What factor most significantly influences stroke volume during exercise?

The factor that most significantly influences stroke volume during exercise is venous return. Stroke volume is the amount of blood ejected by the heart with each beat, and it is largely dependent on the volume of blood returning to the heart from the body. During exercise, several physiological changes occur that enhance venous return, including increased muscle activity, which promotes the squeezing of veins and assists in pushing blood back to the heart. Additionally, the respiratory pump created by changes in thoracic pressure when breathing in and out further aids in venous return.

As venous return increases, the heart fills with more blood, leading to a greater stroke volume due to the Frank-Starling mechanism, where increased end-diastolic volume (preload) results in enhanced cardiac output. This mechanism becomes particularly important as exercise intensity increases, since maintaining adequate blood flow to working muscles is vital for performance.

Other factors, such as heart rate, muscle temperature, and blood pressure, do play roles in cardiovascular responses to exercise, but they are often influenced by the venous return rather than being the primary driver of stroke volume changes during physical activity. Therefore, understanding venous return is crucial in comprehending how stroke volume adapts during exercise.