At a time when yoga is going mainstream, health experts say, anecdotally, the number of people being injured in classes is rising at an alarming rate.

They blame both students and yoga teachers. Students, they say, come to class expecting to work out at the rapid, strenuous pace they did in aerobics or the weight room. Many teachers, on the other hand, are inadequately trained.

Dr. James G. Garrick, an orthopedic surgeon and director of the Center for Sports Medicine at St. Francis Hospital in San Francisco, said most of the injuries patients suffer are to the knee, followed by lower back and shoulder.

The injuries result from people trying to stretch their bodies into difficult poses that are beyond their physical limitations.

“The last couple of years we’ve been seeing a dramatic increase in the number of people injured doing yoga,” he said. “It’s frightened us. As more people have gotten involved with yoga, the demand for classes has gone up, and there are not enough instructors, (and) those that are there are newly or briefly trained.”

Garrick said people could minimize their risk of being injured by finding a seasoned, patient instructor who doesn’t push students beyond what their bodies are able to handle without pain.

“Yoga is as mental an exercise as it is a physical exercise,” Garrick said. “It seems studios and students are putting more emphasis on the physical, to the students’ detriment. To students, I would say if you feel discomfort … getting into a position, you shouldn’t do it. Ignore anyone who tells you otherwise.”

Linda Sparrowe, yoga director at the San Francisco Bay Club, said she carefully screened yoga instructor applicants, seeking teachers with a lot of experience. She checks references and also attends a class to observe technique, looking for instructors who take time to go over poses with individual students, as well as alignment and anatomy.

A nonprofit group, the Yoga Alliance, based in Reading, Pa., has formed a voluntary registry for instructors who have completed a minimum of 200 hours of training and instruction. But there is no national certification program for yoga instructors.

“You’ve got to be paying attention,” Sparrowe said of what she looks for in prospective instructors. “Some students are going to be too embarrassed to admit they have an injury. A good teacher will inquire with the individual student and advise them if they’re having pain to adjust their pose or stop. I look for that kind of rapport and attention.

“I think more continuing education for teachers is a critical thing and more education for (students) to help them understand yoga isn’t about being better or faster. It’s more of an internal practice.”

San Francisco-area yoga teacher Arkady Shirin agreed.

“Unfortunately, it takes pain in order for some people to realize they’re doing a pose wrong,” he said.

“My advice is always: Slow down. Yoga is supposed to restore your body. People are trying to look like Madonna, pushing beyond their limits, when yoga is really about being content with who you are. It’s not about competition.”