After mechanical engineer Ron Wensel suffered a heart attack, he knew his lifestyle needed to change. Wanting to find a way to stay active without overexerting himself, he traded in his street bicycle for a bike with electric assist. Doing so, Wensel said, “changed my life.”

E-biking, he discovered, provides many of the same health benefits of conventional cycling, without causing as much strain on his heart or body because a battery-powered motor provides some pedaling help.

In the dozen years since, Wensel has been joined by countless e-bike aficionados who collectively are changing the world of cycling.

Once the outlier with less than 1 percent of the cycling market in 2012, e-bike sales have climbed steadily over the past decade — accounting for nearly 15 percent of the market in 2019 and reaching a fever pitch during the pandemic.

Edward Benjamin, managing director of eCycleElectric, tracks brick-and-mortar retail sales and counts the number of e-bikes sold directly to customers using import data from overseas e-bike and e-bike component suppliers. He estimates that 220,000 e-bikes were sold in the United States in 2017, compared to 263,000 in 2018, 288,000 in 2019 and 437,000 in 2020. He projects that sales will reach 550,000 this year.

As with many new trends, however, naysayers abound. Some cycling enthusiasts have belittled e-bike users as lazy or elderly. Some consider electric assistance a form of cheating.

But one small study found that while e-bike users burn fewer calories than conventional cyclists on the same ride, it’s not by much. E-bike participants in the study burned between 344 to 422 calories per hour (depending on the e-assist level they were on) compared to the 505 calories per hour that conventional cyclists burned on the same course.

Wensel used his background in engineering to conduct a similar experiment with his own e-bike, concluding that he burned only about 20 percent fewer calories over the same period of time when he rode with e-assist than he did without it.

“I ran the experiment mainly to quantify what I already knew: that judicious use of electric assist can give you close to the same level of exercise, but without the overexertion,” he said.

Aslak Fyhri, chief research psychologist at the Institute of Transport Economics in Oslo, said that even though e-bike users may burn slightly fewer calories on each ride, “given that people do longer and more frequent trips with an e-bike, the difference is canceled out.”

When researchers measured the heart rates of participants who rode the same mountainous route twice — once on a conventional mountain bike and once on a mountain bike with electric assist — they found that riding the e-bike required nearly as much physical exertion as riding without the assistance. They concluded that both bike types “placed the vast majority of participants in the vigorous-intensity heart rate zone.”

Similarly, a 2016 review reported that e-bike users exerted themselves enough to reduce their risk of sedentary lifestyle diseases such as obesity, high blood pressure, Type 2 diabetes, high cholesterol and heart disease.

“E-bikes give you the moderate physical activity that your doctor prescribes and allow you to do so with without finding yourself peaking into vigorous physical activity,” said Chris Cherry, a professor of civil engineering at the University of Tennessee at Knoxville.

Pedal-assistance also makes cycling less physically demanding on joints and muscles, offering exercise opportunities to many who otherwise might be inactive.

“In studies we have done, we have seen e-bike owners able to get people who have never cycled before as adults to get out and use their e-bikes or people with physical limitations to start exercising again,” said John MacArthur, the sustainable transportation program manager at Transportation Research and Education Center at Portland State University.

Despite such benefits, e-bikes also have downsides.

They’re significantly heavier than conventional bicycles because of the extra weight of the battery, control system, motor and wiring; and users are limited by how far they can go on a single battery charge (usually an average of 20 to 50 miles, depending what level of assist the rider is using).

Because they are heavier and can travel faster than conventional bikes, risk of injury from accidents can be higher both for riders and pedestrians.

E-bikes can also be significantly more expensive than traditional bicycles. While specialty nonelectric bikes can cost several thousand dollars, most casual cyclists won’t have to pay more than a few hundred dollars for a standard bicycle. Most e-bikes, by contrast, usually start around a thousand dollars, with some brands charging between $2,000 to $5,000 even for base models. E-bike accessories and maintenance costs can add up quickly, too.

And they may not be quite as environmentally friendly as conventional bikes, but they are better for the environment than many forms of motorized transportation. They also persuade some people to use a bike instead of a car.

Mike Radenbaugh, a cycling expert and the founder of Rad Power Bikes in Seattle, said e-bikes at his company use the “electricity equivalent of about 1,600 miles per gallon of gas,” and “1/120th of the amount of lithium battery cells compared to an electric car.”

Cherry called e-bikes “the most energy efficient and low polluting mode of motorized transportation that exists.”

Advocates are optimistic that e-bike users who enjoy the recreation and exercise benefits of e-bikes will begin to use them for errand-running and commuting, cutting into reliance on cars.

For some, e-bikes have become “the default option for transport, rather than something they spend time considering if they should bother using or not,” Fyhri said.

When Natalie Popovich, a project scientist at Berkeley Lab, interviewed early e-bike adopters in California, they often mentioned they liked the bikes’ pickup, which made them convenient to operate in traffic.

She said they found that e-bikes “made it no longer such a hassle to come to complete stops at intersections and then accelerate up to cruising speed again” compared with conventional cycling where such stops and accelerations are more tiresome.

And they overcome disincentives such as distance, heat, wind resistance, not wanting to work up a sweat and hilly terrain.

“What is great about e-bikes is that they break down a full range of barriers to cycling,” MacArthur said. “If you are a young person that commutes to work, [an] e-bike allows you to travel farther distances in less time and without sweating. For someone else, they might live in a hilly area and don’t feel strong enough to cycle, an e-bike can also help them.”

Enthusiasts said they make transportation fun.

“Because e-bikes take the sharp edges off the biking experience, people use them more, they go more places, travel further, have more fun and most of the time feel safer,” Cherry said. “And the more you ride an e-bike, the more you get that moderate physical activity we could all use.”