Transcranial Direct Current Stimulation Improves the Cycling

Performance but Does Not Alter Neuromuscular Function

tDCS, Cycling Performance and Neuromuscular Function

Leandro Ricardo Altimari

, Marcelo Vitor-Costa

, Henrique Bortolotti

and Nilo Massaru Okuno

Group of Study and Research in Neuromuscular System and Exercise, Physical Education and Sport Center,

Londrina University State, Londrina, Paraná, Brazil

Department of Physical Education, Ponta Grossa University State, Ponta Grossa, Paraná, Brazil

1 OBJECTIVES

The main neurophysiologic mechanisms that

determine performance in physical activities or

sports are not well understood. This is mainly due to

the lack of technology that permits the study of the

human brain in vivo. In the last decades some

neuromodulation techniques have been developed

and, among them, the transcranial direct current

stimulation (tDCS) has been attracting attention as it

is easily applicable and permits to carry out well

controlled studies in humans, and has been shown to

be a strategy to enhance physical and mental

performance in sports (Davis, 2013).

Therefore, the objective of the present study was

to investigate the effects of anodic tDCS on the

physical performance and neuromuscular function in

cycling exercise.

2 METHODS

A total of 11 physically active subjects aged 26 ± 4

years, weighing 77 ± 15 kg and 177 ± 3 cm tall

participated in study. Initially all subjects performed

an incremental test in a cyclesimulator (model

Velotron DYNAFIT PRO™, RacerMate Inc., USA)

to determine the peak power (257 ± 35 W). In the

two subsequent visits to the laboratory the subjects

were randomly submitted to one of the two

stimulation conditions (Anodic tDCS or Placebo

tDCS) to verify their possible effect on a time to

exhaustion task at 80% of peak power (205 ± 28 W).

This study was approved by the local Institutional

Research Ethics Committee.

Stimulation was carried before each test during

13 min, with a current intensity of 2.0 mA. The time

between tDCS and the test was 10 min. Sessions

were separated by a minimal interval of 48h. We

used the 10-20 International System for EEG

electrode placement. The active electrode (9x4 cm)

was placed on the scalp having its center in the

region Cz 4.5 cm on each side of the head (purpose

of stimulating the motor cortex of both

hemispheres), and the reference electrode was

positioned over the bulge.

Additionally, the electromyographic (EMG)

signal of the muscle vastus lateralis (VL) was

monitored during tests after stimulation and

expressed in mean values of RMS - root mean

square (µV) and MF - median frequency (Hz) with a

5-second window period. For EMG signal

normalization a test for torque-speed [T–V test] was

used (Rouffet and Hautier, 2008).

For the recording the of EMG signal, was used

an electromyography model TeleMyo 2400TG2™

(NORAXON Inc., USA) and bipolar active EMG

electrodes (modelo TeleMyo 2400™, NORAXON

Inc., USA), with interelectrode distance fixed at 2

cm, which were placed in the right leg muscle and

fixed with a adhesive tape. Initially, a trichotomy

followed by asepsis with alcohol and curettage of

the electrode site, to reduce skin impedance, was

performed.

The localization of anatomical point for the

electrode placement on the analyzed muscle was

done according to the standardization proposed by

the Surface ElectroMyoGraphy for the Non-Invasive

Assessment of Muscles ISEK: International Society

of Electrophysiology and Kinesiology (SENIAM).

The sampling frequency of the EMG signals was

2.000 Hz. The signal passing limit was ±5 mV, and

the common-mode rejection ratio was 95 dB.

To obtain the values expressed in RMS, the raw

EMG signals were submitted to a band-pass digital

filter of 20 and 500 Hz and then rectified and

smoothed. The MF was determined using Fourier

analysis —‘‘Short-Time Fast Fourier Transform’’ —

and the signals were processed in the mathematical

simulation environment MatLab 7.0™ (Mathworks

Ricardo Altimari L., Vitor-Costa M., Bortolotti H. and Massaru Okuno N..

Transcranial Direct Current Stimulation Improves the Cycling Performance but Does Not Alter Neuromuscular Function - tDCS, Cycling Performance

and Neuromuscular Function.

 2013 SCITEPRESS (Science and Technology Publications, Lda.)

Inc., USA). For statistical analysis of the data was

used paired Student t-test and ANOVA two-way.

Significance level was set at 5%.

3 RESULTS

The results demonstrated that there was an increase

(p<0.05) in exercise time when individuals received

Anodic tDCS (491 ± 100s) in comparison to Placebo

tDCS (407 ± 69s). These results were confirmed by

the size effect (anodic x placebo = 0.77). When the

magnitude-based inference was applied, the anodic

stimulation condition was most probably positive to

individuals when compared to placebo conditions.

However, no significant differences were found

for the parameters of neuromuscular function - EMG

signals RMS (Figure 1A) and MF (Figure 1B) -

among the two experimental conditions.

Figure 1: EMG signal of the muscle vastus lateralis (VL)

monitored during the tests and expressed as mean values

of RMS and MF in the conditions Anodic tDCS or

Placebo tDCS.

4 DISCUSSION

The increase in exercise time with application of

anodic current has been shown previously in

isometric exercise of the upper limb. Cogiamanian et

al. (2007) showed that anodal stimulation (1,5 mA),

applied for 10 min after a fatigue test increased

tolerance to an exercise performed subsequent to

stimulation without changes in EMG. These findings

are in agreement with those found in this study.

Furthermore, some authors have shown that tDCS

can improve performance on other tasks increasing

muscle strength. Tanaka et al. (2009) have shown

that, in healthy subjects exerting pinch strength in

the toes, the anode tDCS causes increases in strength

both during and after 30 min of stimulation. More

recently, in another study with patients who have

suffered stroke, Tanaka et al. (2011) found an

improvement in knee extension strength of the

paretic leg during application of anodal tDCS, but

after 30 minutes there was no difference (Tanaka et

al., 2011). Thus, it may be concluded that anodic

TDCS increases exercise time. However, the

mechanisms responsible for the greater exercise

tolerance are speculative. It is possible that the

increase in intracortical facilitation causes the

individual to support longer in exercise.

REFERENCES

Cogiamanian, F., Marceglia, S., Ardolino, G., Barbieri, S.,

Priori, A. 2007. Improved isometric force endurance

after transcranial direct current stimulation over the

human motor cortical areas. European Journal of

Neuroscience. 26(1):242-249.

Davis, N. J. 2013. Neurodoping: Brain stimulation as a

performance-enhancing measure. Sports Med. [Epub

ahead of print] DOI: 10.1007/s40279-013-0027-z.

Rouffet., D. M., Hautier, C. A. 2008. EMG normalization

to study muscle activation in cycling. Journal of

Electromyography and Kinesiology. 18(5):866-878.

Tanaka, M., Takeda, K., Otaka, Y., Kita, K., Osu, R.,

Honda, M., Sadato, N., Hanakawa, T., Watanabe, K.

2011. Single session of transcranial direct current

stimulation transiently increases knee extensor force

in patients with hemiparetic stroke.Neurorehabilitation

and Neural Repair. 25(6):565-569.

Tanaka, S., Hanakawa, T., Honda, M., Watanabe, K. 2009.

Enhancement of pinch force in the lower leg by anodal

transcranial direct current stimulation. Journal of

Physiology Experimental Brain Research. 196(3):459-

465.