Is stimulating the brain to improve performance really effective?
Fatigue, in the common sense of the term, 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
Beginning 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 considered to be among the major potential organic determinants in the etiology of fatigue and, consequently, 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. However, as early as the beginning ofthe 20th century, muscle fatigue was proposed as a physiological process associated with a sensation in which the brain acts as a decision-making organ—a sort of regulator that protects the body from catastrophic disruption caused by exercise carried out to the point of exhausting its physiological reserves. It is evident that this “catastrophe” approach, articulated more than a century ago, aligns with the most contemporary approaches to muscle fatigue (the so-called “flushing” model or psychophysiological model) debated in the context of the so-called central governor model.
With the introduction and development of new noninvasive devices (neuroimaging and brain stimulation equipment), our understanding of brain activity during exercise has advanced. An initial step was taken through studies using neuroimaging methods that identify different active regions of the brain during muscular exercise.
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Furthermore, over the past decade, a noninvasive technique for brain stimulation—involving the application of a weak electrical current (1–2 mA) via electrodes—has been at the center of intensive research aimed at modifying 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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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 partly 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 session of tDCS.
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 lack of a blinded procedure may have led to a number of unwanted psychological confounding effects that could have played a significant role in the excessive variability of the observed results.
Stimulating the Brain to Boost Performance: Is This a Step Toward Neurodoping?
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 has the potential to enhance athletic performance in two ways: either by modulating brain activation immediately before a sporting event, or by reorganizing cortical activity following multiple applications (the hypothesis of greater 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 improve physical performance, its use has rapidly expanded beyond the laboratory setting. In fact, several tDCS devices are available to the public, and many athletes— both professional and amateur—claim to have incorporated tDCS into their training programs.
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—namely, 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 athletes’ 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 create an unprecedented scenario for anti-doping control strategies.
More concerning from an ethical and regulatory standpoint, the “do-it-yourself” movement 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 high-level 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, Assistant Director of the EuroMov Laboratory, University of Montpellier
This article is republished from The Conversation under a Creative Commons license. Readthe original article.