HIIT: High Intensity Interval Training, Explained

High Intensity Interval Training (HIIT) is one of the biggest trends in the fitness industry right now! But how well do we really understand HIIT? This post will outline the benefits of HIIT and how you can start incorporating it into your weekly workouts. Before beginning a high intensity/vigorous level fitness program we should understand the basics.

What is HIIT

High Intensity Interval Training (HIIT) is a period of high intensity exercise followed by a period of lower intensity exercise.

Intervals are described with a work to rest ratio (work:rest). For example 20 seconds work and 10 seconds of recovery is shown as 20:10. Now that you know some of the terms let’s talk benefits.

Benefits of HIIT

If you are interested in HIIT then you are probably already familiar with some of the benefits of cardio training:

  • Decreased heart rate and blood pressure
  • Increased resistance to fatigue
  • Prevention of weight gain
  • Reduced depression and anxiety
  • Improved activities of daily living

HIIT has the added benefit of:

  • Reduced Time (75 minutes of Vigorous per week or 150 per Week Moderate)
  • Ability to sustain higher intensities of exercise for longer periods
  • Improved cardiorespiratory fitness
  • Increased resistance fatigue
  • Ability to continue to burn calories at rest, aka Excess Post-exercise Oxygen Consumption (EPOC)

By slowly adding bouts of interval training we can decrease the length of our workouts and increase the efficiency, working harder and smarter to meet our goals faster.

Measuring Intensity

How can you tell if your exercise is vigorous enough to be considered HIIT?

The 2 main ways to measure intensity are heart rate (HR) and rating of perceived exertion (RPE). If you have a heart rate monitor I recommend using your target heart rate range (THRR), but if not RPE is another effective way to measure intensity.

Measuring Heart Rate:

First you’ll need to measure your resting HR (RHR). Best to take this right after you wake up. Then you can use the following formula to measure your heart rate reserve (HRR) and your training heart rate (THR):

Karvonen Equation:
Target Heart Rate(THR) = (intensity) x [Heart Rate Reserve = Max Heart Rate(220-age) – Resting Heart Rate] + Resting Heart Rate
Larissa is a 30 year old female with a resting HR of 70 BPM. She wants to know her target heart rate at 80% effort.
THR = (.80) x [ (220-30) – 70 ] + 70 -> THR of 80% = 166 BPM

Measuring RPE:

There are 2 different RPE measurements, the 6-20 scale and the 1-10 scale. The 6-20 scale is nice for us fitness geeks because it matches up with your heart rate. A 6 is equivalent to 60 BPM a 20 is almost 200 BPM. But, a scale of 1-10 is much easier to remember when you’re working really hard. So we’ll focus on your RPE of 1-10:

Rating of Perceived Exertion

% HRR RPE Description
  0 No Exertion at ALL
  1 Light
40-70% 3 Moderate
70-80% 5 Somewhat Hard
80-85% 7 Hard
  9 Very Hard
  10 Maximal Exertion

Vigorous/Very Hard is considered an RPE of > 7.  At this level you will be breathing hard and fast. You are having to work hard to complete the exercise. You are not able to say more than a few words without pausing for a breath.

Moderate to Light is an RPE of < 4, where you are able to catch your breath and talk comfortably.

How to Safely Incorporate HIIT Into Your Current Routine

If you are new to interval training, Fartlek training is a great way to get started. You move as hard and fast as you can (an RPE of > 7) then you slow down or actively recover until you feel you are ready to go again.

American College of Sports Medicine (ACSM) recommends you incorporate Vigorous/Very Hard conditioning no more than 3 days a week at bouts of 20 to 25 minutes per session. Remember to incorporate a 5-10 minute warm up and a 5-10 minute cool down along with your work out.

Advanced HIIT Programming

Now that you are familiar with some basic HIIT programming, let’s look at one of the more popular advanced techniques: Tabata.

Tabata is characterized by a short bout (20 seconds) of high intensity exercise (RPE of >7) followed by a short bout (10 seconds) of recovery (RPE of 3-4). Tabata programming includes 8 sets of 20:10 intervals, for a total of 4 minutes of work. The very short rest periods are what make this such a tough interval program. It’s a great technique for improving overall cardio fitness. And it is one of my favorite programs to teach!

Do you HIIT? What kind of programming have you tried?

Remember HIIT can come in all shapes and sizes so I recommend meeting with a certified personal trainer or running coach to determine which strategy will work best for you.

Health and Happiness,




  • American Council on Exercise (2010). ACE Personal Trainer Manual: The Ultimate Resource For Fitness Professionals (4th ed.). SanDiego, CA: American Council on Exercise.
  • American Council on Exercise (2010). Have Researchers Discovered the Ideal HIIT Formula?
  • American College of Sports Medicine (2010). ACMS’s Guidelines for Exercise Testing and Prescription (8th ed.). Philadelphia: Wolters Kluwer/Lippincott Williams & Wilkins.
  • American College of Sports Medicine (2010). ACSM’s Resource Manual for Guidelines for Exercise Testing and Prescription (6th ed.). Baltimore, MD: Lippincott, Williams, & Wilkins.
  • Mylrea, Mindy (2013). Tabata Bootcamp Instructor’s Guide. Savvier, LP
  • National Strength and Conditioning Association (eds)(2008). Essentials of Strength Training and Conditioning (3rd ed.). Champaign, IL: Human Kinetics
  • US Department of Health and Human Services (2008). 2008 Physical Activity Guidelines for Americans: Be Active, Healthy and Happy

Larissa Brown

Larissa Q. Brown, MS, CHES, ACSM EP-C, ACE-CPT, AFAA-GEI is a self-proclaimed fitness geek. She is a fitness educator and trainer with more than 8 years in the health and fitness industry, educating clients and empowering them to meet their goals. She currently serves as an Adjunct Lecturer at Georgia Institute of Technology and she provides workshops, group fitness, and personal training in the Atlanta, GA area and online. Follow her on her blog, Certified Fitness Geek.

One thought to “HIIT: High Intensity Interval Training, Explained”

  1. I was curious of HIIT until I have tried it once and I dont think it is something that is going to work for me. Losing weight drastically doesn’t seem to be a good idea . If you really want to lose weight and get a long term result, eat healthy and work on a diet plan and exercise but do not over-do it as getting too much exercise can have serious consequences for your body and brain.

Leave a Reply

Your email address will not be published. Required fields are marked *