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What is HIIT cardio? If you are gasping for air every time you walk up a set of stairs and want that to stop – try HIIT. Research studies indicate that people can use high-intensity interval training or HIIT to receive awesome fitness results in as little as two 10-minute sessions per week [1]. Best of all, HIIT can be done with most forms of cardio.
Just make sure you are able to perform those exercises safely and without pain.
I found that many of the articles about HIIT included unnecessary time-wasters and unfounded claims. The articles that did use scientific evidence tended to be full of jargon and were confusing. I spent 20 hours researching and integrated over 40 citations from scientific, peer-reviewed articles.
I wanted to provide a clear, compelling, science-backed response to the question: ‘what is HIIT cardio?’ …without the unnecessary fluff or unfounded jargon.
Keep reading to find out what leading HIIT researchers [2] have found to be the minimum effective dose of HIIT. We’ll dive into clear, science-based action steps that will give you the same awesome health benefits, without the time-consuming, habit-sabotaging extras that prevent too many people from sticking with HIIT.
Why Do HIIT? What Is HIIT Cardio?
If you are healthy and comfortable doing moderate-intensity cardio sessions and would like to mix it up, you might want to include 2-3 HIIT sessions into your exercise routine each week.
HIIT is aimed to improve your body’s ability to take in and use oxygen [3]. To do this, HIIT has you push yourself with high-intensity exercise for short durations (typically between 10-30 seconds). After the high-intensity interval, you move into an interval of lower intensity exercise. Then repeat for 3-10 cycles.
After reviewing multiple randomized controlled trials, Dr. Shigenori Ito et al. [4] concludes that HIIT led to multiple health and fitness benefits based on a wide range of indicators related to:
- skeletal muscles [5]
- risk factors [6]
- vasculature [7]
- respiration [8,9]
- autonomic function [10]
- cardiac function [11,12,13,14]
- exercise capacity [15]
- inflammation [16]
- quality of life [17]
- maximal oxygen uptake (VO2 peak) [18] and
- endothelial function [19].
More good news about HIIT can be found in the Journal of Applied Physiology, Nutrition, and Metabolism. Dr. Patricia Andrews et al. [20] explains that shorter HIIT sessions have similar fat-burning potential over a 24-hour period compared to longer, lower-intensity sessions.
Similarly, Dr. Cristine Lima Alberton et al. [21] describes in the European Journal of Applied Physiology, that HIIT sessions may result in burning more calories even after the workout.
How Do You Know If You Are Exercising At A High Enough Intensity For HIIT?
Leading HIIT researchers, Drs. Niels Vollaard and Richard S. Metcalf [22], advise that many people will see the best results, if they aim to make the higher intensity intervals to feel ‘somewhat hard’ which is about a ‘13’ on the Borg Rating of Perceived Exertion (RPE) scale [23] (described below).
In the Journal of Occupational Medicine, Dr. Nerys Williams [24] explains that the Borg RPE scale [25] can be used to self-assess how intense you are exercising based on physical sensations such as:
- increased heart rate
- rate of breathing
- muscle fatigue, and
- sweat
To illustrate, Dr. Nerys Williams [26] describes that according to the Borg RPE scale, a score of:
- 6 feels like “no exertion at all.”
- “9 corresponds to ‘very light’ exercise which, for a healthy person, is equivalent to walking slowly at his or her own pace for several minutes.
- ‘13’ feels ‘somewhat hard’ but the individual still feels able to continue.
- [‘15’ is hard or heavy exercise]
- 17 is ‘very hard.’ A healthy person can continue but must push themselves beyond their feeling of being very fatigued.
- 19 is extremely strenuous exercise—for most people, the hardest they have ever experienced” [27].
- 20 is maximal exertion.
The higher intensity cycles of HIIT could range anywhere between 13 and 20 on the Borg RPE scale [28]. The lower intensity cycles might be between 9 (‘very light’) and 12 on the Borg RPE scale.
Personally, I prefer to stick to Drs. Niels Vollaard and Richard S. Metcalf’s [29] findings. I have found that taking my HIIT sessions too far past ‘somewhat hard’ or a ‘13’ on the RPE has made me way less likely to show up for my next HIIT sessions.
By focusing on consistency and the minimum effective dose of HIIT, you may soon find that your former self’s ‘maximal exertion’ (or ‘20’ on the RPE) has become your new ‘somewhat hard’ (or ‘13’ on the RPE).
If in doubt, you can also use a heart rate monitor to help you find your target heart rate zone for HIIT.
As described by the Centers for Disease Control and Prevention [30]:
“A high correlation exists between a person’s perceived exertion rating times 10 and the actual heart rate during physical activity; so a person’s exertion rating may provide a fairly good estimate of the actual heart rate during activity (Borg, 1998).
For example, if a person’s rating of perceived exertion (RPE) is 12, then 12 x 10 = 120; so the heart rate should be approximately 120 beats per minute.
Note that this calculation is only an approximation of heart rate, and the actual heart rate can vary quite a bit depending on age and physical condition.”
Can Shorter HIIT Sessions Really Be As Effective As Longer Ones?
At the University of Stirling, Drs. Niels Vollaard and Richard S. Metcalfe [31] explain that 2-3 reduced-exertion intervals, lasting 10-20 seconds may be more beneficial to a wider range of people than longer HIIT sessions:
“In our own laboratory, we have demonstrated that 6 weeks of 3-weekly 10-min sprint interval training sessions involving just two 20-s ‘reduced-exertion HIIT’, or REHIT [completed at a ‘13’ or ‘somewhat hard’ rating of perceived exertion] is sufficient to improve VO2 max by 10–13% [32, 33]”
In their study, Drs. Niels Vollaard and Richard S. Metcalfe [34] found that the time commitment could be as low as two 10-15 minute sessions or a total of 20-30 minutes per week.
This is a fraction of the time that ‘fitness experts’ often tout as requirements for HIIT sessions.
Drs. Niels Vollaard and Richard S. Metcalfe [35] also note that:
“These shorter/easier protocols have the potential to remove many of the common barriers to exercise” [36].
So many people are short on time and would be more likely to commit to shorter workouts. Drs. Vollaard and Metcalfe [37] note that these shorter sessions lead to similar health benefits as programs that require more and longer intervals that take more time:
“To date, all the available evidence suggests that sprint interval training protocols with fewer (two to three) and shorter (10–20 s) sprints are as good as or better than the classic sprint interval training protocol at improving important health markers” [38]
In their recent meta-analysis of 34 research studies, Drs. Vollaard and Metcalfe [39] conclude:
“The improvement in VO2 max with SIT is not attenuated with fewer sprint repetitions, and possibly even enhanced.” [40]
So wait a minute…are you saying that the findings of leading HIIT researchers suggest that I could bust out one of these HIIT sessions during my 15-minute break at work without changing out of my uniform?
Drs. Vollaard and Metcalfe [41] surmise:
“In our experience, the sweat-response to this protocol is low, which removes the need for changing into exercise clothes or having a shower after exercise; our research participants tend to do exercise in their regular clothes” [42].
Don’t have access to a gym? No problem!
Dr. Mary Allison et al. [43] conducted a study with 31 untrained, sedentary women between the ages of 24-34 years old and found that simply climbing stairs can be a practical and time-effective way to noticeably improve fitness using HIIT.
How Exactly Do You Do HIIT? What Is HIIT Cardio?
You can do HIIT just about anywhere. You don’t need any special equipment and there is no one right way to do it.
There are multiple ways to do HIIT. Pretty much any form of cardio that you can safely do free of pain can be used in a HIIT workout.
For example, HIIT can be done through stair climbing, running, skipping, swimming, biking, rowing, and many other forms of cardio exercise.
This makes it a great ‘go-to’ for people with varying schedules and for those who have to travel a lot.
During the COVID-19 shutdown, I did plenty of HIIT workouts in my house (think that motor drill you’ve probably seen in some football movies). After things opened back up again, riding my bike up the same steep hill left me breathing with ease. Before the shutdown, I was gassed for the rest of the ride to work.
Whichever form of HIIT you choose, it is important to remember to warm up first and cool down after.
One way to do HIIT is to do your high-intensity interval for 10-30 seconds followed by dropping it down to a lower intensity for 2.5 minutes or until you catch your breath. Then ramp it back up to another high-intensity interval and repeat.
Depending on one’s fitness and comfort levels, you may start with performing just one 5 or 10-second high-intensity interval followed by a longer low-intensity interval.
As your fitness levels improve, you might want to mix it up by increasing the number of or duration of the high-intensity intervals.
Here Is An Example Of A Super-Effective 10-15 Minute HIIT Workout That Can Be Done With Little Or No Equipment: What Is HIIT Cardio?
- Warm-up (here is a video that can guide you through a full body warm-up
- 1-minute of low-intensity jogging or walking on the stairs (or insert your chosen form of cardio exercise)
- 20-second higher intensity interval (aim for a 13 = ‘somewhat hard’ on the Borg RPE scale)
- Lower intensity cycle for 2.5 minutes: aim to make this feel like somewhere between a 9 (‘very light’) and 11 on the Borg RPE scale.
- 20-second higher intensity interval (aim for a 13 = ‘somewhat hard’ on the Borg RPE scale)
- Lower intensity cycle for 2.5 minutes: aim to make this feel like somewhere between a 9 (‘very light’) and 11 on the Borg RPE scale.
- 20-second higher intensity interval (aim for a 13 = ‘somewhat hard’ on the Borg RPE scale)
- Cooldown: Lower intensity cycle for 2.5 minutes: aim to make this feel like somewhere between a 9 (‘very light’) and 11 on the Borg RPE scale.
There you have it! A HIIT workout that can be done at home or during your break at work in 15 minutes.
Action steps:
- At the start of each week, schedule 3 of the above HIIT sessions into your breaks or other convenient times.
- Answer the following: When, where, and with whom will you complete your first, second, and third 10-15 minute workouts?
- For example, “after I have finished my lunch by 12:40 pm, I will go to the stairs with my co-worker, Jesse, to complete my 15-minute HIIT sessions on Monday, Wednesday, and Friday).”
- Set a reminder on your phone and simply walk to your pre-planned starting location (this will make it more likely that you will complete it.
- Load the warm-up video on your phone, countdown from 5, and begin your HIIT session …in 5-4-3-2-1 – go!
After a few weeks of crushing your HIIT sessions, your fitness will very likely improve. Naturally, you may find that you will have to move your body in order to feel like you are pushing yourself to a 13 (‘somewhat hard’) on the Borg RPE scale.
In a short while, you might also notice that walking up a few flights of stairs no longer leaves you winded.
What are some precautions and considerations before using HIIT?
Despite the research, it is important to consult your medical and health professionals before starting a HIIT program to ensure it is safe for you.
Research studies indicate that HIIT safely provides health benefits to a wide range of people including the following:
Additionally, Dr. Amundsen et al. [47] acknowledges that “Interval training has been shown to improve cardiovascular function in patients with:
- angina pectoris [48],
- metabolic syndrome [49],
- heart failure [50], and
- also in healthy subjects [51].”
As mentioned before, make sure you warm-up. Not only will a warm-up help prevent injuries and strains, but it can also help you start your session with more intensity and will provide a better workout.
It is also essential to stick to exercises that you know how to do properly in terms of form and practice. When learning new exercises it is always better to take it slow to get the proper form down before ramping up the intensity.
If you have issues with your bones or joints, it might be best to choose exercises that are low impact.
If you are unsure, run it by a physical therapist or other health professional. I often ask my physical therapist to check my form and intensity on exercises. He hasn’t turned me away yet and it gives me that extra confidence that I am doing my workouts properly with less risk of injury.
As always, consult with a medical professional before engaging in a new cardio training program.
Summary: What is HIIT Cardio?
If you are looking for a way to improve your health or fitness even faster, check out my article that answers the common question: How many calories for fat loss?
