The Yoga Sūtra describes the flow of prāṇa with this lovely image: If a farmer wants to water his terraced fields, he does not have to carry the water in buckets to the various parts of his fields; he has only to open the retaining wall at the top. If he has laid out his terraces well and nothing blocks the flow of the water, it will be able to reach the last field and the furthest blade of grass without help from the farmer. In prāṇāyāma we work with the breath to remove blockages in the body. The prāṇa, following the breath, flows by itself into the cleared spaces. In this way we use the breath to make possible the flow of prāṇa.
The Heart of Yoga: Developing a Personal Practice
T. K. V. Desikachar
( Contributed by Dr. R Thavasothy)