When Ben McCue first tried CrossFit as an undergraduate about eight years ago, he said he had a feeling that the strength and conditioning program would become a nationwide phenomenon.

"Once I tried it I knew I was going to go all in," McCue said. "I knew people were going to want to replicate it. ... It was pretty obvious it was going to be a big thing."

In 2010 he opened one of the more than 5,500 U.S. gyms now affiliated with CrossFit, the fitness company of the same name that founded the brand and workout philosophy.

Milestone CrossFit, McCue's Hutto gym—or "box," as CrossFit facilities are called—is one of at least 10 that have opened in Round Rock, Pflugerville and Hutto since 2007.

Driving the trend is the sport and fitness program's mass appeal, local CrossFit box owners said, along with the camaraderie that joining a box breeds.

As more CrossFit-related businesses appear and the word about the workout spreads, the greater the competition becomes, said Terry Collie, who is a co-owner of CrossFit Texas in Pflugerville.

"There's been a big influx of CrossFit gyms, I would imagine, all across the nation as well as in Central Texas," Collie said. "I think the more the name gets out there, the bigger the sport will be and the more members every gym will have."

The growing popularity of CrossFit is due in part to the relatively low startup cost of opening a box, many business owners said. Traditional gyms can require expensive exercise machines. CrossFit boxes require only basic equipment.

Lisel Kraus, director of Trauma CrossFit in Round Rock, said that rent and human resources make up the bulk of the box's operating costs. Trauma employs 10 trainers.

"It's very low-cost to start [but] expensive not only to maintain but to be successful," Kraus said.

Delanie Weigand, owner of Defiant CrossFit in Round Rock, said the communal aspect of CrossFit helps maintain membership. Box members work out in groups to encourage friendly competition and communal support.

CrossFit is a high-intensity, hourlong workout. But Weigand said the workout is customizable to one's fitness level.

"We've got grandmas, 8-year-olds and [people with] pacemakers," she said. "Everyone can do it."

The only requirement for opening a CrossFit-affiliated box is obtaining trainer certification, which takes a weekend, Weigand said. Defiant offers a free week of classes to those trying it out, she said.

"We rarely have people walk away," Weigand said. "It gets addicting."