What is considered a primary characteristic of cardiovascular endurance?

Cardiovascular endurance primarily refers to the body's ability to perform prolonged physical activity by utilizing oxygen efficiently over time. This characteristic emphasizes the effectiveness of the cardiovascular and respiratory systems in delivering oxygen to the working muscles during extended periods of exercise.

When someone has high cardiovascular endurance, they can sustain aerobic activities, such as running, swimming, or cycling, for longer durations without becoming fatigued. The sustained oxygen supply to the muscles is crucial because it allows the body to produce energy during aerobic activities, thereby maintaining performance and delaying the onset of exhaustion.

In contrast, the other options—such as lifting weights, muscle strength, and flexibility—relate to other aspects of physical fitness. Lifting weights pertains to muscular strength and hypertrophy, while flexibility focuses on the range of motion in joints and muscles. None of these directly define cardiovascular endurance, making the sustained oxygen supply to working muscles the defining characteristic of this aspect of fitness.