The Research Backing HIIT: High-Intensity Interval Training

The buzzword in the fitness industry this past year was definitely high-intensity interval training, also referred to as HIIT. HIIT reached the number one spot in the 2014 survey for exercise trends published by the American College of Sports Medicine (ACSM). According to one source, HIIT will end up at the number two spot for 2015 on that same ACSM list, replaced by body weight exercise as the new exercise trend. HIIT however is not a new to the spotlight, it has been around for more than a century. Some of the greatest runners in the world have used various forms of HIIT as part of their training. As early as 1912, the Finnish Olympic long-distance runner Hannes Kolehmainen was using interval training in his workouts (Billat 2001). Research has demonstrated that HIIT:

• Improves the performance of competitive athletes.

• Improves health outcomes for recreational exercisers.

• Provides the same benefits of endurance training but with fewer workouts covering less time.

One thing you can bank on, HIIT gets results, when done correctly. HIIT is one of the most effective means of improving cardiorespiratory and metabolic function in both athletes and recreational exercisers. HIIT involves repeated short-to-long bouts of high-intensity exercise (90-100% VO2max) interspersed with recovery periods. The term HIIT can be used to

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describe protocols in which the training stimulus is near maximal effort or the target intensity is between 80 and 100% of maximal heart rate. HIIT typically involves repeated short bouts of exercise (<45 seconds) to long bouts (2-4 minutes) of high-intensity exercise interspersed with recovery periods. Traditional high volume aerobic exercise training has been shown to reduce cardiovascular and metabolic disease risk but involves a significant investment of time. Extremely low volume HIIT has been shown to produce improvements to aerobic function.

Humpreys and Holman credit the famous German coach Woldemar Gerschler, as the person who formalized a structured system of interval training back in the 1930’s. Exercise Physiologists Fox and Matthews have identified the following five variables that need to be adjusted individually for each athlete during a HIIT session:

-Rate and distance of the work interval.

-Number of repetitions and sets during each training session.

-Duration of the rest, recovery or relief interval.

-Type of activity during the rest interval.

-Frequency of training per week.

The following list includes just a few of the many research studies that have been published looking at various health and fitness benefits of HIIT.

  • A 2011 study presented at the ACSM annual meeting showed 2 weeks of HIIT improved aerobic capacity as much as 6-8 weeks of traditional endurance training.
  • A 2006 study found after doing 8 weeks if HIIT subjects could bike twice as long when they started the study while maintaining the same pace.
  • Researchers from Canada’s McMaster University looked at the effects of interval exercise on VO2max. Training was performed on a stationary cycle ergometer for three days each week. The program began with four intervals lasting 30 seconds each, separated by a 4-minute rest period. By the seventh week the number of intervals had increased to ten, while the rest intervals were gradually reduced to 2.5 min. VO2max increased by 9%, demonstrating that significant gains in VO2max could be achieved from exercise of a relatively short duration.
  • A group of researchers from Japan’s National Institute of Fitness and Sport found a high-intensity intermittent training program achieved bigger gains in VO2max than a program of steady cycling. Active male subjects were assigned to one of two groups, each training 5 days per week for 6 weeks. One group followed a training program involving 60-minutes of moderate intensity exercise (@70% VO2max), totaling 5 hours per week. The average improvement in VO2max in this group was 9%. Training sessions involving the other group consisted of eight all-out work bouts, each lasting 20 seconds followed by 10 seconds of rest (Tabata et al., 1997). This group cycled for a total of only 20 minutes per week, but their VO2max still improved significantly by 15%.
  • A study from the University of New South Wales in Australia, found women lost an average of 10.5% of their fat mass after just 15-weeks on a 3x/wk program using 20 minute workouts consisting of 8 second sprints (on a stationary bike) followed by 12 seconds of passive recovery = 60 total sprints. Subjects in a control group lost considerably less fat doing traditional endurance exercise despite spending roughly 400% more time pedaling.


Billat, L.V (2001). Interval training for performance: A scientific and empirical practice. Special recommendations for middle-and long-distance running. Part I: aerobic interval training. Sports Medicine, 31(1): 13-31.

MacDougall, J.D., et al. (1998). Muscle performance and enzymatic adaptations to sprint interval training. Journal of Applied Physiology, 84 (6): 2138–2142.

Tabata I, Irisawa K, Kouzaki M, Nishimura K, Ogita F, Miyachi (1997). Metabolic profile of high intensity intermittent exercises. Med Sci Sports Exerc. 29(3): 390-395.

Gibala MJ, Little JP, van Essen M, Wilkin GP, Burgomaster KA, Safdar A, Raha S, and Tarnopolsky MA (2006). Short-term sprint interval versus traditional endurance training: similar initial adaptations in human skeletal muscle and exercise performance. The Journal of Physiology, 575, 901-911.