Authors:

Whenever asana is done mechanically from the front brain, the action is felt only on the peripheral body, and there is no inner sensation, there is no luminous inner light. If the asana is done with continual reference to the back of the brain, there is a reaction to each action, and there is sensitivity. Then life is not only dynamic, but it is also electrified with life force.

B.K.S. Iyengar, John J. Evans, Douglas Abrams (2006). “Light on Life: The Yoga Journey to Wholeness, Inner Peace, and Ultimate Freedom”, p.39, Rodale
Whenever asana is done mechanically from the front brain, the action is felt only on the peripheral body, and there is no inner sensation, there is no luminous inner light. If the asana is done with continual reference