Which component of fitness focuses on the ability to sustain physical activity for extended periods of time?

The component of fitness that focuses on the ability to sustain physical activity for extended periods is cardiovascular endurance. This aspect of fitness is primarily related to the efficiency of the cardiovascular system, which includes the heart, blood vessels, and lungs, in delivering oxygen to the working muscles during prolonged exercise. High cardiovascular endurance means that a person can perform activities like running, cycling, or swimming for longer durations without fatigue, indicating strong heart and lung function as well as an efficient metabolic system.

In contrast, muscular strength refers to the maximum amount of force that a muscle or muscle group can exert in a single effort, and it does not directly address the ability to sustain activity over time. Flexibility pertains to the range of motion around a joint and is important for overall mobility but does not relate directly to endurance. Body composition refers to the relative amounts of fat and lean mass in the body and, while it can influence overall health and performance, it does not specifically measure the ability to sustain prolonged physical activity. Thus, cardiovascular endurance is the correct focus when discussing sustained physical activity.