The Downside to Upright

Today, roughly 80 per cent of adults experience back problems sometime in their lives – a consequence of our upright posture. Humans have likely suffered this way since our ancestors first stood up, transforming our backbone from a bridge or arch to a column that must bear the full weight of the upper body. Especially vulnerable, is the lower, or lumbar, region of the column, where pressure on the disks that separate our vertebrae can cause them to bulge or herniate.

Yesterday’s Model

Humans come from a long line of ancestors, from reptile to mammal to ape, whose skeletons were built to carry weight on all fours. Our ape ancestors probably evolved around 20 million years ago from small primates that carried themselves horizontally. Then, six or seven million years ago, our ancestors stood up and began to move about on their hind legs. By the time the famous Lucy appeared in East Africa 3.2 million years ago, they had adopted walking as their chief mode of getting around. It was a radical shift.

“Bipedalism is a unique and bizarre form of locomotion. Of more than 250 species of primates, only one goes around on two legs”
– Craig Stanford, anthropologist at the University of Southern California.

 

Stanford and many other scientists, consider bipedalism the key defining feature of being human. Some may think it’s our big brain, but the rapid expansion of the human brain didn’t begin until less than two million years ago, millions of years after we got upright and began using tools. Evolutionary biologists agree that standing upright launched a cascade of anatomical alterations that paved the way, through changes of behaviour, that lead to other evolutionary changes, such as the expansion of the human brain.

Just How Do We Do It?

The biomechanics of upright walking is so drastically different from quadrupedal locomotion that anatomical adaptation became a necessity. The skull and spine were realigned, bringing the head and torso into a vertical line over the hips and feet. To support the body’s weight and absorb the forces of upright locomotion, joints in limbs and the spine enlarged and the foot evolved an arch. As for the pelvis: It morphed from the ape’s long, thin paddle into a wide, flat saddle shape, which thrust the weight of the trunk down through the legs and accommodated the attachment of large muscles, namely the hamstrings, gluteals, and quadriceps. These adaptations improved the stability of upright walking and gave tremendous efficiency over long journeys but severely constricted the birth canal making child birth a considerably trickier proposition than for other mammals.

The Advantages

Why would we give up the stability and speed of quadrupedalism for the fragile joints, vulnerable spines, and difficult, risky births that led to the deaths of countless babies and mothers for bipedalism?

Two theories dominate this debate. First is the significant advantage of freeing the arms from locomotion for gathering food, holding babies, and the development and utilisation of tools. Second and the more popular is the huge energy savings in bipedal locomotion.The efficiency of the human walking action is far superior to our closest relative the chimp by as much as 65 percent. The key lies in our human features:

1. The ability to fully extend our knees,

2. The way our lower back curves forward and our thighbone slopes inward from hip to knee so that our feet straddle our centre of gravity,

3. The action of the gluteal abductors, the muscles attached to the pelvis that contract to prevent us from toppling over sideways mid-stride when our weight is on a single foot.

These adaptations allow the human gait to operate like an alternating pendulum that swings the body up and over a stiff leg, so that the energy required to shift the body in its rise roughly equals the energy conserved in its decent what? Take a two metre plank lying flat on the ground. Lift one end up to 90 degrees, this takes some energy, then let the plank fall away from you, this requires zero energy, and you have moved the end of the plank you originally picked up four metres. The significant advantage lies in the reduced energy required to move from point A to point B. If you can save energy while gathering your food supply, that energy can go into growth and reproduction. If food became scarce individuals who moved across the ground more economically gained a significant advantage.

The Cost

Back pain is one of the most common health complaints, accounting for more than 15 million doctor visits annularly in the United States.

“The problem is that the vertebral column was originally designed to act as an arch. When we became upright, it now had to function as a weight bearing column.”
– Carol Ward, anthropologist/anatomist at the University of Missouri

 

To support our head and upper body weight over the pelvis and legs the vertebral column developed a series of curves. A deep forward curve, or lordosis, in the lower back, and a backward curve, or kyphosis, in the upper back. This system of S curves is energetically efficient and effective for maintaining our balance for bipedal locomotion, but the lower region suffers from the excessive pressure and oblique force exerted on its curved structure by our upright posture.

Key to the function of the spine are cushion types structures called intervertebral disc’s. These structures not only provide the cushioning of load bearing and compression forces but also allow an incredible array of movement.

Lean back, arching your spine (with or without discomfort) and celebrate as you are the only mammal in the world capable of this movement.

 

The area of most compression and strain on these disc’s is in lower lumbar joints. Yet it is not the load or the injury to the disc that will cause you to feel discomfort and pain, it is the irritation of the nerves. Should that nerve be responsible for the proper function of a muscle or an organ the same result occurs. Human health and function will be lost.

Further significant strain is transferred to other joints such as hip, knee, ankle and feet. These joints also attract a lot of attention from health care professionals. The significant amount of hip and knee replacements, caused by general wear and tear, performed each year is testament of the weight bearing nature of these joints and again can in the most part be attributed to our ancestors evolution from four to two limbs for locomotion.

Help?

What’s a upright, walking, mammal to do?

There is no doubt that some people experience chronic lower back pain while others don’t, so what lessons can be learn’t from those who seem to survive better than the general population. It is now commonly agreed that exercise plays a significant role in the care of our spines. Added to this is the need to stretch and keep free these load bearing joints in the lumbar spine. Finally it is vital to maintain a correct structural integrity, which is the domain of your chiropractor.

At Life Chiropractic we aim to correct and maintain your spinal integrity whilst providing a thorough education as to the needs of your health out side of our clinic. This includes appropriate exercise options with daily stretches.

In Summary

Whatever drove our ancestors to get upright in the first place, the habit stuck. In relative terms we quickly evolved the ability to walk and run long distances (over just a few million years). We learned to hunt and scavenge meat. We created and manipulated a diverse array of tools. These were all essential steps in evolving a big brain and human intelligence, one that could make poetry and music and mathematics, assist in difficult childbirth, develop sophisticated technology, and consider the pros and cons of the evolutionary changes adopted by our fore bearers.