FOP or Fibrodyplasia Ossificans Progressiva, is a Very, very rare bone disease in which muscle can become bone. Any, bump, tear, or stress can cause the muscle to turn into bone. This is the only known case where one organ becomes another. The vids are on the Discovery channel
http://www.gawkk.com/tags/fop-skeletonhttp://health.howstuffworks.com/fop.htmIt is sad, crippling disease, imagine if all of sudden you were a healthy person and you started lifting and this happened to you? I haven't done teh research, so I believe people tend have it from birth.
