Śivasaṃhitā 4.38

This verse inaugurates the technical description of Mahābandha with precise anatomical instruction. The double contraction of guda (anus, anal sphincter region) and yoni (perineum, the space between anus and genitals) acts on the region of the mūlādhāracakra, the root center where apāna — the downward wind of elimination — normally resides. The purpose is to reverse its natural direction and transform it into an ascending force.

Gudayoni is a dvandva compound enumerating two zones of the pelvic floor: guda (from Sanskrit gṛ, to swallow, the one that consumes residues) and yoni (womb, source, the generative space). Samākuñcya is the gerund of sam-ā-kuñc- (to contract completely, to close). Apāna — from apa (downward) and an- (to breathe, to blow) — is the fifth function of prāṇa, governing excretion, reproduction, and death.

Physiologically, the contraction of the pelvic floor activates the pudendal nerve and sacral plexus fibers, creating an intra-abdominal pressure that hatha yoga texts interpret as the reversal of the apānavāyu flow. Contemporary researchers such as Swami Digambaraji and M.L. Gharote have documented correspondences between the bandhas and the mechanisms of the autonomic nervous system.