The study published in the journal Current Biology shows that intensive physical training could harm brain capacity, particularly cognitive control.
For the findings, Mathias Pessiglione and his team from Inserm Research Institute in France said that they were interested in identifying the causes of a common phenomenon in top athletes, known as "overtraining syndrome".
This was characterised by reduced athletic performance and intense fatigue.
Athletes suffering from this syndrome might be tempted by products likely to restore their performance.
The primary hypothesis of the researchers were clear: the fatigue caused by overtraining is similar to that caused by mental efforts.
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 per cent longer, on average.
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 was prioritised over long-term goals.
In the case of top athletes, being this impulsive could 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 might also constitute the first stage in the development of a "burnout syndrome", which affects many people across various professional sectors.
( With inputs from IANS )