The screen glows red as Stephanie “Coco” Brewster strikes a pose in a lacy black leotard, channeling Beyoncé. The bass hits as she slinks across the platform to “Partition,” tumbling and dancing while friends and family shout her other nickname, “Punky.” Brewster’s sexy, fierce homage to the Queen seems to fly by without a hitch, but when I run into her backstage, she’s in tears. Her bustier fell down during her routine, she tells me, and though she fixed it in an instant, Brewster is understandably worried.

Less than 24 hours later, I’m back at the Golden Nugget, watching the next phase of Fitness America Weekend. Behind the stage, dozens of buff and bronzed Musclemania America competitors prepare their routines in the cramped hallway, some doing push-ups, others flexing aggressively in the mirror, each sporting a different colored Speedo. A bearded man in metallic briefs puffs on a Marlboro, the swirl of smoke masking the overpowering scent of Bengay.

They call this ritualistic prep-work “getting pumped.” And that smell isn’t Bengay; it’s a body oil that makes muscles pop under the spotlights. As I weave through the bodybuilders in the hallway, slipping and sliding along the greasy floor, I notice things are running behind. The gladiators are getting anxious—but amid the chaos 20-year-old Brandon Flihan seems calm. The Vegas native, who began competing seven years ago, took first place in Musclemania’s teen division last year, and now his goal is to take home the trophy as a junior. I ask him how he measures up against the field while a blonde woman coats his body with more of that shiny liquid. “I’d be lying if I said I wasn’t a little nervous,” he admits. “I wanna make sure everything is on point.”

Throughout the weekend men and women flock to the Nugget to compete in six divisions, ranging from Figure America and Model America to Musclemania Physique. Brewster is there for the Fitness America Championship, a fitness competition/beauty pageant mashup. Like Flihan, she also took first place in her division in 2013, so this year she’s qualified to compete at the pro level.

“I feel like they’re expecting something of me,” Brewster says as she layers on eye shadow, false eyelashes, extra coats of mascara—the works. The Coyote Ugly dancer grew up playing sports in Texas, but at 32, her look is more vixen than tomboy. “I just want to go out there and set the room on fire,” she tells me before her Beyoncé tribute. “I’m doing the whole routine in heels.”

But after a little more than a minute onstage, Brewster experiences her wardrobe malfunction. Exposing herself, even slightly, could be enough to knock her out of the top five, but there’s a chance for redemption in the bikini round. When the time comes for awards to be presented, Brewster’s tears have dried, her eyes full of that sparkle they had when I met her. “In third place,” an announcer’s voice beams through the theater, “Stephanie Brewster.”

Pageantry is only one aspect of Fitness America, now in its 25th year. But as the girls dance, backflip and do one-armed push-ups under the lights, it’s hard to forget that industry’s controversial history. Critics have long argued that pageants exploit women, reducing them to tits and ass and encouraging near-impossible body standards. But for many of today’s performers, including first-time Ms. Bikini competitor and Las Vegan Tenile Pritchard, this competition has challenged them to be healthier, stronger and more in tune with their bodies.

“During the process, my body completely changed,” Pritchard says. “I did not eat healthy at all before. I was eating takeout all the time. I had to cut all the sugar and fat out of my diet [and] learn how to cook. It was a whole new lifestyle for me.”

Diets and exercise regimens run the gamut, but Fitness America is a “natural” event, meaning competitors are tested for performance-enhancing drugs and steroids. Still, there are no rules on plastic surgery, and there’s an abundance of, well, silicone. For many of the female competitors, it’s par for the course. Heavy lifting can reduce a woman’s breast size, creating another hurdle in achieving a perfectly sculpted body.

During Ms. Bikini, women compete in two rounds: sportswear and swimsuit, both involving barely-there bottoms and push-up bras. They’re ranked on outfit selection, personality, appearance, poise and presence, body condition and facial beauty. The men’s modeling division, by comparison, is judged on physical appearance, photogenics, poise, presence and something called “apparel integration.” So what does one gain from baring (almost) all in front of a panel of judges and a sea of onlookers? Most would assume it’s about vanity—or perhaps cash. But there’s no prize money to speak of. It’s about determination, and the power to push the body to extremes.

Although she was a spectator at Fitness America Weekend, Philadelphia bodybuilder Anna Gott says weightlifting helped her get her groove back after she quit her lifelong sport. “Gymnastics is a very individual sport. You work out with other girls but you’re really competing against yourself,” she says, “So I needed to find something that was individual in that nature.”

Following a bout with depression, Gott started weightlifting and got hooked. “I’m not trying to beat somebody else’s deadlift, I’m trying to beat my workout from last week. That’s only compounded upon itself in competing. Now I’m trying to look better than my last competition.” As for the standards of fitness and beauty, “We’re harsh on each other,” Gott admits. “But at the end of the day most competitors will tell you [they] respect everybody onstage, because they went through 12 weeks of prep. That’s something that 99 percent of the population can’t do. Even if you don’t place how you want, if you get onstage, you’re comfortable with how you look. The placing at the end of the day can’t really take that away from you.”

Back in the hallway, Flihan is busting out all of his bodybuilding tricks. “I brought two meals with me, because I know how Musclemania runs—it runs a little behind, always,” he says. On top of his carefully rationed chicken and sweet potato, he’s got a Snickers bar, white rice and a cup full of oats. I watch in bewilderment as he throws back a mouthful, sans water.

The sugars from the carbs will give his muscles a plumper, fuller look, he explains, and the dry oats will draw out the extra water his body is hanging on to (as if he looks bloated). “You’re on a deficiency of carbs and fats the entire 12 weeks,” Flihan says, “so when you throw ’em back in, your body reacts and absorbs everything and it just looks phenomenal. Everything kind of blows up.” Three-thousand calories a day breaks down to a whopping 300 grams of protein, 280 grams of carbs and only 40 grams of fat. Whatever he eats gets meticulously weighed and calculated. He relies on lean proteins like egg whites, chicken and fish—along with green vegetables and sweet potatoes—to keep his body in check.

“I’m not really a size freak. I’m not going to be the biggest guy onstage, and I don’t want to be,” he tells me. At 6-foot-1 and 195 pounds, Flihan is hoping the win is in the details. “What I’m really focused on is symmetry, everything balanced. The finishing touches, like wax on a car.”

Heavy lifting, no cardio, a strict diet and frequent deep compression-massages. Three months of intensive training, nine months of maintenance and seven years of commitment. For Flihan, all of that boils down to what happens in the next few hours, as his division finally takes the stage.

“Frontal bicep,” the announcer calls. “Relax.” “Front-lat spread.” “Relax.” “Turn to the side.” “Side chest.” “Back-lat spread.” “Relax.” Faces strain as muscles flex. Teeth clench and hands shake. Then the posing round is over, and the juniors return to the wing to wait until the next round, routines. It’s nearly 2 a.m. when the votes are counted, and Flihan’s name is called. First place.

There’s no cash, no shopping spree, no new car—just a trophy, a title and a feeling of accomplishment. To an outsider, the life of a bodybuilder is a stereotype: men and women getting sprayed down with Pam, self-obsessed and hell-bent on achieving perfection. But they’re athletes above all, dedicating their lives to the sport because of their passion, an affirmation of identity and what they call “the bug.” No matter how many wins they pile up, the goal remains the same: Be better. The muscled physiques are only the physical result, a testament to their craft. And like an artist’s canvas, a bodybuilder’s work is never truly finished.