Small, specialized fitness studios are changing the way people work out, fitness experts say, as young, peripatetic exercisers prize variation over routine.

Whether it is anti-gravity yoga or underwater cycling, trampoline training or Pilates, exercisers are spoiled for choice for ways to keep fit, and companies are meeting the demand with innovative schemes.

“With boutique fitness, there’s a surge of new studios and a trend toward everyone just trying new things,” said Payal Kadakia, chief executive and co-founder of ClassPass, a paid subscription service based in New York.

ClassPass provides users access to 5,000 studios and gyms in 34 cities across the United States, Canada and Britain.

It is one of several programs, including Groupon and the online sharing marketplace Living Social, that studios and fitness boutiques are using to lure clients.

For millennials, the generation of 18- to 34-year-olds, variety is key.

“Millennials are a bit more free-spirited, more able to go into new places, to feel more assertive and fearless about trying new things,” said Kadakia, 32, who launched ClassPass in 2013.

Boutique fitness studios grabbed 21 percent of the exercise market in 2013, according to the International Health Racquet and Sportsclub Association, despite price points that can be 50 percent to 100 percent higher than the industry average.

Varying an exercise routine alleviates boredom, maintains physical challenge and reduces the risk of injury, said Jessica Matthews, senior advisor for health and fitness education for the American Council on Exercise (ACE).

“In order for the body to continue to make gains, especially in terms of muscular strength and endurance, the body must be continually challenged in ways that force it to continue to make adaptations,” she explained.

Michele Czerpak, owner of RowZone, an indoor rowing fitness studio in Philadelphia, said her clients who use ClassPass are young, fit and adventurous.

“They’re absolutely more interested in roaming around, and that’s OK for us,” said Czerpak, 49, whose small specialty studio offers rowing machine-centered, 45-minute high-intensity interval training classes.

ClassPass member pay up to $99 a month for unlimited classes at studios in the network, but they cannot visit the same studio more than three times per month.

“They have a financial vested interest to make sure they take their three classes,” Czerpak said.

She said her full-price clients are not pleased with some of the discounts offered but said it has not been a problem with ClassPass, presumably because of the monthly cap on visits.