Patanjali collected the yoga knowledge available in 2 A.D. and wrote a treatise called Yoga Sutra. The yoga of Patanjali has 8 limbs to be practiced in sequence. They are Yama (restraint), Niyama (observance), Asana (posture), Pranayama (breathing), Pratyahara (withdrawal of senses), Dharana (concentration), Dhyana (meditation) and Samadhi (ecstasy). The end of yoga after Samadhi would be the union of individual consciousness with the universal consciousness.

In the modern age, yoga has come to mean basically Hatha Yoga, Ha meaning sun and Tha meaning moon unites in Hatha Yoga. It is the symbolic union of active and passive energies, the opposites. The Hatha Yoga aims to unite harmoniously the body, mind and spirit, and create a healthy, supple and strong body and a relaxed, stress free mind.

In the late 19th century, T. Krishnamacharya, a yoga teacher in Mysore Palace in south India, was the source of most modern Hatha Yoga. His disciples B.K.S. Iyengar, K.Pattabhi Jois and Indira Devi, and his son T.K.V. Desikachar, were instrumental in setting up their schools and spreading Yoga throughout the world, particularly in America.

Each one has its own name, but it is only a matter of stress rather than substance. They are Ashtanga Yoga of Pattabhi Jois, Iyengar Yoga of B.K.S. Iyengar, Vishnu Yoga of T.K.V. Desikachar, Bikram Yoga of Bikram Choudhry, Sivananda Yoga of Vishnu Sivandandam, Integral Yoga of Swami Sachidananda and Ananda Yoga of Swami Kiriananda.

Yoga as an exercise is vastly different from calisthenics or aerobics. In yoga the body does not do any movement, but holds different postures that are designed to direct the life energy to all parts of the body. The respiratory and pulse rate drops. The endocrine system increases activity.

The benefits of yoga are many. It helps in managing many illnesses for which there are no cures. It helps in building a supple and strong body. But its major contribution is in relaxing the body and mind, relieving stress and rejuvenating the energy level. Positive thinking and feel-good factors increase amongst practitioners of yoga. The degree of concentration in yoga students is very high.

With some amount of commitment and regular practice of Hatha Yoga, there will be a substantial difference to the quality of life in the modern age.