Why Does Stroke Volume Increase During Exercise?

When you exercise, your cardiovascular system works harder. It needs to deliver oxygen to muscles, transport heat to the skin, transport hormones to meet metabolic demands and deliver nutrients and fuel to tissues.

There are changes in stroke volume during exercise, according to a 2016 article published by the Open Cardiovascular Medicine Journal.

The volume of blood delivered to the rest of your body by each beat of your heart increases when you exercise to increase the circulating blood in your system so your body responds appropriately to exercise.

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Stroke volume is the amount of blood that is pumped out of the left ventricle to the body with each heartbeat. Stroke volume increases with physical activity because your exercising muscles need more oxygen and nourishment, which are both received from the blood.

Your stroke volume increases during exercise but reaches a plateau, as there is a limit to how much blood your body can pump during physical activity. At this point, stroke volume may remain steady up to the point of muscle exhaustion, which causes you to stop exercising.

Stroke volume during activity and at rest has been shown to increase in athletes who participate in endurance events. Over time, the left ventricle, or the part of your heart muscle that pumps blood out of the heart, can grow in size.

As a result, stroke volume increases, according to a February 2015 article published by Journal of Exercise Rehabilitation. Increased stroke volume typically leads to lower resting and exercising heart rates as the heart is more efficient at doing its job.

Body position can have an effect on stroke volume, according to an article published in August 2012 by Journal of Critical Care. It is also important to note that supine physical activities — lying on your back with your face upward, such as certain swimming positions — could result in smaller changes in stroke volume.

This is because a supine activity prevents blood from pooling in the lower extremities — caused by gravity while in a standing position — which enhances venous return and decreases the need for increased stroke volume to meet the body's needs.

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One anatomical explanation for the increase in stroke volume during exercise is the Frank-Starling mechanism, as explained in a June 2018 article published by Journal of Molecular and Cellular Cardiology.

Blood is pumped to the body from the left ventricle and when this ventricle fills more completely, it stretches further and produces a more forceful contraction.

In other words, more blood entering the heart results in more blood being ejected. This mechanism results in a greater amount of blood being circulated through your body during exercise — which is essential for delivering oxygen to your hard working muscles.

An increase in stroke volume is most commonly seen during aerobic exercises or endurance-type activities like running, swimming or cycling.