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Minimal Time

Lack of time is the most common barrier to exercise. If you have minimal time or are otherwise unable to do longer workouts, Reduced Exertion HIIT (REHIT) is the optimal workout for you.

REHIT can be done in as little as five minutes, and we recommend that everyone do 2-3 REHIT rides per week. If your goal is to improve cardiorespiratory fitness, research indicates that 2x REHIT rides per week are sufficient. If you want full metabolic health benefits, 3x rides per week are recommended.

CAROL Bike’s signature workout, REHIT Intense, consists of 2×20-second sprints with a short rest in between as well as a warm up and active recovery. Backed by strong scientific evidence, it is the shortest, most effective cardio workout.

The stages of REHIT

2×20-second sprints may sound little, but if performed at maximum intensity, they will push you to your limits. If the Intense ride is difficult, you can try two alternatives: the REHIT Intermediate (2×15-second sprints) or REHIT Energizer (2×10-second sprints). The Intermediate ride is estimated to deliver 70% of the Intense ride’s fitness benefits, and the Energizer ride has been shown to deliver 40% of Intense ride’s benefits.

Adherence is most important, so a 5-second shorter sprint can make all the difference.

If instead you want to challenge yourself even further, you can try the 3×20-second sprint intervals or the 10×6-second sprint intervals at not much greater time commitment. Both workouts are scientifically validated and provide similar benefits to the REHIT Intense workout. (See the 3×20-second sprint study here and the 10×6 second sprint study here.)


Train in Zone 2 for optimal longevity benefits.

Fitness Tracking

Track Functional Threshold Power (FTP), aerobic performance, and more.

Weight Loss

Burn twice as many calories as regular exercise with Fat Burn rides.

Endless Entertainment

CAROL Bike integrates with entertainment apps like Netflix, Disney+, YouTube and more.

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