What is the main cause of muscle fatigue during high-intensity exercise?

The primary cause of muscle fatigue during high-intensity exercise is the accumulation of metabolic byproducts. During intense physical activity, particularly in anaerobic conditions, the body relies on pathways that produce energy quickly, such as the glycolytic system. As glucose is broken down for energy without sufficient oxygen, byproducts like lactate and hydrogen ions can accumulate in the muscles.

These byproducts contribute to a drop in pH within the muscle cells, leading to a condition known as acidosis, which interferes with muscle contractions. The increase in the levels of these metabolites is correlated with the sensation of fatigue and reduced force production. The more intense and prolonged the exercise, the more significant the accumulation of these byproducts becomes, ultimately impairing performance.

While inadequate oxygen supply, dehydration, and muscle injury can also contribute to feelings of fatigue, they are not the main driving factors in the context of high-intensity exercise. Oxygen supply is more critical in aerobic activities and lower-intensity exercise, dehydration effects tend to manifest over longer durations, and muscle injury is generally associated with overuse or trauma rather than immediate fatigue experienced during high-intensity bursts.