The Sanskrit word bandha means to "hold" or "lock". Bandhas are internal energy valves because they direct the internal energy flow to irrigate the nadis and activate the energy body. They create internal energy reconfiguration. Bandhas are muscular contractions designed to block or seal off certain areas of the body and thus redirect the flow of prana, to intensify its flow in a restricted area. These definitions of binding or locking precisely describe the physical action involved in the bandha practices and their effect on the pranic body. A bandha consists of a series of muscular contractions, which act on the nervous and endocrine systems. The implementation of bandha has to be effortless and natural (Sukshma – subtle practice). More subtle bandha is performed, stronger effect it has. The bandhas are mastered by awareness. The basic principle with each bandha is first to accumulate energy in an area of physiology, then release it. This process of building a force and then unleashing it discharges obstacles from the pathways of energy circulation. The bandhas aim to lock the pranas in particular areas and redirect their flow into sushumna nadi (utghata – opening the door) for the purpose of spiritual awakening. Bandhas thus bind back the dissipative energy and as such they are the embodied aspect of pratyahara. At first bandhas are learned as a physical procedure utilizing muscles and physical movement. Eventually the yogi becomes aware of the underlying neuro-endocrino-physiological, mental, and energetic patterns behind the physical, hence the bandhas are effected by awareness and intention. Bandhas also make sure the flame (Agni) is brought exactly to where the apana "dirt" is concentrated, so that the fire has a greater effect. Bandhas can be practiced individually or incorporated with mudra and pranayama practices. Bandhas also massage the internal organs. There are four bandhas: jalandhara bandha, moola bandha, uddiyana bandha, and maha bandha. The last of these is a combination of the first three.
Course on bandhas and their application to asana and pranayama practice.