1. Anaerobic interval training uses the body's reserves of energy and, after a workout, metabolism stays elevated and continues to burn calories for hours after the workout. This is due to something called the excess post-exercise oxygen consumption (EPOC) effect. With HIIT, you not only burn a lot of calories during the workout, but because of the high intensity you will continue to burn calories as your body replaces energy and repairs muscle proteins damaged during exercise.
2. Not only does your body metabolize fat for fuel during the workout, during the post-exercise recovery period after HIIT exercise the body will tap into fat stores for the energy required to restore it to its normal resting state.
3. Your body burns calories at a rate of 5 calories per liter of oxygen consumed. In general, using exercise to increase the oxygen demands on your body will increase total caloric expenditure both during and after the workout. Short intervals of extremely high-intensity exercise involving a lot of muscle mass require a tremendous amount of oxygen, during both the work interval and the recovery periods.
4. HIIT produces a significant amount of metabolic waste, including hydrogen ions and lactic acid. The major reason for an active recovery interval is to remove these waste products to allow the involved muscles to perform the next high-intensity bout. As a result, HIIT workouts train your body to tolerate and quickly recover from periods of high-intensity exercise.
5. HIIT can promote a number of physiological benefits, such as increased mitochondrial density, improved stroke volume, improved oxidative capacity of muscle and enhanced aerobic efficiency, which was previously thought to occur only as a result of long, slow distance (LSD) training protocols.
6. HIIT places a significant amount of metabolic stress on muscle tissue. As part of the repair process, the body will produce elevated levels of human growth hormone, testosterone and insulin-like growth factor-1 to repair damaged muscle proteins, which lead to increases in muscle volume and definition.
7. Many health clubs and workout studios are applying this science to develop group fitness programs that feature HIIT workouts in formats that are 30 minutes or less. These formats enable you to do more work and receive numerous health benefits in less time.
8. Exercise intensity can be measured with a scale of perceived exertion, where 1 is low intensity and 10 is the highest intensity you can tolerate. For the greatest benefits, HIIT should be performed at an eight or higher for periods lasting 30 seconds or less (or to the point of breathlessness). Recovery intervals should be as long or slightly longer than the work interval (or until breathing is quick, but under control). An effective workout should have a five- to seven-minute warm-up period to elevate heart rate, a minimum of five high-intensity work intervals and a four- to six-minute cool-down period to help start the recovery process.