I have never trained in TKD or any other style which breaking occurs. From what I have learned the human bone is 40 times stronger than concrete. Take a bone for example, and compare it to a piece of concrete that same size and hit them with a hammer. The bone won't break as opposed to a piece of concrete that will just become powder. With that said Do you break board or slabs of concrete more? Do you start with boards then go to concrete? I have seen it on tv and it seems like it is always concrete, and lots of it. Thoughts?