When a business finds a successful formula, the general rule is to stick with it. But NordicTrack seems to think that 15 years is long enough.

The popular maker of cross-country ski machines opened its first retail store in Pentagon City mall Nov. 2 after operating exclusively as a direct marketing and mail order business for years.

"Statistically, there is a percentage of Americans who won't buy a $600 dollar product by direct response," said Jim Bostic, company president. "We were statistically leaving half the population out."

Bostic believes this "other half" will buy exercise equipment despite the sluggish economy, which many industry executives say has not yet hurt their equipment sales. And he believes the best place to sell it to them is in upscale malls, even though most fitness-equipment stores avoid malls because they consider rent prices high.

The Pentagon City store is a prototype for future stores the company plans to open primarily on the East Coast, he said.

NordicTrack, of Chaska, Minn., is a subsidiary of Acton, Mass.-based CML Corp., which also owns the Britches store chain in the D.C. area.

Its new store sells several models of its cross-country ski machines, models of three other pieces of exercise equipment the company has introduced in the last year and a variety of smaller items. The equipment ranges in price from $299 to $1,399.

"The whole East Coast corridor has been a very strong market for NordicTrack," Bostic said.

NordicTrack is banking on a common perception in the industry that sales of home fitness equipment are on the rise, and will only rise more as the economy falls. Last year, sales of home fitness equipment totaled $1.79 billion.

"In times of recession, fitness equipment sales typically rise ... maybe because people are trying to burn off their stress," Bostic said.

Tom Doyle, director of information and research for the National Association of Sporting Goods, said that the market is surprisingly good now, especially for more expensive equipment, given that retail sales in general are slumping. But Doyle said that opening in a mall is unusual for a specialty exercise-equipment store.

"Most ... tend to be freestanding," he said. "Part of the problem is that your mall rents are so expensive that it's hard to maintain margins on hard goods. Traditionally, the hard goods -- the exercise equipment -- tend not to be in malls."

Sales of hard goods tend not to carry the kind of large margins that sales of smaller retail items do, Doyle said, adding that NordicTrack seems to build in excellent margins on its ski machines, given the amount of television and magazine advertising the company does.

Bostic, however, said "you get what you pay for" in malls. "You pay a high-rent factor, but you generally get access to ... people who have the money. It's the demographics," he said.

Still, a few in the industry contend that the market for fitness equipment is not so insulated from the economy's woes.

"I would really categorize it at the moment as fair," said Norman Thier, merchandise vice president for Herman's Sporting Goods stores.

"Throughout this year, the business has been better than the average retail sales figures," Thier said. "But the last month has been really slow. It almost dates to when the Iraq situation arose. Within a week we began to see {equipment sales} fall off."

Thier said the two days after Thanksgiving will give "a good indication of how the market is going to go."

Although NordicTrack's store sold 60 pieces of equipment in its first five days at an average $610 each, which is more than the company anticipated, Bostic expects sales to level off significantly, if not before Christmas, then in January. He said he is aware that home fitness is a fundamentally trendy industry, fueled by consumers' perceptions of what's fashionable.

"If we end up doing a third of the business we've done so far, I'll be just delighted," he said.

Included in NordicTrack's venture into the retail market is the introduction of new products. Bostic said the company has brought out new products because of "where the medical researchers and fitness experts tell us the trends are going to be," and because increased foreign competition has forced U.S. fitness companies to change the pace of the business and "take new product risks."

Doyle, the sporting goods association executive, agreed that fitness companies have to diversify to grow, but offers a different reason.

"It's because exercising is not fun ... so people get bored, and once they get bored of using one piece of equipment, they'll move onto another one," he said. "So it is a prudent thing to do to expand your product line.""

"You can see the cycles this stuff goes through, but it's going to peak," he said. "You can't expect every home in the country to have a home gym or a treadmill."