Your cardiovascular system performs a number of crucial functions in your body. It transports oxygen to cells and removes carbon dioxide, carries away metabolic waste products, and transports hormones to the intended organs. In addition, it helps maintain body temperature and preserve your bodyâ€™s acid balance. Most people are able to accomplish light activity, about the equivalent of walking 2.5 miles per hour, without placing excess demand on their circulatory and respiratory systems. When you perform more intense exercise, however, your musclesâ€™ need for oxygen multiplies. Your heart is forced to pump harder and faster. The amount of blood your heart pumps and the oxygen your body consumes rise in direct proportion to the amount of work your muscles are performing. And once again, your level of physical conditioning dictates how well this system works.
The arteries in your working muscles dilate to accommodate their increased need for blood. At the same time, the heartâ€™s increased output causes your blood pressure to rise. The arterioles (tiny arteries) in your skin expand, allowing for more blood flow there. This engorges the capillaries near the surface of the skin and helps the heat your body generates as you exert yourself escape into the cooler air around you. As you exercise longer, especially in hot, humid weather, more blood is diverted to your skin to maintain a safe body temperature.
While your arteries are dilating, the veins serving the peripheral parts of your body are contracting. At rest, the venous system stores roughly 65% of the bodyâ€™s blood supply. This constriction makes more blood available for use by your heart and exercising muscles. Your body further optimizes the distribution of blood by limiting the amount sent to the kidneys, liver, digestive system, and other organs not immediately involved in the exercise process.Building endurance
Through regular exercise, your circulatory system adapts even more to increase your cardiorespiratory endurance. Your body creates more plasma, the salt-water fluid that carries sugars and nutrients to cells and ferries away waste. Because plasma is a component of blood (blood cells make up the remainder), thereâ€™s a greater volume of blood available to pump. It also means that the blood is slightly thinner, which lowers the resistance it encounters while circulating. In addition, the main pumping chambers of your heart, called the ventricles, stretch to hold more blood and contract with greater force. Over the long term, the heartâ€™s muscle fibers increase in size as well, making the heart stronger.
Likewise, the capillaries that serve the working muscles â€” including the heart â€” increase in number. These additional blood vessels serve two valuable functions. First, they feed the muscles more oxygen-rich blood. Second, the presence of more vessels means that the heartâ€™s powerful pumping chamber, the left ventricle, has a more plentiful energy supply and is able to pump the blood with greater ease. The benefit you get from this more efficient pumping action is to be able to do more work with less effort.
The greater need for oxygen-rich blood that occurs during aerobic exercise can also lead to an increase in the size and number of branches, tributaries, or other coronary arteries feeding the heart. This provides other channels for oxygenated blood to reach heart muscle. If an artery serving the heart becomes blocked, thereâ€™s less risk of heart muscle damage because there are alternative channels to keep the blood supply flowing. The boost in oxygen and other benefits of exercise offer some protection against dangerous heart rhythm disturbances as well.
|Exercise by the numbers |
While you exercise:
Â·Â Â Â Â Â Â Â Â Your heart rate can reach 130â€“150 beats per minute (sometimes higher, particularly in young, fit individuals). Thatâ€™s almost double the resting norm of 70â€“80 beats per minute for most people.
Â·Â Â Â Â Â Â Â Â Your heart may pump up to 20 liters of blood per minute (40 liters for well-trained endurance athletes), which is quadruple the 5 liters per minute thatâ€™s typical while resting.
Â·Â Â Â Â Â Â Â Â Your skin and muscles receive 80% of your total blood flow. This is up from the 20% these areas get during rest.
Â·Â Â Â Â Â Â Â Â Systolic blood pressure (the top number) increases by 20 mm Hg or more during the first few minutes of exercise before leveling off. The diastolic reading (bottom number) remains largely unchanged. After you cease strenuous activity, however, blood pressure drops to lower than pre-exercise levels for two to three hours.
Â·Â Â Â Â Â Â Â Â Millions of capillaries open up to feed muscle fibers.
Â·Â Â Â Â Â Â Â Â Your lungs pass up to 200 pints of air in and out each minute. When not exercising, the average for most people is 12 pints a minute.
Most people who suffer from coronary artery disease have at least one controllable risk factor. But with new and sometimes conflicting reports emerging all the time, it can be difficult to figure out how to best protect your own heart. Now you can personalize your prevention and treatment efforts with The Healthy Heart: Preventing, detecting, and treating coronary artery disease. This special report from Harvard Medical School gives you all the options, so that you and your health professional can decide together what is best for you.
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