Using the Muscles keeps the Body Well.—All muscles must have more blood when they are used so that the heart is made to beat faster and stronger by exercise. In this way its valves and walls become able to do more work. Such a heart not only does its work better in a well person, but is able to keep pumping when the body is weakened by disease. Many persons die because the heart gets too weak to push the blood through the body.
In all the little spaces between the muscles and parts of other organs is some watery part of the blood containing much waste given off from the tissues. Moving the muscles presses on this watery waste in such a way as to move it along into the blood channels. It then can be cast out of the body by the lungs and other organs. One reason why we feel so good after exercise is because the poisonous waste has been taken away.
No one can remain well very long without taking exercise. Children as well as older persons should enjoy one or two hours of outdoor play every day.
Fig. 85 —Various ways of exercising the muscles to keep the body well.
How to exercise the Muscles.—Outdoor games give the best form of exercise. Tennis, baseball, cricket, rowing, and swimming are sports which bring nearly all the muscles into use. Every boy and girl should learn to swim. It is dangerous to go swimming alone or to swim in deep water. Cramp may seize the muscles at any time, so that the limbs cannot be moved. Hundreds of persons are drowned every year by venturing in deep water.
Taking care of the yard and garden and helping with other work about the home is one of the best ways of getting exercise and at the same time doing some good.
Special Kinds of Exercise.—A room with ropes, swings, and machines in it for exercise is called a gymnasium. Under the direction of a teacher the pupils can get quickly just the right kind of exercise to strengthen the weak parts of the body and keep every organ in health. The muscles oftenest neglected are those of the chest. Every one should keep his chest full and round by swinging the arms and practicing deep breathing every day.
Danger from too much Exercise.—Lately it has been learned that very violent exercise for more than a few minutes often injures the heart. The running of many races until you are all out of breath or much jumping of the rope is likely to strain the heart. It is always harmful to urge the body on until it is completely tired out.