The Channels: Iḍā, Piṅgalā, Suṣumnā (Nāḍī)

The nāḍīs are the channels of the subtle body — the conduits along which the vital energy travels, said to number in the thousands. Three matter most: iḍā on the left (cooling, lunar), piṅgalā on the right (heating, solar), and suṣumnā, the central channel running up the spine. Ordinary breathing flows through the side channels; the haṭha-yogin's whole craft is to balance them so the energy enters the central suṣumnā and rises. Much of breath-control practice is aimed at exactly this.