Yoga, an ancient but perfect science, deals with the evolution of humanity. This evolution includes all aspects of one's being, from bodily health to self realization. Yoga means union - the union of body with consciousness and consciousness with the soul. Yoga cultivates the ways of maintaining a balanced attitude in day to day life and endows skill in the performance of one's actions.
B.K.S. IyengarWhen you cannot hold the body still, you cannot hold the brain still. If you do not know the silence of the body, you cannot understand the silence of the mind. Action and silence have to go together. If there is action, there must also be silence. If there is silence, there can be conscious action and not just motion.
B.K.S. IyengarI also say with backbends, you have to be cautiously bold. Not carelessly bold. You have to descend to the dictation of the spine. You cannot command from the brain to do the poses. As you play with a child, guarding the child from injuries, similarly you have to play in backbends, guarding your spine.
B.K.S. Iyengar