It’s 8:47 am, and I’ve just gotten back home from daycare drop-off. That means I have 13 gloriously free minutes before I’m supposed to log in to work. What to do? I could go wild and Swiffer the floors (god knows they need it). I could open up my laptop early like I normally do. Or I could hop on the CAROL Bike in my living room and get in my full cardio workout for the day—with enough time afterward to brew a fresh cup of coffee.
Yes, it’s possible: This high-tech stationary bike offers super-short-but-intense, scientifically-validated workouts that let you knock out your aerobic exercise needs before you even have a chance to get sweaty.
Short “exercise snacks” have become a popular strategy to squeeze strength training or mobility work into spare moments of our work-from-home days. But most cardio workouts still require a decent chunk of time to get the full endurance-building, heart-healthy benefits (think: at least 20 to 30 minutes). Even if you opt for a high intensity interval training (HIIT) workout—which exercise scientists say is far more efficient than moderate-intensity cardio—between your warm-up, cool down, the intervals, and recovery time, you’re still usually looking at a good half hour or so.
That’s why, over the last decade, researchers have pushed to see just how low we can go. The answer? “Just a couple 10- to 20-second all-out sprints is sufficient,” says Lance Dalleck, PhD, a professor of exercise and sports science at Western Colorado University who researches the impact of exercise on our health.
The trick, however, is that those sprints need to be dialed up to max intensity to make them truly effective.
How does the CAROL Bike work?
CAROL stands for “Cardiovascular Optimization Logic,” which sounds very fancy, and, well, it kinda is.
Here’s the Cliff Notes version of the science: Research has found that if you go hard enough for 20 seconds, you use up sufficient muscle glycogen to trigger a cascade of favorable metabolic changes as your body works to restore that glycogen. “You turn on these pathways that make more mitochondria (which leads to improved cardiorespiratory fitness),” says Dr. Dalleck
That’s why CAROL’s signature workout lasts just eight minutes with two all-out 20-second sprints, plus very low-intensity warmup, recovery, and cooldown periods.
This strategy has been coined “REHIT,” or reduced exertion high intensity training. At first, it was only available in labs with equipment that helped you hit those all-out sprints at the ideal intensity. But the CAROL Bike ($2595) brings this science right inside of people’s homes.
Dr. Dalleck has been sponsored by the American Council on Exercise to run multiple studies on the CAROL bike over the past four years, looking into its effects on things like cardiorespiratory fitness, blood glucose regulation, and blood pressure.
“The reason why the CAROL bike is effective is that it’s able to use, I call it a ‘low-grade form of artificial intelligence’ where it’s able to detect your power output with each sprint, and how much you’re fatiguing, and remember that for the next session,” explains Dr. Dalleck. “So it’s personalizing that sprint for you.” Meaning that every time you use the bike, it measures how hard you’re cycling throughout those 20-second sprints, and how your heart rate reacts, then recalibrates the resistance for next time so that it never gets easier—even as you get fitter.
By doing just three of these eight-minute workouts for eight weeks, research shows that you can increase your VO2 max (a benchmark for aerobic fitness) by more than 12 percent, decrease your blood pressure by five percent, and reduce your risk of developing type 2 diabetes by 62 percent.
Such extreme results from such a small time commitment might sound like science fiction, but Dr. Dalleck points out that the design of the workout is based on a couple decades’ worth of exercise science. “You would expect to see these types of benefits,” he says.
What’s included: Each CAROL bike comes with an 11″ touchscreen, heart-rate monitor, and a one-year warranty (with upgrades available)
Membership: An additional $15 per month (includes access for eight different accounts on the bike)
Footprint: 45.5″ x 22″
Bike weight: 120 pounds
Rider requirements: Must be between 4’7″ and 6’7″, up to 330 lbs
Delivery: Free within mainland US
Return policy: There’s a 100-day trial period
What the CAROL Bike is like to ride
The CAROL Bike’s touchscreen gives you access to 18 workouts. During the two months I’ve got with my loaner, I focus on the one that matters (or, at least the one with all the scientific hype): The 8-minute session with two 20-second sprints. Fitting it in the recommended three times a week sounds easy-peasy. I’m a fitness editor, after all, and run marathons for fun.
After a couple of rides ramping me up (starting with 10-, then 15-second sprints to get the hang of them), I’m ready for the real thing. I can choose between a handful of different genres of background muzak, or listen to a lady telling me a story about a tiger trying to eat me. After one go-around with the tiger, I stick with the muzak.
Each ride starts off two minutes of super slow pedaling. As someone with a bad habit of pushing the pace in any cardio workout, it takes me a few tries to get the hang of just how easy I need to take it to keep my heart rate in the right zone. (A heart rate monitor strapped to my chest gives me away any time I get overzealous.) The bike manages the resistance for me, and at this point there’s barely any. Meanwhile, prompts on the screen cue my ideal breathing pattern.
Then, the screen goes red, the resistance turns way up, and I’m supposed to give it everything I’ve got so I don’t become that tiger’s lunch. Let me tell you: Although 20 seconds sounds short, the intensity of these sprints makes them seriously no joke.
Eventually, though, they’re over, and I have three minutes of recovery back at that slow, resistance-free pace. It’s followed by just one more 20-second push, then a three-minute cooldown to gradually bring my blood pressure, heart rate, and breathing back to normal, for optimal recovery.
So technically, it’s an eight-minute-and-40-second–long workout, but who’s counting?
Well, I am. Every single time. As short as the workout is, it doesn’t feel like it goes by quickly. I find the slow pedaling so slow that it’s frankly boring. I’m just waiting around for the sprint, and often end up scrolling my phone until it’s go-time.
To be fair, I’m not someone who loves indoor cycling to begin with, and I typically need a pretty pumped-up instructor or deafeningly loud Taylor Swift tunes to keep me engaged. But before I tried CAROL, I figured eight minutes was too short to get bored.
A few weeks in, something on the motorboard of my bike breaks, and I have to admit I’m a little disappointed when customer service answers my email within an hour, then FaceTimes me right after, and sends a replacement part and a tech out to install it just a few days later. Can’t a girl get an excuse to skip her 8-minute workouts around here?
Who CAROL would be best for
In our conversation, I mention to Dr. Dalleck that I feel like, as efficient as the machine is, I personally find it takes the joy out of exercising for me. He chuckles and explains that even though this is proven to be the most efficient form of cardio, it’s not meant to be the single magic bullet that you use exclusively all year long (unless, hey, that’s what you enjoy).
“People’s seasons and availability to work out ebbs and flows,” Dr. Dalleck points out. “So, if I have a month where it’s like, wow, I’m gonna be really strapped for time, or if it’s the winter and it’s cold and it’s snowing, during those times of the year, CAROL can be really appealing.”
Which makes sense to me: This can be one tool in a periodized approach to training. No one’s telling you it has to take the place of heading out on a leisurely trail run on a beautiful day.
And there are times when this machine is truly ideal. One of the studies Dr. Dalleck conducted involved putting one CAROL Bike in a publicly accessible place at his university, and another in a shared common room at a local hospital. “Our participants were university employees and hospital employees who were really busy,” he says. “And so the idea is, you know, they needed a tiny, efficient workout.” The CAROL Bike was the perfect way for them to get in exercise without even having to change into gym clothes, since the workout is designed to keep you from getting sweaty. (And, adds Dr. Dalleck, most of the participants even reported enjoying it!)
I definitely understand that “tiny, efficient” appeal. As a working mom who’s currently marathon training, there are some days when squeezing in a 30- or 40-minute run just isn’t gonna happen. Hopping on the bike to get similar cardio benefits in the time it takes for my pasta to cook can keep me on track without feeling like a burden on my schedule. Sure, it may not be my favorite mode of movement, personally. But the amount of time it can save in my day makes it an incredibly powerful tool to be able to use.