#379 - AMA #79: A guide to cardiorespiratory training at any fitness level to improve healthspan, lifespan, and long-term independence

Hey everyone, welcome to a sneak peek, ask me anything or AMA episode of the drive podcast. I'm your host, Peter Atiyah. At the end of this short episode, I'll explain how you can access the AMA episodes in full, along with a ton of other membership benefits we've created, Or you can learn more now by going to peteratiamd.com forward slash subscribe. So without further delay, here's today's sneak peek of the Ask Me Anything episode. Welcome to Ask Me Anything AMA episode 79. In today's AMA, we take a comprehensive look at cardiorespiratory fitness, one of the most common topics we get questions about, and of course, an area that is central to not only lifespan, but also healthspan. Now, look, we've done a lot of content on this topic, but we wanted to put together an episode that brought it all together in one place. And as always, to include any of my updated thoughts, something which of course I'm constantly updating my thinking on topics and hopefully sharpening it. So the goal of this episode is to provide a practical guide that allows you to structure your training in a way that meaningfully impacts your health, your functional capacity, and maintains independence as you age. We'll discuss why cardiorespiratory fitness is one of the strongest modophile predictors of healthspan and lifespan, what zone two training actually represents and why it's different from higher intensity work. And there seems to be still some confusion about this, how to think about exercise volume, intensity, and the practicality of training in different zones and using different approaches, how to measure and track improvements in zone two specifically, VO2 max targets, age adjusted goals, and planning for the marginal decade, structuring an effective workout routine around your zone two goals and your VO2 max goals, how to balance zone two with higher intensity work across varying weekly training volumes. Again, this is a very important part of the discussion because as I allude to, there are going to be some of you listening to this that shouldn't be doing zone two at all. And my hope is that by the end of this podcast, you've been able to identify yourselves. Adjusting training for beginners, metabolically unhealthy individuals, longtime trainees, older adults, et cetera. Specific considerations for women specifically, including some misconceptions around zone two or other forms of cardio training, common training mistakes and how to avoid plateaus, burnout, and miss targeted intensities, practical strategies for sustainability, progression, and long-term adaptation. If you're a subscriber and you want to watch the full video of this podcast, you can find it on the show notes page. And if you're not a subscriber, you can watch a sneak peek of the video on our YouTube page. So without further delay, I hope you enjoy AMA 79. Peter, welcome to another AMA. How are you doing? I'm doing very well. Thank you for having me back. Always welcome to have you. I see every time we do these, you bring something more and more to each recording. What have I brought this time? I don't know. I'm not even aware. Nothing you can think of. Nothing jumps out. No new additions to the body. No, but given that we've now introduced carve outs at the end of these, it's made me that much more aware of how much I am the perfect target of YouTube and Instagram ads, because I could create an entire podcast called the carve out where I just talk about the things that I buy when they're served up to me as ads that I end up liking. Have you bought one thing today? Not today, but I did get something really awesome two days ago. It arrived two days ago. Anything you'd like to share with the group? Heck no, I'm saving it for a carve out. Maybe next month. I put these things to the test. Let me tell you, I am a serious tester of product. So the thing that I got so far, I've already tested it once. It was insanely good. I need a few more reps with it. And if I'm still digging it in a month, it might make it to the carve out list. That's great. It's exciting because I don't think people realize what you're talking about could be a legitimate thing that is actually beneficial to health and longevity. And it could be the dumbest $20 gadget that has ever existed. And we have no way of knowing which one it is when it comes to that spectrum. Well, I'll give you a hint. It was served up on a YouTube ad. So it's definitely not the former, but I will say it's also not the latter. All right, right. Leaving people hanging. There's a lot of daylight between those two. Yes. You just tend to live on the spectrums though, right? Like you kind of go one or the other. That's fair. The only thing you do in moderation is moderation, which turns out is the same with engaging in YouTube and Instagram ads. You like to go all in. So with that said, what we're covering today, one topic, cardiorespiratory, fitness, in simpler terms for people, zone two, VO2max. This is a topic we have talked about over the years on different podcasts, different guests, different articles, but it's also a topic that we get asked about by far the most, partly because of the interest in it and also I think because of how open you are on how it is the biggest and strongest modifiable predictor of both healthspan and lifespan, meaning it's the biggest impact that someone can do something about it. So that's why we decided to kind of dedicate this AMA, gather all the questions, and try to make it a one-stop shop for everything relating to how to measure, track, improve, zone two, VO2 max through training. We'll cover how this relates to people who have a lot of time to work out, people who have a little time to work out. We'll look at how it relates to people who are just starting training, people who have been training for a long time, older adults, if anything changes for women in particular, and more. We'll also look at if your opinion has evolved around some recent debates and discussions around zone two, lactate, how to balance volume and intensity with the goal of not having your best exercise month ever and then stopping, but more so long-term. So with all that said, anything else you want to add before we get started. Yes. This was an idea that when the team pitched it to me, my initial response was, I don't think this is worth it. We've already generated plenty of content on this. It certainly would be within the top five things that I talk about. And the team, I think, was able to get me convinced, and I believe rightly so, by saying, yeah, Peter, that's kind of the point is if someone were to try to go out there and aggregate everything you've said on this topic, it would be a full-time job. And I think someone even shared with me how many hours and hours of content it would be. And it was triple digit hours. And they said, that's great for the person with an encyclopedic memory who is a lifelong devotee who doesn't have a job, but most people aren't going to fit into that category. And it would be really helpful to have a practical guide, not just a theoretical guide to this. That kind of won me over. And so I guess I would just say kudos to the team for convincing me that this was the way to do it. I'm really happy with the way they've crafted a story around this. Let's dive in. Before we do a quick question. Do you think if the team started to put their arguments in forms of videos that we ran as Instagram or YouTube ads, you'd be more willing to listen? If you could be good enough, but you have to catch me within the first 10 seconds of the ad or I'm skipping it. Like, I don't know that that's a skillset that exists on our team. We don't practice that skill of catch you in the first 10 seconds. No, we practice more of, we will get you at the end of two hours after explaining in rigor. So with that said, I think what would be helpful to start is looking at real quick, why is cardiorespiratory fitness a central pillar and not only your approach to lifespan, how long you live, but healthspan. Yeah. So again, if you've been listening to me talk about this for years, you can literally go to your podcast player and hit forward for a couple of minutes. You don't need to hear this, But I do want to spend at least a minute on this idea that cardiorespiratory fitness is one of the most important and modifiable. It's very important that we're talking about modifiable predictors of both how long you're going to live and how well you're going to live. So if you look at all the predictors of all-cause mortality, which remember that's the holy grail metric of longevity, cardiorespiratory fitness outperforms every other variable we can measure. This includes blood pressure. This includes cholesterol. This includes BMI, smoking. It even includes age, which just blows my mind. So cardiorespiratory fitness, CRF, represents how efficiently your heart and lungs and blood vessels and muscles can work together to deliver and utilize oxygen. So the more efficient that system is, the more physiologic reserve your body has. And it's this reserve that allows you to tolerate stress. This stress can come in the form of an infection, a surgery, or just frankly the day-to-day demands of living. This has been most typically and most repeatedly measured using a test called VO2 max. You've heard me talk about this, of course, and it's become a very popular thing that people talk about. It's the maximum rate at which the body can utilize oxygen, tested of course during maximal efforts which require exercise So this number is expressed in milliliters of oxygen per kilogram of body weight per minute but it can be estimated using something called METs or metabolic equivalents where one MET is equal to 3.5 milliliters per kilogram per minute of oxygen uptake or utilization. So I would say that the reason that VO2max has become such a popular way to do this is because it is a standardized test. That doesn't mean it's always done correctly. And we've got plenty of examples of how this can be done incorrectly, which is why for our patients, we actually do the test. We got tired of relying on other labs to do it. But for the most part, a well-trained technician can do this consistently. And that makes it easy to study. And that's why in the literature, you're going to see so much discussion where it comes down to METs or VO2max. The two can be used interchangeably. And you won't, for example, see that when it comes to zone two. So we're going to talk a lot about that today, but I just want to point out zone two is a much more difficult area to navigate because it's not a maximal effort. It's an in-between effort. VO2 max is a maximal effort. So when you tell somebody to basically floor it until they're going to keel over, that's actually much easier to achieve. Now, to put some context around the importance of VO2 max and mortality, again, because it's been studied, if you're in the bottom quartile or quintile, so bottom 20 to 25% of the population with respect to your VO2 max, you've got a four to five fold higher risk of mortality, all cause mortality in any given year than those in the top 3%, 2 to 3%. That's a pretty big jump, but keep in mind, even tiny little jumps, say moving from the second quartile to the third quartile will still have easily a 50 to 75% improvement in all-cause mortality. So why is this such a powerful relationship? And I think it comes down to not just what the number represents, which is everything I've talked about vis-a-vis oxygen delivery and utilization. I've said this before, but I think it bears repeating. Measures like VO2 max, just like strength, they're actually integrators of work done. So if a person has a VO2 max that is low and their aspiration is to have a very high VO2 max, they can, but it will take potentially years and countless hours of work done. And that work will be done at the level of their cardiovascular system, their pulmonary system, their hematologic system, muscular system, metabolic system. And all of those things will have to work and work and work for hundreds of hours to get a desired outcome. And if you think about that, that's much more, frankly, impressive from a physiologic perspective than taking a pill that lowers your cholesterol. It's not to say that taking a pill that lowers your cholesterol doesn't improve outcomes, but it's not going to come close to improving outcomes as much as this does on average. There are edge cases. There are some individuals with familial hypercholesterolemia where that pill that lowers their cholesterol will have an outsized benefit. But by and large, this is why things that improve cardiorespiratory fitness or strength tend to have such an impact on mortality. Beyond mortality, can you also talk about the healthspan benefits? So what you refer to as not only how long it can help you live, but how well it can help you live. Yeah, I think the argument here is just as strong. Of course, the data are not quite as objective because health span is not as objective. So what I might aspire to be able to do that would define good health span for me might not be the same as you, Nick, and is not going to be the same as every person that is listening to us right now. But what we do know, and I think we'll show at least one figure to that effect today, is that VO2 max declines quite predictably with age at about 10% per decade, but the oxygen cost of doing things doesn't change. So whether it be climbing stairs or lifting something up or chasing your kids around or playing a sport, those things don't change. So if you have a declining capacity to deliver and utilize oxygen in the presence of constant demand, at some point those curves cross. And what that effectively means is you start losing the ability to do these things. Again, we'll talk about this in much more detail when we get there, but as I think a figure can represent better than what I'm saying necessarily, our objective is to be able to maintain optionality around being physical for as long as possible. And that is tantamount to having as high a VO2 max as possible, in addition to being as strong as possible. When talking about cardiorespiratory fitness in the past, to kind of help people understand it in a simpler way, you've often talked about the base and peak model. Can you just walk through a little bit more about that framework and how different exercise and intensities can contribute to each component of that? I talk about this cardiorespiratory fitness triangle, and I can't take credit for this at all. It was one of my cycling coaches that came up with this. So the idea was that you picture a triangle with a base and a peak. And the base is what we think of as your capacity to do sustained sub-maximal effort over a long period of time. So think of something you could do for hours. And then the peak represents your maximum aerobic output. So what you could sustain for five to 10 minutes. Obviously, there are so many gradations here. your functional threshold power, which is what you could obtain for an hour, is obviously smaller number than the peak and a shorter number than the base. So anyway, the goal here, if you're trying to maximize your total aerobic capacity, is to maximize the area of this cardiorespiratory triangle. And of course, to do that, you want to have the widest base and the highest peak possible. And these require different forms of training. So if you just trained at one intensity level the whole time, you would increase both of these things. I want to be clear on that point because it creates so much confusion. If you only parked yourself at one level of training, you would, through enough volume, increase both of these. But that's not the way to maximize the problem, and it's certainly not the most time-efficient way to do it, nor is it necessarily the best way to do it. In fact, it's almost assuredly not, given the fact that no high-level athlete trains that way. The base is ideally built through adaptations that help you utilize oxygen more efficiently to convert fuel, but mostly fat, into ATP. What this is really geared towards is improving mitochondrial density and efficiency and optimizing fat oxidation and lactate utilization. Conversely, the peak, which again is that VO2 max, represents the ceiling for oxygen delivery primarily, but utilization. And it's driven by how well this system can deliver oxygen to the mitochondria. That's primarily the bottleneck. It's how much oxygen can you deliver to mitochondria versus the base, which is how much can you utilize substrate efficiently. So when it comes to delivering oxygen to the mitochondria, there are really four big drivers. There's the diffusion of oxygen from the lungs into the blood. There's cardiac output, so that's heart rate and stroke volume. Then there's the oxygen-carrying capacity of the blood, namely hemoglobin. And then there's the muscle's ability to extract this. But as I said a moment ago, it's the cardiac output that is the main driver here, and it is the one we are most sensitive to in reduction. So again, what drives cardiac output primarily is stroke volume, how much blood comes out of the heart with each pump, and heart rate. And of course, when you're at a VO2 max effort, you're getting to maximum heart rate. So somewhere between 70 and 85% of the variability in VO2 max is accounted for just by this one variable. In the show notes, we'll include a whole bunch more detail on this if anybody kind of wants to nerd out on this stuff. I love this stuff, but I don't want to spend any more time on it right here. So as I kind of alluded to, it's very tempting to, and I want to apologize if I've ever created the impression or oversimplified this, and it's possible that I have. Zone two is what you do exclusively to build your base, and high intensity workouts is the only thing you do to build your peak. As I said, these systems work together. And if all you did was zone two, you would absolutely get a wider base. You would also raise your peak. Similarly, if you did higher intensity training, you would increase your peak, but you would also widen your base a little bit. The key, as we'll get into in the nuance, is what is the optimized way to utilize time around different volume and intensity requirements? So how much total work can you do? How much cardiorespiratory fitness training can you do? that's probably the single biggest determinant, but that involves a min-max problem, which is a big part of what we going to talk about today So that how I think about the triangle When talking about zone two you often talked about fat oxidation mitochondria lactate Oftentimes I think these terms can be a little confusing for people And so I think it always helpful to kind of relook at them and explain it. So do you mind just spending a few minutes walking through the cellular mechanisms that are involved in cardiorespiratory fitness, just so everyone is kind of familiar with the terms you may or may not use throughout here? Yeah. So it's really funny because I've noticed some amazing memes on Instagram where you basically have people that are making fun of anybody that uses the word mitochondria. So somehow, because I don't really pay attention to the wellness influencer health space, apparently the word mitochondria is now just one of those buzzwords that you should throw around as much as possible. And so if you're playing sort of wellness influencer bingo, you're going to get a lot of points for mitochondria. Can't remember some of the other awesome words that are just basically pathognomonic for buffoonery. Have you seen any of these memes? They're amazing. It's like mitochondria, inflammation, gut biome, like they've got all the buzzwords. Protein, another one. Protein, I'm sure. You've set me up now to trigger a bingo card, but I guess you're right. You can't have this discussion without doing this. So hopefully I'm going to get an exemption for my use of the word mitochondria here. At the foundation of your cardiorespiratory system are these organelles called mitochondria. And of course, all of you who took a high school class in biology will remember that they're referred to as sort of the little power units of the cell. And the majority of our ATP is produced by them. And again, ATP is the currency for energy. Just because I can't resist giving one more level of detail. The way ATP work is they donate. ATP has three phosphates. They donate one of those phosphates, and it's that liberation of energy that comes from that chemical bond that creates energy. The mitochondria can generate ATP from either fatty acids or pyruvate. Pyruvate is an intermediary breakdown product of glucose via a process called glycolysis. And both of these processes are constantly occurring. It's just, the question is, what's the balance in which they're occurring? And of course, are these both equal? No, they're not. Each process has a trade-off. The trade-off would simply be stated this way. If you are optimizing for efficiency and you don't care as much about the speed with which you can deliver ATP, you want to take that more aerobic pathway, meaning utilizing oxygen and shuttling the breakdown product of fatty acid or glucose, either in the form of pyruvate or acetyl-CoA into the mitochondria to use an oxidative pathway to generate lots of ATP per units of carbon that go in. The problem with that is as the demand for ATP accelerates, you have to make a trade-off. You have to make a sacrifice. The body says, I'm sorry, I can't do this anymore. I have to go down this quicker path using glycolysis where I turn glucose into pyruvate, ultimately into lactate, I don't get nearly as many ATP for it, but I can deliver much more ATP to the muscle. Now, I can't do this indefinitely. There's a whole problem associated with that, which we'll talk about, but that's effectively at the high level of the trade-off. So another way to think about this is through the lens of the fibers that are involved. And again, these are terms we've used on the podcast before, but the goal of this podcast is to kind of tie this all together. So at lower intensities, you have these type 1 or slow twitch muscle fibers. And again, I think the term slow twitch, it does to some extent reflect the speed with which they twitch, but I think a more important way to think about them is they're slow to fatigue and they're more endurance-based fibers. So again, at lower intensities, they're the ones that are doing all the work, very rich in mitochondria, deep red. They excel at oxidizing fat and they're very, very efficient. As the intensity increases, we have to start recruiting more of the type 2 fibers. These are fast twitch fibers, which again are more contractile in their force, but they are also fast to fatigue. They have less mitochondria and they're going to recruit and rely more heavily on glycolysis. That's happening outside the mitochondria. So initially lactate, which again kind of gets a bit of a bad rap, but again, we've done an entire podcast on this and we'll link to the podcasts on this topic. But the most important of these is definitely the one with George Brooks. Initially, the lactate gets recycled locally. So it's shuttled to neighboring type 1 fibers. It gets generated in a type 2 fiber, gets shuttled to a type 1 fiber, gets converted back into pyruvate, and then the pyruvate goes into the mitochondria to produce more ATP. That's called the lactate shuttle. But again, these things are constrained by demand. And therefore, as output increases and demand increases, lactate production in the type 2 fibers begins to exceed the capacity for what can be done locally in the mitochondria adjacent. And at that point, lactate spills into the bloodstream. So if you were measuring lactate in the bloodstream with a continuous lactate monitor, which by the way, these things are easily in prototype and there's some that are probably the market. So this will be something you can appreciate in the future. You might start out an exercise session where your lactate is resting at 0.5 millimole. Everything I just described up until this point would not increase that, even though locally lactate levels are rising. But once it starts spilling into the bloodstream, now you actually have to rely on other tissues in the body, the heart, other muscles that are not being utilized at this point in time. They have to start clearing it using lactate as fuel, as we've even learned from George Brooks, the brain will do this as well. The liver also can convert that lactate back into glucose via gluconeogenesis. And this basically allows the body to maintain certain levels of lactate at a new baseline that is above the original baseline. This is usually referred to as the first lactate threshold. And again, for a metabolically healthy individual and someone who's metabolically flexible, meaning they can go back and forth between utilizing glucose and fatty acids, this falls at about two millimole of lactate. That is what we refer to as zone two. Again, if some of those conditions aren't met, if you're not a metabolically flexible person, using that first threshold of lactate at two millimole is not going to happen. There are people who walk around at rest with a lactate level above too. Okay. But the point here is you can maintain, you're now at a new steady state where, if you remember, the first steady state is where the local tissues are able to offset lactate production at the rate that it's being produced. Consumption and production are equal locally. Then you have this second level, which we refer to as the first lactate threshold because it's the first one we're measuring in the plasma. And that's where now the systemic tissues are able to balance it. but now we get to a third level of lactate, which is really called the second lactate threshold, and that's at higher and higher levels. And at this point, once the body gets above that level, and this level varies quite a bit by individual, maybe if we have time, I'll go into how you can measure that. I talked about this at length in the first podcast with Olaf, Alexander, Boo, but we can come back to that. But anyway, these higher levels of output, glycolytic lactate production in the working muscles completely surpasses the body's ability to clear it. At this point, blood lactate starts to rise much more sharply. It's accompanied by hydrogen ion because the lactate is negatively charged. The hydrogen is positively charged. So they're balanced kind of one-to-one. You have this acidity that occurs. It turns out that it's the hydrogen ion and not the lactate that is effectively poisoning the muscle. It actually prevents the actin and myosin filaments in the muscle from being able to relax. Again, And for most people, that second lactate threshold or really third one, depending on how you're counting them, occurs somewhere between four and five millimole of lactate. That's a much more variable number. Okay. So I'm going to stop there. There's a lot we could talk about there, but hopefully that kind of sets the groundwork. Very much so. I think maybe worth clicking on to zone two before we get further in a little bit of a different way, because it seems like there's been a lot of discussion lately on whether it has unique benefits, whether it's just better to focus on higher intensity work only. So how do you think about this question? I think it comes down to context. I think there's a lot of confusion around this. So hopefully I'll do my best to dispel that. There's ideas out there challenging the idea that zone two is special or magical or there's anything that's good about it. And there are certainly people who would assert that high intensity work produces the same or even greater adaptations. and I think honestly in the framework that some people are proposing that it is true. So let's now think through this. For the proponents of high intensity exercise, people who say don't waste your time doing zone two, the shorter the amount of exercise time that a person has, the more true that is. Because remember something I said a few minutes ago, which is if you really want to maximize the area of your triangle, nothing beats volume. Now walking won do it so you have to get to zone two this first place where you have some adaptation but the more time you spend there the better And so if we going to talk about a professional athlete or even a recreational athlete, if you're going to talk about 10 to 15 years ago, the way I train, where by some miracle, I still was managing to spend 14 to 16 hours a week on a bike, then we can get into the nuance of how that time should be divided. So now let's turn this over to someone who's going to adhere to the general guidelines. So the general guidelines says you should exercise ideally 150 minutes per week. So that's two and a half hours per week. And I'm sure the guidelines would be happy if you did more, but that's what we're trying to get people to. Most people are not exercising two and a half hours per week. And truthfully, if that's all you can adhere to, then zone two is not going to be an efficient use of your time because it doesn't provide a sufficient enough training stimulants to drive the adaptations to make the triangle bigger. And remember, that 150 minutes is total exercise. Well, part of that's going to have to be some resistance training. So even if you said, I'm going to carve out an hour for two 30-minute resistance training workouts in a week, then you've got an hour and a half for cardio, truthfully, I would say then all of that time should be done at high intensity. You should probably have two 45 minute high intensity workouts. But when I talk about training, and maybe I should be, but I'm generally not talking to that population. When I'm talking to my patients in that population, it's a different story. And we do. We're very clear that if you've only got two and a half hours this week to exercise, we're going to craft your program around that. But I'm talking to a person who is really thinking about how to optimize and achieve their best results over both lifespan and healthspan over decades. And if that's the case, then you're going to need more volume than 150 minutes a week. And then that means you're going to have to utilize different levels of intensity. So because zone two is this point at which lactate rises to the level where it's now in the bloodstream. So local tissues can't clear it, but your body is able to clear it. You're stressing the system. This is the first place where you're now really stressing the system enough to recruit more glycolytic fibers. But what's nice about this is the intensity is low enough that you can keep going for a long enough period of time. And this is why endurance athletes who are training for 15 to 20 hours a week are indeed spending basically 80% of their time in this zone, because the intensity is low enough that they can do it for so long, and yet they are still getting a training adaptation. So if you are training in zone two, while you're not getting as much adaptation as you're getting at zone five, you're still applying a strong enough training stimulus to activate both fuel systems, right? So you're not maximal, but you're near maximal for fat oxidation. You have some glycolysis, you have lactate shuttle, but you don't have the wear and tear of the acidity and the fatigue that comes when lactate production completely overwhelms clearance systemically. So again, you can pack in volume of training in a way that you can't with very high intensity. There are other benefits to zone two, by the way, if you're an athlete, which is it comes with the benefits of improved movement efficiency. I discussed this on a podcast as well. So I guess I hope that clarifies kind of the context around one versus the other. And looking in terms of spending more time than the bare minimum when it comes to exercise, how does then exercise intensity play a role into the relationship of volume and sustainability? Once you're not constrained by that 150 minutes per week, and honestly, that's my hope. My hope is that everybody listening to us right now, even though once in a while they might be constrained by that, but that they can find more time to exercise, the limiting factors start to become fatigue and recoverability, and even to some extent adherence. And I think that especially as you get older, fatigue and recoverability become real limiting factors. So higher intensity workout, workout in zone five, very important and should always be a part of your training. You can't do that much of it once you get into your forties and fifties. When you're in your twenties and even into your thirties, you can still hammer these workouts, but I can't do those workouts three or four times a week anymore. And I don't think most people listening right now can either. So if you're going to be able to devote more time to your training, you're going to have to be able to do so at a lower physiologic cost. And again, volume drives adaptation. That's the thing to remember. It's volume above all else that's driving adaptation, provided that volume is at least at zone two, where you start to undergo all those changes we discussed. So basically there's a cost of doing high intensity work. And by the way, part of that is an adherence based. It's more painful, it's more fatiguing and it's harder to sustain. So one of the things I tell patients who are bored when they're doing zone two is look, use it as an opportunity to get really caught up on your favorite podcast or your favorite audio book or something like that. Something that frankly is a little bit harder to do during a high intensity workout where you're probably not as able to concentrate rather. So taking it back to basically the critics of zone 2, they're correct in a narrow sense in that per unit time, high intensity training delivers more physiologic adaptation, but they're kind of wrong in the way that it matters. It's not that zone 2 is magical, it's that it's practical and it becomes more and more valuable as your volume increases. So in short, I think zone two is the cornerstone that lets you do enough work, enough volume safely and consistently so that you get the adaptations you need to be an athlete for life. Moving on now to look at how someone can measure zone two and VO2 max, understand what they are. When is it useful? How do you go about measuring it? And let's start with zone two, just because we were on that thread. Thank you for listening to today's sneak peek AMA episode of the drive. 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Users should not disregard or delay in obtaining medical advice from any medical condition they have, and they should seek the assistance of their healthcare professionals for any such conditions. Finally, I take all conflicts of interest very seriously. For all of my disclosures and the companies I invest in or advise, please visit peteratiamd.com forward slash about where I keep an up-to-date and active list of all disclosures.