FoundMyFitness - #082 The Science of Vigorous Exercise — Should We Train Hard or Train Long? | Martin Gibala, Ph.D.

Episode Date: September 19, 2023

Dr. Martin Gibala is a muscle physiologist, professor, and kinesiology department chair at McMaster University in Hamilton, Ontario, Canada. He is best known for pioneering research on the health benefits of high-intensity interval training (HIIT) and his profound understanding of HIIT's physiological mechanisms. He is a co-author of the book "The One-Minute Workout." In this episode, we discuss: (00:00) Introduction (11:00) What is high-intensity training? (11:53) Zone 2 vs. HIIT for VO2 max — which is better? (13:22) The vital role of vigorous exercise (14:40) Why VO2 max matters for longevity (17:45) Why athletes vs. exercisers benefit from different intensity distributions (22:09) Measuring maximum heart rate and VO2 max (30:31) How the heart adapts to HIIT to increase VO2 max (35:47) Why vigorous exercise accelerates mitochondrial adaptation (40:06) Enhancing fat oxidation and mitochondrial growth with vigorous exercise (44:22) How intensive exercise boosts fat breakdown (45:56) Is high-intensity exercise better for autophagy than fasting? (55:15) Exercise snacks (57:55) Why 'choosing the stairs' reduces early death (VILPA study) (1:00:39) Protocol for VO2 max (1:05:50) The effect of HIIT on muscle fiber types (1:10:18) How aging effects muscle fibers (1:14:09) Does high-intensity training produce an "afterburn effect?" (1:16:13) Why vigorous workouts are better for BDNF and cognition (1:23:15) Anti-metastatic cancer effects (1:50:23) Wingate training vs. reHIIT — a comparison of protocols (1:55:38) Perceived exertion vs. HRmax (1:59:23) Interval walking for people with type 2 diabetes (2:01:06) Contraindications of HIIT (2:05:06) Why preconditioning reduces risks from exercise (2:10:44) Can resistance training be a type of aerobic exercise? (2:16:24) Does cardio and strength training interfere with each other? (2:18:45) How many minutes per week of high-intensity training? (2:26:58) Are there sex differences and misconceptions in high-intensity training, for women? (2:27:42) Should post-menopausal women do H.I.I.T.? (2:27:47) Does intense exercise raise cortisol? (2:34:16) Bone density and osteoarthritis (2:36:40) Atrial fibrillation risk (2:39:20) Hypoxic training and blood flow restriction (2:40:45) Tips for training with joint issues Watch this episode on YouTube Show notes are available by clicking here Join over 300,000 people and get the latest distilled information straight to your inbox several times per month: https://www.foundmyfitness.com/newsletter Become a FoundMyFitness premium member to get access to exclusive episodes, emails, live Q+A's with Rhonda and more: https://www.foundmyfitness.com/premium Learn more about the premium podcast The Aliquot: https://www.foundmyfitness.com/aliquot

Hi, friends. Today's episode featuring the world-renowned expert on high-intensity interval training, also known as hit, and author of the one-minute workout, Dr. Martin Gabala, is about the power of having options. The option to be healthy even on the busiest of days. The option to achieve more by doing less, but with greater intensity. The option to make every workout minute count whether you have five or 50. When it comes to how best to achieve the profound benefits of cardiorespiratory training, the faintest hint a mere suggestion of controversy has begun to emerge, dividing the discourse into two camps. On the one side, proponents extoll the virtues of a conversationally paced, lower intensity, but higher volume zone two training. On the other side, advocates argue for the time-efficient and metabolically intense benefits of high-intensity interval training. This begs

the question, should you spend more of your overall time at a vigorous intensity, high heart rate zone, or should you run slow to run fast as the saying goes? In talking to today's guest, I hope to confront that question and those surrounding it head on. Crucially, in the contest between the message of zone two versus the arguably competing message of high intensity training, we must ask ourselves, honestly, where along the spectrum do we most reside? Are we elite endurance athletes optimizing for our 20 to 30 hours per week of training? Or are we the committed exerciser striving to get a few highly effective and impactful hours in every single week? Therein lies a key difference, a crucial piece of context that can help us better understand where we fit in terms of this

concept called intensity distribution. Even if you're a committed exerciser, you may run the risk of non-response. If you're not doing high-intensity training, that's because a surprising 40% of people might not see improvements in their VO2 max, even if they're meeting the guidelines for moderate intensity exercise, roughly two and a half hours per week. But that picture radically changes when we increase the physical demands of the work we're putting in. High intensity interval training in many ways is about doing more with less. It's about creating more physiological stress in a very short period of time, tapping into a time intensity tradeoff where greater intensity yields nearly exponential benefit for the time you put in. Pioneering studies, including those

by Dr. Martin Cabala, underscore the transformative power of hit, revealing that short, intense, but vigorous bursts of exercise can rival and even at times surpass many of the benefits. it's derived from prolonged moderate intensity endurance activities. By incorporating HIT into our routines, we not only optimize our time, but also catalyze the profound metabolic adaptations, enhancing mitochondrial capacity, and improving cardiovascular and potentially brain health. Moreover, HIT's ability to elevate VO2 Max, a definitive marker of cardiorespiratory fitness that tells us how effectively our body can use oxygen and is a strong.

strong predictor of longevity challenges the traditional paradigms of exercise. Some studies show that there is no upper limit to the benefit of cardiorespiratory fitness on mortality. Elite athletes in terms of cardiorespiratory fitness can have a nearly 80% lower risk of mortality than their less fit peers of the same age. As our lifestyles collectively have become increasingly sedentary, the promise of achieving significant health benefits in shorter durations is that, not just appealing, but essential. The science is clear. Hit isn't merely an exercise trend, but a potent tool in our arsenal for longevity and potentially cognitive function. In this episode, we discuss comparisons of various protocols of interval training, such as

sprint interval training versus re-hit versus Tabata, how many minutes or seconds your high-intensity intervals should be. Zone 2 versus hit for VO2 max, which is better. We talk about what hit boosts metabolism, something sometimes called the afterburn effect. We address the misconception that high-intensity exercise is suboptimal for increasing our ability to oxidize fat. This may be counterintuitive, but doing work above and beyond our fat-burning zones actually overall improves our ability to oxidized fat in the big picture. We talk about whether or not high-intensity exercise is a better route to autophagy than fasting. We talk about whether resistance training can be a type of aerobic exercise. Misconceptions on high-intensity

interval training for women should postmenopausal women do hit. Does intense exercise raise cortisol? Is that a problem? Can we train with osteoarthritis? Does it improve bone density? And more. But this discussion of exercise intensity isn't just about cardiorespiratory fitness. Some of the areas we focus on which I believe are unique aspects of vigorous exercise are the effects it has on not only the brain, but also cancer metastasis. Vigorous exercise offers unique, perhaps unrecognized benefits that might remain elusive to those who seldom step out of their comfort zone. Beyond the mere time efficiency of hit, Dr. Gabala and I delve into the potential significance of pushing past the lactate threshold through vigorous exercise for unique cognitive

enhancement. In the world of Zone 2 training, the focus is on maintaining a pace that limits lactate accumulation to a certain point and no further. Contrast this with high-intensity workouts where pushing past certain limits leads to more lactate than your muscles can use. But herein lies an intriguing question. If that, quote-unquote, excess lactate is actually fuel and a signaling molecule for other tissues, including the brain, are we missing out on cognitive benefits by strictly limiting its accumulation as we would with Zone 2. It's a thought-provoking conundrum about the realities of a phenomenon known as the lactate shuttle. We also touch on another fascinating area like how exercise intensity affects blood flow, sheer force, and the role this plays

not only in our brain's health and neurodegenerative disease, but also metastatic cancer resistance. One of the qualities of cancer cells is that they sometimes have vulnerabilities that healthy cells do not. One such weakness of cancer cells is that of mechanical stress. To put it another way, when we exercise, we introduce a new type of stress to cancer. The turbulence that movement creates in our bloodstream can reduce the viability of these cells as they attempt to metastasize. Exercise may reduce the risk of cancer metastasis, and it's possible that vigorous, plays a role amplifying the effect. So whether you're an athlete or a fitness enthusiast or someone

simply keen on aging well and maintaining mental sharpness, today's episode with Dr. Gabala is a treasure trove of information on the many unique qualities of vigorous exercise. Before we jump into the brilliance of hit with expert Marty Gabala, let's pause a moment to appreciate the energy behind this content. You, our community. This podcast is a is not sponsored. It's powered by our fans. Every podcast, every topic article like our new one on photobiomodulation known as red light therapy, even our extensive show notes sent straight to your inbox through our free email newsletter is a testament to our shared passion. But for those wanting to dive deeper, our premium membership is the gateway. Byweekly, my team and I craft

the Science Digest, an email roundup of the latest breakthroughs and interests. Plus, each month, I host an interactive Q&A session discussing everything from recent episodes to popular health and science queries. These sessions, along with the collection of exclusive episodes, find their home in our members-only podcast feed called the Aliquot, organized for easy exploration. If you would like to support our mission, amplify our voice, and immerse yourself in the premium experience, you can learn more at foundmyfitness.com for slash premium. That's P-R-E-M-I-U-M. All right, enough introductions. Let's embark on this intellectual journey with Dr. Gabala. Hi, everyone. I'm sitting here with Dr. Martin Gabala, who is an exercise physiologist and professor at McMaster University in Hamilton, Ontario. I'm pretty excited to be sitting here with Marty. Perhaps he's most well known for his research on, pioneering research

on high intensity interval training. He wrote a very popular book called The One Minute Workout. As you know, Marty, I'm very excited to have you here because I feel like there's a lot of health benefits that can be achieved in a short amount of time if the right intention is there. If you are pushing hard, you are doing a intense workout. And for me, it's very appealing as a full-time mother. full-time, you know, I work full-time. Time is the limiting factor for me. So maybe we could

just jump right in this high-intensity interval training and start with defining some of these terms or differentiating between high-intensity training, H-I-T, and high-intensity interval trading, H-I-T, both short hit, right? So... Yeah, so thanks for the opportunity. Lots of different ways to define things. I think there can be general agreement than when we say high intensity, we're talking a relative heart rate of about 80% of your maximum. But there's no universal definition for high intensity training or high intensity interval training. But that would be a typical or average threshold. So about 80% of max, you're working pretty hard, but it's not an all-out sprint.

Again, the other eye in there is just intermittent. So this idea of going relatively hard, backing off and repeating that pattern a couple of times. And interval training, it's this thing that we seem to rediscover every decade or so. You know, athletes have used it since the turn of the century, but it's certainly become popular with the last decade or so, or renewed popularity, because many people cite time as a major barrier, some more legitimate than others, of course, if it's a real time press issue or not. Is interval training, like when you say interval training, because you said high intensity, you're going like 80% of your max heart rate, if you're doing, is,

interval training also that as well is just kind of interchanged or is it like do you go a little bit less than that? Yeah, I increasingly, I like the term interval training as a more general catch-all term. And again, that's just relatively harder effort and backing off. But it provides, I think, more a broader way of doing that. So if you're just starting out getting into exercise, maybe you just want to start out by walking fast for a few light posts and then backing it off. That's a form of interval training. Don't worry at all about whether you're at 80%. So I think of hit high intensity interval training as one type or one facet of interval training as opposed to being the be all and end all. Got it. So with high intensity interval training hit, there's, I've heard you talk about and you've published research, you've written about it in a popular book, the health benefits of

high-intensity interval training on VO-2-max, which I'm sure you're going to talk all about. But recently, there's been a very, another form that's become very popular of training for improving VO-2 max, which is zone 2 training, as defined by a lower-intensity sort of lactate threshold training. However, that type of training does require a pretty big time commitment, I mean, anywhere between three to six hours a week. So can someone achieve similar improvements or really good improvements in VO2 max from doing, let's say, 20 to 25 minutes of high intensity interval training three to four times a week? And if so, you know, what are we leaving anything on the table if, you know, we're not doing that long duration sort of zone two type of training?

Yeah. So in short, I think you can do more vigorous or high. high intensity exercise for shorter periods of time and at least see similar improvements in VO2 max. So for the individual who is time pressed, I don't think there's a need to do three to four hours of what I understand to be zone two training weekly in order to maximize improvements in VOT2 max. In fact, there's evidence that would suggest that more vigorous intensity exercise, higher intensity exercise can potentiate or lead to greater improvements in VO2 max or eliminate what's known as non-response. So some people engage in training and it's very frustrating because their VO2 max doesn't

change at all. And there's various reasons for that that we can talk about. But for example, some evidence has shown that moderate intensity continuous exercise, even for six months or so, doing guideline-based evidence, roughly 40% of people don't see a measurable improvement in their VO2 max. Now, some of that non-response was eliminated in a group that was doing the same total amount of exercise, but engaging in a more vigorous manner. So, that would seem to argue against Zone 2 somewhat, but I think, you know, there's all roads lead to Rome. You know, there's many different strategies that you can engage in successfully. And I think a big thing is,

What do you like? Do you like and enjoy vigorous intermittent type exercise? Then maybe it's for you. If you prefer continuous lower intensity, moderate exercise training, and that's just what you like and you absolutely hate intervals, that's okay too. Can you talk about what VO2 max is? We hear a lot about it and why it's important for health, longevity, and maybe why athletes would be interested in it as well.

Sure. So VO2 max is the maximum rate of oxygen uptake by the body. It's typically measured during an incremental exercise test. So you get up to very high work rates, and that's where you'll see your highest rate of oxygen uptake. It's determined by many physiological factors and processes, but it reflects the peak integrated capacity of the cardiovascular, the respiratory, the respiratory, the blood, the skeletal muscle system to take up and utilize oxygen.

It's clearly important for athletes. it sort of sets the ceiling, you know, and a challenge for athletes in many events is how close to the ceiling can you work for a defined period of time. And so, you know, the higher the oxygen uptake, the better. It's also that the clinical correlate of VOTU max is cardiospiratory fitness. So VOTU max is the best objective measure of cardiospiratory fitness. And why fitness is so important, epidemiological studies show having a higher cardiospiratory fitness, fitness is associated with a reduction in all-cause mortality, dying from all causes, as well as developing many different chronic diseases, cardiovascular disease, type 2 diabetes. So bottom line is having a higher fitness is better. It protects you. It reduces your risk of dying and develop diseases. And the best way to measure that is through a VO-2 max test. So you mentioned these epidemiological studies, these observational studies that are looking at the correlation between higher V-O-2-Max and, let's say, all-cause mortality.

There's a really, I think, important paper that was published in JAMA in 2018 that showed there was an inverse relationship between VO2 Max and all-cause mortality with no apparent upper limit. And the elite performing athletes or the elite performers had a 80% reduction in all-cause mortality. compared to the lowest performers with their VO2 max. So my question for you is, do you think someone who is doing, let's say, you know, again, doing the high intensity interval training mostly and 20, 25 minutes, three or four times a week, do you think they can be one of those elite? Is that like what you would think would be an elite performer in terms of their VO2 max?

Or do you have to be an athlete? how can someone, do we need to do extra, you know, types of training on top of the hit to really get to that level at 80%. Yeah. And so there's lots of things there. And I think to be clear, the way that an individual may choose to engage in physical activity or exercise for their general health is completely different from a way that an elite endurance athlete might train.

And that has to do with lots of things, including what's the total volume of training. So if you're a serious or an elite or very high level, endurance athlete. You're engaged in 15, 20 sessions of training per week. You're training 25, 30 hours a week of training. And the best evidence, you know, gleaned, there's some scientific evidence, largely, you know, opinion from high level coaches and athletes is about an 80-20 split there is sort of the ideal mixer ratio to optimize endurance performance. So about 80% low to moderate intensity type training and 20% high intensity training, much of it including interval training. Again, that's the way that an elite athlete might train who's putting in

25, 30 hours a week. I think that ratio can change if we're talking about someone who's engaging in one to two or three to four hours a week of physical activity and they're looking to optimize how to structure that type of training fit within their regular lives. And I think there that ratio can change fairly substantially. And you can incorporate, I would submit that engaging in more vigorous intensity type exercise if you're only doing one, two, three hours a week may potentiate or give you a further boost in fitness. So even potentially one hour, one and a half hour hours a week? Because that's also something. I mean, you mentioned the 80-20 split, and that's something I've heard about a lot and I think about it because I am not an athlete.

I am, you know, far from an athlete. I am a committed, you know, exerciser, I guess you would call it. I mean, and I, you know, I am also very interested in longevity in improving my VO2 max. And I want to talk about measuring that, you know, in a minute. But so it's, you know, it's not like finding if, you know, is there a minimum effective dose where we can get 80% of the, you know, improvements in V-O-2 max that an athlete would get. I mean, that, you know, because if I, if I'm in, if I can get like 80, 80%, you know, I'm in, like, that, that's a good amount because there's just, there's, there's no way I will be an athlete. Like, that's not my,

my life. I can't do that, you know. But I want to get those improvements in B02 Max. Correct. No, and, you know, I would consider myself very similar. I'm, I'm a committed exercise. You know, it's in my calendar. I'm sure much like yours is. I'm trying to, but, you know, you're busy, trying to think what's the best way to structure that. But, you know, so a couple of things. I think whatever reason you're active or exercising for, what's the goal? Is it performance? Is it general health? Is it trying to optimize that time? And I think for a lot of people, it does seem to be, this is how much time I have. You know, maybe it's one hour a week, maybe it's two hours a week. What's the best way that I can utilize that time to promote my overall health? And for those

individuals, again, I would submit that there is good evidence that engaging in more vigorous intensity exercise may potentiate the gains. That's not to say it's the prescription for everyone. And the other thing I think we need to remember about VOT2 max is the greatest gains are with the smaller changes in fitness, right? So we look at, you know, people who have low, moderate and high physical activity levels or low, moderate and high VOT2 max levels, the greatest bang for your buck is just getting out of that low range, right? And then you continue to gain benefits, but you get diminishing returns. And the extreme would be the elite athlete who's pretty much doing everything right to maximize their physiology. And now they're really

just playing on that upper margin. You know, what can I possibly do to eke out a little bit more gain? That way, that way of thinking and training is not necessarily the way that average everyday people, even serious committed exercisers who are primary interested in health need to think. Right. Like Stu, I like Stu's analogy of like squeezing the wet towel and like getting the last drops out. You know, that's something that, you know, maybe if I was more of an elite athlete that I would be interested in doing. But right now, I'm like, how can I get to that, you know, where I'm at least 80, 80 percent of getting that VOT2 max? Maybe getting all of it, if I could. Like, going hard and getting it. But you do it. But you do it.

going hard, you mentioned intensity, high intensity interval training, 80% max heart rate. There's these, you know, calculators for maximum heart rate. I guess it's, I would say there's an equation that most people use 220 minus your age. But that doesn't consider fitness levels. I mean, is that, would you say that's still kind of the best way for someone who is not going to go out or should they like go do an all-out sprint or something and measure their max heart rate? So I, and there, you know, 220 minus your age is still probably the most common. There's a number of other formulas, formulas that have been proposed and looked at scientifically. I think the key thing to remember is there's variability around that. And so if we had a thousand of your listeners and they were all 40 years old, we could be reasonably confident that the average maximal heart rate of those thousand listeners is 180, 220 minus 40. But there's going to be tremendous inter-individual variability there. And what we call the standard deviation, it's around

10 beats per minute. But what that means is about two-thirds of your listeners would fall somewhere between 170 and 190. 95% of listeners would fall somewhere between 160 and 200. And there'd be 5% on either tail, 2.5% each, where their maximum heart rate is actually below 160, or or above 200. So there's a huge range there. And so when you just pick, so for an individual listener now, they're going to work at 220 minus their age,

it might be dramatically underestimating intensity or dramatically overestimating intensity. So 220 minus your age, it's fine. I think a better way to do it is just try and measure it on yourself. And there's different ways to do that. The classic would be to go out to a local high school or running track and run a 400 meter

or 400-yard loop one time around as hard as you can, you're going to pretty much get to your maximum heart rate by the end. Or if you're on a bike, you know, a stationary agometer, just ride at higher and higher intensity. So you're increasing the watt every one minute. You're putting it up 10 or 20 watts until you can't go anymore. You're going to be able to measure your individual maximum heart rate, whether you palpate that, whether you're using the hand,

or whether you have a chest strap or your monitor on. So bottom line is measuring it directly on yourself is always going to be better. Well, those are some good suggestions that I'm going to do myself for sure because I have not done the actual test. Is it called a stress test too that some people do? You stress your body to the limits. Exactly. So definitely, you know, we have people come into our lab and get tested all the time on a VOT2 max test and we'll be able to give them their maximum heart rate measured very, very accurately.

but it's also something you do on your own very cheaply, right? As long as you're measuring it with a reasonably accurate device. So it's sort of the simple way of getting it. Yeah. For the VO2 max, like measuring the maximal amount of oxygen you're taking in during, I guess, maximum exercise, there's, you mentioned to me, most people are very interested in that and they're not going to get that measure directly. they're not going to a lab like yours or to their, you know, physician doing it. But they want to know,

should I do it? Or is there a estimator I can do that's good enough? Or how do I decide if I should or shouldn't, like what, you know, like athletes, probably maybe they should. But, you know, so this online calculator, the world fitness level you mentioned, maybe you could talk just briefly about the science behind that and how people can decide. So, you know, I'm not associated with this at all, but world, world fitness calculator. is it's a valid calculator for estimating V-O-2 max. And so what I mean by that is it's based largely on a lot of research that's been conducted in Norway, in particular Norwegian technological university.

They've been real pioneers in a lot of interval training research. And so the bottom line is they have a lot of data on measuring things and seeing how they correlate or are related to or can predict VO2 max. And so of all of the calculators that are out there, I think this is the one that people could trust the most in terms of answering a few questions about their age, their sex, their typical activity levels. And it will give them a reasonable estimate of their VOT2 max. But it's still just an estimate because it's saying you're that typical 40-year-old. It's not going to be able to dial in any better individually. but at least it's going to give you a marker in the sand, a reasonable marker.

And even if it's not precisely accurate, you can rest assured that it's going to allow you to track changes over time. So you plug your answers into the online calculator. It spits out of value and says your VATU max is 38 or 45. And then you engage in some sort of training program for three or six months. And then you do it again. And that if you see a directional change up or down, hopefully up, you can be reasonably confident that you know your training program has been effective at

increasing your VOT2 max, even if the precise number is not 100% accurate. Yeah, that makes sense. You know, there's a few factors in there that were a little more on the personalized level, like your resting heart rate and your max heart rate and BMI and waist to hip ratio or waist circumference, I think it was. So there are definitely some features aside from your age and everything like that. But also the estimation of how intense are you going with your exercise. There's a subjective component to it where I was like, oh, I go hard.

You know, like, so again, it's kind of good to know that you can use that online calculator. People are interested in probably doing that. but for the average person, do you think measuring it directly is really? The other way is, and in between, if you will, is there's submaximal exercise test. And there's a number of validated tests that are out there. We could drop those in the show notes. But where you basically are performing a couple of levels of submaximal exercise, measuring your heart rate, and then essentially plug it into an equation that's going to extrapolate

and said, okay, well, if this is your rate of increase in heart rate, Once you get up to your maximum, this is what your V-O-2 max value would be. Or there's, you know, I don't know if you have these here, but the shuttle run test or a beep test where basically you're running back and forth between a set measured distance. And after a point, you're not able to keep up. But it's called a shuttle run test or a beep test. And it basically, the more power you're able to exert or the more that you can keep up with, as you have to get faster and faster to run between these two.

markers, that also correlates with your VO2 max. So bottom line is all of these are submaximal exercise tests. They're better than just an online questionnaire, even that validated one that I mentioned, because at least it's providing some data about you. You know, so you can't just say, oh, I'm engaging in vigorous activity. It's going to actually measure your heart rate a little bit. So that would sort of be an in-between. But yeah, the gold standard is having a VO-2 max done in an accredited laboratory, and that's going to give you your V-O-2-Max value directly, and it's also going to give you a lot of data on your power outputs, your heart rate, even your lactate, in order to try and look at training zones, for example.

With respect to other cardiorespiratory adaptations, I mean, V-O-2-Max being, you know, the big one here, right? There's stroke volume increases, cardiac output. How does high-intensity interval training affect those? that's what are those? How does high intensity interval training affect them? Maybe compared to, you know, moderate intensity, continuous exercise. Yeah, sure. So, you know, what determines VOT2 max? And as I alluded to earlier, it's, you know, many physiological things. But the primary, there'd be general consensus, scientific consensus, that the primary factor that separates individuals in terms of their

VO2 max is their cardiac output. So that's what is the maximum amount of blood and in turn oxygen or the maximum rate of blood and oxygen that's being pumped out of your heart every minute. And so a typical untrained individual would have a resting cardiac output of about five liters per minute. So if you would measure how much blood comes out of your heart in a minute, it's about five liters. And maximal cardiac outputs are somewhere around 15 to 20. in, you know, an untrained, a moderately trained individual elite athletes have maximal cardiac outputs of 40 liters per minute. Tremendous. And so, again, if you could pick one variable that's going to best predict differences between individuals, it would be maximum cardiac output.

And that's determined by how often is your heart beating every minute, what's your maximum heart rate, times what you alluded to, your stroke volume. And so that's just how much blood with each beat is squeezed out of the heart. The other primer determinant would be how well your muscles mainly extract or utilize that oxygen. So your heart's pumping it out. Your circulation is distributing it through the body. And then your muscles and your mitochondria ultimately have to use that oxygen. And so for a long time there was tension or debate around, is it really the delivery side or the utilization side in terms of oxygen that limits VO2 max? And certainly you can put people in situations where one or the other is more important.

But generally speaking, it's the delivery side and that's primarily determined by your heart and probably why V-O-2-Mex is such a good measure of things like or predictor of things like all-cause mortality, cardiovascular disease mortality, because probably, you know, a failing heart or problems with your heart is a major contributor in a lot of those diseases. Yeah. And high-intensity interval training, I know it affects cardiac output, right? And so is that another way of improving cardiac output? It is. And so science, you know, now we're talking scientifically, VOT2 max is easy to measure. You know, basically any exercise physiology laboratory at any university or private clinics or medical centers, they can all measure VOTU max well because it's a relatively

non-invasive measure, right? You put a tube in your mouth and you measure the amount of oxygen and gas that gets expired. So it's easy to measure. All these other things that we're talking about, certainly cardiac output, even just think about what you would have to do to measure the maximum amount of blood that's being pumped out of your heart every minute. And there are ways to do that, but they're highly specialized. They're very invasive, you know, requiring significant catheterization of your blood vessels. So the point is, there's not a lot of direct measures of cardiac output or stroke volume. But there have been, and there's also ways to, reasonable ways we've used in our laboratory,

to non-invasively assess cardiac output. And so some of those studies have looked at the effective interval versus continuous training on cardiac output. And they've shown that more vigorous or more. more high intensity exercise may be associated with greater improvements in stroke volume and cardiac output as opposed to the same dose or same total amount of continuous moderate intensity training. So maybe if the dose was higher of the continuous moderate training, again, this sort of tradeoff between duration versus intensity.

No, absolutely. And, you know, there are there so many points to consider. and I'm sure your audience is getting the sense. You know, there's a lot of nuance to all of this, which is very frustrating for people because they just want to hear, tell me what to do. What does science say? And science is always really gray, right?

It's not as clear as we would like often. But, you know, when it comes even to exercise training studies, most of them are relatively short term, right? A three-month training study is a long time to measure some of these variables. And so we don't necessarily know, what the maximum potential is for VO2 Max in most individuals, right? And so if they engaged in longer periods of continuous moderate training, would they all get to the same level, you know, and maybe

hit in these shorter term studies just get to their, the rate of improvement is a little faster than with continuous, you know, or are you leaving something off the table by not engaging in the more vigorous effort? You know, we don't conclude, we could get into a reasonable debate. put it that way of the answer to all those questions. Yeah. You mentioned the mitochondrial component, the blood getting, oxygen being delivered to the muscle, and mitochondria using that oxygen to produce energy. So maybe we can talk a little bit about some of the skeletal muscle adaptations from high

intensity interval training, maybe compare and contrast when we can to continuous exercise. But mitochondria are very, I mean, it's probably one of the most important. organelles inside most of our cells, particularly in skeletal muscle cells. And I recall quite a few studies from your lab and others showing that high-intensity interval training was a very potent stimulus for mitochondrial biogenesis or the generation of new mitochondria. So can you talk a little bit about, I mean, how it affects mitochondrial biogenesis, maybe the difference between more continuous exercise. why that's important, mitochondrial biogenesis.

Sure. So you're absolutely right. You know, and I think even if people took high school biology, you tend to think of mitochondria, these sort of bean-shaped things in your body. But we now know mitochondria are this amazing reticular network. So it's a bit like if you can imagine all of your capillaries that go through your skeletal muscle fibers. The best evidence now would suggest that mitochondria sort of worked the same way.

it's this network of organelle that goes through muscle. And they can change, right? The size of the organelle, but you can have increases or decreases in mitochondrial capacity surprisingly quickly. So you can increase mitochondrial content very, very rapidly, certainly within a few days or weeks of training. And it seems to go the other direction pretty quick as well. So when you detrain, you can lose mitochondrial capacity quite quickly as well. You know, so what does exercise do? Any type of exercise, if you can imagine exercise is a stress. And so all of these stress compounds or indices of stress change inside your muscles.

So you immediately have this large increase in demand for ATP. Calcium levels go up, reactive oxygen species, lactate, hydrodion ions, change. And many of those, you can think of those as fuel gauges. So the sort of, or fuel monitors, right? They're seeing, oh, my goodness, we have an energy crisis. Our ATP is going down. This is going to signal that we need more energy. And so many of those compounds, those acute changes, have been linked to cellular, molecular, signaling pathways that are associated with the growth of new mitochondria.

So this is the idea of mitochondrial biogenesis, genesis or growth of new mitochondria. And those pathways are really, really well mapped out now. A lot of it based on animal research and, you know, very sophisticated work. But largely what's seen in humans is it sort of seems to work the same way. So in acute bout of exercise causes increase in those singling compounds. And as I mentioned, within a few days or weeks, you can see measurable increases in mitochondria. Measured with microscopy or western blotting, there's lots of methods. to assess that. Now, how does hit in continuous compare? Again, we definitely have studies on this,

but all of these require muscle biopsies. So a needle biopsy, a small sample of muscle needs to be taken often by a physician or at least a highly trained individual under the supervision of a physician. So they're invasive procedures. And what we get is snapshots in time. We don't have real-time changes of how your mitochondria change over days and weeks. We have these little snapshots. But certainly, you know, my laboratory, a lot of other laboratories that have compared continuous and interval training, there is some evidence that higher intensity, more vigorous exercise, when the total dose is matched, can lead to at least a more rapid or larger increase in mitochondrial content, again, at least over the short term. So is it just getting you somewhere

faster, and if you do enough of it over time, it starts to plateau, we don't really have a great answer for that right now. If you are generating more mitochondria, then, you know, this kind of goes into the fat oxidation. mitochondria are the primary place where you're oxidizing fat, you're using fat to produce energy. What do you think of this concept of, you know, you have to be, or, you're, you're, the substrate you're burning during exercise is, so you have to be burning more fat while you're exercising to have adaptations for better fat, you know, oxidation after you're done

with exercise just, you know, at steady state, at rest. So in other words, like, you know, you have to be more an aerobic type of state to have those adaptations. So, you know, mitochondria consume lots of fuels, right? The primary ones, of course, carbohydrate and fat. So whatever you feed it, feed the mitochondria, as long as the capacity has a sufficient capacity for that, it will burn either of those fuels. But you're right, you know, mitochondrial content largely limits or determines fat oxidation by an individual muscle or fat oxidation during exercise is largely determined by mitochondrial content. And in particular, a very specific enzyme inside your mitochondria called carnitine palmetil transferase or CPT,

That's sort of the gatekeeper that gets fatty acids into the mitochondria. Once they're inside the mitochondria, they can be oxidized. But there's good data to show that that's the critical enzyme. And so with training, you want to increase CPT levels. You know, there's various supplements that are purported to increase CPT activity. You know, one of the reasons why carnitine is a popular supplement is it's purported to increase your oxidation of fatty acids. The date on that's not great. But we could talk about, we could talk about that as well. But yeah, you know, lots of debate around what's the best way

to increase mitochondrial content, because that in turn is going to set the upper limit for fat oxidation capacity. And athletes in particular want to have a very high rate of fatty oxidation because even in very lean individuals, there's lots. There's ample fat on board. And and carbohydrate tends to be a very precious and limited fuel. So ideally we'd like to preserve carbohydrate, you know, until we really need it, like when we're racing and we need a very high rate of carbohydrate oxidation as well. So if you're doing a high-intensity, you know, interval training session and you're going above 80% max heart rate, you're now, you know, going to this lactate threshold where

you're basically producing more lactate quicker than you can consume it. potentially your anaerobic maybe. I mean, so, you know, this idea is like that you're not going to be burning fat during that part of the exercise, but that doesn't necessarily mean that you're not going to be able to burn more fat after because it does, as you just mentioned, increase mitochondrial biogenesis. So you're actually increasing, you know, the capacity to oxidize fat later on. No, absolutely.

So to me, it's, what's important is the increase. in mitochondrial content, the overall increase in mitochondria. And, you know, I think generally mitochondria have hundreds, more than a thousand different proteins that are all necessary to build the mitochondria. And they probably generally all sort of increase and decrease in parallel, right? So there's not necessarily a specific way to really only boost that CPT enzyme that I talked about. So I think that the most important adaptation or a critical adaptation in muscle is increasing mitochondrial content, which then will allow a greater fat oxidation capacity as well as a greater carbohydrate oxidation capacity. And you don't have to only work at a high rate of

fatty acid oxidation in order to get that boost in mitochondria. So there's many different ways to stimulate that, including short intensive types. What do you, just as a sort of side note, I was reading about the effect of like epinephrine, noropenephrine, which are increased when you're doing more of a higher intensity type of exercise, correct? And that also sort of has some fat. I mean, is it lipolisis maybe? It does. So the catacolamines, norophenephyne, epinephrine, they're involved.

And so norepinephrine is an important hormone that will signal adipose tissue to start to break down triglyceride and release those fatty acids. into the bloodstream. So, you know, much like we were talking about, we use the analogy of oxygen, or we're talking about oxygen, it's delivery of oxygen and its uptake of oxygen. When it comes to fatty acid use, it's delivery of the fatty acids, and it's the uptake and oxidation of those fatty acids. And you can definitely give people supplements that are going to increase lipolisis. It's going to make more fatty acids available. It's going to increase the breakdown of triglycerides, but it's not.

necessarily going to increase oxidation. So I think there's quite good evidence that has established that the limit for fat oxidation resides inside the muscle and it's at that level of the CPT, which is that gatekeeper to get the fatty acids into the mitochondria where they can then be burned or oxidized. Yeah, that's great. And then mitochondrial biogenesis is increasing that CPT. I mean, if you're looking at least at a per cell, you know, level, right? If you're more more mitochondria within that skeletal muscle cell. Sort of, we were talking about this a little bit earlier off camera about, you know, the, so talking about mitochondrial biogenesis, the other sort of important factor with

mitochondrial health would be mitophagy or mitophagy, which would be the clearance of actual, like, sort of old damaged mitochondria. As you know, there's definitely not a lot of evidence. There's animal evidence, but how much that can translate to. humans is sort of unclear with respect to exercise and particularly high intensity exercise doing that. But what I did want to touch on was autophagy, which I think we have a little bit, it's a little bit, we've got more markers to measure it, and it has been measured, at least in human skeletal muscle with respect to response to exercise. And I'm just curious what your thoughts are because

it has been shown that high intensity exercise is more potent for stimulating. autophagy in skeletal muscle than just an overnight fast, fast itself. And you don't even have to be in a fasted state when you're doing the high-intensity exercise, which to me was like, you know, so what is the significance do you think for skeletal muscle health? And do you guys look at that? We don't study that in our laboratory. I think the bottom line there is exercise is good for the routine maintenance or turnover

of many of these cellular processes, including my, mitochondria. So it supports mitochondrial health. It sort of promotes the sort of breakdown and the building of new mitochondria. So it's important to maintain mitochondrial health, if you will, the overall health or capacity of these mitochondria. You know, clearly I'm a proponent of vigorous intensity exercise. There's some other studies out there that have shown that really vigorous exercise can temporarily impair mitochondrial capacity. So if you measure it, immediately post-exercise or in the short-term after, you can engage in too vigorous an effort. You basically really hammer yourselves, and they sort of have a decline in function before they

start to come back. And so there's some criticism of interval training out there based on those studies, especially very intensive wingate style, all-out type exercise that can transiently reduce mitochondrial capacity. We're talking about different things there. You know, autophagia in the various processes. But, you know, I think this is the idea that exercises a stress, it temporarily disrupts or damages things, and then it's all about the recovery that makes the cellular process better. And we continually do that. And over time, things get better. But certainly, can we acutely overtrain or acutely over-cause some disruption or it takes a prolonged period of time before it recovers? Sure. It's a bit like, you know,

concentric and eccentric weightlifting exercise. We know that eccentric weightlifting exercise is more damaging to tissues, yet more sore, and so you tend to take a little bit more time to recover. So not as simple as just high intensity good, continuous nod or less good. There's a lot of nuance there depending on the process. Yeah, I'd love to dive into that a little bit more when we kind of, we cover some like protocols because that's really interesting. And the wind gate, you know, also just kind of like, is that like an all-out sprint? It is. You can, it's, so if you've never Wingate done a Wingate test, it's the longest 30 seconds

of your life. The way to, so Wingate tests are done on a specialized aerometer, specialized bike that allows for variable intensity efforts. But the best way to think of it is if you have a stationary bike is basically getting on it, setting it the highest workload possible. So it's even hard to get it going. And after five seconds, you feel yourself starting to slow down because it's so challenging. The workload is so high. And so you just hang on as long as you can. What these specialized bikes do, they sort of push back with just the right amount of resistance. And so we'll optimize that curve over the 30 seconds. But it's an extremely demanding test. And so some of our work. early work was using that as a stimulus as sort of the one of the most intensive types of short, hard exercise that you can do and having people do repeated windgate test. Very, very challenging,

especially laid in exercise. You have lots of pH disturbance, lots of lactic acid production. It hurts. It's uncomfortable. It's not a fun way to train. Yeah. I've never done one of those, I may have to try one. The other skeletal muscle adaptations that I think, you know, there's some interest, particularly like there's this capillary density, you mentioned the mitochondrial network being sort of like that, hit effect capillary density. What is that? Yeah, it does.

You know, as a muscle physiology, I think, you know, the two primary responses in muscle that are critical, especially from an aerobic conditioning standpoint, is the increase in mitochondria. and the increase in capillelarization. So you need more of the blood vessels in order to supply the increase in mitochondria within skeletal muscle. And then, of course, there's other adaptations we've seen increasing muscle glycogen content. So you store more fuel on board that you can then break down. You increase the transport for many things, including glucose transporters. And so one of the reasons why exercise is, you can then.

therapeutic in the treatment of high blood sugar or diabetes, you know, there's lots of reasons, but one of the reasons is you increase glucose transport capacity on the cell membrane. And so what that means is it allows more glucose to be moved into the muscle, maybe then stored as muscle glycogen, and that helps to lower the blood sugar levels, especially if they're chronically high. And so individuals who start and engage in an exercise program, one of the things that they'll find if they are diabetic is they have to reduce their diabetic medication because what's happening is the muscles more fit. And rather than needing the drug to try and clear the glucose, your muscles doing it more naturally, if you

will, or it's grown these new glucose transporters that helps to clear the glucose, the elevated glucose from the bloodstream. How does the difference in increasing the glucose transporters or glute four transporters on muscle differ when you're doing that high intensity exercise versus more moderate. Yeah. So again, I think for a lot of these responses that we might talk about in muscle, there is evidence to show that certainly high intensity exercise can cause changes in these glute four transporters. We've shown that, including in people with type 2 diabetes. But there's just not the body of evidence that we would like to see to definitively,

say one is better than the other, you know, we've done a number of studies showing at least over the short term, more vigorous exercise can elicit superior improvements in some of these markers. But again, the valid criticism is these are relatively short-term studies. They're not always appropriately powered. Many of these, especially our early studies, where what we like to think of as proof of concept or pilot studies, you know, do these things work. And, you know, writ large, we really need these randomized clinical trials to properly investigate all of these questions. What about insulin sensitivity? Is that also? I mean, so there's, like, you get this glucose transport. I mean, that's another, I mean, that's one way of glucose regulation. And certainly

repeated, I mean, acute bouts of exercise are probably, I mean, you're talking even throughout the day. That would be so beneficial. But also, like, people are, you know, insulin resistant, too. How does hit effect? Yeah, so there's various ways to measure insulin sensitivity, but generally exercise increases insulin sensitivity. There are some systematic reviews and meta-analyses that have suggested that maybe more high-intensity, vigorous effort can lead to some greater improvements in markers of insulin sensitivity.

But again, even though, you know, we think of, oh, systematic reviews, meta-analyses, those are really definitive evidence, but many of the underlying studies tend to be relatively small, tend to be relatively low numbers of participants, all of the potential bias, you know, not that researchers are purposely trying to bias their results, but they don't always include all of the proper controls from a research design standpoint that you might like to see. So sometimes the underlying evidence is limited as well, which limits the veracity of the systematic reviews and meta-analyses. But certainly there are, there is some evidence to suggest that Vigure intensity, more intense exercise may lead to some superior benefits there.

You know, just sure we might hit on it later, but this idea of multiple bouts through the day, one of the things that we and some others are looking at right now are what we termed exercise snacks. So these brief bouts of vigorous intensity exercise that are spread throughout the day, and we're running right now to randomized controlled studies at, you know, our lab in the University of British Columbia, my colleague Professor John Little, and one of the main outcomes is measures of insulin sensitivity or blood glucose control in groups that are doing these very short, one-minute bursts of vigorous effort spread throughout the day to try and get it exactly

this question. How many times a day? So we're encouraging people to do at least four or five times a day of those snacks. So, you know, we define an exercise snack as lesson or equal to one minute. of vigorous intensity exercise. It could be jumping on a stationary bike. It could be a series of air squats or bodyweight style exercise. And we're delivering in the intervention.

We partnered with a company that's delivering prompts on people's cell phones. And so they basically get a prompt that says, hey, it's time for your exercise snack. That links to a little YouTube video that shows the individual what they should do. And we're encouraging them to do that four or five times a day. More is better. And we're following them for three months, 12-week intervention. And we're comparing it to a movement snacks control group.

So a group that's getting a very similar intervention, but they're not engaging in vigorous intensity exercise. So it's more stretching mobility exercise. And so the key variable that's changing there is the intensity of the movements. And we're seeing, you know, how do people adhere to that? Like, will people even do that? And if they do it, is it enough to move the needle in terms of things like cardio-spirritory fitness, blood markers of fat, immune function, glucose, and measures of insulin sensitivity as

well? One of the studies that we're doing is going to be using continuous glucose monitoring in individuals with type 2 diabetes. Fantastic. So they're going to be wearing, they're wearing accelerometers as well? Yes, yes. So we're trying to track movement throughout the day. And they're going to be wearing continuous glucose monitors before and after the intervention as well. So this kind of reminds me of some of the vigorous, intermittent lifestyle physical activity studies, Vilpa, as you have called it, that you've been a part of. So are those studies also considered exercise snacks or?

No, so you're right. Vilpa is vigorous intermittent lifestyle physical activity and very much led by my colleague, professor, Emmanuel Stamatakis out of the University of Sydney. So I've been fortunate to be part of a, really an international group that is, that is looking at BILPA in various ways. But to be clear, we're talking not structured exercise. So you could think of VILPA in some ways as the non-exercise equivalent of an exercise snack. And so we're talking activities of daily living that you would be doing anyway.

So I'll give you a very specific example. So to get to the recording studio today, I left my hotel. I had to get here, right? Somehow I had to get here. I took a ride sharing service for most of it. But leaving my hotel room, I had a choice of taking the stairs or taking the elevator. I could have taken the stairs there. Or to get to my ride share service to walk a block, I could have walked to leisurely pace

or I could have picked up the pace, right, and said, I'm going to engage in a vigorous manner here. Arrived at the location. Again, it's another minute to get from the ride share service to the front door. I could do that in a vigorous pace or at a pedestrian pace. Or I could carry my backpack, right, and engage in that. And so the question there with Vilpa is in these activities of daily living that are already part of our lives, if you embed vigorous effort in those, you know, another classic example would be you take a five-hour flight. You get a get off the plane, you have the choice. The escalator's there or you have the stairs. You know, many people are taking the escalator, but you got some heavy backpacks. You could vigorously

climb up the stairs or 30 seconds to a minute. That would be a dose of vilpa right there. And so, again, you got to move from one level to the other. That's not planned and structured exercise. That's just activities of daily living. And the question that's being asked in that research is if people choose to do that in a vigorous manner, is that meaningful? And there's some evidence for that, including a large study that was published in December that was, it mined the UK Biobank data. And so what that allowed the investigators to do was look at over 25,000 individuals who engaged in vilpa-like efforts. They were accelerometers to try and capture this. and they were followed over almost seven years, and the outcomes included all-cause mortality,

cardiovascular disease mortality, cancer mortality. And that work showed or revealed that people who engaged in even three to four minutes total a day of vilpa-like activity had substantial reductions in all-cause mortality risks. We're talking 25, 30%. So that would suggest that, that even brief, non-exercise, vigorous, intermittent physical activity can move the needle in terms of health outcomes. And of course, we would suspect that maybe it has to do with some these cardiovascular or metabolic changes that we know are associated with health. So that's not cause and effect evidence. It's, you know, observational evidence over time, but it was very robustly done the way the work was conducted. It's quite compelling, I think. I agree, because

after you shared those studies with me, I read them. And I think even on the higher end, so you mentioned kind of the conservative, you know, three to four minutes a day when they were getting up to like more like nine. I mean, you're talking, it was like 50% reduction in cardiovascular rate mortality, 40% reduction in cancer-related mortality. I mean, that's really incredible. These people are just doing this, you know, choosing to do these short bursts of, you know, vigorous intensity exercise and then having substantial benefits on, you know, on, you know, longevity and health ban, basically. The other, if I can add, the other key thing from that study, I think, is that all of these people were self-identified non-exercisers. And so the point is

there, even people who self-identifies non-exercisers seemingly are still engaging in vigorous activity through the day. Now, part of that might be their physical capacity is quite low. And so what it takes to get them into a vigorous intensity range is is not very much. And actually, as part of that study, it was repeated in individuals who also identified as exercisers and the same phenomenon were apparent. So even in exercisers, engaging in vilpa-like activity was still protective. So again, lots of work to follow up on, you know, what actually counts as a vilp about, you know, will people do this? You know, but you can Imagine, again, getting back to this idea of prompts, you know, building in Vilpa-like activities in a smartwatch or an app on a phone and encouraging you to accumulate three or four or five or 10 minutes of Vilpa a day. But, you know, three or four minutes of Vilpa is, you know, about 30 minutes of vigorous activity a week and large reductions in risk. Yeah. And that is very doable. That is very, I mean,

To say you can't do 30 minutes a week is, I mean, you're really just saying, I don't want to be healthy. And, you know, the other, it's interesting, and I don't want to go on too much of a tangent here, but, like, you know, you wonder how much also of this, of these vilpa studies and these even exercise snacks has to do with just not being sedentary also because that's like an independent risk factor for, I mean, independent of exercise, right? So like I sit at my, I don't consider myself a sedentary person because I engage in physical activity almost every day, pretty much. So I'm doing something. I'm either doing my Peloton intent, hit workout, I'm doing resistance training. But I also sit at my desk for a good five hours. I'm sitting there, sitting. And that is when I am sedentary.

So I'm actually trying now to incorporate VILPA stuff, I guess, you know, in, I guess it's more structured. So it would be more of an exercise snack in that case. but I'm doing, you know, the burpees or the high knees or something where, I mean, believe me, like one minute of that. I'm like, this is the longest minute of my life, you know? I mean, it's like hard. So. I can empathize in that I'm very similar. I'm a committed exerciser.

Pretty much I do something every day. But, you know, as a university professor, you sit at a computer a lot. And so trying to build them into my day as well. But yeah, I think the key there is, you're right, there may be a double benefit, if you will. All of us should be meeting physical activity guidelines, of course, you know, add these in, sprinkle them in, but there may be a double benefit to a vilpa-like approach or an exercise snack approach in that it simultaneously breaks up prolonged periods of sedentary behavior. Because, you know, I'm sure like you, I don't like to see that evidence and read those studies.

that suggests even if you're committed exercise or prolonged sedentary is increasing your risk. Right. You know, we like to think of exercise as this panacea, and it's not. It's not a vaccine against ill health outcomes. And reducing sedentary behavior is really important as well, as is proper sleep. So I kind of wanted to circle back just for a moment to the muscle biology aspect because, well, one, you're an expert in that arena. we didn't touch on the how high intensity interval training affects the recruitment of muscle

fibers. So type one fibers, type two fibers. What does that mean? How much does individual variation play in that equation? So, so, you know, big picture, generally speaking, there's two main types of muscle fibers. They can be quantified different ways, hystich chemically different. There's different ways to measure them. But there's slow twitch and fast-twitch muscle fibers, those definitions are based on basically how quickly the muscle fibers can shorten or contract. And so the fast-twitch are sort of fast-explosive, very, very quick. So we think of those associated with very fast, explosive, powerful movements where the slow-twitch,

they don't generate as much force, but they don't fatigue very quickly as well. sometimes also known as type 1 and type 2, and those are generally looking at, there's ways to measure basically the oxidative capacity, how aerobic each of the muscle fibers are. So there's different ways to categorize them, but generally speaking two types, and they differ in their characteristics. There's definitely something to the idea that we first recruit, and this is known as the size principle, in part based on the diameter of the muscle fibers. So these slower twitch fibers, these type 1 fibers, tend to have narrower diameters, and they tend to be recruited first. So if I was to get up from the chair right here, we were going to go for a walk around outside

the studio, very low intensity. Those muscle fibers that we would recruit to do that work are generally these slow twitch or type 1 muscle fibers. They're good for low to moderate levels of 4. and they last for a long time without fatiguing. Then we need to get back quickly to the studio or we need to run away from a scare that's outside. We suddenly have to engage in very fast movement. We're going to now recruit or call in these fast-twitch muscle fibers because we need more powerful muscle contractions

in order to go faster. We wouldn't be able to sprint away from the danger for very long because we'd eventually fatigue because these, these muscle, these fast twitcher type 2 muscle fibers are, that's one of the limitations of them. And so that idea of progressive recruitment of muscle fibers is well established. What's not, it's not as clean to just be able to say when we do low to moderate exercise, we only recruit slow twitch or type 1. When we do high intensity, we certainly don't only recruit type 2s.

We've already called on our slow twitch, and then we start to recruit the fast twitch. as well. And the other point is, like a lot of things, it's really hard to study. So, you know, you take a muscle biopsy sample. That's hard enough, right? It's invasive. People have to volunteer. Sometimes it's a little painful. But you get your biopsy out. Now you have to separate these muscle fibers. So you literally have to individually identify whether muscle fibers are fast or slow. And then you separate them into pools. And you analyze the type ones and the type 2s, very intricate, time-consuming work. And so there's not a lot of data out there. There, you know, a lot of animal studies that were done previously in rodents, for example,

they have much more clearly defined muscles. So they will have fibers, muscles that are almost entirely fast twitch or muscles that are almost entirely slow twitch. And so in those, you can just take samples of specific muscles from a rat hind limb. for example, and know that you're pretty much looking at fiber-type differences. Human muscle is much more variable, heterogeneous. And so elite endurance athletes tend to have a much higher preponderance of slow-twitch muscle fibers, 70, 80 percent. Elite strength athletes, power lifters, tend to have much higher preponderance of fast-twitch muscle fibers. But the vast majority of us are walking around

somewhere around 50-50, 40-60. And again, that complicates interpretation when we talk about fiber type differences to different types of exercise. Are people more prone to losing one type over the other with age? Yes. And so definitely there's evidence to suggest that there's progressive loss of these fast-to-witch muscle fibers maybe mainly, or sorry, maybe, mainly due to the inherent aging process. But again, you know, we could have a long

discussion around whether aging is more a physical inactivity per se problem or aging per se. But bottom line is we tend to lose fast-switch muscle fibers, which is probably why, especially as we age, strength training is important in order to maintain the viability of these fast-to-wich muscle fibers. Does that correlate also with an increased risk in like falls? Yeah, you know, I think all of this aligns, or certainly the theories would be that yes, right? And so, you know, we need to maintain flexibility, balance, all of that. But certainly maintaining fast-twitch muscle fibers through strength training is going to be

important in order to help prevent balls and other others. With respect to the metabolism aspect of high-intensity interval training, you know, we talked about the insulin sensitivity, the glucose transport increasing. I mean, all these things are good for both people that are in a disease state, like maybe type 2 diabetes or, you know, high glucose, you know, dysregulation, metabolics, and whatever. also for people wanting to prevent also getting type 2 diabetes, right? I mean, so there's two populations here, right? Yeah, absolutely.

Again, back to the elite athlete, they want to optimize all of those processes as much as they can, right? And the individual who's very sedentary, they really just need to do something to try and raise the bar. So, you know, we're just talking about a massive spectrum there from very inactive, very sedentary, very high-risk behavior to the elite. athlete who has maximized almost all of these processes and is just looking for ways to further optimize that or just to get back to Stu's analogy, ring out the sponge a little bit more.

And of course, most of us fall somewhere in this broad range in between. What about body composition, weight loss? Obviously, diet is an important component in those equations, but can people use high-intensity interval training to help, you know, lose fat, also even help, you know, there's there, increase the muscle. Also, you know, is there, is there a role for high intensity interval training in? So you're right in that, you know, when I tell my students, says this is hardly novel, that, you know, we control body mass mainly through nutrition, but we control fitness through exercise and physical activity. And so clearly exercise generally and high intensity

exercise can play a role, a supportive role in terms of weight management, body composition changes. We've shown in some of our six and 12 week studies that you can change. You can have measurable changes in body composition such that there's a slight loss of fat mass, fat percentage or a slight increase in lean mass with high intensity interval training. But it tends to be relatively subtle. and how it compares with continuous exercise. Again, I think the biggest thing is there's probably a time-saving aspect there. And so you can do less total exercise or certainly have a lower time commitment with more vigorous intensity exercise and burn the same number of calories. There is something to the idea of personal trainers talk about the afterburn effect. This idea of a heightened rate of metabolism in recovery.

we've measured it. You know, you look on the internet and you'll see these massive differences in afterburn, right, where a hit is way up here and moderate's way down here. It's certainly nothing to that magnitude. And but there is a difference, but it tends to be relatively small and it dissipates relatively quickly. But those small differences can add up over time. And so, you know, people will say, well, how can high intensity be effective or how can certainly sprint type training, be effective at this because you don't burn more many calories during the efforts. Well, you do burn a greater rate of calories in recovery and those two things can play off. But again, I think right now the best data is, like a lot of things we've talked about, you might get

away with some time savings or a smaller total dose of exercise and still get to the same place with more vigorous activity. Well, in contrast to that, getting to the same place, In my mind, in my opinion, one of the reasons I am so drawn in addition to the time efficiency aspect of high-intensity interval training is the brain effects. And there's no doubt that exercise in general has global effects on the brain. I mean, there are improvements. You do any type of exercise. You look at any observational study.

Exercisers, non-exercisers, definitely brain benefits. lower risk of, you know, age-related diseases, neurodegenergaseases, excuse me. So, you know, not that there's not, you know, a role for any type of just getting your blood flow higher. However, I'm increasingly convinced when it comes to intensity of exercise, there may be very unique benefits on the brain. And that is where I think, you know, high-intensity interval training or any type of high-intensity training has a special role. Some of that has to do with actually wanting to increase your

lactate levels. So instead of this lactate threshold training that we were talking about, the zone two sort of going, you know, right below the lactate threshold, which I guess is defined various, you know, ways depending on who you're, what you're reading or who is doing it. But the lactate shuttle theory, George Brooks proposed this. You know, it's not a theory anymore. So it kind of, the name kind of, it's a little out of date. But can you talk just kind of briefly about the lactate shuttle theory and maybe like where the brain comes in?

Sure. So, you know, the lactate shuttle theory or lactate, you know, many of us, if you look back at your textbooks, you learn that lactate was this metabolic waste product, end product and it's just a metabolite like like anything else and it can be an extremely valuable fuel and we know that and there's elegant studies including from dr brooks and others to show that you know first of all skeletal muscle can produce lactate under fully aerobic conditions so there's always some lactate production happening and certainly during more intensive exercise where we produce lactate inside the muscles it can be released from active skeletal muscle it can circulate to other

places like the heart, like the liver, like the brain. But certainly in heart, heart can be a big consumer of lactate. And so it takes up that lactate, can convert it back to glucose and then utilize it during exercise. And so this is the idea of cell to cell or interorgan lactate exchange. And I think that's very well established now. Like you and you would be far ahead of me, but I'm following this area with immense interest. I have some colleagues at McMaster. We're, you know, both from a cognitive psychology standpoint and also more a hardcore, you know, neurophysiology standpoint, we're engaged in some collaborative research with them. But generally looking at this question of physical activity and brain health and probing the

role of intensity there. So, you know, my, my understanding is mainly based on talking to my colleagues, trying to read reviews of some of this research. And my sense is, you know, very well established potential mechanisms now from some of the animal studies. And the human data is certainly intriguing. But, you know, that link between lactate, BDNF, absolutely, there appears to be a role for intensity there in terms of higher intensities, the better in terms of, you know, potential Bideneff, bathing the brain, some of these outcomes associated with neurogenesis.

Yeah. It's the lactate, and we can talk about measuring it, but it's interesting because I do measure mine. I do the finger prick, and my workouts, I'm like trying to go higher for my lactate. You know, and I've read a lot of study. For me, I'm very interested in neurodegenergenic disease. There's on both sides of my family, Alzheimer's and Parkinson's. So to me, I'm like, I need to really focus.

on brain health. And so looking at the studies on lactate and, you know, even infusing lactate into humans, it increases BDNF, just infusing it. And I'm like, oh, I get these levels from my really all-out hard workouts. Like, this is great. But also, I feel really good. So I start my day with, including today, most days, you know, at least five days a week, I'm doing a, and I want to talk about protocols, but I'm doing like a 10-minute, you know, Tabata.

So, so I'm doing two back-to-back-tabattas, actually. It's two back-to-back-tabattas. And then I have, there's some, you know, a minute warm up and a minute cool-down. I actually don't. I use them more for, I'm actually still going hard, like half the time. And then I, like, cool down after that minute. So I, like, at the end, I go an all-out minute after my two-back-to-back tibadas. And then I'm like, and then I cool down.

But, you know, I do this for my brain. I feel amazing, and there's actually science showing that executive function is improved, and it totally correlates, and this isn't humans, with lactate after high-intensity exercise. And it doesn't correlate with anything else, no glucose, like nothing. It's specific to the lactate. And like you said, it's a growing area of research. I am particularly interested in it. Like, I, for sure notice a difference in terms of, like, if I go hard, like, I feel

better. I feel smarter. I'm like more on task. You know, so for me, it's a very important part of my protocol. And I do think there's a lot of benefits for the brain. So I'll have to be in touch with some of your colleagues at McMaster because I love sharing studies and stuff that I find and learning what, you know, what other people are doing as well. And so the, and maybe there's data out there on this, but, you know, the scientist in me is innately curious around things like I, you know, maybe now there's really, really good dose response stuff in terms of exercise dose and BDNF increase in some of these other measures. But, you know, so for example, is short, sharp, large changes in lactate better than prolonged moderate levels of lactate. Right. And I'll tell you

something. It's not lactate that I, that I've looked into, but I've looked into blood flow and sheer force. And I think this is a very, I think it's an emerging field looking at the effects of sheer force. And that is where, I mean, we're talking about a flash flood coming through if you're talking about high intensity versus just, you know, a little trickling. And the sheer force itself, at least at the blood brain barrier. And this kind of, when you were talking about muscle capillary, I was thinking about the sheer force, it in and of itself, in a dose dependent manner, is responsible for increasing VEGF and BDNF. at the blood-brain barrier. Again, dose-dependent, all on the sheer force effects. Bechano, you know, these mechano receptors that are on cell surfaces and stuff, like, these are all sensing things, and it's also very important. So I think it's another, so there's the lactate

part of it where you're increasing the lactate, and it's a quick sort of, and it is, like, I've measured, my lactate spikes up, you know, I don't get up to levels that my husband, I'm more like a 7-8 millimolar and he gets up to like 14. But it's, Like, after 20 minutes, I'm back down to one millimeter or to my baseline, basically. So, you know, is it, is there something with that, you know, lactate, you know, going intensely up, but also the sheer force, I think. There's another interesting component to that that I think needs to be calculated into this equation because I'm seeing increasing data on that, not just with respect to brain health,

but also people that have cancer. So there's a lot of work from Justin Brown. He's at, I think it's Tulane in New Orleans, but the sheer force and how it's affecting the circulating tumor cells. So basically people that have been diagnosed with cancer, you'll have a tumor cell that escapes the primary tumor site goes into circulation. And that's how, that's the potential to metastasize, right? So it then goes, you know, is able to travel to another organ and take up camp there or whatever.

So there's evidence that exercise, in general, exercise is involved in basically anything that gets your blood flow up, basically those cancer cells die because they're so disrupted and sensitive to the mechanical forces, whereas normal cells are fine. But it seems to also, again, be a dose-dependent effect. The more intense the exercise, the more blood flow that's going quicker, the more intense the effect. And also blood flow to the brain, too, right?

I mean, just getting that sheer force as well. So I think there is a lot of interest there with the brain. it to me is a differentiating factor from more continuous, moderate exercise, even longer duration. Obviously, there's a lot of compensation probably that can happen metabolically when you're going for a longer duration, you know, period of time. But I do see something unique and I'm, you know, looking, I'm reading the literature. I'm trying to follow it as much. And, you know, I mean, it's emerging, right? I mean, we don't really know. You know, just on the topic of interval training, there's now 700.

papers a year coming out. It makes it very challenging to stay on top of the literature, you know, and that's just in my main area. So absolutely, you know, on the point about vascular stress, we collaborate with some cardiovascular colleagues who are looking at this more endothelial function, flow media dilation, not in the brain, more in terms of muscle or large arteries leading to muscle. So parallels there, I think, in terms of some of the things that you're talking about and sheer stresses and factors that are released, you know, to promote capillary growth there. The other, I want to mention around lactate levels, though, it's a bit like heart rate in that, you know, some people just have low maximal heart rates. Some people just

have low maximal lactate values. We know it's definitely related to fiber composition, more fast-twice muscle fibers have greater potential to drive up lactate. It's related to your enzymatic capacity to produce lactate. So the point I just want to make, maybe you're working as hard as your husband, but you just don't have some of the biological traits that are going to allow you to get to very, very high lactate levels. You know, what is your peak lactate level? Maybe you're already added or very close to it.

So don't be yourself up too much there. Do you think wearing a continuous lactate monitor when those exist will help me, identify. Maybe, right? And so I, you know, I'm sure we're going to get into Zone 2 more and lactate and how we measure things in that. But, you know, I think a challenge with lactate monitoring right now is it relies on occasional finger prick sampling.

There's variability in the monitors in that. When we look at something like continuous glucose monitors and the evolution of that, you know, now we have continuous glucose monitors or combined with insulin. pumps. Amazing, right? So eventually you have real-time monitoring of blood glucose levels, and as they change up or down, the insulin can be potentiated or adjusted to get to, and I'm sure, and I know people are working on this technically, getting to the point where an athlete would use a continuous lactate monitor for training and racing. I could see where that could have tremendous value, whether everyone needs that, I don't know, you know, whether you can use

heart rate and some other metrics to at least get you reasonably into some zones. But I can see why there would be tremendous interest among athletes to monitor that and really dial it in to get an idea of their metabolic stress. Oh, for sure. I'm not an athlete, but I'll tell you my interest would also be because before I was doing continuous glucose monitoring. I wore one for, I don't know, three years or so. I was doing finger prick, and, you know, I noticed before my workout, you know, my blood glucose levels were a certain number, and then, you know, usually sometimes I would do it like three times because of the variation, as you mentioned.

But after I would go higher up and I'm like, what? I'm supposed to be like transporting more glucose into my muscles. Like, this is ridiculous. And it wasn't until I had a continuous glucose monitor on that I saw the change going way down during the exercise and then gluconeogenesis, whatever's kicking in, you know, that it spiked back up. But I wouldn't have known that without that continuous, you know, data. And I wonder with the lactate, because during exercise, the brain consumes, it consumes it more than glucose. So it actually, you know, you have both of them there.

It'll go for the lactate over the glucose. And I wonder, it's like, oh, well, what's happening while I'm, is it going really high? Is my brain consuming more of it? Or is, am I just not producing more of it? Like, what a continuous lactate model would give me some sort of peek into? to that because at least maybe it is going higher and I just don't see that because I'm not, it's a snapshot that I'm getting after my workout, right? No, it's a great point, right?

Even, you know, just monitoring Venus levels, it's not telling you anything about rates of production and utilization. And so, you know, if some, it's a really good test question in my senior class, I will ask my students, is a high blood lactate a good or a bad thing from an exercise capacity standpoint. And we tend to think, well, high blood lactates are bad because, you know, it's a signal that your pH is out of whack and everything like that. But you could also make the case, well, actually transporting for a given amount of lactate production, getting more out of the muscle into the blood might be a good thing because the disturbance to your muscle pH is not going to be

as pronounced. Now you've moved the lactate to where you want it into the blood to sort of protect the muscle. Again, it's just a, it's a good thinking question. I asked it to them to challenge your thought process around all of the things that control lactate. But maybe it's not all about just measuring it in the blood either, is it? Let's dive into that for a minute. You brought up some really good points, I think. A couple, one being, you know, this misconception of, you know, lactate or lactate

or lactic acid and, you know, how, what's actually responsible for, you know, the changes in osmolarity and, you know, that, that, that, fatiguing feeling, I guess, in muscle versus basically high-intensity interval training, whether or not it can help, I guess, improve muscle fatigue through changes, you know, regulating the osmularity better. Yeah. So, you know, certainly there, you can, certainly you can change lactate transporters with exercise and high-intensity training and probably, you know, go back to athletes that

were engaged in high-intensity exercise to engage in high-intensity. events, a major adaptation there is an increase in monorcauboxylate transporters or MCT transporters to help get the lactate out of the muscle. And you're right, you know, lactic acid is produced at physiological pH, it rapidly dissociates into the lactate ion and the proton, the hydrogen ion. And it's the changes in pH associated with the changes in protons that we know can interfere with contract out processes and enzymes and things like that. So, yeah, complicated physiology. But I think the bottom line is lactate is still a valuable measure, and certainly why, whether it's zone two training or others, the notion about it's, you know,

whether it directly causes fatigue, probably not, but it's still a really good surrogate marker or index of a lot of other things that are going on. So whether it relates to osmolity or potassium fluxes or calcium fluxes. You know, I think the people that really study muscle fatigue would say it's not about lactate and pH all the time. But lactate is still something that can be relatively easily monitored. And it's a good proxy for, you know, a global look at what might be going on metabolically. And I think that's where my understanding is where its role in Zone 2 training comes into play. That makes sense. So we talked about some other performance enhancements, you know, that high intensity interval

training can play in real use muscle glycogen, like the storage capacity, talking about the muscle fatigue. But, and then we talked about VO2 max, which would be aerobic capacity. There's also the anaerobic. Is it the anaerobic output? Yeah. Is that? Anerobic capacity, correct. And this gets back to this idea of, you know, if your event is multiple short

sprint. So you play a team sport and your role on the team is to, you know, receive a pass or receive a ball, sprint as hard as you can. And then you have at least a few minutes in between plays to recover or you can then recover on the field. Those individuals require very high power outputs that they can achieve repeatedly, but with some a fair bit of time in between. And so when we talk about anaerobic capacity, the best measure or the most commonly acceptable, measure of anaerobic capacity is a windgate test. And that's because when we do an all-out 30-second effort, a large majority, not all of it, but a large majority of the energy is derived from anaerobic or non-oxidative metabolism. And so we can quantify power output in terms of wattage on

the bike, and a large proportion of that power is derived from anaerobic. And so, for example, you can measure, let's say your VOT2 max test, at the end of that test, you had 300 watts. So your peak power output on a VOT2 max test was 300 watts. Well, you can do a 30 second windgate and achieve 900,000 watts, elite athletes, elite power athletes, 1,500 watts on the bike. So when we talk about someone who was exercising at 300% of V2 max pace, that's, well, max is max. How can we exercise above VO2 max? Normally you're talking about its power outputs above the VOT2 Max power output. And when you're engaged in these short, hard efforts, they can be multiples of VOT2 max power.

So this kind of reminds me of I've heard you talk about this, the sprint from danger, sort of pace or intensity and how, I mean, you know, that could be basically the cornerstone of a highly efficient workout. Now, what is that, can you talk about that and then maybe compare it to the windgate or maybe even the sprint interval training differences? No, for sure. So again, you know, people think V-O-2 max will, and max is max. How can you be above max?

But when we talk about V-O-2-Max, that's maximum aerobic capacity, and then we could have metrics to that. So peak power, work peak at VOTU max. But sprint from danger pace is just that. So if you had to flee a burning building, the pace you might run at to save your child from an oncoming car, it's well above VOTU max. but you might only have to do it for five seconds. So it would equate to top running speed, an all-out sprint over five or ten seconds. You know, even a windgate test is not true max power output. The

highest power outputs during a windgate usually occur within the first few seconds. So we're talking five to ten-second efforts. What's the highest work rate that you could put out? What's the highest amount of ATP that you could generate? Much of it, non-oxidated, over a five, a 10 second effort at most. That sprint from danger pace. And if you're an athlete, you know, we hear these five zone training, six zone training, for many of us, three zones are enough. But when we talk about five and six zone, what that often is referring to is discriminating

work rates or power outputs above VO2 max. And if you're the athlete looking to optimize performance, you know, whether you're working at 150% of VO2 max, which you might be able to do for a minute or two, or you're working at 250, 300% of V02 max for five or 10 seconds, those might be important in terms of discriminating fine changes that could further support your performance. Whereas for most of us, it doesn't really matter. we don't need to get that level of sensitivity in terms of how we structure our training at these very, very high intensities or work rates. So do you think there would, I mean, like, could there be a benefit for sort of changing around our training protocol to incorporate some of that sprint? I mean, VO2 max benefit or, you know.

So I do. And again, this is not scientific, but it makes sense to me at least. and it's the old investing analogy, right? And so you can hit a home run with a hot stock tip. But for most people, they're better off to, you know, spread it around, put your eggs in different baskets. And so I think when it comes to exercise training for many individuals, there's an analogy. And that's it, maybe do different types of training. And that's going to, you know, so whether you're someone who really responds to sprint training or really respond to, to moderate, we can't necessarily predict that. And so varying up your training, just like we spread out our risk when we invest, might be the best approach. You know, so should individuals engage in some

short, sharp, hard efforts? I think, you know, ideally speaking, yes, they should. There's even some recent evidence that I think there's renewed interest in the potential for elite endurance athletes to incorporate sprinting in their training. And there's a series of studies that's come out. Ronestad, Carson Lunby's work showing that when truly world-class level cyclists, we throw these terms around highly trained elite, these are cyclists with starting VOT2 max values, 72, 73, mils per kilogram per minute.

And they randomize them to do either traditional hit four, five-minute repeats, or effort-matched 30-second sprints. And they sort of effort-matched. So whichever group you're assigned you, you're working at the highest effort you could, and they were work-matched. And what they found was the group that incorporated the sprints had a further boost to their performance, 20-minute time trial performance. And they actually had a small but significant improvement in VO-2 max.

And so it would suggest that maybe there might be a problem. place for athletes to incorporate what, you know, some call RST's repeated sprint training as a ways to further augment their performance. Now, you know, still relatively small, three-week interventions, but to go back to your question, I think there is a place for incorporating very vigorous effort sometimes if, you know, again, there's some people who shouldn't do sprinting, right, especially if you're starting out. But all things being equal, yeah. I think varying it up your approach is going to be the best for general fitness. I want to talk.

Let's dive in at some protocols. And this is very, like I'm sitting here getting very, very intrigued because of my training, which mostly, like I mentioned, it's mostly on a Peloton, stationary bike. And it's, you know, again, I do a lot of the 20 second on, 10 second off, you know, back to back. And I'm thinking like maybe I should also incorporate some, you know, I could go outside and do a hill sprint. I hate them, hate them, hate them, hate them. But I mean, you know, if I can get, if I, if I can do it quick, it's still convenient. I just go outside and, you know, do.

This isn't like going around a track or anything, which is something that I can conveniently do. But also maybe potentially get even greater improvements in VO-2-Max. That's of interest to me. I'm not an athlete, but so are your thought, do you think that I'm, so I, you know, far be it from me to tell you how to train. But, you know, from what I've listened to and my awareness of the type of training that, that you're doing, I actually think, you know, maybe you should do some longer intervals at a little bit lower intensity.

You know, maybe you should be incorporating some three, four, five minute intervals as hard as you can go during those rather than almost exclusively doing Tabata style type training. because arguably you're already doing a ton of sprint training. Tabatas are basically sprint training. So I want to be careful here. You know, we could talk. Let's let's at least for now keep it modality specific. So how you would train on a bike before we start talking about different modes in that because that introduces some other wrinkles. But again, from what I understand and what you just said earlier in our interview, most of your training are these for you all out 20 second sprints, 10 second recovery efforts. I'd suggest, you know, And I think Dr. Attila recently suggested you might want to do the same thing in those 10-second recovery periods almost completely stop or at least go down to very low-intensity cycling because part of the thing with Tabat is you go really hard, but those 10-second breaks, you've earned the break. Take it. So don't maintain the intensity too high in the 10-second valleys before you go hard again. But again, it sounds like much of your interval training right now is already sprint-type

training, given your tabattis. We know there's data to say. suggest that all things being equal, three to five minute repeats at the highest sustainable intensity are probably the best way to maximize gains in VO2 max. It's a pretty loaded statement, but I think you probably want to incorporate some of these longer intervals, two, three, four, five minutes. Again, highest workload you can and do four of those, right? Now, that's probably going to take you a 20-minute commitment some mornings. But I would say, or I would encourage you to at least think about incorporating some of that style of interval training. Yeah, absolutely. How many times a week do you think? Yeah. So again, my understanding is you're doing something

almost every day. And I think you sort of, you know, you go back and forth between some resistance stuff. Well, the resistance is on, and we'll talk about this as well, but it's on the same days. It's just later in the evening. But like, so we mentioned Tabata, and then you're saying this, like, like longer duration interval. And it's funny because I had a question about that. It was like what if you, let's say, you know, time, let's say the interval where you're going all out is, or at least high intensity, so 80%, is matched. But instead of doing the, you know, shorter interval repeated, repeated, you do longer

ones. And it sounds to me like the longer one, there is a difference in doing a longer interval, even if you're like, you know, let's say six minutes total going all out for Tabata style versus what you're talking about, which would be... There is. You know, metabolically, the challenge is different. You know, so this is where all interval training is not created equal, right? And again, there's lots of variables there.

Total volume in particular is important. But I think challenging your metabolic system in different ways is a good strategy. Now, again, for you that if you're only doing 10 minutes in the morning, some of these days are going to be 20 minutes, but maybe some days are... you know, three, five-minute intervals with a little bit of warm-up, cool-down, and recovery in between. That could still be a 20-minute workout, but you've gotten in there 15 minutes of relatively intense training. Again, push as hard as you can go. So they power outputs that you're working at are going to be different than when you're doing tabadas. And maybe some days do a minute on,

minute off, repeated 10 times, even five times, right? Because that was a protocol that we've used a lot in our studies, minute on, minute off, repeated 10 times. Took about 25 minutes for individuals. But now there's studies that have looked at 5 by 1 showing that much of the improvements, certainly in V2 Max, is almost as good. So again, when we're doing 10 by 1, we're wringing out the sponge a little bit more, but you get a lot of water out of 5 by 1. So I would say vary up your intervals and recovery periods, ideally, in order to change up the physiological stress on the body. Now again, you're someone who says, I only have 10 minutes in the morning, and I absolutely love Tabadas. Okay. Like, you're so far ahead of the game compared to many,

but I think if you're looking to optimize, or maybe that's going to give a different lactate profile to your brain that may be at least different. I can't guarantee you it's better, but I suspect for improvements in your cardio, your spiritory fitness and that, the different challenge may be a little better. Well, this is great, Marty, because I think, I am, look, if I have 10 minutes, I have 20. And there's certainly some days, I definitely have 20. Others maybe 10, you know, like today, it was like 10 minutes. I got, Marty's coming. I got to do something.

But, you know, I think a lot of people are interested in that because there are different goals, as you mentioned. You know, what are your goals? Are you an athlete? Okay, then 80, 20, like there's lots. I mean, you're putting in the time no matter what. But there's also people time, like anything. So there's those people with like, I can't think about, you know, doing, you know, maximizing what I can out of the VO2 max and squeezing the clock. and getting every last job.

I just got to like, I got 10 minutes or, you know, and I can only do that X many times, like, you know, four or five times a week or maybe some people, like 20 minutes, I can do three times a week. But then, you know, I am interested in, I'm optimizing for VATOMax as much as I can while still being time efficient, you know. And that, I do think there's a large audience that's very, that's in that camp where it's like, I want to be time efficient. I want to still really optimize for VOD.

2MX. And there are really, I would say, pretty strong data correlating VOTUMEX also with brain health. Of course, cardiovascular systems are very related to the brain, vascular health, right? So that is really good. We talked about Tabata, we talked about 10 by 1 or 5 by 1. And you even talked about some of these longer ones, which were like 3 to 5 minutes. And then your one minute, so was your one minute workout based on the... So where the title of the book came from was, so our initial studies, you know, Fast forward 15, 20 years of research. Our initial studies in this area, we were using the windgate test.

There's a long reason for that. But we were doing these 30-second windgates. Again, these are uncomfortable. People hate them. You need four or five minutes recovery at least before we can coax you to do another one. But the point is, four or five wind gates still takes 25 or 30 minutes. And so it's still a significant time commitment. And so people were saying, well, you know, some of the critics,

rightly pointing out, well, if it's taking you 30 minutes and you're doing three times a week, you're already getting up there. So really how time efficient is it? And so we wanted to devise a protocol where no one would argue that it was time efficient. And so that's where, and the other is, it's the last 10 seconds, arguably the last 15 seconds of the windgate that hurt the most. So, you know, basically after about 15 seconds of a windgate, you shut off glycogen utilization. You've just produced so much lactate and your pH changes so much. So if a lot of these responses are in part related to the reduction in glycogen, maybe you only need 15 or 20 seconds to trigger some of these responses.

So all that to say, we came up with a protocol that was three 20 second intervals, five minute total, warm up and cool down, and some recovery in between the intervals. So start to finish, the protocol took 10 minutes, and within that there was one minute, a very vigorous exercise. That was the one-minute workout. I think we've at least talked about it before the notion of re-hit. At the same time as we were sort of coming up with the one-minute workout, UK researchers, Metcalf, Volard, they've done a lot of this work.

They termed what they called reduced exertion high-intensity training on a very similar theme, where they were using a 10-minute start-to-finish workout, but their protocol involves 10 to 20, only 1 to 2, 10-20-second effort. So all of this variations on a theme where we're talking no more than one minute of very intense exercise in a 10 minute time course. And we've done a number of studies now looking at that workout and showing that certainly it can improve view. Many of the things we've talked about, it can improve it to at least very similar extent as more traditional modern intensity continuous training that takes five times longer, five. five times the total exercise volume. That's a really big interest, I mean, I think, to a lot of people.

So, I mean, that's, for me, and I mean, people that I know, I'm a lot of busy people that I know. I mean, it's like, you know. So I guess the moral of the story here is I think the work to rest ratios in a way do matter to some respect because, and that was kind of a big question for me was what I'm doing every day. It was a very specific work-to-rest ratio, but going a little bit harder. And that really does make sense. And I knew it. Like, there was something in me that was like, I just need to hear Marty tell me.

So thank you. You mentioned some of the other protocols like the re-hit. How does that, you know, how would you say that really differs from high-intensity normal training? I mean, with respect to maybe some of these endpoints we're talking about like VO-2MAC. So, again, like, you know, first of all, it's all interval. training, whether it's hit depends on your definition a little bit. And so that's why, again, you know, I really like this idea, this notion or this terminology of interval training, because it covers

all the basis. It's just alternating more intense, less intense periods of work. High intensity for many is 80% or higher, heart rate as a metric. And, you know, and we've done this, but to try and, because our first work, we called everything hit, right? Which is much of the field that the time, everything was hit. But, you know, five minutes at 80% of VOT2 max is a very different stress as we just talked about from a 20 second to battle workout. So at least to try and distinguish the interval training a little bit more, there was this move to try and distinguish hit, which is intense but submaximal efforts from sit or sprint type training, which is much closer to the sprint from danger pace type efforts. So, you know, I would say,

re-hit is absolutely interval training. It's probably closer to sprint-type training than traditional hit, which just because of the power outputs. You know, you're working 10, 20 seconds, but these are very, very high power outputs that you're generating and much higher than V-O-2 max pace. Oh, so I was completely confused about that because reduced exertion, to me, I was going, oh, this is less than 80%. So the reduced exertion, it was 10 or 20 seconds. It feels a lot easier than a 30 second windgate. And it was because, you know, these investigators know,

30 second windgates hurt and all of the lactic acid and the pain and the discomfort and even the nausea and dizziness sometimes it can go wrong with 30 seconds. If you're doing 15 or 10 seconds, much of that is attenuated. So the exertion comes down from the metabolic feelings, and it's not the exertion level in terms of the power outputs on the bike. You know, just to take that one step further, Dr. Ed Coyle at the University of Texas at Austin, big name in the field of exercise physiology. Dr. Coyle's recent work is looking at four-second all-out efforts, but doing a fair number of

them. And it's really just a variation on a theme, and Dr. Coyle's point would be, you can work very, very hard, even fairly deconditioned people can put out extremely high power outputs for four seconds. Then you give them, I think it's 12 seconds of recovery and they do it again. And so the point there is these very short, very hard efforts aren't associated with the feeling, the perceptions of discomfort when we initially think of Wingate tests, sprint from danger pace. And, you know, there's a lot of critics, certainly on the behavioral side of things who are saying interval training is doomed to failure as a public health priority because we know that

anything above lactate threshold, it hurts. It makes people uncomfortable. They're less likely to do it. But there's a whole other group in the exercise behavior field. They're going like, well, wait a minute. Continuous high intensity efforts, even continuous sprint efforts are very different from intermittent high intensity efforts. And so there's a lot of, certainly a lot of arguing right now a lot of Twitter polemics, but I think still a lot of good work to be done looking at these perceptual responses to different types of interval training. It's too simplistic to just go, well, sprint type training, no one's going to do that because it hurts because now there's evidence to show that, well, actually it doesn't. When people rate this, they don't find it as

unpleasant as uncomfortable as some make it out to claim that it is. So the reduced exertion interval training, the re-hit, reduced exertion, high-intensity of training, is you still, they're messing around with more of the work-to-rest ratios, and you are still going, you're still going very hard, but your perceived exertion isn't as high as it would be if you were doing a wingate or sprint for interval training. And so at the end of the day, it really goes to say that, you know, perceived exertion isn't necessarily the best way to gauge how hard you're going, because if you're still going hard on your four or five seconds, you know, you're, you're, you're, you're, you're, you're, you're,

you're doing good. And then, you know, it's just, I, this is great. I think this is very clear to me because, you know, the, the, the, that must be why I'm so drawn to debaught as well, because I'm going hard for 20 seconds versus three minutes. I mean, one minute is hard. Like, it's definitely going to be different. And it is, you know, these behavioral psychologists or whatever Twitter polemics that you're talking about, they don't, they must not know about David Goggins and the whole movement of you have to suffer to get the gains. And, you know, so there are people that are willing to put in that effort. There are people that do want to suffer and they will. There are some days where you just don't, right? There's just some days where you're not going to do that.

But there are days where some people are very motivated. And, you know, to be clear, these are, these these are very good scientists on both sides who are very careful, methodological people. You know, they, so I respect the, the, the scientists on both sides of the issue. But yeah, to your point, I, my sense is when it comes to higher intensity, especially short duration work, the traditional way of thinking when we think of perceived effort, it's just, it doesn't fit as well, right? like classic Borg RPE scales are, you know, based on six to 20 because that generally correlated with, you know, young fit individuals who had a resting heart rate of 60 and a maximum heart rate

of 200. That's where that rating scale comes in. And so, you know, the more intense, especially if it's continuous exercise, the higher the heart rate, the higher the perceived effort. But we just see such a disconnect between ratings of perceived effort and heart rate. heart rate, I'll give you a very specific example. We've done a study looking at that 10 by 1 protocol. So these are 10 one minute efforts at objectively measured maximum heart rates of 85 to 90% of maximum in older individuals, 63 years on average, obese with type 2 diabetes. On a 10 point rating scale, they started out as a 5. They eventually got to about an 8. And so the average RPE was about a seven out of ten, even though these people were doing very high power outputs

at very high percentages of their maximal heart rate. So it's just a striking example. In our initial sprint studies, the one minute sprint studies, three 20 second efforts, our first ones we were saying, go as hard as you can, sprint from danger pace. And in those we were using a 20 point scale. They'd come back, 14, 15 out of 20. because now if we ask them to continue that sprint pace for a minute, I'm sure we got to 20. But since they're so short.

So yeah, to your point, it's exactly right. Perceived effort, I don't want to say it goes out the window, but it maybe needs a rethink when we're referring to these very short, very hard, intermittent type efforts. So where do you think, let's say someone new to hit? Like, would a good place to start be more of these, like, shorter, like, interval. It's a really good question and this is where, you know, we haven't really talked, health risk and all that. I'm sure we'll get into it. But like a standard thing that we'll just tell people is get out of your comfort zone. So wherever your starting point is, your own

perceived starting point, make yourself a little bit more uncomfortable than usual for a short period and then back off. And so, you know, I use this analogy all the time. If your only exercise is walking around the block and you want to get into intervals, it's literally for the next two light posts, I'm going to pick up the pace a little bit and then I'm going to back off. So I feel I feel I'm breathing a little bit more. I can't talk to my partner like I generally can on our moderate walks. It can be as simple as that. Just get out of your comfort zone. If you're someone who's already dialed in on the bike and you got a smart watch and all of that, it's like, hey, get your heart rate up longer or go longer and try and keep your heart rate there, you know, or rather than that, you know, or rather

20 seconds, you're going to go for three minutes as hard as you can. You're not going to be liking me. I know. And next time you're going to do that. But it's going to be a very different challenge for you, right? And this is where I think that the more empowering term interval training, it's okay. Because it doesn't matter if you're magically getting to some 80% level or whatever the experts tell you you should be at. It's just start with the alternating pattern and then build from there. Start to dial it in maybe a little bit more and get more. You can get more. more discerning, but as a starting point, just get out of your comfort zone and back off and repeat that a few times.

This kind of reminds me of the, was it the interval walkers versus the walkers? Absolutely. Yes. You know, excellent data. And these are, you know, relatively small but well-controlled, randomized controlled trials looking at interval walking versus continuous steady state walking, including in individuals with type 2 diabetes, three, four-month interventions. individuals were randomly assigned to an interval walking group, continuous walking, or a control

group, the interval and continuous walkers matched for total exercise volume, total exercise intensity. So you can imagine the continuous walkers. I think their average heart rate was around 65% of maximum. The interval walkers got that up to 70 and then down to 60. So we're just talking gentle hills and valleys. after four months, the interval walkers, greater improvement in cardiorespiratory fitness, greater reduction in, or greater change in body composition, greater loss of fat, and most importantly, individual's type 2 diabetes,

greater reduction in 24-hour blood sugar measured using continuous glucose monitor. So it's not to say that continuous walking is bad, I think it's just a little bit of evidence that adding some intervals or varying the pace, even slightly, we're not talking sprint training, may provide some greater benefit. And this kind of relates to something I was going to ask you about, which is, you know, interval training for maybe elderly and maybe infirm, so people that are more sick, you know, like how they can incorporate interval training into their lifestyle. And also then, like, contraindication.

contraindication. So you mentioned like maybe some people, you know, is there some people that high intensity interval training is not good for and how would you know sort of all of those? Yeah. So in this, you know, this I always make the point here. I'm a PhD scientist. I read the literature. I'm not a medical doctor. I'm not a cardiologist. I read work like that. I try and stay informed on it. And certainly for my book, I interviewed people like Dr. Paul Thompson, right, noted cardiologist who writes many of the guidelines around this very, very issue. But first point I was make is that interval training, as we've talked about a lot, comes in many different flavors. So second point is that many more people than we initially think can perform and benefit

from interval training. And there's just now, there's hundreds and hundreds of studies that have looked at interval training in individuals with cardiometabolic disease, cardiovascular disease, heart disease, type 2 diabetes, older individuals, people with metabolic syndrome. And a lot of this is not new. You can find studies going back to the 70s and 80s, some of the pioneering work looking at interval training in individuals with heart disease. So the notion that people could, you know, individuals with cardiometabolic diseases could engage and benefit from interval training is certainly not new. But there remains, immense debate. And I think it's, we're all reading the same science. And some people, again, I'm talking about the field broadly. Some want to see the science get to a certain level before

they recommend changes. And where that level is is different. So for example, high intensity interval training, my read is is much more ingrained in Europe and certainly in Scandinavian countries, it's, you know, much of the pioneering work around high intensity interval training and cardiovascular disease was done in Norway and the work of Ulrich Wistloff, and that goes back to the calculator that we talked about earlier. But there, I think it's much more generally accepted and integrated into cardiac rehab training, or I think in North America, it's not, right? And so that's not necessarily good or bad. I think it's the experts, the cardiologists, the people who write the guidelines looking at the evidence and saying,

ah, you know, some are more, like I say, there's different viewpoints on that. In terms of risk, and again, I'm not an MD or a cardiologist, but there's no doubt that more vigorous intensity exercise can transiently increase risk of an event during the exercise bout itself. I think there's there's fairly strong evidence for that and you know in preparing for our interview I was reading some of the latest guidelines expert guidelines around that making that point you know

especially in more deconditioned individuals people might already have some silent underlying risk factors and so we can't ignore that or downplay it or say that everyone can do interval training and it's fine but the absolute risk still remains low when you look at events per hours engaged in actual exercise. You know, both moderate and vigorous type effort, whether it's continuous or intermittent, the absolute rates remain relatively low, but statistically there's definitely an increase in risk that's higher with vigorous exercise during the event itself. Now, of course, after the event, relative risk is much lower than individuals who would remain sedentary. So, you know, I think the old adage of the greatest risk of your health has just

remained sedentary is absolutely true, right? And so when I, it was a striking phrase that Dr. Thompson used when we interviewed him for the book was, you know, if your choice is between doing hit and doing nothing, do hit. If the choice is between hit and moderate and you're 60 and you've been pretty inactive, you might have some underlying factors and time is not a worry, do moderate. or at least engage in some moderate as some preconditioning before you start with the more intense stuff. And then on the, you know, who is absolutely contraindicated, atrial fibrillation, there are some very clearly defined no-goes, that if you have certain conditions that you shouldn't be engaging vigorous intensity exercise, unstable angina would be another example.

Yeah, sounds like a lot of the, I mean, things that you would talk to your cardiologist about, you would already have a cardiologist if you would know that you had that sort of disorder. The last point I was make is, you know, in talking to many physicians and cardiologists, you know, we think an exercise stress test sort of gives you that green light or red light to engage in exercise. And certainly in our studies, where individuals had elevated risks, people with type 2 diabetes and that, everyone does, the 12 lead ECG stress test before they're recruited into the study. But, you know, I naively thought, okay, the person doing the stress test, the cardiologist reading it, it's going to come back and it say, green light, good to go in your study, red light, unable.

What we found was a lot of yellow lights. Maybe, you know, this person might be contradicated or there's a change here that might elevate risk. And so, of course, we defer to safety. And so even those yellow lights, generally those individuals were not then recruited into the study, which is no doubt influencing outcomes. but I always wonder, I'm like, so are these people just going to sit around and then and continue doing nothing? And is that in itself raising their risk? So it's, you know, it even, you know, the standard, you know, recommendation, see your doctor, get clearance before you change or engage

in exercise, it's not always a hundred percent guarantee one way or the other in terms of you may deal with a sudden adverse event. We might see it in a 20-year-old. my lab tomorrow. You can't absolutely rule out these things. I think also mentioning the walkers, the interval walkers versus continuous walkers, was really good because, you know, it also kind of highlights the fact that you don't have to go to your 80% max heart rate for interval training. And perhaps people that are older, people that might have some underlying conditions, people that are untrained and are starting later in life. Great. You know. it's never too late to start. They can, they can start by not, you know, by doing, you know,

intervals that are not necessarily all out or even submaximal, right? I mean, just, just going a little bit above what your, you know, steady state being able to talk normally sort of conversation is. And, you know, I don't think that, you know, my sense is that many of your listeners are already aware of this, but I think still for a lot of people, or certainly the general public, they hear the word hit for interval training and they think, oh my goodness, it's this as hard as you can go all out, breakneck pace, and that's not for me. And I think that's a disservice. And again, hopefully this more encompassing term of interval training, it's just this idea of hills and valleys, right? And the other point to that is, I talk to, I'm not name dropping here, but just, you know,

many people have thought about this for a long time. I also interviewed for the the book, Carl Foster, who has done a lot of work around this. And when he first heard, you know, as a scientist in the 80s, that there was a group in Germany that was doing interval training in cardiac patients. He saw one of the scientists at a conference. And he said, oh, how many people you killed this week with that crazy stuff? And he was relaying that story to a cardiac nurse when he got back to his institution. And the nurse, he said, sort of tapped him on the cheek and said, oh, Carl, you're so silly. And she said, look at this patient in the parking lot who's coming for his cardiac rehab setting, or session. They already engage in interval training because they can't,

they have such low exercise capacity. They can't get to a continuous moderate pace. So what they do is they innate the interval train. They get out of their car. They take a few steps. They take a break. They take a few more steps. They take a break. It's a bit like climbers on Everest. right and so again that's a more empowering message i think you're just starting out that's okay you can you can train like elite athletes have trained we just have to set the workout at approximate level that's suitable for you rather than you know oh my goodness people are destined to be a failure because very few can engage in continuous moderate exercise for a period of even 20 or 30 minutes because their capacities are so low so it's a bit of you know the behavioral colleagues talk about

message framing, I think there's a lot of that we can do with interval training. So for those individuals who just think it's this all out crazy stuff, I'd never do it, it's a reframing of it for them. Yeah. And also, again, the modifying the work to rest ratios too is another sort of way. I think that it's like, oh, I have to go all out for a minute or two minutes or three minutes, but oh, what about 10 seconds? You know, what about 10 seconds? So there's a lot of, there's a lot of ways to sort of modify the, you know, the hit program in general. What about this, is it high, the high intensity resistance training or resistance intensity? It goes a different way. You know, some people call it functional training, but certainly there's high intensity resistance training.

You know, I think it can still count, you know, for a lot of resistance training just because the intensities are so high. You know, we're talking about now very high. force efforts that last less than a second sometimes. By its definition, it's interval training, we just never really think about that. But so I think certainly body weight style type interval training or what used to be traditional calisthenics and that, that can play a role here. So I think, again, using this generic term interval training, I think we can have more aerobic style interval training or resistance style interval training. And again, body weight style interval training would sort of be the classic one to me that is interval resistance training. And I think it can have

tremendous benefit. You know, it's often a sort of a middle ground. You're not going to see the gains and strength that you would see with traditional heavy weight lifting exercise. And you're not necessarily going to see the gains in fitness that you would have with the traditional well. structured aerobic training program, but you can get a lot of both right in the middle, you know, especially if, you know, we're talking air squats, burpees sets, pushups, where you also keep recovery periods relatively short, you know, you engage in that for 10 to 20 minutes, you can keep your max, your heart rate up to about 80% of maximum, but you've done a lot of resistance style training that's increasing functional strength as well. I think it's a

tremendous way for people to train. It sounds like a lot of CrossFit kind of things. Yeah, absolutely. You know, now maybe not necessarily as intense as some of these programs that you see. But absolutely, that style of functional training, whatever you want to call it or label it, can be extremely beneficial, I think. And in a time-efficient way, you get strength gains and some aerobic conditioning as well. Can you get any muscle math, math?

gas gains, even strength gains from high-intensity interval training. Let's say if you're on a stationary bike and you're cranking the resistance out. Yeah. So that one really depends where your starting level is. Right. And so if you're already relatively fit and healthy, then the general belief is that you're not going to see massive changes in muscle protein synthesis or changes in fiber size or anything like that, even with fairly intensive sprinting. Now, if you're someone just starting out, you think of a very deconditioned elderly individual who is going to get on the bike and do some moderate pushes there, you know, so we're not talking all out sprint training. They could see some improvements in protein synthesis.

You know, and again, are we talking mitochondrial, myofibular, but I think traditional muscle protein synthesis where we're seeing an increase in fiber size in that, if your baseline is very, very low, then I think even aerobic style interval training can be beneficial there. But otherwise, you know, once you get to a certain level, it's not a hypertrophy stimulus, generally speaking. Yeah, okay. Because I'd crank my resistance up really high on my patent and I'm standing and doing it. You know, like, I'm like, this has to be something on my, my quads and.

Well, you know, you look at, you know, look at two or front cyclists, right? Like, I mean, they're amazingly muscled. Now they're very, very lean as well, right? How much of that is, that was covered in a layer. of fat, how much muscle would there be there? But, you know, I think it's not nothing, but, you know, you can get much greater gains in protein synthesis with some more traditional squat exercise and things like that with a lot, a lot less volume of work. Can you just lift? I mean, like, can you, you know, like, let's say you're doing a more

of a resistance training, like higher intensity resistance training, maybe circuit or like you're talking about. I mean, can you just get by with just doing that? Yeah, again, right compared to what? But, you know, so like, I don't, like, only doing heavy resistance training as traditionally practiced, I think you're definitely leaving something on the table in terms of cardiorespiratory fitness and health benefits and all of that. I think it's a really good question of, you know, again, if it's that person like we talked

about, the classic individual, you know, type A. limited time, still engaged in real life with responsibilities, family job, things like that. And they have an hour a week to train. If they only did high intensity functional training, calisthenic style, body weight style exercise, I could see a lot of value in that, right, in terms of aerobic conditioning and gains in strength. You know, coming back to what we talked about earlier, you know, if it's if it's four sessions a week, week they can do, maybe two of those are high-intensity functional training or body weight style training and two or more interval training for aerobic conditioning on a bike, on elliptical,

things like that. If you only have three, I'm not sure how I divvy those up, but still getting some variation in ideally. But yeah, I have a lot of time for high-intensity functional training. Yeah. What about the combination of aerobic training with resistance training, this chronic interference effect that you've heard about where if I do my aerobic exercise, right, you know, in conjunction with my lifting, I'm going to blunt my gains. I mean, at least that's what I interpreted some of that. Yeah. So, you know, the, I think where the evidence is, and if you look at the latest systematic reviews and meta-analyses, what they're going to say is, maybe there's a slight interference effect. Maybe it's there to a greater extent with high-intensity

interval training. And certainly if you do it within the same session, maybe there's some blunting. But if you look at the work right now, there's some evidence to say cycling is okay, but running is not. There's some evidence to say, actually running's okay but cycling's not so there's no clear answer i think the bottom line is there might be a slight interference effect in some people especially when they do it very very close together or in as part of the same session but it's probably relatively small it's probably relatively negligible in the big picture but if you're someone who's really looking to eke out maximal gains you probably want to leave a few hours in between your training sessions

Yeah, the interest had kind of sparked because, well, one, because you hear about it, but also from, I think it was Stu's recent study where they were combining aerobic exercise with resistance training. And it was like actually there a little bit of a beneficial effect in some regard to blood flow or something like that. So it was, you know. Certainly, I think, you know, it's like a lot of things with interval training, you can pick your study to argue one side of the other. But, you know, I think that. And of course, meta-analyses are based. on all these studies, some good, some less good. But I think that's the sort of the state of the field is it's probably not a big deal for most people, including if, look, I got half an hour

today. I can do both. I can't split this up because I can't train tomorrow. Well, then do both, right? But again, if you want to eke out every bit of the drop, then ideally separate it by a little bit of time, a couple hours at least. Okay. All right. The guidelines that are set, we touched on it a little bit. And this is a big question that people ask all the time. You know, there's these guidelines that are set by a variety of committees.

It seems like there's a lot of consensus in terms of the guidelines for moderate intensity aerobic exercise anywhere between 150 to 300 minutes a week or vigorous intensity exercise. and that's 75 to 150 minutes a week, I think, something like that. Where do you think, in your opinion, does high-intensity interval training fit into that equation? Is there a new timeframe? And let's say for people that are optimizing for general health or also for people wanting to also get that, you know, back to the JAMA study, you know, I do want to be closer to that elite. sort of performer level using kit.

So for those kind of people, there are a guideline in your opinion or what's your opinion on that? So there's a ton there. So first thing, let's remember, these are physical activity guidelines. They're not exercise guidelines. So we're talking about physical activity guidelines.

You're right. There is general international consensus. It hasn't changed that much if anything, it's just increased the number a little bit. And the latest guidelines, U.S. guidelines for Americans, the WHO World Health Organization guidelines are consistent, and they're exactly what you just said, 150 to 300 minutes of moderate or half, if you're doing it vigorous. And how is that defined? Well, moderate is defined in an absolute sense of about,

of, not about, it's three to five point nine met, three to five point nine metabolic equivalence, or five to six on a 10 point rating scale. And what that means subjectively is you can talk, but you can't sing. So you're exercising with a partner. You could carry on a conversation at a moderate effort, but you couldn't sing. Vigorous effort is above six Mets, seven or eight on a 10 point scale. And you could only say a couple of words. So you couldn't carry on a conversation, say a couple of words, short phrases.

So that's sort of the subjective and, objective measurements of moderate and vigorous, and those are fairly consistent. Now, you know, American College of Sports Medicine would have some different numbers there, at least in terms of percentages of heart rate and things like that. But that's generally where we are moderate to vigorous. And those are for what are deemed substantial health benefits. It's not saying that's the best weight. increase your VO2 max. It's saying there's really good data from a wide variety of sources

that if you engage in this level of weekly physical activity, you can expect substantial health benefits, brain, muscle, you know, lots of, lots of things. It's not saying it's ideal either. That's not necessarily the optimal because there's always a caveat that more is better. So you can ring it a little bit more out of sponge if you're going to engage in more. And there's not a, you know, there's, the only other recent change was really that there used to be this guideline that said, you have to accumulate these in bouts lasting at least 10 minutes. And that was removed because it was never really supported scientifically. And so at least that change, I think, has opened up a little window on this notion of all activity counts. And it was partly, I think, some recognition of there's some studies out there showing that very short effort.

can be associated with some improvements in some of these health markers. So the guidelines are just that. They're, you know, suggestions or recommended amounts to derive health benefits when we're talking physical activity. They're not saying this is the way that elite athletes should train in order to optimize their performance. So I think we really need to recognize what the guidelines are. And the last point in this is my understanding, based on talking to these experts, is

they tend to be conservative because ideally they would like metrics like doing this amount, we know, is associated with a lower risk for all-cause mortality or is a lower risk for developing cardiovascular disease and many of these other chronic ailments. And so we just don't have anywhere close to that body of evidence when it comes to interval training. You know, we may eventually. So where does hit fit in the big picture? I think, and again, I spoke to people for my book, people like I'm in Lee at Harvard, Dr. Iman Lee,

who's engaged with some of these committees. And the point was, well, hit already fits within the guidelines. And I said, well, is it only the hit efforts or the recovery intervals as well? So if you do a 20-minute hit session, but half of that is resting and half of that is the exercise, her point would be, no, you count both, right? Another example of interval training is so many team sports, right? I like to play ice hockey. My wife is a soccer player. And so in those, for parts of the game, you're active and exercising very vigorously. And for parts, you're not modern or low intensity effort. So with those, if you engage in a one hour of pick up ice hockey, but you're only playing every other shift, you can probably count the hour within that. So I think interval training and hit, all. already falls within the guidelines, and certainly it would fall within the guidelines of vigorous activity, will we ever see the guidelines say 150 to 300 of moderate, 75 to 150 to 150 of

vigorous, or 30 to 60, a very vigorous exercise. And you know, a new break point, maybe, but I think the people that write the guidelines will want to see a lot more evidence until we're going to get to that point. Or, you know, will there be some acknowledgement of these types of VILPA, you know, or at least engage in vilpa-like efforts for five minutes a day? You know, 30 minutes of VILPA-like efforts have also been shown to be associated with this. You know, the UK guidelines explicitly refer to hit. The WHO and the U.S. guidelines really, do not, at least in terms of incorporating it. So it's going to continue to evolve, but I know that's probably a long-winded answer, but that's probably the best perspective that I could offer on that right now.

Yeah, I think that's good. And I do think that alluding to the vilpa studies, I mean, again, like you said, I mean, you're talking about, you know, to some, I mean, it's a pretty minimum effective dose to get 30 to 40% reduction in all-cause mortality and cancer mortality, right? I mean, it's not the 80% of the, you know, at least the elite performing people that had the highest VO2 max. But, and for that, you know, you may need to do, probably need to do more. But for some people that are just generally wanting to get, you know, 50% reduction or something like maybe, you know, doing, doing 60, 75 minutes a week would. And that, you know, because you're, I get this question a lot. And, you know, you alluded to it earlier, whether we like it or not, a lot of people still want that answer is, how little can I get away with? And the guidelines don't really address that, right? Or at least there's no grudging acknowledgement for saying, look, we know most of you probably aren't going to do this. So at the very least, do this, right? There's been no movement on that. If anything, we're just encouraging people to do more. So it is, it is maybe a gap. Or at least, we're.

we should confront that reality, that there's a big disconnect there for a lot of people. Another sort of, I think, research gap is the sex differences. And it's definitely of interest to many, many women of all stages of life. So acknowledging the research gaps, I'm still going to ask you some opinions to see if there are any. I know there's also, I think, some misconceptions with the general population also. So it'd be nice to kind of even touch on some of those. One being, you know, postmenopausal women, like, is hit good or bad for postmenopausal women. Like, on the bad side, some women are worried about raising cortisol too high.

Do you have any thoughts on doing hit for postmenopausal women? So specifically on the cortisol level, and again, I think the latest systematic reviews, meta-analyses, you know, the studies vary a little bit. But by and large, I don't think individuals need to worry about chronic increases in cortisol levels systemically that are going to cause them damage. Clearly, cortisol levels can go up, just like catacolamines, go up acutely during exercise. but I think there's some evidence now that would suggest that actually in individuals at practice interval training, basal cortisol levels actually stay lower than prior to baseline. So I don't think it needs to be a major concern, especially given a lot of the other benefits that we can see with this type of approach. So that's on the cortisol issue specifically.

Yeah. And that, I mean, given all the benefits we've talked about, the cardiovascular the muscle, you know, skeletal muscle, you know, the brain. I mean, there's just, it's, it's pretty clear to me that, I mean, it'd be hard, it'd be a hard sell to say, oh, no, it's not beneficial for postmenopalala. Exactly. I mean, you know. And very different is, you know, individuals with PCOS, polysystem or are, is there's ongoing work, some really good work out of Norway, looking specifically at hit in individuals of that

condition, so showing some real bad. benefits there. On the sex-based differences, you know, writ large, are there sex-based differences in some outcomes? Yes, I think they're subtle. At least the evidence to this point would suggest there are some differences. They're probably subtle differences, but we do need to know a lot more. You know, are there massive differences between, for example, phases of the menstrual cycle or oral contraceptive users versus naturally cycling females. Again, maybe some, but probably pretty subtle. So that doesn't mean they're not important. But I think the differences are likely small in most outcomes. But absolutely, we just need more research. We need more research on diversity of responsiveness

writ large, not necessarily even just biological males and females. You know, you've talked about this on other episodes. You know, it's an active area of research and it's a frustrating area of research sometimes. So I'll give you a very specific example. Some of our research right now is looking at the mechanisms for the increase in VO2 max with very short sprint type interval training. Right. And so we know that that increases VOT2 max, but we're not sure why. And actually some of the work would suggest maybe it's more of the muscle adaptations than we thought about or at least the cardiac output changes take a while. So I have a PhD student immersed in this area. In his first study, we show that VOTU max goes up, stroke volume was up, cardiac output was up after 12 weeks

of training, and it looked like there were some differences between the males and female participants in the study. So we did a secondary analysis, wasn't appropriately powered, and we thought, yeah, actually, it doesn't look like the women are responding very much, or the females, and the males are. So then we repeat the whole study using more best practice procedures properly controlling for menstrual cycle phase

and properly expressing fitness per fat-free mass. And we're basically unable to replicate the original findings and we certainly didn't see any evidence of a sex-based difference, which tells me something that we've hand-wave

around a little bit around our conversation at this point, there's tremendous inter-individual variation in responsiveness. And so at least right now, to my mind, in terms of potential differences in responsiveness to specifically sprint type training, it might be less about a male or female biology issue. And it might just be there's tremendous variability between individuals. And in the almost 40 participants in the combined two studies, it happened to be men, people identified as males that responded to a greater extent, but it might not have anything to do

with biological sex. And I think that's where a lot, many areas are right now, not all of them, some there's very clear differences, but I think that's where the exercise field is writ large. And the vast majority of studies have not incorporated these best practices for making systematic comparisons between sexes. Right. Yeah. And also I think, you know, differences in like, I at least for me. It's like there's environmental black. How much sleep I got? Like things that'll also affect, you know, my ability to perform and, you know, things like that. So, yeah, I mean, there's a lot of gaps in the field. And, you know, with respect to women and menstrual cycle, it's also a question I get a lot.

And I, you know, I think the reality of it is that, you know, 20 to 30 percent of menstruating women are, you know, during their menstruation are iron deficient. And, you know, they just don't even know about it. They don't even know about it. They're not thinking about it. They're not increasing their dietary intake of iron. They're not supplementing with iron during that period. And maybe that alone also would affect some.

Iron's important for him, right? And that's, no, the other is, and if you talk to these female athletes, they're like, even if there is, I don't get to pick when my race date is. I know I have to peak for this day in four months' time, you know, in this location. Maybe you can structure your training around menstrual cycle a little bit. But I think that's just the reality, obviously, for women who compete in sport. And so, yes, we need to know if there's some differences there. But in the big picture, it doesn't really matter.

It's just one more thing that potentially contributes to variability and responsiveness on the day. And you try and control all the other things as well as you can, you know, to peak as best you can on the day or your event or your key event. Does high-end density interval training affect bone mass or bone density? Do you know? This is where, you know, like to this point, you know, I've encouraged us to think about mode specific when we're making some of these comparisons. I think that's where it depends, right? And so we know that more higher impact events or activities, certainly when we're young,

tend to, you know, lay down more bone. And so, you know, if we're talking high intensity cycling versus high intensity running, those things are very different, right? Are you running on concrete? Are you running outside in beautiful trails? All of those things matter. You know, the flip side to that is if we talk about injury risk, people say, well, I can't do high intensity training. I'm going to increase my risk for injury. Well, you know, I'm someone with classic left knee osteoarthritis. I just tore meniscus in my right knee playing hockey. So I'm going to have osteoarthritis and that knee soon. I can engage in very vigorous interval training on the bike. I can't and I don't run anymore. So, you know, hit training on the bike, no problem. Any sort of running outside is excruciating for me. So joint problems in general, people can, do you think people can engage in cycling? I do, yes. And, you know, certainly, and again, like, I'm not an expert in this area, but, you know, talking to experts and just trying to read and stay abreast of the literature, you know,

we know that people who have joint injuries, certainly menisical injuries are obviously. osteoarthritis. One of the best things that you can do is remain active. And it's obviously frustrating advice for many people because they're like, I want to be active, but it hurts when I'm active. And so moving towards less weight-bearing activities that allow you to be active around the joint and maybe, you know, help with the tissues around the joint, but aren't impactful forces. So cycling is a fantastic exercise for individuals with osteoarthritis because you can still, you can still engage in fairly vigorous activity without hurting or damaging, you know, specifically your knees in this case.

Yeah, that's great. I know there's quite a few people that are under the misconception that they cannot do any type of high-intensity interval training because they have joint issues. So they don't want to do box jumps, right? Yeah, I mean, jumping rope, which may actually be great for the bones. I mean, it's impactful and you can do, certainly do high-intensity intervals with a jumping rope as well. what about, so there's, we talk about like some of this, you know, we're talking about some of these like misconceptions, I guess.

And you kind of touched on this a little bit when we were talking about maybe, you know, people that are, shouldn't engage in high intensity interval training, like the people with AFIB or angina, what is it? Yeah. Yeah. The, the, the fact that doing high intensity interval training could cause, a fib or coronary calcification or just even like elite athletes in general like you at the high level you can see they have a higher tendency for a fib and coronary calcification but on the same in the same breath they also have a lower risk of you know cardiovascular related mortality um is there a way to reconcile those things so again uh not expert but my read of this including you know there's some there's some really good reviews that have come out recently. And again, we could drop those in the show notes to direct people to reading on this. But the old Latin phrase, the poison is in the dose, right? There's definitely evidence that individuals who over a lifetime engage in very high intensity, very high volume exercise may be at greater risk for some of these issues that you just referred to, heart, heart issues.

To my read and my understanding, while there's theories out there, a definitive cause and effect or mechanistic basis hasn't been definitively established. And the other is, it's been pointed out that those days, like, while clearly that risk is there and you see examples of this, it doesn't fit or doesn't line up with the longevity data, which is still that, you know, lifetime runners, will still have, you know, a few more years of life compared to others. So I think it's a, it's an issue that still really needs to be resolved. And probably the safest advice would be, you know, extreme exercise may carry some, some consequences, right? Whether it's the U shape

or the J shape curve, there is something to that. And if you're on, you know, this is, for the vast majority of people, this isn't an issue. But, you know, if you are that extreme, exercise or you just need to be mindful of the fact that that may carry some increased cardiovascular risk. Yeah. So one more oddball question before my last one, which is, what are your thoughts on this, like, hypoxic training? Like, have you heard of like the mouth taping during like a hit or? So my sense, yes, yes, I've definitely heard of it. You know, clearly when you move to more intensive exercise, the vast majority of your ventilation is through your mouth. So it's really hard to engage in vigorous exercise when you're restricting either nasal

breathing or mouth breathing. You're going to compromise your performance. It may feel really hard, you know, because you're inducing this added stress. Whether it's beneficial, I'm not convinced of that. I think the data around blood flow restricted training is much more interesting, and there's some really, really interesting work coming out of that. You know, you can make the case that maybe you're going to see some changes in respiratory or diaphragm muscle or that, but getting back to the idea of what limits VOT2 max, it's generally not a pulmonary limitation. It's a heart limitation. And so strategies that are really trying to additionally stress the pulmonary system. So, you know, if people want to try it, fine, I don't think there's tremendous evidence that that's going to

potentiate training responses. What's the interesting thing about blood flow restriction? Is it? Well, you know, like, I think, you know, as a therapy, so I'm aware of some ongoing work. I guess that's about, and, you know, this isn't our work, but I'm aware of someone. work, looking at blood flow restriction exercise and training in very, very high level, uh, endurance athletes, uh, showing some interesting, uh, changes in performance related metrics or, or, or some measures. Um, and, uh, yeah, so I, like I say, that work is ongoing. Um, the hard thing with these is it's, you can't truly blind someone to blood flow restricted training, right? Like, many of these interventions that we've talked about, it's tough to have. Um, it's tough to

have a true control who's completely blinded to the intervention that can influence some some things. But, you know, the idea of blood flow restricted training allowing individuals getting back to joint issues, maybe working at a lower absolute force or workload, but still seeing the metabolic stresses induced with blood flow restricted training. You know, there's some, there's some interesting work there, I think, so, and applications. Where do you see, this is, this is my last question for you. Where do you see the future of, well, specifically high-intensity interval training research and, you know, like the training methodologies, where's it going, like how we can find really,

you know, how we can define good studies to optimize for VO2 max, to optimize for like mitochondrial biogenesis and these important measures of longevity and health and performance for the athletes, too. But where do you see the field going? So a whole bunch of levels there. And I think it, you know, what's the most, it's like how do we spend our tax dollars, right? What's the most important education, health, all of that? But I think given the pervasiveness of physically inactivity writ large, there's a lot of behavioral work that needs to be done there, is it a viable public health strategy? What are the best strategies to encourage people to engage

in any physical activity behavior, but could brief vigorous physical activity, intermittent physical activity, non-exercise physical activity? Could we have interventions that behavioral interventions that will finally encourage people to do that? So I think that's a massive area that needs to get looked at. Number two is, you know, clearly I'm a proponent for interval training, but I fully recognize that we haven't done, or just they're not out there, these large scale randomized clinical trials, making very good comparisons between traditional endurance exercise and interval type training with proper what we call non-inferiority to designs, which is like, what's the margin of if there was a difference, it doesn't matter, right? So maybe that's

half a met or 0.2 of a met. Whatever you're met, is and design your studies. So it's like if we show that margin of non-inferiority, then it's good enough. We can basically call these things the same because a lot of the comparative studies to date are relatively small. And so there might be real biological or health-related differences there, but the sample sizes just aren't large enough to be able to detect that. And so certainly in my own work, you know, as I progress into what's probably the final phase of my career is, I think we've asked a lot of interesting questions in our work. We've mainly done relatively small-scale proof-of-concept studies, but in our own work,

we're thinking a lot more about rigorous research design. And I think the field of exercise science generally is wrestling with this issue of moving towards proper sample size estimates, proper power calculations, registering trials. So we don't have systemic bias creeping into results, P hacking, things like that. So I think that's a very big area of maybe we need fewer smaller studies that generally look the same and a lot more groups collaborating larger multi-center trials. You know, being engaged in some of this work right now, easier said than done. But I think that's where we need to go to to get to the level of evidence that the people that

write the physical activity guidelines might say, okay. now this issue is more informed, right, to make some decisions there. You know, probably less important for the general public, but the whole area of elite training for athletes, right, which is, you know, invariably almost all of these athletes are experiments of one. So, you know, if Kipchogi trained slightly differently, would the marathon record be slightly lower, you know, probably not. you know, who am I to question Kipchogi's training, but I think we continue to wrestle with this.

Like, we don't really know all these experiments of N of 1 and elite coaching is that blend of art and science, but we don't have these large, you know, interventional studies and athletes saying exactly what's the best way to train. We have some of them we touched on them, but they're really, really hard to do. But if you're interested in elite performance. And then maybe the, I'm sure I'm missing lots, but probably the final. one would be technological advancements, right? There's just been huge advancements, obviously, around sleep research, activity tracking, things like that, you know, continuous lactate monitoring and athletes. Will that really move the needle or, you know, revolutionize training using some of

these markers? Maybe, you know, and also data and activity tracking for everyday people as well. You know, the ubiquity of smartphones and watches and things like that, getting back to the behavior, you know, can we encourage people with activity prompts and things like that? Like, is that a viable strategy or is that it's never really going to work in the real world? So these sort of translational studies that continue to move research out of the laboratory into real world settings so that we can truly move towards effectiveness studies as opposed to efficacy studies, I think is where the field needs to go. Awesome. Well, Marty, thank you so much for taking quite a bit of time to have this discussion with me today. I mean, I learned quite a bit. And I know people are going to really enjoy learning this, you know, everything that we talked about today. I know, so we talked about your book, the one minute workout. People can find that. Amazon. I mean, anywhere, right? So you ebook form, hard copy. Yeah, it's available everywhere, as they say. And then you also have a website. Mart. Is it Mart? Martin Gabbala.com. Martincabala.com. And then a Twitter.

Twitter handle is at Giblom. Gabala M. So G-I-B-A-L-M. So my surname first in the nation. Okay. Awesome. So people can go to those places to learn more about

high-intensity interval training, your website, your book, and also following them on Twitter if they want to get your tools. Absolutely. You know, really, I started the website just so is a one-stop shop

in terms of you can learn about our research. You can learn. I put up podcast interviews like this, links to the book, links to Dr. Phillips and I have a free online course that people can take called Hacking Exercise for Health. Let me just add one last thing is opportunities like this to engage in knowledge, translation, science communication, it's huge, right?

And in writing the book, one of the things I had to get comfortable with, you know, in science, we want to control everything. And if you move, you know, when you're writing research papers, you get a little controversial or you move outside a little bit and you just get whacked, right? Whereas I think when you're boiling down or trying to boil down information for the general public or other knowledge users, and we don't have all the answers, we just have to sort of give our best guesses, not move outside the lanes too much, but say, this is the best evidence right now. It's not perfect. And so the way you do a podcast interview or write a book for the general public, it's very different from your. write how you write a scientific article. And that's okay, right? There's some people who will only write scientific articles, never move outside their area. That's fine. We all do what you're

comfortable with. But, you know, that also has limitations, right? Because that, many of these things are still behind paywalls. People can't get to them. And so science, communication, knowledge translation is, is really, really important. And so thanks for this opportunity and the work that you do on, on this podcast. I think it's tremendously important. Thank you so much. And it's nice to know that other scientists will be listening. And there are collaborations that can also happen out of podcasts as well. So it's been a pleasure, Marty.

And thank you for everything you do and for coming on the podcast today. Thank you very much. As we wrap up this deep dive into the world of interval training, I'd like to offer you an opportunity to continue your journey of understanding and insight on human health and living better through scientific understandings. Consider joining my email newsletter. It's not just about updates. It's a commitment to deeper knowledge.

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