Uddiyana bandha
Uḍḍīyana Bandha, also called abdominal lock or upward lifting lock, is the abdominal bandha described and employed in hatha yoga, in particular in the nauli purification. It involves, after having exhaled all the air out, pulling the abdomen under the rib cage by taking a false inhale while holding the breath and then releasing the abdomen after a pause. The process is repeated many times before letting the air into the lungs, resuming normal breath.
