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The Muscles

Sources: A Handbook Of Health

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,

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.[22]

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


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.

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.

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


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


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


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.