Does heavy training lead to both brain and body fatigue, and bad decision making?

The answer’s a potential yes according to recent research into exercise-derived neural fatigue…

Credit: Daniel Seex

The brain’s impact on exercise intensity, duration and fatigue’s a growing source of interest for researchers, ever since Dr Tim Noakes devised his central governor model of fatigue in the late Nineties.


Broadly, Noakes proclaimed that the brain, rather than the body, is the limiting factor during exercise, reducing pace and exertion levels if it feels under threat. Noakes’ work provided the basis for further ideas like Samuele Marcora’s psychobiological model of fatigue that folds motivation into the mix.

Now, a team led by Bastien Blain from the Max Planck UCL Centre for Computational Psychiatry and Ageing Research has role-reversed the scenario, examining the exercising body’s impact on the brain, specifically the effect on decision making.

Thirty-seven male triathletes were split into two groups before following two slightly different training programmes. For six of the nine-week plans, the training followed the same duration and effort levels. But a three-week block prior to a two-week tapering period saw the overreaching group undertake a 40% greater training load than the control group.

This is where the experiment really kicked in. Two days after this three-week block, the subjects undertook a maximal power output test followed by behavioural testing and functional magnetic resonance imaging (fMRI) scanning experiments. Throughout, they’d also completed questionnaires to assess their feelings of fatigue.

The results showed that the heavier training load led to the overreaching group feeling more fatigued. Nothing surprising there. But this neural fatigue dropped the athletes’ guards, leading to more impulsive decisions when it came to the behavioural tests that included economic choices. But this wasn’t purely psychological indifference. The fMRI results showed ‘diminished activation of the lateral prefrontal cortex, a key region of the cognitive control system’. This partly explains why it’s easy to gorge on rubbish after a big session and, according to the researchers, why constantly fatigued athletes might make the immoral decision and dope.


So what does this mean for you, the age-group triathlete? Well, it’s another shot in the arm to measure your state of freshness, be the technical – cue heart-rate variability training or Training Stress Score on Training Peaks – or a more parochial but still useful wellness app. Further down the line, say the researchers, the aim is to discover treatments and strategies that help to prevent neural fatigue and its athletic, health and economic repercussions.