"I feel great," says Adams, 46, after a workout session. "I should have started doing this 20 years ago."

Adams, principal of St. Simon's Catholic School, joined Lady Circuit after a parent recommended the women-only fitness center and volunteered to pay the annual fee for her. Chuta and Cummings followed once they noticed Adams had become more energetic.

Unlike most gyms that look rather like giant fish bowls with sophisticated equipment, Lady Circuit is only about 1,200 square feet, with 10 hydraulic resistance machines lining up like a circuit and 10 rest stations in-between.

"As people move around the circuit, they perform both a strength training and a cardiovascular workout at the same time," says owner Kristin Gerhard.

One lap takes about 10 minutes. A complete workout, consisting of three laps, burns between 350 and 900 calories, depending on the fitness level of the exerciser and the intensity of the workout.

Gerhard, 24, opened Lady Circuit in August of 2002. She thought of opening a 30-minute fitness center after her mother joined one in San Diego.

"I have been struggling with my weight all my life," she says. "I have joined different kinds of gyms and programs, but I often felt intimidated by the environment. Here you don't need to impress anyone. You don't need to wait to use machines. You just need to do it at your own speed."

The 30-minute fitness program has attracted women of all sizes and ages. Its 325 members range in age from 9 to 82. Although the economy is staggering in Silicon Valley, the membership increases steadily.

"People cannot control a lot of things in their lives, but they can certainly control their health," Gerhard says.

Many regular members have noticed improvement in their health.

Adams lost nearly 6 percent of her body fat, and Chuta lost 5 percent of her body fat. Cummings got a thumbs up from her doctor for the decrease in her blood pressure and a 130-point drop in her cholesterol.

The nuns have inspired other people to join Lady Circuit.

Marti Guidoux, who has a child at St. Simon's Catholic School, became a member after bumping into Adams at the parking lot outside the fitness center last September.

"I didn't recognize Sister Adams because I had never seen her in shorts," Guidoux says. "At that time, my doctor just told me how much I needed exercise for my bones. I told myself I was supposed to do what Sister Adams was doing."

Guidoux now works out four times a week.

"The biggest benefit is how good you feel about yourself," she says. "The weight loss is just a given."

Lady Circuit 30 Minute Fitness is located at 1320 S. Mary Ave., Sunnyvale. For more information, call 408.524.0600.