Human beings originally walked on all fours. Although this would seek awkward today, it is more in keeping with Nature's structural design for our bodies, and provided better support for the backs of our ancestors than our modern-day erect posture does for our backs.
As a result of our shift in posture to the vertical, stand-up position, gravitational forces are no longer distributed evenly among the 24 vertebra of our spinal column, as they are in four-footed animals whose spine assumes a more parallel position with the ground.
Spinal Malalignment
When your spine is upright, the 24 vertebra, which are positioned one on top of each other, are compressed due to the force of gravity. Vertebra are small bones that are unconnected, unlike our long bones which have structural connections. The 24 vertebra are interspaced with pads of cartilage called intervertebral disks.
Intervertebral disks are much softer than their bony neighbors. They are also under constant pressure when our torsos are upright, such as when we sit, stand, walk, or run, and under even more pressure when we engage in sports, recreational activities, work, travel, or exercise. As a result, spinal malalignment of both our vertebra and intervertebral disks has become a common modern-day malady.
Spinal malalignment is especially common in individuals with weak midsection muscles. These muscles, which include the abdominals, obliques, and lumbar erectors, surround and support the entire lumbar vertebra region and the lower portion of the thoracic vertebra region of the spine. When these muscles become weak or out of condition, they fail to provide adequate spinal support, which allows our delicate column of bones and discs to get out of alignment.
Your Most Vulnerable Area
When analyzing your entire spinal column, the most vulnerable area for ailments is the lower, or lumber region of the spine. Anatomically speaking, your body has its least support in this area. Only five little free-moving bones make up the bony connection between the lower body and upper body. Referred to as the "Lumbar Vertebra", these five bones are the largest vertebra in your spinal column. Their weakness is due to the fact that they act independently of other bones...in short, they are not connected to, or surrounded by, any other bony matter.
By studying a skeletal diagram (Chart A), you can see that your chest, shoulders, mid-to-upper back and arms are strongly supported by your ribs, sternum, clavicle, scapulas, humerus', radius', and ulnas. Similarly, on the lower half of your body, your buttocks, hips, and legs also have a great deal of support from the bones of your pelvis, sacrum, femurs, tibias, and fibulas.
When we view the human skeleton from a side angle (Chart B), we see that the frontal and lateral sides of your abdomen are completely absent of bony matter. This area begins at the bottom tip of the sternum and descends to the anterior/superior ridge of the pelvis and is often referred to as the abdominal cavity (with "abdominal" referring to its location and surrounding muscles and "cavity" referring to the fact that it is empty of bone).
The abdominal cavity is Mother Nature's provision for the expansion of the stomach and intestine after food consumption in both sexes, and for pregnancy in women. If connecting bones surrounded the stomach, we would have difficulty in eating a heavy meal, and women would be unable to give birth to a normal-sized child.