The fourth limb of yoga is Pranayama. Etymologically Pranayama can be broken down in two ways: pran (breathe/breathing) + ayam (expansion), or prana (breath, life force) + yama (control, restrain). I’ve come across both explanations in various places, but I feel taking both etymologies together fully encompasses what Pranayama is about.
Prana is our breath, our life energy, and the breath of the soul. It is the vital force of the True Self. Pranayama practices such as Ujjayi, Anuloma-Viloma, Kapalabhati, etc. teach us how to control our breath. Through breath control we can expand our ribcages, increase the oxygen in our bodies which gives us more energy and promotes healing, open up the nadis (energy channels), and decrease stress. Pranayama practices can also be helpful tools for meditation. To still the mind we can turn our drishti, our inner focus, towards our breath.
By learning Pranayama practices, we learn ways to control our breath, but it is through this control of the breath that we learn to expand our life force. As we expand the breath throughout our bodies and minds, we expand our souls. Through Pranayama practices we can expand beyond the limits of the body and mind and connect with the vibrations of the universal prana.
Whatever moves in the universe, whether it is either seen or heard, whether it is within or without – it is pervaded by breath.
– Mahanarayana Upanishad
There is an intimate connection between the breath, nerve currents, and control of the inner prana or vital forces. Prana becomes visible on the physical plane as motion and action, and on the mental plane as thought. Pranayama is the means by which a yogi tries to realize within his individual body the whole cosmic nature, and attempts to attain perfection by attaining all the powers of the universe.
– Swami Sivananda
Prana is the sun…The sun gives light and life to all who live, east and west, north and south, above, below; It is the prana of the universe…Prana burns as fire; he shines like the sun; he rains as the cloud; he blows as the wind; he crashes as the thunder in the sky. He is earth; he has form and no form; Prana is immortality.
– Prashna Upanishad