In today’s fast-paced world, finding time to work out can seem nearly impossible.

Using machine learning, the CAROL (CARdiovascular Optimization Logic) bike aims to solve this problem, claiming to be the fastest way to get fit — all you need is just 8 minutes and 40 seconds, 3 days a week.

Unlike other stationary bikes that are designed for home use, the CAROL bike has a stronger build that’s certified for professional and commercial use, which is important since the workouts are meant to be pretty intense.

What’s more, after just six rides, the software automatically sets your resistance level for a personalized workout experience.

However, while a personalized and effective workout in under 10 minutes sounds like a dream, you may wonder whether it’s too good to be true.

This article provides an in-depth review of the CAROL bike to help you decide whether it’s worth purchasing.

Developed by scientists, the CAROL bike uses a relatively new exercise method called reduced exertion high intensity training (REHIT).

You may already be familiar with high intensity interval training (HIIT) — a popular workout method that involves short but intense bursts of exercise, followed by a recovery period.

REHIT is similar to HIIT, just with fewer and shorter intervals.

The goal of REHIT is to quickly deplete muscle glycogen stores — the body’s preferred fuel source — as rapid depletions of muscle glycogen have been linked to several benefits, such as improved aerobic fitness and insulin sensitivity (1).

In fact, one small study including 8 men found that completing 3 REHIT sessions per week for 6 weeks resulted in a 28% improvement in insulin sensitivity (2).

So how does REHIT work?

The idea behind REHIT is to provide an optimal amount of resistance during each 10–20 second sprint in order to deplete your glycogen stores just as quickly as if you’d exercised for 45 minutes or longer at a moderate intensity.

While REHIT has been studied in lab settings, the CAROL bike is the first to make this time-efficient workout available to consumers.

According to the company, using REHIT, the CAROL bike’s Intense Workout depletes muscle glycogen stores by 25–30%, though more research is needed.

Assembling and setting up the CAROL bike is straightforward and should only take about 45 minutes, though you’ll want the help of a friend.

Once you’re ready to start cycling, the first step is creating your profile by entering your age, weight, and height.

Next, you’ll need to complete six rides before getting full access to the bike’s workouts.

These initial rides are designed to help you practice the maximum intensity sprints and give the bike the opportunity to assess your fitness level and ability so that it can adjust accordingly.

More specifically, the first three rides are called ramp-up rides and include short sprints — just 10 seconds each — allowing you to practice the maximum intensity bursts.

The next three rides are considered calibration rides, in which you choose between 10-, 15-, and 20-second sprints, during which the bike automatically sets the resistance to ensure that you reach your maximum intensity.

After the initial six rides, you’ll have access to all of the programmed workouts, though the bike will continue to learn and adjust the resistance based on your progress over time.

The bike offers several workout options, including fat burn, energizer, constant power, and endurance.

However, to get the most out of the CAROL bike, you’ll want to select the Intense Workout, which is structured as follows:

  • a 2-minute slow warmup
  • a 20-second maximum sprint
  • a 3-minute recovery
  • a 20-second maximum sprint
  • a 3-minute cooldown

The bike’s integrated display screen prompts you through each workout, with the bike automatically adjusting your resistance as your speed increases.

While 20 seconds may not seem very long, keep in mind that the sprints are meant to be very challenging.

During the recovery periods, an on-screen breath pacer will guide you in getting your breathing back under control. You’ll also see a graph of your power output from the previous sprint so that you can try to improve on the next one.

The CAROL bike also includes a “free ride” mode that allows you to use the bike like a traditional stationary bike. In this mode you can manually adjust the resistance level and even stream classes from popular fitness apps.

Furthermore, the CAROL bike’s website offers suggested training plans based on your fitness goals. These plans include recommendations on how often you should use the bike and which workout programs to choose.

The CAROL bike has a heavy flywheel, leveling feet, and a sturdy, stainless steel frame, all of which are important for stability during maximum intensity sprints.

It also features a silent belt drive, which provides a smooth and quiet ride.

The bike’s frame is smaller than many others on the market, measuring 45.5 inches long by 22 inches wide (115.6 cm × 55.9 cm).

It also weighs 130 pounds (59 kg) and includes transport wheels on the front, making it easy to move out of the way when it’s not in use.

Finally, the CAROL bike supports users who weigh up to 285 pounds (129.3 kg).

Safety features

Given that you’re moving at high speeds, customers appreciate the bike’s many safety features, including a freewheel safety clutch and computer-controlled magnetic breaks.

Thanks to these features, you can rapidly increase or decrease your speed. You’re also able to stop pedaling and hop off safely, even if the wheel is still spinning.

Finally, the heart rate monitor, which is located on the handlebars, keeps a constant read on your heartbeat and will alert you if your heart rate gets too high during your ride.

Additional special features

Unlike many competitors, the CAROL bike includes dual-sided pedals, which allow you to use either SPD clips or regular athletic shoes.

However, as SPD clips allow you to pedal faster and more efficiently, many customers note that it’s worth investing in a pair of spinning shoes.

The CAROL bike is also equipped with a 10-inch (25.4-cm) tablet, which displays your heart rate and performance metrics. It’s also where you’ll find prompts for when it’s time to sprint and slow down, along with the breath pacer during recovery.

While the CAROL bike offers six styles of music to choose from, it also includes integrated speakers and Bluetooth connectivity for playing music using your favorite app.

The bike allows for eight user profiles and access to all of CAROL’s guided workouts, though it requires a monthly subscription.

Without a subscription, the bike functions as a traditional stationary bike. As a result, if you don’t plan on buying the monthly membership, you’re better off choosing a different machine.

It’s also important to note that the bike doesn’t include trainer-led classes. However, if you’re a Peloton member, you can install the app directly on the CAROL tablet, allowing you access to Peloton’s extensive class library.

Finally, one of CAROL’s newer features is a global leaderboard that allows you to track your progress and compete with other CAROL users around the world.

CAROL bike accessories

In addition to the special features listed above, CAROL offers bike bundles that include accessories, such as a water bottle holder and heart rate chest strap.

Here’s what’s included with each bundle:

  • Essentials Bike Bundle: CAROl bike
  • Standard Bike Bundle: CAROl bike, chest strap, and tablet holder
  • Premium Bike Bundle: CAROl bike, chest strap, tablet holder, floor mat, and water bottle holder

The bundles also differ in price and warranty.

The CAROL bike ranges in price from $2,395-$2,795, depending on the bundle option.

Here’s the price and warranty for each bundle:

  • Essentials Bike Bundle: $2,395, 1-year warranty
  • Standard Bike Bundle: $2,595, 2-year warranty
  • Premium Bike Bundle: $2,795, 3-year warranty

According to the company’s website, the warranty covers any defects that arise during the 1–3-year coverage period. However, there are specific conditions under which the bike cannot be repaired or replaced, such as if it’s improperly assembled or used.

To make the bike more affordable, the company also offers special financing options for qualified customers, allowing the cost to be split into 12 monthly payments with 0% APR.

Monthly payments range from $199.58 per month for the essentials bike bundle up to $232.92 per month for the premium bike bundle.

Shipping is free within the United States and the United Kingdom, with professional assembly available for an additional $150.

Finally, the bike requires a $12 monthly membership for access to the workouts and user profiles.

While it may seem impossible that a 10-minute workout can be as effective as a 45-minute or longer ride, studies support the effectiveness of RHEIT and the CAROL bike.

Before taking a look at the research, it’s important to understand the following two terms (3):

  • V̇O₂ max. This measure of cardiovascular fitness indicates the maximum amount of oxygen that the body can use during exercise. Improvements in V̇O₂ max allow for better endurance and performance during cardio workouts.
  • MetS Z-score. This measure of cardiometabolic health takes your blood pressure, waist circumference, blood glucose, and blood fat levels into account.

One study from the American Council on Exercise (ACE) found that the REHIT workout on the CAROL bike was more effective than moderate intensity continuous training (MICT) at improving waist circumference and V̇O₂max after just 8 weeks (3).

Furthermore, the RHEIT group’s average MetS Z-scores increased by 75%, compared with just 47% in the MICT group (3).

In another small, 5-week experiment performed by the British Broadcasting Corporation (BBC) for live TV, 6 adults performed the CAROL bike’s intense workout 3 times per week. All of them improved their V̇O₂ max, though there was no control group to provide a comparison (4).

While there’s some evidence to support the effectiveness of the CAROL bike’s workouts, more research is needed.

Here’s how the CAROL bike compares with some of its main competitors:

CAROL BikePeloton Bike+NordicTrack s22i BikeBowflex VeloCore
Warranty1–3 years1-year• 10-year on frame
• 2-year on parts
• 1-year on labor
• 2-year on parts
• 1-year on labor
Size45.5 × 22 inches
(115.6 × 60 cm)
59 × 22 inches (150 × 60 cm)63 × 22 inches (160 × 60 cm)60 × 24 inches (152.4 × 61 cm)
Max user weight285 pounds (129.3 kg)297 pounds (134.7 kg)350 pounds (158.8 kg)325 pounds (147 kg)
Trainer-led classesnoyesyesyes
Automatic resistanceyesyesyesyes
App subscription$12 per month$39 per monthincluded for 12 months then $33 per month$19.99 per month
Pedalsdual-sided, offering SPD clips and toe cagesDelta-compatibledual-sided, offering SPD clips and toe cagesdual-sided, offering SPD clips and toe cages
Display10.1-inch (25.7-cm) touchscreen24-inch (61-cm) swiveling touchscreen22-inch (60-cm) swiveling touchscreen 16-inch or 22-inch (40.6-cm or 60-cm) touchscreen
Other features• short REHIT workouts
• machine learning resistance
• live and on-demand classes using the Peloton app
• rotating display
• live and on-demand classes using iFit
• rotating display
• streaming capabilities
• leaning mode

Overall, the CAROL bike is smaller than its competitors, which might be ideal if you’re limited on space.

It’s also the only bike that offers REHIT workouts.

However, it has the smallest touchscreen and is one of the most expensive options. It also lacks many features offered by other smart bikes, including trainer-led classes.

The CAROL bike offers an incredibly time-efficient workout that’s backed by science, though more research is needed.

Therefore, if your biggest hurdle to working out is time, it’s worth considering the CAROL bike.

Furthermore, as the workouts are highly personalized, the bike is suitable for riders of any fitness level.

However, there are several downsides to consider.

In particular, while it offers a “free ride” mode, the bike is designed specifically for REHIT workouts and includes limited workout options. As a result, exercising on the bike could become monotonous.

Similarly, if you prefer more traditional indoor cycling workouts, the CAROL bike isn’t the best fit, especially as there are several more affordable smart bikes on the market.

Finally, keep in mind that while REHIT may help you improve your cardio fitness, other types of workouts, such as yoga and strength training, should also be included in your exercise routine.

The CAROL bike is ideal if you’re short on time but still want an effective cardio workout.

It’s also suitable for riders of varying fitness levels and easy to install.

However, if trainer-led classes and workout variety are important to you, the CAROL bike probably isn’t your best option, especially given its high price point.