The Great Seal
Executing this pose properly while engaging all three bandhas is considered to be the ultimate test of the breath because mahamudra restricts all the normal respiratory movements out of the body cavities: There is strong stabilizing action in the pelvic floor and abdominal muscles, the rib cage is held in a lifted position, the costovertebral joints are immobilized by thoracic twisting, and the sternum is lifted into the chin by the scalenes. All in all, the body is forced to find another, unusual way to breathe.
This is the structural reason why, when all the usual, visible, external breath movements have been stabilized, something deep in the core of the system must mobilize via a new pathway. That pathway is commonly referred to in Yogic literature as Susumna – the central channel.
Images from the book Yoga Anatomy by Leslie Kaminoff & Amy Matthews displayed on this website are used under license.