Burpies. Their are several different kinds, and they all make you want to puke. Good stuff. Do a search here or on google.

Or you can have my 300 pound trainer put a big pad over his chest and walk you down for 3 minutes yelling at you to push hard and fight him off, throwning nonstop for a full round while being press backward all over the ring. That's a fun one. He told me the next step is he will do the same thing but use a medicine ball and move it around to make me think while I'm tired and pushed. I ain't there yet