Why Mental Fatigue Affects Some People More Than Others

Why does one person perform almost as well mentally after an exhausting physical task, while another shows a clear decline? And what exactly happens in our brains at that moment? Four recent and ongoing PhD studies from the VUB research group Human Physiology and Sports Physiotherapy (MFYS) each approach this question from a different angle.

“Mental fatigue affects not only how we think. It can also determine how we perform and even how long we can sustain physical effort,” says VUB professor Bart Roelands, who is organising the symposium.
Mental fatigue is something we all recognise: after hours of concentrated work, it becomes harder to stay focused and a task requires more effort. For years, the VUB research group MFYS has been investigating how physical and mental fatigue arise and what role our brains play in the process. On Saturday 14 November 2026, the group will bring together researchers from Belgium and abroad during the Mental Fatigue Symposium at U-Square VUB.
With Italian sports scientist Samuele Marcora from the University of Bologna, an expert in mental fatigue and endurance performance, and Dutch movement scientist Florentina Hettinga from Vrije Universiteit Amsterdam, the symposium is bringing two international experts to Brussels. Hettinga investigates, among other things, how athletes distribute their effort and how opponents influence their performance. In addition, four recent and ongoing PhD studies by VUB researchers will take centre stage.

Mental Fatigue Does Not Affect Everyone Equally
Jelle Habay investigated why some people respond much more strongly to mental fatigue than others. He compared existing research and found that mental fatigue has, on average, a small negative effect on endurance performance. However, significant differences lie behind that average. Some people perform noticeably worse after mental exertion, while others experience hardly any consequences. Age, sex, BMI and physical fitness could not explain these differences. This means that the interesting question is not only whether mental fatigue affects our performance, but especially for whom and under what circumstances.

Read the publication on individual differences in mental fatigue 

Fencers Are More Mentally Fatigued During the Decisive Phase
Chao Bian translated the research into sports practice. He investigated mental fatigue among Chinese fencers and fencing professionals competing at national and international level. Fencing is particularly interesting in this regard: a fencer must exert themselves physically while simultaneously assessing their opponent, making rapid decisions and reacting at exactly the right moment.
Bian found that participants felt more mentally fatigued during the direct elimination bouts of the knockout phase than during the earlier pool phase. Decisions about the right moment to execute an action and to launch attacks were perceived as particularly mentally demanding. The research shows why mental fatigue should not only be studied in a laboratory setting: during a real competition, physical load, concentration, tactics and competitive pressure all come together.

Read the publication on mental fatigue in fencing 

A Medication Influences How We Respond When We Are Fatigued
Laurisa Arenales is investigating the role of dopamine and noradrenaline in fatigue. These important signalling substances in the brain are involved in attention, motivation and behaviour, among other functions. She will defend her PhD on 13 November 2026, one day before the symposium.
In a study involving eighteen healthy adults, Arenales examined what happens when the availability of these signalling substances in the brain is increased through medication. After strenuous physical exercise, participants were required to perform a task in which they had to suppress certain automatic responses. Following the use of methylphenidate, which increases the availability of both dopamine and noradrenaline, participants made fewer errors. This effect was not observed with reboxetine, which primarily increases the availability of noradrenaline. The research therefore provides indications about the role specific signalling substances in the brain play in controlling our behaviour when we are physically fatigued.

Read the publication on fatigue and response control 

A Fatigued Brain Does Not Simply Slow Down
Manon Roose is using functional MRI scans to investigate what changes occur in our brains when we become mentally fatigued. For a systematic review study, she combined the findings of nine studies involving 235 healthy participants who performed prolonged cognitive tasks.
Remarkably, brain activity does not decrease everywhere. In some brain regions, activity actually increased as people became more mentally fatigued, while in other regions it decreased. Mental fatigue therefore appears primarily to alter how different parts of the brain are recruited. Because the existing studies differ considerably from one another, it is not yet clear what exactly constitutes the characteristic pattern of a mentally fatigued brain. Roose is continuing to investigate this question in her ongoing PhD research.

Read the publication on mental fatigue and brain activity 

Together, the four studies demonstrate how broad the phenomenon of mental fatigue is: from changes in our brains to individual differences and the consequences for real-world performance. During the symposium, these insights will be linked to contributions from international experts on, among other things, motivation and the experience of effort.