As more and more people practice  Bikram Yoga for weight loss and strength gain, medical professionals, however,  express concerns about the demands of yoga contortion performed in extreme heat.

“The heat increases your metabolic rate, and by that helps you warm up, it also allows you to stretch more,” said Dr. Robert Gotlin, director of orthopedic and athletic rehabilitation at Beth Israel Medical Center in Manhattan. ''But once you stretch  a muscle beyond 20% or 25%  of its resting length, you begin to damage that muscle. ''

Every week, Dr. Gotlin says, he sees at least five yoga-related injuries:  knees or lower back. Postures that require extreme knee flexion — squats and sitting backwards on bent legs, for example — are most likely to cause tears in knee cartilage. In Bikram yoga, students practice the ''toe stand  pose'' (Eka Pada Pranamasana _author_see photo)  sit back with your knees bent.

Eka Pada Pranamasana

“Basically the knee is a piece of bone with two strings of muscle on the top and bottom, and you can tighten those strings,” Dr. Gotlin said. “The more you bend the knee under load, the more pressure is put on the patella. ''

Bikram advocates argue that the constant heat and simple movements at the start of each class are safer than traditional yoga.

''The heat helps people to work  slowly and safely in the postures, and does frequent monk wounds,'' said Jennifer Lobo, an owner of Bikram Yoga NYC.

But David Bauer, a physical therapist in New York who also teaches yoga, said enthusiasm and competition between participants could contribute to injuries.

''When you're in a hot studio filled with type-A personalities (who love the challenge_auteur), and everyone's adrenaline and endorphins are pumped well, you don't feel  no pain," he said, "and the pain can  remain unnoticed  how far you go''.

Mirrored walls in Bikram studios can encourage students to focus on the outer form, Mr. Bauer said. In contrast, more traditional yoga emphasizes an internal focus on breathing and individual boundaries, which can  help reduce injuries.

“Learning where your body is and what your body can do that's what yoga is;  one should not force oneself to be similar to an ideal on  a picture in a book, '' Mr. Bauer said. “If you're just flexible but not strong enough, at the end of your practice you're going to tear a muscle. ''

Practitioners say  that the flexibility and spinal strength cultivated in Bikram Yoga can be vital in the fight with the  aging by posture. Some therapists and physicists, however, question the value of excessive joint flexibility, saying that it  can lead to inflammation and pain.

'' The extreme flexibility of movement developed by the practice of  Bikram Yoga is not  not necessarily an advantage, and she  can be counterproductive,'' said Dr. Shirley Sahrmann, professor of physical therapy at Washington University School of Medicine in St. Louis.

Like dancers, yoga practitioners have overly flexible backs, which cause  often problems in resting posture.

''In my work,'' Dr. Sahrmann says, ''I have more problems with people who have excessive mobility than with those who have the  reduced mobility. ''

Bikram ''tree asana'' (Vrikshasana_author) requires standing on one leg while pulling the opposite foot to the upper thigh. The point is to rotate the top leg joint and go as far as possible; but what looks good may not be what is best for the body.

''More isn't always better when it comes to joints,'' said Lee Staebler, a physical therapist from Long Island who studies movement syndromes.  at the State University of New York at Stony Brook.

“Warmer tissues will yield more easily (Bikram Yoga), but stretching beyond optimal limits can  damage joint tissue,'' said Staebler.

Ligaments, tough bands of fibrous tissue that connect the bones or cartilage of a joint, don't spring back into shape once they're strained, Staebler said. A "loose" seal  can be like a loose door hinge  which prevents the door from closing tightly.

Yet warnings about torn cartilage or aching joints are of little effect.  to keep Bikram fans out of the studio, which is like a  sauna  which they claim to find as pleasant as the beach.

PS from the author: before starting to practice this or another school of Yoga, ask your doctor's opinion, and  find out about the physiological aspects  different schools of yoga.  

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Bibliography:
New  York Times:  http://www.nytimes.com/2004/03/30/health/when-does-flexible-become-harmful-hot-yoga-draws-fire.html

Hot Yoga: The Dangers and Myths You Need to Know:  http://breakingmuscle.com/yoga/hot-yoga-the-dangers-and-myths-you-need-to-know