Which of the following is a physiological adaptation to cardiorespiratory exercise?

• A. Increased stroke volume
• B. Decreased stroke volume
• C. Unchanged heart rate
• D. Reduced cardiac output

Answer: (A)

Regular cardiorespiratory training makes the heart more efficient, and the key adaptation is that each heartbeat pushes out more blood. This means stroke volume increases. The heart fills more effectively (greater preload from higher plasma volume and venous return) and contracts more efficiently, so it can eject a larger volume with each beat. Over time, this also helps lower resting heart rate while allowing higher cardiac output during activity.

The other possibilities don’t reflect typical adaptations: stroke volume doesn’t decrease with training, heart rate isn’t usually unchanged at rest because resting heart rate tends to fall, and cardiac output isn’t reduced—the goal of training is often to increase or maintain it during exercise due to greater stroke volume.