Once a week, I do exercise that could be considered "cardio." It gets my heart pumping. But unlike a traditional cardio workout, where you perform low to moderate intensity activity throughout the workout, HIIT training has periods of rest.
The basic structure of a HIIT workout is a warmup followed by intervals of intense exercise and intervals of rest.
I walk down to my local park. It's about a 5 minute walk, and that counts as my warmup. Then I run sprints across the length of the park. I have never been much of a runner, and I still wouldn't say I'm fast, but when I sprint I give it everything I've got. I try to pretend that a bear is chasing me. Or that my baby is on the other end and a bad guy is going to get him if I don't hurry across that field. Or that I'm in a race and this is the last 30 yards to the finish line. It's that kind of a run. Totally. Intense. Focused. Running.
I walk back to where I started and catch my breath. The first two times, I always think, "Why did I think this was so hard last time? This isn't so bad." By the fourth time, I'm starting to remember why I thought it was so hard. And after the 6th time, I can't run back right away. I have to catch my breath a little longer before heading out for another intense sprint. I do this 6 to 10 times in a row and I walk back home.
The reason HIIT training works is that your body doesn't "get used" to it. Just like with progressively adding more difficult weights, you progressively add more challenges with HIIT training- either by making your rest intervals shorter and your intensity intervals longer, or by lengthening the total time of the workout.
Here are some ideas of exercises to perform doing HIIT training:
sprints or hill sprints
Add your own ideas for HIIT in the comments below!
Kat at Body Incredible has some great thoughts on HIIT if you'd like to learn more.