If you haven't noticed already, I am a fan of HIIT. I mostly like HIIT workouts because they are they're fun, and they are tough as hell. However, some of these workouts can be extremely challenging, especially if you haven't built yourself up to do these exercises quickly and properly.
If you're up for the challenge, here's a really intense HIIT workout that only lasts for 7 minutes.
But don't be fooled -- this hurts. A lot.
Here's A Fit Tip:
Since HIIT workouts are very short (but intense), you will not need to carb load, or replenish depleted glycogen levels post workout. However, if you need a boost, try having a very small portion of sweet potatoes before doing this HIIT workout. Also, focus on HIIT being sorta supplemental. You'll want to do other workouts, too.
But nonetheless, this workout kicks ass, and you'll be laying on the floor wondering where your legs went.