While recent scientific studies have shown no evidence that pre-exercise stretching reduces injuries, warming up the body is a different issue, because it maximizes blood flow to the muscles and makes the tendons more flexible. In fact, overstretching before yoga may actually defeat good intentions by tightening muscles and making them more prone to injury.
However, the need to warm-up prior to class really depends on the yoga style and the instructor. Some yoga styles, like Bikram, are performed in heated rooms, which helps loosen muscles. Also, the teacher may begin with more gentle poses and gradually ease into advanced asanas after the body has had the chance to properly prepare. In these cases, warming up is not necessary. However, if a need is felt, here are some simple steps to warm the body.
A good warm-up is exactly that: a warming of the body by increasing circulation. If walking, bicycling, or in-line skating to class is an option, take advantage of the opportunity, or climb a few flights of stairs to get the heart pumping. Be sure to find something that's simple and enjoyable, because it's far more likely to become a habit. Begin with at least five minutes of activity and increase it to 10 to 15 minutes, long enough to elevate the heart rate and warm the skin.
"I try to have our students elevate their core temperature before yoga by doing another type of workout, such as running, cycling, getting on a treadmill, or even taking a hot shower," says yoga teacher Argie Ligeros, of Yoga for Athletes in Avon, Colorado.
Take advantage of yoga's inherent focus on gradually increasing individual awareness and apply it outside the studio. The best way to prevent overuse injuries to the muscles and joints is to build a warm-up's intensity slowly, so tissues become conditioned to stresses and then respond to them with increased strength and flexibility.