Yin Yoga by Paul Grilley
Most forms of yoga are considered to be predominantly Yang, in that they are active. They have an emphasis on stretching and stimulating the muscle tissue of the body.
Modern meridian theory says that the connective tissue provides the routes for energy to flow around the body (the meridian system). How well this functions is due to dependent on the presence of sufficient hyaluronic acid which holds liquid in the tissues, helping with flexibility.
Yoga postures, particularly deep stretching of the connective tissue helps stimulate the production of hyaluronic acid, so helping to re-enliven the body. The postures also help work against the forces of contraction and the resulting fixation of joints. This can be particularly beneficial for helping relieve lower back pain and in reversing degeneration of the joints.