Working out too intensely for too long can cause our brains to become fatigued. (Credit: Flamingo Images/Shutterstock)

For years, the National Institute of Sports, Exercise and Performance (INSEP) in France had been studying an unusual phenomenon. If an athlete’s workout regiments were ramped up, it didn’t always lead to a better performance — even if that athlete felt like they were working harder than before. 

The organization called this phenomenon overreaching, and knew what the physi