Sarah Lawrence for Vox

At the end of December, users of the popular cycling class Flywheel received an email in their inboxes with the ominous subject line, "An Announcement From Our Co-Founder."

In the vague note, CEO Ruth Zukerman wrote that she will be stepping down from the company, citing a move to undisclosed future endeavors after nearly a decade of cultivating Flywheel into the boutique fitness behemoth it is today.

"As an entrepreneur and creative individual with a thirst for growth, my reflection this year led me to realize — with a heavy but excited heart — that it's time for my next adventure," she wrote. "I know I am leaving you in the best hands with the most talented instructors who have all been trained and nurtured under my method both technically and philosophically."

Internally, the shift had been a long time coming. In recent months, Zukerman — who also co-founded SoulCycle and played a significant role in the rise of the modern cycling movement — had reportedly been relatively hands-off while promoting her new book, Riding High: How I Kissed SoulCycle Goodbye, Co-Founded Flywheel, and Built the Life I Always Wanted. In her book, Zukerman is vocal about her strengths in the idea conceptualization part of entrepreneurship, but less so in the nuances of running a company from the business side.

Zukerman's departure is just one piece of a picture that's forming about the future of boutique classes. While some analysts predict that the spinning bubble is about to burst, it seems instead that cycling's juggernauts are facing a period of readjustment. As consumer demand shifts away from the concept of in-studio luxury spin classes — opting for the convenience of at-home cycling programs like Peloton and cheaper, less amenity-laden classes — Flywheel and SoulCycle are being forced to do some soul-searching of their own.

As a consumer, I discovered Flywheel in April 2016 through the subscription fitness program ClassPass. The company offers a myriad of classes ranging from aerial yoga to "ballet bungee jumping," but Flywheel didn't make me feel self-conscious about my sad excuse for barre class tucks or about falling off a rowing bench.

I was clearly not alone. Along with the boom of spinning classes like SoulCycle — and more recently the rise of independent studios in smaller, suburban markets — the cycling trend seemed to show no sign of going out of fashion.

So I was surprised when in the fall of 2018 I noticed Flywheel was suddenly heavily discounted on ClassPass, which operates on a monthly flat-rate membership model where users sign up for classes using "credits." Even at peak times (typically mornings and evenings outside of work hours), classes in New York were allocated at half their usual credits, along with a note: "Take advantage of our special half-off Flywheel pricing — only for a limited time!"

I would have brushed it off as a promotional anomaly had it not remained this way off and on for several months across all 19 of Flywheel's operating cities. Unlike newer studios that offer discounts in exchange for exposure, Flywheel is one of the top cycling studios in the country, with the added benefit of lack of competition from SoulCycle and Peloton, which are not on ClassPass. (ClassPass did not respond to several requests regarding the process for discounted classes.)

Meanwhile, events behind the scenes leading up to Zukerman's departure paint a more telling picture. In mid-2018, Flywheel quietly let go of several employees on its executive team in a move Flywheel CMO Andy Wong wrote in an email to Vox was a result of restructuring.

"In order to create one unified, efficient team that supports both our studio and on-demand business, we've had to make some very difficult decisions to streamline roles," he wrote. "This impacted fewer than 20 employees. By focusing our efforts in the most crucial areas and eliminating redundancy, we'll deliver on our growth goals and better serve our consumers."

Turns out Flywheel isn't alone in its identity crisis. SoulCycle has been grappling with headaches of its own. In June, Gabby Etrog Cohen, SoulCycle's head of public relations and brand strategy, stepped down from the company after eight years. Then, in early December, Recode reported that Peloton beat out SoulCycle as the most popular cycling company for the first time last quarter, with four percent more consumers than SoulCycle.

A secondary study within the Recode report found that Peloton had doubled its customer count while SoulCycle's had declined by 8 percent — stats SoulCycle vehemently denied.

"The data is not only incomplete, it's wrong. SoulCycle is highly profitable. Studio revenue has increased year over year, paid rides are up, total rides are up, and our active ridership has not decreased. We're also seeing an increase in the number of classes our active riders take each month," a spokesperson told Recode.

Trends, particularly those with the most voracious fan bases, are peculiar in their unpredictable life cycles. Some, like boot-cut jeans, are cyclical. Others, like frozen yogurt, are more of a quick burn, captivating consumers before just as quickly fizzling out, leaving behind empty storefronts.

To understand how we got to where we are today, it helps to look at the explosive growth of boutique cycling and the meteoric rise of Zukerman's empire.

Cycling as an exercise concept is nothing particularly new. Schwinn introduced the first mainstream stationary bike in 1965, shortly before Americans began joining public gyms en masse. Throughout the 1970s and '80s, stationary bikes continued popping up in homes and public fitness centers. By the 1990s, the South African cyclist Johnny Goldberg created the first commercial Spinner bicycle and started offering group fitness cycling as part of the "Johnny G" exercise.

"In the '80s, '90s, and early 2000s, cycling was one of the most popular group exercises at any traditional gym. SoulCycle didn't create that, it was already a very successful phenomena for decades," said Bill Pryor, founder and former CEO of lower-cost spinning franchise CycleBar. (Pryor sold the company in 2017 and now runs Spynergy, a consultancy for boutique fitness entrepreneurs.)

In 1994, Rolling Stone dubbed indoor cycling the "hot exercise" in its "hot list" and soon people around the country were giving it a shot, setting aside their Tae Bo and Richard Simmons workout videos to hop on the bike.

Johnny G classes, along with its various offshoots and independent studios, continued until the early aughts. By this time, Johnny G had paved the way for the next generation of cycling embodied in the form of vivacious entrepreneur Ruth Zukerman.

Zukerman's story has been profiled countless times but can be boiled down to this: A recent divorcee, Zukerman found an outlet in indoor cycling in the mid '90s, inspiring her to become an instructor. After a decade or so of teaching, an enterprising student and acolyte of Zukerman, NFL player Tiki Barber, floated the idea for her to start her own studio.

In 2006, Zukerman, in partnership with Elizabeth Cutler and Julie Rice, started SoulCycle, opening the first studio on the Upper West Side, before she ultimately left the company to create Flywheel in 2010. Though they vary significantly in style — Flywheel incorporates competitive racing elements using data tracking, whereas SoulCycle eschews metrics, instead focusing on spirituality and community through the workout — both classes developed cult-like followings, propelled by the support of celebrity fans.

Thus, luxury spinning was born.

Today, cycling has contributed to the global $87.2 billion health club industry, operating across more than 200,000 clubs in 2017 alone, according to the International Health, Racquet & Sportsclub Association. In total, these clubs serve 174 million members, an increase of 33.6 percent from 2008's 45.6 million members.

At the top of the markets is the US, which leads in total club count and membership. An increasing number of these studios are spin gyms.

SoulCycle and Flywheel no doubt raised the bar on studio cycling, but until recently it had largely been relegated to the coasts. Then came CycleBar. When Pryor sold CycleBar as a franchise company in 2017 after operating a standalone studio in Boston for 12 years, the aim was to appeal to the rest of the nation by tapping into the power of individual local owners.

Today, CycleBar has 200 locations, ranging from Fresno, California, to Fargo, North Dakota, and West Hartford, Connecticut. Pryor's vision was to bring spin studios to underserved areas, including suburban markets beyond the coasts, with classes as low as $18 (compared to SoulCycle's $36).

Flywheel and SoulCycle have yet to capitalize in these markets, Pryor said, due to an inability to scale outside of premium markets where they can successfully charge higher prices without sacrificing quality.

"[Franchise owners] that do a really good job of building an experience locally can secure themselves against places like SoulCycle, which used to have that 'cool vibe' but is now viewed as this massive behemoth," he said.

Lower-cost spin gyms can also be particularly lucrative for aspiring boutique owners. According to a 2016 study by the Association of Fitness Studios, indoor cycling studios generate 55 percent more revenue on average than other types of fitness studios. This is thanks to the flexibility of class sizes and frequency, paired with other offerings like merchandise, water, and snacks.

As more fitness owners around the nation wade into spin, Pryor said that independent studios and franchised CycleBars around the US are starting to have a competitive advantage over places like SoulCycle and Flywheel. Their prices are typically lower, albeit marginally, and some offer large discounts for package deals.

According to Amy Glosser, founder of BYKlyn Cycle in Brooklyn's Park Slope neighborhood, independent studios can also offer a different type of community compared to the clientele of Flywheel or SoulCycle.

"We're not another gym for the 1 percent," she said. "We do everything we can to keep the price down. We don't have showers or lovely bath soaps. We don't offer free bananas. But we do offer an amazing ride experience."

When SoulCycle opened its doors on the same block as Glosser's, she was certain it was the beginning of the end. Instead, she found that her slightly lower price (BYKlyn offers single-class rides for $28) and more laid-back vibe appealed to nearby residents.

"We have riders of all different ages, genders, races, and affiliations," she said. "That inclusivity is who we are. I think a lot of the big gyms can be intimidating. If you look at our instructor profiles, many are older. Many don't have perfect bodies. We have many instructors of color. That speaks to and brings in a clientele that's far more 'Brooklyn.'"

Even in coastal cities like New York where SoulCycle and Flywheel came up, competition is rising. In New York alone, SoulCycle and Flywheel are now contending with the likes of Crank, Swerve, Revolve, Monster, BYKlyn, and Cyc — all while maintaining the 21 and 10 studios they operate in the city, respectively.

Cyc recently cut its individual class cost from $28 to $22, a move that signifies a "burgeoning supply of spin concepts in major metropolitan markets," Jefferies LLC consumer analyst Randal Konik told Bloomberg.

While increased competition in a saturated market is certainly a challenge for the likes of SoulCycle and Flywheel, perhaps their more pressing foe is the rise of the on-demand, at-home bicycle movement — or, more specifically, Peloton.

Peloton is swiftly solidifying itself as the frontrunner in the spinning market, with a current estimated value of $4 billion and an expected IPO in 2019. Meanwhile, SoulCycle has continued to drag its feet on filing an IPO — after first filing paperwork in 2015 — as a result of "market conditions." CEO Melanie Whelan told CNN in May that the company doesn't "require public capital to execute our strategic vision at this time."

To contend with this, SoulCycle and Flywheel are scrambling to find ways to keep up, namely by expanding their offerings. Taking a cue from the success of Peloton (and ultimately spurring a lawsuit), Flywheel has offered an at-home program of its own. For $1,999, a consumer can purchase a bike and take "Fly Anywhere" classes at their own convenience.

Another effort has been the integration of off-the-bike classes, including SoulCycle's Soul Annex and Flywheel's Flybarre (which has been around since 2011). These programs offer new forms of exercise and add new classes to the arsenal. Whether these efforts are working remains to be seen, but the Soul Annex in Manhattan closed following a lawsuit from neighbors over noise. (Both Flywheel and SoulCycle are privately owned companies and declined to share information on sales and foot traffic.)

Still, SoulCycle continues to eye expansion. It now has 90 studios in 20 markets in the United States, and it recently opened its first studios in Las Vegas and Denver. Next up, SoulCycle will expand its international footprint with its first studio in London. The brand has also experimented with new programs like its recently formed media division and a partnership with Apple Music.

"We offer a very different experience — it's joyful, inspirational, musical. We're always focused on innovating to offer the best possible experience for our riders in studio and digitally," SoulCycle CEO Melanie Whelan wrote in an email.

While it might seem that cycling is nearing a saturation point, at least on the coasts, Jenifer Ekstein, senior consultant at Vivaldi, said this is not reflective of the rest of the country. She anticipates the next generation of spinning to include continued expansion of independent studios across the nation and an ongoing evolution of offerings from places like Flywheel and SoulCycle.

"Rather than seeing the spin bubble burst, the slowing down in growth of the big players like SoulCycle and Flywheel is just indicative of the cycle of business," Ekstein said. "Now that they've established themselves in the market and each have their own brand identity, they need to think through new ways in which their brand can reach current customers while expanding to reach new audiences."

Ultimately, Ekstein anticipated that cycling — whether it's a SoulCycle or a BYKlyn — is here to stay.

"Brands today are more than just the products and services they sell — they are an extension of a person's identity," Ekstein said. "If fitness brands are able to take that place in someone's life and become an extension of their personal identity, they will prosper and won't fade out when a new trend comes along."