The health-spa market looks impossibly overcrowded -- and plenty of shakeout victims would line up to confirm it. But Sharlyne Powell and Sharon McConnell say they've found a substantial, untapped market of health-club patrons.

They are sure because they are part of it. Their company, Women at Large, of Yakima, Wash., operates and franchises fitness programs for "large extra-large" women. What began as a physical fitness center has expanded to encompass related products, starting with private-label cosmetics and fashionable exercisewear in large sizes -- all oriented to what Powell and McConnell see as an ignored market.

Women at Large's strategy is part crusade. Because they are overweight themselves, Powell and McConnell recognize that the patrons they call "fluffy ladies" have egos battered by years of living in a thinness-crazed culture. "'Fat' hurts. It's like someone cussing at you," says Powell. "I'm sick of people like Richard Simmons calling you every name in the book."

So their spa caters to its customers' need to feel feminine and accepted. Some members do lose weight, but the program emphasizes fitness, not weight reduction. Powell and McConnell haven't always practiced what they preach, however. They started out with a thin instructor, a "role model" who scared away customers. Now they lead the aerobic-dancing routines themselves and require franchisees to hire overweight instructors.

Mail-order sales have taken off in the past few years. But catalog companies still face the problem of returns when clothing doesn't fit. Siri Vail saw a niche in which she could avoid most returns. After working for department stores and Vogue magazine for nine years, Vail started a mail-order venture aimed at the rapidly growing accessories market. The Siri Corp., in Chicago, publishes what may be the first exclusively mail-order catalog devoted to women's accessories, which don't require complicated sizing.