Tabata, created by Izumi Tabata,
20 seconds sprint as hard as you can... as hard as you can. walk, coast or stand there for ten seconds.
Repeat 7 more times.
If you don't feel like quitting after the fourth cycle, you aren't going hard enough.
Its just four minutes but according to some studies, its better than a whole lot more time at chronic cardio. You can run, ride, push steel, do burpees and chinnups, whatever. I only allowed the spin bike at the moment.
Well, I don't like it until it's over.