In a sense, cardio intervals are God's gift to lazy exercisers everywhere. Why? Well, rather than commiting yourself to an excrutiatingly long exercise routine every day, you can actually cut down the time you exercise in half if you add cardio intervals.
There is one snatch, though: Cardio intervals will kick your ass. The point of intervals is to keep your body guessing (by alternating exercise intensity) and to keep your heart rate up the whole time, so you burn more calories faster.
If this type of hardcore training is something you're interested in, then try out this video featuring Jessica Bergenfield and Sarah Dussault. Try the mountain climber, hover jacks and pike double crunch moves using rags for an added burn!