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EXERCISE AND MUSCLES

The main virtue of exercise does not lie in any increase of muscular strength but in its maintenance of the normal activities of the tissues. When a muscle contracts it uses up a substance called glycogen, which is present in muscles in large amounts. A waste product, lactic acid, accumulates. The blood takes up carbon dioxide, which develops from waste material, and carries it to the lungs, where it is eliminated from the body.
If carbonic acid and lactic acid accumulate in them, the muscles become acid in their reaction. If lactic acid accumulates in considerable amounts the movement of the muscles will stop. Oxygen is required to aid continuous movement of the muscles. When oxygen comes in, the lactic acid disappears, the glycogen accumulates again, and the muscles become alkaline instead of acid. Large amounts of oxygen are necessary for continuous work by the muscles.
A person who is doing hard muscular work requires ten times more oxygen than he needs when he is resting. The extra oxygen, which is provided by speeding up the circulation, increases the rate of breathing and sometimes raises the pressure of the blood in the blood vessels.
During exercise the pulse rate becomes more rapid, the blood pressure rises, and more blood goes through the tissues. The amount of increase depends on the rapidity and continuity with which, and the length of time during which, the muscles are being used.
In addition to the value of exercise for improving the general health, there is its value in improving the condition of tissues that have been weakened by disease. Therefore, restricted exercise is prescribed for people who have such conditions as heart disease or high blood pressure. These exercises must be controlled by trained attendants, so that the sick person never becomes fatigued, exhausted, or subjected to over-exercise.
The balance between beneficial effects and bad effects is so delicate that it is impossible for anyone to regulate the exercise in relation to disease for himself. Even doctors who have such conditions cannot regulate for themselves the amount of effort they may put forth.
Serious harm, at times even death, has resulted from having a doctor tell such patients casually that they need exercise, without specifically prescribing the character and the amount. The tragedies of the handball and tennis courts and the golf course bear eloquent testimony to this fact.
In determining physical fitness the doctor studies the pulse, the blood pressure, the breathing, and the condition of the blood.
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