The shortest,
most effective cardio workout

We’re dedicated to the science of fitness, always backed by proof. To discovery and design that makes training more efficient. And workouts that make every moment mean more.

What is REHIT?

The basis of the science behind CAROL is REHIT (Reduced Exertion High-intensity Interval Training). It’s a new, improved form of HIIT (high-intensity interval training).

A typical HIIT program lasts 30 minutes, and is extremely difficult for many people. But a REHIT session with CAROL session consists of two 20-second sprints, separated by a short recovery. The whole workout lasts from as little as 5 minutes.

Where HIIT offers high-intensity training, REHIT offers maximum intensity training. This pushes your body to new limits, making you much stronger and fitter.

REHIT: next-level HIIT

By following the principles of REHIT, the maximum intensity levels during a CAROL sprint are about 2.4× higher than in HIIT spin classes. This means our workouts deliver bigger health and fitness benefits in 20% of the time compared to regular exercise.

CAROL’s REHIT workouts automatically apply the optimal resistance, at the right speed, at the right time – all based on your personal fitness level. It’s a level of precision that you won’t find from any other form of exercise, with unmatched benefits.

Approved by top exercise researchers

Martin Gibala, PhD

Interval training is the closest thing we have to an exercise pill. A tiny bit of sprint training has the same effect on the human body as a whole lot of endurance training.

Martin Gibala, PhD

Author, The One-Minute Workout

Dr. Niels Vollaard, PhD

CAROL is the only bike that accurately replicates REHIT outside of the labs. This scientific exercise cannot be done on a regular bike because it requires the supra-maximal resistance tailored to each person’s physiology.

Dr. Niels Vollaard, PhD

Exercise Physiology Researcher, University of Stirling

Lance Dalleck, PhD

REHIT workouts generate a meaningful EPOC (excess post-exercise oxygen consumption, known as afterburn), that can have an important impact on the overweight and obesity epidemic.

Lance Dalleck, PhD

Professor of Exercise and Sport Science, Western State Colorado University

Benefits of REHIT with CAROL

Take a closer look at the science-backed benefits you’ll get with CAROL workouts.

Improve your cardio

We measure cardio fitness by VO2max – the maximum amount of oxygen that you can use during intense exercise. In an eight-week study, participants improved their VO2max by 12% – nearly double the cardiorespiratory fitness improvement compared to other forms of exercise.

Read the study

Boost your metabolism

A recent study shows that the calorie-burning benefits of CAROL continue long after you finish your workout. Thanks to afterburn (or excess post-exercise oxygen consumption), you’ll burn 60-70% of your total calories from a CAROL workout once you’re back at your desk.

Read the study

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. The study also showed that HIIT increased insulin resistance in young women.

Read the study

Get healthier

REHIT participants reduced their risk of type 2 diabetes by 62%. Their blood pressure was reduced by 5%, triglycerides (fat found in blood) reduced by 10%, good cholesterol (HDL) increased by 6%, and blood sugar reduced by 2%.

Read the study

Live longer

CAROL helps you get fitter, healthier and burn more fat. In eight weeks, you’ll see a 12% improvement in your VO2max. That’s like turning back the clock on aging by a decade, and adding two years’ healthy life expectancy to your lifespan.

Read the study

Explore our science in depth

CAROL’s been rigorously tested in a number of . We use data from peer-reviewed scientific research to make continual improvements to our products. The end result? The most efficient cardio workout for you.

REHIT training is more effective at improving cardiorespiratory fitness and cardiometabolic health than traditional training.

Lance C. Dalleck

Western Colorado University

January 2019

The Metabolic Responses and EPOC of CAROL: an AI-Powered Exercise Bike.

Lance C. Dalleck

Western Colorado University

January 2021

The effects of high-intensity intermittent exercise training on fat loss and fasting insulin levels of young women.

E. G. Trapp

University of New South Wales

January 2008