Exercise demands that your cardiovascular system responds to the challenge. At the onset of exercise, your body undergoes physical changes that facilitate the need for more oxygen. Vasodilation is just one of these changes. Wider blood vessels allows increased blood flow, which is critical for effective workouts.
Expansion and Constriction
During exercise, both vasodilation -- the widening of blood vessels -- and vasoconstriction -- the narrowing of the blood vessels -- occurs. Your body uses this system as a means to redirect blood flow. It is not necessary for organs that are not working toward an activity to also receive an increase in blood flow. Constriction allows your body to limit blood flow to certain areas and dilation increases blood flow to other areas. Dilation of veins during exercise allows the return of de-oxygenated blood back to the heart for recirculation.
The amount of blood that your heart pumps out per beat is influenced by the amount of blood that is returned. During diastole, your heart's chambers fill with blood, either preparing to go to the lungs for oxygen pickup or to the working muscles for oxygen delivery. The Frank-Starling Mechanism explains this phenomenon. In order for stroke volume, or the amount of blood your heart pumps per beat, to fulfill the needs of the body, venous return must increase. Dilation of the veins allows for a larger amount of blood to return to the heart, increasing the amount of blood inside the ventricles after diastole, allowing for an increase in stroke volume.
Dialation and Diastole
Dilated veins also allow for your heart to function properly during diastole. Total peripheral resistance around your body influences your diastolic pressure. When your veins are dilated, your resistance decreases. During exercise, this is important because your diastolic pressure either stays the same or even decreases, which is due to the dilation of vessels. When your diastolic pressure remains close to rest, the heart is able to fill with blood.
Response to Exercise
It is important for your body to respond properly during exercise. In fact, the practice of vasodilation and constriction that accompanies exercise keeps your arteries healthy. Your endothelial cells line your arteries and veins and are responsible for the changes that take place during exercise. With regular exercise training, your endothelium stays healthy and functions properly.