Running is a cardiovascular exercise because it conditions the heart and blood vessels. The more intense the running, the more oxygen the muscles need. Breathing rate increases to bring more oxygen into the body, and the working muscles generate heat. The body responds with a heart rate increase when you run.
The Facts
Running requires heavy use of the muscles, especially the leg muscles such as the larger quadriceps. As these muscles work, they take up oxygen and glucose from the blood to use for energy production. As energy is created, carbon dioxide and other wastes are produced. These wastes are pumped into the blood for removal from the muscle. The heart increases its rate to deliver more blood to the working muscles and to remove the increasing amount of waste.
Moving and Breathing
Running causes the muscles to contract more often and the lungs to work faster to bring in more oxygen. Both the muscle contractions and the breathing push blood from the veins to the heart. The heart senses the increased blood return and sends a message to the brain. The brain returns an impulse to the heart to increase the heart rate in order to keep up with the rate of the returning blood. The heart monitors the rate of blood return with stretch receptors that are located in the wall of the right atrium.
Decrease Carbon Dioxide
Carbon dioxide is a gas that is created when muscles work. The blood removes the carbon dioxide from the muscles and carries it to the lungs for expiration. If too much carbon dioxide accumulates in the blood, receptors in the aorta and the carotid arteries tell the brain. The brain signals the heart rate to increase so the blood is more quickly carried through the lungs and kidneys for filtration. This increased blood flow allows one to continue to run without accumulating dangerous levels of carbon dioxide in the blood.
Running Generates Heat
Runners get warm and break a sweat. This is in response to the heat that their muscles generate while running. The body temperature rises, which causes the body to work to bring the body temperature back to normal. It does this by dilating the blood vessels in the skin and increasing the heart rate to push more blood into those vessels. Heat from the blood is transferred to the sweat on the skin. The heat is carried away when the sweat evaporates.
Control pH Levels
As the muscles contract and relax to facilitate the motion of running, they consume oxygen and nutrients and produce carbon dioxide. Carbon dioxide lowers the pH, making the blood more acidic. According to the Auburn Montgomery School of Sciences' "Cardiovascular System" lecture notes, "More blood is pumped to the lungs so that more oxygen can be picked up by the blood and more carbon dioxide can be eliminated from the blood."
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