IB Syllabus focus: 'Fatigue can originate at different levels of the motor or energy pathway. Insufficient fuel availability, including phosphocreatine and glycogen depletion, can contribute to fatigue.'
Fatigue in exercise is not caused by one failing system. Performance can decline because neural activation weakens, muscles respond less effectively, or fuel supply no longer supports the required rate of ATP resynthesis.
Understanding fatigue
Fatigue in SEHS refers to a loss of the ability to maintain the desired force, power, speed, or skill level during exercise.
Fatigue: An exercise-induced reduction in the ability to produce force or power and maintain performance.
Fatigue is task specific. A sprinter, rower, and marathon runner may all experience fatigue, but the main source may differ because the movement pattern, intensity, and energy demand are different.
Fatigue in the motor pathway
Practice Questions
FAQ
Phosphocreatine is restored mainly through aerobic processes during recovery, so oxygen delivery and mitochondrial function matter.
A large portion can recover within about 20 to 30 seconds.
Near-complete restoration usually takes several minutes.
If recovery is too short, the next sprint starts with lower phosphocreatine stores.
Muscle glycogen is stored inside the working muscles and supports local ATP production during exercise.
Liver glycogen helps maintain blood glucose. If liver glycogen falls very low, the athlete may feel weak, mentally flat, or unable to maintain pace even if the muscles have not completely run out of stored fuel.
The brain constantly receives feedback about stress, energy status, and how hard the task feels. That feedback can increase the sensation of effort before complete muscular failure occurs.
This means an athlete may slow down or stop because sustaining the task feels too difficult, even though some contractile capacity is still present.
Yes. Fiber type changes how quickly energy is used and how resistant the muscle is to fatigue.
Type II fibers produce high force quickly but use energy rapidly.
Type I fibers are more fatigue resistant and better suited to longer efforts.
Because of this, power events and endurance events often show different dominant fatigue patterns.
Yes. An athlete with better movement economy uses less energy to maintain the same speed or workload.
That can:
slow glycogen use during endurance exercise
reduce unnecessary muscle activation
delay the point at which ATP demand exceeds available fuel supply
Two athletes at the same pace may therefore fatigue at different times even if their fitness levels seem similar.
