The eight limbs of Ashtanga yog as compiled by the sage Patanjali may be divided into three groups. The first group including the Yama's (proscriptions) and the Niyama's (prescriptions) is devoted to the conduct of life. The second group including Asana's (balanced postures) and Pranayam (regulation of the life-force) can be collectively called Hatha Yog and is designed to bring harmony to life by establishing physiological and mental-emotional balance in the body. It is also very helpful in releasing the harmful effects of emotions bound up in the body. The other role of Hatha Yog is to prepare the practitioner for the next phase in yogic progression. The third group includes Pratyahar (introversion), Dharana (concentration), Dhyan (meditation) and Samadhi (absorption in meditation). It is focused on developing consciousness of the Self.
Regulation of the life force coursing through the body with the help of the breath is considered by some adepts to be a more powerful element of hatha yog than the postures. It complements their beneficial effects and is integrated in some fashion with all of them as well. It raises the concentration of oxygen in the blood, making the cardiovascular system more efficient and promoting health. It improves metabolic efficiency by encouraging each cell in the body to use energy and water more effectively. And it promotes better communication from each cell to the rest of the body.