(Apāna Vāyu): The “air that moves away,” one of the five vayus (vital airs). Apana vayu is the downward and outward flow of energy in the body. It is mainly responsible for exhalation and the elimination of waste materials. It governs the eliminative functions (excretion, urination, menstruation, ejaculation, and perspiration) and childbirth. It is situated mostly in the lower part of the body—from the genitals to the knees or, alternatively, from the abdomen to the calves or even the feet. It is a descending energy, used in Hatha Yoga to awaken kundalini shakti. Many pranayama techniques reverse the direction of the flow of apana vayu and unite it with prana vayu. According to the Shiva Samhita, apana vayu and prana vayu are the two most important vital airs. Their union is considered particularly important, bringing profound spiritual effects. It is related to prithivi (the Earth element). Read more about the vayus.