Is Zone 2 Cardio a Waste of Time? The 10-Minute Workout That Beats It (Backed by Science!)

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, 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 maximum. Your cardiorespiratory fitness with much, much less time.

It is a hot topic, I think, amongst many popular exercise, fitness and health podcasts. This idea of what is often called Zone two training, Zone two 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 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 show 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 Carol. 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 Zone2Myth. That's BenGreenfieldLife.com Zone2Myth. Like Zone, the number two myth. So Ulric, 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 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. Um, it's kind of funny. Back when I was studying exercise physiology, we didn't really use the term, you know, zone one, zone two, zone three, zone four, zone five. 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, like, 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. Oreck, 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 two 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 lactic acid values, see a slight bump in lactic acid, typically a little 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 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 50 to 70% ish of your energy from fat with a little bit of carbohydrates providing the rest of 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 definition. 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 horizon 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 ventilatories. Threshold 1 as you said, lactic threshold, ventilatory threshold 2, VO2, max level performance, all out performance. Those are like 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 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 accumulate, 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 in terms of how long one would be exercising. I think you said 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 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. And am I right? Am I remembering that right?

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 also a little bit more of a pain cave aspect. 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 zone. 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.

So 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 buys tries on Monday or chest on Tuesday, shoulders on Wednesday, 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 shoes, 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 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'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, 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. Yeah. Wasted, in effect.

Well, not wasted. I mean, those people would. Would actually see an increase in mitochondrial biogenesis, but maximum oxygen uptake, you know, 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 2 training, it will be for sure good for you 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 two 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 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.

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, you know, versus traditional zone two training, those need to be chunked into different categories.

Absolutely, 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. 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 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.

Yeah, 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. It's so important.

Where, 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 metabolically inflexible, it just becomes much harder to reduce.

Calorie intake. Half 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, 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.

Even 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, 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 two 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 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 kind of spark fat burning early on. So. 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, you're kind of, you know, 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, 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, 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, yeah, 60 minutes or more to get the benefit it offers.

Yeah, 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 a.

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 targets you're trying to achieve with Zone two 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 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, right? 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 like, 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 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? Where'd this idea come from?

We've spoken about HIIT and how HIT is very effective.

And it's got a lot of research to show 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 hit.

And researchers then looked for the minimum effective dose of HIIT and found that two 20 second sprints. So a short workout with just very.

Casual warmup, not 220 seconds to 20 second 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 yeah, 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? You know I just asked you a three part question. I know, but fill me in.

So the warm up 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 warm up guy by the way. If I do the carol I need, I know you have a setting on there to, 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 gotta have a good warmup.

That's all right. And of course that 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 warm up. 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 phosphopreatine system.

Yeah. Creatine phosphate, some ATP.

Exactly. Needs like 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 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 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.

Yeah, yeah. You've actually, I think, seen me at health expos where you've had a booth there. And I'll drop in because I'm super busy at these things. I'm like, all right, I got, you know, five, ten minutes. Let's get the workout in. And it does suck. And you are, you know, you, you're, 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. Ulrich, 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, if the guy flying off.

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 warm up 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 abort 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 the. What kind of pre workout drink did I crank before I got on here settings so that, you know, if someone's heart rate is elevated, the Carol bike knows that they just, you know, doubled up on the espresso that morning.

Yeah. And you can, 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 adjust the wattage. So I like to feel, when I'm recovering, I like to feel more resistance versus, like 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 denfeld 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.