What effect does cardiorespiratory exercise have on stroke volume and heart rate?

Cardiorespiratory exercise significantly impacts both stroke volume and heart rate as part of the body’s physiological response to increased demand for oxygen during physical activity. The correct choice highlights an important aspect of cardiovascular dynamics.

During exercise, stroke volume—the amount of blood pumped by the heart with each beat—typically increases. This occurs because of enhanced venous return, increased contractility of the heart muscle, and improved efficiency of the heart’s pumping mechanism due to training adaptations. As the body demands more oxygen and nutrients, the heart compensates by pumping more blood with each contraction.

At the same time, it's important to understand that while heart rate does increase in response to exercise intensity—reflecting the body’s need to circulate blood more quickly—trained individuals often experience a lower heart rate at a given exercise intensity compared to untrained individuals. This means that as someone becomes more conditioned, their heart can provide adequate blood flow with fewer beats.

Therefore, the correct option summarizes the dynamic where stroke volume increases with exercise while heart rate is relatively lower at the same intensity in trained individuals, illustrating the efficiency and adaptations of the cardiovascular system to physical activity.