Two studies conducted by scientists from the University of Granada have found that, currently, transcranial direct-current stimulation (tDCS) cannot be considered an effective tool for improving sports performance.
Direct-current transcranial stimulation (tDCS) is a non-invasive brain-stimulation technique that can induce changes in the cerebral cortex by means of two electrodes. Typically, the anodal (target) electrode is placed over the area of the brain designated for stimulation, and the cathodal electrode is placed away from the skull (for example, on the shoulder). The electrodes are then connected to a small battery that provides the electrical current. In the areas of Sport Sciences and physical exercise, this technique has been applied using stimulation intensities of between 1 and 2 mA.
The tDCS technique has grown in popularity particularly in the field of Sports Science, thanks to its ease of use and its reputation for delivering positive results for physical performance. For example, at the Rio de Janeiro Olympic Games, held in 2016, several American and African athletes who had incorporated tDCS into their training took part.
But two recent studies conducted by scientists from the University of Granada’s Mind, Brain and Behaviour Research Centre (CIMCYC) have found no evidence to back the claim that tDCS is effective in improving sports performance. The studies were performed by means of practical experiments and also meta-analytical methods (by reviewing the scientific literature to date).
The experimental aspect of the study—recently published in the scientific journal PLOS ONE and previously pre-registered on the Open Science Framework (OSF) platform—employed the largest sample to date among similar studies in this field, comprising 36 trained cyclists.
To test the hypothesis that tDCS is capable of enhancing performance, the cyclists were subjected, on three different occasions, to a period of 20 minutes’ stimulation under cathodal, anodal, or sham (placebo-like) conditions. They were then required to undertake a 20-minute physical performance trial. The results of the study demonstrated that tDCS neither improved the physical performance of the subjects, nor produced alterations in the brain (electroencephalographic activity; either at rest or while exercising).
In light of these findings from the experimental study, Darías Holgado and Daniel Sanabria, researchers from the University of Granada, in collaboration with Miguel Ángel Vadillo, of the Autonomous University of Madrid, undertook an exhaustive literature review. This included a meta-analysis to determine the published effects of tDCS based on objective and subjective parameters related to physical performance.
Limited number of participants
Among the main conclusions derived from the meta-analysis was the fact that the average number of participants in these studies is low— on average, each study was based on just 14 subjects, which would limit its statistical power. Furthermore, although tDCS might exert a small effect on physical performance, this would most probably be mediated by the low quality of the studies and by the tendency of the literature to publish only those studies showing positive effects.
The researchers also concluded that the typical stimulation intensity of 2 mA may not be sufficient to induce changes in the brain, while the effects of long-term use of this technique are not known. This work has been published in the journal Brain Stimulation.
The conclusion of the UGR researchers is that, despite the fact that several companies promote brain-stimulation devices as a functional tool for improving sport performance, claims of their effectiveness are not backed by current evidence. The researchers also point out that this is a very interesting field of study that calls for further rigorous research to establish the potential impact (if any) of such devices on exercise and sports performance.
Bibliography
Holgado, D., Zandonai, T., Ciria, L. F., Zabala, M., Hopker, J., & Sanabria, D. (2019). ‘tDCS Over the Left Prefrontal Cortex Does Not Affect Time-Trial Self-Paced Cycling Performance: Evidence from Oscillatory Brain Activity and Power Output’. PLOS ONE, 1–13.
https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0210873
Holgado D., Vadillo MA. & Sanabria, D. (2018). ‘The Effects of Transcranial Direct Current Stimulation on Objective and Subjective Measures of Sports Performance: A Systematic Review and Meta-Analysis’. Brain Stimulation, 12(2): 242–50.
https://doi.org/10.1016/j.brs.2018.12.002
https://osf.io/preprints/sportrxiv/e2buc/
Photo captions:
UGR Researchers Darías Holgado y Thomas Zandonai, two of the authors of this study.
The experimental study, published in the journal PLOS ONE, was based on a sample of 36 trained cyclists.
Media enquiries:
Darías Holgado
Department of Physical Education and Sports
Mind, Brain and Behaviour Research Centre (CIMCYC)
University of Granada, Spain
Email: dariashn@ugr.es
Daniel Sanabria
Department of Experimental Psychology
Mind, Brain and Behaviour Research Centre (CIMCYC)
University of Granada, Spain
Telephone: +34 958 247875
Email: daniel@ugr.es
