Which statement describes cardiovascular endurance?

• A. It refers to the circulatory and respiratory systems delivering oxygen during sustained activity
• B. It refers to joint flexibility
• C. It refers to bone density
• D. It refers to maximal muscle strength

Answer: (A)

Cardiovascular endurance is the body's ability to sustain prolonged aerobic activity by delivering oxygen to working muscles through the circulatory and respiratory systems. This statement fits best because endurance hinges on how well the heart, blood vessels, and lungs work together to supply oxygen during extended effort, allowing muscles to keep contracting over time. Regular aerobic activities like running, cycling, or swimming boost this capacity by increasing VO2 max, improving stroke volume, and strengthening the capillary networks and mitochondria in muscles, which makes sustained exercise easier and reduces fatigue. The other options describe different aspects—joint flexibility, bone density, and maximal muscle strength—not the ongoing oxygen delivery that endurance relies on.