I think I understand the basics of it. They way I do it now since I am getting used to it is I use a bike and do 30sec @ level 1 and then up to 10, then down to 2 and up to 11, and so forth for 6 minutes. Is this correct, of course there is the warm up/cool down period. But my question is how does essentially 6 min of cardio work so good?