Fatigue and burnout are a figment of our brain

Fatigue in sports may be a “brain illusion”: how expectations affect the limits of endurance

Modern research in the field of sports psychophysiology increasingly shows that the limit of human endurance is determined not only by the physical condition of the body, but also by how the brain interprets fatigue and time.

One study cited by scientists (PMID: 18356107) examines the phenomenon in which the subjective feeling of fatigue and the moment of “I can’t go on” may be linked not so much to real exhaustion as to a person’s cognitive expectations about their own abilities.

Exercise bike experiment

During the experiment, participants completed a high-intensity ride on an exercise bike. Before starting, they were told that lasting for one hour was a good result.

While completing the task, participants could see a timer, but researchers altered its perception: time was visually either sped up or slowed down. This made it possible to assess how strongly the subjective perception of time affects the moment fatigue sets in.

The results were unexpected: most participants stopped the effort roughly when an hour had “passed” by their sense of time, even if the actual time differed by 10–30% in either direction.

How the brain “decides” when we are tired

Scientists concluded that the feeling of fatigue is formed not only by physiological signals — the buildup of lactate, an increased heart rate or reduced muscle power — but also by the cognitive interpretation of these signals.

In other words, the brain evaluates not only “what is happening to the body” but also “how long this has been going on” and “how long it is supposed to go on.”

Additional research in sports psychology confirms this effect. During high-intensity exercise, people often experience distorted time perception: it may seem slower than in reality, which intensifies discomfort and hastens the moment of giving up.

Why time “stretches” during exercise

Scientific work shows that during intense physical activity the brain processes more signals from the body — breathing, heart rate, muscle tension. This increases the “density” of subjective experience.

As a result, the internal “clock” begins to work differently: a person feels that more time has passed than actually has. This effect becomes stronger with fatigue and stress, when attention is focused on unpleasant sensations.

Fatigue as a combination of physiology and psychology

Modern models of endurance view fatigue as an integration of two factors:

the physiological state of the body

the cognitive assessment of effort and time

This means that two people with the same physical fitness may “give in” at different times simply because of differences in how they perceive the load and what they expect.

Practical significance

Understanding these mechanisms is already being used in sports. For example:

external time control (timers, coach prompts) helps stabilize pace

distraction of attention (music, competitive elements) reduces the subjective load

adjusting expectations can increase actual endurance

Some studies show that even small changes in the perception of time (around 10%) can noticeably affect subjective fatigue and the duration of effort.

Conclusion

Fatigue is not only “the body’s signal that it has reached its limit,” but also a complex construct in which the brain plays a key role. Expectations, attention and the perception of time can change the moment when a person decides to stop.

In other words, the limits of endurance may be less objective than is commonly believed — and to a large extent depend on how the brain “negotiates” with the body about how much effort has already been spent.