yoga philosophers tell us that we have three bodies: physical, astral and causal bodies. exercise physiologists say that we have two different physical bodies. a muscular body that thrives on repetition; run, bike, dance, swim, lift, practice vinyasa yoga, anything rhythmic. our second body is a fascial tissue body; the slow moving fabric that knits our individual muscle fibers into small bundles and those bundles into bigger groups, that ties our muscles into our bones and binds our bones to other bones. this second fascial tissue body doesn't respond well to rapid and continuous rhythmic movement. in fact your fascial tissues require a different kind of activity: the slower, longer, non-muscular holds that are at the heart of a yin yoga practice.