Yoga is an ancient physical and spiritual discipline and branch of philosophy that originated in India reportedly more than 5,000 years ago. The word yoga comes from the Sanskrit word yuj, which means to yoke, join, or unite. The Iyengar school of yoga defines yuj as the "joining or integrating of all aspects of the individual—body with mind and mind with soul—to achieve a happy, balanced and useful life." The ultimate aim of yoga, they claim, is to reach kaivalya (emancipation or ultimate freedom).

Yoga uses asanas (postures), focused concentration on specific body parts, and pranayama (breathing techniques) to integrate the body with mind and mind with soul.

The body
Yoga asanas (postures or poses) help condition your body. There are thousands of yoga poses, and in Sanskrit, these poses are called kriyas (actions), mudras (seals), and bandhas (locks). A kriya focuses on the effort necessary to move energy up and down the spine; yoga mudra is a gesture or movement to hold energy or concentrate awareness; and a bandha uses the technique of holding muscular contractions to focus awareness.

The mind
Yoga focuses on the mind by teaching you to concentrate on specific parts of the body. For instance, you may be asked by the instructor to focus deeply on your spine, or let your mind go and have your body sink into the floor. This awareness keeps the mind-body connection sharp and doesn't allow a lot of time for external chatter (like worrying about what you're going to have for dinner or the presentation at the office that you're preparing for). Instead, the focus is internal, between your head and your body. An example is savasana (the corpse pose), which is practiced by virtually all schools of yoga. During savasana, you lie on your back with your eyes closed and just let your entire body sink into the floor. The idea is to not fight any thoughts you have, but to let them come and go while the instructor leads you through visual imagery to help you focus on how your muscles feel. The result is to drift into a peaceful, calm, and relaxing state. Savasana is generally the final pose of a yoga session before final chanting and/or breathing exercises.

The spirit
Yoga uses controlled breathing as a way to merge the mind, body, and spirit. The breathing techniques are called pranayamas; prana means energy or life force, and yama means social ethics. It is believed that the controlled breathing of pranayamas will control the energy flow in your body. It is my experience that controlled breathing helps me focus on muscles that are working, and during savasana, it slows down my heart rate, calms my mind, and leads to a deep, inner calm and sense of relaxation.

There are dozens of types, or schools, of yoga. They evolved over the centuries as different yogis developed their own philosophies and approaches and taught them to eager students, who then passed them on to their own students and disciples. For instance, Hatha yoga, arguably the most popular type of yoga taught in the U.S., was developed by Yogi Swatmarama in India in the 15th century and described by Swatmarama as (1) "a stairway to the heights of Raja yoga (Raja being one of the six orthodox schools of Hindu philosophy, outlined by Patanjali in his Yoga Sutras) and (2) a preparatory stage of physical purification that renders the body fit for the practice of higher meditation." Likewise, Kundalini yoga, which is reported to be more than 5,000 years old, was introduced to the west in 1969 by Yogi Bhajan when he traveled here from India.

Fundamentally, all yoga types lead to the same outcome, a unification of mind and body and spirit, although they may differ in their philosophy and even in the asanas. For instance, I took a yoga class yesterday that the teacher called Anusara, which she described as "opening the heart." I have never taken this type of yoga class, but the asanas were familiar (with just slight variations), the savasana at the end of the class was the same as other classes, and I left feeling the same as I do when I take Hatha or any other; that is, I felt calm, relaxed, stronger, and virtuous for having done it.

I did a quick search for yoga types and compiled the following list (certainly not all-inclusive): Purna, Ashtanga, Jnana, Bhakti, Bikram, Karma, Raja, Hatha, Kundalini, Mantra, Tantra, Iyengar, Astanga, Vini, Ananda, Anusara, Integral, Kali Ray Tri, Kripalu, Kundalini, and Sivananda. There's also yoga on the physioball (truly an American invention), and I even found nude yoga! Some of the most popular in the U.S., and the ones you are most likely to find in yoga and fitness centers, are Hatha, Iyengar, Astanga (or Ashtanga), Bikram, and Kundalini. Your local center may teach other types, and so you should contact the center if you are curious. I will briefly describe the most popular in the U.S. Many of the others are searchable online.

Hatha yoga is the most widely practiced type in the U.S. and is excellent for beginners. It is gentle with slow and smooth movements, and the focus is on holding the poses and integrating your breathing into the movement. It's a great introduction to yoga as it incorporates many different asanas, as well as pranayamas and chanting. Hatha yoga will prepare you for other yoga types that might be taught at your yoga center. Hatha is a great way to stretch, work your muscles, get in touch with your body, relax, and decrease stress.

Iyengar yoga is a form of yoga that uses poses similar to Hatha, but it focuses more on body alignment and balance, holding poses longer, and using props such as straps, blankets, and blocks. It's also a good choice for beginners.

Bikram yoga is practiced in a room (sometimes unventilated) heated to about 105 degrees Fahrenheit. The objective is to loosen muscles and to sweat to cleanse the body and remove symptoms of disease and chronic pain. To my knowledge, there hasn't been any research on the safety or efficacy of Bikram, and so I don't recommend it because of the potential risk of dehydration, blood pressure changes, and cardiac problems with exertion in such an inhospitable environment. This is particularly so for individuals who may have an existing heart problem or high blood pressure but don't know it. Bikram has grown in popularity, and some people swear by it. I recommend that you speak with your physician first if you are determined to try it.

Ashtanga yoga, or power yoga, is an ancient system of yoga taught by Sri K. Pattabhi Jois at the Ashtanga Yoga Research Institute in Mysore, India. In the U.S., it is taught as an aggressive workout where you move quickly from one pose to another to build strength and endurance. There is little emphasis on meditation with Ashtanga, and at the end of the session you will feel more like you have completed a traditional weight-training or callisthenic workout than you would with any other type of yoga. Ashtanga is for you if you're looking for a tough, physically challenging workout.