More Health and Fitness News & Tips at Greatist.THE COMPLETE GUIDE TO INTERVAL TRAININGTargeting Maximum Fat Loss Through High-Intensity Interval TrainingHigh-intensity interval training (HIIT) is a popular 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 ones VO2 max, which is the highest amount of oxygen your body consumes during exercise. Working your body close to its VO2 max triggers the afterburn effect, where the body continues to consume oxygen (and burn calories) up to 48 hours after the workout (it takes approximately five calories to consume one liter of oxygen).The second method is interval training, which alternates periods of intense effort with periods of moderate-to-low intensity effort. Interval training boosts metabolismsignificantly longer than a steady workout of equal or even greater length (for example, a 20 minute workout of alternating high/low-intensity periods burns more calories than a 20 minute workout of stead intensity). Interval training also builds lean muscle tissue faster than steady state training.By combining the above two principles, exercisers can maximize fat-burning and muscle-building potential through significantly shorter workouts. HIIT maximizes increased metabolic rate, optimizes muscle building and muscle retention during fat loss, and increases calorie burn during and after workouts.THE SCIENCE BEHIND INTERVAL TRAININGHIIT taxes and maximizes both aerobic and anaerobic fitness, while cardio addresses aerobic only. Aerobic respiration requires oxygen to generate energy in the form of ATP, while anaerobic respiration does not. HIIT affects muscle tissue at the cellular level, actually changing mitochondrial activity in the muscles themselves. Studies indicate as little as 27 minutes of HIIT three times per week produces the same anaerobic and aerobic improvement as 60 minutes of steady state cardio five times per week.INTERVAL TRAINING PROTOCOLSInterval training protocols differ in terms of length for both high and low-intensity intervals, the ratio of high to low-intensity, and the level of intensity during workouts. Three leading protocols are the Tabata Method, Little Method, and Turbulence Training.The Tabata Method was developed in 1996 by Dr. Izumi Tabata of Japan. It involves high-intensity spurts at 170% of ones VO2 max. The workouts total four minutes and involve 20 seconds of high intensity followed by 10 seconds of rest for eight cycles. The recommended frequency of Tabata workouts is between two and four times per week. Tabata is best for those who are already fit and are looking for a workout that requires very little time. The Tabata Method can also be performed with strength training movements.To implement the Tabata Method, try the following. Start with a three-minute warm-up, then sprint for 20 seconds. Rest (walk) for 10 seconds, then repeat the sprint/walk cycle for a total of eight cycles.The Little Method was developed by Drs. Johnathan Little and Martin Gibala in 2009. It involves high-intensity workouts at 95% of ones VO2 max. The protocol calls for 60 seconds of high intensity followed by 75 seconds