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02B EXERCISE AND YOUR HEART
One of the most important effects of exercise on your body is its stimulating effect on your heart and circulation. An active muscle may have 20 times the amount of blood passing through the newly opened blood vessels as an inactive muscle. When you exercise the large muscles of your body, such as in walking or running, your heart, being a muscle, also exercises by speeding up its beat. When you walk, about 30% of the circulation of your blood is carried on by your leg muscles, and the remaining 70% by the heart.
Your heart is truly a miracle muscle. It is a hollow, for-chambered ball the size of your fist, arranged in circular and spiral layers of muscles. When these contract, your blood is literally squeezed out of its chambers into your arteries, which branch out like the roots of a tree to carry blood to every living cell of the body.
To get an idea of how much your heart works, clench your fist and open it again and again 72 times a minute. Your hand tires very quickly, but your heart does this 100,000 times a day, or 40 million times a year. The sturdiest muscle in your body, it pumps 8,000 liters of blood every day through 100,000 kilometers of blood vessels.
Your heart will take good care of you all your life, providing you take care of it. It is the first organ of your body to lose efficiency if you let it rest too much. If you are a sedentary person, your heart beats 70 to 80 times a minute at rest, and pumps abot 90 c.c. of blood into your circulation with each beat. This meets your needs at rest, but it does not provide much safety margin, If you run for a bus, or up a flight of stairs, there is an immediate need for your heart to pump more blood to the working muscles. If you are not used to exercise, a sudden demand may prove too great for your heart.
In what way does properly regulated exercise strengthen your heart muscle and slow its resting beat? When you exercise strenuously, you increase your need for blood to the muscles by as much as 20 times. This makes the heart also beat faster and the heart muscle becomes more efficient, enlarges and gives stronger contractions. The resting heartbeat of a fit person is only 60 a minute. This means that it needs to pump only 60 times a minute as compared to 70 or 80 times in an unfit person to get the same amount of blood around the body in the same time. This saves about 25,000 beats a day. If your heart is in good exercised condition, it can double or triple its output when necessary without strain, and then slow its speed quickly to normal after hard work. An athlete who is in excellent condition may have a pulse rate of only 40 beats per minute.
Exercise increases the efficiency of your lungs, conditioning them to process more air with less effort. If you are a sedentary person, habitually "at rest", much of your lung surface is little used and a large proportion of your air cells are collapsed. Exercise makes you breathe faster and deeper, bringing in oxygen for your tissues. This strengthens and protects your organs against disease.
Exercise increases the number and size of your blood vessels, as well as your total blood volume. Thus the physically fit person has a better chance to recover from a serious operation or even from a heart attack.
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