Hatha Yoga, first appeared in the ninth or tenth century. Hatha yoga’s principles are based on tantra, and incorporate elements from Buddhism, alchemy, and Shaivism (worship of the transcendental Shiva).
In the tantra tradition, hatha yogis believed that creating opposites or polarities (male vs. female, hot vs. cold, happy vs. sad) caused suffering and brought about disease, delusion, and pain. Hatha yoga believes a lot of strength, discipline, and effort is required to unify these opposing forces and bring the body and mind together.
Hatha yogis strove to transform the physical desires and body into the subtle, divine body and thereby attain enlightenment. The Hatha yogis had to learn the physiology of the body and also had to perform purification rituals before they could begin asana and pranayama practices. The yoga disciples received training from their gurus.
The first and primary text was written by a yogi named Goraksha, the father of hatha yoga. Goraksha founded the Natha sect of yogis and was considered to be a miracle worker, saint, and revered teacher. His earliest writing, the Siddha Siddhanta Paddhati, introduces several important elements of hatha yoga, including the idea that the physical body is only one level of embodiment. There are five others, moving from the grossest (garbha or physical) body to the subtlest (para or transcendental) body. He also delineates nine energy channels or chakras, three signs or lakshya (literally, visions), and 16 props or adhara, upon which a yogi focuses attention (the ankle, the thumb, the thighs, the navel, etc.).
Svatmarama Yogin, a disciple of Goraksha, devised the Hatha Yoga Pradipika, probably during the mid-fourteenth century. This text describes sixteen postures, most of which are variations of Padmasana (the cross-legged Lotus pose), several purification rituals, eight pranayama techniques (primarily to retain the breath), and ten seals (mudras) with specific bandhas, or locks to constrict the flow of prana or life force. As Svatmarama explained, before the mind can even hope to control the senses, the breath must neutralize the mind. Steady, rhythmic breathing calms the mind, freeing it from external distractions; a calm mind in turn reins in the senses.
The Gheranda Samhita offers seven niyamas, or disciplines necessary for yoga practice: cleanliness, firmness, stability, constancy, lightness, perception, and nondefilement, along with an intricate purification system.
The Shiva Samhita is perhaps the most comprehensive hatha yoga treatise. It emphasizes that even a common householder (a common male householder, that is) can practice yoga and reap its benefits a concept that would have startled earlier proponents of yoga. The Shiva Samhita outlines the intricacies of esoteric physiology, names 84 different asanas the most wide-ranging list to date and describes five specific types of prana (or life force), providing explicit techniques to regulate them. Unfortunately, only four of the asanas are described in detail. Just like all hatha yoga philosophy, the Shiva Samhita postulates that performing asanas will cure a yogi of all diseases and bestow upon him magical, superhuman powers.