A typical session includes three disciplines: breathing exercises, body postures, and meditation. You may also be given advice on nutrition and lifestyle. Many proponents feel morning is the best time to practice yoga, but classes are offered throughout the day and evening. It's advisable to avoid eating for 1 hour before class.

Each session usually begins with a set of gentle warm-up exercises. The teacher will then ask you to focus on your breathing, and may take you through several breathing exercises. At the very least, you'll be asked to breathe through your nose, evenly through both nostrils. Then it's on to the yoga postures, a series of poses that typically must be held for periods of a few seconds to several minutes. Unlike the routine in calisthenics or weight training, you will not be asked to repeat postures more than three times, and some will be done only once.

Some of the postures, such as shoulder rolls or neck stretches, will probably be familiar to you, while others may seem extremely complicated or even contorted. Despite the difficulty of such postures, however, contortion for its own sake is never the point. Instead, the goal is to mildly stretch all the muscle groups in the body, while gently squeezing the internal organs. To balance the muscle groups, the postures follow a specific order.

As you assume the various postures, you'll be asked to move gently, without jerking or bouncing. Breathing techniques remain important. You'll need to focus on exhaling during certain movements and inhaling during others. Likewise, as you hold certain postures, you may be instructed to inhale through one nostril and exhale through the other. You'll be allowed to rest after every three or four postures, and at the conclusion of the exercises, there's usually a period of rest or meditation. You should remain comfortable throughout the session, and should leave with both body and mind relaxed.

Treatment Time: Classes usually last 45 minutes to an hour, but experts stress that even short sessions can be beneficial if you make them a regular routine.

Treatment Frequency: Classes may be taken once a week, or more often, as desired. Your teacher will probably ask you to practice new positions at home, and will encourage you to run through at least a portion of the yoga routine each day. Regular practice, even if brief, is recommend for the best results.

The exercises we now call simply "yoga" are actually hatha yoga, a discipline intended to prepare the body for the pursuit of union with the divine while raising the practitioner's awareness of creation to a higher, keener state. Through controlled breathing, prescribed postures (called asanas), and meditation, hatha yoga seeks to enhance the prana, or life force, that resides in the body and achieve a state of balance and harmony between body and mind. Each of these three disciplines contributes to the search for union in its own unique way:

Breathing. The life force prana is believed to enter the body through the breath, and much of hatha yoga is concerned with helping you control your breathing properly. Shallow, hurried breathing is believed to inhibit the life force, and affect mind and body adversely. Deep, slow breathing is encouraged.

Postures. Some yoga postures are intended to stretch and strengthen muscles, others to improve posture and work the skeletal system, while others aim to compress and relax the organs and nerves. The underlying purpose is to perfect the body, making it a worthy host for the soul.

Meditation. Meditation supplements and reinforces the disciplines of hatha yoga, focusing the mind and relaxing the body. Closely linked with focused breathing, it aims to produce a quiet, calm frame of mind. Many people find that it reduces stress and increases energy. The interplay of this and the other two facets of hatha yoga, and the quiet, considered repetition of each, is considered key to achieving yoga's benefits.

Despite its use of physical exercises, yoga is perhaps most closely related to the mind-body family of therapies, which includes meditation and biofeedback. Research shows that, like other mind-body practices, yoga produces measurable physiological changes in the body, including a decrease in the respiratory rate and blood pressure, and an alteration in brain-wave activity reflecting increased relaxation. Yoga has been shown to reduce stress and anxiety, both immediately and over time, and is often recommended to relieve the pain and anxiety of chronic illness. When practiced regularly, it promotes relaxation and enhances the sense of well-being. It also improves physical fitness and circulation, and some advocates say it improves memory. When combined with a low-fat diet and moderate aerobic exercise, it has been found to reverse the build-up of plaque in the coronary arteries--and the more it's practiced, the greater the improvement.

Although yoga's effects are unquestionable, scientists still don't know exactly how it produces them. Some speculate that, like other mind-body therapies, it works largely by relieving stress. Others suggest that it promotes the release of endorphins, the brain's natural pain killers. The Office of Alternative Medicine at the National Institutes of Health has several studies underway to clarify the matter. In the meantime, yoga continues to be practiced by some six million people in the United States.

Although some postures are not recommended during pregnancy, special classes are available for expectant mothers. Some experts also warn against strenuous postures during menstruation, and when you are ill with a cold or infection..

There are no standard certification or licensure requirements for yoga instructors. However, a number of reputable yoga schools do certify their graduates. You can check with the associations listed below for a list of recognized schools. Experts recommend that you look for an instructor who remains an active student himself, and who practices yoga daily.

Be sure to call the doctor immediately if the exercises cause any new symptoms, such as unusual headaches, muscle cramps, dizziness, or severe pain in your back, legs, or joints.