बाह्याऽऽभ्यंतर स्तम्भ वृत्तिर्देश काल संख्याभिः परिदृष्टो दीर्घ सूक्ष्मः (सूत्र II-50)
The 3 parts: inhalation, exhalation and the retentions are observed, the time is measured, and carefully lengthened.

- Yoga Sūtra, Patañjali

The mind is the king of the senses; the breath is the king of the mind.

- Haṭhayoga Pradīpikā, Swatmarama

Prāṇa - life force or simply life is the notion of a vital, life sustaining force of living beings. Its most subtle material form is the breath, but is also to be found in blood, and its most concentrated form is semen in men and vaginal fluid in women. Prāṇa suffuses all living forms but is not itself the Atman. Prana was first expounded in the Upanishads, where it is part of the worldly, physical realm, sustaining the body and the mind.

Prāṇāyāma is the science of conscious control of the flow prāṇa in the organism. The link between the breath and the mind was well known to ancient yogis. It has been described as one of the 8 steps of Patanjali's Yogasutras. In addition to preparing the individual for spiritual singularity or Samādhi, Prāṇayāma has health benefits such as blood pressure management, aiding in digestion and metabolism and the activation of chakras.