Daren Carter got the idea for Contours Express from his mother, Brenda. For years, Brenda would key into her son's gym before it opened -- before the grunting, weight-tossing men invaded.

Brenda was soon joined by a handful of friends, all of whom awoke before sunrise simply to avoid the often-intimidating male clientele.

To many, Brenda and her friends' behavior would mean little. But to Carter, an entrepreneur since age 20, this was an opportunity.

"She just wasn't comfortable in the co-ed environment," remembers the 40-year-old Carter. So if I design a club specifically for woman, Carter thought, mom and her friends would flock.

In 1998, Carter did exactly that, opening the first Contours Express in Nicholasville, Ky. A year later, Carter sold seven franchises. Today, over 400 Contours Expresses span across 10 countries, including Australia, Brazil, Greece, and Ireland. Last year, Contours Express, which Carter owns 80% of, his partner the remainder, did $5 million in sales. Sales are projected to grow 40% to $7 million this year.

Contours Express isn't alone in the female-only gym market. Curves, which started six years before Contours, has over 8,000 locations, all offering a similar workout regiment to Contours: all-in-one strength and cardiovascular training. Besides promising a toner body in 29 minutes, as opposed to 30 minutes at Curves, Carter differentiates himself from his competitor by the equipment he offers. Dissatisfied with the machines on the market, Carter, along with a manufacturer, designed smaller, more approachable machines suitable for his women clients. Carter's machines use real weights, which have the benefit of both positive and negative resistance. Curves, on the other hand, uses hydraulic equipment, which has positive resistance, but not negative.

The health and fitness market has exploded in the last two decades, first with fitness videos, then infomercial gadgets, and now fad diets. Contours Express owes much of its success to this trend, but not all. According to Carter, Contours Express's clients, for the most part, are older than the women who frequent co-ed gyms. "Fitness becomes more and more popular everyday, especially since there are more and more baby-boomers getting older," says Carter.

Along with fitness, baby boomers are predicted to spend much of their $3.4 trillion on other recreational activities, like golf, spas, restaurants and travel. That's why the recreation and entertainment industry is a hot industry to start a business over the next decade. But Carter already knew that, which explains why he confidently projects to open 2,500 Contours Expresses in that time.