High-intensity training 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 one’s 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).
Interval training 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 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 methods, exercisers can maximize fat-burning and muscle-building potential through significantly shorter workouts. High intensity interval training (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 training
HIIT 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.
NOTE: Burst training or high intensity interval training is an incredibly effective method for improving fitness in a short time, but it’s also extremely taxing on the body. It is important to start gradually, and then slowly increase the intensity of your workouts.