Nightly News   |  January 11, 2012

Can yoga wreck your body?

A Yoga instructor warns about the potentially debilitating effects of practicing yoga while out of shape. NBC’s Chris Jansing reports.

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>>> finally tonight, something millions of americans happily turn to to relieve stress. it's in the news tonight and it's yoga. one of the country's best-known yoga teachers touched off a heated debate with a new book called bluntly, "how yoga can wreck your body." that's quite a charge. more from nbc's chris janzen.

>> reporter: all around the country, class is in session. far from its ancient origins in india, yoga has become a modern-day antidote to stress.

>> om.

>> reporter: its growing popularity is raising alarm.

>> as a spine specialist i see a ton of yoga injuries.

>> reporter: there are no definitive numbers, but a columbia university survey reveals injury to the lower back, shoulders, knees and neck and in some rare cases, yoga led to stroke.

>> certain yoga positions put a lot of stress on the blood vessel to the brain.

>> reporter: because of the risks, respected yoga instructor ken black suggest the vast majority of people should give up yoga all together.

>> e-mails are saying i wish i could have had the courage to tell my teacher i just got hurt.

>> reporter: he says many get hurt forcing themselves into positions they aren't ready to do. would you look at somebody like me and say, you're a classic, you should not be doing yoga?

>> what i would say is you need to do a lot of stuff to prepare for a yoga class.

>> reporter: black acknowledges that is not what yoga fans want to hear and they are fighting back.

>> if something bothers you, you back off or find a different way to ask a question.

>> yes there are dangers and risk. there are with everything. there are risks with love. that doesn't mean we don't go forward with something that can be so helpful.

>> reporter: the benefits from yoga can be significant, lowering stress and blood pressure , even improving your sex life . still, while experts disagree about the risks, they do advise caution, because as with love, sometimes yoga hurts. chris jansing , nbc news, new york.