High-Intensity interval training (HIIT) is a form of exercise that combines two of the most effective fat-burning methods!
The first is high intensity training, which pushes the body to maximum effort to achieve muscle fatigue and maximum oxygen use, in a quick burst. The harder muscles work, the more oxygen they require. This is measured relative to your VO2 max, which is the highest amount of oxygen your body consumes during exercise. Working your body close to VO2 max triggers the after-burn effect, where the body continues to consume oxygen (and burn calories) up to 48 hours after your workout.
The second method is interval training, which alternates periods of intense effort with periods of moderate-to-low intensity effort. Interval training boosts metabolism significantly longer than a steady workout of equal or even greater length (for example a 20 minute workout alternating high/low intensity periods burns more calories than a 20 minute workout of steady intensity). Interval training also builds lean muscle faster than steady state cardio.
By combining these two principles, you can maximize fat-burn and muscle building potential through significantly shorter workouts. Metabolic or HIIT maximizes increased metabolic rate, muscle building and muscle retention during fat loss and increases calorie burn during and after workouts!