CAROL Bike Review (2024): Efficient AI-Powered Cardio — For a Price

Sure, artificial intelligence may very well take over the world, eliminate our jobs, and destroy humanity, but we love what it’s capable of when integrated with one of the best exercise bikes we’ve tested. The AI-powered CAROL Bike — CAROL comes from what the company calls “cardiovascular optimization logic” — was designed to deliver adaptable and personalized HIIT workouts. CAROL’s short bursts of cardio are based on the principles of REHIT — Reduced Exertion High-Intensity Interval Training — and can deliver a calorie-torching workout in just a fraction of the time as standard exercise bikes. (1) 

Instead of trudging through a moderate-intensity workout for upwards of an hour, the CAROL Bike uses your metrics to make real-time adjustments to your workouts. Feeling a little sluggish today? It’ll adapt to your pace and stretch out your time frame. Feeling like Neo ready to take down the machines? The CAROL Bike will match your intensity with an equally-challenging ride. Considering the time-saving potential of AI-charged REHIT workouts, we think anyone looking for productive, personalized training can benefit from this high-tech exercise bike — so long as they’ve got the coin to spend on it.

Main Takeaways

• CAROL’s AI analyzes your metrics to craft personalized REHIT workouts that adapt in real time. Studies have shown that in just 10 minutes these science-backed rides can deliver the same benefits as a 30-minute moderate-intensity session. (1) 
• In Free Ride mode, you can stream studio classes or scenic rides from apps like Peloton, Zwift, YouTube, Netflix, or Apple Fitness+ via the 2K 11-inch display.
• At $2,595, it exceeds the average price range for connected bikes — $1,200 to $2,000 — by roughly $600, and that’s not including the required $19.99 per month subscription.
• Its footprint of just 6.95 square feet makes it one of the most compact bikes we’ve tested — just under the average range of 7 to 8.5 square feet.

CAROL Bike Highlights

• Price: $2,595
• Dimensions: 45.5″ L x 22″ W
• Display: 11” IPS touchscreen with 2K resolution
• Weight: 120lbs
• Resistance: AI-controlled, motorized resistance
• Weight Capacity: 330lbs
• User Height Range: 4’7″ to 6’7″
• Warranty: 5-year on frame; 1-year on components

Several of the best treadmills, rowers, and exercise bikes integrate fitness apps into their machines, but the engineers at CAROL took a different tack. They’ve designed a truly smart exercise bike that utilizes artificial intelligence to analyze your output, learn your personal maximum intensity, and adjust the resistance accordingly. With every pedal stroke and heartbeat, your bike learns how to best and most efficiently challenge you during each ride. 

Based on the research-backed concept of REHIT (Reduced Exertion High-Intensity Interval Training), the AI onboard your CAROL Bike leverages what it knows about you to increase or decrease your resistance, while shortening or lengthening your workout. 

As our tester — a certified personal trainer — experienced, the AI is learning from the very first ride. “If you hop on the bike and think, ‘This is too easy,’ that’s because it is learning your movements and how you are progressing.”

[Related: The 8 Best Exercise Bikes with Screens]

Compared to a typical HIIT workout (think “high” intensity), REHIT workouts (think “maximum” intensity) streamline your training by trading longer periods of a moderate power output for shorter periods of a higher output. (1) 

The artificial intelligence on the CAROL Bike then uses your data to optimize your training time. “Essentially, AI learns your patterns and movements through that fitness test and your workouts over time to learn when to push you and when to hold back,” our tester said.

One sneaky plus for the CAROL Bike is its “unlocked” 11-inch 2K touchscreen. The screens on many connected exercise bikes often only support that brand’s proprietary programming, thus preventing access to other fitness or streaming apps — but that’s not so with this bike. 

Free love reigns, as you can download essentially any app available on an Android device, including some of the best fitness apps: iFIT, Peloton, Zwift, and more. Or if you want to zone out with your favorite show on Netflix or YouTubeTV, its display is your oyster.

High-tech gear doesn’t come cheap, however. At $2,595, the CAROL Bike comes in around $600 more than the top of the typical range for app-connected exercise bikes. On top of that, you’ll be hit with a monthly $19.99 subscription to access all that glorious AI capability.

Pros

• AI analyzes your metrics to personalize REHIT workouts, potentially allowing you to achieve results in 10 minutes that would otherwise take 30 minutes. (1)
• Its 11-inch touchscreen is “unlocked,” so you can download just about any fitness or entertainment app, including Peloton, Zwift, Amazon Prime, or Netflix.
• It only occupies 6.95 square feet of floor space, making it ideal for apartments or smaller training spaces.
• With dual-sided pedals, you can either clip into SPD cleats or slip sneakers into the toe cages.

Cons

• Its $2,595 price tag surpasses the upper end of the average price range for connected exercise bikes ($1,200 to $2,000) by about $600.
• It costs an additional $19.99 a month to access its AI optimization, science-backed REHIT workouts, and software updates.
• Wearing the included heart rate monitor is required to utilize the AI-powered features.

Training With the CAROL Bike

To say training with the CAROL Bike is unique would be an understatement. After our team experienced the potential of its AI-powered workouts, we were left fighting over who would get to take it home. Expert reviewer Amanda Capritto, CPT, CES, CNC, CF-L1, CSNC, highlighted the general benefits of exercise bikes when assessing them for BarBend.

“Cycling brings an impressive collection of health benefits to the table: cardiovascular health, endurance, stamina, muscular endurance are all improved with cycling, to name a few,” Capritto said. With CAROL’s cardiovascular optimization logic efficiently crafting your workouts, you may be able to even more quickly boost your cardiovascular health, manage your weight, and improve your mental health. (2)

After spinning the pedals on over 30 exercise bikes, our team of road cyclists, mountain bikers, and Peloton apologists know how to spot a quality bike. After years of using both the original model and the CAROL Bike 2.0, we rated it on a scale of 1 (boo, hiss) to 5 (yippee, hooray) across 12 categories, including tech capabilities, dynamic programming, and durability. 

AI-Powered REHIT Workouts

With so much technology driving the CAROL Bike, it’s important to start with the basics. From your very first ride — the baseline fitness test — the bike’s AI is learning about you.

Our tester, a certified personal trainer, experienced this on their first ride. “On my first ride, I thought, ‘Whoa, this is too easy. Something’s wrong.’ But the baseline starts super low because in those beginning stages, it’s learning about your output and fitness level.”

You’d be forgiven for not being familiar with the concept of REHIT (Reduced Exertion High-Intensity Interval Training), but if typical HIIT workouts are about “high intensity,” REHIT is about “maximum intensity.” (1)(3) In fact, a study commissioned by the American Council on Exercise demonstrated that, in a group of 32 participants over an 8-week period, 10 minutes of REHIT on the CAROL Bike produced more cardiorespiratory and cardiometabolic benefits than 30-minute training sessions at a continuous moderate intensity. (1)

[Related: The 6 Benefits of HIIT]

As our tester experienced, the AI on the CAROL Bike uses machine learning to optimize your training. “Essentially, AI learns your patterns and movements through that fitness test and your workouts over time to learn when to push you and when to hold back.”

To another of our testers, it seemed too good to be true. “At first I was skeptical, but after your warm up, the REHIT sessions are tough as hell. It just requires constant output, so I went all out for a couple 20-second sprints and it was over in 8 minutes and 40 seconds,” they explained. 

You’re probably already thinking of the time-saving benefits. If you’re a busy parent that needs to work out during episodes of Bluey or you have a meeting-packed work day, being able to do a productive workout in under 10 minutes could be a game changer. 

In fact, a 2021 study found that Intense rides (87.7 calories) and Fat Burn rides (186.1 calories) on the CAROL Bike burned significantly more calories compared to moderate-intensity (45.2 calories) or vigorous-intensity treadmill exercise (72.1 calories). (4)

[Related: The 8 Best Budget Treadmills]

While they rated both its tech capabilities and dynamic programming 4 out of 5 or higher, our tester did emphasize that all this AI goodness requires a monthly subscription to track and store data and receive software updates.

“If you don’t want to pay that $19.99 a month, you might want to check out a more affordable option,” our tester advised. 

Free Mode

While the CAROL Bike’s REHIT workouts are its bread and butter, they aren’t the only way to work up a sweat on it. In Free Mode, you can control time and resistance level as you pedal via a slider at the bottom of the screen. You can also take one of the bike’s FTP tests so it can learn your power and heart rate zones, which can also be utilized in Free Mode. 

Let Freedom Stream

A not-so-secret element of many connected exercise bikes is that they lock you into their programming — looking at you, Peloton and NordicTrack — by requiring monthly subscriptions to get the most out of them. However, since the CAROL Bike’s calling card is the REHIT workouts powered by its AI, they seem less concerned about users firing up their favorite fitness or entertainment apps on the 11-inch 2K touchscreen.

[Related: The 9 Best Workout Apps for Women]

The display is essentially — OK, literally — an Android tablet, so you can download apps at your leisure. That means you can switch the bike into Free Mode and take a class on apps like iFIT, Peloton, Zwift, or any other service for which you have a subscription.

Adjustability and Customizations

The CAROL Bike can cater to users ranging from 4 feet 7 inches to 6 feet 7 inches  with its adjustable seat and handlebars. Also, we like its hybrid pedal design — you can either clip in with SPD cleats or slip sneakers into a set of toe cages. “One side has a caged toe box,” said our tester. “I didn’t really want to use cycling shoes, so I just used my cross-training shoes with that cage.” They rated adjustability, ergonomics, and conveniences each a 4.5 out of 5.  

[Related: 14 Best Cross-Training Shoes of 2024]

Our tester did, however, call out one feature from the original model that was scrapped for the CAROL Bike 2.0. “The older CAROL Bike had sensors in the handlebars to monitor your heart rate and I actually liked that better,” they said. 

The current model requires you to use an included chest strap to monitor your heart rate. “If you don’t like wearing the chest strap, you’re kind of out of luck because the AI needs that metric to make the most accurate adjustments for those REHIT workouts.”

Durability

Outside of its space-age technology, the bike itself is a solid piece of home gym equipment. To our tester, the powder-coated steel frame, belt-drive system, and 30-pound flywheel were all indications that the bike could hold up over time. “The powder coating helps fight corrosion, so whether you keep it in the house or in the garage, it doesn’t really matter. It’ll last for a long time,” they said, rating its durability 4 out of 5.

Compared to the chain-drive systems you’ll find on regular road or mountain bikes, the belt-drive systems on high-end exercise bikes tend to be quieter and require less regular maintenance. (5) The CAROL Bike has frictionless magnetic brakes and a rear-positioned flywheel, which according to our tester, is the standard in boutique cycling studios.

[Related: The 8 Best Magnetic Exercise Bikes]

“Most cycling studios use rear-mounted flywheels with belt drives because they just last longer,” they said. “You don’t have sweat and condensation dripping down and causing corrosion.”

They conceded, however, that, despite it being a “really solid bike,” you can find better builds elsewhere. The belt drive and rear flywheel are common on commercial-grade bikes, which is a good indication,” they explained. “But nothing really stands out about the build itself. The AI is what sets it apart.”

What to Consider Before Buying the CAROL Bike

“There are two key groups of people I see benefitting from indoor exercise bikes the most: People who need a low-impact way to do cardio exercise, and athletes training for an event who need a way to perform structured interval training,” says our expert reviewer, Amanda Capritto, CPT, CF-L1, CES, CSNC. Here are a few things to keep in mind as you consider making the CAROL Bike part of your training.

Training Type

A huge consideration before investing in the CAROL Bike is the kind of cardio workout experience you want day to day. The bike is designed to support short, high-intensity REHIT workouts, so if you’re planning on long-distance rides or endurance training, it’s probably not for you. 

[Related: The 6 Best Exercise Bikes with Virtual Courses]

Also, if you fire up a Peloton class or scenic ride on iFIT, it’s fair to say the CAROL Bike’s 11-inch display won’t feel as immersive as the larger 16-inch to 24-inch displays you’ll find on Peloton and NordicTrack bikes. 

But if quick and effective workouts are what you’re after, the REHIT workouts can help produce similar results in a fraction of the time. (1)

Capritto also highlighted the appealing feature of these app-connected options. “Bikes [with streaming capabilities] have become ultra-popular among people who love the fitness studio vibes that come from interactive workout sessions,” she noted. On the other hand, being able to leverage the science behind REHIT workouts to achieve results in less time might be equally appealing. 

Budget

Before bringing home an exercise bike, treadmill, or any home gym essential, make sure that it fits in your budget — especially with an expensive bike like the CAROL Bike. It rings in at around $600 more than the average range for similar app-connected bikes — roughly $1,200 to $2,000. Also, keep in mind that to keep the AI hits coming, you’ll need to fork over an additional $19.99 per month, so we recommend reading up on REHIT workouts before you write that check. 

Footprint

While we wouldn’t place the CAROL Bike among the best portable exercise bikes, it is one of the more compact units we’ve used. It measures 45.5 inches long and 22 inches wide, so it’s only going to take up 6.95 square feet, which is just below the typical footprint we see from upright bikes. 

Even so, Capritto advises to get out the measuring tape before clicking add to cart for any at-home fitness equipment. “Triple-measure your space to make sure it will fit!” On top of that, we also recommend clearing about 2 feet of space around the bike for an unobstructed workout.

Warranty

Along with the 100-day return window, CAROL offers a 5-year warranty on the frame and 1-year warranty on components. Bikes in this price range typically offer 5- to 10-year warranties and, based on our experience, we think it will hold up over time. “We have several team members that have had CAROL Bikes for years and haven’t had any problems,” one tester said.

CAROL Bike Vs. The Competition

The artificial intelligence that powers the CAROL workouts makes it unique in the market, but there are several well-known bikes at comparable price points that serve as worthy comparisons. Take a look at a few other options out there to see how it stacks up.

	CAROL Bike	Keiser M3i	Peloton Bike
Price	$2,595	$2,985	$1,445
Footprint	45.5″ L x 22″ W	51” L x 26” W x 49” H	59″ L x 23″ W x 53″ H
Weight	120lbs	92lbs	135lbs
Weight Capacity	330lbs	350lbs	297lbs
Programming	REHIT	N/A	Peloton app
Resistance	AI-controlled	Micro-adjustable	100 levels micro-adjustable
Pedals	Adjustable toe cages/SPD clips	Adjustable toe cages/SPD clips	Delta-compatible aluminum pedals
Warranty	5-year frame; 1-year components	3-year frame, 90-day labor	5-year frame, 1-year touchscreen, components, pedals, and labor

Obviously, the AI-powered resistance and training on the CAROL Bike is different from the more traditional levels of magnetic resistance on the Keiser M3i and Peloton Bike. However, the M3i is a favorite among boutique studios and serious cyclists for its incredibly smooth ride, higher-than-average weight capacity, and commercial-grade build.

[Related: The 9 Best Exercise Bikes For Heavy People]

While the Peloton Bike is no slouch in terms of durability, its world-class programming is what sets it apart. According to BarBend editorial member and self-professed “Peloton guy,” Randall Colburn, the word Peloton is synonymous with indoor cycling for a reason. “The instructors provide motivation, allow room for adjustments, and routinely make me laugh. I would die for Denis Morton.”

Another of our testers also raved about their experience. “What can I say about Peloton? The experience is top-notch, the instructors each bring their own flair to their classes, and the huge display brings it all to life.”

What sets the CAROL Bike apart from these and other bikes is how it utilizes AI to craft efficient workouts tailored to the rider. “Compared with the moderate-intensity sessions in a manual ride or even a studio class on Peloton, REHIT workouts can deliver in just a few minutes,” our tester explained. (1)

Places to Buy the CAROL Bike

You can buy the CAROL Bike directly from their website.

Customer Experience

The CAROL Bike offers a 100-Day Home Trial, so you can return it during that window for a full refund. There is a 5-year warranty on the frame, as well as a 1-year warranty on components, along with options for extended warranties.

Company Information

CAROL does one thing very well — make the CAROL Bike. As a truly unique AI-powered stationary bike, it stands alone in the industry. You can reach their customer care team at info@carolbike.com or by filling out a form on their website.

Final Word

The CAROL Bike provides a truly unique cycling experience that our team has never seen before. Its built-in artificial intelligence leverages the rider’s workout data and history to create personalized, adaptable REHIT workouts that can maximize your training time. Research shows that the “maximum” intensity periods in a REHIT workout can achieve equal results as the “high” intensity periods of HIIT sessions. (1)

While the short bursts of maximum effort may not be for everyone, the quick workouts and impressive outcomes made us think that CAROL may be on to something. If the hyped-up studio vibes of Peloton or scenic cruises on iFIT are more your speed, the CAROL Bike may not be for you. However, if you’re intrigued by the efficient, personalized training made possible by this tech-savvy machine, we think the CAROL Bike justifies its price tag.

FAQs

References

1. Cuddy TF, Ramos JS, Dalleck LC. Reduced Exertion High-Intensity Interval Training is More Effective at Improving Cardiorespiratory Fitness and Cardiometabolic Health than Traditional Moderate-Intensity Continuous Training. Int J Environ Res Public Health. 2019 Feb 7;16(3):483.
2. Oja, P., Titze, S., Bauman, A., de Geus, B., Krenn, P., Reger-Nash, B., & Kohlberger, T. (2011). Health benefits of cycling: a systematic review. Scandinavian journal of medicine & science in sports, 21(4), 496–509. 
3. (Marketing), A. H. (2021, October 25). Rehit vs HIIT – high intensity interval training. Gym and Fitness. https://www.gymandfitness.com.au/blogs/tips/rehit-vs-hiit-high-intensity-interval-training 
4. Eberly. (2021, July 17). The metabolic responses and epoc of carol: An AI-powered exercise bike – IJREP – international journal of research in exercise physiology. IJREP. https://ijrep.org/the-metabolic-responses-and-epoc-of-carol-an-ai-powered-exercise-bike/ 
5. Sunny Health and Fitness Fit for Everyone®. (2018, March 30). Chain vs belt drive. Sunny Health and Fitness. https://sunnyhealthfitness.com/blogs/products/chain-vs-belt-drive