A (2:19)

Yeah. So to me, you know, interval training is just alternating periods of higher intensity activity with recovery. So that can be all out rest or lower intensity exercise. High intensity 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. And so we can use different metrics. The WHO, World Health Organization would say on a 0 to 10 scale, vigorous exercise is a 7 or 8 out of 10. Right.

B (3:05)

That's defined differently for everybody.

A (3:07)

Correct. Moderate is a 5. Right. We also have other RPE scales, classic 6 to 20 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 or above. And there's Also percentages of VO2 max as well. The point being, there's no single best indicator of what counts as hiit. People can use rpe, people can use heart rate, people can use measurements of VO2 max. And so all of those are anchored to some maximum physiological threshold. Your VO2 max, your heart rate max. Now if you're an athlete, you don't talk like that or coaches and athletes will talk about three fundamental domains. Moderate, heavy, severe. And so once you get into the severe domain, that is high intensity exercise. And in the severe domain it's generally not exercise, it's sustainable, it's non steady state exercise. And so athletes and coaches talk about this really important, I think metabolic thresholds, so things like your lactate threshold, your ventilatory threshold and so high intensity exercise, if you're an athlete is your second lactate threshold, your maximal lactate steady state, your critical power. And so importantly, those are physiological measures, you know, metabolic characteristics that then they will anchor heart rate, RPE2 for them. And so I think this is the real problem when we start talking about zone training, that it, it's so variable for, for everyone. And so unless you happen to actually know your lactate threshold, your fat max, you're sort of care about that.

B (5:04)

And do we care about. So from a, you know, I'm a practicing physician, 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. Yeah, you have a fat max, which I want to talk about, and then a lactate threshold. Do these relate to any kind of health outcome or is it only performance there?

A (5:30)

You know, obviously Zone two is very popular right now. I'm sure we're going to talk about that. There's virtually no studies on Zone 2 per se and health outcomes. Now, depending how you contextualize Zone two, there could be some evidence to support claims about its, you know, effectiveness to boost your, your mitochondria. But back to your point, you're right. If we look at the WHO guidelines, we have physical activity guidelines that say if you do this amount of physical Activity in this general intensity range that's associated with robust health outcomes.

B (6:06)

That's exactly what it said.

A (6:08)

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

B (6:14)

health and metabolic function.

A (6:16)

Correct.

B (6:17)

Mitochondrial function, all of them, because they're

A (6:19)

all related to, fundamentally 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 activity intensity, 30 minutes a day.

B (6:35)

Do you agree with this recommendation?

A (6:38)

Well, absolutely, in the sense that it's, there's very good evidence to support that if people do this volume of, of, of exercise, 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 trinity, traditional moderate intensity intensity, continuous, which is better. And those studies are hard to do. But my contention is that, and I think there's good evidence for this, you know, for a given amount of physical activity, a given dose, there's good evidence that more vigorous physical activity will promote gains in those markers that we care about, you know, those health related markers. And arguably the most important one is your cardiorespiratory fitness, which we objectively measure with a VO2 max test. But you know, if, if there's one health metric that people should worry about, I think you could make a really good case that it's cardiorespiratory fitness because it's just so clearly related to your risk of dying from all causes, your risk to develop type 2 diabetes, cardiovascular disease, metabolic syndrome, certain types of cancers. You know, it's, it's, it's not a guarantee. But we know that if you boost that number, your risk of all these negative things goes down.

B (8:06)

So what I'm hearing you say is that 150 minutes of moderate to vigorous activity, which is defined differently by different populations, that the athletic population is really looking for very specific data points. Is that true? Like a lactate threshold.

A (8:23)

So athletic coaches and athletes are worried about performance. They're not worried about, you know, 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 and they use those metrics because they provide very good indicators of specific zones where they think they should spend the majority of their training. Right. And so if you're a high level endurance athlete, importantly, not doing 150 minutes a week, not doing two and a half hours, doing 25 hours, a week of training, then there's good evidence that about an 80:20 ratio optimizes performance. So 80% of your time is spent at low to low moderate intensity training and 20% is high intensity training. But again, this is for high level athletes doing 25 hours a week. You know where I would quibble with the recommendation that that's optimal for everyone, you know, so if you're, if you're struggling to meet the guidelines.

B (9:29)

I see.

A (9:30)

Or if you're just meeting the guidelines, I don't think there's any evidence to suggest that an 8020 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.

B (9:56)

Well, I don't think that people have thought about it in that way. And what do 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. Optimization for an athlete, arguably. I don't think that that exists because what I see in my own practice is that the better the athlete, the poorer the health outcomes because the more they're training, the less they're recovering. They're getting ready to quote peak for whatever that is. But the general population we are still talking about, people are looking for longevity buzzwords like longevity health span, health span, muscle span, sex span optimization. But the information is largely informed. Not from, I would say arguably the general population. It, it's informed the evidence, or I would say the majority of the evidence, at least that I see is related to sport and performance. And so the populations are different. And the danger in saying, well, if we're doing 150 minutes and 80% of that time is spent at zone two training, which if people are arguably not quite conditioned, might not be as meaningful as we want it to be, then are they really getting the health outcomes?

A (11:15)

Yeah, no. Bingo. Right. 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 I don't think is the best prescription for them. But, but 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. Now I totally appreciate where it's come from. Athletes have very high metabolic capacities. Right. If you're doing 25 hours a week of training and you're training at that classic 8020 mix, and there's definitely good evidence to show that, yeah, athletes have, you know, elite endurance athletes have very high metabolic capacities, have very high mitochondrial function. But again, I come back to then just saying, well, that's the optimal ratio for, for everyone. I just, I don't see the evidence for it. And that would be the, you know, let's talk about the science. What does the science show?

B (12:29)

Let's talk about it. I've got 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.

A (12:44)

Yeah. 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 hiit, high intensity intermittent training, that just means vigorous intermittent exercise. Right.

B (13:00)

That's just so nonspecific.

A (13:01)

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 threshold. Right. If you're above this threshold, that'd be,

B (13:16)

for example, 85% of your VO2 max. How would we define vigorous?

A (13:21)

Yeah, it's 77% of your maximum heart rate or above. And it's even less of that for VO2 max. It's that 14 out of 20. It's that 7 out of 10. So if you're doing that, you know, going back to the talk test. The talk test is, you know, if, if, you know, certainly if you could carry on a conversation, it might be strained a little bit, but you can have a conversation that's moderate intensity. Right. Once you move into the vigorous range, you can't keep a conversation going, you know, and at the higher ranges, you could spit out a couple of words,

B (13:50)

but, but that's about like, don't usually swear words. Yeah, don't talk to me.

A (13:54)

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

B (14:29)

If you were to say so, for example, I don't do any Zone 2 training. I only do high intensity interval training. And I lump that in with my, I do it one of two ways. 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 sprint interval training. I mean, I'm, I'm pretty maxed out. It might be 8, 6 or 8 calories on an air dying or 6 or 8 calories on a skierg and it might be 4, 4 sets in between something else now and then on a Saturday, it's more high intensity. I say that probably 70%. I'm not swearing on the floor in a puddle of mush, but I don't do any zone two. And as people are listening to this, people struggle with time. So where does, would that be acceptable versus Do I also now have to add in zone two training? Again, in the literature, the way that is discussed, zone two is, I don't want to say superior, but that's the foundation and that's the base. But is, is that.

A (15:39)

Yeah, I, 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 approach. I think that's, you know, again, what if there's one thing I've learned, there's no one size fits all approach. And so if, if someone's gonna, you know, you're, you deal with clients all, all the time, but if someone's gonna come to you, it's like, what's the goal? You know, what, what is your primary goal? How much time do you have to train? Right. And when we're suggesting, given what you just mentioned, that so many people are struggling to meet the physical activity guidelines, which are two and a half hours a week of moderate to vigorous.

B (16:27)

How many people meet that?

A (16:29)

You know, depending on the survey, less than half. Right? Yeah. 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 think, you know, yeah, you're, you're losing people there.

B (16:48)

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

A (17:01)

It is. And so to Me and I think many others. Sprint interval training is an intense variant of hit. So basically, once you get above those thresholds that we Talked about there, seven out of 10, you know, 77% of your maximal heart rate, anything up to an all out sprint from danger pace counts as hit.

B (17:22)

Sprint.

A (17:23)

Sprint interval training is that, that, that, that real top range of, you know, we typically, it's typically defined based on power is once you're above your maximal aerobic speed, so the speed or work rate that would cause you to reach your VO2 max, you're even above that or the pace is truly all out. Right. And so typically Those intervals are one minute or less. They can be as short as 10 or 20 seconds.

B (17:51)

One minute sounds long.

A (17:52)

It does. You know, you're pushing at the end, but you know, 10, 20, 30 second sprint intervals are sort of the classic, you know, Tabatas are 20 seconds. Right. And so that's where, so those are those intensity ranges, 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, it's pretty intense. But to be clear, it's a variant of hiit.

B (18:17)

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 a few things. Number one, to actually have a clear understanding as to what high intensity interval training is and what it's not.

A (18:36)

Yeah.

B (18:37)

What it's used for, where its actual benefit is for performance and where its benefit lies for health.

A (18:45)

Y.

B (18:45)

And then finally, protocols. What do we actually have to do? And um, and within that, I want to hear some of the, the controversies and some of the things that we don't commonly think about and then the new emerging research and how we can implement that.

A (19:01)

Yeah.

B (19:02)

So this, this low volume, I have low volume sit. And this says, this generally refers to protocols in which training sessions are 15 minutes or less in duration and involve a total of up to five minutes of intense exercise.

A (19:17)

Right.

B (19:18)

I mean, this isn't, I should ask you, is this important to understand? Because what I don't want people to do is to just try something and be like, well, I tried it, it didn't work, or it didn't have any metabolic benefit, I didn't improve. What can we tell them specifically as to when they incorporate these varying definitions? And you can take that wherever you want. What are they going to get?

A (19:44)

Yeah. So 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.

B (20:11)

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

A (20:22)

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 going to 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 where they're more than willing to trade off or you give them the option. You can do an hour of traditional continuous or you can do 10 minutes of really vigorous and within that one minute of all out sprint training. Which do you like? They're like, yeah, 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. Again, that's not everybody. But the point is to just generally dismiss sprint interval training out of hand is, oh, no one will do that or how could it possibly provide benefits? Is, is unfounded.

B (21:27)

Okay? The worst is going to buy sheets and they look pretty. You get home, unpack them, wash them and they are terrible and scratchy and ultimately just need to be thrown out. And that is why I chose Cozy Earth. As one of the sponsors of the show. I've been using Cozy Earth products for years. They have the softest, coziest, most comfortable home products ever. Beyond sheets, they have towels and they have comforters and their comforters are breathable, temperature regulating, incredibly soft without feeling heavy and scratchy. And it makes winding down at night effortless and beautiful. They also have essential socks that are thoughtfully cushioned and supportive and even are better with a foot rub. So whether you are traveling training or just at home, I love these products and they are built with intention and they are beautiful. And Cozy Earth stands behind their products with 100 night sleep trial and a 10 year warranty. Huge fan have been using them for years. Head to cozyearth.com and use code Dr. Lion for 20% off. You can experience it at home. Foot rubs don't come with it. What are some of the new. There's new sprint interval research that's been published since the last time you were on.

A (22:44)

Yeah, and, and so I a, a, a valid criticism of hidden 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. And so, you know, we don't want to have your listeners and viewers eyes glaze over and talk about statistics, but there are rigorous ways to design experimental studies and there are not. And many proof of concept studies are just that, they're relatively small, they're trying to demonstrate a finding. But, but they're not large scale randomized controlled trials. And what you're seeing, I think in the hit field generally and in the sprint training area is you're seeing much more robust studies being done. True randomized controlled trials where you take a group and you even. I'll use us as an example. We're not working with biostatisticians to plan our scientific studies.

B (23:48)

Should someone be.

A (23:49)

Well, I think absolutely. Your studies should at least be informed by what's an appropriate sample size, what is an effect size? And that just means is this biologically meaningful? Again, in medicine we See examples where 100,000 people take this pill and there's a statistically significant finding, but the effect was a 0.1 change in blood pressure. That's at the other end of the spectrum. You know, often in exercise science it's small studies and so we're not really able to tease out, well, did this work? Is this better than this? Suffice to say, the evidence around sprint interval training studies is, is markedly improving. And now we have robust evidence to say if you do 6, 812 weeks of sprint interval training, you will see clinically significant improvements in your VO2 max compared to an untraining control group. No question.

B (24:48)

Talk to me about timeframe and give me an example of a sprint interval training plan.

A (24:57)

Yeah, 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 warmup, you do your first 20 second sprint, two minutes recovery, sprint again, two minutes recovery and then a two minute cooldown. So basically start to finish there, it's 10 minutes of an, it's a 10 minute exercise session. But within that there was only one minute of very intensive exercise. And there's other protocols. One known as rehit, reduced exertion, high intensity training. That's 10 or 20 second sprints and only two of them. So we're really talking less than a minute of really sprint effort in a typical time commitment of 10 minutes or less.

B (25:55)

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

A (26:10)

Yeah. So it's. As long as there's no underlying joint issues, all of that, you know, those cautions. Hill running would be a classic way to do it, right? So 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 so challenging and so it's hard to do. There's examples of sprint like training that you can do on a bike, but you really, you set a workload. You set a workload that's quite high and then, you know, you try to hold that as long as possible. Now there are.

B (26:57)

Without losing the RPMs, right? I mean, is that important? So, for example, as I think on Saturday, I'm sure I'll be doing 10 cows, which I, I swear I think the bike is broken. Cause I'm like these, these cows aren't increasing. I cannot hold that. The RPM once, you know, I might be 75, 80, 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 be very clear on the dose that I'm getting? For example, if I am taking, I don't know, one unit of insulin. It's one unit of insulin, yeah.

A (27:42)

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 wingate test, right? 30 seconds all out, as hard as you can go. And those are done on specialized pieces of equipment that essentially, if you can imagine, the power output adjusts over time and sort of meets you where you are. So you're giving that example of you start to tire late in exercise in your sprint training, but maybe you could have actually done a little bit more at the start if the power output would have been higher. So there are now devices on the market. Carol Bike. We've used these in our research studies where the bike uses a self learning algorithm so that it adjusts over time.

B (28:41)

We just recently partnered with Carol Bike and one of the reasons I love the Carol bike is its ability to in real time adjustments for a specific outcome. So I want to 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 used.

A (28:59)

Yeah, no, and you know, disclaimer from the outset I've engaged with Carol in terms of providing some scientific advice to them. I've never been paid. We have some of their bikes in our lab because we've seen the research studies, they work. We've tried them in some of our recent studies and applied them successfully in our sprint interval training studies. But yeah, what the bike does is it adjusts workload. And so the, the classic Wingate test, what you do is you set a load on the bike that's about seven and a half percent of your body weight. And why that is for most people that's sort of the optimal combination of load and RPMs you'd imagine. You set the load too high, you can't even turn the pedals right, you set the load too low and you can only spin so fast, but you're not getting a workout.

B (29:51)

That's right.

A (29:51)

So that 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 9% of body weight, less trained people, 5%. And so my understanding then is the Carol bikes have sort of used that initial setting. But then what the self learning algorithm allows you to do is for you, right, it adjusts specifically for, for, for you to sort of optimize the workload setting as you move through a period of training. Bottom line for us is as compared to traditional wingates, we've used it done in our studies as, as an intervention, as a sprint training intervention and shown that it can prove VO2 max after 6, 812 weeks of training. And you know, do you think it

B (30:40)

could be before then?

A (30:42)

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

B (30:49)

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

A (30:53)

Yeah, exactly. Yes, yes.

B (30:55)

Any sprint interval training, 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?

A (31:17)

Yeah. This idea, I don't know if shocking the system or that I, you know, I like to think that, you know, the physiology is the same. It's just the inputs can be different. Right. And so you can improve your VO2 max with a lot of traditional moderate

B (31:34)

intensity cardio, meaning like three hours of zone two. I mean, is that, would that.

A (31:39)

Yeah, with many. Yeah, yes. And again, depending how we define zone 2. 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 612 weeks, you can improve your VO2 max.

B (31:52)

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.

A (32:06)

Yeah. You know, 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. You know, they have progression in their, in their training. But you know, to be clear, you know, people can do moderate intensity physical activity of high volume and, and improve their VO2 max. Now, whether they can improve to the same level with less total exercise performed in a more vigorous manner. Yes, I think there's good evidence for that. And this is how we get into, how do we compare the traditional MRO and high intensity interval training. But the studies also show that more vigorous, for a given dose, more vigorous physical activity would, will lead to greater improvements in VO2 max. And that's not only in apparently healthy individuals. This is in individuals with many different chronic conditions as, as well. So these, you know, high intensity interval training has been applied to individuals with type 2 diabetes, many different types of heart disease conditions, certain types of cancer.

B (33:25)

So talk to me about that. I want to, I want to double down on that. The dose of high intensity or sprint interval training. 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?

A (33:49)

So when you know this word efficiency, again, which gets thrown around a lot, 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 really anything more than, than that. You know, if there's different ways to achieve outcomes. And I think there's exponential benefit to increasing intensity.

B (34:17)

There's exponential benefit to increasing intensity.

A (34:20)

Right. Which means the, the, you know, it, it, 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.

B (34:34)

What about from a physiology perspective? There, Is there a difference between what we know from mitochondria from, you know, various roles of proteins, like, you know, you can.

A (34:53)

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

B (35:22)

90%.

A (35:23)

So basically you can imagine 90%.

B (35:25)

Correct.

A (35:26)

So, you know, that's the idea of the exponential time efficiency. Now, what is 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? We don't have a good answer to that question right now. We definitely know that both can improve your, your mitochondria. And we know in the same way. Yeah, yes. And so in the same way in that how do we measure mitochondria? We measure the maximal activity of representative enzymes. 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 training. So, but why do mitochondria go up? Mitochondria get stimulated by things that we produce during exercise. So your muscle responds to a stress, your ATP levels go down. Right. Calcium levels go up, oxygen levels change, hydrogen ions accumulate. All of those are metabolic signals. You can think of them as like fuel lights on your car that start to turn red. And so what they're signaling is we need some adaptation here. And so all of those signals stimulate the process of mitochondrial biogenesis. So they stimulate proteins and genes that tell the muscle, we need to grow additional mitochondria here. So, you know, the point is those underlying signals are the same. We can turn those signals on regardless of the intensity.

B (37:22)

So regardless if you're, if you're thinking About AMPK or PGC1 Alpha, does it matter if it is a slow, steady state input or a high intensity input if you know, if the outcome is the same?

A (37:40)

I think we know that the. We know that the inputs can vary. In terms of sprint training, you have a very sharp, sudden change. And so I think of it as, you know, if it's. 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 a sudden drop in or a sudden activation of many of these pathways seemingly is at least as good as the traditional long, steady approach. And it might be for different reasons. You know, you do prolonged continuous exercise, takes a long time for your glycogen levels to slowly go down, slowly get the activation of AMPK and these other pathways, or you can have a really sharp drop in your glycogen, 20% in 20 seconds or so, and a really rapid activation of AMPK, you're sort of at the same point in terms of the AMPK activation, but one way you did it really, really time efficient, and the other one took a prolonged time.

B (38:46)

I mean, that's fascinating. The fuel utilization. Talk to me about that. Talk to me about, you know, as 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 session?

A (39:14)

Yeah, well, sprint interval training, you're basically churning only through carbohydrate. And, and a lot of that is, you know, 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? No, when you do repeated sprints, most of your energy comes from aerobic metabolism, and virtually all of it is coming from. From carbohydrate, right? And so then people say, well, how can that improve my metabolic flexibility? Right? Like, how can this lead to an enhanced capacity to oxidize lipids? But it comes back to that improvement in mitochondria Right. So as long as you're boosting your mitochondria, that is going to allow an improvement in metabolic flexibility. So you can use whatever fuel you're, you're feeding the muscle sugars or fats.

B (40:06)

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 sphere, so.

A (40:22)

Well, we've, we've been, 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, you know, study design perspective, the nutrition studies layering that on are very, very challenging to do. And you need huge numbers of participants. I, I think there are studies to show that if you have less carbohydrate on board, so you, you, you lower your glycogen stores. Yeah. Low glycogen training.

B (41:01)

This is, I, I can't believe you brought this up. It's one of my favorite, I'm really nerdy. This is one of my favorite topics in, over the last year, this low glycogen training.

A (41:09)

Yeah.

B (41:10)

So can you explain what that means?

A (41:12)

So that's, you know, especially if you do 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, ampk, some of those can be turned on to a greater extent.

B (41:30)

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 is 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?

A (41:50)

Again, what's your outcome of interest? Right, there are some, 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 proteins.

B (42:10)

And also myokines, the proteins released from muscle, they seem to be more robust. When an individual is training in a lower glycogen state, that doesn't mean they're fasted. It Just means low carbohydrate within the

A (42:24)

muscle, you know, 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. And we gotta be careful here when we're talking about low glycogen training. What it is, is typically selected sessions with reduced glycogen, you know, if to, to chronically reduce carbohydrate availability that actually can impair your capacity to do high intensity exercise because of a key enzyme that seemingly is, is, is suppressed but, but periodic training with reduced glycogen availability. I think athletes sort of naturally do this.

B (43:16)

So 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 relate to long term health outcomes. And when I say muscle quality, I'm not talking about strength, I'm talking about the fat infiltrated the intermuscular adipose tissue, the intramuscular adipose tissue. This idea of the athlete's paradox. And so, and you could perhaps speak to this because I think from what I'm seeing, the way in which people train affects the fuel utilization and the fuel deposition within muscle.

A (44:06)

Yeah, well, you know, the athlete's paradox of course is just that it's sort of that U shaped curve where people are very unfit, will have high muscle triglycerides and athletes have very high muscle triglycerides as well. And sort of active, recreationally active people are, have lower amounts. Obviously the big difference there is that the unfit individuals are unable to use that lipid, whereas the high highly trained athletes are. And that's that whole idea of metabolic flexibility.

B (44:38)

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

A (44:54)

You know, this is, 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 things. But you know, you can see and there's some suggestions of where the lipid droplets are located spatially. If they're near the mitochondria that may be better able to utilize them. So again, I think there's evidence to support some of these contentions. But I think for the person in their health, it all comes back down to do you have metabolic flexibility or not? And probably the best, one of the best ways to improve that is to boost your mitochondrial capacity, right? Boost your health.

B (45:38)

Do you think that it would be fair to compare steady state zone 2? So if 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. In my mind, at rest, a healthy muscle is burning primarily fatty acids. 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 carbs.

A (46:14)

So I would consider metabolic flexibility to be, you know, 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 energy. Arguably one of the best measures of metabolic, metabolic flexibility is maximal. Is fat max, the maximal rating. Let's talk about that.

B (46:41)

I know very little. I'm starting to hear more and more for health outcomes about fat max. Talk to me about fat max.

A (46:47)

So fat max is basically what it sounds like. What is the maximal rate of fat oxidation by the body? So we're talking about 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 bout 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 value, what percent of fats are you, are you using? Does that make sense?

B (47:25)

Right, so what would we want to be using? So what would be considered normal?

A (47:30)

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 Fat Max can range from 40% of your maximum to 90% of your maximum. But for most people, it's going to be around 60% or so. So what you're doing is ideally to, to measure that you're imposing an exercise stress sort of through that moderate range of intensity. And you're going to see, you know, as you go from rest to low to moderate intensity Exercise, your overall metabolic rate goes up and your utilization of fat goes up. And then at some point it starts to go like this, right? So the overall metabolic rate continues to increase as you go to higher and higher intensity, but you really start to shut down your ability to utilize lipid. And so you're looking for where's that peak point right there in terms of your maximum rate of fat oxidation.

B (48:38)

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. And that is why I'm so excited about the Carol bike. It is an AI powered stationary bike that delivers, get this essential scientifically validated reduced exertion high intensity interval protocol in just 20 seconds, two 20 second all out sprints, all of this in under five minutes. And this isn't random hit, it's resistance that adapts in real time to your output. So you get precise and personalized stimulus to improve your VO2 max, which is one of the biggest predictors of mortality. And listen, we've all cheated ourselves our efforts on the treadmill and maybe we didn't push as hard as we could on the rower, but with the Carol bike, there is no cheating. For those of you prioritizing muscle, this allows you to focus on cardiovascular training that complements strength work instead of competing with it. It is efficient, it is evidence based and it respects your time. So it allows you to get after it. Visit carolbike.com and use code lion for $100 off your Carol bike. That's C-A R O L B I K E.com and use the code lion for $100 off your bike. And would a general person care about fat oxidation fat max?

A (50:27)

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, the, the issues with Zone two, I think there, there, there are 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, to what is Zone two? The, the, the most common here would be the most common definitions that we hear. Zone 2 is fat max intensity. Zone 2 is your first lactate threshold or just around 2 millimole or below that. So those are metabolic markers. Right. Fat max and your LT1, those are not the same in most people. Fat max tends to be lower. So even right there, they're not the same in most people. Right. And then these estimates of what those might be. Well, Maybe it's somewhere between 78, 80% of your maximal heart rate, but again, that's where it really depends. And the range is probably 40 to 90%. So I think people are hearing about, they're starting. Okay, I sort of get what zone two is. As classically defined, it's this. But as classically defined, it's really hard for most people to get those measurements unless they go into an exercise lab. So we'll use these surrogate markers. But that only introduces huge variability. So unless you know this and then you start to apply the surrogate measures. That's why I think in practice, zone 2 intensity could be way too low for many. Slash most people. It might be moderate for some, and it might even be vigorous for some, which, again, is the whole problem suggests that this is this magic zone where you should be in 80% of your training.

B (52:38)

That's a hard pill to swallow. 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?

A (53:03)

Not for an individual, no. Right. So again, zone two, it comes.

B (53:08)

I think you just broke the Internet. 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 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?

A (53:33)

It's fat max, or it's your lactate threshold 1 just below 2 millimoles.

B (53:38)

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

A (53:59)

Yes. 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, and so that's where I talked about those moderate, heavy, severe three domains. And then very commonly those are split into two subdomains each. And so you, that's where we get these six zone training models, for example, would be a very classic zone training model. And so zone two is down here. It's that low intensity exercise that many athletes do. So it's rooted in the training of athletes. Right. It's, it's a very well established term in the training of athletes. When coaches use these zone classification schemes, there's very clear surrogate markers for what it is. If you're a high level endurance athlete, we can reasonably assign heart rate ranges to that. But then to say that's optimal and you know, the last point there would be, we're inferring that because athletes do 80% of their training in zone two, that that's optimal for their mitochondrial health. Then we're taking all of that and saying, let's apply it to the regular person. And you know, what's the regular person? The typical person who's either struggling to meet the guidelines or maybe they're meeting the guidelines and they're saying, where should I divide my time? First of all, there's no evidence that that 80:20 ratio is optimal for everybody, especially if you're only doing 150 minutes a week. There's no evidence certainly that that's optimal for your mitochondrial health. And it largely stems from the idea that for people we're really sort of guessing what their intensity is. And it's probably not zone 2 as classically defined for a lot of people. In some ways it's analogous to so many people are doing keto, but. Well, kind of, yeah, right. And probably a lot more eating, a lot more carbohydrate than they think than strict keto.

B (56:21)

You know, 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 that 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, 10% or less. There is no reason where or why it's 10%. The data that individuals quote saying saturated fat is bad and has been moved forward for decades. Do you know where it comes from? It comes from hydrogenated whale blubber in a time of war, that this was a short term fix to be able to feed a population not to be used for 30 plus years. Worried about heart disease. And this quote, saturated fat was hydrogenated whale blubber, which then they ran out of. And so they started hydrogenating other fats. And I know this is like the world's longest story, but all of that is then lumped under the idea that saturated fat causes heart disease. And instead of questioning that and then going back and saying, you know, maybe this isn't right, maybe we missed the mark on this 10%. Another case in point is the Women's Health Initiative. And so now where I think what you and I are talking about is entering into this conversation of, believe it or not, Zone two training.

A (58:00)

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. That's moderate intensity physical activity. If we're going to talk 70 to 85% heart rate max as a guideline, that's moderate to vigorous physical activity per the ACSM guidelines.

B (58:40)

For the general population or for athletes?

A (58:43)

No, for the general population. Right. So let's just if, if that, you know, if, if zone two is fat max or lactate threshold. Okay, but then as athletes. Well, no, 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? Right? And it's. If we're going to 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's no evidence for that. There's virtually no scientific studies on Zone 2 training. If we're saying it's a big deal, if we're saying moderate intensity exercise, well, then there's robust evidence that it's good for your mitochondria and good for your overall health. So, you know, I think people have to Decide. Is Zone 2 this euphemism for moderate intensity physical activity in most people? Okay, then that's fine, but then it's already in the guidelines. And the guidelines are telling us maybe you should do 150 minutes a week of that to optimize your. Not. Sorry, not to optimize to boost your

B (60:15)

health, to boost your.

A (60:16)

But. But to suggest that 80% of time should be spent in this Zone 2 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.

B (60:35)

If you were to design and think about the health of the nation, no pressure, how would you inform them? If you could write exactly what should be done?

A (60:54)

Yeah, I mean, you know, who am I to counter? So how's this physical activity guidelines based 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 if 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. Yes, it's an excuse for a lot of people look at social media time, screen time, all of that. But the reality is that the amount of time that people are willing to commit to physical activity is very limited. Many see two and a half hours as a barrier. And so a lot of our work has been, okay, let's just meet people where they are, let's investigate what are efficacious doses of low volume vigorous physical activity. And so could we say to people, you know, and now again, we have evidence, right? And this is some of the larger studies. These are now epidemiological evidence that I've been involved with, led by Emmanuel Stamatakis from Australia, showing that as little as four minutes a day of vigorous intermittent lifestyle physical activity is associated with 25 to 30% reductions in all cause mortality.

B (62:36)

Right.

A (62:37)

And so this is not cause and effect data, but these are in 25,000 individuals followed. These are individuals who self identify as non exercisers. But if they can do some vigorous effort throughout the day, taking the stairs while carrying a heavy backpack, you know the classic example, getting off an airplane, you grab your luggage and you walk up the stairs for 20 seconds or so, if you accumulate four minutes of that through your day, massively beneficial for you. And so, you know, does your heart

B (63:08)

rate have to, could it also be, do we need to define how that's done? For example, could it be push ups.

A (63:16)

Yeah, it could be. Right. And, and so I think this is where body weight 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 does our heart rate need

B (63:32)

to get up to a certain point?

A (63:36)

No, I think what we should do is then use that, use these subjective markers like rpe. Right. Get into that, push yourself. Right. And 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.

B (63:58)

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

A (64:04)

Exactly. And so, you know, we, we do know that if you're going to 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 of vigorous intensity physical activity based on those traditional markers. So there, yeah, you would want to see your heart rate get up to around 77% or so. You would want to feel this is about at least a 7 or 10 on that RPE scale. So, but I also think like at the end of the day, maybe we don't need to overcomplicate it too much. And the message there is challenge yourself, huff and puff regularly, get out of your comfort zone. Right. That type of messaging for people, we hear these messages around all activity counts. And it's true. But I think in addition to sort of, you know, sit less, move more, that notion of pushing yourself, huffing and puffing with a few flights of stairs, that that's a good thing for, for you.

B (65:10)

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 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 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, I think the clearer that we can be, the better. So for example, if someone is like, well, I don't, I can't do 1030 push ups and maybe they go to muscular failure, then it Would be our responsibility to say, okay, you can do five. Now you have to move to squats because we can't have. You just have a muscular failure and then no cardiac or cardiovascular stimulus.

A (66:04)

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 can't do 30 minutes of continuous exercise. They feel like a failure. The idea with intervals is that's okay, right? Go hard, as little as it needs to be, take a break, then do another one. Right. And we can start to tell people or build the evidence around, you know, what, if you only do three or four minutes a day of this, but it's vigorous, that's going to be beneficial for you. Right. And so maybe eventually we can further inform the guidelines by, by saying here's, here's the minimum, you know, effective dose.

B (66:52)

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

A (66:55)

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 very beneficial. Exactly.

B (67:11)

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

A (67:16)

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. But you don't have to do very much of it. And I think that might be an achievable goal for many individuals or at least if they hear they're like and trying to say there's good science around this now, right? This. Just get to this, right? The more the better. 100%. But just try and get to this.

B (67:54)

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 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. Again, there's a lot of discussion. Well, just add in 30 more minutes of cardiovascular training or potentially high intensity interval training, sprint interval training. From a body composition standpoint, assuming people are doing resistance training, which would you prefer? And why

A (68:37)

not? To hedge, but it would be, how much time are you going to put in? Right. And so I think exercise plays the role in terms of supporting weight management. You're not going to see mass, to my mind, massive changes in body composition with aerobic style training, whether it's HIIT or moderate intensity, continuous. And I think right now that's what the evidence shows, right? The, there's, there's subtle changes in body composition. There's not huge changes in body weight if you're just adding on a little bit more of that exercise stress. Right. And we know in the real world that people, you know, who am I talking to here? But, you know, you like, you talk about this a lot, right? Like, people change their behavior, right? Energy comp. You know, energy intake can change. It's a really, really tough topic to study, Right. To say that, okay, if we tweak this exercise, what effect is this going to have again in the real world? Right. It's. Sorry to hedge on that one, but it's really hard to answer that one.

B (69:40)

Well, it's complicated.

A (69:41)

It is.

B (69:42)

I think what we're getting to is, you know, we're able to. I think that exercise is so much more difficult to study than, you know, in nutrition. I could say, Martin, you know, we are going to have 50 grams of carbs and 50 grams of protein and 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 night before. We have clear outcomes and we have pretty immediate feedback. But if we say, well, you know what your dose is going to be, 10 pushups, four air squats, and, you know, three reps of bicep curls, I have no idea if that stimulus is adequate or meaningful. We're just not there. And that's the biggest struggle in the way that we've been able to get very specific with nutrition. I mean, we're really specific with nutrition and we have good evidence as to what those improvements are. And I can test it. I. You give me three months and I'm going to measure your hemoglobin A1C. You give me two weeks and I'm going to see your triglyceride changes. Once we reduce your carbohydrates to 130 grams or less, I'm expecting your triglycerides to be within normal range and exercise muscle as this lever is arguably the most important. But I have no way to say, you know what, that helped your muscle quality to this degree.

A (71:15)

Yeah, that's you know, we definitely have evidence around, you know, we're going to 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 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.

B (71:40)

Where do you think 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. 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 the determines the intensity, meaning heart rate, power, pace at which your body oxidizes the highest amount of fat as fuel. Like you said, every athlete knows this potentially. And their lactate threshold, how can we look at that from this is what quote, healthy mitochondrial look like. This is what good training adaptation looks like. And then translate this over to, let's say some of my patients who have had Covid and they're exhausted and they are gaining weight and their hormone status looks okay, but they are struggling with mitochondrial efficiency. And I use this term loosely because we're not defining it, but then you see this reflected in their fat max.

A (72:45)

Yeah. And so the problem with mitochondrial health is it's so we don't have clear, call them guidelines, VO2 max. 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 really direct measure in a lab. We have some pretty good ways to estimate it, you know, based on submaximal heart rate responses. So you can get a pretty good indicator of your VO2 max with a submaximal exercise test or a maximal test in a laboratory. And we know then if your VO2 max is this, your risk of developing type 2 diabetes, cardiovascular disease is this. Or at least if you change your VO2 max, your risk will change by this much. So it's such a good metric because we have these quantitative characteristics around it. By saying change it by one met and your risk for all cause mortality is going to go down by about 15%. We just don't have that for mitochondria. Right. So we finally get going mitochondrial health. But this is where you know, if, if the Zone 2 discussion have done anything. It's, it's at least really put these concepts out there of advancing this idea of 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 VO2 Natural.

B (74:19)

You can get there. I, I think that event measured, have

A (74:22)

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 has type 2 diabetes or pre diabetes and maybe start to get those. And it's not going to take a muscle biopsy to look at your mitochondria. We can use fat max as the

B (74:44)

marker, as a proxy marker.

A (74:46)

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

B (74:51)

It's pretty cool, right?

A (74:53)

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

B (74:57)

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. Talk to me about this idea of REHIT and conditions like diabetes and other health conditions.

A (75:17)

Yeah, so REHIT is it really. It's a, 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, classic.

B (75:33)

I'm gonna make you define that now.

A (75:35)

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

B (75:47)

Is that because it's easier to control?

A (75:49)

Yeah, pretty much it is. Um, and so you know those, those are often, sometimes as little as two, but typically three times a week. So you're talking there, you know, 20 to 40 seconds of all out exercise, typically within a 10 minute time frame, a few times a week. But again there, you know, there's, there's some small randomized control trials of rehit. There's definitely studies on rehit showing that it's can be, it's going to boost your VO2 max. Right. Just like the classic sprint training. So it's, it's a variation on sprint interval training that's certainly a lot more tolerable than Classic wingate style training that's

B (76:30)

been done and it's more tolerable because it's shorter. Shorter. So the two and there's, and we can link to these studies. This is two to three 20 second sprints and that is able to. Again, so I'm thinking about these statements to have health and fitness benefits comparable to quote normal exercise in a fraction of the time, 10% of the time. How do we, is that, would you feel comfortable with me saying it?

A (77:05)

What I can definitely say with confidence is rehit style training, which again is 10 to 20 second bursts. 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 bursts. If, if people do that three times a week for six, eight, 10, 12 weeks, most people will see an improvement in their VO2 max. There's definitely studies significant 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 6 to 12 weeks of training. One met. What is that? It's about 10% for the average person. So that 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, that's where the evidence is not as good. But that's where again, coming back to what we were talking about, the beginning of a conversation, those are the studies that we're doing now. We're trying to move into this space and say, okay, there's good solid evidence now that rehit sit works. How does it actually compare when we do these studies? The right way. Right. Like let's true randomized controlled trials in adequate numbers of people to tease out differences if they're there or, or not. Right. And just to geek it up for

B (78:41)

one sec, very exciting.

A (78:43)

It is. So we, we, we, you, you, you, you do these trials called non inferiority, which means not different. Right. And so oftentimes, so let's, let's say here's the well established drug on the market for this condition, right?

B (78:58)

You can pick Metformin.

A (78:59)

We want to test this new drug against it. We want to say it's not worse. Right. So the benefit you might see is not worse than the standard. Well, what does not worse mean? Not. You try to identify a margin that 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 sort of meaningless in a physiological context. Those are the studies now we're doing with sprint training, comparing it to the traditional moderate approach. Right. If we see a change in VO2 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.

B (80:00)

When will these be published?

A (80:01)

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

B (80:05)

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A (81:59)

Yeah. So again I think the general catch all term is high intensity interval training and sprint is that very intense variant of it.

B (82:08)

Does high intensity interval training prevent sarcopenia

A (82:12)

H. As classically practiced on a bike running? No. I think though these body weight style approaches. So we're talking now high intensity functional training.

B (82:30)

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

A (82:32)

So High intensity functional training is really just the classic example would be body weight style training would be simple equipment style training, kettlebells, you know, air squats with dumbbells, you know, classic functional movements, almost calisthenics in a way, push ups, pull ups, that type of training. So that is basically resistance based high intensity interval training. Right. And so this is where again it sounds a bit complicated, but what we're often doing is let's pull it back to the fundamentals. Big picture. We talk about two styles of exercise or two types, two broad types, aerobic and resistance. Right. And so traditional aerobic style training, cycling, running, rowing, swimming, that's traditional hit resistance style HIIT is body weight 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.

B (83:45)

So for. Yes, when I think about running, you're still moving your right, you know, single leg body weight and that's different.

A (83:54)

It is. Then okay, then, then when then, then. So it's 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 tradition, when I say traditional hit, what I mean by that is traditional aerobic style, hiit, cycling, running, swimming, rowing, cardio style hit. We don't see much change at all in muscle fiber size. And so applying that through a sarcopenia lens, then if we're losing muscle size as we age, you know, probably the stimulus is, is not enough, generally speaking. Now if you've never done anything, maybe a cycling stimulus because you're so your capacity there is so low or your starting number is so low, then cycling, yes, could and there's definitely some cycling studies that have reported an improvement in muscle cross sectional area. So then it's like, well, what's the starting number? But to answer your question, I don't think traditional aerobic style HIIT is going to be hugely beneficial in terms of attenuating the decline in sarcopenia. I think that's where you need a resistance stress. But it could be high intensity functional training or interval based using body weight

B (85:29)

style exercises and body weight style exercises. Even for a person who's active, would you think would be enough or is.

A (85:37)

Well, so you're not. Now you change the question. No, no. But no, 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 decline, it's still going to be beneficial.

B (86:15)

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. I don't think we know enough about it.

A (86:32)

Yeah. But definitely attenuate can attack. Absolutely.

B (86:37)

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

A (86:44)

Yes. So 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, some conditions in that increasingly important right to get medical clearance. But you know there's, there's studies being done on octogenarians in Sweden with very intense sprint interval type training in group style classes showing high levels of enjoyment, high levels of benefit. So definitely older individuals can do this as a, you know, as a blanket. All older adults should do sprint training. No, that's not what I'm saying.

B (87:27)

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

A (87:33)

Yeah. 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 biological males and females. Yeah you can see a few subtle differences. You know, coming back to fat max women, females tend to have a higher fat max by a few percentage points than, than males on average.

B (88:20)

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

A (88:26)

Yeah, no type of training. 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 going to look like this. Right. And this is that point of fat max women. It, it happens at a higher percentage of their maximum. It again I'm generally speaking in there, I'm, I'm mixing up sex and gender but biological females. Some of the studies of compared men and, and women 10 on average have a little bit higher fat max than.

B (88:59)

So they oxidize that.

A (89:00)

Yeah. Have a little higher. Yes, exactly.

B (89:03)

A bit better?

A (89:04)

Yes. Yeah.

B (89:06)

Is that clinically significant?

A (89:09)

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

B (89:17)

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, I'm with you. I think it's, from the evidence that I've seen, it's really interpersonal variability. But potentially are there some differences, albeit they might not even be meaningful? For example, a fiber dose, right. We might have a higher, I don't know, type 1 fiber or mixed fiber type, but that difference might be what, 1% or 2%? So yeah, we could say that. But is that meaningful in any capacity? I don't know.

A (89:57)

You're right. And 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? Or do 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, you know, really good. This is where you want to be. Right? We know the higher the fat max, generally speaking, the better in terms of your metabolic health. But I don't think we have, you know, certainly clinical cutoffs to inform practice or something like that.

B (90:51)

What other sex differences? Male, biological, male or female?

A (90:56)

Yeah. In, in 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, so it's not, it's not a mitochondria thing.

B (91:29)

Okay. So it's not a mitochondrial thing. And I think my mind is blown for the second time. Is it a size? So if you have the same size female and the same size male. Do we anticipate one having a higher VO2 max than the other?

A (91:47)

Yeah, generally the male will have a higher, slightly higher VO2 max. Part of that is, you know, females tend to have higher obligatory body fat. Right. So the, you know, the leanest male will be about 5% body fat, you know, 4 or 5%. The leanest female will be about 9, 10%. Right. Because of reproductive reasons. Fat is a less metabolically active tissue than muscle, as you well know. And, and so that explains in part the differences in VO2 max. But there, you know, so the specific question was about training induced changes and there, there may be differences in what explains the improvement in VO2 max with training, where the cardiovascular changes in the females may be a little bit less, but the muscle changes, including the mitochondria, may be a little bit better. So there's hints of that in the literature. You can pick your studies right now. But again, come back to, we just need better quality science.

B (92:48)

Think what do you think? You've been doing this quite some time.

A (92:51)

Again, I come back to you. 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 tensi training. It's an entirely female cohort that we're studying.

B (93:19)

Well done.

A (93:20)

And, and that's for two reasons. Partly that the, the, the number of participants that we need was, was lower when we did the statistical calculations. But also we're trying to do our part to help address the underrepresentation of, of females in science. And so it was a, it was a dual consideration there.

B (93:42)

And do you think that you will find meaningful differences?

A (93:48)

So our hypothesis is no, that there won't be that sprint. So 12 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 matter. So that's our hypothesis and that's informed by our previous studies that were not, you know, state of the art in terms of the grade A evidence. So we're hoping that we're going to have much better evidence to definitively make that statement.

B (94:28)

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 interval training, this interview is totally over. But just from a practical Standpoint, when we think about designing the ideal week for a busy 45 year old person,

A (94:52)

you know, if you can even give a half hour.

B (94:55)

Let's assume they say they're willing to. Yeah.

A (94:58)

What are they willing to give me? Because I was going to be the first question. Right, right, yeah, yeah.

B (95:01)

Let's say they're going to meet the 150 minutes. So you have, they, they want to exercise, give them 150 minutes. That's the baseline recommendation. And yeah, they're willing to do that.

A (95:12)

Yeah. And so I think in an ideal.

B (95:14)

More. They'll give you more.

A (95:17)

Yeah. And so I, 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 continuous exercise and then two sessions. So you know, a one hour ride at the highest possible intensity.

B (95:35)

Darn it. I need to reevaluate my training.

A (95:37)

No, but how's this? I don't train that way. Right. So you know, I, I like high intensity intervals. And so all of my cardio is interval based. Right. Now 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 whole body resistance exercise, whole body functional style training. So myself, I'm meeting the guidelines but rarely am I exercising for more than half hour a day. Now in the summer, late spring, early fall, I like to cycle outside. And so my cycling changes 12 hour rides outside, it ends up being all interval based even though I'm doing a continuous ride because the altitude changes and things like that. What you asked me was if I was going to give a program to someone, Matt, over here, I like interval training. Right. But not everyone does. And so I think doing that continuous but importantly, not zone two, go, go at the highest intensity you could sustain for that hour. I think that's going to give you more benefits.

B (96:51)

That's tough for people to. Yeah, you know, as I think about, because I do the, I mean I don't, I haven't lately, but I love to do a peloton, listen to country music. Don't tell me. It's kind of embarrassing, but it's so fun. I like to push myself, but I'm not sustaining, I'm not jamming out, you know, sustained at a certain exertion pattern. And maybe again when I think what

A (97:19)

you asked me, and 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.

B (97:30)

So in my mind, and I am not a training expert, people should be lifting weights three days a week. If I was going to pick a number and it could be four, I mean, let's have a, I could wave a magic wand, but I want them to get full body resistance training because it's only downhill from here.

A (97:46)

Right? Yeah.

B (97:47)

And from your perspective for the busy 45 year old, how often should they be training?

A (97:53)

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

B (98:02)

What is that?

A (98:03)

Well, again, so I'm talking their foundational movements. So push ups, pull ups, cleans, deadlifts, you know, it could be wall sits, you know, that are engaging large muscle groups. And again, ideally in a functional style way that, you know, translate to improvements in activities of daily living. It allows you to extend, you know, to climb the stairs better. Right. It's that again that challenge of you get off the airplane, you've just been on a five hour flight and the escalator's not working right. Is it a big deal for you to just grab your carry ons and walk up the stairs and it's three flights of stairs and you can do that, no problem. So when you're challenged to engage and go at that, you have reserve capacity. Right. And so I think that's where those functional style resistance training really comes into play.

B (99:02)

You're not off the hook. How many times a week do they have to do that?

A (99:06)

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

B (99:14)

What about rest intervals? And I asked you this very early on when I was working on my first book and I said 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. I remember exactly. I was in Encinitas and there's this hill, there's this hill on the beach. So right behind the beach there's this hill. The parking is terrible. And so we decided that we were going to use this sprint, this hill for sprints. And after the second sprint I'm like, I'm done. I need to rest for, I don't know, five minutes. Just I'm going to chill for five minutes. And what I remember you saying is that you really don't want these long periods in between. It's not a full recovery if I'm not going at 100%. My, my max effort. Is that, is that accurate to say or have things change?

A (100:10)

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. Like I stand by rest interval matters in that, you know, generally the longer the rest interval before you go again, the overall quality of the workout is going to diminish a little bit. Right. Both from a time efficiency certainly, but also in, in, in terms of that, that period of time in, in, in between. But you know, I, I think I would say take as much rest as you need to come back and do another hard interval, right. If, if you're going to really compromise the rest and then the interval isn't very good, like the effort level just isn't there because you're so tired, then probably you need more rest. Right. But where I've come around is our whole exercise snacking approach is based on, it's really prolonged recoveries in between. So people might do three or four one minute vigorous bouts in a day. So they do one in the morning, there's several hours in between, they do it at lunch, one more in the evening. Right. So you've accumulated three or four of those there. The recovery is really, really large and yet we can still see some benefits with that approach. Now ideally, would they put all those together or with short recovery period. Yeah, probably that would be better for them in terms of boosting their health. But we know that other one, which is a way that or a strategy, it offers a strategy that people might be able to build into their lives. It's still beneficial. The last benefit of the second approach with a prolonged recovery is it also breaks up prolonged sedentary behavior, which we also know. So perhaps vigorous intermittent lifestyle, physical activity, exercise, snacks offer a dual benefit. You do the vigorous physical activity to get that stimulus, but you're simultaneously breaking up prolonged sitting, prolonged sedentary behavior, which we also know independently can help with your health.

B (102:23)

How long have you been studying high intensity interval training?

A (102:27)

20 years.

B (102:29)

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

A (102:47)

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, is, and I'm most proud to be a part of as a collaborator is these, these small vilpa doses, this vigorous intermittent lifestyle, physical activity like four minutes a day, 25 to 30% 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 you know, I'm not, I, I'm not a brain researcher. I don't do brain health research. And so some of that research is fascinating to me, but it's not what I primarily do. So in terms of what I've helped to contribute to, I, I, it's, you know, these, just how little you need to really see a benefit. Right. And we're talking mortality. There is the outcome. Right. There's nothing more important.

B (103:53)

Absolutely. And we don't even have a pill that does that.

A (103:58)

Right? Absolutely.

B (104:00)

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 yesterday, 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. And every two week thing, we're talking about four minutes. This is the worst idea of my entire life type of exercise.

A (104:32)

Ideally do it once a week. Yeah.

B (104:38)

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 these four minutes?

A (104:49)

Yeah, no, I would say save those, those sessions for ideally save those sessions. That, that's the only thing to do that day.

B (105:02)

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

A (105:14)

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

B (105:20)

know, he's actually been on the show.

A (105:22)

He has.

B (105:23)

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

A (105:27)

It's, it's going to be called the Exercise Science podcast.

B (105:32)

What is it going to be about? Just kidding. So just kidding. Totally kidding.

A (105:38)

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

B (106:04)

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

A (106:17)

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