The Truth About Zone 2 Cardio, Mitochondrial Health & How REHIT Beats It (In Less Time!) With Ulrich Dempfle

My name is Ben Greenfield and on.

This episode of the Boundless Life podcast.

We'Ve spoken about HIIT and how HIIT is very effective. Researchers then looked for the minimum effective dose of HIIT and found that two 20 second sprints, so 40 seconds total at maximum intensity, and creates a very robust, very strong training stimulus through that AMPK AMP pathway, which actually also releases and activates PGC1 Alpha, your body's master regulator of mitochondrial biogenesis, and creates a very robust stimulation to also develop more and more efficient mitochondria and a number of other adaptations that very substantially improve your VO2 max, your cardiorespiratory fitness with much, much less time.

Welcome to the Boundless Life with me.

Your host, Ben Greenfield. I'm a personal trainer, exercise physiologist and.

Nutritionist and I'm passionate about helping you discover unparalleled levels of health, fitness, longevity and beyond.

It is a hot topic, I think, amongst many popular exercise, fitness and health podcasts. This idea of what is often called Zone 2 training. Zone 2 training, it's all the rage right now. Everybody talking about Zone two for fat loss and Zone two for cardio and Zone two for longevity. But I've never really done a podcast in which I have addressed Zone two or even compared and contrasted it to other methods of training, particularly for cardio. I realize that even I often during this podcast am accused of doing Zone two training on my treadmill while I'm interviewing my guests. Just a quick aside, walking on a treadmill would actually be something more like Zone one. However, we'll address a lot of this on today's show. We with a guest who was on the podcast several years ago. So it's been a little while. His name is Ulrich Demfle. He is not only a guy who has a great deal of knowledge in the realm of cardiovascular training, but he's also the CEO and the co founder of a company called Carroll Carol makes a bicycle, stationary bicycle that I use for interval training, not for Zone two training, but for interval training. And Ulrich and I have been exchanging some emails back and forth about this idea of Zone 2. He has some interesting ideas and I thought it would be cool to have him back on the show. So Ulrich, welcome.

Thanks so much for having me, Ben.

So I know that in our first podcast, Ulrich, we talked a lot about the bicycle that you helped to develop and I'll certainly link to that in the show notes. And the show notes for everybody listening in are going to be at BenGreenfieldLife. Zone two myth that's BenGreenfieldLife.com zone two myth. Like zone the number two myth. So, Ulrich, let's jump right in. What exactly is Zone two training? How do you describe it?

Yeah, so Zone two training is a cardio workout at a slightly lower intensity, as we would usually do it. So where you'd still be able to hold a conversation and speak in full sentences, even though uncomfortably so. The intention is that you train at the point where you. Where you. Where your muscles still use predominantly fat as the fuel to power the exercise, rather than carbs, glycogen. And because of the fairly low intensity, zone 2 workouts tend to be longer and have to be longer to create a meaningful training stimulus. And the suggestion is from some of the leading proponents that sessions are or should be 60 to 90 minutes. And the outcome that we're trying to achieve with that would be increased mitochondrial density and increased mitochondrial efficiency so that over time, you can increase the intensity at which you can exercise while still using mainly fat and increase your capacity to clear lactate. And that becomes really important for athletes to race harder for longer.

Yeah, I think that's a pretty fair description. It's kind of funny. Back when I was studying exercise physiology, we didn't really use the term zone 1, zone 2, zone 3, zone 4, zone 5. And in some cases, depending on what zone training system you're looking at, not to make things too complex, Zone six, typically we would look at what's called ventilatory threshold, meaning you'd have the first ventilatory threshold where lactic acid starts to accumulate. You just noted that that also might be in zone two, where you can be moving, but conversation is beginning to become uncomfortable as lactic acid just starts to accumulate. And then you have a second point we call the Ventilatory Threshold 2 or VT2, and that is often synonymized, if I can kick out that word, with Zone four, which. Where lactic acid is beginning to accumulate or is accumulating at a much faster rate than it can be buffered. And that's where we really get into the burn in what you've seen in terms of looking at Zone two. Ulrich, have you come across the idea of Zone two defined as like a percentage of your maximum heart rate or percentage of VO2 max?

Yes. So there's several prescriptions as to the intensity you should train at, either linked to your maximum heart rate. So can be some. And it really depends on the system you train with. Some people say from 65 up to 75, 80% of your maximum heart rate to hit that zone 2 threshold and the more precise ways to find that threshold would be either through gas exchange analysis or really through blood lactate testing to find that point where you predominately metabolize fat and not yet switch to carb and glycogen metabolism in your muscles.

Yeah, the lactate test is actually something I used to do quite a bit when I was training for triathlon and coaching people for triathlon. We'd have a little blood lactate meter. I wish they'd make a CGM for lactate, a clm, I suppose it would be called. I don't think it exists. But basically people do an exercise session, they ramp up at increasing intensities. During that exercise session you typically from resting, when you lactic acid values see a slight bump in lactic acid, typically it'll approach about around 2 millimole or so in terms of the units that are being used. And we would typically identify that as, okay, you've reached your first ventilatory threshold. We're now detecting more lactic acid than you'd see at rest. And that might sometimes be called the onset of zone two. And then if you look at someone who maybe doesn't have access to a blood lactate meter or maybe they're not as obsessed with exercise as a physiologist, the question becomes, well, could you just approximate that based on a percentage? And you alluded to that, Ulrich. I think back when I was doing exercise phys classes, it was generally 60 to 70% of your maximum heart rate. And your maximum heart rate, if you don't know, it could be somewhat approximated by subtracting your age from the number 220. So like I'm 43, so my age approximated, maximum heart rate might be around 177. And so then if I take 60 to 70% or let's say 65% of 177, that gives me my approximate zone two. And then you alluded to the idea of fat versus carbs. I don't know what you think about this, Ulrich, but it seems like a lot of people think, well, there's an exercise intensity at which you're burning just fat and then there's an exercise intensity at which you're burning just carbs. But really I think a better way to think about it is you're always burning a mix. But at Zone 2, that's where the actual amount of fat oxidation would peak. When I say peak, depending on how fat adapted you are, that's the point at which you're burning like 50 to 70% ish of your energy from fat with a little bit of carbohydrates providing the rest of the energy. So as far as the approximate percentages, I think that's about where I understand that Zone two would lie. Have you come across similar idea in what you've looked at as far as Zone 2 is concerned?

Yes, and this is one of the first issues with Zone 2, that it is actually not a clearly defined term and everybody talks about the same thing when they Talk about Zone 2. In fact, if you did a keyword search on PubMed for Zone 2 training, you would find hardly any matches because it's not a defined term and it's not something that scientists study when they do trials and investigations in their labs. And so because it's really a popular concept, you'll find quite large variations in definitions. So you said 65 to 70 or 60 to 70, then medium 65. Others give quite different recommendations. So another approximation would be 180 minus H and then adding up to 10 if you're fit and well trained and deducting up to 10 if you're not that well trained. So there's a broad range of different definitions and that makes it harder to really discuss it and to back it up with scientific evidence. And we see that that leads to recommendations being put out that actually have quite little scientific evidence and serious scientists and we work with some of the leading researchers in that field just stay out of the debate because it's not a concept that matches their research. So they would research like lactic thresholds or Ventilatory Threshold 1 as you said, lactic threshold, Ventilatory Threshold 2, VO2, max level performance, all out performance. Those are clearly defined things that we have lots of data on. But Zone two is unfortunately not something that we have lots of data on and therefore the recommendations are less clear and there's less rigorous debate around this.

Yeah, I agree. I wish that folks could be a little bit less loosey goosey with what Zone two is and simply say, hey, you're at ventilatory threshold one or maybe slightly above it. And once you've gotten close to Ventilatory Threshold 2, you're going to be out of it. And that would simplify the concept for a lot of people. But for the general layperson listening in, yeah, Zone two you're out on a walk, you start to walk faster, it gets harder to talk, you're pretty much about in zone two and then you start sprinting, things start to burn. You really feel the Lactic acid accumulating, maybe even get that metallic or bloody, as gross as it is to think about tasting your mouth, you're pushing more towards Zone four. Plus at that point. Now, you also mentioned, Ulrich, the amount of time that Zone 2 is generally considered to fall into and in terms of how long one would be exercising. I think you said like a typical session is 60 to 90 minutes.

So that's the recommendation. So if you listen to what some of the leading proponents of Zone 2 training put out, it's suggested one should do 60 to 90 minutes, three to five times per week, which is a phenomenal amount of time. And you have to view that really in the context of most of us, Most of Americans, 95% of Americans struggle to exercise. And the number one reason being lack of time. So having a recommendation for such enormous amounts of exercise volume at low intensity and making that the top priority for the cardio component of your workout program seems for us slightly hard to understand. And in fact, we actually take some issue with that. We think it's the wrong recommendation for the majority of people.

Yeah, I actually talked about this a little bit in my book, the first book I ever wrote on endurance. It was called Beyond Training. And I discussed how there's two different ways to increase mitochondrial biogenesis. One is via pathway called PGC1 Alpha, and that indeed involves like 60 to 90 minute sessions. You could make a case from some newer research that you'll see a little bit at like 30 to 45 minutes, but generally 60 to 90 minutes. And then there's another way to increase mitochondrial biogenesis via a different pathway. I believe off the top of my head it's called, I wrote the book, so I should know. The AMP K pathway. Yes, correct. And am I right? Am I remembering that?

Yes, absolutely, absolutely.

Okay, so the AMP K pathway, and that's kind of like the cheat code way to do things, albeit possibly higher risk of injury if your joints aren't ready for it. Even though I think a bicycle is a safe way to do it. And there's also a little bit more of a pain cave aspect. Right. You have to be willing to say, okay, I'm going to hack time, but it also means I'm going to go to the pain cave. But that's a different way to increase mitochondrial biogenesis. So kind of like two different ways to do it. But I think that one of the things that's interesting, I'd love to hear your take on this is you see people saying, well, a lot of the world's top Endurance athletes, they actually do a lot of training in Zone two and even use a so called polarized training approach, like 80% of the training in zone two and then 20% at very, very high intensities. And not a lot of time spent in the middle in the so called the gray training zone or the waste of time training. Z. What do you think about that concept that a lot of endurance athletes, like professional endurance athletes, use a high amount of Zone 2 training?

First, it's a proven concept for professional athletes, for really athlete athletes that works really well. But you have to ask, why do they do that this way? And there are some really well, simple explanations. One of them is you simply cannot do more than five to seven hours at really high intensity each week. So if you train 25, 35 hours per week, which those professional athletes do, then their maximum at high intensity is five to seven hours. And once those five to seven hours are scheduled in for the week, they fill up the rest of the available time with low intensity work. And that just works out at an 80, 20 approach. In discussions with some of the top researchers in the field, it's very clear that just because that works for a professional person that trains 30, 35 hours per week, it's not at all clear that that should be an optimal approach for a regular person who trains maybe a couple of hours or even less per week. And that's something that has literally trickled down from the leading Tour de France teams into the mainstream.

You took the words out of my mouth, by the way. I was going to say the trickle down effect, similar to what you see in bodybuilding. People are like, well, to build muscle you got to do, you know, buys tries on Monday or chest on Tuesday, shoulders on Wednesday, you know, maybe legs and core on Thursday. And what people don't tell you is that most of the bodybuilders gaining significant amounts of muscle using that approach are spending two plus hours per day in the gym to adequately exhaust each of those muscle groups. Which works if you're a gym junkie and that's your happy place. But most people don't have that amount of time at their disposal. And you were just saying you see this trickle down effect from say like Tour de France cycling, where people see these massively successful endurance athletes doing that amount of Zone two training. But that doesn't mean that unless you're a professional athlete, that approach is correct for the general population. One thing I should note, Ulrich, I'd love to hear your thoughts on this is I think one of the reasons A lot of successful endurance athletes have so much time in the bike saddle or on their feet running, so to speak, at Zone two is because they're racing for very long periods of time. You have to condition, like your butt callous to sit in the saddle for that long, or you have to condition your running issues, your joints, to be on your feet for that long a period of time. But again, how well does that translate to the general population?

Yeah, exactly. So. So if you do these stage races where you, for three weeks spend every day, six hours in the saddle. Yes, absolutely. If you didn't do that with a lot of preparation, having sat in a saddle before you.

Yeah.

You'd get very sore very quickly and probably drop out. So, yeah, it perfectly makes sense for them. But the recommendation for the general public then to say, oh, you should do 80% in zone two and 20% in zone five, and by the way, zone two should be your priority is very questionable because if you look at some of the scientific data that we can try to use to assess Zone two training, there's some not very flattering things in there. So if you were so good to actually follow government guidelines and you did 150 minutes of cardio each week, but you did it only at zone 2, 40%. 40% of people will not see an increase in their VO2 max in their cardiorespiratory fitness. And that would be a lot of time wasted, in effect.

Well, not wasted. I mean, those people would actually see an increase in mitochondrial biogenesis. But maximum oxygen uptake, this VO2 max.

Yes.

You wouldn't see a significant rise in that compared to using something like interval training.

That's correct. Yes. And I should be careful here because exercise is really so positive. I don't want to talk down any type of exercise. And if you love Zone two and you listen to great podcasts or watch your favorite shows, or you're actually outdoors with people you like and you manage to do a substantial amount of zone through training, it will be for sure good for you. Yeah. And improve those aspects of metabolic health and boost your mitochondrial fitness, your mitochondrial density and efficiency. But if your aim is to improve your VO2 max, which is a probably the most important health marker, and you don't do Zone two training. Right. So maybe two short sessions, maybe not getting the right intensity or. So there is a risk that you don't get as much return on the time you invest than you would with other exercises.

Yeah. And I think one thing to note here is that anytime we're talking about exercise research, we have to consider trained versus untrained populations. I think you mentioned that 40% of people will likely not see a significant increase in cardiorespiratory fitness or VO2 max with that 150 minutes of zone 2 per week. But the problem with that research is it doesn't do a good job differentiating between sedentary, totally untrained individuals and people who are already exercising a bit. I think that if people are just getting started, they're going to see increases. And I'm not just saying I think, I mean, research has shown those people are going to see increases in their VO2 max even with Zone 2 training. But it's not going to be the most efficient way to maintain or continue to increase VO2 max once you're actually kind of in that realm of being a trained individual.

Yeah, that's correct. That's correct. But then on the other hand, so actually a lot of research is done on relatively sedentary individuals because that is the broad. Well, that's the majority of the population. There's actually relatively few people who are in great shape. And the research on athletes. So you have basically some research done on athletes, really highly trained, a lot of research done on your average Joe, and I guess less on moderately well trained, well trained athletes, not pro athletes, because it's just a smaller group and maybe of less scientific interest, I guess.

Yeah. I think the other thing to bear in mind here, just so people don't get confused, even though I briefly alluded to it earlier, is there's another term in exercise physiology known as non exercise activity thermogenesis. Moving at low intensities throughout the day. Gardening, cleaning the garage, cleaning the garage with a weighted vest on. Taking the stairs instead of the elevator. Walking around the airport while you're waiting for a flight to depart, rather than sitting there waiting to sit some more, which completely annoys me. All of that would not be considered Zone two training unless you're cleaning the garage like you've just snorted cocaine. For the most part. I don't even classify any of the things that we're talking about when it comes to Zone 2 training as fitting into that category. Even me, like I mentioned earlier, walking on a treadmill while I'm talking to you. This is an easy conversational pace for me. Obviously it's not something I would be considering a way to increase mitochondrial biogenesis or VO2 max. But I will say that moving at these low intensities during the day, I think the biggest value for that approach that Neat approach is, number one, you control blood glucose very effectively, so you have lower amounts of glycemic variability. And number two is you burn some extra calories. Right. So I think moving at these low intensities during the day versus traditional Zone two training, those need to be chunked into different categories.

Absolutely. No, that's right. Those are different things. And zone two is substantially higher than I think sometimes is suggested. So what sounds as low intensity and oh, you can still talk. Once you do that for 60 to 90 minutes, that is actually quite hard. So you will definitely sweat. Well, your butt will hurt if you're on a bike and if you go for a run, your ankles and feet might hurt. So Zone two training, if done as proposed, even though it's relatively low intensity, becomes also quite strenuous.

Yeah, this is, I think back to the calorie burning piece. What does confuse a lot of people because many of the people that we're talking to right now, Ulrich, they're not training for an ironman per se or wanting to break a three hour marathon. Many of them are concerned about body composition, fat loss, et cetera. Now you and I already both said this, that you see higher amounts of fat oxidation when training at Zone two. And as you get harder and harder with your training, you shift more and more towards carbohydrate utilization. Why is it that zone two is so often hyped as something that is the most effective way to improve body composition or burn fat? And what are your thoughts on that approach?

Why is it hyped that way? I don't actually know. I guess if you talk about it's the exercise where you burn most fat to fuel the exercise. The immediate conclusion, well, it must be great for fat loss because it burns fat, but that's just not the case. It's as effective or as ineffective for fat loss as other forms of exercise. Because yes, your muscles during the exercise use mainly fat for fuel, but your body is quite capable of regulating different energy sources dynamically. And if you use more, say sugar or carbs during a workout, that will just lead to increased fat oxidation after the exercise. And for weight loss, everybody should be entirely clear that nutrition and your overall energy balance is just much more important. And so while exercise is clearly very helpful, the primary role is really to make you fitter and stronger rather than to help with weight reduction.

The way I think about this is we have this Zone 2, often called the fat burning zone, which it is, I mean, compared to like lactate threshold or very high intensities. But that doesn't mean it's the best fat loss zone or weight loss zone, meaning that I could be in zone two burning, let's say 60% fat and burning maybe, I don't know, 200 calories per hour. And if I exercise at higher intensities, let's say I'm burning 800 calories per hour, but only 40% fat, I'm burning a much higher proportion of not only overall calories, but overall fat. And then as you just alluded to, I don't think you use this term per se, but my post exercise oxygen consumption because I'm sucking wind afterwards and the body temperature is elevated dictates I continue to burn more calories longer after a high intensity session or an interval session versus a zone two session. That's kind of the way I think a lot of people kind of incorrectly address this is they assume I'm in fat burning zone. Therefore this is the best way to lose fat.

Yeah, absolutely. No, for fat loss and weight loss per se, nutrition is just the 1, 2 and 3 is so important. Where I think exercise can really help. Yes, obviously it increases your calorie consumption and therefore helps with your energy balance. But in terms of improving your metabolic flexibility, improving your insulin sensitivity, your ability to access fat from storage, and therefore being able to also reduce calorie intake and for example, have longer fasts without starving your brain of energy, I think that becomes a really important adjunct and supportive role where exercise helps. Whereas if you're insulin resistant and have metabolically inflexible, it just becomes much harder to reduce calorie intake. Have periods of fasting and your brain is. That's at least how I look at it, is screaming at you when you're not eating enough.

Yeah, I should say I have a lot of clients who are on fat loss programs. I have many of them doing a little bit of fasted zone two in the morning. And I'm very straightforward with this. I tell them, look, this isn't going to improve your fitness or burn calories as quickly as you doing high intensity interval training in the morning. But what I found is I can get an overweight person to roll out of bed and do 20 to 30 minutes of zone two, like brisk walk around the neighborhood. You know, even like walking the kids to school or taking the dog for a walk with a weighted vest, et cetera, consistently, day after day, because there's very little cognitive resistance to getting up and going for a brisk walk. Whereas for a lot of people to get up and within an hour of Waking, like hit it hard, lift weights, do high intensity interval training, they're just that much less likely to do it. I think you even mentioned earlier, the best kind of cardio is the kind that you're going to actually do. So I still use zone 2 training with a lot of my clients, not because I'm convinced it's the superior method, but because I can get people, especially for like a morning session, to do that fasted. And then I simply have them either have a quick fueling session and move into weight training or interval training, or depending on their time limitations and schedule, do the weight training and interval training later on in the day. And I'm a big believer in this idea of a two a day workout session. Anyways, if you want to maximize your results is do something in the morning, do something in the later afternoon or the evening, and in an ideal scenario you're able to do something consistently every single day, preferably in a fasted state. In my opinion, that will spark fat burning early on. So I don't think zone two training is all bad. I just think that if your goals are efficiency and your time, you know, you're kind of needing to hack time. That interval training, which we'll talk about here briefly, is going to be a little bit superior.

Yeah, I think the time efficiency is like a really important consideration for many people. But you're absolutely right. The exercise that you can do consistently is obviously the exercise that's best for you. And then if zone two is something you can do, as you said, like in a fasted state, very much preferable to after like a meal or sugary drink or anything like that if you want to do it. Also, it's much better to do it standalone or in the beginning of your session. Yeah. And if you do zone training, then ideally you'd want to hit the right level of intensity and neither go too low or too high so that you really stay in that maximum fat oxidization window and then work that long enough, ideally 60 minutes or more, to get the benefit it offers.

Yeah, Although I should note that I think most of the research on zone two training, they're looking at cumulative volume per week, not the actual session length, 60 to 90 minutes. I don't know how that has become so popular, but really it's looking at the cumulative session per week or the cumulative volume per week. But it's difficult to get enough zone 2 training volume in unless you actually are doing 60 to 90 minute sessions. One thing I'm curious about though, that we haven't touched on yet with Zone two, Ulrich, is women versus men. Because women have more type one muscle fibers, they tend to oxidize more fat at submaximal intensities. They're not just men who smell nicer than men. Women have completely different physiologies. And I'm just curious if there's anything you found in the type of approach with a woman versus a man when it comes to Zone two intensities.

You're absolutely right in pointing that out. And I think what this leads to is again, it shifts the priority of Zone 2 further to the back. So women have more slow twitch fibers, have greater mitochondrial density at kind of on average than men, and have greater metabolic flexibility. So therefore the that the targets you're trying to achieve with the Zone 2 training are maybe slightly lower priority for women than for men. And then if you consider other factors affecting like perimenopausal women, where it does become fairly like harder to build and retain muscle mass, and where long endurance exercise can actually have a catabolic effect, the priority. And what should you, you should do in your program, whether zone two should be, should be the base. And the first is very, very questionable. So we think some high intensity interval training would be actually much more beneficial and more important. And then there's a lot of other things around resistance and strength training, maybe also mobility and flexibility training that would deserve a higher spot in your priority list of what you want to do. And of course the big Zone 2 advocates say, well, you just have to do it all. You have to do Zone two, you have to do hit, you have to do resistance, mobility, flexibility and so on. Sleep enough. But that's for most people, not a very realistic approach. And so if you have to prioritize, then Zone two would just not be the first thing. Like yes, if you have many, many hours per week, then it's a good addition. But if you're limited in what you can do, then there's other things that will give you just a much higher return for the time you invest.

Yeah, you mentioned it's not realistic. And again, we have to differentiate. I think about it like this. A lot of people think that Zone one is Zone two. I am a huge fan, like I mentioned earlier, of zone 1 training spread all throughout the day. If you want to call it training, I just call it movement. And then high intensity interval training and weightlifting for the actual fitness sessions. So don't consider the fact that Ulrich just said, well, Zone two training along with all the other stuff is not doable if you're not defining zone 2 training as actual ventilatory threshold 1. Right. The part where it's getting difficult to talk, carry on a conversation, you're obviously exercising, et cetera, that is not as compatible with trying to also do weightlifting and interval training as doing Zone one and doing the interval training and resistance training. So make sure that if you're listening, you have your definitions set up properly. When it comes to what is Zone two and what is Zone one, it's very similar to the idea that a lot of people, I don't think even definitionally have interval training set up properly in their minds. I see a lot of people doing, let's say a classic Tabata set, 20 seconds hard, 10 seconds easy, and they're 20 seconds hard, appear to be like 75% intensity when they're actually supposed to be, pardon the expression, balls to the wall, lactic acid bleeding out your eyeballs and ear holes to actually get the benefits of that Tabata set. So a lot of people think that Zone two is Zone one, and a lot of people also don't push hard enough when it comes to the actual interval training. Now the other thing I wanted to note, Ulrich, that you made a point about that I think, if I understand this correctly, is what you're saying is that women are naturally predisposed to do a really good job burning fat. They're probably going to feel even better than a man in terms of what they're naturally inclined towards to, to be doing Zone two training. But that doesn't mean that's what they should be doing. It means that they're already really good at that stuff. So they should be focusing on the stuff that they're not as good at, primarily muscle maintenance, muscle building, interval training, and the type of stuff that's going to be more favorable for long term health, longevity, fitness, et cetera, versus just sticking to what you're good at. Because you feel really good doing Zone two training and your body burns more fat than a man's, you should just do that form of training. Right?

That's absolutely right. Yeah.

Okay, so hopefully people have not been bored to death so far about us taking a deep dive into Zone two training. We've mentioned interval training a few times. The last time that I interviewed you, you talked about reduced. Sorry, it's R E H I T. What's it stand for again? Reduced exertion. High Intensity Interval Training.

High Intensity Interval Training. Yes, exactly. Rehit.

Okay, so get into that. Is that something that you coined? Is it research based, like Where'd this idea come from?

We've spoken about HIT and how HIT is very effective and it's got a lot of research to show, you know, the effectiveness, but it's very hard to do. You set balls to the wall, so the rate of perceived exertion is very high. And then people find it actually hard to perform and stick to. And so that is an issue with, with hiit. And researchers then looked for the minimum effective dose of HIIT and found that two 20 second sprints, so a short workout was just very casual warmup, not.

Not 220 seconds to 20, 20 second sprints.

20 seconds sprints exactly. So 40 seconds total at maximum intensity creates a very robust, very strong training stimulus through that AMPK AMP pathway, which actually also releases and activates PGC1 Alpha, your body's master regulator of mitochondrial biogenesis, and creates a very robust stimulation to also develop more and more efficient mitochondria and a number of other adaptations that very substantially improve your VO2 max, your cardiorespiratory fitness with much, much less time. And because two 20 second sprints are so short, even though you go to maximum intensity and you go all out, it becomes actually a fairly doable workout. One that you can do in a fasted state that you can do in the morning. And yes, two times 20 seconds. The 20 seconds feel they get quite long, but you always see the light at the end of the tunnel. And especially if time as it is for most people is a big barrier, that is just a solution that helps many, many people or can help many people to achieve their cardio fitness goals.

Okay, so walk me through this. Let's use the 2 22nd. Even though I know there's a few other flavors of HIIT, like 310 seconds, et cetera. Walk me through what that actually looks like. How long do you need to warm up to actually be ready to go hard for those 20 seconds? How long do you recover in between those two 20 second efforts? And now how hard does it feel? How hard are you working? I just asked you a three part question. I know, but fill me in.

So the warmup is anything from 20 seconds to two minutes. Whenever you're ready, you can initiate this all out sprint. And this is because it's on a bike that has multiple safety features and is in itself a very, very self safe exercise modality. So you can literally start the exercise and go to highest intensity, to maximum intensity after as little as 20 seconds. But most people spend a minute, up to two minutes warming up.

I'm A long warmup guy. By the way, if I do the carol, I know you have a setting on there to half the warmup time. I always need the full warmup. I've always been that way. For me to have a good workout, I got to have a good warmup.

That's all right. And of course personal preferences is important, but if you're really pressed for time, you could cut that short. The warmup. And you will probably perform a little bit better in your sprint if you warmed up a little bit longer. But in terms of getting a good training stimulus, you can achieve an amazing amount with very, very little warmup. Then in the sprint, you want to hit your peak power. And this works by accelerating to really high cadence and then dialing in your optimal resistance at the optimal time and then just pushing for as hard as you can. And that's what we've optimized our bike for. It does that automatically. You don't have to turn any buttons. We use AI to find the perfect resistance for you every single time. And we can do that because we have a ton of data. So we have now millions of rides from tens of thousands of riders. And that allows us to run really sophisticated models to create a perfect workout for you. So that's your first 20 second sprint. Then you have up to three minute recovery. That allows some of your really fast energy stores to replenish. So your phosphocreatine system.

Yeah. Creatine, phosphate, some ATP.

Exactly. Needs up to four minutes to recharge. Three minutes, you'll be in a good position to do a second sprint again. You go all out for 20 seconds. The first 10 seconds feel fine, then the next five seconds feel a little bit harder. The last five seconds you have to bite and you need to fight through. But you see the light at the end of the tunnel and it's so quick that it's, it's practically over.

I literally just count to 10 over and over again very quickly.

Yes. And then you have a three minute cooldown. That is the time you need for your heart rate to come down a little bit and most importantly, for your blood pressure to normalize. So after those all out sprints you, you create, well, you mobilize a lot of glycogen in your muscles. It gets broken down into some metabolic waste products, lactate, and actually water from your bloodstream, shoots into your muscles, feels all quite pumped and your blood pressure drops a little bit. And then kind of light pedaling after the sprint helps you move the water out of the muscles. Again. And for your blood pressure to normalize and you're finished.

Yeah, yeah. Clear. Some lactic acid, too.

Yeah, exactly. And so that means you can perform this workout if you're really in a rush, you can do it in as little as five minutes. And it takes up to. If you do the full, like, each period to the full length, up to 8 minutes, 40 seconds.

You've actually, I think, seen me at Health Expose, where you've had a booth there and help drop in. Cause I'm super busy at these things. I'm like, all right, I got five, ten minutes. Let's get the workout in. And it does suck. And you're feeling it during, but then it's pretty good after. As a matter of fact, if people are watching the video version. And Again, go to BenGreenfieldLife.com Zone 2 Myth for the show notes, and I'll put the video there as well. The bicycle you see right behind me when I'm recording podcasts, that's the exact bicycle that we're talking about. Ulric, you mentioned two things. You mentioned safety features, built in safety features, and you mentioned the ability to be able to use AI to set your actual resistance. First, what safety features are you talking about?

So first, an exercise bike is a very, very safe mode to train in itself. So if you tried the same on a treadmill, I think it would be outright dangerous.

Yeah. You'd be on a viral TikTok video potentially of the guy.

Absolutely, yes, absolutely that. And that just doesn't happen that much on an exercise bike. And then we've got a number of features to make it as safe as possible. So we have. It's called a freeway clutch freewheel clutch. So you can stop pedaling whenever you want. It's not that the flywheel is driving your legs. So if during the sprints, you get out of the rhythm, out of sync, your feet won't get yanked around. We track your heart rate, of course, during the exercise. And if, for example, your heart rate during the warmup is abnormally high, we would give you warnings. If your heart rate doesn't recover fast enough after the sprints, the bike would intervene and give you a warning or even aboard the ride, if that depends a little bit on the settings. So in gyms or some of our bikes are in offices, it's more restrictive. If you use it at home, you have choice over that. You can have that less restrictive. But there's these safety features built in to make it as safe as possible. And I mean, we've got now we've launched our bikes in 2018 and we've got now millions of rides and I'm very happy to say that we've not had a single severe adverse incident.

That's great. Although you need what kind of pre workout drink did I crank before I got on here? Settings so that if someone's heart rate is elevated, the Carol bike knows that they just doubled up on the espresso that morning. Yeah.

And if it's your bike at home, you can control the settings. So we're not nannying or mothering our users. You have choices there.

I know I personally like to recover at a slightly higher wattage than what you had built into the bike. So I just went in and adjusted the wattage. So I like to feel when I'm recovering, I like to feel more resistance versus it being completely easy. So I add a little bit of resistance for my recoveries. But yeah, it's all modifiable. What about the AI piece? Obviously that word is thrown around all the time these days, I think often overused and abused. So when you say AI, what do you mean?

The technical default is reinforcement learning. So it's the same way say Google trained the deep blue computers to beat the best go players. So it's a form of neural networks and we can run those across the data of now millions of rides from tens of thousands of riders and identify what a perfect ride looks like. If you do those all out re hit sprints, you hit your peak power after a few seconds, like very early on, three, four seconds, and then you fatigue throughout the sprint. And there is such thing as an optimal shape of that curve. So if it's too hard, you will fatigue too quickly and it becomes unpleasant and you grind to a halt if it's too soft. And if the resistance is too soft, you'll just push through and you will never reach your peak, because if it is your peak, you will only be able to hold it for a second. So we know what that optimal shape of the curve looks like by running those models. And we don't just know it generically, but we know it for somebody who looks exactly like you. And therefore we can tailor workouts for somebody who's 75 and maybe hasn't done a lot of exercise and just wants to start now, or somebody who's like a 30 year old CrossFit athlete at the peak of his fitness. We have the ability then to create a workout that's just optimal for that individual and also that keeps adjusting as you get fitter and stronger.

Or.

I had a bit of a skiing accident earlier this year, had to take a break from training. I was actually very grateful that my Carol bike dialed back the resistance. When I got back on it right.

It could detect that your peak power was dropping more rapidly during the sprint and adjusted that for future sprints. I think of this very similar to a lot of these variable resistance training weight training machines. Now, like the Tonall, the arx, they will detect if the amount of force or power in some cases that you're producing drops off and adjusts the weight as you go through the set to allow you to maintain good form and or to maintain proper time under tension or exhaustion by the end of the set. So similar concept but for cardio instead, correct?

Yes, that's exactly it.

Okay, now, bringing this full circle, obviously we've established that rehit is good. We've looked at some of the pros and the cons of Zone 2 training. But have you actually matched up the two in a comparison or in a trial to see? We could theorize all day long, but are there any studies or research that actually look at re hit at very low amounts of time per week, Zone two at higher amounts of time per week, which wins out?

Yeah, so that has been done. We have randomized control trials showing the performance of REHIT with very limited time investment. So three times a week, eight minutes versus 150 minutes of. And that was moderate intensity continuous training, which that is what most people would understand as Zone 2. And we had, yeah, very marked differences in. In the results. So VO2 max in a rehab group that spent less than half an hour a week went up by over 12% in 8 weeks. And in the moderate intensity in the zone 2 group, we had. We only saw improvements of 6.9%. So we, we did see those improvements. As you said, like if you're set in free, you. You get an initial benefit. But also the rate of non responders was higher. So, yes, the average in that group got an improvement. 6.9% is meaningful, is great, but much less with much more time.

You mean there were fewer non responders to The REHIT training versus the Zone 2 training?

Yes. Yes, absolutely. So the research we've seen, and this is the leading research in kind of the most credible research in that field, suggests if you do moderate intensity continuous training, zone 2, 150 minutes per week, that 40% of sedentary people would not see an increase in VO2 max. And this has been reflected in that study too.

Untrained people would see an improvement. Right. With Zone two or with rehit. But trained people would see more of an improvement with rehit, is that what you're saying?

There's less people who don't see an improvement, so you see a greater improvement. So the average is higher. The average is almost twice as high, and the rate of non responding is lower. So you'd have a much lower share of people who don't respond compared to Zone 2 training, where you have a higher share of people who don't respond.

That makes sense. But although back to what we said earlier, if you were to break that out between trained versus untrained individuals. Untrained individuals, you'd probably see a pretty good response rate to either modality, I would imagine.

The other thing is the whole concept of non responders has shifted slightly in the exercise research world. So a few years ago, it was the understanding that, yes, there is just a certain population, a certain share of the population that doesn't respond terribly much well to cardio training and that you have something like 10 to 20%, they can do almost what they want, but they don't respond. That has shifted slightly and it's from non responder more to slow responder. So they need more time. And if they stick to it and continue to do it, then eventually they will also, or the majority of those will also see a response. So that has been. Yeah, the mainstream opinion has really changed from there are non responders to, well, they're mainly slow responders.

Yeah. And that improvement in VO2 max, I mean, I know I've actually personally had people push back and be like, well, the Carol bike's only been around since 2018. How'd they actually study the claims that it adds two years of healthy life? It's actually healthy life expectancy. Because what you guys did, you said, okay, well, we see a 10% improvement in VO2 max. We know that that approximately correlates in exercise science research to two additional years of healthy life expectancy. Therefore, if this is what the Carrel is doing this quickly, we can approximate that you're increasing lifespan healthspan by approximately two years with that increase.

That's right. The research on VO2 max and what its relative importance is for longevity and life expectancy is ultra robust. So there are studies that followed tens of thousands, even hundreds of thousands of participants over long periods of times and where those endpoints were established and where we can see that VO2 max is the most important predictor for life expectancy, the strongest correlate for life expectancy and therefore if you have an improvement in VO2 max, it's quite reasonable to assume that this will have an effect of what you can expect in terms of your lifespan.

Yeah. Higher than, say, lactic acid tolerance. I wouldn't say higher than mitochondrial health, but VO2 max can be ascertained within 20 minutes in an exercise physiology lab. Assessing mitochondrial health is still a little bit loosey goosey. I recently interviewed the folks from a testing company called MI Screen. They've got a decent test for mitochondrial efficiency and mitochondrial health. But I think you can say, and I'm not sure if you agree with this, Ulrich, that If you're seeing VO2 max improvements, you are very likely seeing increases in mitochondrial biogenesis and efficiency without necessarily having to do a fancy blood test to assess mitochondrial efficiency or health.

Absolutely. And if you think about the two sides of VO2 max, one of it is oxygen delivery. So that's your lung capacity, your peak flow and your stroke volume of your heart, your plasma volume, blood capillarization. So everything that brings oxygen to your muscles, that's one part of VO2 max. But the other part of VO2 max is around oxygen utilization. So how much oxygen can you burn and how much oxygen can you metabolize? And that is exactly mitochondrial density and mitochondrial efficiency. And so it's a very, very large part in terms of what drives VO2 Max. And so, yeah, you're absolutely right. And so they're almost, yeah, two things of the same, bigger total and mitochondrial health. And mitochondrial function is critical for life expectancy. I'm absolutely sure about that.

Yeah. Lung volume in addition to blood parameters and oxygen utilization at the cellular level being kind of like the third component of VO2 max. Just basically how big are your lungs? How much volume can you move? So, yeah, if you address all three of those, then you're going to address VO2 max. Ulrich, I know we're getting close on time. Pretty straightforward model here. I know you guys are direct to consumer. So someone can order a Carol bike. And when they order it, the bicycles are not the lightest bicycles out there as far as delivery and setup. Any additional features that you guys have baked in as far as and ease of setup and use. For someone who wants this on like let's say a second floor apartment building.

Or something, we're quite happy. If you order one, the standard would be in a box and you assemble it yourself. And it's actually quite easy. We're very happy to do assembled service to a room of choice. So that is not the thing. That's very Difficult about the bike? No, not at all. We can do that.

Okay, cool. Regular outlet, no special 220 volt, just plugs into a standard outlet and you're good to go, right?

Absolutely, yeah. And maybe just also to in case there's any question, the bike can do a lot more than just rehit. In fact, even though we're not the biggest fans of Zone 2 and we think that Zone 2 has been overhyped, maybe a big claim now, but I would argue that our bike is probably the best tool you can use if you want to use to do Zone two perfectly at the moment. So we have like the zone based training where the bike will keep you automatically at kind of in the zone 2 and you can just go and yes, you can watch a movie and listen to your favorite podcasts and so on.

Heart rate monitor ties to the power and resistance on the bike based on. I don't know if you guys are using 220 minus age percentage of that or 180 minus age for approximating zone 2, but basically I can set that up, start riding and the bike will automatically keep me at that heart rate without me having to worry about pedaling easier or pedaling harder.

Exactly that. And the bike will also allow you to do a number of different fitness tests first so that you actually know what your maximum heart rate is, you know what your VO2 max, your FTP is, and then there is. This is not yet available, but it will be available very shortly because. Because Zone two is a big thing, a feature to lead you very precisely to exactly your zone 2 threshold based on heart rate variability. So this is quite cool new research that has come out that you can use not just heart rate or heart rate variability, but you can use the complexity of your heart rate variability. So this is another higher order to quite reliably find where your lactate threshold, where your VT1 is.

Oh, that's interesting. You mean you're using heart rate variability as a correlate to predict lactate threshold.

The complexity of the heart rate variability. This is, this is one step further. So you have heart rate, you have heart rate variability and then you have the complexity of heart rate variability and you can analyze that. It's called fractal analysis. And you have a metric detrended fractal analysis that you can use to very reliably find the point where your lactate threshold is. And if you think about other ways to measure that, you would need either a prick test and draw some blood. That's not very practical. You can Use gas analysis when you have a device like PNOE or COSMET or so to look at your respiratory exchange rate. But this is all not very practical for everyday use. And using heart rate variability to find that threshold is actually very possible if you have the right analytics built in and have the right heart rate sensor, heart rate monitor that tracks that, that's capable of tracking that and comes as a standard with each of our bikes. And therefore, yeah, I'm quite convinced that Carol Bike, as ironic as it might seem, is actually the most powerful tool to do Zone two training. Right. If that's what you're into.

Well, I'm not a fan of spending 90 minutes on a bike, but that's super interesting. About the test for VO2 functional threshold power and lactic analysis, I assume I have no WI fi at my home, so whenever I want to kind of update my Carol, I just tether it to my phone. I'm assuming that that would just be something that will roll out as a software update once it's ready.

Yes, absolutely. So the analytics are largely completed, and so we're looking probably the next two or three months that will be a software update to make that available to all our members.

That's incredible. All right, you got to remember to email me if I want to be the first to try. Well, cool. This is fantastic. I know we're about out of time, but again, if folks go to BenGreenfieldLife.com Zone2Myth, I know we have some kind of a discount code or something for Carol. I'll make sure I put it in there. I'll link to my previous episode with Ulrich as well, and also anything else related that I've podcasted about when it comes to cardio and Zone two. So, Ulrich, thank you so much, man. This has been incredible and yet another fascinating discussion.

Thank you.

All right, folks, well, if you don't want to build up a butt callus on the bike, you've now learned how to avoid doing that. And until next time, I'm Ben Greenfield along with Ulrich Demfle from Carol Bike, signing out again. The URL is BenGreenfieldLife.com.

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