French researchers found a form of mental fatigue among athletes subjected to a heavy training load. The athletes acted impulsively, having sought immediate rewards instead of bigger ones that take longer to achieve.
This form of mental fatigue affected a region of the brain that was previously linked to decreased cognitive control, said the researchers.
"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," said co-author Mathias Pessiglione of Pitie-Salpetriere University Hospital in Paris.
These findings demonstrate that mental and physical activity both require cognitive control, a finding that can benefit not only athletes but also policymakers, economic leaders, students and dieters.
The researchers came up with the study after observing athletes training under the National Institute of Sport, Expertise and Performance in France, a public organization that runs elite sports programs in preparation for the Olympics.
According to the researchers, some athletes experienced an "overtraining syndrome," in which performance levels drop as a trainee experiences an overwhelming sense of fatigue. The team wanted to know whether the syndrome was caused by the same kind of cognitive fatigue that was linked to excessive intellectual work.
For the study, they enlisted 37 competitive male endurance athletes with a mean age of 35 years. They were assigned either to continue normal training or undergo increased training intensity that went up by 40 percent per session over a three-week period. The team administered physical and behavioral tests and elicited the participants' subjective experience of fatigue through questionnaires every two days.
Results showed that the athletes subjected to increased training intensity reported feeling more fatigued compared to the control group. They also acted more impulsively in standard tests used to evaluate economic decision-making by favoring immediate over delayed rewards. The researchers examined their brain activity as they made those choices and found diminished activity in 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.
The study's findings apply to a broad range of disciplines that include sports medicine, economics, politics, education and nutrition. According to the authors, it may be important to monitor fatigue levels in order to prevent bad decisions from being made. In turn, this can help people choose the right foods, improve study habits and manage finances better, among other applications.
Other studies also found that fatigue may have adverse effects on cognitive health.
One study examined the link between exercise and poor mental health. Participants were asked to self-report the number of days in the previous month when they felt mentally unwell. They were also asked how often they worked out during that period of time.
The researchers found that exercising for 45 minutes a day for three to five times a week offered the best mental health benefit. However, those who exercised for more than three hours a day displayed poorer mental health than even those who did not work out at all.
The researchers commented that people who exercise too much may be working themselves out to the point of exhaustion.
Meanwhile, another study looked at burnout and its effect on cognitive function. Researchers enlisted individuals who were clinically diagnosed with burnout and healthy individuals. All participants went through tests that measured their ability to regulate negative emotions.
The team found that burnout patients had a more difficult time modulating strong negative emotional responses compared to the healthy control group. (Related: Experts determine burnout and depression are closely linked.)
The findings of these studies serve as an important reminder that any physical and mental work should be done in moderation. Exhaustion has serious effects on brain health.
Brain.news has more on how exhaustion affects brain health.