Discs
Discs are found between the vertebra and they have soft centres which allow movement and a tough outer layer. Discs help to absorb shock and strain to the spine and as you move forward the disc centre moves.
The annulus gradually cracks open allowing part or all of the nucleus to prolapse or seep out. Usually this occurs at the back of the disc to where the spinal nerves emerge from the spinal cord.
Slipped / Prolapsed Discs
The pressure created by this situation causes severe pain in the lower back and legs and can incapacitate one for some time.
Damage is usually caused by moving forward, i.e. stooping and bending. The further the load is away from the body the greater the strain on the back.