Air - vayu.

Jai achyuta
What is the role of vayu in yoga.
How yogi regulate his energy through Japan sadhana.
According to yoga, air within the body is classified under five types i.e prana, apana, vyana, udana and samana vayus. Among them the apana vayu has a downward movement towards the base centers of the inner body and hence it is responsible for everything that has to do deal with the lower three centers of the body i.e for provoking basic instincts like sleep, sexual urges, creating the jatara agni that causes hunger in human beings and also for excretion. On the other hand, prana vayu has an opposite movement and it is responsible for the sustenance of life energy within the body. As a yogi advances in his spiritual practices, the apana vayu ceases to move downward, it begins to move upward to join its way with the prana vayu that naturally moves upward. As a result gradually there will be lesser and lesser intake of food and thereby lesser excretion as well. Moreover, there is little or no physical action done when a yogi resorts to total penance. He seldom moves from his asana, even the breath becomes very shallow. If he is very advanced in his progress, the complete breath comes to a stand still which technically means that 0 calories are burnt in a yogi's body.
Hence the yogi lives long.
Ramakrishna.