Exercise seems to be the only effective intervention for the prevention of low back pain

Prevention of Low Back Pain: A Systematic Review and Meta-analysis – JAMA abstract (full text require subscription)

To prevent back pain, orthotics are out, exercise is in – Commentary on The New York Times

Exercise May Help Prevent Low Back Pain, Meta-Analysis Finds – Commentary in NEJM Journal Watch

Exercise Reduces Risk for Low Back Pain – Commentary in Medscape (free registration required)