Which of the following best describes muscular endurance?

Muscular endurance is best described as the ability to perform repeated muscular contractions over time without excessive fatigue. This quality is essential for activities that require sustained effort, such as long-distance running, cycling, or swimming, where muscles must repeatedly contract to maintain performance.

In contrast, the other options focus on different aspects of physical fitness. The ability to exert a lot of force in a short time is more aligned with muscular strength and power, which refer to the maximal effort in a brief duration rather than sustaining repeated efforts. The maximum amount of weight that can be lifted corresponds to strength training and maximal strength, which is distinct from endurance. Lastly, the extent of flexibility in muscles and joints pertains to flexibility training and range of motion, not muscular endurance. Thus, the ability to sustain repeated contractions clearly defines muscular endurance, making it the correct choice.