A new study shows that excessive athletic training not only makes the body tired, but also the brain.
When researchers asked elite athletes to increase their training, the athletes showed a form of mental fatigue that included reduced activity in a portion of the brain important for making decisions. The athletes also acted more impulsively, opting for immediate rewards instead of bigger ones that would take longer to achieve, according to the researchers.
“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 corresponding author Dr. Mathias Pessiglione of Hôpital de la Pitié-Salpêtrière in Paris. “This brain region therefore appeared as the weak spot of the brain network responsible for cognitive control.”
The studies suggest a connection between mental and physical effort — both require cognitive control, the researchers said. And maintaining physical effort to reach a distant goal requires cognitive control, the researchers noted.
“You need to control the automatic process that makes you stop when muscles or joints hurt,” Pessiglione said.
The researchers, including Pessiglione and first author Dr. Bastien Blain, said the initial idea for the study came from the National Institute of Sport, Expertise, and Performance (INSEP) in France, which trains athletes for the Olympic games. Some athletes suffered from “overtraining syndrome,” in which their performance plummeted as they experienced an overwhelming sense of fatigue. The question for the researchers was: Did this overtraining syndrome arise in part from neural fatigue in the brain — the same kind of fatigue that also can be caused by excessive intellectual work?
To find out, the researchers recruited 37 competitive male endurance athletes with an average age of 35. Participants were assigned to either continue their normal training or to increase that training by 40 percent per session over a three-week period. The researchers monitored their physical performance during cycling exercises performed on rest days and assessed their subjective experience of fatigue using questionnaires every two days. They also conducted behavioral testing and functional magnetic resonance imaging (fMRI) scanning experiments.
The study’s findings showed that physical training overload led the athletes to feel more fatigued. They also acted more impulsively in standard tests used to evaluate how they’d make economic choices. This tendency was shown as a bias in favoring immediate over delayed rewards when the athletes were offered $5 now or $50 later.
The brains of athletes who’d been overloaded physically also showed diminished activation of the lateral prefrontal cortex, a key region of the executive control system, as they made those economic choices, the researchers reported.
“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,” Pessiglione said.
The findings may be important not just for producing the best athletes, but also for economic choice theory, which typically ignores such fluctuations in the neural machinery responsible for decision-making, the researchers said. It suggests it may be important to monitor fatigue level to prevent bad decisions from being made in the political, judicial, or economic domains, they added.
In future studies, the researchers plan to explore why exerting control during sports training or intellectual work makes the cognitive control system harder to activate in subsequent tasks. Down the road, the hope is to find treatments or strategies that help to prevent such neural fatigue and its consequences, they concluded.
The study was published in the journal Current Biology.
Source: Cell Press