Which of the following best describes muscle fatigue?

Muscle fatigue can be best described as the inability of a muscle to sustain contraction. This condition arises when a muscle is unable to maintain optimal performance during prolonged or intense physical activity, leading to reduced strength and endurance. Factors contributing to muscle fatigue include the depletion of energy sources, accumulation of metabolic byproducts, and the failure of neuromuscular transmission, all of which impede the muscles' ability to contract effectively.

Understanding muscle fatigue involves recognizing that it is a complex physiological phenomenon. While options like maintaining strength during exertion or the inability to perform after rest touch on aspects related to muscle performance, they do not accurately encapsulate the core definition of fatigue itself. Similarly, the failure to recover muscle glycogen entails a specific metabolic consequence of fatigue but does not define the condition itself. Therefore, the most comprehensive description of muscle fatigue is its inability to sustain contraction during exertion.