Enough books and articles have been written on the topic to fill an independent library. Along with the increase in interest and concern, the social and economical costs have risen as well. Despite all of this knowledge, a detailed understanding of its causes and potential remedies is still elusive. Articulation is made possible by the spinal discs, the cartilage wafers tying each vertebra to its neighbor and by facet joints that link each vertebra. This movement is controlled by the contraction of muscles in the lower back and abdominal region.
Ligaments support and strengthen the joints and prevent abnormal movement from occurring.
The spine is the only bony support for the body between the rib cage and the pelvic bones. As indicated in Figure 1, the area just above the pelvis appears to be the most common site of injury in the lower back especially between L4 and L5. Lifting a concrete block causes both a load and a moment, created by the weight of the block F w and its distance from the body. While the load F Bc is transferred via the spinal column to the pelvis creating an evenly distributed compression in the disks and the vertebrae of the spine, the moment adds a triangular stress distribution component f Dc to the disks and a tension force T M . This tension force has to be carried by the muscles attached to the end of each vertebra.