One of the movements we often do in yoga is uddiyana. Uddiyana involves the contraction of three core muscle groups: the perineal muscle located between the genitals and the anus, the diaphragm and the oblique abdominal muscles. These three muscle groups are contracted while coming up from a squat during exhalation. The perineum is drawn up wile the stomach muscles are drawn in and the diaphragm up. All of this is done while breathing out coming up from the squatting position. This movement does take practice and sometimes takes years to master.