Training Too Much Can Fatigue Your Brain

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

4 thoughts on “Training Too Much Can Fatigue Your Brain

  1. I can see this happening not just to more elite athletes. I do yoga 4-5 times a week, sometimes meditation, sometimes strength, a full body workout at least twice, and I walk most days. Even this can fatigue the brain, especially since right now I have other stressful events in my life. I’ve given myself most of the week off to just walk and rest, get some emotional energy back. But rest periods are very important even if you don’t feel mentally fatigued, to prevent injury, and keep those emotional reserves strong. Easy to overdo it.

    1. Hi Lynn,

      Too many exercisers fail to understand the value and management of recovery. In truth, the fitness profession does a terrible job of educating on this topic. For the 20 years I’ve been working with clients, I’ve always explained one simple truth: all training is cumulative and so is all fatigue.

      What that means is that if you fail to interrupt the downward cycle of continuous fatigue, it will accumulate and break you down. It also means recognizing that other factors play a role in allostatic load, or the total physical, mental and environmental stress placed on a body and it’s systems. You mentioned stress. Chronic stress is a huge factor in the increase of allostatic load and our inability to recover well from bouts of exercise.

      It’s great to see you being mindful of all the factors and taking appropriate actions to let yourself recover, heal and prepare for more. Thanks for reading my stuff and thanks for your wonderful input!

      1. It always seems like these sports teams are over-training their athletes to me. Maybe they do better these days. And of course at my advanced age, I’m not trying to be a major athlete, but all these principles apply to everyone. Right at the moment, I have multiple family members ill, some seriously, and I could just tell I was stressing my adrenal glands and needed not to impose a strict exercise regimen this week. Just some walking and maybe some meditation. I enjoy your blog! Very nice.

      2. Thank you, Lynn. Yes, there have been remarkable advances in training and recovery at the highest levels. Many are making their way to the mainstream of fitness, thankfully. You’re absolutely right when you say the principles apply to everyone. I’ll say a prayer for you and your family. Keep the faith and keep after it!

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