Bally's and 24 hour fitness who sponsor the biggest loser have a piece of equipment that looks like a yoga or balance ball that has been cut in half and put on a round black disk style platform that people can either stand on the ball side or flip it over to use it for balancing when doing upper body exercises. I can't figure out what this piece of equipment is called so that I can buy one. Does anyone know what it is called or where I can find one? Thanks!