Amy Toosley was standing in a split pose when her yoga instructor gave her leg a little prod. "I heard the loudest pop I've ever heard, and the instructor said, 'Ooh! Good release, huh?'" Toosley recalls. "Not really--I could hardly walk." With her hamstring muscle snapped, Toosley, 32, avoided yoga for the next three months, and almost a year later, she is still in pain.
Bad-mouthing yoga seems like begging for a hit of unfavorable karma. But with more than 14 million people practicing yoga or tai chi nationwide, up 136% since 2000, orthopedic surgeons, physical therapists and chiropractors across the...