How Yin yoga works
Yin yoga is a combination of hatha yoga and Chinese Taoist disciplines. Paul Grilley, one of the founders of yin yoga, found that traditional types of yoga did not prepare his body for seated meditation. It was then that he combined concepts from Taoist yoga with his hatha yoga practice and found that he could sit for extended periods of time.
In Indian and Chinese thought, the body has pathways through which energy flows. In India this energy is known as prana. In China it is qi. It has recently been speculated that the connective tissue surrounding the joints are the conduits of this energy. In yin yoga, poses are held for several minutes, allowing this tissue to stretch and the energy to flow.
For a proper study of yin yoga one must understand a bit about the concept of yin and yang. The world is comprised of yin and yang. They are the polar opposites out of which movement is created. The yin is static and calm while the yang is flowing and dynamic. Hatha yoga, with its emphasis on movement, is predominantly yang orientated. Muscles are dynamic, thus yang-oriented. The connective tissue is predominantly static and comprised of yin. Sitting in meditation is a yin activity. The intent of yin yoga is to restore the proper balance of yin and yang within the body.
To compensate for the over emphasis that traditional yoga places on yang, the yin poses were created. They are derived from hatha yoga poses, but vary to some degree. The focus of the poses is to release the muscles, not contract them.
Forcing the muscles surrounding the connective tissue to stretch is to impose yang energy on the joint. This is precisely what yin yoga seeks to avoid. The muscles surrounding the connective tissue must be relaxed. Some poses in hatha yoga are impossible to perform if the muscles are to be relaxed. Those poses cannot be used as they bring about disequilibrium and are detrimental to the intended purpose.
If performed properly, the channels through which the vital energy (the qi and prana) flows will be opened. These channels, and the network of energy are the very ones that acupuncture taps into. Illness is thought to arise when one or more of these channels are blocked. Acupuncture restores the flow. In a similar way, the poses of yin yoga seek proper balance, thus restoring flow.