Does stimulating the brain to improve performance really work?
Fatigue, in the common sense, is a sensation of physical or cognitive weakening, and translates into difficulty in continuing an effort. The physical limits of human performance have been the subject of study for a considerable time.
Stéphane Perrey, University of Montpellier
From the 1890s onwards, two works by Dr Fernand Lagrange and Dr Angelo Mosso marked the beginning of the history of the study of the phenomenon of muscular fatigue during exercise in humans. Most of the research carried out in the 20th century focused on the locomotor muscles, the lungs and the heart, all of which were seen as possible major organic determinants in the etiology of fatigue and hence of exercise performance.
The brain's role in fatigue
For many years, much of the literature ignored the importance of the brain in regulating physical performance. Yet muscle fatigue was suggested in the early 20th century as a physiological process associated with a sensation involving the brain as a decision-making organ, a sort of regulator to preserve the organism from any catastrophic disorder engendered by exercise carried out to the point of exhaustion of its physiological reserves. We can see that this "catastrophic" approach, formulated over a century ago, is in line with the most contemporary approaches to muscular fatigue (the "flush" or psychophysiological model) debated through the so-called central governor model.
With the introduction and development of new non-invasive devices (neuroimaging and brain stimulation equipment), knowledge of brain behavior during exercise has progressed. A first step has been taken with studies using neuroimaging methods to identify different active areas of the brain during muscular exercise.
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In addition, over the last decade, a non-invasive technique of brain stimulation using electrodes to apply a low electrical current (1-2 mA) has been at the heart of intense research into ways of modifying brain function. Reading scientific publications, one is tempted to believe that the application of transcranial direct current stimulation (tDCS) to different areas of the brain can enhance physical performance. But what is the reality?
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Significant lack of evidence of the effects of brain stimulation on performance
The number of experimental studies on the effect of tDCS on physical performance is increasing rapidly, but with important methodological limitations to be taken into account. To date, the number of studies remains limited, and the physiological mechanisms by which tDCS might improve physical performance are partly unknown. The potential improvement in physical performance identified in a few studies seems to result from greater transient activation of cortical neurons after a short 10-20 min sequence of tDCS.
However, few studies have measured brain activity after and during (online effects) a tDCS sequence coupled with exercise. Secondly, the propagation of the electric field induced in the brain by tDCS is very diffuse. Thirdly, the vast majority of studies are based on very small samples, which could increase the likelihood of false-positive results, as is often the case in neuroscience. Finally, the absence of a blind procedure may have led to a number of unintended confounding psychological effects, which may have played an important role in the excessive variability of the results observed.
Stimulating the brain to boost performance: towards neuro-doping?
Some authors have already argued that tDCS can be considered a new form of doping, although skepticism about the validity and reproducibility of tDCS effects has also been voiced. tDCS can potentially enhance sporting performance in two ways, either by modulating brain activation just before a sporting event, or by reorganizing the activity of the cerebral cortex after multiple applications (hypothesis of greater neural efficiency). As discussed in the previous section, recent meta-analyses take a very reserved stance on the acute effects of tDCS on performance, and no studies have yet been conducted on the effects of chronic tDCS administration on physical performance.
Despite recent experimental research into the potential of tDCS to enhance physical performance, its application has rapidly evolved outside the laboratory. Indeed, a number of tDCS devices are available to the public, and many professional and non-professional athletes and teams claim to have adopted tDCS in their training programs.
In the field of sports doping, brain stimulation was first experimented with by Soviet athletes in the 1970s. Although still in its early experimental stages, tDCS appears to satisfy only a single criterion defined by the World Anti-Doping Agency, namely the potential to enhance sporting performance. It remains to be established whether this represents a violation of the spirit of sport, and whether tDCS represents a real or potential risk to the athlete's health. Although no serious adverse side effects have been reported in healthy participants, many uncertainties exist regarding the prolonged use of tDCS. Determining whether or not an athlete has used a tDCS protocol prior to a competition is impossible and could open up an unprecedented scenario for anti-doping control strategies.
More worryingly from an ethical and regulatory point of view, the "do it yourself" concept has grown rapidly, with online forums and social media offering kits and instructions on how to build tDCS devices with the aim of improving cognitive or physical abilities.
These devices are not approved by official bodies such as the Food and Drug Administration. Attempts to stimulate the brain with "homemade" electrical devices are not new, and have been known since the end of the 19th century. XIXᵉ century. Although tDCS is not considered a means of improving physical performance due to a lack of convincing evidence, it could add an extra level of performance. marginal" gainwhich could be enough to provide a high-level advantage. Whatever the potential of tDCS, its use must be based on rigorous evidence, and not be driven by commercial interests and media hype built on anecdotal evidence.
Stéphane Perrey, University Professor, Deputy Director of the EuroMov laboratory, University of Montpellier
This article is republished from The Conversation under a Creative Commons license. Read theoriginal article.