See the rest of Slate’s Fitness Issue.

One time, on a shoot for Women’s Health, Kim Strother jumped in the air 84 times. Strother started keeping track because she’d done this particular move—run and leap, run and leap—hundreds, probably thousands of times, and she figured it was time to get a strict accounting. Strother has leaped for sportswear ads and for magazine workout spreads, the images set apart in her portfolio by the color of her sports bra. In these shots, she is the picture of feminine fitness—a powerful woman suspended in midair, her muscles taut but not overwhelming.

Strother is the Gisele of the gym, the go-to fitness model for Nike, Target, and magazines like Shape, Health, and Runner’s World. That’s her ripped stomach in a Fitness spread on “sculpting amazing arms, legs, abs, and butts,” and that’s her doing a back handspring for Self’s primer on how to “put the spring back in your step.” She adopts serene yoga poses for clothes catalogs—photographers tend to prefer tree, Warrior I, Warrior II, and upward dog—and, for reasons she doesn’t understand, often gets asked to glide around on Rollerblades.

Despite her thriving career, the blond, 28-year-old Strother says she “always finds it really awkward” when people ask what she does. Fitness modeling is not a well-known occupation, and those who have heard the term, Strother says, have some misconceptions: “They think you would be one of those girls that’s ‘roided out on the cover of some hard-core fitness magazine.”

Indeed, fitness modeling has traditionally been associated with hypertrophied dudes and dudettes. Fitness competitions and muscle mags, which grew out of the world of bodybuilding, remain a realm of Schwarzenegger-ian physiques. Alicia Marie, owner of the title Ms. Muscle & Fitness and a one-time paramour of John Rocker, is the best-known female fitness model of this ilk. And ex-Army Ranger Greg Plitt, the self-proclaimed top fitness model in America, is something like the Joe DiMaggio of ginormous pecs, having appeared on a magazine cover for 53 consecutive months.

Marie and Plitt are both represented by Topher DésPrés, the senior agent for Wilhelmina’s two-year-old fitness division. A former model himself (“I was too short to do anything except take my shirt off”), DésPrés says the industry had yet to take shape when he started out 16 years ago—he didn’t even realize he was doing fitness modeling. Increased popular interest in health and nutrition led to more demand from magazines and clothing companies for models who could hold their own on a yoga mat. This led to more professionalization and specialization in the modeling world, as fitness-specific agencies sprung up to meet clients’ demands for a new kind of fitness model—gym-savvy men and women who didn’t look like they’d overdosed at the pharmaceutical counter. Someone, essentially, who looked great in spandex and could demonstrate the proper form for a push-up.

Strother came to the business during this uneasy transition. In 2001, she went in to see an agent at the urging of a fitness model friend. The initial evaluation made her cry: “She told me I was too short, I needed to lose weight, didn’t like the way I dressed.” (In the agent’s defense, Strother—a competitive cheerleader at the time—says she might have gone to the audition in a rhinestone-studded T-shirt.) Despite those supposed flaws, Strother managed to book a test shoot for the cover of Muscle & Fitness; she didn’t get the job, she believes, on account of her lack of implants.

But fitness modeling was no longer just about bulging muscles and skimpy bikinis. Although she didn’t have the fitness pageant look, the 5-foot-8 Strother was the new-school archetype. Meaghan Murphy, Self’s features director/fitness, calls her the magazine’s “go-to girl”—a model who is “healthy, strong, and aspirational.” While runway models have bodies like coat hangers, fitness types have healthier, more recognizably human forms—the samples sportswear companies send to Murphy come in size medium. “The supermodel won the genetic lottery,” Murphy says. “The fitness model worked damn hard for that body, and you can tell.” (OK, full disclosure: Murphy says that the mediums are sometimes too big—these women are models, after all.)

Fitness models don’t just have to look sleek and strong. Magazines and sportswear firms need toned talent, DésPrés says, because “[fashion] models can’t run like a runner. … They can’t do shit right.” Fitness models are often yoga instructors and personal trainers by trade, and are experts in the poses and techniques they’re asked to perform. At least, they’re supposed to be. Every booker has a story about a model who looked the part but couldn’t do a squat, or a guy who lied about his max bench press. (It can be especially challenging to find women who can do pull-ups. In some cases, a trainer holds the model up, then runs away quickly so the photographer can snap a shot before she falls.)

Strother, a former trainer, keeps getting work because she’s easy on the eyes and has no problem maintaining a Pilates position. “They’re always so happy because they know I can do the exercise, which makes me feel like I’m doing something with my life,” she says. Fitness modeling is, in large part, about atomizing exercise. To teach someone how to do the perfect lunge, you have to break it into components and showcase the most-intensive parts. This requires holding yourself in an uncomfortable, halfway position as the photographer searches for the perfect angle, the one that highlights the move without zooming in on your crotch. “They want the dumbbells to be parallel in the picture,” says Justin Hileman, a 29-year-old former pro baseball player who’s modeled for Men’s Health, Men’s Journal, and Under Armour. “You’re in an extremely awkward position, you’re dying, the lady wants to pin your shirt differently, and there’s a wrinkle in the shorts.”

And don’t forget to look delighted (a set of crunches—oh, happy day!), even if you’re posing on cement. To make exercising seem effortless, you have to practice at home: no grunting, no squinting, no pursing your mouth, no stretching your face. “A lot of times they want you to smile while you’re holding a squat for two minutes. It’s burning, and you’re trying to keep your form,” Strother says. “Sometimes you forget to smile.”

Strother is blessed in one significant way: “I really don’t sweat that much, and I don’t know why.” This lack of perspiration sometimes leads the wranglers on set to mist her with water or dab baby oil on her arms to mimic a glistening look. Along with donning fake sweat, Strother must also exercise in skimpy gear she wouldn’t sport in her civilian life. In nonsimulated workout sessions, she wears Capri pants (never shorts) and big, baggy shirts. “If you put a girl in the magazine with what I wear to the gym, it would be unflattering,” she says, explaining the need for the unrealistic wardrobe. “I wouldn’t even look like I work out.”

Perhaps on account of her big, baggy shirts, Strother says she rarely gets recognized. Despite her relative anonymity, she is one of the few fitness models who are able to make it a full-time career. While Strother hasn’t worked as a personal trainer since she signed with Ford Models in 2005, most of her peers can’t quit their day jobs. While the field is growing, magazine shoots typically pay just $200 or $250, and lucrative catalog work is less plentiful than in the high-fashion world.

The fitness model’s best days might still be ahead of her. Self’s Murphy says the magazine’s increasing reliance on video—both on the Web and as part of a new iPad app—has led her to cut loose the women who merely look good in a still position. “You cannot fake it,” Murphy says—you have to hire athletes and trainers who can really do the moves. Strother, who starred in a series of instructional videos that Ford created in partnership with YouTube, seems better-positioned than anyone to take advantage of this shift. Video made Jane Fonda a workout queen in the 1980s. Thirty years later, perhaps it will mint the next generation of fitness stars.

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