Washington, Oct 25 (IANS): One of the largest US studies on yoga certifies that it does ease chronic back pain and other associated symptoms.

"We found yoga classes more effective than a self-care book," said Karen J. Sherman, senior investigator at Group Health Research Institute (GHRI), who led the study.

Back-related function was better and symptoms were diminished with yoga at 12 weeks and benefits - including less use of painkillers - lasted at least six months for both yoga and stretching, with a thorough follow-up of more than nine in 10 participants.

In the trial, 228 adults in six cities 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", the journal Archives of Internal Medicine reports.

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, according to a GHRI statement.

Interviewers who didn't know the patients' treatment assignments assessed their back-related function and pain symptoms at six weeks, 12 weeks and six months.

The type of yoga used in the trial, called Viniyoga, adapts the principles of yoga for each individual and physical condition, with modifications for people with physical limitations. The yoga classes also used breathing exercises, with deep relaxation at the end.

"The most straightforward interpretation of our findings would be that yoga's benefits on back function and symptoms were largely physical, due to the stretching and strengthening of muscles."

"People may have actually begun to relax more in the (yoga) stretching classes than they would in a typical exercise class," she added.

"Our results suggest that both yoga and stretching can be good, safe options for people who are willing to try physical activity to relieve their moderate low back pain," Sherman concluded.