When you train hard in sports, you usually feel how tired your body is afterward. You'd expect it after a training session. What you might not expect, though, is that excessive physical training can also tire you mentally.
A new study published on Thursday in Current Biology discovered this link and explained just how this works.
How did the researchers make this discovery?
The researchers of this study placed an excessive workout load on athletes, and in doing so, realized that they became mentally fatigued as a result.
What's interesting is that this fatigue led the athletes to make impulsive decisions, as the section of their brains linked to critical decision-making was tired out, and working less quickly.
The athletes would end up choosing options that would offer them immediate results, instead of pushing through a more extended training system that would give them bigger rewards down the line.
The corresponding author of the study, Mathias Pessiglione of Hôpital de la Pitié-Salpêtrière in Paris, said: "The lateral prefrontal region that was affected by sport-training overload was exactly the same that had been shown vulnerable to excessive cognitive work in our previous studies."
Pessiglione continued, "This brain region, therefore, appeared as the weak spot of the brain network responsible for cognitive control."
According to the study, both physical and mental exertion requires cognitive control. In demanding sports training, specifically, the need for cognitive control goes hand in hand with maintaining physical effort. Otherwise, you could hurt yourself.
Pessiglione pointed that part out by saying: "You need to control the automatic process that makes you stop when muscles or joints hurt."
Why did the researchers decide to carry out this study?
The team, including Pessiglione and first author Bastien Blain, caught onto the idea of this study thanks to the National Institute of Sport, Expertise, and Performance (INSEP), in France.
INSEP trains athletes for the Olympics, and as some of their athletes struggled with over-fatigue due to excessive training schedules, the team was curious to dig deeper into the matter. They wanted to find out whether the overtraining syndrome found in athletes led to the same type of fatigue caused by intellectual work.
So the team recruited 37 competitive male endurance athletes, with an average age of 35. Some athletes were told to continue with their regular training schedules, while others were told to increase it by 40% per session. The test was carried out over three weeks.
The team monitored the athletes, conducted behavioral testing, as well as functional magnetic resonance imaging (fMRI).
What did they discover? Physical overtraining led the athletes to feel more mentally fatigued. The over-worked athletes ended up choosing immediate over long-term rewards. They also showed lowered activation of the lateral prefrontal cortex.
"Our findings draw attention to the fact that neural states matter: you don't make the same decisions when your brain is in a fatigue state," said Pessiglione.