How To Get the Benefits Of A 45-Minute Run In Under 9 Minutes (& A 12% VO2 Max Increase & 62% Lower Risk Of Diabetes): The New AI Bike That Is Taking The Fitness World By Storm.

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Ever heard of the AI-powered smart bike that gives you the benefits of a 45-minute run in under nine minutes?

Here's the deal: we already know HIIT training is a great way to work out. The bike uses REHIT—Reduced Exertion High-intensity Interval Training—which is HIIT taken to the next level.

With REHIT training, you can get better health and fitness results compared to steady-state exercise, in 20% of the time, just 26 minutes a week—and you’re not putting your body under the kind of stress that you get with chronic cardio, which can actually be damaging to your health and stall your weight loss.

I have a CAR.O.L. bike in my office, and I now use it for my REHIT breaks. You just get on the bike, you start riding, and in less than nine minutes you’ve checked your cardio off for the day. This thing is a game-changer—it was developed in collaboration with fitness researchers and is clinically proven to give you the shortest, most impactful cardio workout you can get.

The CAR.O.L. bike will get you fitter, healthier, and leaner. In eight weeks, you’ll increase your cardio fitness and see a 12% increase in VO2 max, which may add two years to your lifespan. You’ll reduce your risk of type 2 diabetes by 62%, and lower your blood pressure, triglycerides, and blood sugar. And you’re going to burn more fat because the CAR.O.L. workout increases excess post-exercise oxygen consumption, which boosts your metabolism and keeps your body burning fat for hours after a workout.

My guest on today's show, Ulrich Dempfle, is Chief Product Officer and co-founder of CAR.O.L. Ulrich holds degrees in business administration and mechanical engineering, and leads all aspects of product development at CAR.O.L., from data science to software and hardware. Previously, he was the director of PwC’s healthcare AI initiatives in the UK and has a wide range of experience in healthcare, engineering, and startups.

The idea for CAR.O.L. was conceived in 2012 while working on chronic disease management programs for people with diabetes. The team found it very challenging to get people to exercise, and the main excuses they heard were a lack of time and frustration with slow results. The beauty of CAR.O.L. is how REHIT solves these problems, offering a scientifically proven workout in under nine minutes. After discovering REHIT, the team embarked on creating CAR.O.L., the first and only consumer REHIT exercise bike available.

Ulrich practices what he preaches, and uses CAR.O.L. regularly. He says his cardiovascular fitness has improved by 50%, and he has lost about 10 kg and can now easily manage his weight without counting calories. His blood pressure was slightly elevated but is now optimal, and he’s in better shape than ever.

During our discussion, you'll discover:

-HIIT or HIRT?…03:30

-How did Ulrich come up with the idea?…07:30

  • CAR.O.L. = Cardiovascular (CAR) Optimization Logic
  • The idea for CAR.O.L. was conceived in 2012 while working on chronic disease management programs for people with diabetes
  • Excited about how this technology could help people with significant health concerns

-What's unique about the bike…08:43

  • Helps people achieve their maximum fitness gains with minimum time requirement using the power of REHIT and AI
  • The core REHIT ride using the bike is 8 minutes and 40 seconds
  • Every ride is personalized according to each user's data and level of fitness

-How REHIT is different from HIIT…18:58


  • A new, improved form of HIIT
  • REHIT session with CAR.O.L. consists of two 20-second sprints, separated by a short recovery
  • Total workout time – 8:40
  • REHIT offers maximum intensity training; pushes the body to new limits, making you much stronger and fitter

-The benefits you can expect with CAR.O.L. and REHIT…21:17

  • Partnered with the leading REHIT researchers
  • Improve your cardio – 8 weeks to turn around your cardiorespiratory fitness—improve cardiorespiratory fitness (measured by VO2 max) by 12.3%
  • Get healthier – lower your risk of Type II Diabetes by 60% in 8 weeks—that’s the same level of change you’d see actually taking Metformin
  • Boost your metabolism – burn twice as many calories minute-per-minute compared to traditional exercise, because of the “after-burn” effect, which means you keep burning calories for hours after a CAR.O.L. workout
  • Lose weight – in a 15-week study on the benefits of HIIT, participants saw a 2.5kg reduction in total body fat, particularly in the legs and tummy

-How cardio with CAR.O.L. impacts chronic disease…23:35

-How cardio with CAR.O.L. impacts longevity…29:26

-Does the CAR.O.L. achieve the same benefits as other types of cardio?…30:50

  • You’d need to spend a lot more time on it: with other cardio, you would need 2.5 hours per week and more whereas with CAR.O.L. it is as little as 26 minutes per week
  • Feedback from users is that CAR.O.L. makes it easy to establish a healthy habit because it is so short and you can fit it easily into your daily routine
  • It’s fantastic to see how quickly you can improve your fitness, but the flip side is that you have to stick to your routine to maintain it
  • If you stop exercising, you lose much of the fitness gains within a 4-week period
  • If you don’t have an extra 2 hours a week for exercise, it’s no good to have a bike with great music and celebrity instructors
  • Such external motivation might work for a while, but you ultimately need something that fits into your life and that you can stick to
  • CAR.O.L. can be a backstop for longer forms of cardio

-The science behind the bike…38:03

  • Pretty much everyone is familiar with HIIT, so REHIT is a specific form of HIIT, developed by Drs. Niels Vollaard and Richard Metcalfe at the University of Bath
  • They developed an exercise protocol that is MUCH more time-efficient than both conventional exercise and HIIT, while still providing the same or better health and fitness benefits
  • “No pain, no gain” has put a lot of people off exercise; a minimal amount of pain can give you very big gains
  • The sprints create a sudden spike in energy demand that’s 100-fold greater than rest
  • Sprints tap into your body’s emergency energy reserve as it anticipates and prepares for a “fight or flight” situation
  • You don’t have to do more or longer sprints because the mobilization of the glycogen is triggered by the rapid onset of the energy demand in the sprint (why it doesn’t matter so much how long you sprint but how quickly you start)
  • Rapid glycogen depletion triggers the release and activation of certain signaling molecules (AMPK and PGC-1α), which triggers mitochondrial biogenesis, i.e., your body develops more mitochondria, which are the “power plants” in your cells, which means you are better at utilizing oxygen in your muscles
  • Beyond Training by Ben Greenfield
  • New study shows that your body gets better at delivering oxygen to your muscles by improving your cardiac output, your heart gets stronger and pumps more blood through your vascular system
  • Two 20-second maximum intensity sprints “saturate” the signaling response mechanism—which is like a switch, so more or longer sprints have no additional benefit, so after those two sprints that’s it, you’re done for the day, and you only need to do it 2-3 times per week

-Why do you need a special bike?…39:43

  • The maximum intensity levels during a REHIT sprint are about three times higher than in other HIIT cycling classes
  • On a regular exercise bike you’d need to:
    • Apply the correct resistance (just in your sweet spot)
    • At the right time (just after you’ve built up speed at a low resistance)
    • In a fraction of a second (instantly go from very low to very high)
    • In other words, it’s very difficult without an exercise physiologist or an expert personal trainer by your side

-How Ulrich uses the bike…44:33

  • He does a ride in the morning,  in a fasted state, and burns 215 kcals straightaway
  • That’s more than 10% of his baseline calorie need and it helps him manage his weight with very little effort
  • Ulrich finds it suppresses appetite and helps him stay in the fasted state longer

-Can CAR.O.L. be combined with other biohacking tools?…47:40

  • This year CAR.O.L. reached 10,000 riders in the community so definitely have lots of feedback from riders on combining CAR.O.L. with biohacking tools
  • Fasting
    • One of the exercises that is easier during fasting as it is so short
    • If you do a longer, strict fast, it is probably sensible to be careful with exercise
  • Katalyst
  • Can work beautifully with time-restricted eating or intermittent fasting
  • Cold exposure
    • Very popular but some concern and evidence that ice baths after resistance training blunt the effect
    • However, the same problem is not present with cardio and endurance training
  • Some riders love to combine CAR.O.L. with blood flow restriction bands
  • Other riders combine CAR.O.L. with LiveO2 trainer with increased or reduced oxygen supply

-How to mitigate the EMF the CAR.O.L. bike produces…52:45

  • The bike has an off-line mode automatically activated if the bike is set to airplane mode
  • The bike was designed as a connected fitness equipment
  • Connect the bike to wi-fi for initial set-up
  • Connect once in a while to upload and download personalized data

-How one can get started with CAR.O.L.?…55:06

-And more…

Upcoming Events:

Click here for the full written transcript of this podcast episode.

Resources from this episode:

– Ulrich Dempfle:

– Podcasts And Articles:

– Books:

– Gear:

– Other Resources:

Episode sponsors:

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Do you have questions, comments, or feedback for Ulrich Dempfle or me? Leave your thoughts below!


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11 thoughts on “How To Get the Benefits Of A 45-Minute Run In Under 9 Minutes (& A 12% VO2 Max Increase & 62% Lower Risk Of Diabetes): The New AI Bike That Is Taking The Fitness World By Storm.

  1. Matt says:

    I have now done 3 sessions on the bike. It is great! I wear an Oura ring and my resting HR and HRV scores have already seen a dramatic improvement. Your legs feel it after you are done. You really don’t break a sweat. It is so easy to incorporate in your daily routine. I’m very happy with the purchase.

  2. Tom Griesel says:

    I’ve owned one since the summer and use it 3X per week whenever I’m not traveling. Although there are several different programmed sessions available and it can also use the Peloton app, I have been using the “Intense” session as discussed in this podcast. I like that it is structured in that it keeps you totally focused on what you are doing and pushing you for a maximum effort. This is the key to getting the claimed benefits in such a short period. It’s not easy. I was very surprised how my legs feel after I finish a session. The bike “learns” about you with each session and adjusts resistance during the sprints accordingly. I have seen all of my scores gradually increase over time and they still keep getting better. Improvement comes in waves not in a strict linear progression. You can view your progress on the app and also see where you rank in global standings of registered users. I’m 67 years old and currently rank at #130 however, there is a huge gap to #1 so it’s very motivating as well.

  3. Jason Pecjak says:

    How does this type of training data compare to the Mayo 2017 HIIT study on (3x a week cycling at 90> for 4 x4 min intervals with 3 min recovery) on the cellular level?

  4. Ben Sanford says:

    Lots of folks like me already have already paid good money for an exercise bike. Would be great if they could just sell an app or subscription for the program to be used on another bike.

    1. Thanks for the suggestion Ben! Feel free to contact the CAR.O.L. team directly: [email protected]

  5. Sean says:

    So what happens to all that glycogen that was mobilized but not burned?

  6. Michael Pace says:

    I have a cheap Sunny bike from Amazon $300 and it has the old school rubber resistance knob. If you just press down straight down (not turning) it engages the break. I can easily adjust the resistance rapidly and my choosing without comprising cycling exertion. I can then pull up on the break and all the resistance is gone immediately. I never knew this break feature was so useful for HIIT, HIRT, or ReHIT style training. Hope this helps.

  7. Jay Smithson says:

    I’m with Ulrich all the way until he says that ReHITT requires the special bike. I could see why automating the changes makes it much easier but don’t see why one can’t just use a normal spin bike (or Versaclimber, rowing machine etc.) to roughly accomplish the same thing with 2 to 4, 20 second super high intensity bursts over an 8 to 15 minute protocol to get to some sort of 1 to 6 ratio of work to rest per the HIRT protocols. Obviously, you have measurement and motivation challenges without the program being automated but it seems like those also should be possible to overcome. Two questions that were unclear from the podcast:

    (1) How do ReHITT and HIRT differ if at all?

    (2) To my comments above why can’t a skilled personal trainer program something similar with a standard spin bike and data from the session?

    Another question, is there value to varying the modality for ReHITT/HIRT between bike, row, run, snowshoe etc. as opposed to limiting yourself to just one modality?

    p.s. Treadmills aren’t listed because sprinting all out on a treadmill seems unsafe. Obviously, sprinting outside is totally different.

    1. Michael Pace says:

      See my previous comment on how to do this on a standard bike.

      As for modalities it’s a game of mobilizing but not necessarily burning glycogen. Thus whatever exercise chosen should engage the largest muscles in the body. Glutes, legs, back have the advantage.

      Also I would image that X3 bar style workouts would provide similar effects.

  8. Brian Dennis says:

    Does this bike offer an ethernet connection as I don’t use wifi?

    1. Hi Brian! That’s a great question, please email them directly: [email protected] I know you get a 100-day home trial, free delivery, and $250 off with code BEN, so you can always try it out and see what you think: https://bengreenfieldfitness.com/carol

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