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Physical overexertion causes mental fatigue and impulsive behavior

A new study published by Cell Press has revealed that excessive athletic training can cause mental fatigue that is associated with impulsive behavior and poor decision making. The effects of physical overexertion appear to be the same as those which have been tied to overworking the brain. 

Taken together, the studies suggest that both mental and physical efforts require cognitive control. The research also indicates that this control is required during intense training to maintain physical effort and stamina. 

“You need to control the automatic process that makes you stop when muscles or joints hurt,” said study co-author Mathias Pessiglione of Hôpital de la Pitié-Salpêtrière in Paris. 

The mental fatigue observed in athletes after excessive training included reduced activity in a portion of the brain that is critical for decision-making. The athletes also acted more impulsively, choosing smaller rewards they could receive right away over larger rewards that would be delayed. 

“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,” said Pessiglione.”This brain region therefore appeared as the weak spot of the brain network responsible for cognitive control.”

The idea for this study was conceived by the National Institute of Sport, Expertise, and Performance (INSEP) in France, which trains athletes for the Olympic games. Some athletes had experienced “overtraining syndrome,” which was characterized by an overwhelming sense of exhaustion that sabotaged their performance. 

The researchers set out to understand if this fatigue may be related to the mental impacts of excessive intellectual work. They recruited 37 competitive male endurance athletes with an average age of 35, instructing them to either proceed with their normal amount of training or to increase their training by 40 percent over three weeks.

The experts conducted behavioral testing and functional magnetic resonance imaging (fMRI) scanning experiments. The team also monitored the physical performance of the athletes, and evaluated self-reported levels of fatigue.

The study revealed that physical training overload led the athletes to feel more fatigued. They also acted more impulsively in standard tests used to evaluate how they would make economic choices. As they made these decisions, the brains of athletes who were physically exhausted showed diminished activation of a key region of the executive control system called the lateral prefrontal cortex.

The researchers concluded that while endurance training is generally good for your health, overdoing it can have adverse effects on the brain. “Our findings draw attention to the fact that neural states matter: you don’t make the same decisions when your brain is in a fatigued state,” said Pessiglione.

The study is published in the journal Current Biology.

By Chrissy Sexton, Staff Writer

Image Credit: Shutterstock/RomarioIen

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