The brain governs limits before muscles fail
Exhaustion is usually not muscles or heart reaching a hard physical ceiling. The ceiling you feel is a safety margin set by the brain, not the true physiological limit.
Endure
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Perceived effort as the real limiter
In the psychobiological model, you quit when perceived effort matches the most you are willing to tolerate, not when your muscles give out. Anything that lowers how hard a task feels, or raises your tolerance for that feeling, extends endurance even if the body is unchanged. Examples include mental fatigue, subliminal images of smiling faces, and caffeine.
The finishing sprint exposes hidden reserves
Runners who feel fully spent often speed up sharply in the final stretch once the finish line is in sight. If fatigue were pure physical depletion, this end spurt would be impossible. Its existence shows the body was holding capacity in reserve, and that pacing is set by the brain's knowledge of distance remaining.
Carbohydrate mouth rinse boosts performance
Swishing a sports drink and spitting it out, without swallowing, measurably improves performance in hour-long efforts. Receptors in the mouth tell the brain that fuel is coming, so the governor relaxes its restraint before any energy reaches the muscles. Sensing a resource can change output as much as having it.
Train the brain to tolerate effort
Brain endurance training pairs physical workouts with mentally fatiguing tasks, such as cognitive tests done while exercising. This raises the level of effort a person can bear, and in trials it improved endurance beyond physical training alone. Tolerance of effort is treated as a trainable capacity, like aerobic fitness.
Belief shifts where limits sit
Because the brain sets the limit using predictions, anything that changes those predictions moves the limit. Deceptive feedback, placebos, and seeing a barrier broken all have this effect. Limits are best seen as flexible, context-dependent forecasts rather than fixed properties of the body, which is why records often fall in clusters once one person proves a feat possible.