As taught in this way the bandhas are energy valves as much as locks, not muscle contractions. They are locks in such that they prevent the energy from being dissipated or distracted at various key energy centers. They are more valves in the sense that they redirect these energies from being dissipated into activating the inner circuitries at these centers and breaking up the knots (granthis). As such many hatha yogis teach the bandhas as the means to breaking through the granthis which in themselves operate not only in the body/mind/energy fields, but in the more subtle realms of vijnanamaya (higher transpersonal non-dual wisdom) and anandamaya koshas (the spiritual reams).
. The vajroli in the energetic state affects the opening of the swadhistana chakra so that no energy gets stuck there. It is very valuable that we do not approach vajroli mudra nor mulabandha (the latter occurs in the muladhara chakra) as muscle contractions (at least in the West) in order to avoid tension, blockage, stress, or rigidity. Of course "most" movement involves the activation of some muscles (except movements that take the advantage of the force of gravity) or relaxation of a previous tense/spastic muscle. ALL MOVEMENT (isotonic activity) involves a corresponding relaxation of the holding muscle (called the antagonist muscle). For most of us, it is this relaxation (and resultant activation of the parasympathetic nervous system) that is key to mulabandha and vajroli. This allows the energy to flow through this area, irrigating it with chit-shakti. THEN it no longer feels trapped nor is there a need for it to flow out and discharge its energy once the charge gets dammed up. This is what gives us "the lift" in mulabandha (at least in part).
Since we are addressing specifically mulabandha, the two main points to consider then, are the sacrum/tailbone complex in the posterior of the body and the pubic bone in the front. Through observation one may notice that most adults move their pelvis and sacrum all at once i.e., there is no independent motion of the sacrum and pubic bone from the rest of the pelvis (the innominate bones of the ilea and ischium). Yet closer anatomical study shows that the healthy sacrum is not fused with the pelvis, but forms a joint (the SI joint). Also the pubic rami (left and right) forms a joint at the pubic symphysis. So what happens is that the sacrum/tailbone complex moves down and forward at the same time the pubic bone moves down and forward. These two movements toward each other form the subtle SCOOP of mulabandha. More subtly it is the perineal area moving up as the cauda equina moves down and forward. That gives us the lift.
Mulabandha thus mobilizes the previously stagnant energy and repositions places it into its rightful energetic and aligned place. The correct application connects the front and back of the body, the left and right, the ida/pingala -- it aligns the spine as well. Although the bandhas are ENERGY valves, this is too subtle for most, thus the energy is first gotten in touch with through the physical form of physical movement. So if you follow this so far, then you will be utilizing your asana practice to go deeper inside -- feel the energy and especially to feel the synergistic and mutually electro-magnetic relationship between the pubic bone and tailbone. This is subtle at first. If one hasn't experienced it, then of course one may not even entertain its possibility, but that is how we grow -- entertaining the possibility -- moving from coarse/gross and outer to the more subtle, energetic and inner. This is very much like pranayama where the coarse breath leads us to the energy (prana) awareness and then to communion the implicate integrating intelligence at the Source of this energy.
So too in mulabandha the tailbone and pubic bone no longer move with the rest of the pelvis but rather form the base of the pelvis and the spine where the physical body moves around that root foundation. Here the tailbone and sacrum drop at the same time the pubic symphysis drops down -- they both move toward each other INDEPENDENTLY of the rest of the ileum and ischium (heresy that this may be). Here the sacrum moves away from occiput and the entire spine becomes long-- in traction while at the same time the torso is lifted away from the chest and armpits. We don't have to know the anatomical terms to know the energy of mulabandha, but yes it has an anatomical relationship as well. This mulabandha makes backbends, forward bends, twists, sidebends, contralateral poses, etc. all work in a functional and energetic alignment, and in turn these poses should make the energy of mulabandha work -- they are mutually synergistic and thus an energetic partnership is thus engaged and is able to become fulfilled in the practice -- all of which is self instructing if one balances and harmonizes these energetics with this awareness in mind.
In other words Mulabandha should be found in all poses (unless one rounds the back). When mulabandha occurs there is less effort and more energy so it is not a contraction. Physically the fascia (pelvic diaphragm) in the perineum lose tension and hardness and are able to dome upward but rather a lift up creating space for the tailbone and pubic bone to move inward toward each other. As this diaphragm domes upward, the sacrum and pubis drops downward to meet the earth (if you are standing). So there co-exists both an upward motion and a downward motion simultaneously occurring. Physically the pubic bone and tail bone no longer move glued to the rest of the pelvis. Freeing up this motion is the subject of much "technique" in the kundalini and hatha yoga literature.
Similarly in standing forward bend, like uttanasana, bending forward the pubic bone into the front groin crease toward the sacrum. Simultaneously the sit bones (ischial tuberosities) rise up toward the sky away from the knees, but also simultaneously the sacrum/tailbone complex sinks down toward the knees moving in to connect with the pubic bone giving lengthening the spine and the legs also simultaneously. Here let the perineum move in and up internally, then draw it posterior toward the cauda equina.
Traditionally, mulabandha is practiced selectively and sometimes in combination with other bandhas at certain stages of pranayama, asana, mudra, meditation, and tantric practice. Some modern schools recommend a light mulabandha throughout the entire asana practice. It is one of the three bandhas in tri-bandha (together with uddiyana and jalandhara bandha), used in most pranayama retention cycles. Classically there exist many nadis that may have obstructions to be opened, but only three granthis of which their location is not always agreed upon, but which some hatha/kundalini yoga schools suggest that the three bandhas serve as their remediation. Here mulabandha opens up the Brahma Granthi providing knowledge of Brahma Loka.
- Exhale all the breath out applying mulabandha, uddiyana bandha, and cap it off with jalandhara bandha in that order. Play with accentuating mula and uddiyana bandha here. Hold the breath out while the torso and spine remains long.
- Release jalandhara first, then uddiyana, then mulabandha, as you inhale drawing the air down into the lower abdomen as the diaphragm and abdomen expands.
- At the end of the inhale apply mulabandha first and then cap it off with jalandhara bandha (binding the prana inside) while lifting the spine and torso (crown raises up toward the heavens).
- Increase this inner "lift" and feeling of internal space playing with mulabandha and jalandhara bandha while holding the breath in (antar kumbhaka) without any strain.
- Before any tension or stress (or when the lift has peaked), then release the jalandhara bandha first, then the breath and mulabandha, while implementing uddiyana bandha slowly until all the air has been expelled.
- Repeat as in 1 above 10 times.
- Be gentle and go for the vital healing energy.
- Exhale all the breath out applying mulabandha, uddiyana bandha, and cap it off with jalandhara bandha in that order. Play with accentuating mula and uddiyana bandha here. Hold the breath out while the torso and spine remains long. This is called external retention (bahya kumbhaka or sometimes rechaka kumbhaka).
- Release jalandhara first, then uddiyana as you inhale.
- At the cap of the inhale, bind it with jalandhara bandha and lift the spine and torso up off the pelvis even more with an uddiyana bandha and gentle accentuation of mulabandha. This is called internal retention (antar kumbhaka sometimes called puraka kumbhaka).
- Release the cap of jalandhara bandha first, then the breath
- Repeat as in 1 above
- Inhale through the nose while visualizing the prana coming in from Infinite Source through the crown of the head through the entire body down into the muladhara in a subtle wavelike motion.
- After the full inhalation is complete apply mulabandha and then top off the short and light retention of breath with jalandhara bandha to hold the breath inside (antar kumbhaka).
- Then smoothly release the jalandhara bandha first, while spontaneously starting a gradual uddiyana bandha to expel all the air out moving the apana in an upward motion starting in the lower abdomen, through the torso, to the top of the head melting any hardness and purifying any poisons.
- Inhale again as in one and repeat this tribandha visualization practice 10 times
- At the end of the inhale compound the muladhara region allowing for a more reflexive, efficient, and spontaneous simultaneous implementation of both mulabandha and uddiyana bandha and extend the antar kumbhaka (internal inhalation). The belly slightly expands during the inhalation, but at the end of the inspiration the lower belly goes inward toward the sacrum as the floor of the pelvic diaphragm spontaneous lifts through mulabandha, and the spine lengthens. This is the beginning of classic vase breathing (discussed in the pranamaya section).
- Optionally, after the exhalation when one visualizes the apana rising through the very thin central threadlike channel which ends at the brahmarandhra (hole of brahma at the vertex) one can practice external retention of the air (bahya kumbhaka). This is the hole where the spirit in the form of vital life supporting prana leaves the body at death and is part of more advanced practice called Phowa in Tibetan. It should NOT be practiced by beginners (external retention) and focus at the crown because of the danger of premature death.
"... in hasta bandha the weight of the body has to be shifted from the wrists ... to the central bones of the palms .... Then the center of the palms are sucked upward in the same way as in pada bandha, thus trapping the energy in the typical arch construction, and sending it upward through the arm and shoulder joints. The fingers are kept long, and flat on the earth and they root together with the wrists, forming the rim of the cyclone or bandha. This corresponds to in the action of pada bandha, where the toes are elongated on the earth and root together with the heel bones."
Pg 44. "Dancing the Body of Light", Dona Holleman and Orit Sen-Gupta, Pegasus, 1999.