Where much of classical Indian ascetic thought treats the body as a burden the soul must eventually shed, the Naths, working within a Shaiva tantric milieu that had long treated the body as a microcosm of the cosmos, taught that liberation could be achieved in and through the body rather than by escaping it. Central to the doctrine is the subtle physiology of nadis, channels through which vital energy, prana, moves, and chakras, centers along the body's central axis; hatha yoga's postures, asana, breath retention, pranayama, and internal locks, bandha, are practiced to draw a latent energy, kundalini, upward through these centers, refining the practitioner's ordinary body into an immortal or adamantine one.
The Hatha Yoga Pradipika, compiled by Svatmarama and drawing on older Nath teaching, systematizes much of this practice and remains the tradition's most widely read manual outside specialist lineages. The doctrine treats physical longevity and even claims of deathlessness associated with legendary Nath siddhas not as incidental side effects of yogic practice but as a genuine sign of spiritual perfection, since a body that has become fully divine has, on this view, no further reason to age or die in the ordinary way.