A thin, tough intervertebral disc lies between two vertebrae. The intervertebral disc consists of a tough, outer layer of cartilage and elastic tissue, surrounding a soft, gelatin-like material known as the nucleus. This soft, pulpy filling enables the disc to act as a shock absorber. The subsequent sensation can range from a mild tingling to severe pain depending on the amount of pressure being placed. Your nerves carry the signals from your brain to the various parts of your body, pain is natures way of telling us that something is wrong.
Inflammation also sets in which puts even more pressure on the nerves in question.
Muscles that are stiff are far less able to deal with sudden changes and this is why stretching is great to prevent back injuries. The key to a pain-free back for most of us is to regain the flexibility and strength of our youth.