High Intensity Interval Training.
Basically you have two intervals, one is flat out at 90% of your max heart rate, the other is going slowly.
So you would do 30 seconds flat out on an excersize bike on lvl 10, then go slowly for 30 seconds on lvl 3.
It doesnt burn as many calories as regular cardio, but the rapid change in heartrate is supposed to boost your metabolism and increase endurance. 5 minutes is supposed to be the equiv of half an hour of regular cardio, so its quicker too.