People who suffer chronic lower back pain saw about the same improvement after taking yoga classes taught by highly trained teachers as they did from stretching classes, said a US study Monday.
The findings, described by authors as the largest US randomized trial on yoga to date, appear in the October 24 issue of the Archives on Internal Medicine, a journal of the American Medical Association.
"We found yoga classes more effective than a self-care book -- but no more effective than stretching classes," said lead study author Karen Sherman, a senior investigator at Group Health Research Institute in Seattle.
"We expected back pain to ease more with yoga than with stretching, so our findings surprised us," she said.
The same group of researchers conducted a smaller trial in 2005 based on a randomized sample of 101 adults. That study suggested yoga was the best remedy for back pain because those who practiced it used fewer pain relievers and had better back function.
The latest data is derived from a sample of 228 people across six cities in the western state of Washington, and while it showed a slight lead by the yoga class, the difference was not enough to matter statistically.
The subjects were assigned to 12 weekly classes that lasted 75 minutes each.
The yoga was a type known as viniyoga, which features poses adapted for the individual condition of those in the class, breathing exercises and a deep relaxation period. Classes were taught by instructors with more than 500 hours of training.
The stretch classes were taught by licensed physical therapists with teaching experience and two hours of training in techniques that focused on the trunk, legs, hamstrings and hips. Some strengthening exercises were also included.
The third group was given a self-care book called "The Back Pain Helpbook" to read for tips on alleviating pain.
"Back-related dysfunction declined over time in all groups," the study said, noting that compared to the handbook group, the yoga group reported superior function at 12 and 26 weeks.
The stretching group reported superior function at six, 12 and 26 weeks. At no point in the follow-up analysis was there a statistically meaningful difference between the stretching and yoga groups.
"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," Sherman said.
She also acknowledged that the stretching classes were longer and more intense than those typically offered at neighborhood gyms, so the trial may have been inadvertently comparing two very similar exercise methods.
"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," she said.
"But it's important for the classes to be therapeutically oriented, geared for beginners, and taught by instructors who can modify postures for participants' individual physical limitations."
A separate study released earlier this year suggested yoga can lower stress and improve quality of life among breast cancer patients.
Another research team found that regular yoga practice by cardiac patients was able to cut irregular heartbeat episodes in half.