Here’s another reason to encourage exercise enthusiasts not to overtrain. New research shows that cognitive fatigue is as much an effect of overtraining as physical fatigue.

To evaluate whether overtraining can “tire” the brain, researchers at l’hôpital de La Pitié-Salpêtrière in Paris compared the effect of normal training with training overload on the ability of 37 trained male endurance athletes (average age, 35 years) to make decisions. In addition to offering questionnaires, investigators used fMRI scanning to measure brain activity during cognitive exercises.

Data analysis confirmed the researchers’ hypothesis that training overload might affect the brain in much the same way as prolonged intellectual work. Overtrained athletes felt more fatigue overall and showed more impulsiveness in decision-making and less ability to defer rewards, even though this conflicted with longer-term goals. Brain scans revealed lower activity in the brain region related to cognitive control. The study authors concluded that their results provide causal evidence for a functional link between enduring physical exercise and exertion of cognitive control.

The study appeared in Current Biology (2019; 29 [19], 3289–97).