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How the new 5-minute REHIT workout works

The shortest, most effective cardio workout just got even shorter.

01 Jun 2022

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Since the CAROL bike launched in 2018, it’s been possible to get the health and fitness benefits of a 45-minute run in just 8 minutes 40 seconds.

It may sound too good to be true, but this short, effective cardio workout is based on peer-reviewed scientific research into a time-efficient alternative to regular exercise called reduced exertion high-intensity interval training (REHIT).

Four years later, we’re proud to announce our latest CAROL Bike update now makes it possible to get the health benefits of REHIT from just 5 minutes. That’s right, the shortest, most effective cardio workout just got even shorter! To tell you how we did it, we first need to explain the science of REHIT…

How does REHIT work?

In simple terms, the physiological basis of REHIT is that maximum-intensity exercise makes your body enter fight or flight mode, increasing its energy demands 100-fold. After all, your body has no idea you’re doing a sprint on an AI-powered exercised bike and not escaping a predator.

Your body also has no idea how long you will need to sprint for, meaning this increased energy demand causes your muscles to mobilize significantly more glycogen (stored sugar) than actually required for two short sprints. This rapid energy reserve depletion activates physiological adaptations that make you fitter and stronger. After all, maybe next time you’ll need to run even faster and further to safely escape the ‘predator’.

Delve deeper into the science of muscle glycogen depletion

CAROL is the only exercise bike that offers true REHIT because its AI personalizes your workouts to ensure you hit your own personal maximum intensity every time. Or as health and exercise science in sport researcher at the University of Stirling, Dr Niels Vollaard, puts it: 

CAROL is the only system that accurately replicates my research outside of the labs. This scientific exercise cannot be done on a regular bike because of the supra-maximal resistance required that also needs to be tailored to each person’s physiology.

The science behind CAROL bike’s new 5-minute REHIT workout

The REHIT protocol used in CAROL’s original 8-minute 40-second Intense ride uses this structure:

Warm up – 2 minutes

Sprint 1 – 20 seconds

Recovery – 3 minutes

Sprint 2 – 20 seconds

Cooldown – 3 minutes

Research shows REHIT’s physiological impact stems from the maximum effort sprint periods. That got us thinking: would it be possible to shorten the non-sprint periods without impacting the overall health and fitness benefits?

Putting that question to Dr Vollaard, here’s what he had to say: “The health and fitness benefits of REHIT are triggered by two 20-second maximum intensity sprints. Warm up duration has no impact on the effectiveness of REHIT.

So far so good. But what about recovery between sprints? “To get the full health and fitness benefits of REHIT your recovery between sprints needs to be long enough to allow for a strong second sprint.

We know what you’re thinking: How long is ‘long enough’? That’s up to you. As a rule, it’s sensible to wait until you’ve caught your breath, but it’s simply whenever you feel ready to go all-out again.

The cooldown period remains three minutes long. As CAROL CEO and co-founder, Ulrich Dempfle, explains: “It’s important for blood pressure, to normalize again after the sprint. Research shows light pedalling does this faster than just sitting or standing would. That’s because keeping the muscles active assists in pumping blood back to the heart and speeding up the removal of ‘waste’ products from the muscle, reducing the imbalance between the concentration of such particles inside and outside the muscle cell.

To summarize, the health benefits of REHIT lie in the maximum effort sprints. And while cooldown is essential to ensure your body normalizes before you get off the bike, warm up duration has no impact and recovery phase duration is unique to you.

In other words, we’ve put the power in your hands, or – more precisely – your legs!

How to do CAROL bike’s new 5-minute REHIT workout

  1. Hop on your bike and log in to the CAROL app
  2. Choose Intense ride
  3. From 20 seconds into the warm up and one minute into the recovery phase, a checkered flag will appear on the RPM dial
  4. When you see that flag and feel ready, simply pedal faster to begin the sprint

Got a question? Let’s book a call.

All our experts have MSCs in Exercise Science, and they’re here to answer your questions. Whether it’s about these workouts, or the science behind CAROL Bike, whatever’s on your mind—we’re here for you.

Book your free call
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