it seems we’ve exhausted every possible exercise trend, from bikram yoga to Soulcycle.

It’s ClassPass’s fastest growing category and Peloton is selling a $4,000 smart treadmill. How did it get so expensive to go for a jog?

ClassPass is a gym class subscription service that is basically like the Netflix of fad exercise trends. For a monthly fee you can arrange a series of one-time stints doing every imaginable workout: from pole dancing to hydrospinning.

So its recent announcement of the fastest-growing category on the platform in 2018 may surprise you: it’s the boring old treadmill. Offerings like interval classes from the Mile-High Run Club and something called “Tread ’n Shed” at Crunch Gym were particularly popular, but basically they all involve running indoors in a treadmill pack while an instructor intones mantras, shouts encouragement, and critiques your running form.

Yes, it seems we’ve exhausted every possible exercise trend, from bikram yoga to SoulCycle, and now we’ve finally come full circle. Running is the hot new fitness trend – only this time it somehow costs lots of money.

It’s a trend that is being reflected across the world of fitness. Running classes at the fancy gym Equinox have amassed such a following that the chain is opening a line of treadmill-only studios. The “precision running labs” are, more or less, darkened rooms full of people running in place at the whims of a fiery, toned instructor. Under the supposedly appealing promise that “you don’t have to go outside to blaze new trails”, Equinox, ever on-brand, provides an exclusive running environment, transforming a run to “an out-of-body experience with immersive light and sound” and “air enriched by an O2 vaporizer” – because what kind of loser breathes regular, un-enhanced oxygen?

Thanks to the superhuman amenities and hands-on coaching, a single hour-long treadmill course can run about $35 a pop – compared with the outdoor running price of “free”. The price has not been off-putting: locations have already opened in Santa Monica, California, and Chestnut Hill, Massachusetts, and they will be followed this spring by New York and Los Angeles.

But you don’t need to live near a studio to pay someone to tell you to run.Peloton, the company best known for selling hi-tech exercise bikes, has expanded into the running market as well. Its prestige offering is the Tread, a touchscreen-enabled treadmill that lets you stream live and pre-recorded fitness classes from the Peloton studio.

Featuring a shock-absorbing slat belt, a 32in HD touchscreen and a carbon-steel frame, this $4,000 machine, which also requires a $40-per-month membership to stream classes, is garnering rave reviews. (The Verge reviewer Lauren Goode called it the treadmill “I want but can’t afford”). It has competitors, too: Life Fitness sells another software-enabled machine for upwards of $2,600, while NordicTrack, the home-fitness brand of early-90s fame, makes one for $3,000.

If you want, there are even more ways to spend your money as the running sector continues to grow, with new, “disruptive” technologies (as if an uneven sidewalk weren’t disruptive enough). There’s Zwift, a treadmill with a screen that offers avatar runs on virtual courses, and IPO, a machine whose belt keeps up with your natural pace.

Will the running resurgence ultimately lead the treadmillers outside to the trail, for them to discover you can run almost anywhere for nothing? Or will we keep rotating through the cultural vortex, iterating our way through its cycle? Best not to overextend yourself looking for answers – try as you might, you can’t outrun a trend.