Is stimulating the brain to improve performance actually effective?
Fatigue, in the common sense, is a sensation of physical or cognitive weakness, and manifests as difficulty sustaining effort. The physical limits of human performance have been the subject of study for a considerable time.
Stéphane Perrey, University of Montpellier
Starting in the 1890s, two works by Dr. Fernand Lagrange and Dr. Angelo Mosso marked the beginning of the study of muscle fatigue during exercise in humans. Most research during the20th century focused on the locomotor muscles, the lungs, and the heart, all of which were considered potential major organic determinants in the etiology of fatigue and, consequently, exercise performance.
The role of the brain in fatigue
For many years, much of the literature overlooked the brain’s role in regulating physical performance. However, as early as the beginning ofthe 20th century, muscle fatigue was proposed as a physiological process associated with a sensation involving the brain as a decision-making organ—a sort of regulator designed to protect the body from catastrophic failure resulting from exercise carried out to the point of exhausting its physiological reserves. It is evident that this “catastrophe” approach, articulated over a century ago, aligns with the most contemporary approaches to muscle fatigue (the so-called “flushing” model or psychophysiological model) debated within the framework of the so-called central governor model.
With the introduction and development of new non-invasive devices (neuroimaging and brain stimulation equipment), our understanding of brain activity during exercise has advanced. Initial progress was made through studies using neuroimaging methods that identify different active regions of the brain during physical exercise.
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Furthermore, over the past decade, a non-invasive technique for stimulating the brain by applying a weak electrical current (1–2 mA) via electrodes has been the focus of intensive research aimed at altering how our brains function. Reading scientific publications, one might be tempted to believe that applying transcranial direct current stimulation (tDCS) to different areas of the brain can enhance physical performance. But is that really the case?
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A significant lack of evidence regarding the effects of brain stimulation on performance
The number of experimental studies on the effect of tDCS on physical performance is growing rapidly, but there are significant methodological limitations to consider. To date, the number of studies remains limited, and the physiological mechanisms through which tDCS might improve physical performance are still largely unknown. The potential improvement in physical performance identified in a few studies appears to result from greater transient activation of cortical neurons following a short 10- to 20-minute tDCS session.
However, few studies have measured brain activity after and during (online effects) a tDCS session combined with exercise. Second, the propagation of the electric field induced in the brain by tDCS is very diffuse. Third, 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 blinded procedure may have led to a number of unwanted confounding psychological effects that may have played a significant role in the excessive variability of the observed results.
Stimulating the brain to boost performance: Is neuro-doping on the horizon?
Some authors have already argued that tDCS can be considered a new form of doping, although skepticism regarding the validity and reproducibility of tDCS effects has also been expressed. tDCS can potentially enhance athletic performance in two ways: either by modulating brain activation immediately before a sporting event, or by reorganizing cerebral cortex activity after multiple applications (hypothesis of increased neural efficiency). As discussed in the previous section, recent meta-analyses take a very cautious 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 use has rapidly expanded beyond the laboratory setting. Indeed, several tDCS devices are available to the public, and many athletes— both professional and amateur—claim to have incorporated tDCS into their training regimens.
In the field of sports doping, brain stimulation was already experimented with by Soviet athletes in the 1970s. Although still in its early experimental stages, tDCS appears to meet only one of the criteria defined by the World Anti-Doping Agency: the potential to enhance athletic performance. It remains to be determined whether this constitutes a violation of the spirit of sport and whether tDCS poses a real or potential risk to the athlete’s health. Although no serious adverse side effects have been reported in healthy participants, many uncertainties remain 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 concerning from an ethical and regulatory standpoint, the “do-it-yourself” trend 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 agencies, such as the Food and Drug Administration. Attempts to stimulate the brain using "homemade" electrical devices are not new and have been known since the late 19th century. Even though tDCS is not considered a means of improving physical performance due to a lack of convincing evidence, it could add a "marginal" gain, which could be enough to provide a significant advantage. Regardless of tDCS’s potential, its use must be based on rigorous evidence and not driven by commercial interests or media hype built on anecdotal evidence.
Stéphane Perrey, University Professor, Associate Director of the EuroMov Laboratory, University of Montpellier
This article is republished from The Conversation under a Creative Commons license. Readthe original article.