The three principal nadis are the ida, the pingala and the sushumna. The pingala is known as the right channel because it flows to the right as it leaves the muladhara (root) chakra and weaves in and out of the other chakras before ending at the right nostril. The ida (left) nadi is a mirror image of the pingala nadi as the two travel up the spine. Sushumna, the center nadi, travels through all the chakras and directly up the spinal column.
Pingala nadi controls essential life processes and imparts vitality, efficiency and strength. It is associated with extroversion, masculine energy, the left (logical/linear) side of the brain, and the right side of the body. Pingala nadi energy must be balanced by the ida energy, which is creative and introverted. A major focus of Hatha yoga is balancing these nadis. For example, someone with a free-flowing pingala nadi who has a blocked ida nadi may have lots of energy for a physical yoga practice, while lacking the introspection needed to achieve spiritual awakening.
One of the principal ways of balancing the nadis in yoga practice is through a form of pranayama called nadi shodhana, or alternate nostril breathing. With the fingers of one hand, the nostrils are alternately closed off while the individual completes cycles of breath.