If you've read my previous fitness posts you will know that I love workouts that incorporate High Intensity Interval Training (also known as HIIT training). This style of training burns the most amount of calories in a small amount of time,and keeps your body burning calories for up to 24 hours after your workout. Tabata training, is a class of HIIT training that works in the same way, but it can be very intense.
Here's a great 4 minute Tabata workout that seems simple, but can really kick your butt.
For more of a challenge, take a 1-2 minute break after completing this circuit then repeat.