For instance, motion segments are rather resistant in lateral flexion as compared to when they are in flexion. When subjected to a constantly applied load, and then attempting to maintain this load, the discs slowly lose a certain amount of fluid and gradually change their height until deformation is reached. Hence, the disc loses its capacity to attenuate shock and can no longer distribute the load uniformly as the disc becomes less viscoelastic. Spinal mobility involves a functional mechanism that allows us to perform a wide range of tasks each day of our lives. During spinal motion, the amount of movement is largely attributed to the size of the disc.
Mobility is dependent upon the fluidity, elasticity and thickness of the disc.
For example, fluid pumping in and out of the disc in response to changing loads is thought to be vital for the transfer of nutrients and wastes within the disc which speeds up the diffusion process. Since fluidity, elasticity and thickness of the disc is important for mobility, there are variances from area to area. The shape of the disc also varies from area to area. In the cervical spine, the discs are more rounded, while in the lumbar spine they are more kidney shaped. The matrix of the disc consists of a mucopolysaccharide substance which is basically collagen fibres embedded in a proteoglycan-water gel.