When you don't have time to do your 60 minute low intensity cardio, you can achieve the same results with this 20 minute high intensity program.
Sorry, but this is bullshit, scientifically. Think about it logically. Give your friend a 40 minute headstart in a race, and see if you can catch him using HIIT running. Of course, you can't even run half the distance he/she has. Moving mass across distance with the force of gravity taken into account is how you measure work performed, in other words, how many calories you burn. So you'll be lucky to perform half of the work, i.e. burn about half the calories someone doing 60 min. of cardio is doing (which is still saving ten minutes, ).
Unless you define "low output" cardio as crawling at less than 1 mph for 60 minutes, there is no way in hell that 20 miuntes of sprint/walk/sprint matches the caloric consumption and work performed over 60 minutes of even light jogging.
I think true interval training is more effective than HIIT over the long term, although HIIT is probably a good thing every once on a while. True interval training, Olympic style, never lets your heart rate dip below 75% and will take you all the way to the upper reaches of your cardiac abilities and VO2 max. You may puke. This is not a bad thing.
Intervals have been the bedrock of biking running-sports training for decades. The pre-programmed workouts on treadmills and bikes that they call "intervals" don't take your heart-rate high enough, so you have to make your own.
Here's an easy treadmill interval workout:
Jog 400 meters @ 12 minute/mile pace
Sprint 400 meters @ 6-7 minute/mile pace
Jog 200 meters @ 12 minute/mile pace
Sprint 200 meters @ 6-7 minute/mile pace
Jog 200 meters @ 12 minute/mile pace
Sprint 200 meters @ 6-7 minute/mile pace
Jog 800 meters @ 9 minute/mile pace
Sprint 200 meters @ As fast as possible
Jog 400 meters and cooldown
The whole workout only takes a little over 20 minutes, and you will feel your meatbolism really kick up.
I'm sure 20 minutes of HIIT is better than doing nothing, and perhaps for Bodybuilders looking to minimize catabolism it is the best way to do cardio, but for long-term fat burning or fitness goals, I think it is overhyped. If is was so effective at making you fast, professional runners would only do 20 minute workouts.