High-Intensity Interval Training (HIIT)

The popularity of high intensity interval training is on the rise. High intensity interval training sessions are commonly called HIIT workouts. This type of training involves repeated bouts of high intensity effort followed by varied recovery times. The intense work periods may range from 5 seconds to 8 minutes long, and are performed at 80% to 95% of a person’s estimated maximal heart rate, the maximum number of times your heart will beat in a minute without overexerting yourself. The recovery periods may last equally as long as the work periods and are usually performed at 40% to 50% of a person’s estimated maximal heart rate. The workout continues with the alternating work and relief periods totaling 20 to 60 minutes.

What are the benefits of HIIT? HIIT training has been shown to improve:

  • Aerobic and anaerobic fitness
  • Blood pressure
  • Cardiovascular health
  • Insulin sensitivity (which helps the exercising muscles more readily use glucose for fuel to make energy)
  • Cholesterol profiles
  • Abdominal fat and body weight while maintaining muscle mass

Why is HIIT Training so Popular?

HIIT training can easily be modified for people of all fitness levels and special conditions, such as overweight and diabetes. HIIT workouts can be performed on all exercise modes, including cycling, walking, swimming, aqua training, elliptical cross-training, and in many group exercise classes. HIIT workouts provide similar fitness benefits as continuous endurance workouts, but in shorter periods of time. This is because HIIT workouts tend to burn more calories than traditional workouts, especially after the workout. The post-exercise period is called “EPOC”, which stands for excess postexercise oxygen consumption. This is generally about a 2-hour period after an exercise bout where the body is restoring itself to pre-exercise levels, and thus using more energy. Because of the vigorous contractile nature of HIIT workouts, the EPOC generally tends to be modestly greater, adding about 6 to 15% more calories to the overall workout energy expenditure.

How do You Develop a HIIT Exercise Program?

When developing a HIIT program, consider the duration, intensity, and frequency of the work intervals and the length of the recovery intervals. Intensity during the high intensity work interval should range ? 80% of your estimated maximal heart rate. As a good subjective indicator, the work interval should feel like you are exercising “hard” to “very hard”. Using the talk test as your guide, it would be like carrying on a conversation, with difficulty. The intensity of the recovery interval should be 40-50% of your estimate maximal heart rate. This would be a physical activity that felt very comfortable, in order to help you recover and prepare for your next work interval. The relationship of the work and recovery interval is important. Many studies use a specific ratio of exercise to recovery to improve the different energy systems of the body. For example, a ratio of 1:1 might be a 3-minute hard work (or high intensity) bout followed by a 3-minute recovery (or low intensity) bout. These 1:1 interval workouts often range about 3, 4, or 5 minutes followed by an equal time in recovery. Another popular HIIT training protocol is called the “spring interval training method”. With this type of program the exerciser does about 30 seconds of ‘sprint or near full-out effort’, which is followed by 4 to 4.5 minutes of recovery. This combination of exercise can be repeated 3 to 5 times. These higher intensity work efforts are typically shorter bouts (30 seconds with sprint interval training).

What are the Safety Concerns with HIIT Training?

Persons who have been living rather sedentary lifestyles or periods of physical inactivity may have an increased coronary disease risk to high intensity exercise. Family history, cigarette smoking, hypertension, diabetes (or pre-diabetes), abnormal cholesterol levels and obesity will increase this risk. Medical clearance from a physician may be an appropriate safety measure for anyone with these conditions before starting HIIT or any exercise training. Prior to beginning HIIT training a person is encouraged to establish a foundational level of fitness. This foundation is sometimes referred to as a “base fitness level”. A base fitness level is consistent aerobic training (3 to 5 times a week for 20 to 60 min per session at a somewhat hard intensity) for several weeks that produces muscular adaptations, which improve oxygen transport to the muscles. Establishing appropriate exercise form and muscle strength are important before engaging in regular HIIT to reduce the risk of musculoskeletal injury. Regardless of age, gender and fitness level, one of the keys to safe participation of HIIT training is for all people to modify the intensity of the work interval to a preferred challenging level. Safety in participation should always be primary priority, and people should focus more on finding their own optimal training intensities as opposed to keeping up with other persons.

How Many Times a Week Can You do a HIIT Workout?

HIIT workouts are more exhaustive then steady state endurance workouts. Therefore, a longer recovery period is often needed. Perhaps start with one HIIT training workout a week, with your other workouts being steady state workouts. As you feel ready for more challenge, add a second HIIT workout a week, making sure you spread the HIIT workouts throughout the week.

Interval training has been an integral part of athletic training programs for many years because a variety of sport and recreational activities require short bursts of movement at high intensities. Interval training is becoming an increasingly recognized and well-liked method of training. The incorporation of interval training into a general conditioning program will optimize the development of cardiorespiratory fitness as well as numerous other health benefits.

Give HIIT a try

Republished with permission of the American College of Sports Medicine. Copyright © 2015 American College of Sports Medicine.

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