The rapid spread of yoga in various forms warranted standardization of it. Patanjali took upon the responsibility himself in the second century CE. He created Yoga Sutra text with clear definition on classical yoga. Yoga Sutra comprises of 195 Sutras (aphorisms) rallied on Raja Yoga. Raja Yoga is an eight fold practice. 1) Yama (restraint), 2 Nyama (purity observance), 3 Asana (physical exercise), 4 Pranayama (breath control), 5 Pratyahara (preparation for meditation), 6 Dharana (concentration), 7 Dhyana (meditation) and Samadhi (absorption in the sublime).
Yoga Sutra advocates cleansing of spirit by separation of Purusha (spirit) from Prakriti (matter) as against Pre-classical Vedic Yogas. The Pre-Classical and Vedic Yogas advocate unification of spirit and body.
Later, Yogis gave more importance to meditation, side-lining the Asanas. This was not deliberate, but was based on a conviction that the mortal coil should be merged through deep contemplation with the end reality. Again, later, in tune with the advent of alchemy, the Yoga proponents reconciled to the belief that the body is a temple and directed the thought to the aspects of health, longevity and its upkeep. The new Yoga techniques are based on these aspects. This naturally necessitated going back to Pre-classical and Vedic Yoga foundation Asana and to the advent of Post-classical Yoga which is ruling the roast now.