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

Zone 2 vs. HIIT debate: do you need both, and how to choose?

Martin Gibala discusses whether time-efficient HIIT can replace zone 2 training, and why most non-elite exercisers benefit from higher-intensity.

"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?"

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"And so elite endurance athletes tend to have a much higher preponderance of slow twitch muscle fibers, 70, 80%. 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 so and and so definitely there's evidence to suggest that there's progressive loss of these fast twitch muscle fibers uh maybe mainly or sorry maybe uh 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 twitch muscle fibers, which is probably why, especially as we age, strength training is important in order to maintain the viability of these fast twitch muscle fibers. Does that correlate also with an increased risk in like falls? Yeah. I think all of this aligns or certainly the theories would be that yes, right? And so 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 falls and other risks. 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, metabolic syndrome, 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, if, you know, 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, wring 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 their increase the muscle. Also, you know, is there a role for high-intensity interval training in? So you're right in that, you know, and I tell my students that 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 X. 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 and recovery. We've measured it. You know, you look on the internet and you'll see these massive differences in afterburn, right? Where HIIT 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, you know, brain benefits, lower risk of, you know, age-related diseases, neurodegenerative diseases, 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 level. 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 ways depending on who you're – or 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 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'll learn that lactate was this metabolic waste product, end product, and it's just a metabolite 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 inter-organ 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 who are, 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 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 BDNF 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 studies. For me, I'm very interested in neurodegenerative 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 I'm doing two back--to-back Tabatas, actually. It's two back-to-back Tabatas. 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 Tabatas. 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 is in humans, with lactate after high-intensity exercise. And it doesn't correlate with anything else, you know, glucose, like nothing. It's specific to the lactate. And like you said, it's a growing area of research. I'm 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, um, I do think there's a lot of benefits for the brain. So, um, I'll have to be in touch with some of your, your colleagues at McMaster, um, cause 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 the, you know, the, the scientist in me is innately curious around thingsately curious around things like, maybe now there's really, really good dose response stuff in terms of exercise dose and BDNF increase and some of these other measures. But 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'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. Mechano, you know, these mechanoreceptors 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 is like I've measured my lactate spikes up, you know, I don't get up to the levels that my husband, I'm more like a seven, eight millimolar and he gets up to like 14. But it's after 20 minutes, I mean, I'm back down to one millimolar 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 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, like, 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-mediated 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, know to promote uh 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 twitch 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 at it 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 two 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 and that when we look at something like continuous glucose monitors and the evolution of that, you know, now we have continuous glucose monitors are 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, you know, 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 in among athletes to monitor that and really dial it in to get an idea of their metabolic stress. No, 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 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 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 am I just not producing more of it, like you were saying? Like what, a continuous lactate monitor would give me some sort of peek into 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 venous 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 their 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? Yeah. 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 lactic acid and, you know, how what's actually responsible for, you know, the changes in osmolarity and, you know, 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 osmolarity 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 type events. A major adaptation there is an increase in monarcalboxylate transporters, 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 contractile 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 osmolality or potassium fluxes or calcium uh fluxes you know i think the people that really study muscle fatigue would say it it's not about lactate and ph all the time um 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 two 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 muscle glycogen, like the storage capacity. We're talking about the muscle fatigue. And then we talked about VO2 max, which would be aerobic capacity. There's also the anaerobic. Is it the anaerobic output? Yeah. Anaerobic capacity, correct. And this gets back to this idea of you know if if your event is multiple short sprints so you 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 those, when we talk about anaerobic capacity, the best measure or the most commonly accepted measure of anaerobic capacity is a wingate 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 VO2 max test. At the end of that test, you had 300 watts. So your peak power output on a VO2 max test was 300 watts."

Why longer intervals (4 min) differ metabolically from Tabata-style sprints

Not all interval training is equal. Longer intervals challenge the metabolic system differently, and 5x1-min intervals achieve nearly as much VO2max.

"All interval training is not created equal. Total volume in particular is important. But I think challenging your metabolic system in different ways is a good strategy."

Joint-friendly HIIT: cycling works for people who cannot run

People with osteoarthritis or joint injuries can still do vigorous intervals on a bike. Staying active is key for joint health.

"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 issues. um 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 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 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 exerciser, 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, 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. You know, I think the data around blood flow restricted training is much more interesting and there's some really, really interesting work coming out of, out of that. You know, you can make the case that maybe you're going to see some changes in respiratory or diaphragm, muscular or that, but getting back to the idea of what limits VO2 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, just, you know, like I think definitely, you know, as a therapist, 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 some 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 a true control who's completely blinded to the intervention that can influence some, some things. But you know, the, the, 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 is 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? Yeah. 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 around, 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 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 your metric 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 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 to go, 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 Kipchoge trained slightly differently, would the marathon record be slightly lower? You know, probably not. You know, who am I to question Kipchoge's training? But I think we continue to wrestle with this like we don't really know all these experiments event of one and elite coaching is that blend of art and science uh 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."