That which enters the body is called prana and that which leaves it is called apana. The term apana also refers to the region of the lower abdomen and all the activities that take place there. Apana describes that part of prana that has the function of elimination and provides the energy for it, and it also refers to the lower belly and the rubbish that collects there when the power of prana is not in a state of equilibrium. When a person is slow and heavy we sometimes say that he has too much apana. Apana as pranic energy is something we need, but apana as refuse left from activating this energy actually prevents prana from developing within. All forms of prana are necessary, but to be effective they must be in a state of balance with each other. If someone has a lot of rubbish in the region of the lower abdomen then he or she consumes too much energy there, and this imbalance should be addressed. The goal is to reduce apana to an efficient minimum.

Apana as waste matter accumulates because of many factors, some of which lie within our control. The practice of yoga aims to reduce these impurities. People who are short of breath, cannot hold their breath, or cannot exhale slowly are seen as having more apana, whereas those who have good breath control are considered to have less apana. An overabundance of apana leads to problems in all areas of the body. We have to reduce the apana so that we can bring more prana into the body.

When we inhale, prana from outside the body is brought within. During inhalation, prana meets apana. During exhalation, the apana within the body moves toward the prana. Pranayama is the movement of the prana toward the apana and the movement of the apana toward the prana. Similarly, holding the breath after inhalation moves the prana toward the apana and holds it there. Holding the breath after exhalation moves the apana toward the prana.