Doctors at The Spine Center in Boston did a computerized search of studies on exercise and back pain. They found regular exercise decreases the risk of future back pain or spinal degeneration. Exercise improves flexibility, strength, and function. Exercise doesn't increase the risk of another injury or episode of back pain. In fact, there's some evidence that it can protect against back pain.
The authors conclude exercise is safe for people with back pain. It can be used to overcome fears of re-injury. Strength and motion can be improved. Pain intensity can be reduced. Regular stretching should be done, and even within the painful range of motion. Muscles of the spine, trunk, hips, and legs should be included. The stretches must be held for at least 30 seconds and done at least three times each week.
James Rainville, MD, et al. Exercise as a Treatment for Chronic Low Back Pain. In The Spine Journal. January/February 2004. Vol. 4. No. 1. Pp. 106-115.