Why does HIIT training work better than conventional cardio for fat loss? When you do cardio at the same pace, your body adjusts itself to the workload and tries to conserve calories. (After all, your body doesn't know how long or hard you plan to work out.) Interval training forces your body to burn more calories -- and tap into fat stores -- because it has no choice. Science says so: One study at Laval University found people who performed HIIT cardio lost nine times more fat than people who performed moderate cardio at a consistent speed.
The following workouts are simple to follow, just not very easy to do. For each major muscle group, after following the HIIT 100s protocol on your first exercise, you'll do three more sets to failure of the same exercise using your 10-rep max (10RM). Of course, after doing 10 sets of 10 reps, you'll no longer be able to complete 10 full reps with your 10RM weight—probably more like 5-7 reps. On the third set, you'll do a dropset with the same weight you used for HIIT 100s (50% of your 10RM) and do as many reps as possible.
In a way, moderate-intensity physical activity is that "magic pill" a lot of people are looking for, because the health benefits go beyond keeping your waistline trim: Not only can it reduce your risk of cancer, stroke, diabetes and heart attacks, but studies have shown that physical activity can significantly improve the moods of patients with major depressive disorders.