Part I: Short intervals
For the first interval session, perform five (and possibly up to ten, if you’re a real masochist) minutes of short, near-maximal intensity sprints, such as 15:45 work:rest intervals.
Rest for five minutes, then do 20-40 minutes of steady-state cardio, as in protocol 3.
Part II: Long intervals
For the second interval session, perform five (and possibly up to ten, if you’re clinically insane) minutes of LONGER intervals – say 30 seconds work, 30 seconds recovery to a maximum of five one-minute work, one-minute rest intervals.
Don't hesitate to cut volume or duration if your legs are fried – there is no fat-loss benefit in getting injured, okay?
Unlike the first set, this second set of intervals can be done whichever way you can bring yourself to do them – by this point, you are probably ready to fall over. Familiarity is your friend. Finish with a few minutes of easy cool-down so your heart doesn’t stop, and you’re done.