It can be hard to get in cardio when you have a tight schedule. You need to do classic cardio like running and biking for an hour to make it effective. Instead, you can keep your workout short and sweet by trying High Intensity Interval Training (HIIT). These types of workouts burn more calories in a shorter amount of time. As an added bonus, they keep you burning calories all day long. Let's take a look at some workouts that come in under 20 minutes!