All forms of yoga emphasize either muscle (Yang) or connective tissue (Yin). Today, all the popular forms are Yang, but balancing the two has many benefits in any Yoga practice - particularly for meditation. Connective tissue does not stretch or respond to brief stresses as muscle will, so Yin postures are held a long time, with the muscles relaxed. Acupuncture meridians are also in connective tissue, and Yin Yoga is designed specifically to stimulate them.