An intervertebral disk is rather like a stale jelly-filled donut: It consists of a tough outer layer (the annulus) with a soft jelly-like interior. Disks are incredibly durable, but there are limits to the abuse they can take. Disks rarely go bad all at once, however. Rather, poor posture, pushing the joints past their range, lifting heavy objects carelessly, excessive rotating movements, and repeated shocks to the spine create microscopic tears in the fibers of the annulus. Over time, these tears accumulate and the annulus weakens and begins to bulge or even tears completely, pressing on the root of nerves where they leave the spinal cord. Thus older adults are more prone to disk disease than younger adults because they've had more time for these microtears to accumulate.
More Answers from Eric Olsen