High Intensity Interval Training: The Basics

U.S. Navy photo by Photographers Mate 1st Class Aaron Ansarov/Released

Talk of HIIT and the associated benefits has been around for many years, and its popularity continues to grow. HIIT is short for high intensity interval training or high intensity intermittent training, and the concept is becoming increasingly popular among athletes and recreational exercisers alike. But what exactly is HIIT, and perhaps more importantly, is HIIT right for you?

What is HIIT?

HIIT is short bouts of high-intensity exercise (lasting anywhere from 10 seconds to five minutes) alternated with brief periods of either rest or low-intensity exercise.1,2 The most accurate method of determining exercise intensity is continuous monitoring of maximal oxygen consumption (VO2 max), however, this is not a practical or accessible method for most people. A more practical measure of exercise intensity is rate of perceived exertion (RPE). High intensity bouts are performed at either an "all-out effort" or at a hard to very hard RPE.2,3 While HIIT has traditionally been employed as a training method for endurance athletes, it is now also recommended for sedentary individuals, recreational athletes, and in clinical settings to manage disease.3

What are the benefits of HIIT?

Recent studies have found HIIT to be as effective or more effective at enhancing physical performance than traditional endurance-based training.2,3,4 Some of the benefits that lead to performance improvements may include enhanced3,4:

  • Cardio respiratory function (improved heart and lung function)
  • Metabolic function (how well your body creates and uses energy)
  • Peak-power output
  • VO2 max (often used as a measure of physical fitness)

HIIT also offers potential health benefits, including3,5:

  • Resistance to metabolic disorders (such as insulin resistance)
  • Reductions in subcutaneous fat (the kind under the skin, such as around your abdomen and thighs) and total body mass
  • Decreased total and LDL (bad) cholesterol levels and increased HDL (good) cholesterol levels
  • Improved left ventricular ejection fraction (a measure of how much blood your heart pushes to your body with each beat)6

How often should HIIT be performed?

Improved cardiovascular health is seen with just one session of HIIT per week7 although up to three sessions per week have been demonstrated to be effective without increasing risk of injury.8 Regardless of what schedule is chosen, it is important for the body to have time to completely recover in between sessions.8 Recovery may take longer for those who are less conditioned.

Should I include HIIT in my workout routine?

The relatively recent interest in HIIT means there have not been long term studies done to evaluate effectiveness or safety over time, however current research indicates a multitude of health and physical performance benefits.2-9 No studies to date have shown adverse effects or increased risk for injury when proper guidelines are followed.9 These guidelines include not exercising beyond your capabilities, allowing for adequate rest between exercises and workout sessions, and using proper form to complete all movements. For best results, try adding one or two HIIT sessions per week to your exercise routine and work towards a balance of HIIT with continuous aerobic exercise.

How can I learn more?

HIIT workouts should be tailored to each individual's current fitness level and goals. If you are interested in a high intensity interval program, talk to your command fitness leader or local MWR fitness expert. You can also find additional information on the following sites:


1. Dallek L. High-intensity interval training for clinical populations. ACE Fitness. Accessed July 11, 2013.

2. Buchheit M, Laursen P. High-Intenisty Interval Training, Solutions to the Programming Puzzle. Sports Med. 2013;43(5):313-338.

3. Gibala M, Little J, MacDonald M, et al. Physiological Adaptations to Low-Volume, High-Intensity Interval Training in Health and Disease. The Journal of Physiology. 2012;590(5):1077-1084. Accessed July 11, 2013.

4. Gibala M, McGee S. Metabolic Adaptations to Short-term High-Intensity Interval Training: A Little Pain for a Lot of Gain? Exercise & Sport Sciences Reviews. 2008;36(2):58-63. Accessed September 16, 2013.

5. Shiraev T, Barclay G. Evidence Based Exercise: Clinical Benefits of High Intensity Interval Training. Australian Family Physician. 2012;41(12):960-962. Accessed September 16, 2013.

6. Cornish A, Broadbent S, Cheema B. Interval Training for Patients With Coronary Artery Disease: A Systematic Review. Eur J Appl Physiol. 2011;111:579–589. Accessed September 16, 2013.

7. Wisløff U, Ellingsen Ø, Kemi O. High-Intensity Interval Training to Maximize Cardiac Benefits of Exercise Training? Exercise and Sport Sciences Reviews. 2009;37(3):139-146. Link to article. Accessed September 17, 2013.

8. Zuhl M, Kravitz L. HIIT vs. Continuous Endurance Training: Battle of the Aerobic Titans. IDEA Fitness Journal.2012:35-40. Accessed October 3, 2013.

9. Ewing G, Blissmer B, Deschenes M, et al. Quantity and Quality of Exercise for Developing and Maintaining Cardiorespiratory, Musculoskeletal, and Neuromotor Fitness in Apparently Healthy Adults: Guidance for Prescribing Exercise. Medicine & Science in Sports & Exercise. 2011;43(7):1334-1359. Accessed September 17, 2013.