8 Reasons HIIT Workouts are So Effective

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8 Reasons HIIT Workouts are So Effective

Time is one of our most precious resources and we never seem to have enough of it. Some days, it might be easy to skip a workout because you feel that you might not have enough time to make it worthwhile. But you don’t need to spend hours in the gym to see results—you simply need to make sure that the time you do spend exercising is as efficient and effective as possible.

Here are eight reasons why you can spend less time exercising with high-intensity interval training (HIIT) and still get great results:

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.

One of the most common misperceptions about exercise that it is necessary to spend hours busting your butt and sweating buckets to obtain benefits like weight loss, muscle growth and improved overall health and well-being. Instead of working longer, work smarter by using short intervals of extremely high-intensity exercise. HIIT is extremely effective, but it can place a tremendous amount of stress on the body. Therefore, it should only be performed two to three times a week with at least 48 hours between exercise sessions to allow a full replenishment of energy stores and to repair of involved muscle tissue. It is still possible to exercise the day after a HIIT session, but it should be a low- to moderate-intensity activity and use different muscle groups or movement patterns than those used in the high-intensity workout.

For individuals with a training goal related to increasing aerobic endurance, such as competing in a 10K, marathon or triathlon, it is still important and necessary to do high-volume LSD training. For individuals training for an endurance event, using a HIIT protocol can help to maintain your training efforts on those days when time is short and the temptation to skip a workout is at its peak.  

Pete McCallPete McCall Contributor

Pete McCall, MS, CSCS, is an ACE Certified Personal Trainer and long-time player in the fitness industry. He has been featured as an expert in the Washington Post, The New York Times, Los Angeles Times, Runner's World and Self. He holds a master's degree in exercise science and health promotion, and several advanced certifications and specializations with NSCA and NASM.

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