Which of the following describes the body's capacity to maintain vigorous physical activity for a period of time?

The body's capacity to maintain vigorous physical activity for a period of time is best described by cardiovascular efficiency. This term refers to how well the cardiovascular system—comprising the heart, blood vessels, and lungs—works to supply oxygen to the muscles during sustained physical activity. When someone has high cardiovascular efficiency, they can perform physical tasks for longer durations without becoming as fatigued, indicating a healthier and more effective cardiovascular system.

In contrast, muscular strength pertains specifically to the amount of force a muscle can produce; body composition relates to the proportion of fat and muscle in the body; and flexibility measures the range of motion in joints. While these factors contribute to overall fitness, they do not directly define the ability to sustain vigorous activity for extended periods as cardiovascular efficiency does.