Agnisara is one of the many cleansing practices in Yoga. Another name for it is Vahnisara. Agni and Vahni are Sanskrit words for fire. Sara is movement. The technique is called so because it involves movement of the internal stomach muscles around the navel, which is accepted in Ayurveda as the seat of fire/heat in the body.
In Gheranda Samhita (I.14), this technique is mentioned as one of the four types often employed for cleansing the stomach. For this, water or six meter long strip of cloth is used. Cleansing with this cloth is described in Hatha Yoga Pradipika (II.24). Agnisara does not require any equipment or material. It only involves movement of the abdominal wall.
Agnisara process is described in Gheranda Samhita (I. 19-20) as follows: “The navel is moved back towards the spine a hundred times. It helps to remove impurities from the abdomen and increases the power of digestion. The knowledge of dhauti should be kept secret. It makes the body shining and pure like that of gods.”
Traditionally, agnisara is practiced in a sitting or standing position. Pressing the hands on the knees and slightly stooping forwards, the breath is drawn out as completely as possible. Holding the breath out for a while, the abdominal wall is moved quickly forward and backward, say, ten to twenty times. Then, after inspiration and a few normal breaths, the breath is again held out and the movement of the abdominal viscera, promote blood circulation, removes congestion, and improves the tone of the organs in the abdominal cavity. These effects can be enhanced if a round of side-to-side movements of the navel is also practiced after the two rounds of back and forth movements as described above.