Altogether there are more than six hundred muscles in the body. Some are large and some are very small. In general, they are distributed over the outside of the skeleton, although some make up parts of the vital organs inside. The largest are always found where the heaviest work is to be done. Most of them are therefore found in the back and in the arms and legs, especially in the upper part.
Muscles make the body a machine.
The body is so built that it can do a great many kinds of work. It can easily change position. It can walk, run, sit or Iie down, balance itself in many different positions, and work with both hands and feet. The muscles help to make it possible to do all these things. Every motion in any part of the body comes from the work of muscles. If a person merely bends a finger, the action comes from the muscles. Although the movement is very slight, it is brought about by the working together of muscles; with bones. Thus the muscles tend to make the parts of the body work together like the parts of a machine.
How the muscles work.
The greater part of a muscle is made up of tissues that expand and contract like rubber. At each end of every muscle is a tendon. This is a very strong tissue used to fasten the muscle to other parts of the body. It does not stretch. Often a tendon fastens a muscle to a bone. For example, the muscle at the front of the upper part of the arm, known as the biceps, is fastened by a tendon to the bones of the lower part of the arm just below the elbow. When the biceps muscle becomes shorter, the tendon holds fast and pulls up the lower part of the arm. At the back of the upper part of the arm is another muscle known as the triceps. It, too,’ is fastened to the bones of the lower part of the arm by tendons. When the muscle contracts, it pulls and straightens the arm out. Thus many parts of the body are moved in opposite directions by groups of muscles. In fact, it is by means of various muscles working together that a person is able to walk, raise and lower the head, and do other similar things.
What the muscles are like.
A muscle is made up of fibers somewhat as a rope is. These fibers are very small. If 500 of them were laid side ‘by side, they would measure only one inch across. Each fiber is about one inch long. It is protected by a membrane that fastens it to the other fibers beside it. The most important fact about a fiber is that it can swell out sideways and shorten its length, or become thinner and longer. This explains why a muscle as a whole can contract and expand.
The cells of the muscles are fed by the blood just as are those of all other parts of the body. Not only does the blood bring in food, but it carries away the waste materials left from oxidation. More waste materials are found in muscle cells than in other kinds of cells because muscle cells do so much work. The more work they do, the more oxidation takes place.
When muscles are used, they become larger and do their work better. If they are used very little, they become weak and do their work poorly. This is because activity causes more cells to form, and lack of activity prevents cells from forming. In fact, work seems to be almost as necessary for muscles as food.
Muscles of two kinds.
Muscles are of two distinct types, voluntary and involuntary. The voluntary muscles are those controlled by the mind, such as the muscles of the arm. They are sometimes called striated or striped muscles, since they are marked by bands that go around the fibers from one end to the other. They are usually easily controlled if they are regularly used. Some, however, such as those of the outer ear, are seldom used and therefore not easily moved. A donkey or mule, of course, can move his ears forward or backward easily, because he uses them frequently.
The involuntary muscles are those over which the mind has no control. They do their work without direction. Most of them control the heart, lungs, liver, and other vital organs. They take care of certain necessary activities that must be carried on in the body whether a person is awake or asleep.
Training the muscles.
Voluntary muscles must be trained to do most of their work. Children learn to walk and talk only by long periods of practice. Before they can write they must learn to hold a pencil properly in the hand. Practice is even necessary in learning to throw a baseball or in running a race.
Fortunately, after muscles are trained, they are able to do their work with very little attention. The action takes place whether or not the mind is thinking of it and thus becomes a habit. A pianist, for example, may carry on a conversation while playing a difficult piece of music. The same muscles may be trained to do several kinds of work. A person, for instance, may use his fingers to repair watches, play a violin, paint pictures, or write letters. Practically the only limits in training muscles are time and strength.
Muscles and good appearance.
What clothes are to the body, muscles are to the skeleton. They round out the skeleton and give a pleasing figure. A person with flabby muscles usually makes a poor appearance, no matter how pleasing he is in every other way. A person with very large muscles, on the other hand, may also make a poor appearance, especially if the muscles in some parts of his body are developed much more than those in other parts. To be most pleasing to the eye, · muscles must be equally developed in all parts of the body. Even clothing cannot completely hide the muscular make-up of a person.
The appearance of a person depends upon not only the size of his muscles but also his posture. Boys and girls frequently fall into bad postures by sprawling about in chairs or on couches. Sometimes they walk in a stooped-over manner,. looking down at the ground. Doing these things leads to stooped shoulders and crowds the lungs, heart, and other vital organs. The best way to correct stooped shoulders is to sit and stand in an erect position, not stiffly, but naturally.