercise performance was recorded
as an indicator of autonomic response.
Taken together, the study randomized the subjects into sham and real tDCS then switched
and compared results between stimulations. The difference in variable scores following
truevs. sham-tDCS (through paired t-test) was attributed to the potential effect of the intervention.
Transcranial direct current stimulation (tDCS)
In this study, a two channel tDCS device (Neurostim-2, Medina Teb) was used to transfer a
2mA electrical current for 13 minutes with ramping up and down of 30 seconds. In one
channel, the anode electrode was placed over the Cz (35 Cm2) overlying C1 and C2 (M1 leg area)
responsible for leg movement and the cathode (16 Cm2) was placed over the right shoulder.
For the second channel, the anode (16 Cm2) was placed over the TC (T3) and the cathode
electrode (16 Cm2) was placed over the left shoulder. The electrodes were placed based on the
international 10?20 EEG electrode placement system and the saline-soaked sponges (NaCl 150
mM) were used under the electrodes over the scalp. To induce a sense of stimulation in the
sham session, an electrical current was delivered for 30 seconds and then, the current was
switched off; however, the count-down indicator and the indicator light on the device screen
were on throughout the session. In the real tDCS session, the electrical current was delivered
for 13 minutes.
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According to some studies, the stimulation of motor cortex for 10 minutes does not have a
significant effect on muscular performance. Nitsche et al. [
] showed that the effects of a
tDCS session (2mA, 13min) continued to remain for 150 minutes. In addition, some other
studies into cyclists indicated the effectiveness of stimulation (13min) in enhancing their
athletic performance [
]. As a result, we considered a stimulation for 13 minutes as an optimal
stimulation duration already examined. It is worth noting that the length of stimulation was 20
minutes in the majority of studies. We considered a shorter length of stimulation as it could be
more convenient before sport competitions.
With regard to the stimulation sessions, subjects were briefed about the possible fine
tingling sensation they might feel during the stimulation. They were also reassured about the
safety profile of the process. During the tDCS session (13 min), the participants were
instructed to sit still comfortably on a chair and do nothing, keeping their eyes open.
At the end of each stimulation sessions, the participants were asked about their feeling
regarding the sham versus real tDCS. Since the participants were stimulated for 30 minutes in
the sham session with 30 second ramp?up, they could not accurately distinguish between the
sensation over the real and sham sessions.
The tDCS montage used for brain stimulation is depicted in Fig 1C.
Instruments, measurements and metrics
The instruments and materials used upon data collection.
Visual Analogue Scale (VAS): used as a continuous single-item fatigue scale ranging from
0 (no fatigue) to 10 (severe fatigue). This scale evaluated the participants? motivation in
performing the tasks and continuing the exercises.
Heart Rate (HR) recording: the HR was recorded by a NeXus-4 (MindMedia,
Netherlands) Biofeedback setup. The electrocardiography (ECG) sensors were attached to the
participants through chest leads and the HR data were recorded while the participants were working
out the knee extension endurance exercise. The average HR of each two knee extension
exercises was calculated for further analysis.
Rated Perceived Exertion (RPE): This is a 6 (no exertion) to 20 (maximal exertion) scale
developed by Borg et al.  to assess the body PE during exercise. The RPE was shown to the
participants and they were instructed how to report their PE. The reliability index of this scale
reported by Borg et al. was robust (r = 0.92). Our study employed the validated Persian version
for the same purpose.
One-Repetition Maximum (1RM) scale: muscle strength is the capacity of a muscle to
exert force. 1RM is regarded as one-repetition maximum used to determine maximum
strength calculated through 1RM = w (1 ? 3r0), considering r >1 [
], where r is the number of
repetitions performed and w is the amount of weight participants could lift by their knee
Short-term Endurance Index (SEI): To assess this factor, the participants were asked to
choose 30% of their 1RM and perform as many as the knee extension exercise they can. The
SEI was calculated by multiplication of the amount of weight (30% of their 1RM) by the
number of successive exercise.
The Cambridge Brain Science Cognitive Platform (CBS-CP): Cognitive performance is a
crucial substrate of athletic function in many instances [
]. In order to distinguish the
positive or negative impact of our brain stimulation protocol on cognitive performance of the
participant?s cognitive assessment was pursued. To do so, a media-rich computerized online
platform addressing three higher-order cognitive components of reasoning, memory and
verbal ability  was used. From each component, a test was chosen to see the effects of tDCS on
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different aspects of cognitive performance. The ?Rotation, Monkey Ladder and Digit Span?
tasks were chosen from reasoning, memory, and verbal domains, respectively.
Prefrontal hemodynamic response: the assessment was used to identify local intracranial
hemodynamic changes in prefrontal cortex (PFC) using a Hemoencephalography (HEG)
device (a peanut near infra-red HEG kit, BIOCOMP Research Institute, Los Angeles, CA).
Thereby, the optical density in left frontopolar (FP1) area was recorded during completion of
the three aforementioned CBS-CP tasks after either sham or real tDCS intervention.
Surface Electromyography (sEMG): A Nexus Biofeedback setup was used to record sEMG
from the rectus femoris muscle, a factor representing the neuromuscular dynamics. Due to
limitations in the device channels, we had to stimulate only one muscle and record the heart
rate at the same time with other channel of the polygraphy device. The rectus femoris muscle
is one of the most important muscles involved in knee extension. Since the motor cortex of the
leg was stimulated through tDCS, the contraction of this muscle was considered as a sample
resembling the activity and contraction of the rest of muscles within quadriceps. However, the
selection of this muscle does not indicate its superiority over other quadriceps femoris
Before placing the electrodes, the site was shaved, disinfected by alcohol, and given time to
dry out completely. Employing Surface EMG for Non-Invasive Assessment of Muscles
(SENIAM) guidelines [
], the sensors were attached to the midpoint of anterior superior iliac
spine and patella through chest leads and the sEMG data were recorded during the 1RM
exercise. The sEMG recordings were pre-processed and denoised to eliminate peaked sharp
artifacts. EMG sampling rate was 1,024 per second. A band pass filter from 100 Hz to 500 Hz was
applied during online recording. Raw EMG data were then recalculated through the root
mean square (RMS) method to transform EMG signals into amplitudes. The resulting
amplitudes were then subject to statistical analysis.
In addition to raw signals, Biotrace+ software (V2017A, Mind Media B.V., The
Netherlands) provided root mean square data (epoch size: 1/8 s, 32 samples per second). Results are
illustrated in Fig 4.
Based on the normality of distribution, parametric and non-parametric statistical tests were
employed. A series of paired sample t-tests were run to compare the differences between sham
and real tDCS with regard to different factors including motivation, HR, RPE, 1RM, SEI,
CBS-CP, and HEG data.
Wilcoxon signed-rank test was used to analyze data lacking normal distribution. The
differences between the sham and real tDCS sessions were evaluated based on the Mean?SEM
(Standard Error of Mean). The p values below 0.05 were considered as statistically significant.
The SPSS statistical package (Version 22.0.0) was used for data analyses.
12 experienced bodybuilders were randomly chosen from those who volunteered to participate
in the study.
The participants? demographic data [Mean?SEM (standard error of mean)] included: age
in years = 25.6?6; years of training in bodybuilding = 5.7?3.4 and years of formal
education = 15?3.
One-repetition maximum (1RM): With regard to the 1RM used to evaluate the maximum
weight lifting performance, the real tDCS vs. sham could improve mean muscular strength
score by 4.4% (p = 0.002) (Fig 2).
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Fig 2. Dot plots representing the participants? performance for the task outcomes including muscular strength
(1RM), motivation, muscular endurance (SEI), perceived exertion (RPE), and HR. Panel a shows a significant
difference between the 1RM of the athletes in true vs. sham tDCS sessions (p <0.05). The 1RM was calculated through
1RM = w (1 ? 3r0), considering r >1 (48), where r is the number of repetitions performed and w is the amount of
weight. Panel b indicates no significant difference for the motivation of bodybuilders in sham vs. real sessions
evaluated through VAS, a continuous single-item fatigue scale ranging from 0 (no fatigue) to 10 (severe fatigue)
(p<0.05). Panel c indicates a significant difference in SEI [multiplication of the amount of weight (30% of their 1RM)
by the number of successive exercise] for the sham vs. real tDCS session (p<0.05). Panel d shows a significant
difference between the RPE in sessions 1 and 2 (p<0.05). Panel e shows a significant difference between HR in the last
12 lifts (the average HR of each two leg extension exercises is plotted in the graph) in sham and real tDCS sessions
(p<0.05). Paired t-test was used with the p value significance level set at 0.05. ns: non-significant.
Short-term endurance: The findings revealed that compared to sham, real tDCS could
significantly (p = 0.004) increase the participants? mean short-term endurance score (SEI) by
16.9% (Fig 2). This indicates the potential impact of true tDCS vs. sham on muscular
Rated perceived exertion: The analysis revealed a statistically significant difference
between the participants? PE in sessions 1 (sham) and 2 (real) tDCS. The real tDCS vs. sham
could decrease RPE mean scores by 14.2% (p = 0.007) (Fig 2).
Heart rate: The results of HR recording over the last 12knee extension exercises showed a
significant difference between real vs. sham tDCS session and the 6 final p values were 0.006,
0.008, 0.03, 0.009, 0.01, and 0.008, respectively, suggesting decreased HR by 4.9% following
brain stimulation (Fig 2).
Based on our findings, there was not a statistically significant difference between the
participants? motivation in sham and real tDCS sessions; however, the mean score increased from 6.1
in sham session to 6.5 in real tDCS session (Fig 2).
Cambridge brain sciences-cognitive platform: The results of paired-sample t-tests on
CBS-CP tasks showed a statically significant difference between the sham and real tDCS
sessions in memory (p = 0.02) and verbal (p = 0.02) tasks. However, with respect to the reasoning
task, brain stimulation could not enhance the mean score from sham to real tDCS session
A series of paired-sample t-test were used to compare cerebral blood flow in FP1 in the sham
and real tDCS sessions. Our findings indicated a statistically significant increase in FP1
hemodynamic response upon memory (p = 0.001) and verbal (p = 0.003) cognitive tasks (Fig 3).
Nevertheless, for the reasoning task, no statistically significant difference was noted in HEG
response from session 1 to session 2.
Surface electromyography (sEMG)
Results of the sEMG indicated that anodal M1 and TC stimulation could significantly increase
the sEMG amplitude (p = 0.01). Moreover, as shown in Fig 4, the protocol could increase the
sEMG frequency during the knee extension lift task (Fig 4).
Over recent years, brain stimulation has become a trend for athletic performance
enhancement; however few studies [
2, 13, 14, 34
] have systematically investigated the issue so far.
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Fig 3. Dot plots showing the performance of bodybuilders in CBS-CP tasks i.e. reasoning, memory, and verbal
and the HEG data recorded while taking the tasks over two sessions, 72 hours apart. Panel a shows no significant
difference between the performance of the athletes on a reasoning task in sham vs. real tDCS sessions. Panel b indicates
no significant difference between the HEG responses upon reasoning task in sham and real sessions. Panel c represents
a significant difference in a memory task scores from sham to real tDCS session (p<0.05). Panel d indicates a
significant difference between the HEG responses upon a memory task in sessions 1 and 2 (p<0.05). Panel e shows a
significant difference between the verbal task scores in sham and real tDCS sessions (p<0.05). Panel f shows a
significant difference between the HEG responses upon a verbal task in sham and real sessions (p<0.05). Paired t-test
was used with the p value significance level set at 0.05. ns: non-significant.
Nevertheless, most tDCS studies on athletic performance have addressed the issue of athletes?
], while the impact of brain stimulation on maximal muscular strength of
athletes is yet to be further defined. Taking into account the critical role of brain in exercise
], the present study aimed to determine whether a tDCS-induced cortical
excitability of M1 leg area and TC would enhance neural processing and, as a result, improve
maximal muscular power, muscular endurance and fatigue, motivation, HR, prefrontal
hemodynamic response, and cognitive functions in experienced bodybuilders.
With respect to the athletic performance, ANS activity is shown to be associated with
exercise performance [
] and perceived fatigue [
]. Confirming the association between the TC,
and ANS [
], specifically HR and blood pressure [
], our findings showed that TC
stimulation regulates the athletic performance potentially due to a decreased perception of exertion in
relation with the ANS function. Through modulating the ANS, this technique reduced the
bodybuilders? HR by 4.9% during the 12 final moves of the muscular endurance exercise,
presumably through increasing and decreasing parasympathetic and sympathetic functions,
respectively. Hence, our results proposed the facilitatory effects of tDCS applied over TC
associated with ANS activity which has previously been shown to improve cardiac autonomic
control during exercise [
9, 10, 12, 38
Indeed, greater vagal modulation is shown to result in regulated cardiovascular autonomic
function, which potentially improves athletic performance [
]. Moreover, athletes are shown
to have higher vagal modulation than non-athletes [
] and consequently, their heart rate
increases more slowly than non-athletes under a specific task [
]. The athletic performance
can be enhanced by stimulating specific brain regions related to the autonomic nervous system
and increasing vagal modulation. As such, vagal modulation can be assessed by comparing
changes in heart rate before and after the tDCS [
]. The vagus nerve fibers are more richly
innervated in the atrium than in the ventricle, where energy for the contractions of the heart is
provided. This may justify the effect of vagal stimulation, which typically slows down the heart,
while the contractibility of cardiac muscles does not reduce much [
]. In fact, a slight
reduction in heart rate during an intense exercise may improve cardiac muscles? contractibility. In
our study, the heart rate significantly reduced almost at the end of the physical task.
Moreover, our results indicated that 2mA anodal tDCS for 13 minutes significantly boosted
maximal strength and endurance performance of bodybuilders by 4.4% and 16.9%,
respectively, compared to sham stimulation. The results of enhanced maximal power (1RM) and
endurance (SEI) could justify the impact of anodal tDCS over M1 to improve muscle strength
], muscle synergy, muscular endurance [
], motor performance of the lower limbs
], locomotion and balance in patients with Parkinson?s and stroke [
]. This has also
been extended to more complex tasks such as static [
] and dynamic balance learning though
induced excitability [
]. Yet, our results contradict the report showing that the maximum
capacity of professional pianists in motor learning is limited [
]. Our findings suggest that
the maximal strength of experienced bodybuilders can be enhanced following brain
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Fig 4. sEMG recording from bodybuilders? rectus femoris during 1RM exercise. The image represents the ?raw?
EMG signal of rectus femoris muscle (Blue) and the ?RMS? (Root Mean Square) of rectus femoris muscle (Red). Panels
a and b represent the gross pattern for muscle contraction including the sEMG amplitudes were calculated (epoch size:
1/8 s, 32 samples per second) after sham and real tDCS, respectively. The peaks correspond to the lifts performed
during the 1RM exercise. Comparing the panels a and b, the frequency is shown to get increased after real tDCS. Panel
c represents a significant difference in RMS from sham to real tDCS sessions (p<0.05). Paired t-test was used with the
p value significance level set at 0.05. ns: non-significant.
Anodal tDCS is shown to potentially reduce the release of the inhibitory neurotransmitter
]. This has also been postulated through the evidence from magnetic resonance
spectroscopy (MRS) [
] showing that the anodal stimulation inhibits the release of GABA
]. In the current study, GABA reduction probably improved the functions of cholinergic
and glutamatergic neurons . As a result, the excitability of motor neurons increases which
may: 1- increase the release of acetylcholine neurotransmission in the synaptic terminal of
neuromuscular system, 2-involve more muscular units,3- increase the mean neuronal firing
], and 4-increase 1RM.
Formerly, it was shown that despite improving cycling performance and time to
exhaustion, anodal tDCS over M1 did not affect PE and HR factors [
]. Nonetheless, our
investigation confirmed positive effects of tDCS on HR and perception of exertion besides enhancing
maximal and endurance exercise performance. Our findings were in agreement with the
studies which demonstrated the positive effects of anodal stimulation of M1 in decreasing muscle
3, 7, 8
]. Therefore, it may be concluded that simultaneous anodal stimulation of M1
and TC can be an optimized protocol to potentiate the overall performance of athletes
considering important athletic factors of muscular power, endurance, fatigue perception, and HR.
The existing evidence support the fact that the temporal region retains a defining role in the
functional regulation of autonomic nervous system [
]. According to a study, when people
have a good feeling, like when a mother sees her child?s photo, their left insular cortex in
activated . In the current study, in addition to the motor cortex, the temporal cortex was
concurrently stimulated. This has potentially resulted in a reduced perceived exertion (rated
through RPE) and heart rate, supporting the effect of anodal tDCS on autonomic functions.
In our study, the enrolled athletes rated their perceived intensity of a physical exercise using
the RPE. The RPE results are used to determine the maximum exertion in a physical exercise.
Studies have shown that the RPE scale is well correlated with serum as well as muscle lactic
acid, which are biochemical markers for muscle fatigue . Therefore, an open question to
address in future research is to investigate whether reduced RPE is proportionately linked to
altered levels of serum and muscle lactic acid.
Being involved in emotional awareness and recognizing emotional stimuli, TC was
stimulated in order to examine its effect on the bodybuilders? motivation. In agreement with the
finding of the reports showing the positive effects of tDCS over the right motor cortex of
healthy subjects in improving motivation [
], our study similarly found that the motivation
mean score increased. However, statistical analysis did not reveal any significant difference
between sham and real tDCS. This might be preliminarily due to the focus of the tDCS since
we have not placed the anodal stimulation on the specific areas (frontopolar brain regions)
 which are potentially linked to the motivational capacity of the participants undergoing
the training exercise. Although the anodal stimulation of T3 may result in positive feelings [
it could not significantly improve the bodybuilders? level of motivation in our study.
With respect to cognitive functions, according to Furley et al. in addition to muscular
performance, the cognitive functions such as working memory and reasoning, are among
potentially defining factors in athletic performance mainly at professional level. An enhanced focus
and working memory function can reduce executive lapses and improve tactical decisions in
14 / 20
sport competitions . The cross-link between cognitive capacity and athletic performance
following transcranial electrical stimulation need to be defined not only to show the safety of
applied stimulation but also the possible benefits on athletic performance.
To assess the cognitive aptitude of examinees in relation to muscular performance
following cortical electrical stimulation, we chose to employ the Cambridge Brain Science-Cognitive
Platform (CBS-CP). This tool is among the mostly used and validated media-rich computer
platforms with an ongoing normative database comprising over 40000 subject entries
]. Since the peak effect of single session tDCS remains for almost one hour [
faced time-constraint and had to limit cognitive assessments to maximum 3 tasks. As such,
one task from each domain within the CBS-CP (i.e. Memory, verbal and reasoning) was
selected and administered. More comprehensive cognitive assessments would better be
assessed in future research works of similar context where time-constraint is not an issue.
In the current study, the motor cortex stimulation resulted in the enhancement of working
memory, which could also affect long-term memory. Proji et al.  showed that anodal tDCS
over the primary motor cortex (M1) would potentiate synaptic plasticity through modulating
NMDA receptors and ultimately result in the enhancement of long-term memory.
One way to measure neuronal activity is to record cortical hemodynamic changes . The
hemodynamic changes in the left frontopolar cortical region (FP1) can be measured using
hemoencephalography (HEG) response. Based on the existing evidence, a higher HEG
response at prefrontal cortical regions corresponds to proper cognitive capacity . In our
study, there was probably a direct relationship between the cognitive function improvement
(memory and verbal) and increased HGE response following anodal tDCS.
Our study was consistent with that of Toomim et al. conducted on people with attention
deficit showing that people with increased HEG response in FP1 scored higher in the TOVA
test (Test Of Variables of Attention) which assesses several cognitive and behavioral domains
including attention, reaction time and impulsivity . In our study, the cognitive test scores
(Digit Span and Monkey Ladder Tests) were significantly improved proportionately with the
gain in HEG response. These two tests are categorized as visuospatial and verbal working
memory testing tools [
]. A key large-scale brain network involved in visuospatial scanning
and working memory is located within the prefrontal cortex where the HGE response
significantly increased in our investigation [
]. Since in addition to the muscular strength, cognitive
functions are also effective factors in athletic performance, we investigated three different
cognitive tasks taking into consideration the research limitations. Our intervention was shown to
improve some cognitive domains and this was reflected in frontopolar hemodynamic changes.
Considering the cognitive functions, anodal tDCS over the M1 leg area and TC was not
only safe in terms of hampering cognitive functions but also effective in improving mean
scores in some domains memory and verbal ability tasks. However, no significant effect was
noted regarding the reasoning task. Outperformance on ?Digit Span task? (verbal) could be
justified by repetition in the task associated with superior longitudinal fasciculus and arcuate
fasciculus modulated through T3 stimulation. The results on verbal task could be compared with
a study  indicating the positive effects of tDCS over M1 in word-retrieval, a verbal task.
However, the results are in contrast to earlier researches which showed that anodal tDCS over
M1 had no significant effect on working memory in healthy individuals  and patients with
Parkinson?s disease .
We preliminary hypothesized that the safety of this intervention would need to be
warranted by no potential impairment in cognitive capacity of the participants who underwent
this process, surprisingly, it was found that not only they did not have any decline in cognitive
function, but in some specific domains it showed to have outperformance in terms of memory
and verbal capacity. This could potentially be justified through stimulated networks which are
15 / 20
practically implicated in cognitive functions including memory and verbal ability. Moreover,
tDCS induced excitability resulted in increase in prefrontal hemodynamic response upon
memory and verbal cognitive tasks as suggested by previous studies showing an increased
blood-oxygen level due to anodal brain stimulation [
] which is probably caused by cortical
Moreover, anodal M1/TC stimulation could increase sEMG amplitude (RMS) in line with
the reported effectiveness of anodal motor stimulation on biceps brachii muscle activation and
increase in elbow flexor muscle activity . However, the results cannot be generalized to all
age groups since it is already revealed that tDCS over the motor cortex in old adults exerted no
effects on their elbow flexion muscle strength and sEMG amplitude 
Moreover, the Type II fast muscle fibers are often innervated through high-threshold
neurons. This type of muscle fibers is often closer to the surface and their contraction variations
can be well traced with the sEMG [
]. As a result, a small change in using motor units can be
traced with the sEMG . In the current study, a significant increase in RMS was observed
following tDCS reflecting empowered motor units during an isotonic task. However, further
studies are required to determine a more accurate mechanism for muscular activities following
The current study was subject to some shortcomings including a relatively small sample
size, lack of further objective assessments techniques to label fatigue such as magnetic
resonance spectroscopy of muscles for lactic acid level, lack of further dose-response examinations
in tDCS including varied protocols based on timing and amplitude. In addition, brain
mapping upon bodybuilders? task performance through quantitative electroencephalography
(qEEG) would be of great help in future research.
Although this study indicated the efficiency of simultaneous anodal stimulation of M1 leg
area and TC in enhancing the performance of bodybuilders in terms of muscular strength,
endurance, HR, fatigue, prefrontal hemodynamics, sEMG amplitude, and cognitive ability,
further investigations should attempt to define optimized protocols to be used in real practice
Furthermore, due to the important role of cerebellum in movement and muscular
coordination and strength as well as its close relationship with motor cortex, the question about
application of cerebellar tDCS for bodybuilders? performance can be sought is future research.
With a larger sample size, another issue to tackle is to examine whether there is a
correlation between athletic performance in bodybuilders (i.e. 1RM) and cognitive profile. Some
cognitive domains including emotion, drive, motivation and attention may potentially be linked
to optimized performance in athletic field [66, 67]. Though, the hypothesis would need to be
systematically addressed in future well-designed research.
Finding from this research is expected to add to the emerging body of evidence toward
incorporating applied neuroscience insights in to sports. Further systematic research on
similar topics need to gain momentum to bring such novel insights in to real life applications.
Taken together, our present report suggests that the integration of anodal M1 leg area and TC
tDCS may assist bodybuilders to improve their overall performance. This study may pave the
path towards designing brain stimulation protocols to enhance strength and subsequently
the muscle mass in bodybuilding which is known as a basic competency in many sports.
Additionally, since sustainable training may hardly affect the autonomic nervous system tone,
auxiliary methods such as tDCS to assist athletes with decreased fatigue perception could be
16 / 20
The present results may appeal to the interest of athletes, coaches and policy makers to help
improve athletic performance.
S1 Table. Raw data.
S2 Table. CONSORT checklist.
Conceptualization: Ali-Mohammad Kamali, Mohammad Nami.
Data curation: Ali-Mohammad Kamali, Mohammad Nami.
Formal analysis: Zahra Kheradmand Saadi, Seyedeh-Saeedeh Yahyavi, Mohammad Nami.
Funding acquisition: Mohammad Nami.
Methodology: Ali-Mohammad Kamali, Asadollah Zarifkar, Hadi Aligholi, Mohammad Nami.
Project administration: Ali-Mohammad Kamali, Asadollah Zarifkar, Mohammad Nami.
Resources: Ali-Mohammad Kamali, Mohammad Nami.
Software: Seyedeh-Saeedeh Yahyavi.
Validation: Ali-Mohammad Kamali.
Visualization: Ali-Mohammad Kamali.
Writing ? original draft: Ali-Mohammad Kamali, Zahra Kheradmand Saadi,
Seyedeh-Saeedeh Yahyavi, Hadi Aligholi, Mohammad Nami.
Writing ? review & editing: Ali-Mohammad Kamali, Zahra Kheradmand Saadi,
Saeedeh Yahyavi, Mohammad Nami.
17 / 20
18 / 20
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