The normal spine viewed from the side forms a gentle "S" shape. When viewed from the back, the normal spine appears straight. The naturally occurring soft curves of the spine are designed to distribute mechanical stress in the body when at rest and during movement. When the curvature is even slightly abnormal, a person may experience occasional mild or annoying discomfort. If the curve is severely abnormal, the pain is usually severe and accompanied by disability. Abnormal curves are referred to as spinal deformities, and include scoliosis, kyphosis, excess lordosis, and flatback.