While many people are motivated to build better fitness habits for the aesthetic consequences, there are copious other, better reasons to stay active. Dozens of studies come out each year explaining the rewards of exercise and one of the top recurring benefits is improved brain function. This leads some to ask the question: is there a point when fitness goes too far?

Weightlifters may facetiously offer the phrase “going too hard in the gym” as an explanation for some negative consequence after a grueling workout, and most people are familiar with the ordinary soreness that follows a strenuous run. However, there may be a more immediate reaction that influences the brain, according to an article this week from WebMD, which referenced a new study published in the journal Current Biology.

Story author Steven Reinberg summarized the news, writing:

Excessive exercise can tire out your brain to the point that you have trouble making decisions, a new study claims. 

The findings show that despite the benefits of endurance sports, an excessive training load can have ill effects on your brain, French researchers said.

“Our findings draw attention to the fact that neural states matter: You don’t make the same decisions when your brain is in a fatigued state,” said study author Mathias Pessiglione of Hopital de la Pitie-Salpitriere in Paris.

For the study, the researchers had 37 male endurance athletes either continue normal training or increase training 40% a session over three weeks. 

Functional MRIs showed the overloaded athletes had a slower response in the lateral prefrontal cortex.

Athletes who exerted themselves to the point of exhaustion showed reduced activity in an area of the brain important for making decisions. And they appeared more impulsive in tests that evaluated financial decision-making, going for immediate rewards instead of larger ones that would take more time to achieve, the researchers found.

As the article goes on to point out, fatigue is the chief threat to this impaired decision-making ability. Certainly no one should interpret these findings and draw the conclusion that working out is not helpful for overall optimal brain function.

To read Reinberg’s full writeup, click here.