ujjayi It is one of the eight respiratory retention exercises mentioned in the Hatha Yoga Pradipika (manual written by Yogi Svatmarama in the middle of the XNUMXth century AD where the integration between the physical disciplines and the highest spiritual practices of the Raja Yoga) Its main characteristic is that it is not a silent breath, but rather the opposite, since it consists of breathing by partially closing the glottis, which slows down the entry and exit of air, producing a uniform, regular and continuous sound. by friction of air against the glottis.