The spinal column is made up of a series of vertebrae separated by disks that act as cushions and absorb shocks - which is why they are often referred to as the spine's "suspension."

More precisely, the disks are composed of a gelatinous nucleus (of egg yolk consistency) surrounded by a more rigid ring. At times of physical exertion, especially when the back is bent forward or is kept in certain positions, tremendous pressure is exerted inside the disk, which may cause the outer ring to crack. A herniated disk occurs when the fracture is large enough for the gelatinous nucleus to protrude from the disk. A herniated disk often presses on the root of a nerve (nerves exit the spine through the spaces between the vertebra), causing numbness, pain, reduced sensitivity, or even weakness along the nerve's pathway. Surgery is now rarely considered for this type of problem. However, physiotherapists can help relieve and sometimes even eliminate symptoms through the use of traction, manipulative therapy, and strengthening and stretching exercises.