Define the term "Muscular Endurance."

Muscular endurance refers to the ability of a muscle or group of muscles to perform repetitive contractions over a period of time without significant fatigue. This quality is essential for activities where sustained muscle activity is necessary, such as running, cycling, or performing multiple repetitions of an exercise with lighter weights.

This definition illustrates that muscular endurance is not about lifting heavy weights or exerting maximum strength in one effort; rather, it focuses on how long muscles can continue to perform over time. The other options, like the ability to lift heavy weights or the maximum strength a muscle can exert in a single effort, pertain more to muscular strength rather than endurance. Additionally, the duration of rest required between sets relates more to training recovery and overall workout structure rather than a direct definition of muscular endurance itself. Thus, the emphasis on repetitive contractions clearly defines why this option accurately captures the essence of muscular endurance.