This is it..!!!...Lord help me....
An old friend of mine, a former politician fromWest Virginia, has difficulty remembering names. He saves himself from embarrassment with a simple trick: He delivers a hearty handshake and asks, "So how's your back?" Four times out of five he strikes gold. Names become unnecessary when the acquaintance, flattered by the personal inquiry, launches into a saga of lumbar pain, slipped disk, or mild scoliosis.
Back pain is one of the most common health complaints, accounting for more than 15 million doctor visits each year. That most of us will experience debilitating back pain at some point in our lives raises the question of the spine's design. "The problem is that the vertebral column was originally designed to act as an arch," explains Carol Ward, an anthropologist and anatomist at theUniversityofMissouriinColumbia. "When we became upright, it had to function as a weight-bearing column." To support our head and balance our weight directly over our hip joints and lower limbs, the spine evolved a series of S curves—a deep forward curve, or lordosis, in the lower back, and a backward curve, or kyphosis, in the upper back.
This change took place at least four million years ago, probably much earlier. Ward and her colleague Bruce Latimer, director of the Cleveland Museum of Natural History, recently analyzed the vertebral column of Lucy, along with two Australopithecus africanus skeletons from more than two million years ago. They found that the spines of all three possess the same S curves present in the human spine, confirming that Australopithecus walked on two legs.
"This system of S curves is energetically efficient and effective for maintaining our balance and for bipedal locomotion," Ward says. "But the lower region of the column suffers from the excessive pressure and oblique force exerted on its curved structure by our upright posture."
Lean back, arching your spine. You're the only mammal in the world capable of this sort of backbend. Feel a cringing tightness in your lower back? That's the vertical joints between your vertebrae pressing against one another as their compressive load increases. The curvature in your lower spine requires that its building blocks take the shape of a wedge, with the thick part in the front and the thin part in the back. The wedge-shaped vertebrae are linked by vertical joints that prevent them from slipping out from one another.
"These joints are delicate structures and very complex," Ward says. "They allow our spines to move with great flexibility, to twist and bend and flex, pivoting on the disks between the vertebrae." No other primate experiences such back problems—except, Ward and Latimer say, our immediate ancestors. The two scientists have found fossil evidence that back trouble likely plagued our bipedal forebears. The bones of the Nariokotome boy, a young Homo erectus (a species preceding our own Homo sapiens) who lived some 1.5 million years ago, reveal that the youth suffered from scoliosis, a potentially devastating lateral curvature of the spine.
The cause of most scoliosis cases remains a mystery, Latimer says, but like spondylolysis, it appears linked to the spinal features associated with upright posture, particularly lordosis, the deep forward curvature and flexibility of our lower spine. "Because scoliosis occurs only in humans and our immediate bipedal ancestors, it appears likely that upright walking is at least partially to blame," he says.
Considering the pressures of natural selection, why are such seriously debilitating diseases still prevalent? Latimer suspects the answer lies in the importance of lordosis for upright walking: "Selection for bipedality must have been so strong in our early ancestors that a permanent lordosis developed despite the risk it carries for spondylolysis and other back disorders."
But in the lower back region, where the load is heaviest and the wedging most dramatic, strains such as heavy lifting or hyperextension (say, from doing the butterfly stroke or cleaning the gutters) can cause your lowest vertebrae to slip or squish together. When the vertebrae are pressured in this way, the disks between them may herniate, or bulge out, impinging on spinal nerves and causing pain. Or the pressure may pinch the delicate structures at the back of the vertebrae, causing a fracture called spondylolysis, a problem for about one in twenty Americans.
