Patanjali Yogsutras were given 4,500 years ago. They do not give description of any asana. There is only one line - sthir sukham asanam. That is, a posture in which you are still and at peace. So any posture that can be maintained for long hours without movement or discomfort is an asana. Sage Patanjali is known as the fountainhead of yoga. The purpose of asana is cleansing the body–nadis (etheric channels) and chakras (energy centres). 4,500 years ago there was no requirement for this cleansing—the thought, actions and environment were relatively pure and conducive to the practice of yoga. Therefore there is no mention of asanas in Patanjali Ashtanga Yoga.

With passage of time, the bodies and minds started becoming polluted as did the environment. Various forms of yoga, therefore, came in and around 500 years back. Hatha Yoga was formulated by yogis like Matsyendranath and Gorakhanath which describes certain physical postures to cleanse the nadis and chakras. These were given because by then the karmas of man had started becoming polluted. It became necessary to improve these karmas to facilitate the onward journey, thus several postures were prescribed. Asanas then may be understood as exercise for the purpose of removal of toxins. The purpose of yoga, however different, is self-realisation. Asana is a preparatory exercise to condition the body for yoga, it is not yoga. Dog yoga, power yoga, hot yoga and other modern innovations are rooted in the physical, none of them lead to self realisation. Only guru knows what is best for the shishya and gurus don’t teach enmasse. There is no dearth of yoga teachers these days, advocating modern innovative exercises enmasse, on television or in camps, some even selling CDs, calling it yoga. There is a vast majority of population learning and practicing those exercises and paying a hefty price—not just for the course, but also in terms of their health and body.