The Sanskrit word "bandha" usually translates into “lock” but for our purposes, it is
more appropriate to look upon it as meaning “valve”.

To use a
bandha means to contract certain groups of muscles, to use them as a valve
that can control the direction of the flow of energy that we create while we practise
asanas (yoga postures).

There are three
bandhas used in the Ashtanga yoga practice: moola bandha, uddiyana
bandha
and jalandhara bandha. They can be used individually or all three at the
same time.

  • Moola bandha (the “Root Lock”) is the most important bandha. It should be held
    almost throughout the whole practice. To hold moola bandha means to contract
    the muscles of the pelvic floor (perineal muscles) which helps to produce the heat
    needed in the practice and to keep the energy flowing through the body instead of
    leaving it. The location of moola bandha is, obviously, not exactly the same in
    males and females. Please compare Swami Chela Buddhananda´s book “Moola
    Bandha, The Master Key” in our "books" section for more detail.

  • Uddiyana bandha (the “Upward Flying Valve”). It should also be held almost
    throughout the whole practice. To hold it means to exhale and contract the lower
    belly (three fingers below your navel) inward and upward. Imagine that your navel
    is tied to a string and you affix this string to your spine.

  • Jalandhara bandha (the “Chin Lock”). To hold it means to extend the chin forward
    and then draw it back into the notch between the two clavicle bones. It is used  
    only once, during the practice of pranayama (breath control) in padmasana (the
    lotus posture).

Holding
moola bandha is perhaps the most important aspect of Ashtanga yoga – even
more important than the breathing rhythm and by far more important than performing
an
asana “correctly”. Originally, bandhas were the first thing that was taught to
beginners, followed by the breath and only then
asanas were taught.

You will find a more extensive discussion of the role of the
bandhas in Ashtanga Yoga
in Matthew Sweeney´s book "Astanga Yoga as It Is" in our
books section.
Bandhas