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, according to a US study.

The findings were described by authors as the largest US randomised trial on yoga to date. “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.