Some nights, Kelly Nyquist gets her heart rate up by going to a fitness studio that offers TRX moves while hanging upside down from an aerial hammock.

Other times, she pops over to a different studio to take in a rowing class.

Nyquist is among the hordes of gym nomads bouncing around Twin Cities area fitness classes seeking variety and a cheaper way to enjoy the newest and trendiest workouts and gyms.

“I had gotten into a rut of doing barre classes and yoga,” said Nyquist, of St. Louis Park. Changing things up enables her “to get out of my comfort zone.”

The gym-hopping trend nationally and in the Twin Cities area is fueled, in part, by the recent arrival of ClassPass, a fast-growing company offering users access to an unlimited number of fitness classes at participating studios for a monthly $89 fee.

The pass has one caveat, though: Users can visit no more than three classes at one studio per month. The studios also may choose to close off the most popular class times, reserving space for their members only.

The ClassPass fever is a reflection of a larger shake-up in the fitness industry, with big-box gyms facing increasing competition from boutique fitness studios. These smaller, sleeker gyms are flourishing, according to the International Health, Raquet and Sportsclub Association, an industry trade group.

In the Twin Cities area, there are 145 fitness studios participating in ClassPass, which entered the market in late 2014. Classes range from barre to spin to boxing to CrossFit to yoga. The company won’t disclose the number of Twin Cities area subscribers, citing proprietary concerns, but it did say that more than 66,000 class reservations have been made, to date.

Nyquist has been on the ClassPass bandwagon for about a year.

An attorney, she said she likes the flexibility of being able to find a class she likes at a time that works for her busy schedule.

“The one huge thing that I love is that I log on and I know I want to work out at 5:30 right after work,” she said. “Then I have about 25 classes to pick from. That’s been a huge help to get me to go” work out.

Having more fitness choices is something many young gym-goers embrace.

“A lot of our core customers are millennials, and they’re used to having a lot of flexibility in all facets of their life,” said Michael Wolf, global head of partnerships and operations for ClassPass. “They’re taking that same flexibility and bringing that to the fitness equation.”

The element of discovery is another big draw. Many gym-hoppers say they discovered a class they love that they wouldn’t have tried on their own.

“It’s fun to change it up,” said Mellissa Solin, of Stillwater. “I get bored really easily.”

Finding new classes and trying out all the hot studios in town make exercising more enjoyable, she said. In the year since she first started gym-hopping, she’s discovered workouts she really loves (barre) and others she does not (pole dancing). “Not my thing,” Solin said.

End of gym memberships?

While the workout-warrior-without-borders approach works for the gym-hoppers, some wonder if it’s paying off for the fitness studios.

For the most part, it is.

For one thing, empty spaces in group classes mean lost dollars for the clubs. Studios collect an undisclosed amount for every class reservation booked by a ClassPass user.

In addition, the studios can introduce their classes to people who might choose to convert to full-fledged membership status if they like the experience.

“People coming in from ClassPass didn’t know we were there, and then they found us,” said Katie Lewin, founder and co-owner of the Shed in south Minneapolis. “Some of them have converted to us from ClassPass.”

Wolf said his company doesn’t see ClassPass as competition for gym-goers. Instead, he sees it as supporting the emerging boutique studio fitness movement.

“Ultimately, most studios are small businesses,” said Wolf, who said that the company retains 97 percent of its studio partners. “They’re passionate about their crafts [but] they might have less ability to market their studios. That’s where we can help.”

Lewin said she has no intention of ending her deal with ClassPass. “I’ve been very happy with the experience with them,” she said.

As a consumer, Nyquist feels the same. No matter how much she might like one of the classes she samples, the odds of her giving up her pass to join one of the studios is slim.

“Some of these studios for a month unlimited is upward of a hundred-plus bucks,” she said. “And ClassPass is $80. So I’m never going to sign up no matter how much I love the gym, because I just can’t afford that. And I like the variety.”