Inside a converted warehouse in Pigtown, off limits to most company emplyees, designers and engineers dream up and test equipment for one of the nation's fastest growing sports.

They follow in the foot steps of company founder Richard B.C. Tucker, a 1951 Johns Hopkins University graduate and lacrosse player, who revolutionized the lacrosse stick 42 years ago and forever changed the sport.

Today, Baltimore-based STX LLC claims the biggest share of the U.S. lacrosse equipment market, even though it never has made products such as helmets and footwear. Though STX won't disclose revenue numbers, the privately held company said its sales have tripled over the past five years. The company employs about 100 workers at its corporate and research headquarters on Bush Street and makes its gear in about 20 factories around the world.

The division of Wm T. Burnett & Co., a polyurethane foam and sythetic fiber manufacturer also based in Pigtown, is riding the sport's swelling popularity.

"The sport is on the cusp of breaking out of being a niche sport and more into a mainstream sport," said Bill Schoonmaker, chief operating officer of US Lacrosse, based in Baltimore. "People are exposed to the game who haven't been exposed to it before."

The sport saw a 10 percent increase in organized team participants at all levels last year from youth leagues through high school and college, according to US Lacrosse, the sport's governing body. This year, one of two professional lacrosse leagues added two expansion franchises. And media coverage of games at the collegiate level has increased, with ESPN airing dozens of games each season, including the NCAA final four, which concluded Monday in Foxborough, Mass.

To remain on top as competition intensifies with brands such as Brine and Warrior, STX must keep coming up with new ideas to make the game more accessible and help athletes perform better. Through a cooperative agreement with Nike, STX also has been designing and producing lacrosse equipment under the Nike brand.

"This is an innovation machine," said Jason M. Goger, STX general manager. "We have enough innovations and ideas to fuel two brands."

The work is so secretive given the intense competition among rival manufacturers that most employees are not granted access to its year-old research and development space, where STX is investing $1 million.

The company's success is pushing it to work harder to stay on the cutting edge, officials say.

"The game is changing so rapidly," Goger said. "You have athletes who are bigger and stronger, then you have athletes playing longer throughout the year," in a range of climates. "We have to keep on the leading edge of that growth and change."

Employees create new designs, build prototypes and put products through rigorous tests that simulate repetitive use on the playing field under a variety of weather conditions. Researchers can work for years to develop a new product or design, but can also turn ideas around quickly, from concept to on the shelf in a matter of months.

At work stations adorned with lacrosse sticks and protective gear, designers create three-dimensional models on computer screens.

In a back room, an engineer demonstrates some of the equipment that puts sticks, heads and goggles to the test. In one glass chamber, a men's lacrosse head, the part of the stick that forms a frame for the pocket, is pounded by a machine, sometimes for hours, in an attempt to arrive at just the right balance of stiffness and flexibility.

"We can determine if it's going to break in the field or not," said Mike Schmittdiel, a senior mechanical engineer.

At another station, Schmittdiel shot a ball with compressed air through a tunnel into the head of a mannequin wearing women's goggles. STX said it has a 70 percent market share in women's lacrosse goggles.

Another machine, resembling a copier, produced a computer designed prototype of a lacrosse stick head, made of glue and cornstarch. In another test, a metal rod pushed down on aluminum sticks, simulating conditions on the field, where sticks have been known to snap in two.

"Our heritage is borne of playing on the field," Goger said. "We try to combine field testing with lab testing."

Further testing of new equipment is done by student athletes, many at Johns Hopkins, who are asked to use the equipment and offer feedback. The company has sponsored Hopkins for the past 12 seasons, providing the team with STX sticks.

"They've listened very, very well," Dave Pietramala, Johns Hopkins lacrosse coach, said of the company's product developers. "They keep their ear to the ground. They are anxious and interested to find out what the players like, what they don't like and how to come up with something protective. They are a substance, not flash, company, and they pride themselves on doing things the right way."