Ask pretty much any trainer what he or she recommends to clients who want to BURN FATfastest, and the answer will likely be HIIT. The reason that high-intensity interval training is so effective is twofold: first, by including big multi-joint exercises (i.e., ones that utilize multiple muscle groups), it requires the body to burn a lot during the workout itself. Second, and more importantly, the body continues to burn calories for hours afterward as it re-seeks equilibrium. What’s even cooler is that you don’t need hours to dedicate to your workout—even 10 minutes can reap results.