Read CHAPTER XVIII of A Handbook of Health , free online book, by Woods Hutchinson, on ReadCentral.com.

THE MUSCLES

Importance of the Muscles. It wouldn’t be of much use to smell food, if we couldn’t pick it up and bite it after we had reached it; or to see danger, if we were not able to move away from it. Every animal that lives, moves; and every movement, whether of the entire body from one place to another, or of parts of the body changing their relations to one another, or altering their shape, is carried out by an elastic, self-moving body-stuff, which we call muscle.

All the work that we do, whether in earning our living, or catching our food, or chewing it, or swallowing it and driving it through our food tube, or pumping the blood through our arteries, or drawing air into our lungs, is done by muscles. Hence, a very large part of the body has to be made of muscles. In fact, our muscles, put together, weigh almost as much as all the other stuffs in the body, making over forty per cent of our weight.

How the Muscles Act. The commonest form of muscle that we see is the red, lean meat of beef, mutton, or pork; and this will give us a good idea of how our own muscles look. All muscles, whatever their size or shape, are made up of little spindle-shaped or strap-shaped cells, or wriggling “body-cells” arranged in bands or strings. The size of a given muscle depends upon the number of cells that it contains.

The astonishing variety of movements which muscles can make is due to the fact that they have the power when stirred up, or stimulated, of changing their shape. As most of the muscle substance is arranged in bands, this change of shape on the part of the tiny cells that make up the band means that the band grows thicker and at the same time shorter,-just as a stretched rubber band does when it slackens,-so that it pulls nearer together the bones or other structures to which it is fastened at each end by fibrous cords called tendons, or sinews. This shortening of the muscle band is known as contraction.

When you wish, for instance, to lift your hand toward your face, you unconsciously send a message from your brain down the nerve cables in your spinal cord, out through the nerve-wires of your neck and shoulder, to the big biceps muscle on the front of your upper arm. This muscle then contracts, or shortens, and pulls up the forearm and hand, by bending the elbow joint. Just in proportion as the muscle becomes shorter, it becomes thicker in the middle; and this you can readily prove by grasping it lightly with your fingers when it contracts, and feeling it bulge.

The food tube is surrounded with muscles, as you will remember, for moving the food along it, or churning it. These internal muscles, requiring only the presence of food to cause them to act, and not needing attention on the part of the brain or the will, are known as the involuntary ("without the will”) muscles.

The great group of the voluntary, or bone-moving muscles, which move “with the will” and are under our direct control, may be divided roughly into two divisions-those that move the trunk, or body proper, and run, for the most part, lengthwise of it; and those that move the limbs.

On the body, they may be divided into two great sheets-one running up the front, and the other up the back. When those running up the front of the body contract, they naturally bend the back, and pull the head and shoulders forward and downward. Or, as when you spring up and catch the branch of a tree or a horizontal bar with your hands, these same muscles will pull the lower part of the body and legs upward, so that you can climb into the tree.

The largest and thickest bands of these front body muscles are found over the abdomen, or stomach, where you can feel them thicken and harden when you bend your body forward and pull with your arms, as in hauling on a rope. By their pressure upon the intestines, they give the bowels valuable support, assist in their movements, and help the circulation of the blood through them; so that it is of considerable importance to keep this entire group of muscles well toned up by exercises, such as swinging your arms back over your head, and then down between your legs; bending the head and shoulders backward and forward; swinging the legs up over the body, either when hanging from a bar or lying on your back. Proper exercising and toning up of these muscles will often cure constipation and dyspepsia, by their influence upon the bowels and stomach, and also keep one from taking on fat around the waist too rapidly.

On the back of the body, the muscle-sheet has grown into great, thick ropes of muscle on each side of the backbone, which you can feel hardening and softening in the small of the back, when you stoop down or lift weights. These are the muscles that hold the body erect, and keep the back straight when you stand, and are the largest and hardest working group of muscles in the body. Every minute that you sit, or stand, they are at work; and that is why they so often get tired out, and ache, and you say you have “a backache.” They have to work harder to keep you erect or upright when you are standing perfectly still than when you walk or run, so that standing perfectly still is the hardest work you can do. Next to standing still, the hardest thing is to sit still, as you probably have found out. If it were not for these great muscles of the back and abdomen, we should double up like a jack-knife, either forward or backward, when we tried to stand up. It is not our skeleton that keeps us stiff or erect, but our muscles.

Showing how the muscles, overlapping and interlocking, give shape to the body.]

If you want to keep straight and erect, and thus have a good carriage, you must keep these great body muscles well trained and exercised by swinging movements, such as bending the back forward, standing with your feet apart and then swinging your head and shoulders down and between your legs; or, with your heels together, swinging your hands down till the fingers touch the ground; or by the different exercises that either bend your back, or hold it stiff and erect. Swinging from a bar, rowing, digging with a spade, chopping or sawing wood, dancing, rope-skipping, ball-playing, hop-scotch, and wrestling, all develop these muscles finely and are good for both boys and girls.

Other strands of these muscles branch out to fasten themselves to the shoulder blades and shoulders, where they help to draw the arm back as for a blow, pull the shoulders into position when you stand upright, or, when you have leaned forward and grasped something with the hand, help to pull up the arm and lift it from the ground. These muscles are quite important in holding the shoulders back and giving a good shape to the chest and good carriage of the upper part of the body and head. They are called into play in all exercises like striking, batting, tennis-playing, ball-throwing, swinging, shoveling, swimming, as well as in pulling, in lifting weights, in swinging an axe or handling a broom.

Showing A thickening of flexors on front of arm, as forearm is swung forward, and B thickening of extensors on back of arm, as forearm is swung backward.]

The muscles of the limbs are almost as numerous as those of the trunk of the body, and even more complex. Most of them, on both arms and legs, are in two great groups-one known as the “benders,” or flexors, which, when they shorten, bend the limb; and the other, the “straighteners,” or extensors, which straighten or extend it.

On the front of the arm, for instance, we have the large biceps ("two-headed”) muscle, which runs from the shoulder to the bone of the forearm just below the elbow and, when it shortens, bends the elbow and lifts the arm toward the body.

On the back of the upper arm is the triceps ("three-headed”) muscle, which is fastened at its lower end to a big spur of bone, the “point” of the elbow; when it shortens, acting lever fashion, it straightens or extends the arm. If this is done quickly, the fist is swung outward with force enough to strike quite a sharp blow, though, as you know, if you wish to hit really hard, you have to strike with the weight and muscles of the full arm and the body behind it, or, as we say, “from the shoulder.”

Showing A thickening of flexors on front of thigh and leg, as foot is swung forward; and B thickening of extensors on back of thigh and leg, as leg is swung backward.]

P, patella (knee cap); M, muscle; L, ligament; T, tendon.]

In the lower limbs, the muscles are larger because they have heavier work to do, supporting and moving the whole weight of the body; but they are simpler in their arrangement since they have not such a variety of movements to carry out. The principal muscle in the thigh is the great muscle running down the front of the thigh, and fastening to the upper border of the patella, or knee cap. This muscle, when it shortens, straightens or extends the limb, or lifts the foot from the ground and swings it forward as in walking, or raises the knee up toward the body when we are sitting or lying down. You can easily tell how much it is used in walking by remembering how stiff and sore it gets when you have taken an unusually long tramp, particularly if there has been much hill-climbing in it. On the back of the thigh, runs another great group of muscles, which bend or flex the limb when they shorten. When the knee is bent, you can feel their tendons, or sinews, stand out as hard cords beneath the knee; hence, this group is called the ham-string muscles.

How the Muscles are Fed. Our muscles are not only the largest, but the “livest” part of our bodies. Their contractions and movements are caused by their tiny “explosions” (like the chugging of an automobile, except that we can’t hear them); and in this way they burn up the largest part of the food-fuel which we eat-mostly in the form of sugar. When they have burned up their surplus food-fuel, they call for more; and when this demand has been telegraphed to the brain, we say we are hungry, and that exercise has given us an appetite. While the muscles are at work, they demand that large supplies of fresh fuel shall be brought to them through the blood vessels; and this makes the heart beat harder and faster, and improves the circulation. As they burn up this fuel, they form smoke and ashes, or waste materials, which must be got rid of-the fluid part by perspiration from the surface of the skin, and through the kidneys, and the gas, or “smoke,” through the lungs. This is the reason why, during exercise, we breathe faster and deeper than at other times, and why our skin begins first to glow and then to perspire.

If these waste-materials form in the muscles faster than the blood can wash them out, they poison the muscle-cells and we begin to feel tired, or fatigued. This is why our muscle-cells are often so stiff and sore next morning after a long tramp, or a hard day’s work, or a football game. A hot bath or a good rub-down takes the soreness out of the muscles by helping them to get these poisonous wastes out of their cells.

Thus when we play or run or work, we are not only exercising our muscles and making them gain strength and skill, but we are stirring up, or stimulating, almost every part of our body to more vigorous and healthful action.

Indeed, as our muscles alone, of all our body stuffs, are under the control of the will, our only means of deliberately improving our appetites, or strengthening our hearts or circulation, or invigorating our lungs, or causing a large part of our brains and minds to grow and develop, is through muscular exercise. This is why nature has taken care to make us all so exceedingly fond of play, games, and sports of all sorts, in the open air, when we are young; and, as we grow older, to enjoy working hard and fighting and “hustling,” as we say; and that is the reason, also, why we are now making muscular exercise such an important part of education.