“An asana is a posture which acts on a specific pressure area, thereby releasing the built-up prana, energy, or vital force. In your physical body, the flow of energy takes place through your nerves; in the astral body, the flow of prana or life energy takes place in the nadis, or meridians. Many people think that you get your energy from eating proteins, carbohydrates, fats, vitamins and minerals, but prana is the real force by which all living beings exist.
Sometimes blockages develop in the nadis so that the prana accumulates and does not flow; in other areas there may be insufficient prana. Yogic exercises release this energy by applying pressure through placing the body in various positions, or asanas.”
From Swami Vishnudevananda’s Upadesa, on the Eightfold Path.