But a rising form of yoga aims to protect those parts so vulnerable to wear and tear. "Yin yoga is joint rehabilitation," says Paul Grilley, the godfather of the movement. "The poses work your joints in a way similar to how other types of exercise work your heart."
Rather than flowing vigorously between postures, as you would in a fast-paced, "yang"-style ashtanga or vinyasa class, yin teaches you to relax in simple poses that you hold, and hold—so that the stretch penetrates the connective tissue in your spine, hips, and other joints. "Holding a pose for a long period can be beneficial," says Claudette Lajam, MD, assistant professor of orthopedic surgery at NYU Langone Medical Center. Over time the fascia—the tissue that binds groups of muscles—may become inflamed and stick to the muscles, Lajam explains, which can cause pain and stiffness. "But repeated, gentle stretches can help release those sticking points."
A class might begin with a seated forward bend, held for three to five minutes. Almost imperceptibly, your body settles into the pose. Your breathing slows. And since you're not straining, you're less likely to get hurt.
Not that yin yoga is easy. Any long hold can bring on a dull ache. But that can lead to a bigger payoff, says Sarah Powers, author of Insight Yoga. "Instead of needing to be comfortable to relax, we learn to relax with discomfort. That is a very transferable skill."
After a few breaths, the ache vanishes and is replaced by a feeling of openness and length in your body. Still, the best argument for yin may be how it calms your mind, creating a sense of deep refreshment—as if, in Powers's words, you've taken "an inner shower."
Next: 3 beginner's postures that can help anyone feel better