Study says brain fog after a marathon is real, and brief

The mush-brain feeling after a long race shows up in testing. Researchers measured cognitive function and neural signal conduction in 43 marathon and ultramarathon runners at three points, before a race, within 48 hours of finishing, and again one month later, Brady Holmer says.

Brady Holmer

@Brady_H

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the brain after a marathon isn't damaged. It's metabolically stressed and temporarily adapting

Conduction times, meaning how fast nerve signals travel, stayed stable after the race. Cognition was temporarily worse.

What actually dipped

The control group improved on a processing-speed test, which is what you expect when people take the same test twice and get some practice benefit. Runners improved less right after the race. By one month they had caught up.

On the Stroop test, a classic measure of how well you can override an automatic response, runners showed a temporary increase in interference. In plain terms, it was briefly harder to ignore the obvious wrong answer. That normalized by one month too.

The simpler stuff was fine. Holmer says basic visual-motor, attention and executive tasks held up.

Holmer's read

Holmer is clear that this is his interpretation, not a claim the study makes for him. He says the brain after a marathon is not damaged, it is metabolically stressed and temporarily adapting, protecting essential signaling while higher-order thinking runs a little less efficiently for a day or two.

His practical takeaway is to treat the day or two after a long race as cognitive recovery time. He adds the personal note that he has run four marathons and after each one his brain feels like mush for a few days.

What it actually means

This is not evidence that marathons hurt your brain, and nothing in the study says anything about long-term effects. The wiring kept working at normal speed. What slipped was the slower, effortful kind of thinking, and it came back within a month.

So if you bomb a work presentation the Monday after a goal race, or you cannot do mental math at the aid station of a training run two days later, there is at least one study of 43 runners pointing in that direction. Plan the big decisions for the following week.