“One who controls his breath also controls his mind.”
(Hatha Yoga Pradipika)
Pranayama

The literal meaning of the word pranayama is control of prana (Sanskrit: life energy), and is usually translated as breath control. It is not known how the first yogis developed pranayama. We hypothesize that these yogis first examined the natural breath and gradually discovered its rhythm, various stages, and tendencies. They understood the importance of the cycle of breath – exhalation, inhalation, and the pauses between them. Out of these observations and insights, over time, possibilities of directing the breath were created. These techniques allowed the practitioner to control prana in the body.
Pranayama practice is a subtle yet very powerful practice. We must proceed in a measured manner and do less than we think should be done.