AQA A Level PE – The Cardiovascular System Practice Test 2026 - Free Practice Questions and Study Guide

Plasma volume expansion increases the amount of blood returning to the heart (venous return). With more blood filling the ventricles, the preload is higher, so the ventricles stretch more and contract more forcefully (the preload–stroke volume relationship). This raises stroke volume, and because cardiac output equals heart rate times stroke volume, the heart can pump more blood per beat or per unit time during exercise. The greater blood volume also boosts the heart’s ability to do work (stroke work) during activity.

Beyond pumping more blood, the extra plasma supports thermoregulation. With a larger circulating volume, there’s more blood available to be directed to the skin for heat dissipation and to support sweating, helping maintain core temperature during training. Together, these changes improve endurance by enhancing oxygen delivery to muscles and keeping the body cooler during sustained exercise.