Millennials are ditching big-box gyms and signing up for smaller boutique fitness classes that promise a toned body and a fun experience.
In an effort to learn more about this growing trend, CNBC tried out a variety of classes in New York City, including boxing at Rumble, high-intensity interval training at F45 Training and the Fhitting Room, yoga at Y7 Studio, and balancing it all out at Pure Barre.
Most of these classes are occupied by millennial women
According to IHRSA, customers of fitness "studios" tend to be between 18 and 25 years old, while traditional fitness facility members skew higher, into the 35-54 age range.
The cost
Taking a class at Rumble — backed by celebrities Justin Bieber and "Rocky" himself, Sylvester Stallone — will set you back $34 per class.
A pack of 10 classes goes for $320.
At F45 Training Flatiron and at the Fhitting Room the cost of 10 classes jumps to $350.
But these prices aren't scaring millennials away.
"It is way more fun than a gym. ... You have 45 minutes, you're in and out, and I don't have to worry if I did everything," said fitness enthusiast Casey Cohen.
NYC model Talia Richman, who has 67,000 Instagram followers, says her image is her job, so these classes are worth the big bucks.
"Working out is part of my job. My job as a model is my image, my look, my body. Sure, these classes are really expensive. But I find it to be the most motivating for me to do classes. It is a lot harder to work out by yourself," Richman said.
Data show that high prices aren't hurting demand.
From 2012-2015, memberships in traditional fitness clubs grew by just 5 percent, while the smaller specialty studios jumped by over 70 percent, according to research from IHRSA.
A highly engaging environment
Dark lighting, blaring music, positive phrases shouted out by the instructors (like "keep your eye on the prize") and the ability to socialize are appealing to fitness buffs who take specialized workout classes.
Rumble co-founder Noah Neiman explained why his studio offers much more than just punching a bag.
"It's not just about burning calories, it's about the experience. You can justify it [the cost] because this is your entertainment dollar and on top of that you're getting a great workout," Neiman said.
Experts say it's this enticing combination of socializing and working out that has driven more young professionals to sign up for classes.
"Instead of going to get a drink, we now work out and do 100 burpees together," said Cohen.
Social media has played a powerful role in driving engagement as well, offering a way for these fitness studios to build a community online.
Australia-based F45 training, which has about 800 studios around the world, focuses almost exclusively on online marketing for future growth.
"I don't think people pay a lot of attention to billboards and TV and radio and things like that anymore as they do to social media — Facebook, Instagram — so that's been our biggest tool for getting people in the door," said Luke Catenacci, co-owner of F45 Training Flatiron.
"Social media is an important tool for us as far as building awareness," said Kari Saitowitz, founder of Fhitting Room. "It's such an easy way for our current clients who are ambassadors of our brand to share their experience with others."
But skeptics question whether the strong demand for these boutique classes can continue, arguing that the barrier to entry is relatively low plus millennials have a reputation for being fickle.
However, for now it seems to be working.
"Our retention rate for paying customers is extremely high — probably around 75-80 percent," said Catenacci.
Saitowitz and Neiman said retention rates are high at their respective studios as well.
But competitors are popping up to meet this thirst for innovative workout regimes. Several millennials CNBC spoke to said Barry's Bootcamp, Tone House, Peloton Interactive and FlyWheel, among others, are frequented. Rowing (yes, that's right, like row your boat) has also been getting some buzz, with CityRowe in Union Square.
Fitness pros say sustainability, scale and building a niche brand will be the key challenges for these studios. These long-term risks are not just relevant to new entrants but even companies such as indoor cycling veteran SoulCycle, which was founded in 2006 and is still waiting to go public.
So, how would I, as the target audience of all these offerings, rate my experiences?
While the high price is annoying, the lively energetic atmosphere in these group classes is a great motivator, and makes me want to keep coming back — something many of us have struggled with at traditional gyms.
It may seem corny to some ...
... but the team-oriented classes and motivational jargon used by the instructors does help when you're trying to get through your last set of pushups.
Of the group, Rumble probably does the best at marketing to my demographic. Its long list of star clients and models certainly boosts its "coolness" factor.
But the best workout? Surprisingly, I liked them all. The Pure Barre class, which consists of a workout centered around a ballet barre, reminded me of my days in dance class. It may have lacked the intensity of circuit training, but I could definitely feel the burn afterward.
But everyone has their preferences, and we're just seemingly at the beginning of this latest fitness craze.
So, for a while longer, you have your options. Just the way a millennial likes it.
— George Manessis contributed to this report.
CORRECTION: Y7 Studio is a yoga studio. Its name was misstated in an earlier version of this article.