The vast majority of people in the United States who practice yoga should give it up altogether, Glenn Black, who has taught yoga for nearly 40 years, told William J. Broad of The New York Times.
Too many of the nearly 20 million Americans who practice yoga are hurting themselves, said Mr. Black, who studied in India under the legendary B.K.S. Iyengar. Mr. Iyengar created his own style of yoga (Iyengar yoga), which emphasizes doing yoga postures (asanas) in a particular sequence, and breath control.
One of the Americans who hurt himself is Mr. Broad, a science writer for The New York Times, whose back gave out while he was doing a yoga pose in 2007. "How Yoga Can Wreck Your Body" was published in The New York Times magazine earlier this month.
"Yoga is for people in good physical condition," Mr. Black told Mr. Broad. "It's controversial to say, but it really shouldn't be used for a general class."
Surveys by the Consumer Product Safety Commission indicate yoga injuries are spiking, Mr. Broad said. The most common yoga injuries are to the lower back, the shoulder, the knee and the neck. Yoga also has been known to cause strokes.
Betsy Blazek-O'Neill, head of the integrated medicine program at Allegheny General Hospital, practices yoga almost every day. She said she mostly agrees with Mr. Black.
"Yoga has enormous potential to be harmful," Dr. O'Neill said.
The problem, she said, is that "yoga puts people in lots of positions where it puts joints at the limits of their range of motion."
Injuries occur when people try too hard to get into the proper pose.
The risk is greatest for people in poor condition. Indian practitioners of yoga typically squatted and sat cross legged in daily life, Mr. Black told Mr. Broad. Yoga postures were an outgrowth of this. Americans who sit in chairs all day and only practice yoga a couple of times a week lack the flexibility they need.
Americans also expect more from yoga than Indian practitioners do, Dr. O'Neill said.
"When yoga was developed in India, it was designed to make people flexible enough for meditation," she said.
Yoga has well-documented health and fitness benefits. But people who practice yoga primarily to obtain these should do something else, Mr. Black said. Other forms of exercise can provide the health benefits without the risk of injury.
Dr. O'Neill said she is attracted to yoga for its mental and emotional benefits. "When you go to the gym and work out on the machines, that's not really calming," she said.
Tai Chi also provides a calming effect without imposing stress on the joints, Dr. O'Neill said.
Yoga can be practiced safely, but people should be aware of the dangers, she said.
"It's really important to start with an easier class," Dr. O'Neill said. "You want to find an instructor who creates an atmosphere that allows for individual differences.
"It's really up to the person to listen to their body and get a sense of where their limits are. Don't try to do something just because other people are doing it."
Jack Kelly: firstname.lastname@example.org or 412-263-1476.