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• Last updated: March 25, 2024

Podcast #970: The Misconceptions of HIIT (And the Role It Can Play in Your Fitness Routine)

You’ve probably heard of HIIT — high-intensity interval training. In fact, you may feel so familiar with the idea that you think you understand it. But do you?

People often hold some popular misconceptions about HIIT, and today we’ll unpack what some of those are with Dr. Martin Gibala, a foremost researcher of this fitness modality and the author of The One-Minute Workout: Science Shows a Way to Get Fit That’s Smarter, Faster, Shorter. Martin explains the main, underappreciated advantage of HIIT, which revolves around the “intensity-duration trade-off”: the higher intensity you make exercise, the shorter your workouts can be while still triggering improvements in metabolism, cardiovascular health, and mitochondrial capacity. We get into the fact that the intensity of HIIT needn’t be as high as you might think and that, contrary to popular belief, sprinting at intervals is actually a predominantly aerobic rather than anaerobic workout. Martin answers questions like whether Zone 2 cardio has an advantage over HIIT, if the so-called “afterburn effect” of HIIT is real, if you can do HIIT if you’re older or have heart problems, and whether you should worry about the way HIIT can raise cortisol in the body. He also shares specific HIIT workouts you can do, including a walking interval workout and one of the best higher-intensity protocols to try.

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Brett McKay: Brett McKay here and welcome to another edition of The Art of Manliness podcast. You’ve probably heard of HIIT, high intensity interval training. In fact you may feel so familiar with the idea that you think you understand it but, do you you? People often hold some popular misconceptions about HIIT, and today we’ll unpack what some of those are with Dr. Martin Gibala, a foremost researcher of this fitness modality and the author of The One Minute Workout. Science shows a way to get fit that’s smarter, faster, shorter. Martin explains the main, underappreciated advantage of HIIT, which revolves around the intensity-duration tradeoff. The higher intensity you make exercise, the shorter your workouts can be, while still triggering improvements in metabolism, cardiovascular health, mitochondrial capacity.

We get into the fact that the intensity of HIIT needn’t be as high as you might think, and that, contrary to popular belief, sprinting at intervals is actually a predominantly aerobic rather than anaerobic workout. Martin answers questions like whether zone 2 cardio has an advantage over HIIT, if the so-called afterburn effect of HIIT is real, if you can do HIIT if you’re older or have heart problems, and whether you should worry about the way HIIT can raise cortisol in the body. He also shares specific HIIT workouts you can do, including a walking interval workout and one of the best higher intensity protocols to try. After the show’s over, check out our show notes at And that’s H-I-I-T. All right, Martin Gibala, welcome to the show.

Dr. Martin Gibala: Thanks for having me.

Brett McKay: So you are a professor of kinesiology at McMaster University in Canada, and you spent a lot of your career researching high-intensity interval training, or HIIT. I’m curious, what led you down that path?

Dr. Martin Gibala: Yeah, sort of a personal and professional interest. The personal interest is, when I first got to McMaster, I was a busy young assistant professor, had a working spouse, two young kids at the time. And so quite ironically for a professor of exercise physiology, I found myself with very little time to exercise. And that dovetailed with a professional interest. For a long time, I’ve taught a fourth year course called the Integrative Physiology of Human Performance, and my students are always interested in the training regimes of high-level athletes. And so I would ask them, why do these elite endurance athletes sprint? Why do they run hard or do these short, intense workouts to enhance their aerobic performance? And so it was those combination of things that led me down this path.

Brett McKay: I think everyone at this point has probably heard of high intensity interval training or HIIT. I mean, it really had a moment. I mean, this is about when your book came out, the One Minute Workout came out and you wrote some articles for the New York Times, like went viral. Like you could just do a short workout, really intense and get all these benefits. But I think when most people think of HIIT, and I know I did this before I read your book, they typically think it’s got to be a bootcamp style, super intense, CrossFit, workout of the day type workout. But one of the points you make in the book is that idea of HIIT, well that is HIIT, that idea of HIIT is too narrow. So how do you define high intensity interval training?

Dr. Martin Gibala: Yeah, absolutely. And for sure, this idea that you need to go all out or as hard as you can go, that’s a big misconception. Certainly that’s one type of high intensity interval training, but it’s not the only type. And so to me, HIIT is very simply alternating bouts of relatively hard work and recovery periods. Now, high intensity, we can generally equate that with vigorous intensity effort as compared to light or moderate. And there’s well-defined metrics in physical activity, exercise, prescription guidelines for what constitutes vigorous intensity. So if you can imagine a simple 10-point subjective scale where one is laying on the couch or complete sedentariness and 10 is sprint from danger pace or save your child from an oncoming car. Vigorous exercise or HIIT is about a seven. It roughly corresponds to about 80% of maximal heart rate. And for an athlete, it means the severe intensity domain. And we use other metrics such as critical power, critical speed. But key point here is that it is not only all out exercise, absolute intensity can vary dramatically between individuals, but the relative intensity can be quite similar.

Brett McKay: Yeah, I think that’s a good point. What constitutes intensity is going to vary from person to person. So someone who’s super fit, cross-fitter type guy, what that person has to do to get to a high enough intensity to have a high intensity interval training workout, it’s going to be different from someone who hasn’t worked out or exercised in 30 years. And their intensity might just be they get up off the couch and they walk briskly for a little bit. That’s going to be intense for them.

Dr. Martin Gibala: Absolutely. There’s a figure I like to show in presentations to different stakeholders and it’s two heart rate tracings from two individuals on very far ends of the fitness spectrum. And the top heart rate tracing is from a olympic athlete and the bottom tracing is from an individual with coronary heart disease, but they’re both doing the same interval training workout normalized to them. They’re both doing four-minute intervals at about 90% of their maximal heart rate. Now, of course, the Olympic athlete is working at a very high pace. And as you alluded to, the deconditioned patient is hardly doing much more than a walk or a brisk walk. But it really is a dramatic illustration of this notion that we can really scale absolute intensity to elicit the same relative stimulus, even if people are on very far ends of the fitness spectrum.

Brett McKay: Okay. So another important part of HIIT is the interval part. So it’s not just you’re going hard for as long as you can. The idea is that you take a break from it every now and then, and then go back up. So you’re trying to create just this wave of extremes in your workout.

Dr. Martin Gibala: That’s right, we talk about hills and valleys. And going back to athletes a common refrain is make your hard days hard and your easy days easy. And so it’s the same notion right and those recovery periods are very very important in order that you can go hard in the subsequent intervals, but this ungeni-lating pattern is intrinsic to the method.

Brett McKay: Okay so basically HIIT is alternating higher intensity bouts of exercise with lower intensity in the same session. And you’re alternating because you can’t stay very high intensity for long. I mean, the idea is, and we’re going to talk about this more as we go along, but by ramping up the intensity, just a few short bouts of exercise can give you a lot of the benefits, just like longer sessions of exercise, but in a shorter amount of time.

Dr. Martin Gibala: Yeah, that’s exactly right. And so the underlying physiology is the same, your body really does. There’s an old saying that your heart doesn’t know what your muscles are doing. It just realizes it’s some sort of physiological stress or challenge. And what we’re finding is that intensity really plays a key. And so we can definitely trigger responses through traditional moderate intensity, continuous training, relatively high volume, but many of those hallmark adaptations, it seems we can trigger with a surprisingly small dose of the vigorous intensity work as well.

Brett McKay: So, well, HIIT really burst on the scene, I’d say the middle of the 2000s, early 2010s. One thing you do in your book is that you highlight that athletes and other professions like the military as well, they were using HIIT without even knowing they were using HIIT to get in better shape.

Dr. Martin Gibala: Yeah, absolutely. So athletes tended to perform high volume, high intensity interval training. And so there’s very famous examples of people like Paavo Nermi, Emil Zatopek. These were Olympic champions in multiple events. And for example, legend had it that Zadopek sometimes completed 15 miles a day of intervals as 200 and 400 meter repeats. So these very, very high volume protocols. But also there were individuals like Roger Bannister, who famously trained with intervals on his lunch hour when he was a very busy medical student running repeats on a quarter mile track.

Brett McKay: And then you also highlight, I thought it was interesting, the Canadian, is it the Air Force? It was one of the military units in Canada. This guy stumbled upon HIIT, and he used it to help get new recruits in shape.

Dr. Martin Gibala: That’s right. One of the first exercise physiologists was hired by the Canadian military at sort of the height of the Cold War. Because at one time, you can imagine these service members stationed in very remote outposts literally near the North Pole. And at one time, so many Air Force pilots were unfit. About a third were deemed unfit to fly on missions. And so the government realized they had to do something about it. But you’re stationed in the far north, not a lot of specialized equipment. You don’t want to be outside very much. And so they came up with this plan called 5BX, which stood for five basic exercises. And sort of the tagline was you could get fit with these simple bodyweight style exercises. It only took about 11 minutes a day. And this spread well beyond the military. And eventually about 20 million of these pamphlets were distributed to Canadian households in the early 1960s. There was an equivalent plan for women called XBX. But again, it was this idea that you could get fit, didn’t have to be fancy, didn’t require a lot of time, but it was based on this idea of getting up to a vigorous pace in order to stress the cardiovascular system.

Brett McKay: Well, we’ve been talking about you can use HIIT to get fit, increased fitness. Let’s talk about what we mean by fitness. And in the book you talk about there’s, we have different systems in our body, the anaerobic system and the aerobic system. How does HIIT make us more fit? We’re doing a lot of rhyming here. How does HIIT make us more fit both anaerobically and aerobically? And I guess we’d have to explain what the anaerobic systems are and the aerobic systems are for those who aren’t familiar with it. Let’s start there.

Dr. Martin Gibala: Yeah, absolutely. So basically two ways of generating energy within the body. And so aerobic means requiring oxygen. So you can imagine we literally are burning fuels such as sugars and fats, using molecular oxygen to produce energy and so very much like a fire you need wood for the fire. That’s the glucose or fatty acid molecules. You need oxygen and you need the spark as well to keep the fire going. Now, we can also produce some energy without the use of oxygen. And so this is the notion of anaerobic or non-oxidative energy and you could think of a spectrum or a continuum rather where the aerobic system is great in terms of capacity, very high overall amounts of energy, but it comes at a cost, it’s slower. And so non-oxidative or anaerobic energy, it doesn’t require oxygen. It’s very, very fast in terms of the rate at which it produces energy, but its capacity is very, very limited.

And so for a long time, it was thought, or you still hear this very commonly today, that HIIT is anaerobic exercise. And again, very much a misnomer. Any type of repeated sprint is primarily fueled by the aerobic or oxidative energy supply system. And so you can think of team sports or that, but repeated sprints, very much an aerobic stress. And so it’s not surprising then that we see these profound responses within the aerobic energy supply system. Even during a 30 second, as hard as you can go all out sprint, about 20% of the energy is coming from aerobic metabolism. And then when you do repeated 30 second all out sprints, the predominant energy providing system is aerobic metabolism.

Brett McKay: Yeah, that’s really interesting ’cause, yeah, I’ve heard that same thing that sprinting is an anaerobic metabolic conditioning. And if you wanted to get aerobic conditioning, you have to do the more steady state cardio. What do you think is going on there? Why does that idea still exist that sprinting only engages the anaerobic system when sprinting at intervals at least, you’re actually engaging the aerobic system too?

Dr. Martin Gibala: Yeah, well, there’s no doubt if you want to become a better sprinter, you better sprint train, right? And so sprint training, it will definitely stimulate non-oxidative energy metabolism and again, literally make you a better sprinter and develop those enzymes in that supply method. It’s a fact that when you do a single sprint, most of the energy is anaerobic. But again, it’s very, very different when we do these repeated sprints. And so I’m not really sure why that endures so much or we use these terms like aerobic and anaerobic. And another misconception is that we only utilize one system or the other. We’re very much virtually every type of exercise that we do, whether it lasts a few seconds or many, many hours, there’s always going to be some blend or some contribution for both of those main systems. And really it’s whatever system predominates. But again, Again, suffice to say, repeated sprints, very potent aerobic stimulus, and that’s associated with a wide array of health benefits as well when we develop the aerobic supply system.

Brett McKay: So what are the aerobic responses our body has when we take part in repetitive sprinting at intervals?

Dr. Martin Gibala: Yeah, probably the biggest one is cardiorespiratory fitness. And that’s that notion of cardio health. It’s largely determined by the capacity of your heart, your blood vessels to circulate oxygen through the body. We measure that clinically or in a laboratory with a maximal oxygen uptake test. So that’s a VO2 max test. That’s clearly very important for athletes. But there’s very strong and compelling epidemiological evidence to show that having a higher cardiorespiratory fitness is associated with a lower risk of dying from all causes, a lower risk of developing many different chronic conditions like cardiovascular disease, type 2 diabetes, and so any way that we can enhance our cardiorespiratory fitness is really, really important. So you can sort of think of your cardiorespiratory fitness as the ceiling, right?

And we want our ceiling to be as high as possible. And then the other aspect to fitness is metabolic fitness. And that’s largely determined by our muscles. And that sort of regulates how close to the ceiling you can work for a prolonged period of time or your resistance to fatigue. And so athletes want high cardiorespiratory fitness and a high metabolic fitness. They want a big ceiling and they want to be able to work close to that for a long time. But it’s again the underlying physiology is the same and so individuals who are very deconditioned they often have low ceilings but they have a very low percentage of the ceiling that they can work at as well. And so any type of exercise training will tend to enhance both of those things but, again we’ve learned that the vigorous intensity intermittent exercise can be… We talk about an efficient way to train. What that really means is there’s some time efficiency there and we can get away with less total time and probably exercise and still get to a similar level of improvement.

Brett McKay: Yeah. So you could do an hour of steady state cardio and get X amount of benefits in terms of VO2 max or increase in mitochondria in your cells, or you could do a 10 minute high intensity interval training and get roughly the same benefits. Is that the pitch, the sales pitch?

Dr. Martin Gibala: Yeah. No, it is, right? And arguably we should do both and you very much see these arguments where people will try to demonize traditional cardio or now there’s sort of a pushback against HIIT, I don’t really have a ton of time for those, try to say what is the best type. Again I think, at least from our research, what we’ve been trying to do, we talk about expanding the movement menu, which really means we’ve largely been telling people to do the same thing for a long time. And that’s fine. The physical activity guidelines are based on excellent science, but we know a lot of people aren’t listening, right? And one of the perceive barriers, whether it’s real or not, is a perceived lack of time, or people think, oh, if I don’t have an hour in the day, I’m going to blow off my workout. And I think what the interval training literature is showing is, you know what? You don’t need a whole lot of time and still get some bang for your buck there.

And really, that’s been our, the focus or a focus or through line of our research is trying to establish the scientific credibility of these brief, vigorous type workouts. And then hopefully presenting that as an option to people. We’re not saying it’s the only work that you should do or, if you don’t like interval training, okay, that’s fine go do the moderate stuff but trying to expand that movement menu give people more physical activity options just like we try to give options for dietary strategies, pick the food you like you can sort of pick the exercise approaches that you like ’cause the best one is what you enjoy you’re more likely to stick with it over the long term.

Brett McKay: It seems like people keep rediscovering HIIT or interval training every 10 years or so. You’ll see this in the fitness industry, you’ll see these trends we’re like, oh it’s steady state cardio. Like, no, no, no, we’re going to do HIIT now. HIIT’s the best thing in the world. Like, no, actually, it’s steady state cardio. ‘Cause I think in the past five years, I’ve seen a lot of talk about zone 2 cardio, where it’s, you want to stay in zone 2 for 60 minutes and get so much of it a week. And I’ve been doing that. I’ve enjoyed it. It allows me to watch movies and television shows that I don’t otherwise wouldn’t watch. But I think what your research is showing is that, there’s nothing wrong with zone 2 cardio. It’s very healthy for you, but if you don’t have time, HIIT might be an option for you.

Dr. Martin Gibala: No, I agree. And so I think some of the, and you’re right these things come in and out of fashion a little bit, but I think some of the pushback against HIIT comes certainly from some overstatement regarding potential benefits of HIIT, hopefully not from our laboratory or interviews like this, but definitely you see some overstatement, you can get away with a few minutes a week and that’s the solution for fitness. So when we start saying this is the solution to our inactivity problem, or this is the best way to exercise or the optimal approach. I think that’s where it becomes problematic. To my mind, the rise of zone 2 is owing in part to, that’s how high level endurance athletes train in terms of roughly an 80-20 split. So if you’re a high level endurance athlete training 25, 30 hours a week, there’s very good evidence to show that they tend to center around this 80% low intensity, 20% high intensity. Much of that being intervals. And so it’s interesting because classically zone 2 has meant the heavy intensity domain. And this is where there’s a classic three zone training model for athletes. But now zone 2 has commonly been interpreted as low intensity sub lactate threshold based training. And you’re right. It’s…

Definitely can be beneficial. I’m unconvinced, or I just don’t see the data that zone two is best to optimize your mitochondrial capacity. There’s many different ways to do that. And so I think, again, ideally, we should train across a range of intensities. But I’d come back to this idea that I think as volume decreases, intensity is arguably more important. And so where I would take some exception to the commentators is suggesting that because athletes who do 25 hours a week train this way, that’s how everyone else should exercise. Regular people who might have an hour a week or two hours a week to exercise, or maybe they only have 20 minutes that they’re willing to do. I think they’re doing anything is clearly better than nothing, but engaging in a more vigorous effort, again, not necessarily all out, it’s better bang for your buck, certainly, given the time investment.

Brett McKay: Yeah, I know I made a big emphasis on zone two starting two years ago, ’cause the sales pitch on, oh, it’ll help increase the amount of mitochondria in your cells. It’s like, well, that sounds like it’s important. And so I’m doing two to three hours a week on the elliptical, watching Cobra Kai on YouTube, but I’d have days where I couldn’t get a session in, a zone two session, it’s like, man, it’s an hour, I don’t have an hour, and so I just wouldn’t work out. It’s like, well, I’m not gonna get that mitochondria that I need, but then after I read your book, this happened to me last week, I didn’t have time. I had literally had 15 minutes, so I just got on my Airdyne bike, the fan bike, and I did a interval thing. I was like, hey, I got it in. I got some of those aerobic benefits from doing that 10-minute interval training workout.

Dr. Martin Gibala: Fantastic, right? And that’s the key takeaway, I think, is lots of different options, even for a given individual. You know, I’m a committed exerciser to this approach. Well, if I can’t do my approach on that day, maybe I’m gonna try something different. And so, again, vary it up, and to your point, when time is pressed, maybe engage in some of the vigorous stuff. And even if only you do it for five or 10 minutes, know that you’re still getting some benefit there, at least to maintain your fitness, until you can get back to your regular routine.

Brett McKay: Okay, so, HIIT, you can get the same aerobic benefits as doing the long and slow and steady cardio. I think that’s good to know. You talk about how you can improve our cardiovascular health, reduce our risk of heart attacks, heart disease. You also talk about how HIIT can help improve or manage diabetes and insulin resistance. What does your research say there?

Dr. Martin Gibala: Yeah, and so, again, I wanna be, I wanna really emphasize here, any type of exercise can do these things, right? And so, these are not necessarily exclusive benefits to HIIT, but certainly, some evidence from our laboratory, a lot of other laboratories, shows that HIIT can improve measures of insulin sensitivity or blood sugar control. And so, part of the reason for that is that, we have in our body these things called glucose transporters. They’re in all of our tissues, but they’re responsible for sort of moving the glucose molecules or the sugar out of the bloodstream into our cells, or it can be taken up and stored or used for energy. And so, exercise generally, and in particular, vigorous exercise, enhances the capacity for glucose transport. And so, that’s likely one of the reasons that blood sugar control can be managed a little bit better, or certainly if you’re an individual with type 2 diabetes, and you engage in regular exercise, one of the things that you’ll find is your physician is gonna say, well, you need less of your medication, because the exercise is doing that for you. And so, we don’t now need to give you drugs or as many drugs in order to try and regulate your blood sugar, ’cause you’re sort of doing it on your own through physical activity.

Brett McKay: But another benefit I’ve seen touted for HIIT is weight loss, this idea of the afterburner effect. What does the research say about that? Is that legit?

Dr. Martin Gibala: Yeah, definitely something to it. Again, it’s one of these things I think that’s often overstated. And so, you look online and you might see someone’s comparing an interval versus a traditional cardio workout and see this massive afterburn effect. It’s definitely real. So, this idea of a heightened metabolic rate in recovery, you have this transiently higher calorie burn, and it can add up over time. So, people say, how can HIIT, especially if it’s short, result in any calorie burning at all? Well, it does relate to this idea of the afterburn effect. But again, it’s relatively small and we shouldn’t overstate it. And HIIT can play a role in weight management efforts, just like other types of exercise, but the nutrition side of the equation is the primary driver there.

Brett McKay: We’re gonna take a quick break for a word from our sponsors. And now back to the show. Okay, so HIIT can improve our aerobic capacity, it can improve our cardiovascular health, can help with insulin sensitivity, with weight loss. How much HIIT do you have to do to get these benefits? Like, how long do the sessions need to be? And like, how many sessions do you have to do before you start seeing these benefits? Have you guys looked at that?

Dr. Martin Gibala: Yeah, we have. And so definitely the responses, the adaptations, they can occur surprisingly quickly. So we’re talking within a week or two. We’ve done a study, for example, in older overweight individuals with type two diabetes, and we put them on a HIIT protocol that was only six sessions over two weeks. And even after two weeks, we saw marked improvements in some of those things that I was talking about, their glucose transport capacity, some markers of blood sugar control. So the responses can occur very quickly, and probably the more deconditioned you are, the faster the response is. You probably have a lot more room to improve. We’ve gotta be careful there, because we’re not saying to these people that, especially if you’re very deconditioned, HIIT does not mean jumping off the couch and pedaling your heart out on a bike. It’s just getting out of your comfort zone, going a little harder than you may have before. So it definitely can occur quickly in terms of how long the sessions have to be. Again, this is where it really comes back to what’s the intensity. And so there’s many different HIIT protocols, but certainly 10-minute total time commitment involving one to two minutes of vigorous intensity exercise can be enough if you do that over a few weeks to start to see measurable improvements in various health and fitness markers.

Brett McKay: And just to recap, the intensity we’re going for is on a scale of one to 10. Seven is about what we want to hit.

Dr. Martin Gibala: That’s right, seven out of 10 is that vigorous range. And for reference there, a traditional moderate intensity would be about a five on that range to help people try and scale it.

Brett McKay: How do people typically feel when they’re at a seven? It’s like you’re breathing really heavy, you’re sweating. Like what are some of the physiological responses?

Dr. Martin Gibala: Yeah, and so one of the classic ones is, moderate exercise being that five, You could carry on a conversation or you could talk in sentences, but you wouldn’t want to sing. Whereas if you’re into that vigorous range, you can grunt out a few words, but you really don’t want to speak in sentences or have a conversation. So that’s what we’re talking about there in terms of these subjective cues to know you might be in the right range. The interesting thing is especially with the shorter the intervals, some of these traditional metrics, whether it’s heart rate or relative to VO2 max or heart rate reserve, they don’t seem to align as well. And so if we’re talking 20, 30 second efforts, people can go at a surprisingly high pace, but they don’t perceive it as such because the effort is over quite quickly. And so it’s a real challenge, frankly, in terms of trying to apply some of these brief, vigorous protocols widely and try to translate this into exercise prescription for people because a lot of the metrics that we normally use don’t necessarily apply. But this idea of perceived exertion, that zero to 10 scale, it’s probably about the best we have in terms of applying this widely and in a way that people can understand.

Brett McKay: And then what your research has shown, the higher you go up in intensity, the shorter the duration can be. Is that correct?

Dr. Martin Gibala: Yeah, there’s clearly an intensity duration trade-off. It’s not necessarily linear either. It’s almost exponential. So as the intensity really gets up there, the dose that you need, the volume or the time that you need can really, really drop off. And there’s some very clear research to show that.

Brett McKay: Does HIIT affect men and women any differently or is it the same?

Dr. Martin Gibala: Yeah, so there’s definitely some differences related to biological sex, but they appear to be quite subtle. There’s a much greater range or scale for just fundamental inter-individual differences between humans, but some of our work, some research from others has shown subtle differences. And you can point to some underlying biological variables there, maybe related to hormone concentration or the estrogens that could potentially impact on this from a mechanistic basis. But again, suffice to say, a little bit of evidence, maybe females don’t have as pronounced a cardiovascular response as males. But again, I think that’s more related to just inter-individual differences between humans or that’s much broader. And clearly both men and women can benefit from interval training and benefit from many different types of exercise.

Brett McKay: What about age and HIIT? There might be some older men listening to this podcast, maybe they’re in their 60s and 70s, and they’re like, oh, I don’t wanna do that HIIT because I might have a heart attack or something. Is there any risk to HIIT if you’re older?

Dr. Martin Gibala: Yeah, so I would, and to that specific example, no one has to do HIIT if they don’t like it or prefer it. So there’s a couple of ways to look at this. Number one is if we look at the physical activity guidelines that generally recommend moderate to vigorous exercise in prescribed amounts, the suggestions or the recommendations are essentially the same for adults 18 to 64 and older adults 65 plus. Now that’s not saying that if you’re 65 plus, you should explicitly do vigorous exercise or high intensity work. But again, when we look at the guidelines, adults of all ages are recommended to do vigorous intensity exercise. I think we clearly need to be mindful of chronic conditions, both musculoskeletal and as people age, there tends to be increased potential, silent risk factors, cardiovascular disease risk factors. And so, the standard advice of course, is that people should see their doctor if they’re gonna start or change an exercise regime, start slowly, right? So if You’re just getting into exercise, physical activity, start with the moderate stuff, then add the vigorous stuff.

But also, people do not necessarily need to be afraid of vigorous exercise and more people than we think, many more people than we think, can perform vigorous intensity exercise HIIT safely. And I think there’s fairly compelling data in that regard and definitely HIIT has been applied to individuals with many different chronic conditions, including cardiovascular disease, metabolic syndrome, older individuals, people with cancer. So again, my take home points, there are many more people than we think can do vigorous exercise, but of course, people need to be smart, ideally get checked out and the older you get, maybe back off on the sprint and all out stuff unless it’s really suited to you and you’re suited for it.

Brett McKay: And you also point out what’s interesting in the past 20, 30 years, cardiologists or heart hospitals, at first they’re very leery of HIIT ’cause they’re treating people who had cardiac events, heart attacks, like, wow, that’s just gonna hurt them even more, we don’t wanna do that ’cause it’s so stressful in the heart, but you’re starting to see a lot of them incorporate that in the recovery process of heart attack patients. They’re not gonna do the all out 10 sprint, but they’re getting their patients to do vigorous exercise in a supervised manner ’cause what the studies have found is that it helps strengthen these people’s hearts that have gone through a heart attack.

Dr. Martin Gibala: Yeah, that’s exactly right. You know, and at one time, rest was all that was prescribed after a heart attack, and at one time, we wouldn’t think that anyone who was a post-MI patient would lift a weight, and now we know that many cardiac rehab programs incorporate resistance training, and so I think it’s the same with vigorous exercise. Ideally, it’s properly supervised, but, and it depends across the world. Everyone’s reading the same science, but, for example, in Scandinavia, I think interval training is much more an accepted part of cardiac rehab practice. We’re a little bit less, I would say, in North America, and that’s fine, but clearly, vigorous intensity exercise, HIIT, is being utilized widely in cardiac rehab.

Brett McKay: Does HIIT raise your cortisol more than other forms of exercise?

Dr. Martin Gibala: Maybe a bit. I’m less concerned, or I’m not convinced sort of these acute fluctuations in hormones post-exercise matter that much, and I don’t think there’s evidence that, for example, you have sustained rises in cortisol or other hormones that, might be associated with muscle breakdown or stress. So I don’t think it’s something that people need to be concerned about.

Brett McKay: So since your research has started, you’ve had other researchers in other fields look at HIIT, and you’ve had exercise psychologists look at HIIT. And one thing that some of these exercise psychologists are finding that HIIT is a really effective way to get novice exercisers to start the exercise habit, which seems kind of counterintuitive because HIIT can be really unpleasant, and unpleasantness is one reason why people don’t stick with an exercise plan. So have they figured out why is HIIT such an effective way to get beginning deconditioned exercisers to keep exercising?

Dr. Martin Gibala: Yeah, this is a real hornet’s nest, I would say. And among the exercise psychology community, and I’m not a behavioral expert, there are really polarizing opinions around the potential for HIIT as a public health strategy. And you’re absolutely right. One camp would say, if exercise is vigorous, if it’s intense, people find it unpleasant. And so they’re unlikely to do it. And so HIIT is bound to be a public health failure. I don’t subscribe to that notion. And there’s definitely a lot of exercise psychology, behavioral research coming out to suggest that, okay, wait a minute, brief, vigorous, intermittent exercise, it’s completely different from continuous vigorous exercise. It also depends when are you asking people the question? If you ask them during the bout, they might rate HIIT a little bit lower, but after the bout, they’re like, you know what? Didn’t take me as long. I’m getting the same benefit. I’ll take that. And there was a recent meta analysis based on over 100 studies, almost 9,000 participants that found similar rates of measures like compliance and adherence to high intensity interval training and moderate intensity continuous training. So such that those were not different.

So I think, you know, you can cherry pick individual studies and for the critics of HIIT, I would say, well, you know, what’s the fallback? Because we know that the adherence to the broad public health adherence to moderate exercises is not very great. And so to demonize any form of physical activity doesn’t make sense to me if arguably we’re all in the same team here. And we agree that the biggest thing that we need to do is just get more people active and more people moving. You know, again, coming back to this idea, the more exercise options, the better. Let’s expand that movement menu rather than sort of demonize one particular approach.

Brett McKay: I think one point a psychologist made was that when you take a deconditioned person, someone who hasn’t exercised, and then put them on the path to run a 5K, when they’re first starting, they’re doing interval training but unintentionally. ’cause they can only like run maybe a few hundred feet, and then they got to stop and walk. And then they catch the breath and they start. Like they might, In the person’s head, they think they’re doing steady state cardio, and they think they’re failing because they’re not running the entire time. It’s like, no, actually, you’re just doing interval training. That’s fine. You’re getting all these great health benefits doing that.

Dr. Martin Gibala: 100%. It’s sort of like changing the narrative or flipping it on its head. And it can be a very empowering way to exercise. It’s like, no, no, wait a minute. You’re not a failure because you can’t sustain a pace for 30 minutes. You’re training like Olympic champions. That’s what they do. They sort of go hard. They take a break, and they do it again. So that’s completely okay. And so I think if you’re looking for buy-in or that, rather than telling someone they’re a failure ’cause they can’t do 20, 30 minutes continuous because their starting capacity is so low, saying, hey, an intermittent approach works just fine. So keep it up.

Brett McKay: I love that. Okay, so the HIIT workout, you’re not saying it’s better than or steady-state cardio. It’s another option to choose from in your fitness repertoire. So if you don’t have time for an hour-long zone two cardio session, just do a 10-minute interval workout. And you get all these benefits in terms of aerobic metabolism, cardiovascular health, insulin, diabetes, weight loss. You get all those benefits with just maybe 10 minutes of work.

Dr. Martin Gibala: I think that’s how people should look at it. It’s an option. It’s a particularly time-efficient option. It’s not necessarily the best or for everybody, but definitely work it into your fitness menu.

Brett McKay: All right, well, let’s talk about some HIIT workouts that people can do. So after listening to this episode, they’ll do some or have that as an option. What are the type of movements you can do for HIIT?

Dr. Martin Gibala: Almost anything. So again, getting back to this idea of your heart doesn’t know what your muscles are doing. Again, generally speaking, I don’t think it matters. And our research would suggest it wouldn’t matter if it’s indoor-based cycling, if it’s stair climbing exercise, if it’s uphill, if it’s body weight style exercise, all of those things can be utilized effectively as an interval training workout to stimulate improvements in all of those metrics that we were talking about there. So I don’t think, and again, we’re talking general health improvement here. If you’re an athlete, you try to train very sports specifically. And so if you’re a cyclist, you better train with interval cycling to try and get better. But for most people, that’s not the key driver. They just want to enhance their cardio respiratory fitness and other health metrics. And so probably varying it up is a good strategy, but the specific type of movement doesn’t matter so much.

Brett McKay: Just whatever you like, whatever you enjoy doing.

Dr. Martin Gibala: Correct.

Brett McKay: It’s a good interval workout for I could say a rank beginner.

Dr. Martin Gibala: Yeah. So two ways to answer this question. One is, probably you want to get out of your comfort zone, but again, you’re not doing this all out nine or 10 on a 10-point scale exercise. And so, if your standard exercise is walking around the block or continuous moderate exercise at about a five there, in getting out of your comfort zone, start with a six, maybe get into a seven and do that for a minute or so, and then back off. But classic examples would be three minutes on, three minutes off. And there’s a ton of research, much of it out of Japan, that has looked at this interval walking as a strategy and just showing the tremendous benefits that that can elicit. Again, we’re just talking brisk walking here. Another classic protocol largely developed in Norway is the four-by-four. So that’s four, four-minute efforts that are relatively high in intensity. And then you go from there and what tends to happen is the intensity goes up and the duration of the intervals goes down. So we’ve looked at a 10 by 1 protocol. And so how hard you’re working there for a minute is harder than the four-minute protocol.

But again, you’re only doing a minute, not four of it, right? And you repeat that in a sort of on-off pattern. And I think that’s also one of the beauties of interval training is the infinite variety. People say, what’s the best interval training protocol on it? I don’t think it matters, right? Again, generally speaking, unless you’re a athlete training for a very specific performance outcome, for most of us, it doesn’t matter. And hopefully, that’s empowering and hopefully, it takes away the boredom a little bit because vary up the intervals. There’s only so many ways to get on a treadmill and jog at a moderate pace for an hour or so. But with intervals, you can really vary it up intensity, duration of both work, recovery periods, all of that.

Brett McKay: That Japanese protocol, is that the Tabata protocol?

Dr. Martin Gibala: No, I get, no, it would sort of be one over the Tabata protocol. So there has been some classic interval training workout in Japan, almost at the ends of the spectrum. So that three minutes on, three minutes off, that’s just very much brisk or interval walking, whereas Professor Izumi Tabata is the father of Tabata intervals, that’s at the complete other end of the spectrum and that’s 20 seconds at a 10 out of 10 pace, as hard as you can go, 10-second recovery and then you do it again eight times. So, a Tabata workout classically lasts four minutes, 20 seconds on, 10 seconds off, repeated eight times, but a Tabata workout is one of the most challenging interval protocols that you can do.

Brett McKay: Okay. So yeah, the key takeaway there is the more intense you go, the shorter your workout can be, but the less intense, if you do them just a walk, your intervals will have to be longer. And so your workout overall will take longer.

Dr. Martin Gibala: That’s right. You know, at the end of the day, there’s no free lunch, right? And so if you definitely want the benefits of brief exercise, it needs to be intense and that’s not necessarily for everyone. And at the other end of the spectrum, you can still do interval training. It doesn’t has to be this all out as a. As you can go, but you’re invested then for a couple of minutes and repeating that at least three, four, or five times.

Brett McKay: One you highlight that I like is the Wingate Classic. What’s that one about?

Dr. Martin Gibala: Yeah. So the Wingate is sort of a classic test in exercise physiology. It’s also known as the Wingate Anaerobic Test, going back to our earlier discussion, and that’s because it’s 30 seconds as hard as you can go. And it’s actually performed on a specialized bike or a specialized ergometer that sort of gives back just what you’re able to put out. And so, even as you’re fatiguing, you’re still having to go. It’s about the longest 30 seconds of your life. And so our initial work was utilizing a Wingate protocol as sort of the extreme, right? It was a proof of concept studies at the time. And so people would do these protocols where it took, four or five, six of those wind gates with a few minutes in between, these were very, very demanding workouts. And you know, over, you know, it’s almost a variation on a Tabata workout. And then over time we’ve sorta dropped the overall time, dropped the overall intensity, and looked at other protocols.

Brett McKay: Yeah. You have the, it’s the 10-by-one is your variation of the Wingate.

Dr. Martin Gibala: That’s right. And again, you know, all different protocols appeal to different people, but probably if I had to pick one that seems to be widely suited or widely rated as not bad, it’s this 10-by-one protocol. Almost seemingly hits that sweet spot between it. The intervals are not too long, but they’re not too hard either, or at least they’re not all out. And then more recent research by others has shown that five by one can be almost as good as 10-by-one. And so it’s a bit like bench press exercise.

Three sets of bench, you’re going to be better than one set, but maybe only 5% better, you know? So if you do one set of heavy bench, you might improve your strength by 25 or 30%. If you do three sets, maybe you’re going to do 35 or 40%. But again, if your time pressed, that one set might be enough. And so, you know, maybe a few intervals are giving you 80, 90% of the benefit that a much larger dose of intervals might do.

Brett McKay: Right. So yeah, the 10 by one, just for listeners, your first sprint is at an intensity of five. You do that for a minute, then you rest one minute for recovery, then your second sprint is going to be at a slightly higher intensity level. So six, do that for a minute. And then you just keep that cycle going until you get to an intensity level of nine.

Dr. Martin Gibala: That’s right. And so, one of the reasons we came up with that is because, for a lot of people, they’re not outside trying to tailor their specific intensities or that. You can imagine if you’re exercising on a machine or you jump on a stationary bike, it allows you to set a workload and just leave it there, right, for the intervals. So, you know, whatever, if it’s a 20-point scale and you dial it up to a 12, the first minute at 12 only feels like a five out of 10. But of course, as you start to fatigue over the course of the workout, you’re still at a 12 but the relative effort starts to creep up. And so again, it’s a way to make it sort of simple. Okay. I’m going to just keep it at a 12, but it’s going to feel harder and harder each time as I move through the workout.

Brett McKay: So your book is called The One-Minute Workout. It’s a catchy title. I’m sure the publisher, your editor is like, we got to call this The One-Minute Workout because it’s going to sell books. But is there a workout that lasts about a minute that can give you all these health benefits we’ve been talking about?

Dr. Martin Gibala: Yes. And I’ll get to that in a minute, but you’re right. The One-Minute Workout, sort of a tongue-in-cheek, but it was based on some of these micro workouts where we’re having people do three, 20-second hard efforts. Now, you know, the workout took about 10 minutes start to finish, but the hard stuff was only a minute, three 20-second efforts inter spaced with a lot of recovery in between. Why I say a minute could be good is now we’re starting to look at, what we call exercise snacks. And so how we define an exercise snack is a vigorous bout of exercise that lasts for a minute or less. And you do these periodically throughout the day. So you can imagine on your way to work in the morning, you do a one-minute vigorous effort, maybe you come into work, you take the stairs rather than the elevator as you’re leaving at night for the subway, you exercise at a vigorous pace to get to the subway rather than a pedestrian pace. And so that’s known as an exercise snack and you sprinkle these through the day and definitely in small laboratory-based studies, if people do that a few times a week for a couple of weeks, we can see measurable improvements in their cardiorespiratory fitness.

That work, this small-scale lab work is complemented by some other work that I’ve been involved with led out of the University of Sydney, where the terminology, and again, you alluded to it earlier, there’s, you know, it’s almost an alphabet soup when we start talking about this, but the notion is vigorous intermittent lifestyle physical activity or VILPA. But if we break that down, so vigorous is the effort that you require, and hopefully your listeners have a good idea what vigorous is by now. Intermittent, so it’s periodic, spread throughout the day, and it’s lifestyle, physical activity. This is not structured exercise that you build into your calendar. This is as you’re going about your day. You know, you’re leaving work, you gotta get to the subway, you can get there at a vigorous pace or at a pedestrian pace. You know, you get off a long flight, you have the choice of the escalator, or you can grab your built-in workout gear, your suitcase, and you can walk up the stairs, and that takes you about a minute.

That would be an example of VILPA, carrying a heavy backpack as you’re doing your shopping. And research, again, that I was involved with in a very large sample, over 25,000 individuals who had worn accelerometers showed that as little as three to four minutes of accumulated VILPA per day was associated with marked reductions in all-cause mortality. We’re talking 30% reductions as compared to people who engaged in no vigorous-intensity physical activity through the day. And the risk reduction was even greater for cardiovascular disease. So I think compelling, not cause and effect evidence, but compelling epidemiological evidence that small amounts of vigorous physical activity can really move the needle in terms of enhancing our health. And so, I’ve just talked about there about larger epidemiological evidence, small laboratory-based studies. And where our research is moving now is sort of trying to round out the middle there, larger, longer, randomized controlled trials, where we’re trying to look at this type of lifestyle intervention and see, how does it work when we try and use a best practice design with control groups and things like that.

Brett McKay: Right. So the takeaway there, take the stairs.

Dr. Martin Gibala: Absolutely. Take the stairs, a few minutes of vigorous effort a day really, really pays benefits and it feeds into the notion that every little bit counts.

Brett McKay: Well, Martin, this has been a great conversation. Is there someplace people can go to learn more about the book and your work?

Dr. Martin Gibala: Yeah, sure. So I do have a website and sort of that’s a one-stop shop for, other podcast interviews like this. People learn about the book. People learn about a free online course that some colleagues and I at McMaster offer. I’m not on X a lot, but you can find me at Gibala M.

Brett McKay: Fantastic. Well, Martin Gibala, thanks for your time. It’s been a pleasure.

Dr. Martin Gibala: Thank you.

Brett McKay: My guest today was Dr. Martin Gibala. He’s the author of the book, The One-Minute Workout. It’s available on Check out his website at where you can find more information about his work. Also, check out our show notes at AOM. Is slash HIIT, and that’s spelled H-I-I-T. You’ll find links to resources, including links to more details about how to do some of those specific HIIT protocols we talked about towards the end of the show.

Well, that wraps up another edition of the AOM Podcast. Make sure to check out our website at where you can find our podcast archives, as well as thousands of articles that we’ve written over the years about pretty much anything you think of. And if you haven’t done so already, I’d appreciate it if you take one minute to get us reviewing up a podcast or Spotify. It helps out a lot. And if you’ve done that already, thank you. Please consider sharing this show with a friend or family member. You think we can get something out of it. As always, thank you for the continued support. Until next time, this is Brett McKay reminding you to not listen to AOM Podcasts, but put what you’ve heard into action.

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