Science Feb 10, 2023

Next-level HIIT

CAROL’s the only bike with REHIT, the next-level HIIT workout that gives you superior health benefits, in 90% less time.

Hands gripping the CAROL Bike handlebar mid-sprint, black and white

Reduced Exertion HIIT (REHIT) was developed by scientists looking for the shortest, most effective and accessible way to exercise.

REHIT creates the most potent training stimulus with just 2×20-second sprints. It’s scientifically proven to deliver superior health and fitness benefits compared to normal exercise—in 90% less time.

CAROL’s AI-personalization and Instant Resistance help you push to your limits during the sprints. Like in a ‘fight or flight’ situation, your muscles are forced to mobilize about 25-30% of muscular glycogen—your emergency energy reserve—which releases key signaling molecules (AMPK and PGC-1a), telling your body to get fitter and stronger.

You develop more mitochondria, your blood plasma volume increases, and your heart gets stronger. Resulting in increased aerobic capacity.

The adaptation pathway

What 2 × 20 seconds sets off

1. The sprint depletes muscular glycogen

Pushed to your limit, your muscles mobilise about 25–30% of muscular glycogen — the emergency energy reserve your body keeps for a fight-or-flight moment.

2. Signalling molecules are released

Depletion releases AMPK and PGC-1a, the molecules that tell your body it must get fitter and stronger. This is the stimulus; the sprint is only the trigger.

3. Your aerobic machinery is rebuilt

You develop more mitochondria, your blood plasma volume increases and your heart gets stronger — the adaptations that raise aerobic capacity.

4. VO₂max rises

The result shows up as a higher VO₂max: the single best measure of cardiorespiratory fitness, and the one that tracks with how long you stay healthy.

Each step happens after the sprint, while you recover. Longer or extra sprints do not add to it.

Previously REHIT was only possible in a lab setting. But we teamed up with the world’s leading exercise researchers to get REHIT into the real world. And 40 prototypes later, CAROL Bike—the world’s only home REHIT exercise bike—was launched.

Dr. Niels VollaardPhD, Exercise Physiology Researcher, University of Stirling

Read the full study here.