Regular exercise is essential for good health. Too much exercise, however, can tire out the brain and cause mental fatigue associated with impulsive behavior and poor decision-making, according to new research.
Published in the journal Current Biology, the findings showed that exercise overload led to the diminished activation of the lateral prefrontal cortex, an area of the brain that is critical for decision-making.
They also show that, at the behavioral level, athletes subjected to excessive training demonstrated more impulsive behavior, opting for small but immediate rewards over larger ones that would take longer to achieve.
The findings underscore the fact that neural states matter when exercising. Cognitive control is essential in demanding athletic training, which often involves long-term goals.
During demanding athletic training, athletes need to control the automatic process that makes them stop as soon as their muscles or joints hurt, said Mathias Pessiglione, the study’s corresponding author and a research director at the Brain and Spine Institute in Paris.
However, this research demonstrates that athletes are less inclined to make informed decisions when their brains are in a state of fatigue due to training overload, to the detriment of their long-term goals.
Excessive training affects decision-making
Overtraining syndrome is a form of burnout that affects athletes in endurance sports. It is characterized by a significant decrease in performance that typically persists even after a substantial resting period.
Pessiglione and his colleagues hypothesized that a neural mechanism could be behind the effects of excessive training. Their idea is that excessive training induces fatigue in the area of the brain responsible for cognitive control, which is needed whenever habitual processes, such as those involved in training, must be monitored.
To test their hypothesis, the researchers split 37 competitive triathletes into two groups over nine weeks: normal training and training overload.
Those in the normal training group were asked to continue with their current training regimen. Meanwhile, those in the training overload group were asked to increase their training by 40 percent over weeks five, six and seven.
Throughout the trial, the researchers measured the athletes’ performance on a cycle ergometer they rode on their rest days. The team also assessed the athletes’ fatigue levels with a questionnaire given every two days. Finally, the team ran behavioral tests and functional magnetic resonance imaging (fMRI) scans as well.
Their results showed that athletes in the training overload group felt more fatigued. These athletes also made more impulsive decisions, choosing small but immediate rewards over greater but delayed ones.
While making their impulsive decisions, fMRI scans revealed diminished activation of their lateral prefrontal cortex, which is involved in cognitive control.
Cognitive control allows athletes to continue training despite aching joints or muscles for the sake of long-term goals. These results suggest that fatigued athletes are less inclined to do so due to their impaired cognitive control, even if such a decision will hurt their long-term goals.
Furthermore, the researchers found that excessive training led to reduced power output. Like mental fatigue, reduced power output is also detrimental to the pursuit of long-term goals.
Given these findings, the researchers concluded that training overload limits lateral prefrontal cortex activity, gives rise to impulsive decisions and leads to burnout syndrome.
Signs of excessive training
Many athletes, especially those that push their bodies for competitive sports, may be oblivious to the early signs of overtraining syndrome. (Related: Training too long and hard can damage your thyroid.)
It’s important to catch these signs as soon as possible to avoid suffering from health complications later on. Listed below are the tell-tale signs of excessive training.
- Halted progress
- Lowered self-esteem
- Decreased motivation
- Persistent or recurring injuries
- Loss of concentration
- Frequent sickness
- Personality changes
- Extended muscle soreness
- Insatiable thirst
- Altered resting heart rate
Exercise is good for overall health and well-being. However, excessive training can affect not just muscles and joints but also the brain. Watch out for signs of excessive training to avoid health problems later on.