During exercise, your prefrontal cortex overrides pain signals from your muscles and joints so you can continue training despite discomfort, says study author Bastien Blain, Ph.D., research associate at University College London who specializes in cognitive fatigue.
This part of your brain is also responsible for decision-making. When it’s overworked, you’re more likely to make impulsive choices rather than deliberate ones, Blain explains. The effect can kick in after a single five-hour session (like a hike or triathlon) or after increasing your exercise volume by 20 to 30 percent for at least two weeks, Blain says.
The bottom line:
Blain and his team aren't sure how long the effects last. If you make decisions with long-term implications—like those about finances or relationships—after long workouts, at least make sure you're not hungry at the time. Research suggests that can lead to even worse decisions.