Yoga as practiced in the U.S. is almost exclusively yang or muscular in nature. The yin aspect of yoga (using postures that stretch connective tissue) is virtually unknown but vital for a balanced approach to physical and mental health. Paul Grilley's Yin Yoga outlines how to practice postures in a yin way.
Grilley includes an explanation of Modern Meridian Theory, which states that the meridians of acupuncture theory are currents flowing through the connective tissues of the body. Yin Yoga is specifically designed to address these tissues.
The two major differences between a yin and a yang yoga practice are that yin postures should be done with the muscles relaxed and should be held a long time. This is because connective tissue does not stretch like muscle and will not respond well to brief stresses. In addition, Yin Yoga better prepares people for meditation.
For yoga practitioners looking for something beyond physical postures. Yin Yoga addresses the deeper spiritual dimensions of yoga, with helpful sections on chakras, breathing exercises, and meditation. Illustrated with thirty-five black and white photos of Yin Yoga postures and six color illustrations of the body's connective tissue and meridian lines.
Excerpt From the Book From: "Meridian Theory" Muscle Tissue is Yang, Connective Tissue is Yin:
Yin or Yang description of any object is relative, the description varies as different aspects are considered. For example, when considering its location the heart is Yin to the breast bone because it is more inside, more hidden. But when considering its substance the heart is Yang to the breast bone because it is soft, mobile and elastic. Most relevant to a consideration of Yoga practice is the elasticity of muscle and connective tissues. When we move and bend our joints doing Yoga postures, both muscle and connective tissue are being stretched. The muscles are Yang because they are soft and elastic, the connective tissue is Yin because it is stiff and inelastic...