07/09/2020 The Science Behind HIIT

Allison Walsh

The Science Behind HIIT

If you’re into fitness at all, you’ve likely heard the term high intensity interval training (HIIT) over the past several years. These intense but effective workouts have been well-loved for years now – and for good reason.

During HIIT workouts, participants take part in repeated, brief rounds of high-effort exercise and rest periods. Because of the intensity required for the high-effort periods, these workouts tend to be shorter in nature than traditional exercise formats. The period of intense exercise is followed by a short period of rest.1 An entire workout may be as short as 15-20 minutes total. For time-crunched folks, HIIT fits nicely into the day, and the gains prove impressive.

HIIT how-to

In HIIT workouts, intense periods of work, ranging from 5 seconds to 8 minutes long depending on exercise difficulty and fitness level, are performed at 80-95 percent of maximum heartbeat. (Here's how to find yours.) 2 A recovery period follows each burst and involves low intensity moves performed at 40 to 50 percent of maximum heart rate.

The main goal during these workouts is to do as much work as fast as possible.[1] Many HIIT workouts use traditional exercise equipment such as cardio machines or weights, but many can be done using only your own body weight making them easy to maintain during times of travel and perfect for a short break during the workday. Perhaps the most famous of the HIIT workouts is the New York Times 7-Minute Workout which was originally published in 2013. Seven years later and it has its own app and a loyal following.3 The workout asks users to do 30 seconds of 12 high intensity moves such as jumping jacks, planks, and lunges, with a 10 second break in between.

How it feels

Simply put, HIIT is hard. It’s supposed to be as it generates greater results in shorter time periods compared to traditional exercise. While doing a HIIT workout, arms and legs feel shaky and exhausted and participants must push through exhaustion to get to the next rest period.4 

Research shows that HIIT workouts may deliver gains more quickly than other types of exercise. Additionally, many may favor it for less fit folks who experience higher rates of the cell stress that increases endurance from HIIT workouts.5 Experienced or endurance athletes experience cell stress as well, but not to the same extent.6

How it works

So what’s the scientific secret behind HIIT? It’s in the details behind that cell stress. During high intensity exercise, chemical channels inside muscle cells that manage calcium variances become confused. This confusion creates a cellular-level change that requires energy production to become more efficient.

To exercisers, this translates into increased endurance and faster muscle gains.7 And the benefits of HIIT go beyond the workout. Overall calories burned are higher on average than traditional workouts because excess post-exercise oxygen consumption, or the post-exercise period where the body is in restoration mode, uses more energy after HIIT workouts, burning more calories than other types of exercise.8 The American College of Sports Medicine reports overall benefits that include improvements to:

  • Aerobic and anaerobic fitness
  • Blood pressure
  • Cardiovascular health
  • Insulin sensitivity
  • Cholesterol profiles
  • Abdominal fat and body weight9

How to get started

There are risks to consider with any new exercise program, so discuss HIIT with your doctor prior to starting. Once you have the go-ahead, do your research. The internet, app world, and streaming television are full of sample HIIT workouts to try, that can be easily modified to fit your fitness level. Start slowly, maybe once a week, and increase to two to three workouts each week.10


1-High intensity interval training (HIIT): Benefits and how to start. (n.d.). Retrieved July 10, 2020, from https://www.medicalnewstoday.com/articles/327474
2-HIIT Workouts to Get You in the Best Shape of Your Life. (2020, February 20). Retrieved July 09, 2020, from https://www.mensjournal.com/health-fitness/hiit-workouts-to-get-you-in-the-best-shape-of-your-life/
3-Reynolds, G. (2013, May 09). The Scientific 7-Minute Workout. Retrieved July 10, 2020, from https://well.blogs.nytimes.com/2013/05/09/the-scientific-7-minute-workout/
4,5,6- Brookshire, Bethany. "High-intensity interval training has great gains - and pain." Science News. Society for Science & the Public, 05 Jan. 2016. Web. 08 July 2017.
7- Park, Alice. "Interval Training: Scientists Explain Why It Works." Time. Time, 3 Nov. 2015. Web. 08 July 2017.
8,9,10- Kravitz, Len, PhD. "High-Intensity Interval Training." American College of Sports Medicine. American College of Sports Medicine, 2014. Web. 08 July 2017. 




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