New Study Shows Intense Exercise Exhausts Your Brain (and Your Body)

Molly Hurford
by Molly Hurford
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New Study Shows Intense Exercise Exhausts Your Brain (and Your Body)

Have you been heading out for lunchtime intervals only to find that when you’re back in the office for the afternoon, you’re lagging and having a hard time focusing on work? What about trying to get paperwork done or make major decisions — like car-shopping — after your Saturday long run?

Sure, exercise is good for your brain, but it seems only up to a certain point. It turns out the effects of overtraining (or just a high training load for you) could be exhausting your mental reflexes as well as your physical ones, according to a new study published in Current Biology. Athletes put under a heavy training load showed lower impulse control and had a harder time making decisions. It happens because pushing yourself to get through a training session can take a lot of cognitive control — essentially, you’re draining your brain as much as you’re draining the energy in your legs.

“I was interested in how we make decisions, and I was interested in how certain areas of the brain used in decision-making were influenced by physical fatigue,” says Bastien Blain, PhD, the lead researcher. Researchers looked at triathletes training at high volume and assessed brain function in decision-making and impulse control and found the sensation of overtraining and athlete burnout was actually due to mental fatigue as well as physical.

“We found that cognitive control is heavily involved in sports,” Blain explains. “When we keep exercising despite signals like pain and fatigue in muscles, then we have to exert cognitive control to keep moving. You have that urge to stop, and you keep going — that’s your brain working to control your body, which can lead to that feeling of mental fatigue.”

So, how does this new research impact you? It’s all about how you schedule your work and training.


“Exercise is still good!” Blain laughs. This study is just another reminder that your easy runs should be honestly easy — which admittedly can be hard to do in practice. If you find every run leaves you physically exhausted, drop the pace on your easy runs enough to finish easy runs feeling almost as fresh as you did before you began. This way, you aren’t taxing your body’s ability to recover during long workouts, and you can finish those feeling fresher as well.


If you know your workout is going to be a long or hard one, try to lighten your cognitive load as much as possible. The study noted the athletes had a harder time resisting temptations after long workouts, so consider preemptively packing a healthy post-run meal so you make smart choices rather than giving in to the impulse to eat a sugary donut. Additionally, consider aligning your work schedule with your runs as much as possible. For example, if you have a hard run during lunch, plan your big meeting or presentation for before your run, not after.


Athletes may be able to tell when they’ve crossed that line and overtraining is impacting them by paying attention to performance cues. “They can’t reach their usual level of performance and they have a sensation of mental and physical exhaustion,” says Dr. Mathias Pessiglione of Hôpital de la Pitié-Salpêtrière in Paris, who ran the study with Blain. “Note that you know when you’ve crossed the line, but you don’t see it coming!”


If you’re feeling signs of mental or physical burnout, take them seriously even if you aren’t logging big miles. “Overtraining is different from person to person,” Blain reminds us. “The athletes in the study were highly trained triathletes so they were doing big hours, but were trained to recover well. Someone else may be overtrained just by starting to do an hour a day from nothing. If you suddenly increase your training, it’s reasonable to assume you’re at a higher risk for overtraining — it’s impossible to say where that line is from person to person.”


It’s tempting to read the study headline and assume all exercise will sap your mental strength, but that isn’t the real message. Rather, this study points out that hard, extreme training can make you foggier than normal. Overtraining won’t just leave you feeling physically beat-up, it will take a mental toll as well. So if you have a big report due at work, it might be a good idea to take an easy week and stick to low-key runs that clear your brain, not tax your system.

About the Author

Molly Hurford
Molly Hurford

Molly is an outdoor adventurer and professional nomad obsessed with all things running, nutrition, cycling and movement-related. When not outside, she’s writing and podcasting about being outside, training and health. You can follow along with her adventures on Instagram at @mollyjhurford.


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