My Honest Review of the Carol Bike’s Five-Minute Workout

I tried a very short REHIT fitness regime, and asked experts to weigh in on its effectiveness.

Maybe using the F word is a little strong, but it’s accurate: I completely failed at exercise for the entirety of my 30s. At least the sweaty, heart-pounding, happy endorphins, cardio-burn kind of exercise.

I love to ski (downhill), I love a hike or brisk mental-health walk, a gentle yoga class. I did a lot of postpartum Pilates core classes, toting my babies along. But a chronic hip injury, the demands of working full-time during the pandemic with kids mostly home, and a general state of overwhelm meant I just never got into a solid cardio routine, especially anything approaching high-impact. The last time I went on a jog was literally when I was forced to, while chasing a runaway toddler. But I’ve read enough about fitness and aerobic activity, especially as we venture into middle age, to know that it’s essential for my heart health.

What is the Carol bike?

That’s why an efficient, effective and short workout was so enticing to me. Carol, the “smart” spin bike I’ve been trying out at home for the past year, promises five minutes to peak fitness and is designed to help users “swap out their 45-minute run” for super-fast high-intensity workouts that are easy to slide into a busy daily calendar.

The science behind it is REHIT, which stands for reduced exertion high-intensity interval training. Carol delivers AI-personalized, tailor-made spin rides set at your optimal resistance each time you hop on, factoring in your age, weight, height, sex, rate of fatigue, maximum pedal speed, past resistance and heart rate, from a chest strap monitor worn at your bra line.

The “signature” five-minute workout is two maximum-intensity sprints lasting 20 seconds each, spaced out with low-intensity warm-ups and a cool-down period. Two or three rides a week, at five minutes each, is really all you’re supposed to do to increase your aerobic fitness levels. Trainers or elite athletes sometimes refer to this as your “VO2 max” – or your maximum rate of oxygen uptake during exercise. A higher VO2 max is an indicator of better cardiorespiratory fitness—meaning improved heart health and lung health, and it’s easier to run, swim or do any other kind of cardio.

Niels Vollaard, a lecturer in health and exercise science at the University of Stirling in Scotland, is a senior author of multiple widely cited studies examining the biological and biometric gains of REHIT forms of exercise. He looks at exercise in an evolutionary context, comparing our modern sedentary lifestyles—complete with delivery apps and grocery stores—to the physical demands of our hunter-gatherer days.

“We don’t have to do any exercise anymore to be able to eat—and our genes haven’t evolved to cope with that,” he says. “So in order to stay healthy, you have to exercise—there’s no way around it.”

Effective exercise must create what Vollaard calls “a disturbance of homeostasis.” You need to shake it up, he says. “Your heartrate has to go up, and your muscles have to start using their fuel, and you have to breathe faster.” But if you’re choosing low- or moderate-intensity exercise as your preferred method, says Vollaard, “you have to have lots of it.” And because not everyone likes to exercise, and it takes longer, compliance is low.

(Related: Bungee Cord Fitness: The High-Intensity, Low-Impact Exercise You Need to Try)

The science behind REHIT

REHIT sessions can be very short, he says, because “REHIT incorporates ‘supramaximal’ or ‘all-out’ exercise. Doing more of it will not further enhance the benefits you get.”

“This is why we’ve been looking at, ‘What is the exercise that will disturb homeostasis the most?’ Because if you can disturb homeostasis quickly, then you won’t need to do too much of it,” he explains. These very short bursts of explosive activity—pedalling like your life depends on it—are what make the Carol cycling workouts stand out from other stationary bikes.

In fact, the British female voiceover that accompanies the cycling intervals and cool-downs asks riders to imagine they’re cave men, essentially, trying to outrun a tiger. How hard and how fast you pedal results in a tablet screen full of numbers: wattage, cadence, heart rate, fitness score, calories burned, energy output. They all add up to your overall fitness and whether you would have survived in a racing-across-the-savannah, man-versus-animal chase scenario. Not exactly a peaceful or anxiety-reducing exercise. (I promptly disabled the voice and chose music instead.)

Sometimes the tablet-screen readouts, which are meant to be inspirational, seem lost in translation or suffer from cultural differences. For example, if you choose a longer, more traditional “fat burn” ride, the prompts are mired in outdated admonishments about junk food, and seem out of touch with current body-positivity trends. One read, “My sprints burn a lot of sugar in your thighs,” and another joked, “But no KitKats when I’m not looking!”

My personal Carol bike review

Unlike the popular Peloton, this bike—which came to market in late 2018—isn’t really about building camaraderie with group classes, or the fun soundtrack, or the standout instructor personalities. Carol, which stands for CAR-diovascular Optimization Logic, is a German company, and it’s designed for people with no time. In fact, it’s main selling point is how little time you need to spend in the saddle. You don’t really break a sweat, and you probably won’t have to shower after. I’ve used Carol in between Zooms, while still in my pajamas in the morning, or while my kids conduct raucous playdates in the basement around me. And like any indoor exercise machine, it’s great for when you don’t have childcare, or when the weather outside is grim.

Truth be told, it’s one of the only forms of cardio I’ve ever stuck with. Trainers and fitness gurus call this consistency; doctors and researchers call this exercise adherence. The best form of exercise is the one you’re actually going to do, week after week, month after month, Vollaard told me, even if it doesn’t feel like you’re logging lots of miles or getting sweaty.

This is one of the trickiest hurdles that doctors and cardiologists encounter with patients at high-risk of heart disease, or recovering from heart disease, says Jennifer Reed, the director of the Exercise Physiology and Cardiovascular Health Laboratory at the University of Ottawa Heart Institute. Her research focuses on women’s heart health and the role exercise plays in cardiovascular disease prevention and rehabilitation.

She says that HIIT or REHIT may sound intense or intimidating, but it’s actually doable for many people, even her patients with heart disease. “It allows them to train at a higher level, and then achieve those cardiovascular health benefits that they probably wouldn’t have achieved if we said, “Go exercise for 45 minutes on the elliptical at moderate to vigorous intensity.’”

In a way, the shorter intervals simulate very real-world scenarios, Reed explains. “If you’re a patient with heart failure, you struggle to even walk up a flight of stairs, right? You may walk a few stairs and then take a break, and then walk a few more stairs and take a break. And that very much aligns with interval training.”

In short, it works, she says. “If you can exercise at moderate-to-vigorous intensities, you will reduce your risk for cardiovascular morbidity and cardiovascular mortality.” I don’t have heart disease, but I do worry that all my yoga, stretching and mobility classes—mostly floorwork—mean I’m neglecting my cardiovascular health. So I was heartened (forgive the pun) to hear that I was on the right track with REHIT.

It’s quick, it’s easy and perfect for people who don’t actually enjoy exercising. What it isn’t: cheap. At $3,395, plus $19 per month in membership fees, it isn’t realistic for most individuals to purchase a Carol bike for their home. Vollaard believes the best use of the Carol bike is in the workplace. Because workouts don’t take long, multiple employees can use the same bike, quickly counteracting the negative health effects of their sedentary workdays while the employer shoulders the hefty price tag.

“We need a range of solutions and more preventative care,” Vollaard explains. “If you do only one thing – and if you would stick to this – you only need two or three sessions a week. That really becomes a cost-effective intervention that is easy to fit in. Just hop on and get it over with.”

Cycling with the Apple Watch

If the price tag on a Carol bike makes you gulp, there is an easier way. The latest operating system update for the Apple Watch has new bike and spin workout features that will allow you to use your watch as your own personal AI while cycling, at a fraction of the cost. With watchOS 10, you can connect to Bluetooth cycling accessories—such as power metres, speed sensors and cadence sensors—to capture metrics like cycling power and RPMs. The watch will show you your heart-rate zones and cycling speed, as well as elevation and race route, if you’re actually cycling outside. Personally, I found that the heart-rate monitor built into my Apple Watch was just as consistent and accurate as Carol’s chest-band heart-rate monitor, and it’s way more comfortable to wear while exercising.

Apple Watch Series 9,, starting from $549.

Next: Kickboxing is the Fun, Full-Body Workout You Never Knew You’d Love

Originally Published in Best Health Canada