Vajroli mudra at the physical level is executed by a contraction of the muscles surrounding the bladder and concentration on the fourth adhara – medhradhara. Helps to control apana and redirect it from the senses to the sushumna.

In traditional texts, for example, Hatha-Yoga Pradipika, one can find a description of the practices of vajroli-mudra, associated with the introduction of a catheter into the genital organ and the absorption of fluids into the bladder due to muscle contraction. In Nath Tradition, it is now believed that this is more a metaphorical description of the subtle processes that the yogi experiences in the kaula ritual.

At a higher level, vajroli-mudra can be understood as the incorporation in oneself not of physical substances, but of the renewed prana, anugraha-shakti of the Divine, bestowing siddhi.

A list of the main mudras can be found here.