High-Intensity Interval Training (HIIT)


High-intensity interval training (HIIT) involves alternating brief bouts of higher-intensity sessions with either rest or lower-intensity workloads throughout an exercise routine.


Regular exercise training confers various health benefits including preventing and managing hypertension, obesity, type 2 diabetes, dyslipidemia, and cardiovascular disease. Despite the long history of exercise-related health promotions, the general population engagement in regular exercise remains infrequent, with “lack of time” often cited as a barrier to regular exercise training. HIIT therefore has captivated the attention of many researchers due to its superior ability to improve cardiorespiratory fitness and cardiometabolic health for a lesser weekly timecommitment relative to moderate-intensity continuous training (MICT). HIIT is characterized by short bursts of high-intensity training separated by periods of active or passive recovery. This strategy enables unfit individuals to accumulate periods of exercise that would otherwise not be possible if executed continuously. Traditionally, HIIT has encompassed aerobic modalities ( Table 1 Table 2 ).


Table 1. Recommendations for Aerobic HIIT

Dalleck, Lance C. American Council on Exercise ProSource. February 2013. “High-intensity Interval Training for Clinical Populations.”


The HIIT program consists of six separate components:


The first issue that must be addressed prior to integrating an aerobic and/or resistance exercise HIIT into the exercise program is safety. Properly performed, exercise is harmless for the majority of individuals. In fact, a greater risk is associated with remaining physically inactive as compared to commencing regular exercise training. The absolute risk of sudden death during vigorous-intensity, physical activity has been estimated to be one per year for every 15,000–18,000 people. In terms of the specific risk associated with HIIT, it was reported in a 2012 study that after 129,456 hours of moderate-intensity exercise and 46,364 hours of high-intensity exercise in 4,846 high-risk participants, one fatal and two nonfatal cardiac arrests occurred.Researchers in that study concluded that the risk of a cardiovascular event with HIIT was low.


Table 2. Recommendations for Resistance Exercise HIIT

Dalleck, Lance C. American Council on Exercise Certified. January 2017. “How to Integrate Resistance-Exercise HIIT into Your Clients' Programs.”


The physical activity recommendation for American adults is 150 minutes per week of moderate-intensity exercise. Completion of this weekly amount of exercise confers numerous health benefits. Unfortunately, the majority of American adults fall short of recommended physical activity guidelines. The most frequent barrier is a lack of time. It is largely for this reason that HIIT was first considered by the scientific community as a viable option. A large number of scientific studies performed in the decade spanning 2006 to 2016 reported aerobic and resistance HIIT to be a time-efficient and effective strategy for improving cardiorespiratory fitness and cardiometabolic health in both healthy and diseased persons.

Cardiac arrest—
A condition in which the heart suddenly and unexpectedly stops beating.
Cardiorespiratory fitness—
The highest rate at which oxygen can be taken up and consumed by the body during intense exercise, typically determined by maximal oxygen uptake, or VO2max.
Cardiovascular disease—
A class of diseases that involve either the heart or blood vessels; the most common form is coronary artery disease.
Abnormal amount of lipids (e.g., triglycerides, cholesterol) in the blood.
Endothelial function—
The balance between dilating and constricting substances produced by (or acting on) the endothelium (the inner lining of blood vessels).
Excess post-exercise oxygen consumption (EPOC)—
Refers to the overall oxygen consumption (VO2) above resting values during the post-exercise period.
Heart rate reserve (HRR)—
A method used to prescribe exercise intensity (also referred to as the Karvonen method). The heart rate reserve is the difference between maximal heart rate and resting heart rate.
High blood pressure; systolic blood pressure greater than or equal to 140 mmHg, and diastolic blood pressure greater than or equal to 90 mmHg.
Metabolic syndrome—
A constellation of conditions consisting of elevated waist circumference, increased blood pressure, dyslipidemia, and impaired blood glucose. The presence of metabolic syndrome increases one's risk of Type 2 diabetes and coronary artery disease.
Moderate-intensity exercise—
Continuous exercise performed at an intensity between 40%–59% of heart rate reserve (HRR).
Myocardial infarction—
Also known as a heart attack. Occurs when there is a disruption in oxygenated blood flow to part of the heart.
Type 2 diabetes—
Long term metabolic disorder that is characterized by high blood sugar, insulin resistance, and relative lack of insulin.

A group of researchers also studied the effectiveness of 16 weeks of HIIT compared to traditional moderate-intensity, continuous training as a treatment for individuals with metabolic syndrome. The HIIT program consisted of four interval bouts of 4 minutes at 90% HRmax, interspersed with 3-minute active recovery bouts at 70% HRmax, for three sessions per week. It was found HIIT was superior to moderate-intensity, continuous training at improving endothelial function, blood glucose control, and fat metabolism. Another group of scientists investigated the effects of 2 weeks of low-volume, HIIT on metabolic health in a group of patients with Type 2 diabetes. The HIIT program consisted of ten interval bouts of 60 seconds at 90% HRmax, interspersed with 60 seconds of passive rest or very light active recovery, for three sessions per week. The scientists reported that, after only six total exercise sessions, blood glucose control was significantly improved.

  • Is it safe for me to start an exercise training program given my current medical condition?
  • Would it be appropriate for me to try high-intensity interval training?
  • What are some abnormal signs and symptoms I should be aware of when performing high-intensity interval training?
  • What are some of your recommendations for high-intensity interval training in terms of days perweek, interval bouts per session, and interval intensity?
  • Can you refer me to an exercise professional who could assist with designing and implementing a safe and effective high-intensity, interval-training program?

See also Aerobic training ; Cardiorespiratory fitness tests .



American College of Sports Medicine. ACSM's Guidelines for Exercise Testing and Prescription. 9th ed. Philadelphia: Lippincott Williams & Wilkins, 2014.

Porcari, John P., Cedric X. Bryant, and Fabio Comana. Exercise Physiology. Philadelphia: Davis, 2015.


Francois, Monique E., et al. “'Exercise Snacks' Before Meals: A Novel Strategy to Improve Glycaemic Control in Individuals with Insulin Resistance” Diabetologia 57, no. 7 (July 2014): 1437–45.

Francois, Monique E., et al. “Resistance-Based Interval Exercise Acutely Improves Endothelial Function in Type 2 Diabetes” American Journal of Physiology: Heart and Circulatory Physiology 311, no. 5 (September 16, 2016): H1258–67.

Giessing, J., et al. “A Comparison of Low Volume 'HighIntensity-Training' and High Volume Traditional Resistance Training Methods on Muscular Performance, Body Composition, and Subjective Assessments of Training” Biology of Sport 33, no. 3 (September 2016): 241–9.

Rognmo, Øivind, et al. “Cardiovascular Risk of HighVersus Moderate-Intensity Aerobic Exercise in Coronary Heart Disease Patients” Circulation 126, no. 12 (September 2012): 1436–40.

Weston, Kassia S., Ulrik Wisløff, and Jeff S. Coombes. “High Intensity Interval Training in Patients with Lifestyle-Induced Cardiometabolic Disease: A Systematic Review and Meta-Analysis” British Journal of Sports Medicine 48, no. 16 (August 21, 2014): 1227–34.


Dalleck, Lance C. “High-Intensity Interval Training for Clinical Populations.” American Council on Exercise. https://www.acefitness.org/certifiednewsarticle/3051/high-intensity-interval-training-for-clinical.htm (accessed February 5, 2017).

Dalleck, Lance C. How to Integrate Resistance-Exercise HIIT into Your Clients' Programs.. American Council on Exercise. https://www.acefitness.org/certifiedarticle/6203/how-to-integrate-resistance-exercise-hiit (accessed February 5, 2017).

Mayo Clinic Staff. Rev Up Your Workout with Interval Training. Mayo Foundation for Medical Education and Research. http://www.mayoclinic.org/healthy-lifestyle/fitness/in-depth/interval-training/art-20044588.htm (accessed February 5, 2017).


American Council on Exercise, 4851 Paramount Dr., San Diego, CA, 92123, (858) 576-6500, (888) 825-3636, ext. 782, Fax: (858) 576-6564, https://www.acefitness.org .

Mayo Clinic, 200 First St. SW, Rochester, MN, 55905, 1(507) 266-7890, http://www.mayoclinic.org/ .

Lance C. Dalleck, PhD

  This information is not a tool for self-diagnosis or a substitute for professional care.