Which component of fitness is best measured by the ability to perform prolonged activities?

Cardiovascular endurance is best measured by the ability to perform prolonged activities because it reflects the efficiency of the heart, lungs, and circulatory system in supplying oxygen to working muscles during sustained physical exertion. This component of fitness is crucial for activities that require stamina, such as running, cycling, swimming, or any activity that lasts for an extended period. When an individual has good cardiovascular endurance, they can maintain their performance level over time without excessive fatigue.

In contrast, muscular flexibility relates to the range of motion in the joints, which doesn't specifically measure endurance. Muscular power focuses on the ability to exert a maximum amount of force in a short time, which is more about short bursts of activity than sustained effort. Body composition refers to the proportions of fat and non-fat mass in the body, not necessarily indicating how well a person can perform extended activities. Therefore, cardiovascular endurance is the component most directly associated with prolonged physical activity.