What should be a gentle form of exercise sometimes isn't. Deborah Sandy of Brentwood, California, was practicing a common yoga position called "downward-facing dog" when the class instructor came over and pushed hard on her hips. The idea was to help stretch Deborah's spine, a key to greater flexibility. The 48-year-old psychologist felt a sharp "ping." She limped away from the class with a back injury that took months of physical therapy to heal. And this wasn't the first time she had been hobbled. Two years earlier, Deborah was in therapy for a pulled knee ligament caused by an advanced yoga posture. Although yoga is often thought of as a gentle practice, injuries are not uncommon, says Dr. Nicholas DiNubile, a Philadelphia-area orthopedic surgeon and spokesman for the American Orthopaedic Society for Sports Medicine. "Overall, yoga is safe," he says. "But if you have a weak link -- whether it's your lower back, knees, or Shoulders -- you're at higher risk of injury and need to be more careful doing yoga." Arkady Shirin, a San Francisco-based yoga instructor who has been teaching it for 25 years, says the two main causes of yoga-related injuries are unqualified teachers and overzealous students. "We live in a competitive society that likes whatever is new," explains Shirin. "Hybrid forms of yoga have been created with no respect for the ancient traditions. Poorly trained instructors are teaching improper form. Many people are pushing themselves beyond their physical limits. Yet, yoga is about being content with who you are." None of this is to say you should steer clear of yoga and its many benefits: Just approach it cautiously until you know what you can do and, more importantly, what you can't do. And as yoga itself teaches, make sure you listen to yourself and to your body. "I'm learning to be aware of my limitations and to stand up to instructors who demand I do things I'm not ready for," says Deborah.