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The Melanie Avalon Biohacking Podcast Episode #214 - Ulrich Dempfle (CAROL AI Bike)

Ulrich Dempfle is the CEO and Co-Founder of CAROL, the company behind the only AI-powered exercise bike that gives you scientifically proven REHIT workouts in just 5 minutes. Ulrich practices what he preaches about CAROL and uses his bike regularly. His cardiovascular fitness has improved by 50% as noted with CAROL’s fitness score (a proxy for the VO2max test) and he has lost over 20 lbs. After graduating in mechanical engineering from Germany’s leading tech university, Ulrich worked with Europe’s top automobile manufacturers. Finding this path too narrow, he started a career as a management consultant and worked with hospitals and healthcare systems in the UK to improve care and make it more efficient for patients. It was there that he pioneered the use of AI for operational efficiency. After learning about reduced exertion HIIT (REHIT), Ulrich realized its potential as the most effective cardio workout, however, at that point, it was only possible in a lab setting. Working with the leading exercise researchers, Ulrich co-founded CAROL to take REHIT out of the lab and give people a chance to optimize their health more efficiently and effectively.



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The Melanie Avalon Biohacking Podcast Episode #38 - Connie Zack
The Science Of Sauna: Heat Shock Proteins, Heart Health, Chronic Pain, Detox, Weight Loss, Immunity, Traditional Vs. Infrared, And More!

get $100 off with code MELANIEAVALON at carolbike.com!

The Melanie Avalon Biohacking Podcast Episode #194 - Dave Asprey

creating the CAROL bike

how does Re-Hiit work?

the studies on re-hiit

Perceived rate of Exertion

finding the time to exercise

how often should you exercise?

exercise and sleep

improving VO2 Max

signaling molecule Activation during re-Hiit

blood sugar control and calorie burning

weight management

The Melanie Avalon Biohacking Podcast Episode #115 - Valter Longo, Ph.D.

the fat burning track

using sauna or cold exposure

optimizing using the CAROL bike with strength training

the CAROL program

an optimized workout

wearing the heart rate strap

the available tracks

the mental motivation

the warm up and recovery

meditative breathing

are cycling shoes needed?

adding stretching


Melanie Avalon: Hi, friends. Welcome back to the show. I am so incredibly excited about the conversation that I am about to have. I've been waiting for this conversation for a few months now. I've been talking about it preemptively on the Intermittent Fasting Podcast all the time. My experience with something I received called the CAROL Bike. And so, the backstory on this whole moment that's happening right now is quite a while ago now, I read Dave Asprey's book, Smarter Not Harder and that was the first time that I heard about a concept called REHIT. So, I know people are pretty familiar with HIIT, high-intensity interval training, as was I, but I never heard of this concept of REHIT, which we are going to dive deep into in today's episode. And specifically, he was mentioning this product called the CAROL Bike that it sounded like from reading his book, it actually gave you the perfect REHIT workout. So, it seemed really cool.

And then around that same time, the reps for the CEO and co-founder of CAROL, Ulrich Dempfle [chuckles] I was working on saying his name, reached out to see if he wanted to come on the show, and also offered to send me the bike to try and okay, I'm going to be completely honest and listeners know this. I'm not a gym person. I'm not a workout person. I like to just make my life exercise. Like, I walk around a lot, I stand, I wear weights around to the store. I do EMSculpt. I'm not a gym person. Like, I have a mirror gym thing at home. I don't ever really use it, so I wasn't sure receiving it if I was actually going to enjoy it or use it because it's just not normally my thing. Oh, my goodness friends, this [chuckles] bike is the most epic life changing thing ever. It's incredible. And I know you guys have probably heard me talk about it on The Intermittent Fasting Podcast, but basically their signature workout that I'm sure we'll talk about is only 8 minutes. You only do it two or three times a week and then on top of that, it's interactive, like you wear a heart rate strap so it's monitoring you.

The track that [laughs] it does if you pick it is instead of, I mean, you can pick music if you like, but if you do their main track called Tiger, it actually creates this whole scene, this narrative where it acts like you're a hunter-gatherer and it has you doing breathing exercises while you're pedaling. And then it screams at you, [laughs] yells at you to run away from the tiger for two short 20 second sprints. And it's just so fun, so easy, so incredible to implement into your life. And then on top of that, I was like, "I need to track my biomarkers and see if things actually change." So, after doing CAROL for, I should get the exact timeline, it's probably been about two months or so, my cholesterol panel, everything plummeted. And I guess it could have been other factors as well, but it's pretty significant. And then on top of that, my HbA1c-- and I'm sorry, Ulrich, this is like the longest intro ever [laughs] my HbA1c, I kind of set myself up. Basically, my HbA1c is typically always low, but then I had made a dietary change where I started cooking my fruit, which I didn't change the amount of fruit I was eating, I just cooked it and my HbA1c actually went up from 5 to 5.8, which terrified me and shocked me. I immediately stopped cooking the fruit and at the same time, I started doing CAROL. 

So, again, there was two factors going on there, but within a month, it dropped to 4.9. So that was very impressive. And just on top of all that, I have seen changes in my body composition, my legs, the CAROL actually also gives you markers in the device on your fitness improvement. And this is becoming the longest episode intro ever. So, I'm going to stop, point being, this is the most amazing thing everybody needs it in their life. Ulrich, thank you so much for being here and for creating this bike, because I'm obsessed, as you can clearly tell. 

Ulrich Dempfle: Well, thank you for having me as your guest. Thank you for the wonderful introduction. I don't think I've ever had such a nice and kind and meaningful introduction to a podcast, so thank you very much. 

Melanie Avalon: No, of course. [laughs] I think that might have been my longest introduction ever. But I'm honestly, like I said, really shocked because I really didn't think I was going to-- I thought I was going to dread using it because I'm not an exercise person and I'm just actually, that's a well, I have so many questions for you. I'm going to circle back to that one. To start things off, I would love to hear a little bit about your personal story. So, what led you to creating CAROL? What happened?

Ulrich Dempfle: Coincidence. I think when I was in my teenage years, my dream was to design, like, a physical product, and ideally something you can sit on. At the time, I thought about a car or an airplane. And so, I studied mechanical engineering and realized at some point that a car or an airplane is not built by or designed by one person. That's designed by thousands and thousands of engineers. And if you're lucky, you design, I don't know, the rear entry handle on the left backdoor or so, because they're so large, complex products. And so, I worked in automotive for a while, but then actually changed into healthcare and worked for the longest time of my professional career in healthcare to make care for patients more better and more efficient and effective and the largest ever prevention and preventative care. And so, my cofounders and I designed and managed chronic disease management programs for people with heart failure, diabetes, and so on. And for that patient population, exercise as for anybody else, exercise is the most important, most powerful intervention you could think of. It's really fundamental. 

The problem is just it's really, really hard to get people to exercise and we struggled with that. And then in 2012, more than 10 years ago, we came across a BBC documentary about REHIT and they showcased this new type of workout, how it was incredibly short, incredibly effective, and literally you could do it in your suit. So that was how they portrayed it. it was so easy you wouldn't sweat. You can do it in your suit. And we fell in love on first sight and thought, "We have to do this both for ourselves and it might be a solution for the patient groups we've worked with." And so, I went the next day after seeing the show out and bought myself a conventional exercise bike. But I paid very close attention to what they've said, so I tried to get the best one, the most suitable one, and tried it at home. And it was nothing like how it was portrayed in the documentary, in this science program. And so, we called up the scientists that were featured there, Dr. Niels Vollaard, and asked, "What are we doing wrong?" And the first thing he said, "Well, you need a special bike." I was like, "Oh, why did you not mention that?" [chuckles] And it turns out the research in scientific labs has been conducted on special bikes that facilitate this REHIT workout. And the research equipment was first really quite expensive and not suitable for consumers. And it needed to be operated by a second person, by a lab technician. So, you needed somebody by your side to operate the equipment for you.

And that's okay for scientific research, but it's not okay for a consumer. And so, we stumbled, we literally stumbled across this gap in the market and thought we can do better and we can actually close that gap. And so, we decided to develop an automated consumer friendly bike to make these REHIT workouts as simple and easy as possible. And okay, this is 10 years ago now, probably 40, 50 prototypes later, we have the CAROL Bike, and it works very nicely and have actually managed to bring some brilliant science out of the lab and into the real world. And, yeah, it was really all a bit coincidence, but we're very happy with it. And going back to the intro, it is a product that I'm very much involved in the design, and I can actually sit on it. So very happy that my teenage dreams actually have come true. 

Melanie Avalon: Oh, my goodness. I love that so much. Okay, wait. So, what are you sitting on right now? Do you sit on some special chair? 

Ulrich Dempfle: Nah. [laughs] Fairly normal office chair?

Melanie Avalon: Okay, [laughs] that's so funny. I love that's about-- that's so specific. Well, just to iterate on what you said, you were talking about how hard it is to get people to exercise and I guess it depends on the type of person. But like I said, for me I'm not that type. I just don't like concentrated workouts and I really am, like my mind is a little bit blown about how you have accomplished that goal completely. Like all you have to do is one session on CAROL and I almost don't believe it. I'm like, "Can this really be giving me all the benefits?" So, question to that, I guess starting with HIIT, high-intensity Interval training, how does it create so many benefits in a short amount of time? And then how was REHIT created from that?

Ulrich Dempfle: Yeah, sure. So, REHIT stands for reduced exertion high intensity interval training. So HIIT or high-intensity interval training most people will be familiar with it. The effectiveness is very clear. And a HIIT program lasts-- there's a great variety but lasts usually around 20 to 30 minutes. You have multiple higher intensity intervals, could be four, five, six, eight, 10 that last between 40 seconds up to 4 minutes. There's great variety and the benefits are clear. It is just difficult for many people to do so. The perceived rate of exertion is very high and it's also not that time efficient. So, scientists basically sought to find out what is the minimum effective dose. So how little do you have to do to get the benefits? And that was successively-- basically they went shorter and shorter until they found what seems to be the limit. And that is 220 seconds at maximum intensity. And that is a really important distinction. So, where HIIT offers high intensity training, REHIT offers maximum intensity training and you're able to do maximum intensity because the sprints are so short, it's only two 20 seconds, but in those two 20 seconds you push your body to its limit thereby triggering a physiological adaptation and the release of certain signaling molecules that are unique to this rapid increase in intensity and working out, even if it's for such a short period of time, at your maximum intensity. And that's really the secret that you do push to your limits even if it's very short. And that you switch from basically very casual, very low load to maximum load in an instant and have this very rapid increase in intensity.

Melanie Avalon: For those studies to determine that, how many studies did they conduct and what was the patient population and the time frame, like when they were measuring the benefits to see if the benefits were equivalent to HIIT? Were they looking at immediate benefits or were they looking at the longer-term benefits?

Ulrich Dempfle: Yeah. Obviously, it's an emerging field, but there's by now a large body of evidence. So, the first studies on REHIT came out about 15 years ago by now. I've seen one of the latest meta-analysis that quoted some 40 high quality studies and was able to aggregate all the data of those. So, this has grown and the evidence is fairly robust by now and then in terms of the periods that are under investigation, so it varies a little bit. Usually, the minimum is six weeks that such studies take. Eight weeks seems to be the norm and then it goes longer, some are 12 weeks, 20 weeks. There's rarely a scientific study that goes longer than 20 weeks because it's a lot of effort, I mean, think about it. Especially if you use that equipment where you need basically always a lab technician next to the person that is a fair amount of effort. The numbers also vary greatly. So, we had one study done specifically with CAROL Bike and comparing it to moderate intensity exercise. There were 32 participants, 16 in each group. I'm aware of a new one also on CAROL equipment. They had 75 participants split in three groups of 25. So, there is a growing body of evidence and by now I think we can be pretty confident that it does work. 

Melanie Avalon: Just to clarify in the studies, when they were doing it, how do they make sure the patients are doing the full out sprints? Not when they're not using CAROL, like when they're just using a normal bike. 

Ulrich Dempfle: So, they're not using a normal bike, they're using a specialized research bike that is built for, they call it Wingate tests. So, for all out-sprint testing and it looks a little bit archaic almost, but you have like metal weights, plate-loaded bikes, and the subject accelerates very fast without the load. And then the operator of the equipment would release the weight and the resistance would get applied and the subjects are just instructed to go all out. And the correct resistance is applied by the lab technician based on-- so there're reference tables that they've established as to what the right resistance level is for each person. That would be very difficult to do on a regular bike because you wouldn't know what the right resistance level is for you. And then just the mechanics of accelerating to a high speed at low resistance, then dialing in the right resistance at exactly the right time to the right level very rapidly. It's very hard to do. 

Melanie Avalon: Okay, so that's what you were saying earlier about being a special bike, but also a person there. It's kind of like a person physically implementing the technology that CAROL does.

Ulrich Dempfle: Exactly that. So, you had basically a bike that was operated by a lab technician.

Melanie Avalon: Okay. And I do have questions about the technology in CAROL, quick question about the perceived rate of exertion that you mentioned. Thinking back to it, I think that's another reason I was hesitant, not hesitant-- but that was another reason I thought with CAROL that it wouldn't really stick with me, was I would do high-intensity interval trainings, especially in college, like all the time. And I appreciated how they were shorter in time, but also, they seemed very hard draining, [chuckles] like the all-out sprint part and everything. And with CAROL, it seems like it's a lower perceived rate of exertion. Is it for the sprints? 

Ulrich Dempfle: Yes, because it is. I mean, de facto, it is reduced exertion high-intensity interval training. So, the overall rate of exertion is much lower. And there's a bit of a psychological trick almost, in that the sprints are so short that you can actually push to your limit. And I talk personally and then that's also feedback I get from our users. The discomfort that kicks in at some point is-- it only comes in once you're almost done. So, I can do the first 15 seconds almost without any discomfort, and then my legs start burning in the last 5 seconds, but then I'm literally done with the sprint. So, you know how they say in fitness, "No pain, no gain." I think there's a little bit of truth in that but with REHIT and with these extremely short sprints, you get a lot of gain for really very little amount of pain. So, the cost-benefit ratio, the ROI, both on your time invested and on the level of discomfort you suffer, is extremely good. And that makes it a really attractive proposition for many people. 

Melanie Avalon: I mean, it truly is incredible. It's one of those things now integrating it into my life, I just think, how was I not doing this before? Because I do plan to use it for the rest of my life. [chuckles] 

Ulrich Dempfle: You should. That's great. And you know what? In some ways you have to, because with the exercise, exercise is in many ways comparable to nutrition or diet, let's say with a crash diet or so, you can lose a lot of weight in a very short period of time. But when you stop and you go back to your normal ways, you just put on the weight. Most people do, anyway and with exercise, sadly, the same applies. So, you can get, in a very short period of time, six weeks, eight weeks, very noticeable, very meaningful, big improvements in your fitness. When you stop exercising, this also goes away again. So, you detrain about as fast as you train. And that's obviously sad. It would be much nicer if it was a one off and it would just stay with you but that's just not how life works. So, you really have to find something that you can turn into a sustainable habit. And we believe that CAROL could be that for many people. If you look at how many people actually exercise enough, it's quite shocking. It's less than 5% of Americans meet the guidelines for aerobic exercise 5% and by now, I feel the benefits of exercise are very well understood. 

Most people know and understand it and would like to exercise, but we don't. And if you survey people why? they don't exercise consistently, the main perceived barrier is lack of time. And there might be a little bit that lack of time is just a better excuse than saying, "I'm lazy," but I think it is true. There's intense competition for our time. So, people have busy schedules absolutely. And you can spend unlimited time on Netflix, on reels, on TikTok and so on. And people don't sleep enough, which is so important and so easy, but people still don't find enough time to sleep. So, I think there is having time efficient exercise is really important and having exercise that you can stick to and create a sustainable habit with it. And we hope that the CAROL Bike gives many people a tool to achieve exactly that, to build that sustainable habit.

Melanie Avalon: It really, really is that because I know for me and again, some people what they love is going to the gym and that is part of their routine and that's what they use for stress mitigation. And so, for them, keep on keeping on but in addition, with CAROL they have like been actually-- I've had this whole dialogue in my head, like this time dialogue where I will think about if I'm going to do it or not that evening. And then I just say to myself, I'm like, "Melanie, it's 8 minutes." Like I literally have 8 minutes, I can do this. And then like I said, doing it is so easy to engage with. Question about that, like the habit piece of it. So, it says you know, I've been reading on your blog and I believe CAROL says this as well, when you receive it, that the recommendation-- and it says it on the screen, the recommendation is two to three times per week. Is there any difference? If somebody did it daily, would that better than two to three times per week? 

Ulrich Dempfle: So first, there's no downside to doing it daily because the exertion is so low. And we've talked that through with our academic partners, with the researchers who do that. The exertion is so low, there's no downside to doing it daily. And in fact, at the moment I don't but I have done for extended-- for long periods that I just did it every single day, every morning, because it was a habit. And same as I brush my teeth, I would just first thing, get up, get my ride done and then go about my other daily routines. At the moment I do it every other day because I've got into weightlifting now. So, I do one day CAROL, another day I do a bit of weights in the morning, so that's how I alternate it. So, you can do it every day, absolutely no problem. In terms of how often should you do it. The two main benefits and there's a long list of other benefits, but the two main benefits is an improvement in cardiovascular fitness measured in VO2 max and improvements in your metabolic health. And depending on what your priorities are for cardiorespiratory fitness, studies seem to suggest that two times per week is actually is enough of a training stimulus to improve your cardiorespiratory fitness and then once you've reached your set point, maintain it at that level. For metabolic health, so if you're more concerned about blood glucose level and insulin sensitivity and so on, it seems to better to do it more often. So do it three times, maybe even four times a week. So, it depends a little bit what your objectives are. It's very efficient and very effective for both. Our recommendation is just to do it like three times a week, that's I think a very good and very doable amount of work to fit into your life. 

Melanie Avalon: You mentioned doing it in the morning, so for me, I'm an evening girl, so I do it in the evening. How does it affect sleep? I was reading something really interesting on your blog. This was really helpful for me saying that studies show that as long as it's at least 2 hours before bed, that it does not negatively impact sleep and may actually improve it. What are your thoughts on sleep and doing it? 

Ulrich Dempfle: I agree with that statement. Personally-- so this is what the consensus view is, because then you give your body time to basically wind down. Again, through the REHIT workout, you definitely boost your metabolism. And we have shown with academic partners, done studies on kind of how long the afterburn lasts after a REHIT ride. And that's like 90 minutes to 2 hours. So, we would recommend to leave some time before your bedtime 2 hours is good. Personally, I love to just get it done in the morning. This is my preference, just the first win of the day is banked. I also enjoy having a shower afterwards. There are people who don't need to have a shower, like many people don't actually sweat because it's so short, some people do. I enjoy having a shower afterwards, and I also enjoy doing it in a semi-fasted state, at least not after a meal. So, for me, morning is just the best time. We've discussed this with some of our academic partners and there's no research into whether morning or afternoon is better. So, this is really just personal preference. So, you try it and see what works best for you.

Melanie Avalon: I'm prepping to interview Dr. Gabrielle Lyon, for her book Forever Strong, and I believe she referenced a study that actually showed that HIIT workouts during periods of sleep deprivation actually helped mitigate the negative effects of sleep deprivation, which would be the opposite of what you would normally think. Because normally you would think when you're sleep deprived, like overstressing might make things worse. I'll have to find that if I can, I don't know if that rings a bell.

Ulrich Dempfle: Seen a study that has shown that. So, first people should sleep. Sleep is super important. 

Melanie Avalon: Oh, yes. Yes, I know. [laughs] I'm like ]this is the antithesis of what I normally would say.

Ulrich Dempfle: It's not like, "Oh great, you don't have to sleep." So, one thing that sleep deprivation does is that it causes acute insulin resistance in healthy people. So, if you're very sleep deprived, if you're restricted to say 4 hours per night or so, my understanding is that and we've found a study on that can cause acute insulin resistance. But that's in people who don't exercise and that in fact high-intensity exercise, vigorous interval training can ameliorate some of that insulin resistance caused by poor sleep. So, if you're, for whatever reason, maybe you're traveling, maybe you're just not a great sleeper. REHIT and high intensity exercise can offset some of the negative consequences of lack of sleep. But again, I do sleep. It's so important. 

Melanie Avalon: No, so important. I actually and-- I found it in her book. So, this is from her book Forever Strong. She said, "Both short-term and long-term sleep disturbances cause disruption in circadian rhythms and decrease muscle protein synthesis rates. However, implementing high-intensity interval training during periods of sleep restriction has been shown to preserve the rates of muscle protein synthesis." In other words, exercise can mitigate some of the negative effects of reduced sleep patterns on muscle protein synthesis rates. 

Ulrich Dempfle: That matches what we found. It's really high. We also don't want to give the advice like exercise less. I really don’t want to-- I bite my tongue every time I'm-- I would never say something that it's stupid to work out longer. If you have something that you enjoy and if you're a gym rat, like a runner who gets into different mental state with running, yeah, that's perfect. Keep doing it. So whatever works for you, exercise is super. If you're struggling with exercise, then CAROL Bike and the REHIT workouts might be an excellent solution. And in fact, I was actually really surprised at some point we thought that our bike would attract mainly like non-exercisers. So, people who had maybe an aversion to exercise or who didn't enjoy exercise, but that's not the case at all. So, we have many people who are enthusiastic exercisers and who exercise a lot and who just want to add something very efficient to their routine or want a backstop for periods of the year where they're really busy and they can't do longer runs or longer rides. So, the range of users is very large and it's certainly not all just people who want to do as little exercise as possible. 

Melanie Avalon: So actually, to that point, when I was first kind of feeling [chuckles] CAROL out, I was reaching out to a lot of people in the biohacking sphere asking them their opinions and it was overwhelming. Everybody was so on board, but it was a range of people. So. Brad Kearns, Mark Sisson's coauthor and writes like Primal Endurance and a lot of those books. And he's a really intense athlete. And I was asking him about it, he's like, "Oh, yeah," this is like what you just said. He's like, "This is the most effective thing ever, I use it all the time." And he's somebody who's a very intense endurance athlete. So, yeah, it's all across the board. 

Ulrich Dempfle: It is really for a large variety. If you ask us who's using CAROL, the range is huge. It's from people who just start out and who may never have exercised in their life before, but have health concerns or just realize at some point, but once you HIIT the mid-40s, people start to think about their health a bit more, that they have to do something. And really Olympic gold medalists like top class athletes. And because we have these algorithms and our AI that personalizes the workout for everybody, we can cater for all those. So, we have-- [laughs] my mom, she's 80 years old. She's one of our most regular users. So, she religiously uses her bike every other day. She's pretty much at the bottom of the leaderboard but she's still very enthusiastic user and tells me all the time how much she enjoys it and how good it is for her. So that's kind of one end of the spectrum and the other is really like Olympic gold medalists who use it and use it as one tool to be in peak condition. 

Melanie Avalon: Some other questions about that because I think people often think with most exercise, especially like muscle building, strength training, they say that the lower baseline that you start at, the faster you'll see improvements in the beginning, just because you're starting somewhere where you have so much to benefit from. So, your starting baseline for CAROL, so those elite athletes who started versus somebody who's sedentary, who doesn't normally exercise, the benefits that you get, what does that graph look like as far as how fast people get benefits?

Ulrich Dempfle: The honest answer is I don't know because most of the research is done on people with either sedentary lifestyles or normal people, not top athletes. And to be completely like, logic dictates that for a top athlete, the marginal gain is obviously much, much lower than for a person who just starts out. So, the newbie gains that you see in the gym, in weightlifting absolutely must be also here for CAROL. And so, for a trained athlete, maybe it's more about how can I get the same stimulus in quicker or how can I get in the same stimulus with less stress on my body so that I can focus more on recovery or focus on my skills? or so it's not so much. So, if somebody is a pro athlete, they obviously train to a level that the stimulus is almost maxed out. So that would be something, how can I get the same stimulus with less stress on my system? 

Melanie Avalon: And actually, to that point, because for listeners if they go to the website, it's carolbike.com, correct?

Ulrich Dempfle: That's correct. Yeah.

Melanie Avalon: So, if they go to the website, there are so many blogs there about all of this and the science. So, you can dive deep into everything. There's a lot on VO2 max. I was curious if you could talk a little bit about that. And I was reading on your website that VO2 max is 50% defined by our genetics, and so we can actually hit a limit that we can't surpass, which is kind of upsetting sounding to me.

Ulrich Dempfle: If it wasn't, we'd be all participating in the Olympics, and that's just not-- so yeah, obviously the people have genetic limits, so to speak, and with CAROL, we see. So, most of the studies show that you can gain in the first eight weeks about a 12% improvement in your VO2 max. So, VO2 max is your ability to burn oxygen during exercise. And it's probably the-- now it is the-- I'm being definitive about this now. It is the most important health marker. It's the strongest correlate to life expectancy. So, it's really fundamental. And a 12% improvement in only eight weeks is very significant. And in fact, that's what we see with our users as well. So, we see on average, a 12% improvement in their fitness score, which we've designed so it tracks VO2 max in the first eight weeks. And then studies show that over the first 20 weeks, you can go up to 20% on average, but then it obviously tails off and people will reach their genetic set points at some point. That's unavoidable, but we try to, again, through the algorithms and the AI, the bike will make the resistance harder as you get fitter and stronger. So, it will adjust the workout and personalize the workout for you so that, that plateau is basically reached as late as possible. How do you say, that you don't plateau before-- It's absolutely kind of you maxed out your potential.

Melanie Avalon: Question about that life expectancy, does that relate to-- because I interviewed James Nestor for his book Breath and he was talking about how in the Framingham Heart Study, the factor they found actually most correlated to longevity was lung capacity. Do you know if that was related possibly to VO2 max then or do you think that was a different marker?

Ulrich Dempfle: So, I'm familiar with the Framingham study. So, to the best of my knowledge and this is what I'm referring directly to the professors that we work with, the scientists we work with, that they said that VO2 max is the strongest correlate to life expectancy. So, I hadn't heard that it's lung capacity. I'm sure the two are correlated as well. That might explain it, but to the best of my knowledge, it is VO2 max. 

Melanie Avalon: Yeah. I was just thinking about it more because I remember that blew my mind when I learned that. And now I'm just wondering even if they didn't attribute it to VO2 max with a lung capacity that all involves [laughs] oxygen and breathing. 

Ulrich Dempfle: Yeah, exactly. And the circulatory system, I mean, VO2 max is-- there're multiple mechanisms how you improve your VO2 max. So, either they split it into central and peripheral adaptations, or oxygen delivery and oxygen consumption. So, REHIT very clearly affects both parts of the system. So, one part is oxygen consumption. That is the ability of your muscles to basically metabolize oxygen. And that's achieved through primarily, basically mitochondrial biogenesis that you develop more and larger mitochondria, which are the power plants in your cells that metabolize oxygen and then the central adaptations that's around how strong your heart is and how much blood plasma you have. And lung capacity might also be correlated to that. So, it's all connected to your cardiorespiratory system, yeah. 

Melanie Avalon: Something else you mentioned a little bit earlier, the metabolic effects that are happening and the physiological effects that are happening when you're doing REHIT what things are activated. Like, I know it can affect AMPK and like GLUT4, what signaling molecules are activated when you're doing these workouts.

Ulrich Dempfle: So, what happens during that sprint is basically and that's what we facilitate and make as simple as possible, that you go from resting energy demand to 100-fold greater. So that's roughly the order of magnitude energy demand. And you simulate something like an emergency situation. Imagine you have to run for your life or fight for your life, and you have to switch on from zero to 100 in a fraction of a second. In such a scenario, your muscles have to utilize immediately available locally stored sources of energy. There're three energy systems. There's phosphocreatine, anaerobic and aerobic. The aerobic is most efficient, but it switches on most slowly. Phosphocreatine is fast, it's immediate, but it lasts for only 10 seconds. So, in those sprints, you exhaust the phosphocreatine system. And then you have to burn anaerobically glycogen, which is a storage form of sugar that's stored locally in your muscles. And what's really clever is that your body doesn't know how long this sprint will last, how long you have to fight for your life or run for your life. 

So, it mobilizes lots of glycogen, and in fact it mobilizes a lot more glycogen than is actually needed for those two 20-second sprints. But nevertheless, the glycogen is mobilized, is taken out of its stores, and bound to that glycogen is a molecule called AMPK, which is an important signaling molecule. And that, in turn, releases a further signaling molecule called PGC-1alpha, which is the master regulator for mitochondrial biogenesis. And so that is one mechanism how you improve your fitness levels and how you increase your VO2 max. And because it's basically triggered by the mobilization of the glycogen, what appears to be the case is that these two 20-second sprints are simply enough to saturate this signaling response mechanism. And therefore, you basically don't have to do more or longer sprints because you've flipped the switch already. And that's very clever or convenient because longer sprints would be really a lot harder. So, a 20-second sprint is a lot harder than a 15-second sprint and a 30-second sprint, oh, my God, that's a lot harder. So, if you had to do 30-second sprints four or five intervals, this would be a very grueling exercise and very hard to do for most people, whereas two 20-second sprints are actually quite doable. So that's one of the mechanisms. 

There are other mechanisms. Another thing that happens is because you mobilize so much glycogen and kind of partially metabolize that during the sprint, you create an osmotic imbalance between your bloodstream and the muscles. So, lots of water shoots into your muscles and blood plasma volumes momentarily drop by 15-20%. So, you have a transient drop in blood plasma volume and that is thought to stimulate an increase in blood plasma and then that improves basically the central component of oxygen delivery. Yeah, so there are several fascinating and curious mechanisms and that's how scientists believe this works that are quite unique to REHIT and that just don't occur like that in other workouts. 

Melanie Avalon: Okay, some questions about the glycogen. Glycogen is used by the actual muscle being used, correct? Is this just working with the glycogen in your legs? 

Ulrich Dempfle: That's correct. So, you have glycogen stored in your muscles and in your liver and during the workout-- and a tiny amount is floating around in your bloodstream but that's really marginal. That's like much, much lower compared to what's stored in the liver and in your muscles. And because you need to rapidly access it, the only available source of energy is basically muscular glycogen, which is already there and can be mobilized very rapidly. So, the first 10 seconds, it's phosphocreatine, but then the glycogen is already available for the cells to burn essentially. We call it the emergency energy reserve. That’s really-- and it's a huge amount of glycogen that you store actually in your muscles. And you could perform, in calorie terms much, much longer endurance workouts based on the level of glycogen that's stored in your muscles and that you burn. But we're actually not interested in burning all that glycogen, we're just interested in mobilizing it. And because it's the emergency reserve, your body really wants that to be available because you have to be ready for the next bad thing that might happen. So that sends a very strong signal to your body that it has to adapt, that it has to get fitter and stronger. And after the sprints, your body also wants to replenish those glycogen stores as quickly as possible. And that's a process that's basically governed and controlled by insulin. And that's the reason why your insulin sensitivity improves and your metabolic health improves.

Melanie Avalon: If a person is on a low carb or a keto diet with presumably less glycogen stores, how might that affect their experience with CAROL? 

Ulrich Dempfle: I don't actually think so. So, I do think also people who are on a low-carb diet, the body is perfectly capable to convert different types of fuel into glycogen and store it in the muscles. So, I'm quite certain that you'd still have those glycogen stores available and be able to access them in situations where you simulate an emergency or where you have a peak energy demand, because that's just the only system that's available at such short notice. If you didn't have that, you'd run out of energy in 10 seconds and that's not what happens.

Melanie Avalon: Yeah. I actually want to find an expert to come on to talk about this because I was reading some studies, because most people-- because I'm sort of saturated often in the low carb keto world, and they'll say that you have to completely deplete your body of glycogen before entering ketosis. And I don't know that's accurate because I've seen studies on entry into ketosis and how it relates to glycogen depletion and it seems to be independent of muscle glycogen, I think it involves more liver glycogen.

Ulrich Dempfle: Maybe do find an expert that's even more expert than me on this because I'm hypothesizing here a little bit. So, in the intro, I said I'm a mechanical engineer, not a biochemistry, biology expert but my understanding is that glycogen is quite fundamental in terms of having that stored in your muscles. But fair enough, others might have more informed opinions on that.

Melanie Avalon: That's what I'm saying is I think it's in support of what you're saying. I think there's some confusion there. So, I'll make a note about that. I actually also was reading on your website that there was an eight-week study where, I'm just reading from my notes, it says, "Participants risk of type 2 diabetes was reduced by 62%, the same as metformin." That's really impressive. And I know we're not saying for people to stop taking their medicine, but their metformin.

Ulrich Dempfle: No. In terms of the impact, yes. So, VO2 max and cardiorespiratory fitness is one big component, but the other is improvements in metabolic health. And what was measured there it's called the MetS z-score. So that's a compound score that measures your risk of developing metabolic diseases like type 2 diabetes. And a number of things go into that so your blood pressure, HDL cholesterol, triglycerides, waist circumference and blood sugar, the improvements that were seen in only eight weeks were a risk reduction of 62%. So that's very significant. And that is the same order of magnitude as you would expect from taking medication like metformin. And metformin is not without side effects, whereas this type of exercise is without side effects. So, you get a very substantial improvement in your metabolic health with something that's actually quite doable. And it is very relevant so, again, I've seen a statistic that only 12% of Americans meet the criteria for being metabolically healthy. So, it is really sadly, I call it an epidemic, but it affects many, many people. It affects most people in our society.

Melanie Avalon: Yeah. And I just think also in the metabolic health area. So, weight loss and weight, how does it affect calorie burning? How about this afterburn effect that you get? What happens there? 

Ulrich Dempfle: So, the first thing I should say, so weight loss is obviously primarily driven by nutrition. So, if your prime concern is weight management, you have to look at your nutrition first and foremost. However, there're, I think, two things I'd like to say about that. So first, CAROL does burn, even though very short REHIT workouts burn a substantial or significant amount of a meaningful amount of calories because of the afterburn, that's excess post-exercise oxygen consumption. So basically, calories that you burn after you finished your workout, over the next 90 to 120 minutes, when your body basically returns to its baseline and in fact, it's two thirds of the calorie consumption from REHIT rides occur in that afterburn period. And maybe I just give a personal example, when I do a REHIT ride, I spend like 6, 7 minutes on the bike. I burn around 210, 220 calories through that very short workout including the afterburn. And that's meaningful.

That's like almost 10% of my normal calorie needs on that day. I know not everybody believes in calories in calories out there and there're many more nuances, but if you consume more calories, that wherever you stand on that discussion should be a helpful thing. So that's one thing, so there is meaningful calorie burn. The other thing is and that's something-- so I talk a little bit also just my own experience. If you're metabolically flexible and you're not insulin resistant, it is easier to access basically the fat stores and energy stores that you're carrying around with you. So, I'm not super huge on fasting all the time, but I do maybe two, three times per year, like one of those Valter Longo's fast, the prolonged things. And I feel I can get through those with actually very limited sensation of hunger and certainly not sensation of starving. And I attribute that to being able to access and being metabolically flexible, being able to access the fats, the energy stored in my adipose tissue, and therefore my body has actually energy available and doesn't feel like it's starving. Whereas if you're insulin resistant, that becomes, I believe, a whole different thing, that it's really hard to access those energy stores and you feel like you're starving. And so that helps with weight management. 

Melanie Avalon: I was reading on your website as well about the potential effects on appetite and how it could reduce appetite. 

Ulrich Dempfle: That is actually true. So that's another thing, and I'm not into on that at the moment because at the moment I'm really focused on gaining muscle. That's kind of my thing right now [chuckles] but a while back I was more focused on weight management and I would do like a 16:8 routine or so with time restricted eating and maybe also like slight calorie restriction. And I found that doing the ride in the morning did actually suppress hunger and made it easier for me to not have breakfast and wait till, I don't know, 1, 2 o' clock in the afternoon to have lunch as my first meal essentially.

Melanie Avalon: Yeah, which I think is different than what most people associate with cardio-related workouts because you do those and you feel starving after. So that's a really nice hack in a way. And for listeners, I'll put links in the show notes. I think I've had Valter Longo on twice, so I'll put links to the interviews. He's been on this show and he's been on The Intermittent Fasting Podcast. 

Ulrich Dempfle: Yeah. That's exactly what I do. Like the ProLon Kit, I love it. It's such a nice structure to go through it. I tick off every tea bag and every bag of olives. I'm really proud that after five days that I've ticked off every single component. No, I do this. So, I do those maybe two, three times a year and I find them very beneficial. I'm very proud when I've done it. While I do those, I definitely also do every day a CAROL ride. Now, see whether it's good for you. I don't know whether that should be the recommendation for everybody, but certainly I can still maintain those whereas a longer cardio session I think would be much more challenging. 

Melanie Avalon: That's super cool. I will say I attempted ProLon. It was the [laughs] example. So, I gave the example in the beginning of how I thought CAROL was going to be really hard and I wouldn't like it and it was amazing. ProLon, I was like, "Oh, I can do this," [laughs], I could not, I could not. I think because I'm so used to just complete fasting and then feasting. So having just like a little bit of food just made me starving and I think if I kept at it--

Ulrich Dempfle: Okay, that's interesting. No, I found it's actually quite helpful to have just a little bit to keep you entertained and occupied and so you're not breaking your fast out of boredom or habit-- yeah, that's a different experience. Ultimately you do you and you have to find kind of what works for you. But no, I find a very good way to fast. 

Melanie Avalon: I want to. I thought about, I was like, maybe I can have all of the ProLon meal, like all at one time and I'll just kind of do what I'm doing but have a ProLon meal every night but yeah, that's super cool. I had another question. Oh, it related to all of this. There is a program and we haven't gone through how it actually works on the bike, so we can do that. But there is a fat burning track, which actually I think I've only done that once or twice and it actually was pretty hard [chuckles] for me. So, I'm wondering that track, the one I'm talking about, does contain a lot of short sprints. So how is that being better for fat burning than the normal track?

Ulrich Dempfle: So, may I just make clear that the CAROL Bike has been really, really optimized for REHIT and sprint interval training. That's what we major on and that's kind of the reason why people get a CAROL Bike. On the other hand, it's a very versatile bike. So, we have, I think at the moment, a range of 20 workouts on the bike that all have scientific validation and backing. And as new concepts or new science comes up, we'll add those. But you can use it with a range of third-party apps. So, there're things like Zwift and Kinomap, enthusiastic cyclists will be familiar with that. You can use it with the Peloton digital app if that's your thing or you can just also with whatever YouTube and Netflix cycle, like for example, do your Zone 2 sessions or so, like longer sessions. So, it's also a quite versatile bike. 

Now, the fat burn series that you refer to, so there indeed you have a much larger number of sprints of 30, 45, or 60, they are shorter, they're only 8 seconds long and you have a 12-second break between them and they're done at lower intensity. So that's more akin to high-intensity training. So those sprints are not maximum intensity, they're just high intensity. So, the primary thing is that you burn a phenomenal amount of calories and that will aid weight management. There are studies behind that that also showed that this type of workout is superior to reduce. So, there were studies with young women and they found that these workouts were superior in terms of body fat reduction. But the research is a little bit more mixed and we do emphasize. What's very clear is that they just burn a phenomenal amount of calories. And yes, you will sweat like hell. But really for weight management, the number one thing is nutrition. That's what you have to. I think it's almost the consensus now that exercise alone wouldn't be a successful strategy for weight management. You have to primarily address nutrition.

Melanie Avalon: Now I'm thinking because I tried that one way in the beginning, I should try it again now and see my perception of it.

Ulrich Dempfle: I mean, it's more for people who-- that is really for people who first enjoyed longer and harder workouts because that exists. So, there are people who-- when I'm lifting weights, for example, that is also-- there I find longer, harder workouts also enjoyable, strange, but that's what it is. Similar thing is some people do enjoy longer, harder cardio sessions and they get in a different mental state. They love to really exhaust themselves and leave the world behind in some way. So, you have that option and if that's what you're after, you also have very good means to achieve that.

Melanie Avalon: Well, speaking of sweating and muscle, two related questions. One, if somebody is doing a sauna session, does it matter before or after? Because my pattern right now is I do the CAROL and then I usually will do a sauna session after.

Ulrich Dempfle: So, I have no idea and I don't think there's any research on that. I do think it's probably a good idea to be well hydrated before you do the exercise, but that's just a common-sense answer, not because there's any research that I'm aware of. I do know for-- So for cold exposure, as far as I know, it doesn't matter whether before or after. But for cardio in general, I think the research position was it doesn't matter. And even for strength training, I think the opinion has somewhat moved that even their cold exposure afterwards is not something that attenuates your gains, it's not killing your gains. So, for many of those things, there's just not the research there. So that would be something to just try and do your N = 1 and you try it and see what works best for you.

Melanie Avalon: That was my takeaway just with the cold exposure and the muscle strength training, because I went down that rabbit hole with all the studies and they were so mixed that I was like, "You just do you, [laughs] you just see what works for you." So, I read on the site that to do strength training before the CAROL workout and to avoid doing leg workouts on the same days, what are your thoughts on that? And then, okay, huge question here, very big question. So, is there a difference between sitting on the bike or what if you stand on the bike?

Ulrich Dempfle: So, in your sprints you do as works best for you and it's okay either way. I know many people stay seated, I go out of the saddle during the sprints, but that's a personal preference. And both works well because the resistance is so high that you will have, how do you say, like a round pedal stroke. One thing that some of our customers sometimes regret or is a point that feedback, but it was a conscious decision, is around the transmission from crank to flywheel. So, we have a free wheel, which means you can stop at any time, and the flywheel doesn't drive the pedals. Whereas normal stationary bikes like a Peloton or like what you would find in your gym, generally have a fixed transmission. So, the flywheel drives the pedal and that makes it, at low resistance, easier to go out of your saddle and pedal basically standing. And in these Peloton classes, the instructors go out of the saddle now and even at relatively low resistance and that works on a CAROL Bike. So, you need some practice to maintain around pedal stroke and you need to put the resistance a little bit higher up. But it is what it is because we find when you have these explosive sprints, and you really accelerate as fast as you can at a low resistance, you must have the ability to just stop whenever you want. 

If you were forced to maintain the rhythm of the flywheel, if you basically lost the rhythm, there would be possibly an injury risk. So, it could happen then that if you tried to basically do these explosive sprints on a normal bike and you lose the rhythm, then there would be a lot of force and energy stored in the flywheel and there would be actually a potential injury risk, which especially if somebody's not very used to using a spinning bike. So, we've made a very conscious decision in the REHIT sprints, it's entirely fine to either be seated or stand, and both works very well if you want to cycle standing at low resistance. When you do like, I don't know, like, your Zone 2 training or you do want to follow along a Peloton class, it requires a little bit more practice to maintain a round pedal stroke. It's a bit more like an outdoor bike rather than a spinning bike. 

Melanie Avalon: I'm fascinated by this because when I first started doing it, I was only sitting, and then it occurred to me, I was like, "Oh, I could try standing a little bit during this." And when I do, it seems way easier for me. So, I was like, "Maybe I'm not getting all the benefits." 

Ulrich Dempfle: No, no, no, that's fine. If it seems easy, that's good. And the bike and our algorithms will make it harder for you from workout to workout and we want you to reach your maximum power. And if you reach higher power when you're out of the saddle, by all means do that.

Melanie Avalon: Well, that's what's interesting, is it seems easier and it also seems like I'm going harder. This is a very casual question, but I think especially women, people will get worried with cycling. Will they get big thighs? I know that was always a concern of mine growing up. I was wondering if that would happen with this. I actually have seen, I've been shocked the increase in tone I have seen and it has not given me big thighs. It's very noticeable, at least to me, but yes, body composition. And will it give women, like, really big muscles?

Ulrich Dempfle: No, I don't think so. No, so you do get an increase in strength and I think a positive improvement in tone and definition, so you do develop your leg muscles, but that you get, like, massive thighs, no, I've not heard any complaint. And we've got, by now, a community of some 25,000 users. This is not something and we really try to understand what users like, what they don't like, where we can improve things. Nobody's complained that their thighs have gotten too strong and too big. I think generally, even if you start weightlifting, it's actually not that easy to put on muscle, so that somebody was getting bigger and stronger than they wanted. That's a rare thing. I think that's a myth. I wish I had that happen to me. So, I have to work hard to put on muscle. 

Melanie Avalon: That's funny. Oh, I have definitely seen muscle tone improvement. It's very very impressive to me. Okay, some questions about the actual program itself, because we've mentioned it a lot how it adjusts the resistance. And you said you went through 40 to 50-- 

Ulrich Dempfle: Prototypes, yeah, yeah. It was not easy to put this together and build a nice consumer friendly package. It took us, well, the journey has been over 10 years now. 

Melanie Avalon: Wow. So, the version that's out right now to consumers, has it gone through multiple versions or not? 

Ulrich Dempfle: So, now we've got our CAROL Bike 2.0. So, we had, before our market launch, yeah 40 prototypes. Then we had CAROL Bike 1.0 that went from late 2018, early 2019, until August 22. And then last August, we launched CAROL Bike 2.0 as just a better and improved version to address some of the things that-- some of the feedback we got from our users and some of the things that we wanted to be better about the bike. Because we are very avid users, we try to obviously make a product that we enjoy to use pretty much every day. So, the current model has been out now for a year. Yeah, pretty much a year.

Melanie Avalon: Is it basically you're pedaling and then the AI is adjusting the resistance to assure that you are putting all the effort that you need to. So basically, like, if you slack off, it just adds more resistance. 

Ulrich Dempfle: So, the AI dials in your optimal resistance and it tells you when to push and it controls the bike and makes it as simple as possible for you. The only thing that you have to do is push to your limit. So that part is still with you. So, I can explain how this works. So, we've got the, by far, largest REHIT database in the world. So, we've got many, many hundreds of thousands of rides. And that's vastly more data than any of our academic partners have available.

Melanie Avalon: Literally, in the world, you have the highest? 

Ulrich Dempfle: Oh, absolutely. Yeah, yeah absolutely.

Melanie Avalon: That's really cool. [laughs] 

Ulrich Dempfle: Yeah. So, if you think about it, a typical clinical trial or academic trial would have maybe 40, 50 participants. They do that three times a week over eight weeks. So, they would get what's that's 150,1200 data points. Now we've got order of magnitude more, so we have way, way more. And we can analyze that and for a much wider range of participants like most universities, they recruit students to do the research. They find subjects so it's not only students, but if you read a paper that was done with healthy young individuals, then you know, oh, students. So, we have a much wider database. And so, we know how these sprints look like for a huge number of people, for a huge number of workouts. And so, we know what an optimal sprint looks like for a person just like you. And so, we know you've reached your peak power just after the sprint starts, like 3, 4 seconds in and then you fatigue throughout the sprint. And that's intended, so if you don't fatigue then it wasn't your peak power.

Basically, we optimize that shape of the curve and can basically make it harder for you if that curve suggests it was too easy or easier if the curve suggests it was too hard. And so, we have first for people who start new, we set the resistance at an optimal level for an average person of those characteristics. So, characteristics would be your age, your weight, your height, your gender, your activity levels, and based on that we can come up with a very good estimate. But of course, we're not sure whether everybody's different. So, then our algorithms find very quickly what's the optimal for you in that state. And then as you get fitter and stronger, it keeps getting more challenging. Or if you had an injury or you were traveling or for whatever reason you couldn't do your rides, it also backs off again and makes it easier.  So, to basically give an optimal experience every single time and that's a way how we can cater for this really large variety of different users from Olympic gold medalists to people who are 60, 70 and are not in great shape at all. So, we can cater for a very large variety of people. 

Melanie Avalon: Is it adjusting in real time or is it adjusting like when you do your first sprint? 

Ulrich Dempfle: It happens in between the workouts. So, you do a workout, the data gets uploaded to our servers and the next time you basically log in and do a workout, you get an adjusted, optimized, and personalized version for the ride. So, it happens from right to right.

Melanie Avalon: Oh wow. So, would there be different implications then? So, say a person did two times in one week and person A was really tired for the first workout but not the second and then person B was really tired for the second workout but not the first. Would that mess up the algorithm a little bit?

Ulrich Dempfle: The algorithm would adjust it, but it would find it-- so we've built it that it basically very rapidly dials in on your optimal point. So, here's the thing, this may still come. We've not found the perfect implementation for it. So, for example, the bike and the sensor that you wear, it does actually track your heart rate variability. And so, the thought was we look at your heart rate variability and then basically adjust the workout based on your form on the day. Yeah, but that's harder than we thought. So, we haven't cracked that nut yet. This might still come. This is a more challenging problem. The other thing that is also, look, we have a rich pipeline of things that we want to implement and so we will still have-- very enthusiastic about it and we chip away at it, but we have a long list of things that we want to do. 

Another thing that may come is just integration with other wearables and use those signals to further basically flex the workout based on your form on the day. But at the moment it gets optimized from right to right and it basically takes into account your-- I don't want to call it longer term trends because the adaptations are quite quick actually and it dials in very fast, but it basically your trends, it follows your trends and adjusts it based on you getting fitter and stronger. There may well be, hopefully, in the not-so-distant future, away where we also can take into account your recovery state on a given date that isn't linked to your longer term fitness level, but that's kind of just for example, how well did you sleep or so, things like that. 

Melanie Avalon: Well, I'm going to put my fingers crossed that maybe someday it would integrate with Oura Ring because that would be epic. 

Ulrich Dempfle: I know, I know, I know. Yeah, me too. And I'm wearing mine now but as I said, we have a rich list of things that we would like to do and we're working away and we still have-- it's a really exciting thing to be working on. So, I'm very passionate about it and very grateful that I can work on such a great product. Yeah, that's still in our pipeline.

Melanie Avalon: Very exciting. So, the strap that you wear, does that also affect the actual workout or was that just the anticipation of heart rate variability? 

Ulrich Dempfle: So, you wear a strap for two reasons. One is fitness tracking. So, when we calculate your fitness score, that takes into account your heart rate, so it takes into account your power output or energy output and it takes into account how high your heart rate shot up after the sprint and how quickly it recovered. So, heart rate recovery is an important marker of fitness. And so, if we take into account basically the input, your power output and the heart rate recovery, we can calculate our fitness score, which is, in essence, it's power per heartbeat that allows us to give you a meaningful, precise tracking of your fitness level. So, it's absolutely not VO2 max kind of conceptually. It's very different from VO2 max, but we designed it so it tracks VO2 max closely. So, if you have a 10% improvement in fitness score, we're quite confident you also had a 10% improvement in VO2 max. 

So that's one reason to wear the chest strap. Another is just to see whether being honest with yourself, whether you push yourself hard enough so you get an indication as to where your peak heart rate was. And we want to see you between 80% and 90% of your peak heart rate during the workout after the sprints. And then the final reason is we do have some safety algorithms implemented in the bike. So, if your heart rate in the warm up, for example, was too high or higher than we think it should be, or if your heart rate doesn't recover fast enough after the first sprint, so we would display a warning if you want and suggest kind of you can check in on yourself. Is this because I've done a different workout beforehand then it's perfectly fine. But if you're approaching it rested and your rested heart rate is too high, then this might be something you want to check with a physician. Those are the reasons, it's tracking and then also as a safety measure.

Melanie Avalon: And can people also, if they hold the handlebars, does it do the same thing? 

Ulrich Dempfle: So not in our CAROL Bike 2.0. The 1.0 Bike had handlebar electrodes. The 2.0 doesn't. The 2.0 comes with a chest belt. So, every bike has a chest belt that gets delivered with the bike. The reason behind that was, one, it gives just a great deal more. It's basically you can ride hands free, so you don't have to keep your hands on the handlebar and you have multiple grip position. And that really improves the comfort level of the bike quite a lot, even though it's so short. If you always have to have the hands in the same position on that straight handlebar of our first-generation bike, that's something that users fed back, some found uncomfortable. And so, we responded to that with our second-generation bike. And the other thing is, just with the chest strap, you measure the heart rate pretty much at the source. So, it's just by far the best and most accurate way to measure heart rate. So, we've tested also all the heart rate bands, whether they would be sufficient with optical sensors, but they're not responsive enough for this type of workout and they use too much averaging and blunt the signal that it's not a useful way to measure heart rate. So, the chest strap is just the gold standard. 

Melanie Avalon: Okay, awesome. And then just a few quick questions about the actual track because I've had these questions almost every time I do it, so I've been dying to ask you. So, as I mentioned to listeners, there's this cool tiger track. Did you come up with that idea? 

Ulrich Dempfle: My cofounder came up with it, yes. And yeah, it is a much beloved feature of the bike. And let's see, I love it too, many people love it. I think that's the lady, we found her because she did the voiceover of the videos in British Airways on the planes, and she has this lovely British voice. So that's how we found her. Yeah, it's a nice feature. I mean, there's generally like some quirky bits in there because we're basically also kind of trying to build a product that we love that's how those things come about.

Melanie Avalon: I love it. It is an experience. Really, she talks to you like you're a hunter-gatherer in the woods and walking, and breathing and--

Ulrich Dempfle: That's exactly kind of what the workout simulates. And you go like you're running from a tiger. That's exactly what we want to achieve. So, here's the thing many people will probably-- they might not have experienced in a very long time what it means to be sprinting. So, we felt that having this scenario, this paleolithic landscape and scenario would be good to get people in the mindset to really that's what we want. We want you to run from a tiger. It's only very short, but approach it in that way and physiologically it's exactly what happens. We simulate an emergency situation and that what triggers the adaptation.

Melanie Avalon: You know what would be so fun is if you had a whole series of different stories and they're all like different adventures, where for whatever reason, in the adventure, there was these two sprints. So, there could be like a zombie one and it's like you're like, "Zombies are coming." 

Ulrich Dempfle: I know. So that's also one on our list of things. 

Melanie Avalon: Oh, yes. [laughs] Oh, man. If you want to have a brainstorming session, [laughs] it's so fun. 

Ulrich Dempfle: I know. It's like a child in a candy store as to, "All right, we want this or we want this." And on the other hand, we have to obviously. We're a premium priced product, let's be honest about it. So, I think it's exceptionally good value because it's a very good bike and it takes so little time, but we are already at risk of putting all sorts of things into the bike because we want it to be the best product possible. And I want my bike every day to have all the bells and whistles, but at the same time, we can't, how should I say, price ourselves completely out of the market. Because obviously people have a certain expectation as to how much an exercise bike can cost. And if we're double that, then at some point it becomes also challenging. 

Melanie Avalon: So, the questions I have when I'm doing the tiger track, which again, I really do think the psychological benefits really help. When she's yelling at you during the sprint, she's like, "Your family needs you." That gives me the last motivation to, "Yes, [laughs] they do." 

Ulrich Dempfle: That's what powerlifters or weightlifters do. So, they go to very-- and this is the kind way, I think what powerlifters do when they really want to push to their absolute limits, they go to some dark places in their mind to really motivate and mobilize the last bit of energy and power to lift that iron. Yeah, the psychology of it is important. There's no question about it. 

Melanie Avalon: It works for me. And she says it right at the end and that's just like the final boost. I need. The questions I have while doing it, though, is, she says for listeners, there's a screen in front of you that has a lot of data and there's a Watt's section. And she says to walk very slowly and she says that a lot to stay under 20 Watts. My question is, should you be doing it like 2 Watts or 19 Watts? Does it matter? Where should you be when she says very slowly.

Ulrich Dempfle: Slowly so you recover and slowly so you don't sweat unnecessarily. The warm up recovery and cooldown certainly are not part of the workout that contribute to the adaptation and making you fitter and stronger. In fact, the warm up doesn't have-- so you can keep the warm up as short as 20 seconds. I often also do the whole 2 minutes because I focus on my breathing, I loosen my joints a little bit. But if you've warmed up already or if you feel ready for the sprints, there's little that stops you from cutting the warm up shorts. So, you can do it in as little as 20 seconds. The recovery between the two sprints does have more purpose. So, the default would be 3 minutes and then depending on your fitness levels, you can keep that and whether you're in a rush, you can keep that shorter, the minimum is 1 minute. And the reason for the recovery is just to give your phosphocreatine system the short moment it needs to recharge so you can have a strong second sprint. 

Again, it varies a little bit by individual. I think for most people generally that's my understanding, phosphocreatine system would be fully recharged after about 4 minutes. 2 or 3 minutes is plenty sufficient for most people. And if you're very fit or if you're in a rush, then 1 minute is also fine. So that is something, again, you can compress. The cooldown is really important and you can't compress it. So, you should give yourself the full 3 minutes for the cooldown. And the main thing there is touched upon that earlier. So, you do have this osmotic imbalance and the transient drop in blood plasma volume and that means you have a transient drop in blood pressure and the 3 minutes are enough for your blood pressure to normalize. And as you come off the bike, then you shouldn't feel dizzy or somewhat worst case, that you faint or so. So that doesn't happen if you give yourself the cooldown period. If you were to just jump off the bike after your second sprint, I'm sure for most people nothing would happen, but some people would feel dizzy. So therefore, you can't shortcut the cooldown. And we very much recommend or advise that you take that moment and you can do-- The other thing is this actually helps to calculate your fitness score and give you good tracking data because that's the critical period where we want to see how fast your heart rate actually recovers. So, there're many good reasons to do these 3 minutes cool down in full.

Melanie Avalon: Okay, that's interesting. Is there another track that doesn't have the warm up or how do you skip the warm up? 

Ulrich Dempfle: Oh, that's done automatically. If you have the-- we call it the adaptive feature or user-controlled sprints, it's in essence, if you're in a rush, you feel ready, you can just sharply accelerate and the bike will then automatically initiate the sprint.

Melanie Avalon: I just start sprinting and it will--

Ulrich Dempfle: Correct. And if you're in a rush and then you could do the workout in, so the minimum is 5 minutes. And yeah, there are people who appreciate that. I usually do it in, so, I do quite often cut the warm up shorter and maybe not do the whole recovery so then it takes me like 6.5, 7 minutes or so to do my rides. It becomes marginal whether it's 7 or 8 minutes, but nevertheless, we focus on so we want to make every moment, every second count. And that's part of what we want to offer. If people don't want to pedal at a low resistance for 2 minutes, they don't have to.

Melanie Avalon: Even on the tiger narration track.

Ulrich Dempfle: That's correct. Yes.

Melanie Avalon: Will she stop talking or will she keep-- 

Ulrich Dempfle: She will skip to the ride.

Melanie Avalon: Really? Oh, I'm excited. I want to try this. Okay, that's super cool. The other question I had about-- A few other just quick questions about the, like, when the tiger is approaching and it's like 5 seconds until you sprint, the screen turns red like 5 seconds before, which signals to-

Ulrich Dempfle: 3 seconds before 

Melanie Avalon: -or 3 seconds, okay. Which kind of psychologically signals to me to start going faster? Am I supposed to start going faster or do I wait until the actual sprint commences? 

Ulrich Dempfle: So basically, when the counter hits the zero, you should be at your maximum cadence, your maximum pedal sprint, and different people manage to accelerate more explosively or not. So, some people need like the 3-second warning, others 2 seconds is enough, some people get in 1 second from, I don't know, 60 RPM to 150 RPM. You'll figure that out very quickly. And then the other thing is that and this is a settings question, so if you have that user-controlled sprint initiation, so that's in the bike settings you can select it or not, then if you basically start a bit too early, the bike would just apply the resistance at the perfect time for you. Because what's kind of less if you started at -3 seconds and you immediately reached your peak cadence, then you'd be spinning at a very high pace without resistance for like 2, 3 seconds. And that wouldn't feel optimal, so therefore it's better to have that user-controlled sprint starts enabled and then it basically takes that little bit of guesswork out as well. And it's just the resistance gets applied at the optimal moment automatically.

Melanie Avalon: So, when she says the tiger is approaching in the 3-second start, I start going.

Ulrich Dempfle: Exactly and then it will just happen.

Melanie Avalon: The AI resistance is sort of-- I mean, I'm not very consciously aware of what it's doing but that was something I did notice. I did notice it adjusted the resistance on that 3 second for me. I was like, "Oh, it made a change here." The other question I had about it. If you do the meditative breathing that she walks you through versus not, is there any difference? 

Ulrich Dempfle: So yes, there is actually. First kind of this 4 seconds in and 6 seconds out. So it's a parasympathetic nervous system balancer, it helps you calm down and to activate your parasympathetic nervous system and generally for most people that's the part that our sympathetic nervous system is usually fully dialed in. So, to take a moment and have this exhale focused breathing does help with calmness and mindfulness and I think Andrew Huberman over the last few months popularized very similar breathing pattern. So also exhale focused and he has this little double tap still which I've incorporated in my breathing and if you follow that it accelerates your heart rate recovery and it does help you calm down much quicker and normalize much quicker when I say much noticeably quicker after the sprints. So, I keep a close eye on that and when I focus on my breathing after the sprints, I see noticeably that my heart rate recovers faster and I come to basically a more normalized state quicker. Very clearly for me it works and there is actual research that shows that these exhale-focused breathing practices are effective.

Melanie Avalon: Also, it's just good for getting people into the habit of doing something meditative like that. So, it's basically like double whammy exercise and meditative practices and getting your workout.

Ulrich Dempfle: Exactly. It's kind of making most out of that time on the bike and there we can stack different things on top of each other. Yeah, exactly. 

Melanie Avalon: Because I will say sometimes, I do the breathing but a lot of times I do stuff on Instagram during the in between [laughs] and then I do the sprints. 

Ulrich Dempfle: That's okay. You do. 

Melanie Avalon: [laughs] Because then I'm like multitasking working and doing it. But the thing is I'm saying this to myself now and I say it every time I'm on the bike. I'm like, "Melanie, you should be doing the breathing." This would be such a good exercise and you know doing that meditative practice. So, I'm going to a try. [laughs] I do have one note for listeners and slight question for you about it. I turned the setting off and it was because the default right after you do the sprint it puts a message on the screen and says, "How do you feel?" And she stops talking and you have to select. I found for me it really took me out of the zone because I'd be in the zone listening and sprinting. And then when it went silent, [chuckles] not that I had a heart attack, but it always startled me a little bit.

Ulrich Dempfle: So that's okay, we're not upset that you disabled that, that's fine. It's absolutely a choice and we think it's maybe more helpful for new users. So, this reflects a very basic belief of ours that adherence is the most important thing. So, you can have the most wonderful, effective, efficient workout. If you don't do it, it's all meaningless. So, adherence is the most important thing. So, if you did feel not great or if you did feel, so it's basically two questions how do you feel today? And do you believe you can do it again? If you didn't feel well and you don't feel you could do it again, then we would really encourage you to try the REHIT versions with the shorter sprints and see whether those work for you and you feel well after those. It makes a huge difference whether a sprint is 20 seconds or 15 seconds or 10 seconds. And the shorter versions also have some evidence behind them. Obviously, it's not quite as effective, but if that's what you can do and then build up your strength and build up your fitness, then that's what you should be doing. And so, this is to encourage people to really find the workout that they can adhere to because that's really what counts.

Melanie Avalon: Is there a way to make it still ask me that without it going silent, because that was the only thing that bothered me, it goes quiet. 

Ulrich Dempfle: I'll check. Let me check that. So, I actually don't know the answer on that right now, but I'm very happy to check and I'll get back to you. 

Melanie Avalon: Cool, yeah, because it startles me when it goes quiet. Does it matter what shoes I wear?

Ulrich Dempfle: Yes, in a way it does. Not hugely and there are options. So, you can use just trainers, sneakers, possibly dress shoes, so you can definitely wear trainers or sneakers and use the toe cage and the toe strap to strap yourself to the pedals. And that works perfectly fine and it's perfectly adequate. However, if you like, cycling shoes are not a massive investment and the bike comes with some compatible cleats. And then you have clipless pedals. So, it's pedals that you can click in and you can eke out some extra power, actually, when you work out with cycling shoes so I use my bike with cycling shoes, I get a little boost in terms of peak power, and my performance is certainly a little bit better if I use cycling shoes. You don't have to, but it's a relatively small investment and yeah, I do it and I would probably recommend it as well. You don't have to, but it's a good thing. 

Melanie Avalon: Okay, awesome. Yeah, like I said, "I'm so naive with all this stuff," so I was like, "How can it really make a difference?" But I was talking to Brad, he's like, "You need to get the right shoes, it really matters." And I was like, "Okay."

Ulrich Dempfle: You can exert force across the whole pedal stroke, basically, and you need a little bit of practice there as well. But it's just it gives a better connection, a more solid connection between your foot and the pedal. So, it's marginal, but worthwhile. 

Melanie Avalon: Awesome. And then just a fun fact I'll share with listeners that I also learned on your blog. It was talking about stretching and it was saying most people think stretching beforehand is what's important, but it was saying that you might get more benefits with stretching after because of the blood flow release and everything. So, I thought that was super cool.

Ulrich Dempfle: [chuckles] Yeah. I have to admit, I've never thought of mobility exercises and stretching as anything important, but I've actually come around now and yeah, I do incorporate almost every morning a mobility and stretching routine into my daily morning routine. 

Melanie Avalon: Are you doing it before or after? 

Ulrich Dempfle: So, I do it after. Again, there's probably whatever feels best to you, I find, especially then if you've warmed up a little bit. I do after, but I'm sure there's again, you do you and as you feel best about it. Generally, I do think that the building blocks of a good workout routine is something for cardio, something for strength, something for mobility. So those are three pillars that everybody should, if they can at all, include in their routine and with CAROL Bike, the cardio component is taken care of and lower leg strength or leg strength is taken care of so quickly and efficiently. 

Melanie Avalon: Awesome. Well, thank you for your time. For listeners, Ulrich is in London, so I know it's your evening, so I really appreciate this. And this bike is changing my life. I want everybody to have it, [laughs] like everybody. You're so kind. So, for listeners, if you would like to get your own CAROL Bike, you can go to carolbike.com. You can use the coupon code MELANIEAVALON to get $100 off. I know a few people have already told me because I've been talking about it on The Intermittent Fasting Podcast and a few listeners have said they already got one. But I know you're talking about the barrier to entry and the price and everything. I just think if you step back and look at it compared to a gym membership or the long-term investment, it's really the way to get the ultimate cardiovascular REHIT. All these benefits that we've talked about throughout this episode in your life. Oh, and I didn't even mention so it doesn't take up. I mean, it's an exercise bike, but I was able to fit it in my apartment pretty nicely. It's just amazing. Thank you for making it. 

Ulrich Dempfle: Thank you. It means a lot to hear that. Thank you very much. 

Melanie Avalon: And actually, so the last question that I ask every single guest on this show, speaking of thank yous and it's just because I realize more and more each day how important mindset is, so what is something that you're grateful for? 

Ulrich Dempfle: Honestly, that I have the opportunity and privilege to work on a product like this. That first is really what I enjoy doing and that I'm passionate about and that touches now a growing number of people and their lives. So that's one of the things. There're many other things I'm also grateful about, but certainly that is one thing I'm grateful for. 

Melanie Avalon: I love it so much. Thank you again. I just can't give a higher endorsement for this product. It's amazing and I can't wait for listeners to hopefully be able to try it. Yeah, I really look forward to all of the updates in the future. 

Ulrich Dempfle: Thank you so much. Thank you so much for having me. I really enjoyed that conversation. Thank you. 

Melanie Avalon: Me too, me too. Have a good evening and I will talk to you soon. Thanks. 

Ulrich Dempfle: Thank you. 

Melanie Avalon: Bye.

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