HIIT vs. Moderate Intensity Exercise - Which Is Better for Your Health? | Dr. Martin Gibala

So many people are struggling to meet the physical activity guidelines. We should all be doing about 150 minutes a week of moderate to vigorous physical and activity intensity.

People struggle with time. So where would that be acceptable?

There's a number of people. For you given the option, an hour of traditional continuous, or you can do 10 minutes. Of really vigorous, which do you like? I really don't like that sprint training in the moment, but I certainly like it when I'm done in 10 or 15 minutes, and I would much prefer that to doing an hour or 90 minutes of the traditional approach. The studies also show that

Talk to me about where high intensity interval training could be applied to the regular person.

It all comes back down to do you have metabolic flexibility or not? One of the best ways to improve that is to boost your mitochondrial capacity, right? Boost your health.

We're entering a new era where people are very interested in female specific exercise. Are there some differences?

There might be some subtle differences there, but overwhelmingly it's not a little bit.

Dr. Martin Gabala, welcome to the show.

Nice to see you again.

Now, uh one reason out of many I wanted to have you on the show is that high intensity interval training, sprint interval training, all of these modalities. What we're really after are outcomes. And you are arguably one of the world leading experts in these various types of exercises.

It's great to be back. You're too kind with your uh opening remarks there, but uh happy to happy to get into it and I really appreciate the opportunity.

So we're gonna talk uh really basics, and then we can get into some of the more controversial aspects because you know, as we think about evolving science. Um, one of the criticisms that we've heard over and over again is that there just, it's just not a lot of large data sets, highly powered uh studies. But before we get into that, let's just talk about what it is. High intensity.

Yeah. So to me, you know, interval training is just alternating periods of uh higher intensity activity with recovery. So that can be all out rest or lower intensity exercise. Uh high intensity, it It really depends, are you talking in a performance context or in a health context? And so, you know, in a health context, exercise prescription, we talk about light, moderate, vigorous intensity exercise. And so vigorous intensity exercise is that high intensity range.

But that's defined differently for everyone.

Correct. Moderate is a five. Right. We also have other RPE scales, classic six to twenty scale. Their vigorous is a 14, 14 to 17. If we're talking heart rate ranges, you know, in the American College of Sports Medicine would have authoritative guidelines. We're talking a heart rate of about 77% of your maximum or uh or above. Uh, and there's uh also percentages of VO2 max as well. The point being there's no single best indicator of what counts as hit.

And do we care about so from a, you know, I'm a practicing physician. Yeah. I care about health outcomes. I want to know how much high-intensity interval training that I need to do to improve insulin sensitivity for outcomes like better glucose control. Well you're spot on. Fat max, which I wanna talk about, and then a lactate threshold. Do these relate to any kind of health outcome or is it only performance?

There, you know, uh obviously zone two is very popular right now. I'm sure we're gonna talk about that. There's virtually no studies on zone two per se and health outcomes. Now, depending how you contextualize uh zone two. Uh there could be some evidence to support claims about its um, you know, effectiveness to boost your your mitochondria. But back to your point, you you're right. If we look at the WHO guidelines, we have physical activity guidelines.

That's exactly what I said.

Improving things like your insulin sensitivity, uh your glucose control, your blood pressure, uh your brain health.

Metabolic function. Correct. Mitochondrial function.

All of them because they're all related to fundamentally to to health. And so the general guideline is we should all be doing about 150 minutes a week. That's two and a half hours of moderate to vigorous. physical and activity intensity.

Thirty minutes a day. Do you agree with this recommendation?

Well, absolutely. In in the sense that it's there's very good evidence to support that if people do this. volume of of of exercise, uh, like I say, it's associated with many, many, many health outcomes. I think where we start to quibble or you start to see debates happening is around, well, Vigorous versus moderate, high intensity versus trinit traditional and moderate and ten ye intensity continuous. Which is better? Uh and though those studies are hard to do, but my contention is that

So what I'm hearing you say is that a hundred and fifty minutes. of moderate to vigorous activity, it which is defined differently by different populations. That the athletic population is really looking for very specific data points. Is that true? Like a a lactee threshold.

Yeah. Athletic coaches and athletes are worried about performance. They're not worried about, you know, they they can do many athletes can be quite healthy, many athletes can be unhealthy if they do too much. But, you know, fundamentally, athletes are interested in performance. Um and they use those metrics.

I see.

Or if you're just meeting the guidelines, I don't think there's any evidence to suggest that an 80-20 split is optimal there for you. And again, 80% of what? These notions of your lactate threshold or your or your fat max intensity, which is really hard, I think, for people to to to grasp. And then when we start giving these approximations of it, it just doesn't It doesn't apply well.

Um, I don't think that people have thought about it in that way. And what I mean by that is that online there's a ton of information and it really there is a line that people are always talking about optimization.

House band.

Health ban, mussel span, sex span, optimization. But the information is largely informed not from, I would say arguably the general population.

Yeah, no bingo, right? And and so I think depending on the person and depending on the metric. You know, 80% of that 150 minutes a week telling people that they should be doing low intensity training for that. Um, I I don't think is the best prescription uh for them. But I I would just say, show me the evidence that it is, right? So where is the evidence that? Three hours, four hours a week of zone two is optimal for your mitochondrial health. And there isn't any.

Let's talk about it. I've got um a few great papers here. Talk to me about, I suppose clarify as to where high-intensity interval training could be applied. to the regular person who is listening or watching this podcast.

Yeah, so so first of all, if we accept and I think there's good reason to accept that high intensity exercise, when we hear that term, hit high intensity intermittent training. That just means vigorous, intermittent exercise, right?

It's just so nonspecific though.

But but why I say that is because vigorous is well established in the public health guidelines, in ACSM guidelines. So let's accept that it's vigorous and then we know the thresholds, right? If you're above this threshold,

That'd be, for example, 85% of your VOT max. How would we define vigorous?

Yeah, it's it's 77% of your maximum heart rate or above. And it's even less of that for VO2 Max. It's that fourteen out of twenty. It's that seven out of ten. So if you're doing that, you know, going back to the talk test, the talk test is, you know, if if

Like don't and they usually swear words, yeah. Don't talk.

Exactly. Right. So, you know, so so that let let's just say hit is vigorous intermittent exercise. Then we know here's all the metrics that you can use to determine if you're doing HIT or or not. Right. And so I I think hit is a very effective way for people to integrate vigorous physical activity uh into uh into their day. And and we know there's just robust evidence that HIPAA protocols of varying durations, intensities, uh can certainly improve your VO2 max.

If you were to say, uh, so for example, I don't do any zonch training. I only do high intensity interval training and I lump that in with my I I do it one of two. I have a strength training workout and then I will put a high intensity burner at the end. And I would argue it's probably closer to a sprint interval training. I mean, I'm I'm pretty maxed out, it might be.

Yeah, I I don't I don't think you're missing out on on anything. In this given the time that you want to put into it, right? And so I think you can be completely healthy. You can improve your health. By a largely interval based uh approach. Uh I think that's uh you know uh again, what

Two and a half hours a week of moderate to vigorous You know, le pr depending on the survey, less than half. Right. And so then suggesting that, well, you have to do actually three to four hours a week of zone two, it's just raising the bar. It's such a high barrier to entry that I I I think, you know, it it Yeah, you're you're losing people there.

Talk to me about some of the the new research on sprint interval training. And um before I before we jump into sprint interval training, is it important to differentiate between high intensity and sprint interval training?

It it is. And so um to me and I think many others, um Sprint interval training is an intense variant of hit. So basically, once you get above those thresholds that we talked about there, uh seven out of 10, you know, 77% of your maximum heart rate, anything up to an all-out sprint from danger pace. counts as hit, sprint sprint interval training is that uh that that that real top range.

It sounds a long time.

It does. You know, you're you're you're pushing at the end, but uh, you know, ten, twenty, thirty second sprint intervals are sort of the classic, you know, tabatas are twenty seconds, right? And so uh that's where so those are those Um intensity ranges. Uh, you know, you're if if you do repeated sprints, you're getting up above 95% of your maximal heart rate when you're doing repeated ones. So it's uh it's pretty intense. But to be clear, it's a variant.

Of hit. It's a variant of hit. And how important is it to progress into some of these other definitions? Because what I want, my goal for people when they are finished with this podcast is. uh a few things. Number one, to actually have a clear understanding as to what high intensity interval training is and what it's not. what it's used for, where its actual benefit is for performance, and where its benefit lies for health.

So um at the end of the day, there's no free lunch, right? And so if if you want the benefits of brief, very vigorous intermittent exercise. You have to go very hard. It's an extremely uncomfortable way to exercise and train. We're not suggesting that it is for everyone. We're not suggesting that everyone likes that type of training.

Uh, to be clear, nobody likes that type of training. And I would argue everybody should experience it because how uh the only way we grow is is uh resistance and

But I would say too, you know, the the the general contention is, well, if exercise is vigorous or intense, if it's above your lactate threshold, if it's uncomfortable, it's aversive, you don't like it, you're not gonna stick with it. Now there's there's really good evidence. To show that it's well, well, wait a minute. We need to think about total dose here or total volume. And certainly there's a number of people.

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Yeah, and and so I a a a a valid criticism of uh Hit in general, and especially the sprint training literature, is like a lot of areas of exercise science. Many of the studies, they're relatively small, they're relatively short term. Uh, and so, you know, we don't want to have your Listeners and viewers' eyes glaze over and talk about statistics, but you know, there are rigorous ways to design experimental stuff.

So it's should someone be?

Well, I I think absolutely your your studies should at least be informed by, you know, what what's an appropriate sample size? What is an effect size? And that just means is this. biologically meaningful. You know, uh again, in in medicine we see w examples where, you know, a hundred thousand people take this pill. and there's a statistically significant finding, but the effect was a zero point one change in blood pressure. That's at the other end of the spectrum. You know, often in

Talk to me about time frame and give me an example of

Yeah.

A sprint interval training. plan.

So we've used a protocol, and where the name of the book, my book, The One Minute Workout Came From, was our protocol was three 20 second sprints. within a total time commitment of 10 minutes. So start to finish, you come in, you do about a three minute warm-up, you do your first 20 second sprint.

And how does someone who's listening to this are like, all right, well, I'm pumped up. Martin's awesome. And I'm gonna go do Three 20-second sprints. Are they running? Are they on a bike? Are they on a rower?

Yeah. It as long as there's no underlying joint issues, all of that, you know, those cautions. Um, hill running would be a classic way to do it, right? So you you can you can really go all out, but you can imagine as you're running up a hill, what happens? If you're truly sprinting uphill, you slow down about halfway up the hill. Even after a few seconds, you start to slow down because the load of the hill is is so challenging. And so

Without losing the RPMs. I mean is that important? So for example, as I think on Saturday, I'm sure I'll be doing ten calculations. Which I I swear, I think the bike is broken. Cause I'm like these these cows aren't increasing. I cannot hold that um the RPM. Once, you know, I might be 7580. But I can't hold that. And then mentally I'm gassed. If I can't hold it for the next set and say I'm on just set number two, is that considered high intensity interval training? Do I need to

So, you know, just about the the bikes themselves, traditional bikes. It's you can still do sprint training on it, but you know, in laboratory studies, the classic bike or the classic test has always been a wing gate test, right? 30 seconds, all out, as hard as you can go.

So um we are we just recently partnered with Carol Bike and one of the reasons I love the Carol Bike is its ability to in real time adjust for a specific outcome. Uh so I wanna just make a note of that. And now I would love to chat specifically about what the Carol Bike does and how it can be

Yeah. No f and you know, disclaimer from the outset, I I've uh engaged with Carol in terms of providing some scientific advice to them. I've never been paid. Uh we have some of their bikes in our lab because um we've seen the research studies. They work. We've tried them in some of our recent s uh studies and and applied them successfully in our sprint interval training um studies. But yeah, what the bike does is it adjusts workload. And so the the

Right.

So oh that's seven and a half kilogram load on the bike was sort of that optimum. Now, if you're a high-level athlete, it might be nine percent of body weight, less trained people, five percent. And so my understanding then is the Carol bikes have sort of used that initial um setting, but then what the self-learning algorithm allows you to do is

He could be before then.

I we've seen changes as early as two weeks. So it it you know depends on lots of things, but

And this is any, and I'm talking about now any sprint interval training, right? Yes.

Exactly. Yes, yes, yes.

Yes. Yes. There is this almost novice. What do they call it? The newbie training phenomenon when all of a sudden they gain more muscle than say someone who's been training for years. In sprint interval training, is that the same effect? Is it kind of the same architecture?

Yeah, this idea, I don't know, of shocking the system or that. I you know, I like to think that the you know the physiology is the same. It's just the input Can be different, right? And so you can improve your VO2 max with a lot of traditional moderate intensity cardio.

Meaning like three hours of zone two. Because I don't know, I mean, is that, would that tell me?

With many, yeah, yes. And and again, depending how we define zone two. But yes, bottom line is, you know, if you do continuous moderate exercise for several hours and you train that way three times a week for six, twelve weeks, you can improve your VO2 max.

Can you though? You can't and the reason I I say can you is because, you know, we all know those people that are going on the treadmill and for the last five years they've done exactly the same kind of training.

You know, I I think you always want to have progression in your training, right? And so to be clear, most of these studies are where people are starting out at some level, you know, they're exposed to this new stress and then their VO2 max goes up. You know, it's not necessary that it's going to continue to increase unless they then adjust.

Dose of high intensity or sprint interval training. And now I'm kind of self-conscious. Are we using them interchangeable? Are we saying that it really should be sprint interval training that is going to be the most effective for the outcomes that we care about? Is it really sprint interval training?

So when you know, this word efficiency again, which gets thrown around a lot, I I think sprint interval training is the most time efficient way to improve your VO2 max. It doesn't mean it's the best. It doesn't mean um really anything more than than that. There's different ways to achieve outcomes.

And I think there's exponential benefit to increasing intensity.

There's exponential benefit to increasing intensity.

Right, which means the the h you know, it it the it goes like this. So the more intense you're able and willing to go, you can have exponentially less total time commitment to get to the point where you want to to be.

What about from a physiology perspective? There is there a difference between uh what we know from uh mitochondria, from you know, various roles of Proteins like

No, it's it it's a great question. And I think, you know, this is something that keeps me excited as as as a scientist, is there's still we have a lot to learn about the mechanisms. So let's even stick, you know, let's start with VO2 mechanism. VO2max, we can see similar improvements in VO2max with 12 weeks of sprint training, where the total amount of exercise is 90% less. Then the traditional modern intention.

Ninety percent.

It's so basic you can imagine.

ninety percent correct.

So that you know that's the idea of the exponential time efficiency. Now, what does VO2 max? It represents the integrated function of a lot of underlying physiological systems. Your heart, your lungs, your blood vessels, your mitochondria in your muscles. So is the reason why VO2 Max is going up to a similar extent with those two types of training the same or not?

Mm.

Yeah, y yes. And so in the same way in that how do we measure mitochondria? We measure the maximal activity of representative enzymes. We, you know, there's different ways that you can measure mitochondrial content, but you can see similar improvements in mitochondrial content, again, with those two very different types. of uh of of training. Um so you know but why do mitochondria go up? Mitochondria gets stimulated by Things that we produce during exercise. So your muscle responds to a stress.

Regardless of the intensity. So regardless if you're if you're thinking about AMPK or PGC one alpha, you Does it matter if it is a slow, steady state input or a high intensity input if you know, um, if the outcome is the same.

I think we know that the We know that the input can vary in terms of sprint training, you have a very sharp, sudden change. And so I think of it as, you know, if if it uh you're dropping the gas pedal really hard, right? And so is it the rate of change or is it getting to some level? And I think we still have to answer that question, but we definitely know that sudden drop in or a sudden activation of many of these pathways

That's fascinating. The fuel utilization, talk to me about that. Talk to me about, you know, is the we know that the new dietary guidelines came out. There has been arguably on the surface potentially a reduction in carbohydrates. What is the difference in fuel utilization of a sprint interval training session versus a slow, steady state? Training sessions.

Yeah, well, sprint interval training you're basically churning only through carbohydrate. Uh and and a lot of that is um uh you know, d what what's known as anaerobic metabolism. But to be clear. You know, when we do repeated sprints, most of the energy is coming from the aerobic system. So will people talk about, oh, it's anaerobic training.

How would you think about dosing? Again, you've done this in in research. Do you think about dosing carbohydrates for the participants in the studies or just in general. I don't know if you work outside of the academic

So well we'll we've we've been in you know we've been interested in nutritional manipulations and it it looks like exercise is the big hammer, right? And so maybe you get some very subtle changes with dietary manipulations, but They've been really subtle in our studies. And you know, if we're just talking about, we're still trying to compare the exercise doses right from a uh, you know.

This is I I can't believe you brought this up. It's one of my favorite I'm really a nerd. This is one of my favorite topics in over the last year, this low glycogen training. Yeah. Um so can you explain?

So that's, you know, especially if you do uh vigorous exercise with reduced glycogen stores, the metabolic stress is higher. And so there is evidence to show that those signaling proteins we talked about. MPK, some of those can be turned on to a greater extent.

Isn't that fascinating? So we have to we have to just talk about this for a second. And this is where the semantics become interesting. In the conversation is should you train fasted or not? I don't know if that's really the question. It's in my mind, should we train in a lower glycogen state or not?

I I again, what's what's your outcome of interest, right? There are some sh again, I'll use the caution, sorry, but we have to call the evidence as it is. relatively small short term studies that show acutely if people train with reduced glycogen, you can have greater activation of some of those signaling.

And also myocine. the proteins released from muscle, they seem to be more robust when uh an individual is training in a lower glycogen state. That doesn't mean they're fasted. It just means low carbohydrate within the the muscle.

Yeah. Um you know, and and there are studies to show that Again, over six, eight weeks or so, you can see some measurable increases in mitochondria to a greater extent with reduced glycogen training than when your carbohydrate replete. Now, if you're an athlete, it didn't appear that that translated to an improvement in performance. Uh and we gotta be careful here when we're talking about low glycogen training. What it is is typically

And the reason I was interested in it is for health outcomes. Yeah. So I'm thinking about, okay, muscle quality is important. We don't know enough from my perspective. How muscle quality relates to long term health outcomes. And when I say muscle quality, I'm not talking about

Yeah, well you know, the athlete's paradox of course is just that it's sort of that U shaped curve where people who are very unfit uh will have high muscle triglycerides. Um, and and athletes have very high muscle triglycerides as well and sort of Active recreationally active people are are have have lower amounts. Obviously, the big difference there is that.

And what about the location of the mitochondria where the fat are the triglycerides? From what I understand, the triglycerides are not within um a good location. to the mitochondria. So the fuel utilization is

Yeah. You know, this is w you know, and again, these hard studies to do, right? You need to take biopsies, you use electron microscopy to try and look at spatial orientations of of things, but Um, you know, you you can see, and there's some suggestions of where the lipid droplets are located, uh, especially if they're near the mitochondria, that may be better better able to utilize them. So Um so again, I I I I think there's evidence to support some of these um

Do you think that it would be fair to compare steady state zone two. So we just talk about metabolic flexibility and we can define, I'll give you my definition of metabolic flexibility and then you can tell me where I'm wrong, please. I love it. Um In my mind, at rest, a healthy muscle is burning primarily fatty acid. As exercise intensity increases, it then switches to being able to use carbohydrates as opposed to overfeeding carbohydrates and muscle at rest would be forced to utilize.

Uh, so I would consider metabolic flexibility to be, you know, um, it's the ability to have a high rate of oxidation of either fuel. So whatever you feed the muscle, whether it's carbohydrate or fat. it's able to utilize that to produce uh energy. Arguably one of the best measures of metabolic metabolic flexibility is maximal, is fat max, the maximal

Let's talk about that. I know very little. I'm starting to hear more and more for health outcomes about FatMax. Talk to me about FatMax.

So fat max is basically what it sounds like. W what is the maximal rate? of fat oxidation by the body. So we're talking grams per minute. Right. And so that's going to be a combination of two things. What's your overall metabolic rate? So as we're sitting here, rest right now, our metabolic rate is low. If we go and do a vigorous boat of exercise, our metabolic rate is going to go up. So fat max is a combination of what's the overall metabolic rate, and then of that um value. What percent?

What would we want to be using? So what would be considered normal?

Yeah. Well and so for most people their fat max occurs around 45 or 50% of their VO2 max or around 60% or so of their maximal heart rate. But such, again, coming back to zone two, such huge variability. So mat. Fat max can range from forty percent of your Maximum to ninety percent of your maximum, but for most people it's gonna be around sixty uh per percent or so. So what you're doing is ideally to to measure that, you're imposing an exercise stress.

I'm thrilled to announce one of the new sponsors of the show, and that is the Carol Bike. Now, if you've listened to the show, you know that I believe muscle is the organ of longevity, and of course, you need resistance training. But you also need high intensity interval training. And I would say nothing improves cardiovascular fitness like a targeted program and tool.

So from a health perspective, fat max matters, but It's very challenging to measure. And so, unless you go into an exercise laboratory and have this test done. You don't know. And so it's difficult to estimate it. And this is where I think. Again, that the issues with zone two, I think there's they're they're multiple, but one of the ones is. There's not a good way for people to estimate their fat max. And so, you know, let's even go back to what is zone two? The the

That's a hard pill to swallow.

Yeah.

You know what I mean? It's a hard pill to swallow because we have these Large I don't know, large information highways saying this is we need to be doing zone two because of this. And this is what it looks like. And here is your formula to be able to show you if you are in zone two. Are those accurate?

Not for an individual. No, right? So I uh again, zone two, it comes

I think you just broke in or not. Zone two training, what he's saying, so I'm talking to my producer over here. What he's saying is that all this discussion around zone two is arguably I don't want to say irrelevant because I have a scientist here, but it's We're not defining zone two appropriately. And even if we were, even if we were, so we are saying zone two is what? What is the traditional definition?

Yeah.

But that is totally different. for I suppose an athlete, any athlete at any, right? So a zone two. So for Matt, for me, for you, our zone twos are totally different, even if it comes out as Um, you know, on the heart rate monitor that I'm in zone two. Is that

Exactly. No, that that that's correct. Right. And then so, you know, let let let's you know let me try and clarify a couple of things or or explain myself, if you will. You know, zone two. Really well established in the athletic training area. Right. And so that's where I talked about those moderate, heavy. Uh, severe three domains. And then very commonly those are split into two subdomains each. And so you that's where we get these.

You know, it it presents a a whole new level of challenge. And I from my perspective, why it's so important is One of the challenges I think as the world grows and as we are exposed to more and more information is the there's a level of critical thinking that we're starting to see that's a bit reduced. For I'll give you an example. Saturated fat was set at the guidelines ten percent early. There is no reason where or why it's 10%.

I just think precision in terminology is is critical, right? And so if we're talking lactate threshold one, fat max. Most people have no idea what that is for themselves. And there's no good way for them to estimate it. If then we're going to use a surrogate marker like the talk test, so you could carry out a conversation, it would be strained, but you could still do it.

For the general population or for athletes?

No, for the general population, right? So that's just if if that, you know if Zone two is fat max or lactate threshold. Okay. But then as athletes well know, because athletes know exactly what that is for them, because they get that testing done. If the average person wants to get that testing done, then they know exactly what their fat max or lactate threshold is. Then they could start to utilize these training regimes of athletes. But if we're just using a surrogate marker to guess what it is,

What are we doing?

Doing, right? And and it's if we're gonna use surrogate markers that are already well established within guidelines, then just call it. It's moderate intensity training, right? And so I think my point is. If zone two is classically defined, if we're suggesting that this is optimal for mitochondria. There is no evidence for that. There's no there's virtually no scientific studies on zone two training. If we're saying

Big deal.

If we're saying it's modern intensity exercise, well then there's robust evidence that it's good for your mitochondria and good for your overall health. So I you know, I I think we have people have to decide is zone two this euphemism for moderate intensity physical activity in most people.

To be strong.

But to suggest that eighty percent of time should be spent in this zone two range, which is a nebulous concept for most people. There's no evidence for that, certainly no evidence to say that this is optimal for your mitochondrial health.

If you were to design and think about the health of the nation. Uh no uh no pressure. How would you inform them if you could write exactly what should be done?

Yeah. I mean I mean, you know Who am I to counter that so how's this? Physical activity guidelines. based on on robust evidence. Clearly I'm a proponent of vigorous intensity physical activity. And so I would suggest to people that the more vigorous, high intensity you can do. probably the better for you in terms of boosting these physiological markers that then are associated with health outcomes. also, we know that So many people cite time as a barrier.

Does your heart rate have to g could it also be um Do we need to define how that's done? For example, could it be push-up?

Yeah, it could be, right? And and so I think this is where bodyweight style interval training comes into that, right? So, you know, right now we could do an exercise snack by by getting up from here and do a series of air squats or burpees, right? Starting to do that. And so, um

Does our heart rate need to get up to a certain

I I I the the No, I I I think what we should do is then use that use these subjective markers like RPE, right? Get into that um push yourself. Right. And and these are I know these are sounding like wishy washy a little bit, but When these bouts of effort are so short, it's also hard to use some of the traditional metrics. Right.

It's nearly impossi it's it's nearly impossible to to prove or to program with a specific outcome.

Exactly. And so you know, we we do know that if you're gonna do something for a minute. You're going to get into those traditional metrics of what vigorous is that we started talking about in this, in this interview. Right. And so that's why our, when we talk about an exercise snack, we've suggested that it's a minute.

And I also believe that we have to hold ourselves accountable in a way that if we don't, there is this aging trajectory. And the more clear that we can become and the more unified, I I think, with the expectation of Yeah, if we're talking about zone two, then we're talking about zone two. If we're talking about athletes, then then we need to put this over here. But if we're saying you need to do moderate to vigorous intensity training and you have to have these snacks.

Yeah. Bingo and you know, so going back to the the guidelines are based on really good science. We know a lot of people aren't listening. And so for some people it's so daunting the guidelines. Or Boy, I I can't do 30 minutes of continuous exercise. They feel like a failure. The the idea with intervals is that's okay, right? Go hard as

Do we know what that is for this type of training?

I I think the best so two ways to answer that. Epidemiologically, we're starting to get the answer there. And again, clearly around four minutes a day of intermittent, vigorous lifestyle physical activity is

Everybody can.

Very beneficial. Exactly. Right.

challenge everybody to do that and we should be doing that too.

And The other studies, you know, what we were talking about, the sprint training studies, those also give us some clues around what's the minimum dose. Now that's Extreme intensity effort, but it's a surprisingly small amount. And so for me, I think the sweet spot is this. Vigorous exercise, um, but you don't have to do very much of it. And I think that might be an achievable goal for for many individuals, or at least if they hear, they're like,

And once someone has gotten to that point. So now we've moved into someone like myself, who might is an is averagely athletic. I'm I'm not, you know, I'm not a great athlete and I've been training for a long time. For someone who's listening to this podcast, who let's say they're really into fitness and interested in it, if they wanted to change their body composition.

Not to hedge, but it would be how much time are you gonna put in, right? And so I I I I think Exercise is exercise plays the role in terms of supporting weight management. You're not gonna see mass, to my mind, massive changes in body composition with aerobic style training, whether it's hit.

Well it's complicated. It is. I think what we're getting to is um, you know, we're able to I think that exercise and is so much more difficult to study than you know, in in nutrition, I could say, Martin, you know, we're gonna have fifty grams of carbs and fifty grams of protein. And uh let's see what your oral glucose tolerance test does. Or let's give you 90 minutes and let's study. So we'll fast you the the night before. Uh we have clear outcomes and we have pretty immediate feedback.

Yeah, that's uh, you know, we definitely have evidence around, you know, we're gonna do this exercise dose or this manipulation and then look at your HBA1C or your insulin sensitivity. You know, we we do have evidence around that. that, you know, okay, this this dose is effective uh to do that. But you're right, in terms of muscle quality, you sort of got to look inside the muscle, right? What's the best way to assess that? A little more challenging for sure.

Where do you think um This fat and I I know that I'm like harping on this fat max. I just think it's it's interesting because if we take If we think about athletes as the pinnacle, just you know, my perspective is health. If we think about athletes as a pinnacle and we know what right looks like when I say right, meaning if I'm looking at this definition here, it's

Yeah, and so it it uh the the problem with mitochondrial health is it's so it We don't have clear Again, let's come back to that. It's relatively easy to measure in that it's non-invasive. You know, you can do it with really direct measure in a lab. We have some pretty good ways to estimate it, you know, based on sub-maximal heart rate responses.

Get going, get going, get working.

Chondro health. But this is where, you know, if if the zone two discussion have done anything, it's it's at least really put these concepts out there of advancing this idea of What the hell is Fat Max actually? Right. And so people are thinking about it. People are are are, you know, and so You could definitely see fat max being added as a marker, a measure that again, you need to do an exercise test in a laboratory. It'd be like getting a view.

I I think that eventually

Measured, have it measured and then start to say, this is what a good fat max looks like, or this is, you know, fat max in a very high performance athlete or in a very deconditioned individual, you know, who's uh has type two diabetes or or pre-diabetes and and maybe start to get those and it's not gonna take a muscle biopsy to look at your mitochondria. We can use FatMax as the marker.

As a proxy marker.

Absolutely, right? And that's where, again, if you're measuring fat max, I do think it is highly beneficial.

It's pretty cool.

Right. But just estimating it on your own, you're you're you're just guessing.

I think as there's advancements in this focal point of skeletal muscle just as this organ of longevity. This is the future of where we're going from an architecture of healthcare. Um Talk to you about this idea of rehit and conditions like diabetes and other health conditions.

Yeah, so rehit is it really it's a the so re hit stands for reduced exertion, high intensity training, a bit of a misnomer in that it's really a version, it's a variation of sprint interval training, because rehit is pretty high intensity. But you know class.

I mean we can define that.

Yeah. Yeah. Um, but you know, re rehit protocols would sort of be 10 to 20 seconds of all out effort, uh, usually on a bike, these these studies have been uh done.

Is that because it's easier to control?

Yeah, pretty much it is. Um, and so you know, though those uh are often um sometimes as little as two, but typically three times a week. So you're talking there, you know. Twenty to forty seconds. of all out exercise. Uh Typically within a 10-minute time frame, a few times a week. But again, there, you know, there's there's some small randomized controlled trials of rehit. There's definitely studies on rehit showing that it's

And it's more tolerable because

Shorter.

shorter. So the two and there's and we can link two of these studies This is two to three twenty-second sprints. And that is able to again so I'm I'm thinking about these statements. to have health and fitness benefits comparable to quote normal exercise in a fraction of the time, ten percent of the time, how do we Um, is that would you feel comfortable with me saying it?

So what I can definitely say with confidence is rehit style training, which again is 10 to 20 second bursts. Um two or three of those. Our studies, which are classically three 20-second bursts. So there we're talking two or three, 10 to 20 second births. If if people do that. Three times a week for six, eight, ten, twelve weeks. Most people will see an improvement in their VO2 max. There's definitely studies to show

See an improvement.

Yes, yes. And you know, we normally power our studies on a one-met change. So frequently you will see a one met change in your VO2 max with. six to twelve weeks of training. One met. What is that? It's about ten percent for the average person. Okay, so Met is a very specific term. So there's there's solid evidence to demonstrate that. When we start to talk about how does it compare to the traditional approach.

Very exciting.

It is. So we we we you you you you do these trials called non inferiority, which means I have Different, right? And so oftentimes a j so let's let's say Here's the well established drug on the market for this condition, right?

We want foreman.

We wanna test this new drug against it. We wanna say it's not worse. Right. So the benefit you might see is not worse than the standard. Well yet what does not worse mean? You try to identify a margin. doesn't matter, non-inferior, right? And so we it's basically saying If we see a change, but it's within this difference of the gold standard, it doesn't matter, right? Because this margin of non-inferiority is is sort of meaningless in a physiological context.

Max.

And the margin is within this compared to the traditional approach, then they're the same. They're they're not inferior. The new method is not inferior to the old one. And again, those are that's a very specific way of designing experimental study.

Well these two.

We're literally running it in our lab right now. So yeah, can't wait.

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Yeah, let's let's so again, I I I I think the general catch all term is high intensity interval training and sprint is that very intense variant of it.

Does high intensity interval training prevent sarcopenia?

as classically practiced on a bike running No. Um, I think though these bodyweight style approaches, so we're talking now high-intensity functional training.

Now you have to define it and give me an example.

So high intensity functional training is really just uh the classic example would be body weight style training, would be simple equipment style training, kettlebells, uh, you know, uh, um Air squats with dumbbells, uh, you know, classic functional movements, almost calisthenics in in a way, push ups, pull ups. Type of training. So that is basically resistance-based high-intensity interval training, right? And so this is where, again,

Resistance style hit is bodyweight style training, calisthenics, high-intensity functional training. But the key difference there is the resistance is higher than with the traditional approach, right? And so that type of training, I think. Can be beneficial.

Even if it's body weight. So for

Yeah.

When I think about running, you're still moving your right, you know, single leg body weight. And that's different than

Okay. The the load on the muscles has to be sufficient enough. to stimulate muscle protein synthesis or at least to prevent declines in in in muscle protein. And there I think you need a more resistance like stimulus, as classically, you know, done. than an aerobic style stimulus. So tradit when if I when I say traditional hit, what I mean by that is traditional aerobic style hit, cycling, running, swimming, rowing, cardio style hit.

And bodyweight style exercises, even for a person who's active, would you think would be enough? Or is

No, no, but uh no, it's it's it's a fair point, right? And I think what we're not dancing around or what we're talking about is those two situations are different, right? And so I think generally speaking, you know, to to promote our health span, we want

Strength slash muscle quality to be high as possible. We want aerobic capacity to be as high as possible. And it's like insurance, right? And then over time, as we decline. You want to start higher off, right? Now we can still intervene here after you've started to decline. It's still going to be beneficial. Um, so.

We'll say high intensity interval training does not help prevent sarcopenia, but high intensity interval training with resistance training. Could and potentially resistance training. I don't know if we can ever prevent sarcopenia. Yeah. I don't think we know enough about it. Yeah. But

Definitely attenuate.

We can attempt. Absolutely. And you've already answered this question. Older adults are capable of doing sprint interval training safely.

Yes. So the yes to answer the question, we would still advocate, of course, that you know, the older you get, as you start to develop, you know, um some conditions that increasingly important, right? To get medical clearance. But, you know, there's there's studies being done on octagenarians in Sweden with very intense sprint interval type training and group style classes.

What about this is I don't know if you're gonna like this question.

So there's definitely evidence of subtle sex-based differences in certain responses. all the usual caveats around small studies and things like that. My own opinion is I think inter-individual differences are much greater than a biological sex specific difference per se. But you know, if you take groups of uh biological males and females, yeah, you can see a few uh subtle differences. Um, you know, coming back to fat mass.

Meaning they will burn more fat during um Do we say it's a particular

Yeah.

Type of training.

Well gen so generally during exercise you can imagine if you know if if if this is So over you know, over the course of exercise intensity, you're gonna look like this, right? And you this is that point of fat max. Women, it it happens at a higher percentage of their maximum. It again. I'm generally speaking, and there I'm I'm mixing up sex and gender, but biological females, some of the studies have compared men and and women. ten on average have a little bit higher fat max than um

So they oxidize that.

Yeah, have a little higher. Yes, exactly.

Um a bit better. Is that clinically significant?

Ah I I think that's where um it it really depends on what Um

what we would define as clinically The reason I ask these questions again, this is I think we're entering a new era where people are very interested in female-specific answers. Yeah. Uh, I'm with you. I think it's From the evidence that I've seen, it's really interpersonal variability. Yeah. But potentially are there some differences.

You're you you're right. And I I think there, you know, and again we're talking these we can talk about percentages of where your fat max is. Again, it comes back to I think what's the actual fat max value. And again, we're just not there in terms of here's the numbers. You know, this is a clinically healthy fat max. Right.

We have those numbers.

Well, we we know that, you know, you can look at fat max values in very untrained deconditioned people and it's much lower than in a high level endurance athlete. You know, we can say in this clinical condition it tends to be lower than this. But I don't know, I don't think we have certainly the level of evidence like we do for VO2 max, where this number is.

What other sex differences male, biological male or female?

Yeah. Getting back to the reason why your VO2 max goes up when you do exercise training, the for most people. The limiting factor is the pumping capacity of your heart, so your stroke volume. So if we took a hundred people, measured their VO2 max. The main reason to explain the differences between those individuals would be their stroke volume. And so.

It's not um

It's not a mitochondria thing.

Yeah.

Okay, so it's not a mitochondrial thing. Um I did my mind is blown for the second time today. Is it um a size? So if you have um the same size female and the same size Male, do we anticipate one having a higher VO2 max than the other?

Yeah, generally the male will have a higher, slightly higher uh VO2 max. Part of that is you know, uh females tend to have higher obligatory body fat, right? So the, you know, the leanest male will be about five percent body fat, you know, four or five percent. The leanest female will be about nine pen, ten percent, right? Because uh Reproductive reasons, fat is a less metabolically active tissue than muscle, as you well know. And so that explains in part the differences in BO two max.

What do you think? You've been doing this uh uh quite some time.

Again, I come back to you. I there's some of there might be some subtle differences there, but overwhelmingly it's innate biological differences between humans and not a specific. Sex based difference per se, writ large. Now, the last point I'd like to make there is. Our current randomized controlled trial that's looking at sprint versus modern tense training, it's an entirely female cohort that we're studying. Well done. And and that's for two reasons.

And do you think that you will find meaningful differences.

So our hypothesis is no that there won't be that that sprint so um twelve weeks of sprint interval training in a true randomized design. Will yield the same improvement in VO2 max as traditional modern intensity continuous training. Like that difference will be non-inferior. It won't, it won't matter. So that's our hypothesis. Um

If you were going to design a week of training for someone who is moderately active, or how about yourself? You I mean, if you tell me you don't do any high intensity and training, this interview is totally over. But um Just from a practical standpoint, when we think about designing the ideal week for a busy forty-five year old person.

You know, if you can even give a half hour

Let's assume maybe.

Yeah, what are they willing to give me? Because that was gonna be the first question, right? Yeah. Yeah.

Let's say they're gonna meet the 150 minutes. So you have they they wanna exercise, give them 150 minutes. That's the baseline recommendation. Yeah, they're willing to do that.

Yeah. And so I I I think in an hour.

They'll give you more.

Yeah. And so I I think in an ideal world, you'd like to do something continuously for an hour at the highest possible pace. Right. So do that continuously. uh exercise and then two session so you know a one hour ride at the highest possible intensity.

I need to reevaluate my training.

But how's this? I don't train that way, right? So, you know, I I like high intensity intervals. Um, and so all of my cardio is interval based, right? Now It in in the winter when I have to ride inside, I rarely ride on the bike for more than half an hour and it's entirely interval based. And I typically do that three times a week. And then on the days in between, three other days, I'm doing

Matt over here.

I like interval training, right? But not everyone does. And so I I think doing that continuous, but importantly, not zone two. Go at the highest intensity you could sustain for that hour. I think that's going to give you more benefit.

That that that's tough for people to yeah, you know, as I think about'cause I do the well, I mean, I don't I haven't lately, but I love to do a Peloton, listen to country music. Don't tell me about it, it's kinda embarrassing. But it's so fun. I like to push myself, but I'm not sustaining. I'm not jamming out, s you know, sustained at a a certain uh exertion pattern and maybe again.

When I think what you asked me, and I'm again, I'm really not meaning to hedge, but like nuance is so important here was the question, you know, what would be optimal for their health versus what generally should they do, right?

So in my mind, and I am not a training expert, people should be lifting weights three days a week. If I was gonna pick a number and it could be four, I mean listen, I I could wave a magic wand, but I want them to get full body resistance training because it's only downhill from here. Um and from your perspective, for the busy 45 year old, how often should they be training?

Yeah. I mean I you know, uh I I I think at least at least two days a week of whole body functional style training.

We say not by what is that?

Well again, so I I I'm talking their foundational movements, so push ups, pull-ups. cleans, deadlifts, um, you know, uh it could be wall sits, you know, that are engaging large muscle groups. Um and again ideally in a functional style uh way that you know translates to improvements in activities of daily living. It allows you to ascend, you know, it t to climb the stairs better, right? It it's that again, that challenge of You get off the airplane, you've just been on a five hour flight, and the

You run off the hook. How many times a week do they have to do that?

So, you know, as I said to you, I I try to do it at least three, but if I'm gonna give a general guideline, get two in, right? For sure.

What about rest intervals? And I asked you this very early on when I was working on my first book. And I said, um, maybe it was the second. I feel like I call on you for every book. The You know, I said, Well, could I just do a I think so we I remember exactly. I was in Encinitas and there's this hill. There's this hill, um on the beach. So right behind the beach there is this hill. The parking is terrible. And so we decided that we were gonna use this sprint, h this hill for sprint.

So my thinking has changed a little bit. And again, the advice I would give to you, you know, thinking, knowing what you're most interested in from optimizing your health to, you know, the average person who just wants to boost their fitness a little bit. I like I stand by rest interval matters in that, you know, generally the longer the rest interval.

How long have you been studying high intensity nearby training?

Twenty years.

Have you found new evidence that has been just has been very surprising. Like Like sleep, or just something that you hadn't anticipated and you weren't even looking for.

I'm a physiologist and so I'm primarily interested in the basic mechanisms of how the body responds to these challenges and the health-related outcomes. So probably one of the things that's surprised me the most is And I'm most proud to be a part of as a collaborator is

Okay.

These these small Vilpa doses, this figures intermittent lifestyle, physical activity, like four minutes a day. 25 to 30 percent reductions in all-cause mortality. It's that that's probably been most stunning in terms of what could have impact. You know, I we're doing some BDNF stuff now, but I, you know, I'm not

Absolutely. And um we don't even have a pill that does that. Right. The last question, and then you're off the hook, how often should people really be and again, we're talking about people that are really going for something that they don't want to be just not worse than you? But they want to make improvements for that sprint interval training, that that really hard effort that you cringe that you have to do. Is that an every two-week thing? We're talking about four minutes.

Ideally do it once a week.

Yeah.

Um yeah.

And would you would that be the only training that They would do that day, aside from walking around, or would you say, go ahead and do your resistance training, and then we're going to do at least four minutes.

Yeah, no, I would say save those sessions for Ideally, save those sessions that that's the only thing you do that day.

Martin Gabbala, you are one of my favorite scientists as I um I just have so much respect for you and your dedication to this field. You also have a new podcast coming out.

Uh I do. Thanks for the opportunity to give a plug. Uh it's with my friend and colleague, Dr. Stuart Phillips, who I know you know.

He's actually been on the show.

He has.

I've been trying to get him on the show now for the last easily four years to come back.

It's uh it's gonna be called the Exercise Science Podcast.

Uh what is it gonna be about?

So

Just kidding. Totally kidding.

Oh.

Um, hard facts, no hype. That's what it's gonna be about. And it's with our our friends at uh Ghost Bureau, uh Chris Shulgan and Chantal Gurden, who are partners. Uh Chris uh co-authored my book with me. So we have a good working relationship. Uh we're starting to record episodes and we hope that those will drop in the spring. So uh hopefully uh some of your listeners might find the content that we're gonna talk about to be uh informal, informative and useful.

What we'll do is we'll link it. Um and when that comes out, we'll send it out to everybody. Thank you so much for your time and your work. And I'm excited, I'm actually excited to know what's gonna be next for you.

Amazing. It's great to talk to you again and uh thanks for the opportunity to talk about stuff we do.