A disc is a circular structure that sits between each vertebra in the spine. It has a tough outer layer surrounding soft inner tissue. When a disc is under pressure and damaged, the tough outer layer is damaged and the soft inside protrudes through the gap. This protrusion compresses nearby nerves causing pain. Traction pulls the vertebra away from the disc, releasing the pressure on the disc. This assists the soft part of the disc to return within the disc. This decompresses the nerve and reduces pain. This also helps to rehydrate the disc.