This article was medically reviewed by Joey Thurman, CSCS, CPT, FNS, a Chicago-based fitness expert and creator of Fast Results program. HIIT workouts, or high-intensity interval training ...

Today we're going to do a High-Intensity Interval Training workout, or HIIT, H-I-I-T. What we'll do is 20 seconds of an exercise, pushing as hard as you can, then taking 10 seconds' rest.

There are several reasons why this happens. Firstly, during HIIT training, your body’s oxygen demand exceeds the supply, so your body needs to replenish this post-exercise, and this in turn burns ...