Yoga: The Eight Limbed Experience

These are just a few books on yoga (or related to it) that I have personally enjoyed.

The Yoga Sutras of Patanjali:
Commentary on the Raja Yoga Sutras by Sri Swami Satchidananda

Inside the Yoga Sutras:
A Comprehensive Sourcebook for the Study & Practice of Patanjali's Yoga Sutras

Yoga Anatomy

The Heart of Yoga:
Developing a Personal Practice

The Language of Yoga:
Complete A to Y Guide to Asana Names, Sanskrit Terms, and Chants
(Sanskrit Edition)

Pratyahara is derived from two Sanskrit words: prati and ahara. Ahara means food, or anything taken into ourselves (physically). Prati is actually a preposition meaning away or against. When both words are combined together they come to mean "weaning away from ahara (food)" or simply ingestion.

Building off of this literal English translation, Pratyahara as the fifth limb of yoga has come to represent the withdrawal of the senses. In earlier stages (specifically Asana), yoga attempts to bring an individuals mind and body together. From the fifth limb on, the focus becomes less on the physical body and more on the "spiritual" composition. It could be said that one can not reach an enlightened state with the body, because the physical realm deterrs from some truth (yet, undeniably is necessary to be experienced). Throughout this limb, a focus is also set on controlling one's breathing to a further extent. Ideally, an individuals breath must be controlled and in harmony with the mind and body. In more ways than not, Pratyahara is directly related to the fourth limb of yoga Pranayama.