"We found yoga classes more effective than a self-care book -- but no more effective than stretching classes," said study leader Karen J. Sherman, PhD, MPH, a senior investigator at Group Health Research Institute. Back-related function was better and symptoms were diminished with yoga at 12 weeks; and clinically important benefits, including less use of pain medications, lasted at least six months for both yoga and stretching, with thorough follow-up of more than nine in 10 participants.

In the trial, 228 adults in six cities in western Washington state were randomly assigned to 12 weekly 75-minute classes of either yoga or stretching exercises or a comprehensive self-care book called The Back Pain Helpbook. Nine in 10 of them were primary-care patients at Group Health Cooperative. Participants in the trial typically had moderate -- not severe -- back pain and relatively good mental health, and most had been at least somewhat active before the trial started.