What describes the ability of a muscle to exert submaximal force over time?

The ability of a muscle to exert submaximal force over time is best described as muscular endurance. This concept focuses on the muscle's capacity to sustain repeated contractions or maintain a contraction for an extended period, making it crucial for activities that require prolonged effort, such as long-distance running or cycling.

Muscular endurance is distinct from muscle strength, which pertains to the maximum amount of force a muscle can exert in a single effort. While strength emphasizes the peak performance in one motion, endurance highlights the muscle's capability to perform consistently over a duration, which involves both the muscle's energy efficiency and its resistance to fatigue.

Muscle power involves the rate at which strength can be exerted, often in explosive movements, rather than endurance over time. On the other hand, muscle hypertrophy refers to the increase in muscle size resulting from strength training, which does not directly relate to how long a muscle can sustain activity without fatigue.

Thus, muscular endurance is the most accurate descriptor of a muscle's ability to exert submaximal force over an extended time, making it the correct choice in the context of this question.