I've dabbled in yoga nearly all my life, but I've never been totally convinced of its claimed benefits. Iyengar's book 'Light on Yoga' appears to list 'cures' for just about any malady. Popular today is 'Iyengar Yoga', a watered down version of the postures from the original book. I used to go to classes in this discipline, but couldn't feel any real benefit to health. I think you are more likely to get an injury than anything else, so I think it's just a social event or a craze. On the other hand, if anything related to yoga can do something, I would say the '5 Tibetan Rites' (many Google sites) are very interesting, but I don't know if a proper scientific study has been made of these. All I can say is that I've been doing them for over 2 years now, and appear to have seen benefits. It might simply be that they shake the body in a way that the body is not normally accustomed to, a bit like jogging. I can't comment on Tai Chi or Kum Nye because I've never tried them.