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The Science of High Intensity Interval Training | Martin Gibala PhD

Episode 56, duration 1 hr 04 mins
Episode 56

The Science of High Intensity Interval Training | Martin Gibala PhD

Dr. Martin Gibala is a professor and the Faculty of Science Research Chair in Integrative Exercise Physiology at McMaster University in Hamilton, Canada. His research examines the mechanistic basis of exercise responses and the impacts on health and performance. Dr. Gibala’s laboratory is internationally recognized for studies on interval training. This work has attracted immense scientific attention and worldwide media coverage. Dr. Gibala’s science communication efforts include a bestselling book on the topic of time-efficient exercise, The One-Minute Workout: Science Shows a Way to Get Fit That’s Smarter, Faster, Shorter. He also co-teaches a massive open online course, Hacking Exercise For Health. The surprising new science of fitness. Developed with McMaster colleagues, the course content can be accessed for free through the Coursera learning platform, and to date it has attracted over 60,000 learners.


In this episode we discuss:
– Is high intensity exercise just as good as longer workouts?
– The minimum amount of high intensity training for health benefits.
– How to individualize your exercise plan to optimize results.
– Do supplements really enhance fitness performance?

00:00:00 Intro

00:02:39 High-Intensity Interval Training

00:08:41 Are You Working Hard Enough?

00:17:40 Exercise and Cardiac Fitness

00:21:23 The Impact of Interval Training Have on Body Composition

00:24:28 Which Metrics are Affected?

00:26:48 VO2 Max to Measure Aging

00:31:14 What is Sprint Interval Training?

00:34:19 Minimum Effective Dose

00:38:57 The Benefits for Muscle

00:41:41 Metabolic Flexibility

00:43:40 Nutrition for HIIT

00:56:58 How Does Exercise Affect Your Brain?

01:00:10 What’s Next?

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Dr. Martin Gibala, Dr. Gabrielle Lyon

Dr. Gabrielle Lyon [0:00:01]

Welcome to the Dr. Gabrielle Lyon Show where I believe a healthy world is based on transparent conversations. In today’s episode of The Dr. Gabrielle Lyon Show, I sit down with Dr. Martin Gibala. He is a professor and the Faculty of Science Research chair in Integrative Exercise Physiology at McMaster University in Hamilton, Canada. His research examines the mechanistic basis of exercise responses and the impacts on health and performance. Dr. Gibala’s laboratory is internationally recognized for studies on interval training. This guy is truly a world leading expert and maverick in examining interval training. This work has attracted immense scientific attention and worldwide media coverage.

In today’s episode, we dive deep into interval training, high-intensity interval training, sprint interval training, the mechanisms by how these things work, the minimum amount you need, how an individual designs a protocol based on age and outcome desired, and what does the science actually say about high-intensity interval training compared to other training modalities? I absolutely loved sitting down with Dr. Gibala. He is an amazing interview, very charismatic, and a brilliant science communicator. As always, if you like this episode of the show, please rate it, subscribe, share it. We do our best to bring you evidence-based information with world leading experts. Let’s dive in.

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Dr. Martin Gibala, thank you so much for joining me on the Dr. Gabrielle Lyon Show. It is a great privilege to talk about all things high-intensity interval training.

Dr. Martin Gibala [0:05:01]

Thank you for the opportunity.

Dr. Gabrielle Lyon [0:05:04]

This is going to be great. Basically, when I asked Stu Phillips, this is a handful of years ago, I said, tell me who is the guy to go to for high-intensity interval training? Of course, you were number one on the list. I would love for you to share a little bit about your research, how you got where you are, and what you are currently doing in your lab.

Dr. Martin Gibala [0:05:28]

Yeah, so happy to delve into that. I think interval training, right off the top, is one of those things we tend to rediscover every decade or so. Sometimes I’m called the guru, but it makes me quite uncomfortable because clearly, there’s many good people working in the area, and a lot of good folks have come before me even in studying this from a scientific perspective. But athletes have been using interval training since the turn of the century. It’s actually been advanced as a means to enhance health for many decades. We started getting into this research probably about 15 years ago. The classic story that I tell is, I teach an undergraduate course, a senior course, called the Integrative Physiology of Human Performance. The students were always very interested in the training regimes of elite athletes, so I would ask them, why does sprinting help aerobic performance? Why do athletes practice interval training to enhance their endurance performance? It was a way to teach them a little bit about the biochemistry. When I first got into this, I was a busy young professor with a working spouse, two young children, and so, quite ironically, for a professor of exercise physiology, I found myself with little time to exercise and train. That led to a personal and professional interest that has lasted now, almost 20 years.

Dr. Gabrielle Lyon [0:06:46]

And you still love it?

Dr. Martin Gibala [0:06:47]

I do. I definitely practice what I preach. We’re not only saying it’s the only way to get fit or to enhance your health, but it’s certainly a very effective option, I think.

Dr. Gabrielle Lyon [0:07:00]

I would say that a lot of people really agree. My patients always ask me, how do we define interval training? In the literature, and obviously, on social media, it just seems as if there’s a lot of discussion, but truly, there’s various kinds of interval training. I would love for you to lay the foundation of those definitions.

Dr. Martin Gibala [0:07:20]

Absolutely. Interval training, to me at least, is just alternating periods of more intense effort with recovery, and how we define more intense, we can get into, and recovery can be complete rest or just lower-intensity activity. Let’s first separate interval training from high-intensity interval training. You can do moderate interval training, which might be an example of intermittent walking, the classic example where you’re out for a walk with your spouse or partner at night or walking the dog, you just pick up the pace for a few light posts. You’re not necessarily getting into the high intensity or vigorous intensity range, but that’s an example, to me at least, of interval training. I like to have this broad, all-encompassing philosophy for what constitutes interval training.

Now, what is high-intensity interval training? This is front of mind because I’m actually writing a review article right now with my postdoc and a couple of other distinguished professors on this topic of what means high-intensity interval training, whether you’re interested for health or performance. On a health side, if we look at the WHO guidelines, the authoritative guidelines for physical activity intensity classification, the WHO basically has three: light, moderate, and vigorous. Of course, vigorous is defined by RPE or METs. I like to position or think of high-intensity interval training as generally equating with vigorous-type effort. If you look at the American College of Sports Medicine guidelines, they expand out the exercise categories to include very light and near maximal to maximal type exercise, but they also have a vigorous intensity range.

The point here is, often people will say, it’s around somewhere about 80% of your maximum heart rate or above. We’re trying to reframe the messaging a little bit or propose, let’s just think of it as vigorous intensity-type effort, whether you define that based on heart rate, RPE, percentages of VO₂ max, vigorous intensity effort range is well-defined in the public health and exercise prescription guidelines. That’s how I would like people to think about high-intensity interval training. Then there’s a more intense version called sprint interval training that would be in that near maximal to maximal type effort range.

If you’re an athlete, and just to finish on the athlete side, athletes talk about domain-based training. There’s a classic three-domain model for athletes, moderate, heavy, severe intensities, and then of course, many athletes want to break that down further into zone training 4, 5, 6, 7, 8 zones. On the athlete side of things, I think you’re in the severe intensity domain, which is typically defined as being above your second lactate threshold or critical power, critical speed. In some, I think we can have this broad definition of high-intensity interval training, and then contextualize it, whether you’re an athlete or whether you’re someone who’s interested in general health and performance. There’s no single metric that’s appropriate for everyone, or explicitly defines it based on one marker.

Dr. Gabrielle Lyon [0:10:54]

That’s really fascinating because oftentimes, when we think about dosing something as it relates to a treatment, in my mind, we also need to think about dosing exercise. What I’m hearing you say is that dose is different for everybody. As it relates to perceived exertion, how would an individual know that they are working hard enough to get a physiological or metabolic adaptation?

Dr. Martin Gibala [0:11:17]

I don’t want to hedge with all my answers or be the classic scientist who says, well, it depends, and there’s a lot of gray. But for all of this, of course there is. It depends what your starting point is. I could take 100 individuals, and for some, a given dose of exercise is hardly a physiological stress at all for them if they’re relatively fit. If they’re quite fit, of course, it may be too much for them or overwhelm them. But in terms of RPE, the classic scales, there are two classic scales. If you go back to the work of Gunnar Borg, there’s the 6 to 20 scale. Typically, there we’d be talking 14 out of 20 on that scale would be getting into the vigorous intensity range. If you use a 0 to 10 or a 1 to 10 scale, which I think makes intuitive sense for a lot more individuals, or people can think of okay, 0 is laying in bed, complete rest, and 10 is sprint from danger pace, or sprint to save your child from an oncoming car. If we say that vigorous intensity exercise is a 7 on a 10 scale, you can start to contextualize that a little bit. In terms of the RPE, that’s what we’re talking about in terms of high intensity if we’re going to say that’s into that vigorous intensity range.

Dr. Gabrielle Lyon [0:12:40]

Let’s say someone is an individual who’s relatively fit, and they’ve really focused on strength training. How much high-intensity interval training should they impart?

Dr. Martin Gibala [0:12:51]

That’s the classic question. Again, my first answer to that would be everyone’s different. For a given exercise program, some are going to thrive, some are going to wither. It really depends on the individual and their tolerability. From a strength training perspective, and we really haven’t even talked about high-intensity resistance exercise or high-intensity functional training, that’s even more challenging, or there’s even less clarity around what constitutes that. So maybe even just back up a bit, the first question is, is resistance exercise high-intensity interval training? Maybe. I think this idea of high-intensity functional training, where we’re talking functional-style movements, often bodyweight-style movements, that can broadly count as interval training, but it’s a different stimulus than when we think of traditional high-intensity interval training, which is aerobic-based, running, cycling, things like that.

How much is too much? I think it depends on first of all, what are your goals? Why are you doing this type of training, and what’s your specific goal? What’s the overall volume of work that you’re doing? Are you lifting or training six days a week? Are you also employing cardio with that? When we talk about potential risk of overtraining, it does depend on the overall volume of exercise. So regrettably, I can’t give you a definitive answer and say, two sessions a week, or three sessions a week is the ideal or perfect for most individuals. You look on the internet or read a magazine, they’ll say, you can’t do more than one HIIT session a week if you’re doing it right because you’ll break down. Some people say, I only do interval training, and I’m fine. It really depends.

Dr. Gabrielle Lyon [0:14:45]

As it relates to some of the metabolic adaptations, would you say classic high-intensity interval training is the, like you said, bike training or sprint training? It’s some kind of movement, not body weight or weight training. If we were to define high-intensity interval training, what are some of the metabolic responses? Do you anticipate in how long does it take to see some kind of metabolic response?

Dr. Martin Gibala [0:15:14]

High-intensity interval training, when we use traditional aerobic/endurance-type activities, cycling, running, elliptical, swimming, things like that, those would be the classic examples, it’s a pronounced physiological stress. The major responses that we see are an enhanced aerobic capacity and increased ability to transport and utilize oxygen. The physiological systems involved there are heart, lungs, blood vessels, skeletal muscle, their ability to use the oxygen, and so, absolutely, we can then see an enhancement or improvement in cardiac function. Stroke volume goes up. Peak cardiac output increases. Blood volume can increase. Skeletal muscle, mitochondria, the components of skeletal muscle that utilize oxygen to burn fuels like sugars and fats to produce energy, we can see very rapid remodeling or an increase in mitochondrial content, literally, within a couple of sessions. You can see those changes, again, depending on the starting point.

Now, we can have many of those same changes with traditional continuous aerobic-style training. I like to think of it as the physiology is the same, but how you stimulate the physiology in order to adapt and respond, there are different inputs there that can be effective. Now if you look at what elite endurance athletes do, any serious elite endurance athlete practices interval training because the evidence is very clear that they’re going to optimize or further enhance the physiology in order to optimize performance, as opposed to just continuous, moderate steady-state training all the time.

Dr. Gabrielle Lyon [0:17:06]

That’s very valuable. When an individual thinks, I’m going to sit down on my Airdyne bike and do an interval training session, is there a certain amount of time? For example, does it need to reach 20 seconds? Does it need to reach 10 seconds? Is there a goal that an individual can shoot for? Let’s just assume that this is a non-sedentary individual.

Dr. Martin Gibala [0:17:29]

My personal opinion here, but I think backed up by some research, my personal sense is, ideally, you want to get your heart rate into that vigorous range. You want to get into that vigorous range, let’s say, based on a heart rate response for at least 10 minutes in order to have a minimal training stimulus. Now, there’s many ways that you can do that. For example, you could do three 20-second all out bursts of activity with a short warm up, a short cooldown, and a little bit of recovery in between. If we look at the heart rate response, it gets up very quickly, and it stays elevated for about 10 minutes. That’s where the title of my book came from based on some of our research looking at three 20-second efforts. Now, that’s not saying it’s the optimal way to train. It’s not saying that that’s appropriate for everyone or the best. You could also use less intense intervals with shorter recovery periods. One minute on, one minute off is another example and just doing five of those sessions. Again, you’re going to get into that 80% heart rate range for at least 10 minutes.

I tend to think that’s about the minimum stimulus that’s required. The caveat there to that is some of the work that we’re starting to do now looking at what we’ve called exercise snacks, we’re not the first to use that term, but we’ve defined this as one-minute bursts of vigorous effort that are performed periodically throughout the day. The analogy there is you’re heading to work in the morning, one-minute vigorous effort, a couple of times a day, maybe at lunch before you leave for the day. This could be bodyweight style exercise at your desk. Imagine me getting up right now doing a series of air squats or burpees for a minute. There, the recovery periods are very long, but there’s some preliminary work to say even that type of stimulus is enough to enhance cardiorespiratory fitness or VO₂ max. Again, it’s not ideal, but it’s another strategy that someone might employ. Maybe that’s cumulative, adding it up over the course of the day.

Dr. Gabrielle Lyon [0:19:49]

Would that be less ideal than doing it all at once?

Dr. Martin Gibala [0:19:53]

I think so. I’ll give you a very specific example. When we’ve looked at those three 20-second bursts of effort, and people do that over a 10-minute period, start to finish, so you can imagine one session during the day, three 20-second bursts over a 10-minute period. If they do that three times a week for six weeks, we see a 1 MET improvement, about a 10% boost in their cardiorespiratory fitness. Now when we’ve looked at the exercise snacks approach, so basically a very similar dose of exercise but spread over the course of the day, the improvement in fitness is smaller. These are small studies, not all head-to-head comparisons, not systematic randomized controlled trials, but the takeaway there is the longer the recovery period, the less the stimulus. When you stack the stimuli close together, it makes intuitive sense, but there is scientific data that would suggest that.

Dr. Gabrielle Lyon [0:20:50]

What would be at the higher end? If 10 minutes is the lower, would you say doubling that would be adequate per an ideal session?

Dr. Martin Gibala [0:20:59]

20 or 25 minutes of intervals, I think, is a more standard or traditional or typical HIIT session, again, for that average individual or the general person who’s already fit and looking to further enhance their performance. Now for the elite athlete, obviously, you sometimes go much longer than that. But yeah, I think 20, 25 minutes, I hate to use that term sweet spot, but it seems to be an appropriate dose. In many of our studies, for example, we’ve done that 10 x 1 workout, so one minute on, one minute off, repeated 10 times,  or we’ve used other ways where the interval training session lasts about 20 or 25 minutes.

Dr. Gabrielle Lyon [0:21:43]

How often could an individual do that? I know you’re going to say it probably depends on the other activities. Let’s say that this was the only thing that they were going to do. How many times a week could they do that?

Dr. Martin Gibala [0:21:52]

The vast majority of studies are three times a week. Again, not that I’m suggesting anyone go on to train the way that I personally train, but I’m sure that question I’ll come up, what do you do personally?

Dr. Gabrielle Lyon [0:22:03]

No, we do at our house.

Dr. Martin Gibala [0:22:06]

I’m a committed exerciser. I don’t need to be motivated to exercise like many of your listeners, of course, but I tend to go three sessions a week of aerobic-based cardio-style interval training, much of that is on a cycle ergometer or stationary ergometer, or outside, if I can ride, obviously, when the weather’s nice. That’s interspersed with what you’d call high-intensity functional training, bodyweight-style exercise, small equipment-style exercise. That’s typically six sessions a week. Three of those are exactly what I just described to you as high-intensity cardio-style interval training.

Dr. Gabrielle Lyon [0:22:44]

The other ones, how long do those other sessions last?

Dr. Martin Gibala [0:22:48]

Rarely am I exercising for more than half an hour. The bodyweight sessions tend to be around the same thing. You’re looking at probably 15, 20 sets in total of various bodyweight-style exercises that lasts about half an hour. Now in the late spring, the summer, the fall, I like to cycle a lot outside, and so my cycling moves from 20-minute, 30-interval sessions on a stationary bike to much longer rides outside because I enjoy that. Of course, any cycling outside almost invariably involves interval training, unless it’s a very flat course that you’re only riding. But around here, there’s some hills and valleys, and so it’s natural interval training, of course.

Dr. Gabrielle Lyon [0:23:34]

It actually sounds like a lot of fun. What impact does interval training have on body composition?

 Dr. Martin Gibala [0:23:41]

Like most forms of exercise, interval training can be used as a strategy to assist with weight management and elicit some changes in body composition. I think it’s important that we don’t overstate it, of course, and as you well know and many of your listeners, I’m sure, nutrition is the primary driver there. But there are data to suggest that you can see an increase in lean body mass or reduction in fat mass with interval training. They tend to be subtle. We’re not talking massive changes in body composition, unless there’s a pronounced dietary component to that. It would also depend on the type of interval training. If we’re talking what we’ve defined here as functional-style interval training with more of a resistive element, you’re going to see greater increases in muscle hypertrophy potentially, your strength gains, and so a greater stimulus for a lean mass improvement.

Often people will say, how can intervals be effective at all for weight loss or weight management because they’re often very short? Personal trainers talk about the afterburn effect, there’s definitely something to that. The more vigorous the preceding exercise, even if it’s short, metabolic rate increases in recovery. Again, it’s often overstated, but there’s definitely something to these small transient boosts in metabolic rate adding up over time and supporting weight management, body composition changes especially over time.

Dr. Gabrielle Lyon [0:25:11]

In any of your studies, did you also look at blood biomarkers, like triglycerides, glucose, or insulin?

Dr. Martin Gibala [0:25:16]

We look at those a lot. We’ve looked at a lot of glycemic metrics. We’ve looked at static blood glucose measures and various measures of insulin sensitivity. We’ve used continuous glucose monitoring in some of our studies. Yes, we can see improvements in various metrics, certainly of glycemic control, with the various interval training models that we’ve used. Some others have shown some changes in blood fats, again, consistent with an enhanced health profile when we look at numerous commonly measured blood markers of health.

Dr. Gabrielle Lyon [0:25:54]

In a weight-neutral individual, let’s say that they’re healthy, athletic individual, in the study, do you see changes that are short term as it relates to triglycerides or insulin regulation? Or does it really require a 12-week period?

Dr. Martin Gibala [0:26:13]

You can definitely see changes within about six weeks or so. Now, how long those would persist if someone just stopped? We’d probably see a fairly rapid decline. You would be well aware of the whole, I don’t want to call it a controversy, but does exercise training elicit chronic improvements and insulin sensitivity, or is it just the fact that you’re doing repeated acute bouts and you’re seeing the residual effect of that previous bout, and as soon as you stop, it’s going to go away? Often, our studies are six weeks in duration. We see measurable improvements in various markers of glycemic control glucose parameters, so that’s the timeline that we’re looking at. It depends on the starting capacity of an individual. We’ve seen marked changes in glucose control using continuous glucose monitoring with six sessions over two weeks in individuals who are older with type 2 diabetes. You can see very rapid changes, again, depending where the starting level is. You alluded to people who are already quite fit, there’s only so much improvement you can get when you already have good tight glycemic control to start.

Dr. Gabrielle Lyon [0:27:31]

As it relates to the aging population, there’s a lot of discussion about how VO₂ max decreases as individuals age. I often wonder, is this also related to muscle mass? Are there changes that we anticipate for an older individual, or can those be mitigated based on their activity level in general?

Dr. Martin Gibala [0:27:52]

Arguably, and probably inarguably, the most common metric looked in the literature across ages, different types of interval training, is cardiorespiratory fitness as objectively measured with the VO₂ max test as you allude to because it’s such an important marker of health. Direct correlations between risk of dying from what causes, risk of developing type 2 diabetes, cardiovascular disease, and so if you can enhance or maintain your cardiorespiratory fitness as long as you can, that’s generally a good strategy, and interval training can be a very effective way in order to do that. You alluded to sarcopenia. I think there could be a really good debate around if you could only do one, do you want to try and enhance cardiorespiratory fitness, or do you want to try and enhance muscle strength as you age? Clearly, you want to do both. That’s where functional-style high-intensity interval training can be very effective because you’re getting the strength benefit, especially lower body strength, depending on the movements that you’re using. If you keep the recovery period short, high-intensity functional training can lead to improvements or at least the maintenance of cardiorespiratory fitness as well. We know that there’s many types of interval training, including functional-style training that have been applied safely and efficaciously in older individuals. We’re talking even into octogenarians. Like many forms of exercise, we can appropriately tailor it to the individual. To just say that every everyone can do interval training, or no one can do interval training, those blanket statements just aren’t appropriate.

Dr. Gabrielle Lyon [0:29:42]

Are there ever times where an individual say, they’re relatively untrained, and they’re unable to utilize their skeletal muscle enough to bring up their heart rate? Do you see that?

 Dr. Martin Gibala [0:29:53]

We have not in our studies, even with some fairly deconditioned individuals. I have not done these studies, but some of my colleagues have. There is work, for example, looking at individuals with spinal cord injury, especially lower body spinal cord injury, where those individuals can perform arm-cranking exercise in order to try and elicit a cardiorespiratory stress. That style of exercise in individuals like that can also be effectively applied. My short answer to your question is no, we have not seen a situation where people are unable to sufficiently activate their skeletal muscles to get a cardiovascular training stimulus.

Dr. Gabrielle Lyon [0:30:39]

So, essentially, everybody could do this.


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Dr. Martin Gibala [0:33:42]

Essentially, yes, unless there’s an explicit contraindication. If someone is just very deconditioned, just starting out, I don’t think they need to be afraid of interval training. They might not necessarily want to jump right into high intensity, certainly sprint interval training. But just that idea of hills and valleys, light to moderate, alternating pattern of activity can be extremely effective. Ideally, I think we would always suggest that people start with moderate preconditioning before they start to push themselves. That being said, high-intensity interval training has been applied to many different individuals. Again, I’m not a medical doctor nor a cardiologist, but there are explicit conditions, unstable angina, for example, where this might be absolutely contraindicated. But it’s more, I would say, the exception than the rule for as a general statement can most people perform interval-type exercise.

Dr. Gabrielle Lyon [0:34:44]

That’s very valuable because oftentimes people will think about all the roadblocks to training, and nothing is more important than the physical health, really leveraging that skeletal muscle. Can you define sprint interval training, and when that would be utilized?

Dr. Martin Gibala [0:35:00]

Our working definition, and I think this generally aligns with how it’s often used, why don’t I start with the performance side because maybe it’s a little bit easier there. Sprint interval training would be at a pace that’s above maximal aerobic work rate, so maximal aerobic speed; if you’re a runner, maximum aerobic power; if you’re a cyclist, so you can imagine what is the power or speed that elicits your VO₂ max? But of course, you can work well above that up to what coaches and athletes refer to maximal sprint speed. That difference between maximum aerobic work rate and maximal sprint rate is sometimes called your anaerobic speed reserve. But the bottom line is working above VO₂ max work rate pace constitutes sprint interval-type training in a performance setting where there, we’re usually often aware of what peak workloads or peak work rates are.

On the health side, I would go back to the ACSM definition of near maximal to maximal exercise, and there, we’re talking above about 91% of VO₂ max, above 95% of heart rate max, 17 out of 20 on an RPE scale. Those are contextualized reasonable values, if you will, or thresholds for what distinguishes this particularly intense variant sprint interval training from other forms of lower intensity high-intensity interval training.

Dr. Gabrielle Lyon [0:36:42]            

It’s very uncomfortable.

Dr. Martin Gibala [0:36:45]

It is. There’s no free lunch here. If you want the benefits–

Dr. Gabrielle Lyon [0:36:49]

You are not going to look forward to this session, or if you are, you are definitely doing it wrong.

Dr. Martin Gibala [0:36:55]

Absolutely. It’s an uncomfortable form of exercise. The pace required to do it right is uncomfortable. This is where it’s really important to understand the nuance of well, what is HIIT? What is SIT? I would submit that sometimes for the folks who aren’t fans of interval training, and there’s some vocal ones out there, of course, they will try to sometimes position interval training as only sprint-type interval training or these all out Wingate-type efforts and say, no one’s going to do that. Many people are unwilling or unable to do that style of training. But there’s a there’s huge range there, I think, when it comes to high-intensity interval training.

Dr. Gabrielle Lyon [0:37:37]

Essentially, everyone can do high-intensity interval training. Sprint interval training is somewhat of its own beast to even know that you’re reaching that max capacity.

Dr. Martin Gibala [0:37:47]

I think that’s fair to say. Even when we say everyone can do HIIT, the vast majority of people can, and there may be some who it’s contraindicated for. But I think that’s a fair analogy, how you just placed that.

Dr. Gabrielle Lyon [0:38:01]

We discussed that the length of time, a minimum effective dose would be about 10 minutes of high-intensity interval training, a sweet spot would be 20 to 25 minutes. Where does sprint interval training fall in that?

Dr. Martin Gibala [0:38:13]

When I said that 10 minutes, those three 20-second bursts of training are our sprint-type efforts. That would be an example of where one minute of intermittent sprinting over a 10-minute period, we know that is sufficient to get into that elevated heart rate range. We know that type of training leads to marked and robust increases in mitochondrial content. Again, if you’re able and willing to do that sprint-type effort, it can be an extremely, certainly, time-efficient way for people to train, but it’s just one flavor.

Dr. Gabrielle Lyon [0:38:55]

One minute, over 10 minutes at max effort. One minute total.

Dr. Martin Gibala [0:39:01]

That’s exactly right. To say it explicitly for your listeners, in the studies, we’ve generally done a three-minute warm up, 20-second all-out sprint, two minutes recovery, another 20-second sprint, two minutes recovery, a final 20-second sprint, another two minutes of recovery. If you add that up, it’s 10 minutes from start to finish, and within that, only one minute of hard effort, one minute of all-out effort as three 20-second bursts.

Dr. Gabrielle Lyon [0:39:33]

That’s incredible. That’s so efficient and effective. As it relates to sex differences, men and women, do you see that some individuals respond better than others? How can we think about that?

Dr. Martin Gibala [0:39:47]

Yeah, absolutely. There are definitely suggestions in the literature, including from our own laboratory, where biological males and biological females show some slightly different responses. For example, there’s some evidence that the cardiovascular, the cardiac output response in females may be blunted compared to males. But these studies tend to be relatively small. It’s hard to say, is this a true biological sex difference, or is this just inter-individual differences in training responsiveness? I think the best answer could be, I think there’s much greater inter-individual differences in training responsiveness, regardless of if you identify as a man or a woman, or you’re a biological male or biological female. That’s not to say there’s no sex-based differences at all. But I think in a lot of things, they tend to be relatively subtle. They may be real, but we really need some very large-scale studies to pull this out and tease this out. To be clear, males and females can both respond robustly to interval-style training. There might be some subtle differences there that may be related to biological sex.

Dr. Gabrielle Lyon [0:41:09]

You had mentioned that there’s an influence on mitochondria or mitochondrial health. I’m curious as to what are some of those influences. My next question is, do you also see changes in fiber type? My listeners are very interested in aging and protecting themselves about, at least you guys better be, aging, protecting themselves against sarcopenia, which we know that there are fiber-type changes. What are some of the fiber-type changes that you’ve seen in high-intensity interval training, and also some of those other adaptations like mitochondria?

Dr. Martin Gibala [0:41:45]

A very primary focus of my laboratory has been on mitochondria. You can measure those in different ways. We can look at, for example, acute markers of mitochondrial biogenesis. You can imagine these are molecular proteins that are turned on or triggered after a single session of exercise, including HIIT or sprint-type protocols. We can see robust phosphorylation or increased activation of many of these mitochondrial biogenesis proteins. After a few days or weeks or months, we see measurable increases in mitochondrial protein content. We’ll pick specific proteins that we know are integral to mitochondria, and we’ll measure those in different ways, either in the maximal activity or the content of those, and we see that they’re increased.

You can also measure something called mitochondrial respiration, which is a measure of how functional the mitochondria are, literally, how much oxygen is that unit of mitochondria using. There’s various metrics that we’ve used and shown that all of them can be increased to varying degrees. These are hard studies to do, but in collaboration with some colleagues down in Australia, we have done some fiber-type specific responses both acutely and after a period of training. We can see stimulation of both of those things, acute biomarkers as well as training markers, in both fiber types, type one, type two muscle fibers. There’s not a massive hypertrophy response. You can basically, with traditional aerobic-style interval training, if we use that broad term, you see an improvement in the metabolic profile of the fibers and enhanced mitochondrial content, which should suggest greater ability to burn fat and sugars. But we don’t see marked hypertrophy growth of those muscle fibers. Sprint and HIIT are not really a massive hypertrophic stimulus, but they do target the fibers to make them more metabolically healthy, if you will.

Dr. Gabrielle Lyon [0:43:52]

Metabolic health, there’s a lot of discussion in the literature and just within probably mutual colleagues of ours about flux, glycogen flux. Can you talk a little bit about the substrate utilization, I think, would be very valuable for people as they’re thinking about it?

Dr. Martin Gibala [0:44:08]

Yeah, absolutely. Again, generally speaking, when we talk about substrate flux, or often the term is metabolic flexibility, so you’d like to provide or you’d like to have muscle fibers that are very flexible in terms of what fuels they’ll utilize and how much in different rates. Broadly speaking, that aligns or correlates very well with mitochondrial health and function. If you enhance your mitochondria, you tend to have a greater capacity to utilize both sugars and fats, muscle glycogen, triglyceride, bloodborne fats, bloodborne sugars. In my view, many types of exercise training will enhance mitochondrial content, mitochondrial function, mitochondrial health, and that in turn trans lates into greater metabolic flexibility and the ability to use sugars or fats, depending on when the need arises. What we’ll often see is in resting conditions, the ability to utilize lipid at rest or burn fat at rest is enhanced. It’s also enhanced during exercise, and then when you really have to drop the hammer and perform hard, you can oxidize or burn through sugar glycogen at a higher rate as well. It’s like the overall capacity increases, and then at a given situation, rest, moderate exercise, high-intensity exercise, you can shift the type of fuel that you’re using in those various states.

Dr. Gabrielle Lyon [0:45:41]

Essentially, you train your body not just physically, but you’re training your body to use substrates effectively, especially the times in which you should be, whether it’s using free fatty acids or glucose. As it relates to nutrition, have you thought much about nutrition for improvement in an individual’s capacity to perform HIIT or even sprint interval? Now that we’ve just talked about high-intensity interval, and we know that sprint interval is its own beast, I am very hesitant to even lump those nutritional aspects together. So I will let you take it away and decide if they should be lumped together or not.

Dr. Martin Gibala [0:46:14]

No, that’s great. We have been interested for the potential for nutrition to augment responses. I would say that exercise, whether it’s HIIT or SIT, that’s the big hammer, and there’s maybe subtle influences of nutrition. For example, we’ve given specific supplements or compounds in an effort to try and enhance various indices, and we see very subtle effects. We’ve had people trained in the fed or fasted state, for example. Other work that’s looked at carbohydrate restriction or carbohydrate supplementation, again, maybe on the restriction side, there’s suggestions of maybe some enhancements in mitochondria. That’s a really loaded issue, and it doesn’t mean that people should train glycogen depleted or anything like that, or certainly not race glycogen depleted. But suffice to say, nutrition can subtly modify some of these responses that we see to HIIT and SIT, but it tends to be small and subtle, and the main stimulus is the exercise stimulus.

Dr. Gabrielle Lyon [0:47:28]

Is it small and subtle because of the amount of time of the activity?

Dr. Martin Gibala [0:47:33]

Possibly, but I think just more exercise is such a powerful stimulus that the modifications that you can get through nutrition tend to be relatively subtle. Of course, writ large, a limitation of the field is many studies, they tend to be relatively small in terms of number of participants, and they tend to be relatively short-term. A three-month training study, if you do it well, it’s hard to do, and that’s a relatively short period of time. There certainly aren’t large-scale randomized clinical studies looking at the interactive effects of nutrition and interval training. There are now some very long duration, high-intensity interval training studies. For example, the Generation 100 study followed older individuals over five years of interval or moderate continuous-style training. There are some longer duration studies now, but they’re more the exception than the rule.

Dr. Gabrielle Lyon [0:48:40]

I have a feeling I know what you’re going to say, so I’m going to say, don’t say as long as you get it in. I’m laying it out there. The capacity to perform high-intensity interval training probably affects the nervous system, and potentially, the body would experience say, a stress different than an individual who is going to do maybe deadlifts or squats. Does timing matter? You’re not allowed to say, only as long as you get it in that day. Is there some benefit to doing it earlier on in the day from perhaps asleep or some kind of recovery, or metabolic benefit or cortisol benefit versus if an individual is doing a sprint interval training at eight o’clock at night?

Dr. Martin Gibala [0:49:34]

Maybe, and why I say maybe is if you do it in the morning, you’re more likely to get it in. I have colleagues who will talk about you got so much battery life through the day. Stuart Phillips definitely talks about this from exercise behavior colleagues, talk about the battery, and over the course of the day, the battery drains down. You could argue that while the battery is nice and high at the start of the day, you get it in and maybe you’re going to give it a little more effort or something like that. Maybe that then primes your system and again, we’re using very loose words here, but somehow, primes your system, then you’re going to hit it with big breakfast after that, and the muscles are primed to absorb the sugar stored as muscle glycogen, maybe less of the blood sugar gets shunted off to more negative effects. I think that you could you could make a case for doing interval training in the morning, but you said I can’t say it, so that’s the best evidence that I could give you.

Dr. Gabrielle Lyon [0:50:40]

As it stands right now, it doesn’t really matter if you’re going to do it in the morning or do it at night. You have to know yourself; potentially it could disrupt your sleep. Have you looked at any hormone responses, cortisol, testosterone? Is that anything that you guys are working on in your lab?

Dr. Martin Gibala [0:50:55]

No, we haven’t done a lot of that. I’ll just leave it at that and say, I can’t speak authoritatively to the role of hormones other than clearly, you have massive catecholamine responses when you do this type of training. But we also know that they spike, and then they come back down. I know there’s some suggestions out there that you have chronic increases in cortisol, and that could lead to some deleterious effects. But I don’t see a lot of evidence for that when I look at the literature currently.

Dr. Gabrielle Lyon [0:51:33]

I would agree with you. Perhaps it’s people that are not wanting to exercise.

Dr. Martin Gibala [0:51:38]


Dr. Gabrielle Lyon [0:51:40]

As it relates to supplementation, do you ever recommend creatine or things of that nature? Are there particular supplements that you think are useful?

Dr. Martin Gibala [0:51:54]

I’m a proponent of using natural foods and natural diet. When you look at the number of supplements that are out there where there’s robust evidence that they really may work, it’s precious few, of course. Could an individual supplement with creatine, for example, and would that potentiate responses? I think you’d make a really good theoretical argument for that. I would say the evidence right now for that is limited. Again, there’s good theoretical rationale. Caffeine would be another example because we know with either creatine or caffeine, if you do repeated sprints, you can see an increase, a slight boost in power, and so presumably then, the cumulative stress over time may facilitate some greater adaptations or responses. There’s no doubt that you if you look at acute situations, you can see that. There’s just not great data right now, in my mind, to suggest that any particular supplement is going to absolutely potentiate responses.

Can selected supplements be used quite effectively by athletes? Absolutely. I’m a big fan of the Australian Institute of Sport pyramid; you’ve probably seen in various versions where you have to get the base right in terms of fundamental nutrition, sleep, and training. If all of those things are right, then right at the top of the pyramid, you can potentiate some selected responses. But for the vast majority of us, we don’t have the pyramid right, or there’s so much variability in the pyramid, and that’s where I think any slight benefit that you might get from supplementation is going to be washed out by all this variability up, I didn’t sleep very well last night, or my diet hasn’t been consistently well, or I missed those training sessions.

Dr. Gabrielle Lyon [0:54:05]

I can definitely appreciate that. You’ve been doing this for how many years, 15 now?

Dr. Martin Gibala [0:54:11]


Dr. Gabrielle Lyon [0:54:14]

That means that you know what is coming on the forefront, that there are probably things emerging on the forefront that we have no idea of that are deeply embedded in academics that we have not seen, what are those things?

Dr. Martin Gibala [0:54:32]

A holy grail, for example, would be individualized exercise prescription. It’s a bit like personalized medicine; it’s an attractive concept. I think it’s going to be actually very hard to achieve, but there are definitely people looking at what are these molecular signals. It’s too simplistic to say we’re going to identify the exercise gene or the sprint gene or the HIIT gene or something like that; people have it or they don’t. We know they should train in that manner. But I know there’s very robust work that’s happening right now with these incredible metrics, and these amazing research platforms that are trying to look at these clusters of proteins that you see are only activated to go up with this particular type of training. That’s where then you might be able to get to, well, if we know an athlete has this sort of molecular signature, maybe they might respond more to this type of training or that type of training.

There’s a field of metabolomics, which is similar analogy, but maybe you’re looking at a saliva sample or a blood sample. Ideally, you see, well, if they have this chemical signature, we know that they may respond robustly to this type of exercise to enhance their glucose control. There are definitely studies going on that are looking at that. But again, you need a lot of people. You need to train lots of people different ways and see who responds or not and what their metabolic profiles were to begin with. But I think that’s just a fascinating area of research where there will be advances, the pace of which are hard to say, like we see examples of that in medicine, oncology and cancer biology would be a very clear example of that.

Dr. Gabrielle Lyon [0:56:41]

How far away do you think that we are from being able to push that lever?

Dr. Martin Gibala [0:56:47]

We’re far away if we’re thinking in terms of a parent might take their kid in and get a tissue sample and say, Jr. is going to be a world class sprinter. We’re away from that. I don’t think we’re that far away from starting to identify people who have this metabolic signature or profile. Particularly if they have these few explicit proteins lumped together, we know that they respond very robustly to heavy resistance training. I don’t know yet that we’re going to do much about that. We’re certainly not talking about gene manipulation or anything like that, but it just might help people. Especially the hard gainers or whatever type of exercise you find you’re not responsive to that, it may just help explain that for you.

Dr. Gabrielle Lyon [0:57:39]

I think that would be really incredible. There’s a lot of people in Copenhagen, like Bente Pedersen and a handful of people in Copenhagen, that are really looking to think about and provide a dose response. Do you think that there’s going to be a role for, say, for example, blood markers that we’re not typically measuring, like myokines?

Dr. Martin Gibala [0:58:01]

Yes. That was going to be another example that I was going to point to. There, we’re looking at these myokines, exerkines,  they go by different names. BDNF with the brain is getting a lot of attention right now. I do think some advancements can be made in terms of, what are the best stimuli in order to enhance or stimulate changes in these specific proteins or markers? Can we tie those to neurogenesis or brain health or other specific metabolic health outcomes? Yes, I think there’s going to be advances in that area. Absolutely.

Dr. Gabrielle Lyon [0:58:43]

That is something I’m so interested in, and I think it’s incredibly profound. If that can happen, think about the impact and influence that would have on individuals’ health. I’ve been seeing patients for over a decade, and often, people will say, well, I go to the gym, I work out, and you see them and they may be working out, but you know that their body composition hasn’t changed. They may be very dedicated, but they’re just not getting the stimulus that they need, and perhaps it’s that they’re just not doing the activity that is necessary for their body to produce the myokines or the gene expression that we need. If we could really target that from a muscle-centric medicine perspective, we could change the trajectory of health. As a researcher, you’re probably cringing because I’m talking in an absolute here, but muscle health and that input of exercise is everything.

Dr. Martin Gibala [0:59:37]

I agree 100% with you. By the same token, if you go back to the classic studies of heritage and other studies, we know there are individuals who can do six months of supervised structured exercise training, and their VO₂ max doesn’t budge. It’s not like they weren’t putting in the effort or doing the work or they are cheating on their training diary, but what explains that? What explains those people, or the very few people who might go down in their VO₂ max. Now we call them non-responders; it doesn’t mean they’re non-responders to everything. They might still have an improved blood pressure profile or glucose control profile. But it would be profound, I think, to start to be able to explain, why does that happen? Could we identify those individuals in advance and say, this type of traditional approach to exercise or diet is not ideal for you, and there is some evidence to say that if you tweak it, or you’re trained in this way, or you take this particular supplement, that might help potentiate responsiveness in you.

Dr. Gabrielle Lyon [1:00:47]

That would be incredible, and hopefully, we’re not too far off, and we can start leveraging that. What’s next for you?

Dr. Martin Gibala [1:00:54]

We’re big on the exercise snack stuff. A lot of our studies are what I call, small proof of concept studies. I like to think that we sometimes ask cool questions, but these studies have limitations, of course. If you do very invasive human research, you’re typically not doing thousands of participants because these studies are expensive, and again, very invasive. So definitely one aspect of my lab is moving towards larger, randomized controlled trials. We have two studies ongoing right now with my primary collaborator, Dr. John Liddell at the University of British Columbia, looking at exercise snack interventions, what we call technologically enabled, and we’re working with an industry partner. People will get a prompt on their phone, a message that says, hey, it’s time for your exercise snack. Then they can choose what snack they want to do that shows them a video to do this snack hard. It’s right there in front of you; you just got to follow along and do the exercise snack. Those snacks are vigorous in nature, and there’s another group who’s also getting a snack, but it’s lower intensity in nature. Obviously, our hypothesis is the groups that do the more vigorous exercise snacks over a couple of months of that type of training are going to see a greater improvement in their cardiorespiratory fitness and greater blood profile.

That work is ongoing right now. We’re just about to start a very similar study in individuals with type 2 diabetes. Clearly, lack of time is an excuse for many people. It’s not the primary barrier, it’s an often-cited barrier for why people are not active. But the reality is that many people are looking for time-efficient options, or they will say, I see the guidelines, but how little do I really have to do? How little can I get away with? We think that work will make a contribution by saying, you know what, if you do three exercise snacks a day a few times a week for 12 weeks, you can see improvements in your blood sugar profile. That work is ongoing.

I was very privileged to be part of a very large study that was published at the end of last year that was mining UK Biobank data. You may be aware of the UK Biobank’s very big collection of data in the United Kingdom. It enables you to follow large groups of individuals over time, and that work showed that as little as three to four minutes a day of vigorous intermittent physical activity, not even structured exercise, three to four minutes a day of vigorous intermittent lifestyle physical activity was associated with about a 25% lower mortality compared to people who did not have that. That work to me is quite compelling. Clearly, I’m a proponent of low-dose vigorous intensity exercise for those who are unwilling to engage in large volumes of exercise. We’re trying to now look at that on several fronts, certainly the small basic mechanistic work, controlled randomized trials, and collaborating with some other experts on these larger databases. To me, they’re all suggesting the same thing, and that’s brief vigorous exercise or physical activity can be extremely beneficial to your health.

Dr. Gabrielle Lyon [1:04:31]

I think that’s incredible. I’m so grateful for your time and just the contribution that you’re doing is wonderful. You are articulate and charismatic, which scientists don’t always get to have those qualities. I really appreciate it, and you also have a book.

Dr. Martin Gibala [1:04:48]

I do. It’s a couple years old now, but it’s called One-minute Workout, but it basically talks about a lot of the underlying science, hopefully in an accessible manner. The way that we write scientific articles is obviously very different from how we might try and explain or communicate science to the general public. But we touch on many of the things that we spoke about today. I appreciate that plug, and I appreciate your interest in our work. I hope some of this conversation is of interest to your listeners.

Dr. Gabrielle Lyon [1:05:22]

It will be. We’ll link where to find you on Twitter, and we’ll link a few of your papers. We’ll put that in the newsletter. We have a newsletter. We’ll review one of your papers and put it in there. Thank you again, so much for your time.

Dr. Martin Gibala [1:05:35]

Thank you.


Dr. Gabrielle Lyon [1:05:37]

The Dr. Gabrielle Lyon podcast and YouTube are for general information purposes only and do not constitute the practice of medicine, nursing, or other professional health care services, including the giving of medical advice. No patient-doctor relationship is formed. The use of information on this podcast, YouTube, or materials linked from the podcast or YouTube is at the user’s own risk. The content of this podcast is not intended to substitute for professional medical advice, diagnosis, or treatment. Users should not disregard or delay in obtaining medical advice for any medical condition they may have and should seek the assistance of their health care professional for any such conditions. This is purely for entertainment and educational purposes only.