In top athletes, excess physical activity can be harmful, as cases of 'overtraining syndrome' suggest. It is associated with major fatigue and reduced athletic performances. A study has now shown that intensive physical training can harm brain capacity, particularly cognitive control. The full results have been published in Current Biology.
Inserm researcher Mathias Pessiglione and his team were interested in identifying the causes of a common phenomenon in top athletes, known as "overtraining syndrome". This is characterised by reduced athletic performance and intense fatigue. Athletes suffering from this syndrome may be tempted by products likely to restore their performance, hence the involvement of the French Anti-Doping Agency in the project.
The primary hypothesis of the researchers was clear: the fatigue caused by overtraining is similar to that caused by mental efforts. It is thought to be linked to the same brain mechanisms. Another recent study had already shown that mental fatigue affects cognitive control and leads to impulsive decisions.
To test this idea, the team spent nine weeks working with 37 triathletes, who were split into two groups. The first underwent the "usual" high-level training whereas the second had additional training during the last three weeks of the experiment, with sessions lasting 40% longer, on average. The participants were all monitored at the Brain & Spine Institute, both behaviorally and via functional MRI.
From this, the researchers were able to identify similarities between overly intensive physical training and excessive mental work. This excessive physical activity leads to reduced activity of the lateral prefrontal cortex (a key region for cognitive control), similar to that observed during mental effort. This reduction in brain activity was associated with impulsive decision-making, in which short-term gratification is prioritized over long-term goals. In the case of top athletes, being this impulsive can lead to their decision to stop right in the middle of a performance or to abandon a race in order to end the pain felt during physical exertion.
The researchers believe that fatigue and reduced cognitive control may also constitute the first stage in the development of a "burnout syndrome", which affects many people across various professional sectors. The next step for the researchers is to design and test interventions in order to avoid the onset of actual burnout - and the total exhaustion of an individual.