In the classical Indian Yoga the breathing has been given a very important place. Many Yoga teachers teach that aspect while taking the Yoga classes. Every Yoga pattern has a rhythmic application of breathing in it and depending on the positions the breathing sequence would vary. One has to consult some authentic Yoga practice book in this regard to learn the subtleties of breathing in and breathing out in that particular Yoga position or Aasan.
As a general rule whenever we are stretching our body we should exhale that is we have to breath out. On the other hand when we are coming back to normal position we have to inhale that is to breath in. Using this simple principle one can have the breathing sequence in any Aasan including Surya Namaskar.
Surya Namaskar has 12 positions starting from the initial standing and leaning back posture and coming back to it after completing one cycle. The exact timing of the breath in and breath out has to be taken from the authentic text book on it but the general pattern is as follows -
During positions 1, 3, 5, 7, 9, and 11 - Breath in.
During positions 2,4,6,8,10, and 12 - Breath out.
Please note that during positions 5 and 9 there will be a combination of breath in and breath out.
The above details might appear complicated but once we practice it a few times then it becomes easy to follow it when we are doing Surya Namaskar regularly.
It is difficult to tell the exact role of this breathing pattern in any Aasan including Surya Namaskar but probably it was formulated to give the uniform supply of oxygen to the various body parts during the Aasan. We have to remember that our ancients had evolved this system after a great pondering and research so that the whole cycle of these exercises help in keeping the body healthy and in good shape.
Knowledge is power.