Why Does Your Heart Beat Fast When You Exercise?

The heart pumps blood through the body to provide nutrients and remove waste from the body's tissues. The body requires more nutrients and produces more wastes as you exercise. Your body reacts to these and other changes by increasing the speed at which your heart beats.

Increased fitness causes your heart to beat slower. (Image: Jupiterimages/Photos.com/Getty Images)

Definition of Heartbeat

With each heartbeat, your heart fills with blood and quickly contracts to pump it through the body. Your resting heart rate equals the number of times your heart beats per minute while you are at rest. The normal resting heart rate runs between 60 and 80 times a minute, but it may be normal to have a heart rate between 50 and 100 beats per minute, according to Montana State University.

Neural Control

The sympathetic and parasympathetic nervous systems control the rate at which your heart beats. Just in preparation for exercise, your sympathetic nervous system increases the heart rate. As exercise begins, the sympathetic nervous system stimulates the heart to beat even faster in response to the body's demands.

Blood Vessel Dilation

Muscles need more oxygen and energy during exercise. The blood vessels of the active muscles dilate to increase the blood flow and the amount of nutrients delivered to them. As these blood vessels dilate, the vessels in the stomach and kidneys constrict. However, more vessels dilate than constrict, requiring the heart to pump faster to maintain a normal blood pressure.

Waste Elimination

Exercise causes the muscles to produce large amounts of waste in the form of lactic acid, adenosine, carbon dioxide and hydrogen ions. The increased heart rate and blood flow produced by the circulatory system allow the body to carry these wastes away from the muscles and excrete them through exhalation, sweating and urination.

Regular Exercise And Heart Rate

Getting regular amounts of exercise will increase the size of the heart and increase the amount of blood the heart can pump with each contraction of the ventricles. This training effect causes your resting heart rate and average exercise heart rate to decrease by as much as 20 to 30 beats per minute. Throughout your lifetime, this can equal millions of saved beats by your heart, which will no longer have to work as hard to keep up with the demands of your body.

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