Interval training burns fat, spares (or builds) muscle, and takes a fraction of the time of traditional cardio. These things we know.

But what you might not know—what you might never have had beaten into your brain—is the fact that you don’t have to feel confined to a treadmill to make it work. That's right: You don’t have to just do lower-body focused work. You can use weights. You can even—wait for it—have a little fun.

These four interval options help you to add some variety to your HIIT routines and speed up your body’s get-lean response. Train hard, have fun, repeat.