The second practice of the shat-karma is the Nauli which can be learnt by a student who has given a few months to the practice of Uddiyana. Uddiyana may be termed as the foundation of the Nauli. The Uddiyana may be practiced as described below.
Stand with the feet apart and hands on the bend legs, in a semi-squatting position. Make the posture comfortable and then empty the lungs. With the breath out, forcibly contract the abdominal muscles, raising the Viscera until a large depression is made under the diaphragm. Then suddenly relax. Repeat this alternating contraction and relaxation till the breath could be conveniently held. This is one round. Before the next round, stand up straight and rest for a few second until the normal flow of breath returns. Never force any exercise or impose strain upon the system.
When the student has mastered the Uddiyana, he is ready to attempt Nauli. It consists of the isolation and rolling of the rectus abdominis, the straight muscle of the abdomen. Assume the same semi-squatting position used in Uddiyana but instead of placing the hands far down on the thigs, raise them a little and turn the arms so that the fingers are on the inside of the leg rather on outside as in the other position. This enables one to get a better leverage. Empty the lungs and contract all the muscles of the abdominal area. While holding this position, try to protrude whereas on both sides it forms like two cavities. Move the protruded section round and round in order to churn the contents of abdomen. But the student will have to experiment with various ways of getting control of these muscles; however, before starting, it is of paramount importance that he attains a fair degree of efficiency with Uddiyana and other will come in time.
This exercise serves as a powerful gastro-intestinal tonic and cures many of the diseases. Besides, this is a must for the next practice i.e. Basti. Regular practice of Nauli gives a sharper appetite, better vision and better physical tone. One experiences excellent health and remains free from minor ailments of sedentary life.
The advancement in the practice of Nauli is measured by the number of movements of the abdominal muscles backward and forward, to the left, and to the right, in one breath. One might start by working the muscles backward and forward ten times in one breath. After resting a while one might try the same number on the left side. And after another breath one should do similar movements on the right. The practice in due course of time might be increased to 25 rollings in a breath, which would perhaps by the maximum.