Yoga, a term from Ancient Sanskrit has the literal meaning of "yoke" from the root "yuj." It was introduced by Patanjali in the 2nd Century BC as a term for mental abstraction. The Yoga philosophy believes in breath as the most important aspect of health, as it is the largest source of Prana (life force,) with Hatha Yoga therefore, one of the schools of Yoga, utilizes Pranayama which literally means the science and control of breathing .
The six schools of Yoga
There are six schools of Yoga: Jnana (based on knowledge,) Karma (based on action,) Hatha, Bhakti, Raja and Tantra Yoga. The goals of Yoga are varied and range from improving health to achieving Moksha, which is liberation from all worldly suffering and the cycle of life and death (Samsara). Having understood that we will now study each component carefully, beginning with the health bit.
Modified versions of Yoga have become popular as a kind of low-impact physical exercise and are used for therapeutic purposes, with a survey released in 2008 by the US National Center for Complementary and Alternative Medicine showing that Yoga was the 6th most commonly used alternative therapy and that 6.1 percent of the population participated. This is a case of modern Yoga that involves physical exercise, with significant deviation from the original one which greatly emphasized on discomfited sitting postures called "Asanas." It is believed that both the meditative and exercise components of Yoga show promise for non-specific health benefits, with some teachers asserting that it stimulates the flow of healing life energy or Prana. It is also used in some parts as a supplementary therapy for diverse conditions such as cancer, diabetes, asthma and AIDS.
In many instances however, the general perception is that there is more to Yoga than the above stated, otherwise there would not be as much controversy as there is about it. This brings us to the latter part, where the goal is to enter the world of Brahma (god of creation) and have an eternal relationship with Vishnu (god of maintenance,) referred referred to as the Supreme god by some schools of Vaishnavism. One who practices Yoga is referred to as a Yogi, and to enter the world of Brahma you have to release your spirit, which explains the meditation postures and why people stay motionless for extensive hours. The result is that you allow terrestrial forces to mechanically control you, and you end up living as a remote-controlled object. Do it if you will, but I would not give up my spirit for the whole world.