Excessive athletic training not only makes the body tired, but can wear the brain down too, according to a study which cautions that people must be concerned about their fatigue levels in order to prevent bad long-term decisions. In the study, published in the journal Current Biology, researchers put triathletes on an excessive training regimen, after which they exhibited mental fatigue. The researchers, including those from University Hospitals Pitie Salpetriere in France, found that the fatigue experienced by the athletes included reduced activity in a portion of the brain that was known to be important for making decisions.
The study noted that control over one's own mind was essential for intense athletic training since the process is directed at a distant fitness goal, while also maintaining physical effort.
After the intense training, the researchers said that the athletes acted more impulsively -- opting for immediate rewards instead of bigger ones that would take a longer time to achieve.
"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 Mathias Pessiglione, corresponding author of the study from University Hospitals Pitie Salpetriere.
He added that the brain region appeared as the weak spot of the brain network responsible for cognitive control.
The researchers suggested that a connection existed between mental and physical effort with both requiring cognitive control.
"You need to control the automatic process that makes you stop when muscles or joints hurt," Pessiglione said.
The researchers recruited 37 competitive male endurance athletes with an average age of 35, and assigned them to either continue their normal training, or to increase their efforts by 40 percent per session over a three-week period.
Pessiglione and his team monitored the physical performance of the athletes during cycling exercises performed on rest days, and assessed how they experienced fatigue using questionnaires every two days.
They complimented the questionnaires with behavioral testing, and functional magnetic resonance imaging (fMRI) scanning experiments.
The findings revealed that excessive physical training led the athletes to feel more fatigued, making them act impulsively in standard tests used to evaluate how people made economic choices.
The physically exhausted athletes, the study noted, had a tendency to opt for immediate over delayed rewards.
The researchers found that the brains of the energy drained athletes showed diminished activation of the lateral prefrontal cortex -- a key region of the executive control system -- whenever they made those economic choices.
According to the study, while endurance sport is generally good for one's health, overdoing it could have adverse effects on the brain.