Are HIIT Workout Benefits All They’re Made Out to Be?
Key takeaways:
HIIT refers to “high-intensity interval training”, which alternates between work intervals (where heart rate > 85% of maximum heart rate) and rest intervals.
HIIT workout benefits include a higher post-exercise calorie burn, muscle mass preservation during caloric deficit, and VO2 max improvements.
That said, such benefits do not translate to superior health and weight loss outcomes in the long term when compared to steady-state training.
Doing HIIT as it’s meant to be done is incredibly challenging; ultimately, it isn’t a great fit for everyone.
You’ve probably seen headlines like “Do HIIT Workouts to Lose Weight and Get Fitter in Less Time” while scrolling online.
And chances are, while you might have heard the faint ringing of alarm bells (clickbait alert!), your eyes have already snagged onto these words: “less time”. Do less but get more? It’s an irresistible offer — calling out to your soul as sugar does to ants.
But do HIIT workout benefits truly stand up to scientific scrutiny? That’s what we’ll explore in this article.
What is HIIT?
HIIT stands for “high-intensity interval training”. It’s a type of cardio. For full context, structured cardio is usually categorized into two types based on intensity level:
Steady-state training: Features lower-intensity efforts that can be maintained for a prolonged period. Splits further into two:
Low-intensity steady-state (LISS) cardio: Your heart rate typically stays below 70% of your maximum heart rate (the highest number of beats your heart can pump per minute under high stress).
Moderate-intensity steady-state (MISS) cardio: Where your heart rate gets elevated to 70% to 84% of its maximum heart rate.
Interval training: Features higher-intensity efforts, where heart rate routinely exceeds 85% of maximum. Because it’s physiologically impossible to sustain such high-intensity efforts for an extended period, intermittent rest periods are required, leading to an alternating series of work and rest intervals. Also splits into two:
High-intensity interval training (HIIT): Alternates between work intervals (where your heart rate reaches or exceeds 85% of the maximal value) and lower-intensity rest intervals, which can consist of active recovery (continuing to exercise at a very low intensity) or passive recovery (stopping exercise and resting completely).
Sprint interval training (SIT): Involves maximal-intensity (i.e., you go all out) work intervals interspersed with active or passive recovery intervals.
Does the HIIT workout provide any unique benefits?
Or, in other words, how is HIIT (supposedly) superior to steady-state training? Let’s see what the research says.
#1: Induces excess post-exercise oxygen consumption (EPOC)
A HIIT workout forces your body to tap into the anaerobic energy pathways to produce the ATP or energy it needs to fuel the activity.
So, in some sense, your body would need to make up for the “oxygen debt”, also known as excess post-exercise oxygen consumption or EPOC, incurred during the exercise before it can return to homeostasis.
And it does so by consuming more oxygen post-exercise.
As a result, your metabolic rate will remain elevated, and you’ll burn more calories (compared to steady-state training) even after wrapping up a HIIT workout.
A 2006 study published in the Journal of Sports Sciences found that the EPOC effect associated with high-intensity interval training could produce a 6% to 15% increase in overall calorie consumption.
#2: Builds and maintains muscle mass
In an attempt to create the calorie deficit necessary for weight loss, many people turn to and rely exclusively on steady-state cardio.
That’s problematic because the body doesn’t care how it sheds the kilograms (i.e., whether it comes from muscle or fat mass), only that it does. And it turns out, the more muscle mass an individual loses during a diet, the more likely they’ll:
Experience higher levels of hunger and, thus
Regain the weight they’ve lost
Meaning? You should always try your best to maintain or even build muscle mass, even in a calorie deficit.
Compared to steady-state training, HIIT better resembles the demands of resistance-based training — the “gold standard” for preserving and/or promoting muscle mass.
This, in turn, explains why a 2023 study published in Sport and Exercise Nutrition found a 3-month HIIT regimen prevented the loss of muscle mass caused by a hypocaloric Mediterranean diet. And also why several studies have found HIIT effective at promoting muscle growth.
#3: Enhances exercise capacity
Here’s a new exercise terminology to know: VO2 max.
It measures your capacity to take in, transport, and use oxygen during exercise.
The more you train, the more efficient your cardiorespiratory system (i.e., lungs and heart) becomes at delivering oxygen-rich blood to your body during exercise, and the better your VO2 max.
Which do you think is better at improving your VO2 max — steady-state training or HIIT?
The latter wins. A large body of scientific literature shows that HIIT increases VO2 max to a greater extent than steady-state training for a given training volume.
#4: Improves insulin sensitivity
Many studies indicate that HIIT could improve glycemic control in population groups with and without type 2 diabetes and metabolic syndrome.
But here’s the important question. Does it improve glycemic control to a greater extent than steady-state training? Apparently not, according to a 2015 meta-analysis of 50 studies published in Obesity Reviews.
More specifically, the researchers found that while HIIT led to clinically relevant improvements in glucose control (with regards to fasting glucose, HbA1c, and fasting insulin), they were not superior to those seen with steady-state training.
Rethinking HIIT as a weight loss and health “hack”
On that note, it’s time we re-examined the HIIT workout’s benefits.
Yes, it could ramp up your calorie burn and preserve/build more muscle mass than steady-state training, but does that actually translate to better weight loss results in the long term?
Well, a 2021 meta-analysis published in Sports compared the effects of HIIT and steady-state training on body composition to see which resulted in the most fat loss and found … no difference between the modalities.
Why? Doesn’t HIIT burn more calories than steady-state training?
Ah, see, here’s the catch. We never explicitly said that — we only mentioned that HIIT would help you see a 6% to 15% increase in calorie burn post-exercise.
To illustrate, a person with a basal metabolic rate of 1,600 calories would burn:
243.3 calories performing steady-state training (7.3 METs*)
183.3 calories doing HIIT (11.0 METs), with a one-to-one work-to-recovery ratio (60 seconds on, 60 seconds off)
*MET is short for “metabolic equivalent for task”.
It’s a ratio of your working metabolic rate (e.g., when you’re exercising) relative to your resting metabolic rate. One MET is the energy you spend sitting at rest — or, in other words, your basal metabolic rate.
Now, even if we were to assume a generous 15% increase in energy consumption (from EPOC), that would only result in 210.8 calories burned through HIIT.
That’s still less than (although arguably not by much; explaining why HIIT and continuous aerobic training produce comparable weight loss results) if you were to perform steady-state training for the same amount of time.
Ouch. OK, but what about the health side of things? No luck with that, too.
In a 2015 study published in PLoS One, researchers randomly assigned 28 sedentary men to two groups:
HIIT group
Continuous moderate intensity training (MIT) group
Guess what the researchers found after six weeks? Both HIIT and MIT training improved cardiometabolic risk factors in the participants, with no clear advantage between the two regimens.
It’s also worth noting that HIIT workouts don’t appear to be sustainable for most people.
According to the researchers of this 2023 systematic review published in the Psychology of Sport and Exercise:
“Compared to steady-state training, more individuals assigned to high-intensity interval training did not adhere to their prescription when unsupervised, most likely because they could not. Some dropped out, whereas many of those who continued exercising did so at lower-than-prescribed levels of intensity.”
When done right, a HIIT workout is extremely challenging.
It’s not for the faint-hearted. Not many can keep pushing to and sustaining a near-maximal effort (> 85% heart rate maximum) for an extended period.
Is HIIT right for you?
Now, this isn’t to discourage you from doing HIIT.
Instead, it’s simply a reminder that you need to avoid viewing the benefits associated with the HIIT workout through rose-tinted glasses — and have realistic expectations about its weight loss and health outcomes.
So, how would you know if you should do HIIT? It’s ultimately a highly personal decision that comes down to your preferences, but here are a few factors that could guide your decision:
Medical history: HIIT may not play nice with certain chronic health conditions (e.g., cardiovascular disease). So, please get your primary healthcare doctor’s go-ahead before starting a HIIT routine.
Time availability: If you have a really tight schedule, HIIT is a fantastic option due to its time efficiency.
Enjoyment: If long, continuous cardio sessions bore you to tears, HIIT provides a great way to get your cardio over with while keeping it short and engaging.
Think HIIT is a great fit for you? If you can’t wait to HIIT the start button (oops, couldn’t resist!), give these three HIIT routines a go.
But what if you’ve decided that HIIT doesn’t make sense for you?
What should your exercise routine look like, then? There’s no one-size-fits-all answer for that — there are just too many individual factors (e.g., current fitness level, medical history, and fitness goals) to consider.
For highly personalized guidance, check out NOVI Optimum. With the professional help of a dietitian and fitness coach, understand how to work out and eat in a way that best suits your lifestyle and preferences while making solid, lasting progress toward your health goals.