Bandha allows energy to flow. This is technically something very subtle. Therefore physical action and muscle contraction are only a small part of bandha. Mula Bandha and Uddiyana Bandha are the two most important valves in Ashtanga Yoga.
This article is form 1998. I did not recommend the technique of Keigel then and do not today. I'm just quoting it.
Mula Bandha is introduced with the contraction of the pelvic floor muscles. Imagine, that you urgently need the toilet, but there isn’t one around, you’re probably already using Mula Bandha. To strengthen weak pelvic floor muscles, Keigel recommends that you practise stopping the flow of urine when using the toilet. Alternately contracting the muscles to the front and then the rear and then concentrate on achieving a gentle contraction somewhere in the middle, you are now one step closer to Mula Bandha. Activate this Mula Bandha at the end of an inhalation, as the exhalation starts. Draw the pelvic floor in and up.
You achieve Uddiyana Bandha, by gently drawing the stomach inwards. At the end of an exhalation, when the need to inhale begins, imagine a golden thread that is attached two fingers width under the navel, that is pulling in and up. From and anatomical viewpoint, the transverse abdominal muscles will be lightly activated.
Mula Bandha is linked to exhalation, Uddiyana Bandha to inhalation. Both bandhas remain continuously activated throughout the whole practise. To begin with this is very difficult and you will keep noticing that you’ve forgotten the bandhas. See this though as a success as you have reminded yourself. With practise you’ll remind yourself about bandhas time and time again, until it will become a constant companion to your practise.
From and anatomical viewpoint, these two bandhas support breathing. Try it out for yourself (Read the text slowly aloud, with a short pause after each section):
Lie completely relaxed on the floor, on your back. Shut your eyes and breathe calmly in and out through your nose. Lay one hand on your navel. You can feel how your abdomen rises with each inhalation and falls with the exhalation. What you are actually feeling, is the action of your diaphragm, which contracts under the ribcage during inhalation thereby pushing the abdominal organs forward.
With the next exhalation, activate Mula bandha and then Uddhyana Bandha with the following inhalation. Now the stomach can no longer rise up, but the diaphragm is contracting like before. The diaphragm presses against the abdominal organs that are being supported in front by Uddiyana Bandha and from below by Mula Bandha. As a result of this support of the abdominal organs during inhalation, the diaphragm lifts the ribcage.
Notice that during breathing, these two bandhas are inseparably connected. Both are necessary, to firmly support breathing.
Due to the combined effect of the bandhas with the breath, firmness in the torso, length in the spinal column and room for movement are created. Stability in the torso is essential for powerful body movement. Only a stable torso can be raised into almost breathtaking handstands. The length created in the spine minimises pressure on the intervertebral discs during deep forward bends and avoids a possible impact of the spinous processes of the vetebrae during seemingly impossible backbends. The sucked-in belly also achieves space for various Asanas (postures) in which excessive volume in this area would be a disadvantage.
Bandha is frankly a natural reflex for powerful movement of the body. You can observe how bandhas are activated on their own when you lift a heavy object. Gymnasts, acrobats, bungy-jumpers, ballet dancers and other athletes know this power house under various names and use it as an essential aid in their sport.
Energetically, the bandhas create two opposing forces like the poles of a battery, between which energy can flow. Mula Bandha draws energy towards the lower end of the spine, into the Muladhara Chakra; It stands for the element Earth. Mula Bandha connects you with this earthed energy, giving you firmness and stability. Uddiyana Bandha literally means „flying up“. Uddiyana Bandha draws Prana (energy) out of it’s foundation, the Muladhara Chakra, up through the spinal column. Uddiyana Bandha connects you with the element air, the energy of the Anahata Chakra in the middle of the ribcage. Uddiyana Bandha gives lightness, helping you to overcome the force of gravity.
In the beginning there was nothing and out of the nothingness there came sound. This original sound is called Spanda. The vibration of this first sound divided the nothingness into two opposing forces. Like plus and minus, which together again give nothing. The whole universe exists in the field created by these opposing forces, in the vibration of this original sound. If the sound fades into silence, then the universe will disintegrate again into nothingness. As it is described in the Tantra. The whole cosmos is a temporary dance between the two opposing forces, ascending energy (Prana) and descending energy (Apana), inhalation and exhalation, male und female, light and dark, hard and soft, positive and negative, sun and moon, destroying and procreating – Uddiyana Bandha and Mula Bandha.
The practise of Ashtanga Yoga symbolises the dance of opposites, that the world make up. With each inhalation you strive to move upward, to expand, with each exhalation you root yourself firmly in the ground, becoming small and compact. With each inhalation, Uddhyana Bandha conducts energy upwards, allowing you to become light, connecting you with the air. With each exhalation Mula Bandha conducts energy downwards, letting you become heavy, connecting you with the earth. If the forces of opposition in you are in balance, then you will find yourself in internal harmony and bodily health.
Jalandhara Bandha is the third energetic valve that you can use in Ashtanga Yoga. You can achieve Jalandhara Bandha, when you lower the chin a little. Roll your tongue back and up against the palate and smile slightly. Jalandhara Bandha redirects the ascending energy in the spinal column in a spiral motion forwards. Jalandhara Bandha connects you with the ether element, with the Ajna Chakra in the middle of the head. The chin is not lowered in all positions. Nevertheless the energetic quality of Jalandhara Bandha persists.