If you work out too much, you’d expect your body to be fatigued. You’d expect to feel tired, run down and maybe like a garbage truck had its’ way with your muscles. But according to a new study published in the journal Current Biology, your brain can take a beating, too.
Working with triathletes, who are already accustomed to a high level of training output, researchers increased the workloads to excessive levels. The result? A form of mental fatigue for the athletes.
The fatigue manifested in several ways, including reduced activity in a part of the brain important to decision-making processes, higher levels of impulsivity and an increase in the need for near-term reward and immediate gratification, rather than bigger or better rewards requiring longer periods of effort. The outcomes have implications not only for athletes, but for anyone seeking rewards from sustained effort in the areas of diet and exercise.
“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 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 seem to make a clear connection between mental and physical effort. Both of them are dependent on cognitive control. Reaching any medium- to long-term athletic goal requires cognitive control to maintain demanding physical training.
“You need to control the automatic process that makes you stop when muscles or joints hurt,” Pessiglione says.
The researchers, including Pessiglione and first author Bastien Blain, said that the original idea for the study came from the National Institute of Sport, Expertise, and Performance (INSEP) in France. Athletes are trained for the Olympic games in this facility.
Researchers noted that some of the athletes training there were suffering from “overtraining syndrome,” with their physical performance tanking as a result of a deep sense of overwhelming fatigue. Researchers asked the question “Did the overtraining syndrome occur in part from neural fatigue in the athlete’s brains? In other words, the same kind of fatigue noticed in the brains of people performing excessive intellectual work?
Pessiglione and colleagues recruited 37 competitive male endurance athletes (average age: 35.) Each was assigned to either maintain their normal training schedule or to increase the training load by 40% each session, over a three week period. Researchers monitored their physical performance and output during cycling sessions done on rest days. The athletes subjective experience of fatigue was measured every two days using questionnaires. Behavioral testing and functional MRI (fMRI) scans were also used.
The team found that those whose physical training had been overloaded felt more fatigued. They were more impulsive, according to standardized tests used to evaluate their economic choices. Their bias favored immediate rewards over delayed rewards.
Physically, the brains of the overloaded athletes showed reduced activation of the lateral prefrontal cortex while making those choices. The LPFC is an important region of the executive control system in the brain.
The findings seem to show that, while endurance sport may be generally good for your health, overdoing it can have adverse effects on your brain, the researchers say.
“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 say.
These 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 say. It suggests it may also be important to monitor fatigue level in order to prevent bad decisions from being made in the political, judicial, or economic domains.
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.
So if you’re planning to train hard for something, or even just commit yourself to a challenging fitness and nutrition program, you may want to be aware of the risk of “brain fatigue.” It may lead you to make some decisions that might just derail your desired ouotcome!
Keep the faith and keep after it!
Journal Reference – Blain et al. Neuro-computational impact of physical training overload on economic decision-making. Current Biology, 2019