HIIT Workout videos whip you into shape fast - these fat burning workouts burn a very high number of calories, place a high amount of demand on the muscles, and require some exercise experience - these are tough! HIIT should be done 4x/week maximum; you can do Fitness Blender's non-HIIT, but still challenging lower impact cardio workout videos for calorie expenditure through the rest of the week (see bodyweight cardio playlist). less