Excessive athletic training can adversely affect part of the brain involved in decision making
Excessive athletic training not just makes the body tired, it can also cause fatigue in a portion of the brain important for making decisions. The findings show that while endurance sport is generally good for health, overdoing it can have adverse effects on the brain, says a research team from France.
When the researchers imposed an excessive training load on triathletes, they showed a form of mental fatigue. This fatigue included reduced activity in a portion of the brain crucial for decision-making. The athletes also acted more impulsively, opting for immediate rewards instead of bigger ones that would take longer to achieve.
"The findings demonstrate that physical training overload induces some fatigue in the cognitive control brain system, associated with more impulsive economic decisions," says the study published in Current Biology.
The results suggest a "neural mechanism" that might explain not only why overtrained athletes fail to overcome pain or fatigue signals but also why they are at risk of doping, which may help with immediate performance, but compromise long-term achievements. "They could also account for the rise of fatigue syndromes observed in amateurs of extreme sports, such as ultra-trail, who may put in danger not only their heart and knees but also their brains," the findings state.
According to the researchers, the findings suggest a connection between mental and physical effort: both require cognitive control. “The reason such control is essential in demanding athletic training is that to maintain physical effort and reach a distant goal requires cognitive control,” says the team from Hôpital de la Pitié-Salpêtrière, Paris; and National Institute of Sport, Expertise, and Performance (INSEP), France, among other institutions.
The initial idea for the study came from INSEP, which trains athletes for the Olympic games. Some athletes had suffered from "overtraining syndrome," in which their performance dropped as they experienced an overwhelming sense of fatigue. The question, says the research team, was whether this overtraining syndrome arises in part from neural fatigue in the brain, the same kind of fatigue that also can be caused by excessive intellectual work.
"A few decades ago, a marathon superstar at the peak of his career suddenly stopped running for several years, citing mental and physical exhaustion, in the absence of apparent injury. This extreme state of fatigue is at the heart of the so-called overtraining syndrome, a form of burnout that strikes athletes in various types of endurance sport," says the study.
The team recruited 37 competitive male endurance athletes with an average age of 35. Participants were assigned to either continue their regular training or to increase that training by 40% per session over three weeks. The researchers monitored their physical performance during cycling exercises performed on rest days and assessed their subjective experience of fatigue using questionnaires every two days. They also conducted behavioral testing and functional magnetic resonance imaging (fMRI) scanning experiments.
The analysis shows that physical training overload led the athletes to feel more fatigued. They also acted more impulsively in standard tests used to evaluate how they would make economic choices. The researchers explain that the brains of athletes who had been overloaded physically also showed "diminished activation" of the lateral prefrontal cortex, a vital region of the executive control system, as they made those economic choices.
"Training overload in triathletes reduces the participation of prefrontal cortex in decision-making, such that their choices become more impulsive. These findings suggest that excessive physical training and intellectual work might both interfere with cognitive control and hence lead to burnout syndrome," the findings state.
According to study author Mathias Pessiglione from Hôpital de la Pitié-Salpêtrière, the results indicate that neural states matter. "You don't make the same decisions when your brain is fatigued," says Pessiglione.
The researchers say their findings might be important not just for producing the best athletes. It suggests that it might be essential to monitor fatigue level to prevent bad decisions from being made in the political, judicial, or economic domains, they add.