What aspect of fitness does "muscular endurance" refer to?

Muscular endurance refers to the ability of a muscle or group of muscles to sustain repeated contractions or to continue exerting force against a resistance for an extended period. This aspect of fitness is crucial for activities that require prolonged performance, such as long-distance running, cycling, or repetitive weight training with lighter loads. It emphasizes stamina and the capability to maintain activity without fatigue over time, distinguishing it from other strength-related qualities.

For instance, while lifting heavy weights relates to muscular strength and refers to short bursts of exertion, muscular endurance might involve performing a set of lighter weights numerous times. The focus is not on the maximum effort but rather on how long the muscles can perform a specific task before tiring. This distinguishes muscular endurance from flexibility, which pertains to the range of motion of the muscles and joints.