S1, E3: Kill two birds with one stone in this brutal HIIT workout for fat loss! Get a high energy workout that will burn fat and slim you down, while sculpting lean muscle by throwing dumbbells into the mix. This HIIT workout is only 20 minutes, but HIIT routines are intended to push you to your cardio threshold, so when you are going through this workout, remember that you are in control of how hard each exercise is. You'll need a set of light weights (3-10lb(. For best results, use a pair of weights that make the last 2 reps challenging.