Spinal discs are an integral part of the spine, acting as shock absorbers for the impacts of daily life. They take approximately 80% of the force exerted on your spine by compressing under stress and spreading the force into the surrounding vertebra. They are primarily made of 2 main parts; the nucleus pulposis and the annulus fibrosis. The nucleus pulposis is a water-based structure which acts as a compressive cushion for your spine, similar to a waterbed. Since water cannot be compressed very much when in a container, it pushes back against the force being applied which decreases the weight being held by the rest of the spine. The annulus fibrosis on the other hand acts as the container for the water cushion of the nucleus. It is made up of crossing fibres of thick collagen which can twist and conform to forces from all angles very effectively. This stops the fluid centre from slipping around like a water balloon when you squish it. These two parts make up the disc and help to keep the pressure off the less sturdy spinal joints, which are made to allow motion and as such sacrifice their strength.
Increasing forces on these discs, either by adding more weight, bending forwards or by shifting the body’s centre of mass can cause pressure to be put onto areas which are less suited to handling these forces. Bending and twisting forces strain the annular fibres surrounding the disc and can cause repeated weakening of these fibres. As such, with enough weakening, small gaps and tears can allow the nucleus to move within the disc and can cause the weight to distribute a lot less evenly in the joints. This can cause the bone-based joints at the back of the vertebra and the vertebra above and below the disc to take more pressure and start to wear down and degenerate.