We’d be better off on all fours
The terrible force of gravity causes us untold discomfort because we simply weren’t built to walk on two legs. If you’ve ever suffered from an aching back or a creaky knee read this —
NORMAN J. BERRILL
Professor of Zoology, McGill University
GRAVITY is a terrible force. It not only holds us in our place but smashes us to bits if we don’t take care. The wonder is that we are able to move around as well as we do, for like all backboned animals on the land we are essentially fish out of water and were not originally designed to support our own weight. Most of the time we take gravity for granted and it is only when someone leans too far or jumps from an upper-story window that we realize its power, not to mention the splashy nature of our bodies. Yet from the time we are born until we die in our bed, life is one continual fight against the force of gravity, or time spent out to recover from its effects.
It is harder for us than it is for most other animals. The first great battle was won when fourlegged creatures, which had once been fish, succeeded in lifting their bodies clear of the ground. The limbs became enormously strengthened to support the weight, but at least the body itself remained in the horizontal fishlike position, with its tissues and organs partly slung from the vertebral ridgepole, partly supported by the ribs and the thick muscle sheets of the body wall. Even at that all of them, reptiles and mammals alike, need to take the load off their feet and lie down and rest whenever possible. We ourselves have gone much further and are now upended, poised on two feet
instead of four, with the same kind of effect on suspended organs as you see when a line of clothes is tied at one end only and hangs straight down. It is not as bad as that but there is strain and a lack of support, and the peculiarly human fight against gravity is far from ended.
In four-legged animals the body is slung like a hammock between four posts, with the various internal organs and the long digestive tube partly suspended by ligaments from the upper side and partly supported by the horizontal body wall below. Stand the same kind of body upright, as we do, and the stomach and intestine no longer hang straight down from the backbone but sag parallel with it. Moreover, the supporting ligament has a smaller and less secure hold on the backbone. Another result of the shift in the weight-bearing thrust of the abdominal viscera against the weak wall of the lower abdomen is that we are prone to rupture or hernia.
We contend with gravity in two ways. Except when we are lying down, gravity works its more or less destructive will on us whether we move about or not. While every time we move, whether to take a step or scratch our head, the weight of the body or the arm must be shifted with levers of muscle and bone. Work is performed and energy expended simply to counteract and overcome the gravitational pull. With each step forward we lift the full weight of our body, from 100 to 200 pounds, although it is done in such a way that we hardly notice the effort.
A 200-pound man, for instance, who has no business being so heavy, takes about 2,000 steps to walk a mile and in so doing lifts the equivalent of 200 tons, although not all at once and not very far. Yet an 80-ton whale swims through the seas with the greatest of ease and lifts nothing at all. A housewife not unusually walks 12 miles a day, or about 27,000 steps, each of which moves some 130 pounds a couple of feet forward.
You feel gravity most, however, when climbing stairs, for climbing a flight of stairs 15 times a day is equal to lifting a ton from one floor to the next. It is no wonder we suffer from wear and tear, especially when we consider how long we live. The great whales grow fast and burn out quickly in about twenty years, with their enormous hulk completely supported by water, whereas we grind along
In youth we can laugh it off, but gravity always catches up. Here’s why . . .
for three or four times as long with our weight forever pressing on our feet and joints. The longer we live the more time there is for gravity to play havoc with our anatomy. For 15 or 20 years we rise and shine. Thereafter time grows heavy.
Our feet feel it first since they carry all of our weight, but even those little bags under our eyes that so many of us eventually acquire are gravity effects. The cushioning fat lying beneath the eyes too often breaks through its own support and presses down and out against the skin, which it would never do if we had remained horizontal. Paunches and aching backs are equally penalties paid for our presumption.
The trouble begins when we are born. Until then a baby is supported comfortably by the liquid within the fetal membranes. Only the mother feels the weight of her burden. But once birth has occurred and the buoyant water has been replaced by insubstantial air, the infant is held down as though by a giant magnet wherever it is put. The body is too heavy for the limbs to raise and the neck muscles too weak to raise the head. Only slowly, as the muscles strengthen and arms and legs become stronger, does the baby find it possible to roll over and finally, still on all fours, lift itself clear of the bedding. It is a triumphant moment, usually when the baby is four or five months old. Yet even this is but a halfway stage, for the greater triumph comes later when the child laboriously hauls itself up and balances precariously on its feet alone. After that comes the mastery of walking, a truly remarkable performance from any point of view.
As walking animals, human beings start off with the old pattern of four-footed progression, supporting the weight of the body and moving it forward by using all four limbs and regularly shifting the centre of gravity to and fro. Even when we stand erect and walk in our usual manner, our right arm
swings forward with the left foot and the left arm with the right foot, just as we did before. The movements however tend to keep our centre of gravity over the foot which is on the ground. Otherwise we lose our balance and are pulled violently to the earth. Nerve impulses from all the muscles, tendons and ligaments, and from the balancing organ of the inner ear, help us keep this precarious balance, although for the most part we become unconscious of them and respond automatically.
So it is that even a five-year-old child can toss his fifty pounds of body weight about with a minimum of effort, always keeping the centre of gravity over one foot or the other and exploiting the force of gravity as far as possible rather than fighting it, a trick something like jujitsu. For the foot serves not only for support and as a cushion for the descending leg, but as a lever, a jack and a catapult as well. Twenty-six small bones combine to form an arch capable of supporting several hundred times their own weight. The big toe alone takes a load of 12 to 14 pounds.
So much for the machinery. It works marvelously for a while. But no matter how skilfully we have raised ourselves up, no matter how well we exploit the very force that tends to pull us down, that force is felt throughout the body as long as we are erect, or even partly so. And the longer we live the greater the wear and tear, and the more the imperfections begin to show.
Let us start at the top. The skull weighs little and the brain is too light to be much of a burden upon the neck. But as we pass down the vertebral column
the load increases steadily. If we consider again those animals that walk on all four legs we find that the vertebrae are fairly uniform cylindrical sections and that they are separated from one another by thin cylindrical discs of cartilage. In our own case the single curved arch is broken into an S-curve as an aid to maintaining our balance. We get a forward curve in the backbone’s neck region when we are about four months old, and when we stand up at about a year we get a forward curve in the lower trunk. In the upper trunk and the pelvic region the backbone keeps its old backward curve.
This is all very well but a price has been paid for all this twisting and bending. Nature has had to change the original shape of the vertebrae to that of a wedge, with the thicker edge in front and the thinner in back. This allows them to pivot on their front ends as on hinges. It also weakens the backbone, and if we suddenly increase the effect of gravity by lifting a heavy load, the lowermost lumbar vertebra starts to slip backwards along the slope of the next one, and we complain bitterly about our aching back.
The other source of trouble however can be more serious. Those discs of cartilage which separate the vertebrae were never meant to carry weight, but in the upended man they bear much of the weight of the body, particularly those farthest down, and they become compressed and gradually wear thinner and thinner as time goes on. As we grow older, slipped discs become more and more a hazard and a disc out of place may put pressure on the nerves which is excruciating. No wonder stretching out in bed gives us the relief it does.
Farther down is another trouble area, the hip region or pelvis. This is where we reap the worst consequences of standing on our hind legs, for it is where the backbone, the hind end of the body, and the legs come together. The pelvis had enough to do in the beginning as a support for legs and for attachment of muscles. When we stood upright it had to change its shape in order to bear the weight of the upper part of the body. To a great extent our pelvis now forms a floor that helps support our abdominal organs and also takes the brunt of sitting through a double feature. The changes however have created an area of instability which too frequently results in low back pains or slipped sacroiliacs.
Many of us however sooner or later will feel the load we carry most acutely in the knees. We rock back and forth on them with every step we take, and our weight is upon them even while we stand still. This of course is nothing new, for the knee joints of all four-legged animals also bear the weight of the body. Still, we make two joints do the work of four, and they eventually show it. The moving surfaces which cover the ends of the long bones are made of cartilage, like that of our vertebral discs; and also like the discs, the cartilaginous layer is continually compressed and wears thin with years of incessant use. Whenever they wear through in places to expose the underlying bone, the bone tissue grows out in irregular ridges to give you arthritis of the knees. It’s not the crippling kind that spreads to the other joints and finally leaves the victim helpless and perhaps bedridden, but is simply the result of the force of gravity pulling the body down against tissues not hard enough to stand it indefinitely. The remedy is the obvious one, to diet off what excess weight there may be and to spare the injured surfaces as much as possible.
Finally, so far as the skeleton goes, we reach the base. Feet take the biggest beating of all. How great is the force of gravity acting within the foot is shown by the heavy build and thick walls of the thigh and shin bones which transmit it. In effect, however, what the foot does is to divide and conquer. The force is channeled to many small bones, and each bone in the foot plays its part in carrying the total load.
It’s the division of these heavy stresses upon the slender metatarsal bones in the first half of the foot that is most critical, the first segment being the most important. In walking, for instance, half of the total body weight is thrown upon this segment alone, while the other Continued on page 74
We'd Be Better Off On All Fours
CONTINUED FROM PAGE 27
half is divided between the four metatarsals on the outer side of the foot. At least this is the way it is in wellconstructed feet.
The trouble arises when the first metatarsal is short or loose and too great a load is diverted onto the second one. Then we gel one of the two preva-
lent types of foot disorder, either the fallen metatarsal arches of the forepart of the foot, or flat feet or fallen arches of the instep region. And when highheeled shoes are worn by women who have short first metatarsal bones, the results can be devastating. Pain from such a source may spread to very different regions of the body; nerve irritation may in fact become so serious that a general nervous disorder results that far overshadows the mechanical cause, for no matter how much we analyze our bodies we remain all of one piece and no part suffers alone. Pain, ner-
vous tension and emotional disturbance follow in sequence.
Our feet and legs in fact are adapted for carrying just so much weight and no more. Our ancestors were at one time arboreal creatures and in all probability were of relatively light weight and ran along the branches with feet that were much more handlike than our feet are now. Since then however we have left the trees, grown heavier and have made a strong arched foot out of the more flexible grasping organ we once possessed.
It has been a marvelous piece of re-
construction but it can carry only a certain load without breaking down, and it is that which limits our size and weight to about 200 pounds. Even those animals that use all four legs to support the body eventually reach a weight limit determined by bone strength and the force of gravity. Elephants are about as heavy as a purely land animal can become, and then only because the legs are thick pillars with the bones of each foot forming a compact mass beneath the shin bones. If elephants were twice as large, their legs would have to be about four times as thick to support the weight and locomotion would hardly be possible.
The larger dinosaurs of the reptilian past were those that lived in swamps and for most of the time water supported much of their weight; there is little doubt they became too big and heavy for their own good, and their very size led to their extinction. Whales, the largest animals the earth has ever known, are warm-blooded mammals that have gone back to the sea and are able to exist only because they are completely supported by water. No limbs could possibly be devised that could lift their enormous bulk on land. As it is, when one of the larger whales becomes stranded on a beach, its own body weight is such that it cannot expand its lungs and so dies from suffocation. Only the smaller species are able to recover after being stranded.
Considering the nature of our own anatomy there is little doubt we’re already as large as we’re ever likely to be. We’d probably be better off if we evolved into a smaller human race, for we would walk with a springier step with much less fatigue. Julius Caesar and his hosts of Roman soldiers were all small, yet they outmarched, outfought and outmanoeuvred the much larger barbarians to the north. He said so himself.
Gravity however does more to us than flatten our arches, grind our bones together and cause parts to slip out of place. It pulls on the internal organs as well, particularly when we stand or sit up. In most persons fat is stored around the vital organs to keep them in place, but all too often, especially in women who are excessively thin, the internal supporting fat is lacking, and heart and kidneys dangle or float in a distressing and dangerous way.
A more serious danger concerns the circulation of the blood. Two great vessels, an artery and a vein, run along the backbone and at the level where they divide into two branches, one for each leg, the right-side artery crosses over the left-side vein. In a fourlegged, horizontally placed animal this presents no problem but in humans they cross just over a bony vertical projection where the intestine, piled up by its own weight in the pelvis, presses down upon them.
Usually there is no trouble but when the downward pressure is increased, during the weight of pregnancy for instance, the vein is pressed almost flat and the swollen so-called milk leg of pregnancy results. After abdominal operations, more fatal postoperative blood clots arise from the congestion of vessels in this region than any other.
When we are lying down the heart has little work to do, for the force of gravity does not interfere with the flow of blood to and from the brain and the
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body extremities. When we are standing the heart not only has to pump the blood directly upward to the head, against the pull of gravity, but has to get blood back from the toes four feet below the heart.
Ring-shaped muscles around important veins help the return by squeezing the blood up the leg by relaxing and contracting, but they work only as long as we move about, which is why policemen rock on their heels and soldiers shift from one foot to another after standing at attention. Otherwise the blood in the veins of the leg tends to collect in a kind of pool, to form varicose veins, and may escape by rupture into surrounding tissues. It is a long pull from the feet to the heart and a weakened heart has difficulty pumping blood through them; swollen ankles may be the first sign of trouble ahead.
So much for gravity as we find it—or as it finds us. There is also the question of gravity as we make it. For in this age of dive bombing and rocket travel we are subjecting the human body to gravitational forces far greater than the one we have been designed for. When a pilot pulls sharply out of a dive it is as though his weight suddenly increases to nearly half a ton, with every constituent part of his body, including the circulating blood, participating in this weight change.
If normally the heart forces a column of blood 12 inches upward into the head, when the body as a whole is subjected to an acceleration equivalent to five times gravity the heart has to develop five times as great a pressure to raise the blood the same distance. This is more than the heart can adjust to and most persons lose consciousness after six to seven seconds.
We’d Be Flat on Jupiter
Giant centrifuges are employed to test the effect of such conditions on human guinea pigs. As the normal force of gravity is exceeded, the body feels heavy and the soft tissues are drawn downward, giving the face a sudden appearance of ageing. Movement becomes difficult and at two and a half times normal gravity it is impossible to get up from a sitting position. At four times gravity, the legs cannot be lifted. At five times gravity a complete blackout occurs after about five seconds. The blood is too heavy to reach the brain and unconsciousness follows quickly.
Pressure suits and other complex devices are used to keep enough blood in the upper part of the body and our superiority in this respect was one reason we won the war in Europe. The more serious problem comes from the rockets where accelerations of twenty to forty times gravity are developed in starting even ordinary rockets like the German VI or V2. No human can stand such a strain unless lying transversely to the direction of acceleration. The limitations to flight, whether in air or outer space, are in fact much more human than questions of engineering.
Whether we like it or not, we are earthlings and there are penalties even for walking erect upon this earth. We would not be human if we did otherwise but we pay a price. On another planet—the moon for instance—the force of gravity is so weak that if we ever land there and walk around the thrust of each step would take us several yards. But on Jupiter, which some space addicts have thought of visiting, gravity is such that we would be flattened out against its surface; or if we did manage to raise our head, the blood would never reach it.
All in all we are better off at home. And we’d be even better off on all fours. ★