How Does Exercising Effect Your Cardiac Output?

Just as exercise can strengthen your pectorals, abdominals or biceps, it can also strengthen your heart. In addition to improving general heart function, exercise also helps improve blood flow. The net effect that exercise has on your heart, and on blood flow or cardiac output, depends on type, intensity and duration.

Identification

Cardiac output refers to the total volume of blood your heart pumps through your body each minute. At rest, cardiac output can average about 4.8 to 6.4 liters per minute and climb, depending on the exercise you perform, to as much as 40 liters per minute. You can calculate cardiac output using the formula heart rate x stroke volume. Heart rate refers to the number of times your heart beats each minute, and stroke volume refers to the amount of blood, measured in milliliters, ejected by your left ventricle with each beat.

Type

Exercise intensity directly affects cardiac output. Low intensity exercise, such as walking, biking and low-impact aerobics reduces heart rate and cardiac output, according to a report published in the "American Journal of Physiology," by decreasing the effect your sympathetic nervous system has on heart rate. In contrast, high-intensity exercise, such as weight training, sprinting and many sporting activities, places greater strain on the heart muscle, increases your heart rate and therefore increases cardiac output.

Effects

Increased cardiac output brings oxygen-carrying blood to your muscles. As evidence, Montana State University at Bozeman states that when at rest, muscles receive only 15 percent of your total cardiac output. However, during periods of intense exercise, such as when you go cross-country skiing, 60 to 70 percent of cardiac output goes to your muscles. This occurs first as your sympathetic nervous system redirects blood flow from organs to your muscles, and second as the blood vessels in those organs constrict to prevent blood from returning.

Significance

As you move from rest and begin exercising, cardiac output rises according to the increase in your heart rate and stroke volume. However, once you reach about 40 to 60 percent of your maximum exertion level, your stroke rate will either level off or increase at a slower rate. This means that to keep increasing cardiac output you must keep increasing your heart rate.

Considerations

Cardiac output will level off as your heart muscle strengthens and your body becomes accustomed to physical activity. For example, when first getting started, walking 5 minutes may be enough to increase your heart rate, but within a few weeks, you will need to increase the intensity of your walk to increase your heart rate by the same amount.