The following articles are very well researched, and also based on the writer's own experience as a 'guru' turned frum Jew. The last link takes you to a page on Mystical Paths that has 30 articles setting out why yoga is idol worship, and not something that believing Jews who really care about the quality of their relationship with Hashem, and about their own souls, should be getting involved with, in any way, shape of form.
Someone asked me: 'But, if people tell you that they're just doing the exercises themselves, and they're not into all the other stuff, why isn't that OK?'
The short answer is that as soon as you call those exercises 'yoga' - spiritually, you're attaching yourself 100% to the forces of idol worship and spiritual tuma that come along with the whole progamme.
Stretch and exercise all you want - just call don't call it 'yoga'.
And if you can't not call it 'yoga', then ask yourself what the big deal is, with calling your exercise programme something else that doesn't link it to centuries of idol worship and spiritual impurity of the highest order.
As the posts from Mystical Paths show, the truth about yoga is staring us clearly in the face. I'll write more 'proof' as I get at - although it's really hard to add more facts to the excellent information already written over on Mystical Paths. Which brings us to the main problem:
The people who are wedded to yoga don't want to know that it's bad, and 100% idol worship and hence, 100% forbidden. Even when you show them the sources, and point out the problems, they somehow can't or won't see the problem and keep coming back with more spurious arguments and double-talk.
For any truthful person out there, who doesn't already have a vested interest in 'proving' how good and kosher yoga is, this is already in the category of being a 'no-brainer'. And for those other people? Probably no amount of truth or facts or scriptural support will be enough to convince them that they're up to their necks in idol worship, and spiritually in a lot of trouble.
So I'm primarily writing these posts for those people who are being evangelised by the yoga-addicts in their own community that yoga is the panacea for all ills, the answer to all ailments, and the spiritual exercise par excellence, and who don't know how to 'answer the heretics', to paraphrase Rebbe Nachman.
If these posts help even just one person to stay away from these terrible idolatrous practices, or give just one person the courage to start challenging the myth of 'kosher yoga', they did their job. And now, without any further ado, I highly recommend you take a look at the following articles over on Mystical Paths.
If the last two posts here on Emunaroma didn't convince you that yoga is 100% idol worship, then by the time you're done reading these links, I think they will blow the idea that any form of 'yoga' could be kosher completely out of the water.