Could you list the simple principles behind this type of cardio and its benefits over longer endurance type cardio?
What are its affects on muscle loss? How often should it be done? Can you give us a sample routine?
Can you share any good articles and additional resources that might help us learn mroe about it?
Thanks! 
First of all, I apologize for taking so long to respond. I seriously forgot
Ok, in answer to your first question;
The basic principals behind this are pretty simple in theory and it basically boils down to your bodies three energy systems (ATP-PC, Glycolytic and aerobic systems). While both HIIT and sustained cardio burn calories after a certain amount of time of constantly going at sustained pace, you start to get used to and the body starts not only burning fat but muscle as well since the energy has to come from somewhere, carbs first, then fat and then muscle. Thats what in a nutshell happends when you start tapping into the aerobic energy system in addition, slow twitch muscle fibers (bodybuilding is primarily fast twitch). I've used this analogy before, look at a sprinter then look at a marathon runner, the sprinter will always carry more muscle and less fat than the marathon runner, this is actually a concept that hasn't caught on in the bodybuilding world and still thinks the sustained cardio is the way to go even though there are ton of published studies that show otherwise..but oh well!
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The benefits of training the anaerobic systems ATP-PC, Glycolytic;
Intervals of about 20-30min can burn up to 4-500kcals during training, carbs give alot of the fuel during the high intensity part of the exercise while fat is also burned during the low intensity recovery. Unlike the long sustained "cardio" after your interval training, some studies have shown that your resting metabolic rate is actually still burning by 15-20% more for up to 24hrs. Since you're training at an intense level for a short amount time, muscle will not be tapped into as an energy source (catabolic) thus you retain more muscle.
I remember a couple of years ago Flexingtonsteel and I had a pretty good debate on here about that. He was saying that long sustained cardio was the way to go and I basically said what I did (if I remember correctly)..NOW, if you go to a gym, almost any gym, the interval craze has caught on big time...why? Because it works, and yes even for bodybuilding! Want more efficient training, look to your three energy systems. Here's a little guidline on the three........
Anaerobic System
Time To:
ATP-PC
Glycolytic
Aerobic System
Peak Power/System
<1sec.
20sec.
2-3min.
Maintenance of Peak
10sec.
20sec.
3min.
Total Capacity
10-30sec.
1-2min.
hours
Full Time For Recovery
3min.
1-2hr.
24hr.-48hr.
½ Time For Recovery
30sec.
15-20min.
5-6hr.
Haider, this is just a brief synopsis of why interval training is sooo much better than long sustained type of cardio, if you're doing it for cardiac health fine, but not nearly as efficient as good intense interval training. I will try to post more on this tomorrow.
