How does stroke volume (SV) change in response to increased exercise intensity?

Stroke volume (SV) is the amount of blood pumped by the heart with each beat, and its behavior during exercise is critical to understanding cardiovascular physiology. As exercise intensity increases, stroke volume initially rises due to factors such as enhanced venous return, improved myocardial contractility, and increased preload. However, this increase in stroke volume does not continue indefinitely.

Research shows that stroke volume typically peaks at around 40-60% of VO2 max, after which it plateaus or levels off. Beyond this point, other factors like heart rate (HR) take precedence in further increasing cardiac output, which is necessary for sustaining higher levels of exercise intensity. This plateau occurs due to a combination of factors, including the reduced filling time of the ventricles at faster heart rates and the limits of myocardial stretch and contractility.

Overall, the correct answer captures the essential physiological response of stroke volume during exercise, reflecting the body's adaptations to increased intensity and the dynamics of cardiovascular function.