07/18/2017 The Science Behind HIIT

Alli Walsh, Social Media Strategist

The Science Behind HIIT

If you’re into fitness at all, you’ve likely heard the buzz over recent years regarding high intensity interval training (HIIT). In these 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.1 For time-crunched folks, HIIT fits nicely into the day, and the gains prove impressive. Here’s more on HIIT and the benefits it delivers.

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 determine yours. 2) A recovery period follows each burst and involves low intensity moves performed at 40 to 50 percent of maximum heart rate. Total workout time of alternating high and low intensity moves is 20 to 60 minutes.3

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 But research shows that HIIT workouts may deliver gains more quickly that other types of exercise. And it may favor 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 postexercise 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



1,3,8,9,10 Kravitz, Len, PhD. "High-Intensity Interval Training." American College of Sports Medicine. American College of Sports Medicine, 2014. Web. 08 July 2017.
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.
2 "Exercise intensity: How to measure it." Mayo Clinic. Mayo Foundation for Medical Education and Research, 19 May 2017. Web. 08 July 2017.
7 Park, Alice. "Interval Training: Scientists Explain Why It Works." Time. Time, 3 Nov. 2015. Web. 08 July 2017.

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