Even as workers put the finishing touches on the newly opened Brooklyn Boulders Somerville, climbers had already packed the rock climbing gym, carefully placing feet and fingertips as they muscled their way up the bouldering wall.
Six miles west, in Watertown, the scene was much the same at the slightly older Central Rock Gym, where climber after climber pulled their way up a rock wall, carrying rope and clipping into anchors as they made their way to the top, nearly 50 feet above the floor.
These gyms, both opened within the past three months, are indicators of the growing popularity and business of indoor rock climbing. Once a place where serious rock climbers stayed in shape during winter months, or honed techniques for ascents up sheer cliffs, rock gyms are appealing to a broader audience, making an extreme sport accessible to kids, families, and anyone looking to mix thrills into their exercise.
“In the good old days, you learned it through an apprenticeship: You knew somebody who climbed, they took you out,” said Bill Zimmermann, chief executive of the Climbing Wall Association, a trade group based in Colorado. Today, he said, “you don’t even have to own your own rope.”
In Massachusetts, there are 26 climbing gyms or indoor walls regulated by the state, with more than a half dozen in Greater Boston. Most of the growth has come in the last decade; as recently as 2003, there was only one other dedicated rock gym in the Boston area, according to local climbers.
“Certainly, it has been a case of build it and they will come,” said Chris O’Connell, who now owns the area’s first climbing gym, Boston Rock Gym in Woburn, which was opened by its original owner in 1989.
Rock climbing is a growing segment of the $646 billion that Americans spend annually on outdoor recreation, according the Outdoor Industry Association, another Colorado trade group. While the association does not break out gym climbing, its data show that nearly 6.8 million people participated in some form of climbing in 2012, up 7.4 percent since 2006.
The first US gym dedicated to indoor climbing opened in Seattle in 1987. Boston Rock Gym followed two years later.
Boston Rock had the Greater Boston market pretty much to itself for more than a decade, despite the sport’s popularity in New England, where day-tripping climbers gravitate to destinations like Quincy’s quarries or Newton’s Hammond Pond Reservation, while the more ambitious make climbs in New Hampshire’s White Mountains.
In 2003, MetroRock opened in Everett, then added a Newburyport location three years later. Other climbing gyms followed, including Rock Spot Climbing in Hyde Park and Central Rock’s first location, in Worcester, both in 2009.
Operators of some of the area’s newer gyms credit pioneers such as Boston Rock for paving the way, showing that climbing gyms can be viable businesses. That has made it not only easier to obtain financing to open a gym, but also to build chains of locations with a host of amenities to cater to both hard-core and occasional climbers.
Watertown, for example, is the third New England location for Central Rock Gym, which opened its second gym in Hadley in 2011. The Watertown gym includes 28,000 square feet of climbing surface, traditional exercise equipment such ellipticals and treadmills, and a snack area with vending machines. Central Rock is scheduled to open a location near Hartford as early as next week.
“In four and a half years,” said Kevin Pickren, general manager at Central Rock, “we’ve gone from no gyms to four gyms.”
Babson College graduates, Lance Pinn and Jeremy Balboni, first tried to launch a climbing gym in Boston several years ago, but had difficulty obtaining financing. Instead, they went to New York, where they opened Brooklyn Boulders, an 18,000-square-foot gym with ceilings that top out at 32 feet high and turned it into one of the area’s climbing hot spots.
Last week, Brooklyn Boulders opened its Somerville location, which at 40,000 square feet — nearly the size of a big box store —
Climbing gym operators say there is plenty of room for growth in the Boston market, particularly by attracting casual climbers who might never, or only rarely, climb outside the gym.
While climbing, whether indoors or outside, remains inherently dangerous, rock gyms make the sport more accessible to casual climbers by renting out otherwise expensive gear and providing instruction.
“My concern is to educate the 97 percent of the population that isn’t climbing today,” Pinn said, “and get them climbing. We’re going to have no shortage of customers for everybody.”
Among those at Brooklyn Boulders Somerville earlier this week were Harvard University graduate students Justin Feng, 23, and friend Alix Chan, 22. Both started climbing in gyms about a year ago.
“It was something cheap to do on weekends,” Chan said.
“For me, it kind of replaces weight lifting,” added Feng. “It’s a sport I can do with my friends. It’s more social.”
Ultimately, gyms here will develop niches, with some catering to climbing enthusiasts, others focusing on children and families, said O’Connell, the Boston Rock Gym owner. The growth of the industry has other benefits, O’Connell said, only joking slightly.
“Having more gyms around, on a personal note, is really great for me because it allows me to enjoy climbing more,” he said. “It’s really hard to climb in your own gym. You get interrupted.”Erin Ailworth can be reached at email@example.com. Follow her on Twitter @ailworth.