This article: Key to High Intensity Interval Training found outside comfort zone looked interesting. Thought I would link it!

I've heard of HIIT before and as a matter of fact, an instructor at the gym was just talking about it. It's basically a short but hard workout. I have an app on my phone called Max Capacity Training. They're 16 minute workouts. It gives you the exercises to do and times you. It's great. I only wish I knew approximately how many calories it burned.