Excessive athletic training does some wear and tear on the body; but according to new research, it can also make the brain tired, leading to poor decision-making.
In a paper recently published in Current Biology, researchers imposed a mild excessive training regimen on triathletes and participants showed behavioral and neural signs of mental fatigue. This mental exhaustion, called “cognitive control fatigue”, included reduced activity in a region of the brain important for making decisions. The athletes also acted more impulsively; in a decision-making test, they chose more immediate rewards rather than waiting longer for better ones.
"The lateral prefrontal region that was affected by sport-training overload was exactly the same that had been shown vulnerable to excessive cognitive work in our previous studies," says corresponding author Dr. Mathias Pessiglione of Hôspital de la Pitié-Salpêtrière in Paris. "This brain region, therefore, appeared as the weak spot of the brain network responsible for cognitive control."
The original idea for the study arose at an Olympic training facility in France. During training, athletes often suffered from “overtraining syndrome”, in which their athletic performance declined as they experienced an overwhelming sense of fatigue. Pessiglione and first author of the study Dr. Bastien Blain questioned if this syndrome arose in part from neural fatigue in the brain – similar fatigue experienced after taking a difficult exam, or a long day at work.
To address this, Pessiglione and his team recruited 37 male endurance athletes (triathletes) with an average age of 35. They assigned participants to one of two groups: some of the athletes continued their normal training, while others were asked to increase their training by 40% per session over a three-week period. Researchers monitored participants’ subjective experience of fatigue using questionnaires, conducted behavioral testing, and scanned their brains using fMRI.
Physical training overload made athletes feel fatigued. Behavioral economic assessments of decision-making revealed that the overtrained athletes acted more impulsively. Lastly, the brains of these athletes showed decreased activation of the lateral prefrontal cortex (LPFC), a region involved in executive control, while they made economic choices. Cognitive control is needed to align behavior to long-term goals. Researchers suspect that a dysfunctional LPFC may explain why athletes fail to overcome fatigue or pain symptoms; a cognitive strategy that may help with immediate performance but results in damage to muscles and joints, ultimately compromising long-term goals.
These findings suggest that despite the benefits of endurance sports on fitness, an excessive training load can have detrimental effects on the brain, researchers said.
"Our findings draw attention to the fact that neural states matter: you don't make the same decisions when your brain is in a fatigue state," said Pessiglione.