What is a necessary condition of muscular endurance?

Muscular endurance refers to the ability of a muscle or group of muscles to perform repeated contractions over a period of time without becoming fatigued. This capacity is essential for activities that require sustained physical effort, such as long-distance running, cycling, or various sports that involve continuous movement. The correct choice highlights this fundamental aspect, focusing on the sustained physical activity required to maintain performance over time.

In contrast, the other options focus on different aspects of physical fitness. Lifting heavy weights quickly relates to strength and power rather than endurance. The capability for explosive movements is connected to power and speed, which are distinct from the longer-duration activities that muscular endurance entails. Giving up when tired does not contribute positively to any fitness criterion and is contrary to the ideals of endurance training, where persistence and the ability to continue despite fatigue are crucial.