If the models in this year's swimsuit pictures (pages 54-73), shot on the North Coast of Jamaica, appear to be in pretty darn good shape, it's no accident. In screening models, Associate Editor Jule Campbell has always looked for what she calls "a natural, healthy beauty." The models she chooses have this, and they work to keep it.

Cheryl Tiegs, who returns to our pages after four years, has adopted a strict daily workout schedule in the past year that involves some 45 minutes of exercises, followed by 10 miles of bicycling near her Long Island home in good weather or an equivalent amount of stationary cycling in bad.

Kim Alexis swam the butterfly and backstroke competitively for 12 years, starting when she was six. Nowadays she works out for two to three hours a day when she's home—doing aerobics, "the kind that make the muscles burn"—and running three to five miles. To prepare for this assignment she also went on a strict diet ("I wouldn't necessarily recommend it"), which featured steamed vegetables and fish with "lemon, no butter," and grapefruit. Kim is engaged, incidentally, to a Florida real estate broker who happened to be on safari in Kenya during the shooting of last year's SI swimsuit issue.

Carol Alt has been an all-around jock since sixth grade. She played basketball, volleyball, field hockey and lacrosse in high school on Long Island. Her conditioning these days includes workouts on a Nautilus machine at a Manhattan club, aerobics—while traveling she carries a cassette player that details aerobic routines, which she executes in her hotel room—and 23 minutes of biking. Why 23? "I don't know. It's a nice number, I guess," she says. Alt also ice skates, an activity she took up after meeting Ron Greschner of the New York Rangers last March. They are also engaged now.

Kelly Emberg was a competitive gymnast through ninth grade, after which she was a member of her high school drill team. Her regimen now includes 100 sit-ups a day, and she takes aerobics classes in Manhattan.

The shoot in Jamaica was 15-year-old Hillary Satire's first job as a model. She attends Colin McEwen High School in Malibu, Calif. until noon, then heads for the stables. She has been riding since she was three and has shown her horses, My Little Lady and Free 'n' Easy, since she was 10.

Paulina Porizkova, who's 17, also leads an active life. When she was three the Russians invaded her native Czechoslovakia to suppress the Dubƒçek regime, and three days before the borders closed her mother and father escaped on a motorbike. "Two weeks later I got a postcard saying, 'Hello, we are in Sweden,' " says Paulina. Paulina was 10 by the time her parents got her out of Czechoslovakia and 14 when a woman on the street in Lund, Sweden suggested that she become a model. "Two weeks later I was in Paris," she says. She currently resides in the Latin Quarter and has picked up a little karate—from a single lesson in Lund and two black-belt boyfriends.

As for Senior Writer Kenny Moore, whose story on Jamaican sprinters begins on page 94, you should be as fit. Moore was an Olympic marathoner in 1968 and '72, and, as our readers are well aware, has never stopped running. The world got a look at his physique in the 1982 film Personal Best that was more revealing than any we've offered of our swimsuit models, past or present.