I don't know if it's unusual or not, but I haven't seen anybody else doing it. Occassionally, I will have my students lay down on the floor on their backs lying side to side, but alternating which end their heads are facing. They interlink their arms so that their stomaches are all nicely lined up. Then I will have the lightest student walk along their stomachs one at a time, pausing on each person in turn as the student that is getting stood on recites the alphabet. They are required to breathe during this...inhale and exhale. Then, I will get a heavier students and do the same thing. Object of the exercise is tightening your stomach while still being able to breathe. It's an old technique that my high school choir teacher, Miss B, did now and then. She also would hit you HARD in the stomach multiple times while singing...but I've heard some of my students sing before, so I don't do that. We also do what are called (hope this is spelled correctly) kotoate drills. Basically, body toughing. We kick as hard as the person can take (I won't bore you with exact procedures and precautions) to the outside/inside of the thigh, forearms, shoulder blades and lower ribs (watching out for the kidneys/spine). I tell my students that you are doing your partner no favors by being to gentle on them, and the person being kicked is told to tell the other person whther it is hard enough and they can take more...or "that's just a wee bit to much". I would like to be in your dojo lol