As you become more religious, can you continue to do yoga? Or maybe you'd like to try yoga for its scientifically-proven benefits to health and wellbeing?
Answer: it depends. It depends on whether your community forbids it outright or whether your community allows the practice when done in a tznius manner. I'm not aware of any major groups who say it's totally ok in every context, though there are certainly people who treat gyms differently in regard to tznius (like going to the doctor - this can play out in several ways as we'll mention below). The opinions probably differ whether you're a man or woman, given the potentially-suggestive nature of the movements and the tightness of most people's clothing. (In case that's not clear: the men are going to have a harder time getting "permission.") So whichever way you go, and you can change your approach over time, you'll find other people doing it too. Whether that's right or wrong isn't for me to say.
The best advice I can give you is don't ask a shailah (halachic question) if you aren't willing to abide by the ruling. If you feel strongly toward yoga and will find it hard to give it up, you shouldn't ask unless you know the answer you're going to get. "But that's rabbi shopping!" you might say. No, I'm saying don't ask the question; I'm not advocating that you look around for a rabbi who will give you the answer you want (though you wouldn't be the first or the last to do that). In theory, just because you're not ready to abide by a negative answer now doesn't mean you won't be ready one day. And then you can ask. Can ask; I'm not saying you should ask. I can't answer that for you either.
Whatever you do, don't set yourself up for failure by asking a shaliah when you're not ready; it can snowball into disregarding other rulings. More immediately, it can lead to a lower self-esteem: Why don't I have more willpower? Why am I not pious enough to give this up for Gd? Have I made a horrible mistake with this Jewish stuff?
A major problem is that most rabbis know nothing about yoga, how it's practiced, what the practice is actually like, how the types of yoga differ (which could make a difference), etc. If you ask a question and the rabbi responds too quickly, be wary. He should certainly ask follow-up questions about the specific situation, and he should probably ask another rabbi who is more knowledgeable on the topic.
So let's talk about some options.
Beware of religious stuff. There are many yoga customs and practices that involve Hindu religious practices, and Hindus are polytheists, so we get into real old-school Biblical pagan problems. I didn't know much about them (and you're not liable for punishment if you don't know what you're doing) until I read the book Wrestling with Yoga by Shelly Dembe. However, most people believe there is a danger in subconsciously exposing yourself to these things, even unknowingly. She writes extensively about how she encountered these problems as a baalas teshuva and yoga teacher. Some of the things that can be problematic, as I remember it: the bowing (watch out for idols in the room!!), "Namaste," and the Sanskrit names of postures. Maybe you find teachers who don't use those practices or ignore them when they come up. Just because the class bows and says Namaste doesn't mean you have to too. (And no one cares that you don't, speaking from my practice years ago.) Some authorities believe it is beyond redemption and is exclusively an idolatrous religious practice. I'm not sure anyone could possibly leave a Bikram hot yoga class with that opinion, but that was my experience.
You're fine by most people when you're in your home with a DVD or other video class (well, maybe not men). Depending on how you normally dress inside your home, you may be able to wear as little clothing as is comfortable or familiar for you. Of course, that also depends on your practice during niddah if you're married, and around roommates if you have those.
There are frum yoga teachers who teach single-gender classes! However, the men are probably out of luck. These teachers are hard to find because they're usually private teachers who host classes in homes, rather than in a studio. Ask around. Facebook Pages is usually a good place to search for individual yoga teachers. Yoga by Leah is one teacher popular among my friends.
Some people are able to find public single-gender yoga classes. In my experience, this has been surprisingly harder in NYC than the other places I've lived. And there's a lot more demand from men here than I've encountered before. Of course, the frum men are out of luck yet again. I've never seen an all-male class. Here and with the frum teachers I mentioned above, your experience will vary based on your interpretation of how you can dress in a single-gender situation outside your home (some follow all the same rules, some say anything goes, and there's plenty of middle ground too). Haircovering can be a sticky issue in these situations, depending on how you interpret the mitzvah/custom. That's a problem in any exercise situation, but yoga is more problematic because of how much your head moves.
Some people attend regular yoga classes. Some hope that no men will show up, and some don't care. Some dress like everyone else, some dress tznius, and some dress more modestly but perhaps not to their normal tznius standard. Some start the class tznius and will lose some clothing (and/or a headcovering) if no men show up. Potential problem: windows and glass doors exposing you outside the yoga room.
Overheating can be a real concern if you do yoga while tzniusly or modestly dressed, so stay hydrated and invest in great wicking exercise clothing. If you always cover your toes/feet, make sure you buy socks with grippy bottoms to prevent sliding. Safety first!
Now here are some Jewish books about yoga!
Wresting with Yoga is the only one on this list I've read. It's a spiritual memoir about a frum woman's Indian-influenced past colliding with her now-orthodox present and how she tried to reconcile the two. I wish it had gone into more detail, particularly about repeated mentions that her rabbi prohibits blank-mind-meditation without ever saying why it might be a problem.
Mussar Yoga: Blending an Ancient Jewish Spiritual Practice with Yoga to Transform Body and Soul I love Alan Morinis' mussar books, so I'm sure this is a great book.
Torah Yoga: Experiencing Jewish Wisdom Through Classic Postures I don't know anything about this book, but it sure looks interesting!
Alef Bet Yoga: Embodying the Hebrew Letters for Physical and Spiritual Well-Being Now this one is just fascinating-looking. It reminds me of acting out letters in Kindergarten, which explains why there's also a kids' version of the book!
Are you curious about yoga? If you are already a yogini (look, another religious word!), has your yoga practice changed as you progressed along your spiritual journey? Did you give it up when you became religious or are you thinking about starting a practice now? Have you had unexpected run-ins with yoga in your community?