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It’s a warm Southern California morning, and I'm meeting Zac Efron in Studio City at a place called Weddington Golf & Tennis. With a name that stuffy, I expect marble and money. The course turns out to be public, with a plastic-cup snack bar where a waitress, without looking up, informs the 24-year-old movie star that she doesn't take credit cards. They've reserved us a private tee, which is approximately 4 feet away from the adjacent public one.

Here at the practice range, Efron—in T-shirt, oversized cap, shorts, and Vans—strolls around in disarming anonymity, though to be fair, it's hard for even the preeminent teen pinup of the 2000s to attract notice in a crowd that includes this many codgers in lavender pants. After talking and meandering (not especially well) through a bucket of golfballs, we encounter Roger Dunn, a California golf-shop magnate who gives lessons wearing a Panama hat and smoky sunglasses. We'd heard that Dunn is just shy of his 50th year of teaching, and he's been introduced to us as a man of considerable local repute. Mostly Dunn has something to teach, and Efron is drawn to that.

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"I could pick up almost anything," Efron had told me earlier. "If you put it in front of me, I could always find a way to tackle it. I was never a natural at anything, but I could always outwork everybody." He'd mentioned Bruce Lee, a man he's been reading about. "What you got from him was the work ethic," Efron said.

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"Constant diligence. He was so focused, constantly pushing his body." And so, at the eventual behest of the old teacher, the former star of High School Musical sets up on the range, absorbing Dunn's sharp tips and rebukes. Dunn tells him to watch his back foot ("Keep it steady"), twist his wrists on the follow-through ("Rotate, come on, give me a break"), and focus ("Aw, there you moved your feet").

To illustrate a point about how golf uses martial-arts-style balance, he asks me to push against his right biceps. Again, this gentleman is about 80, so I confess to being a little tentative with the pressure. Wrong call. "You're mad at somebody, you say, 'Get away from me,' and then give them a full shove," Dunn says, and then, in a move reminiscent of Bruce Lee himself, he hauls off and shoves me.

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This goes on for 20 minutes. Half a dozen strokes later, Efron's hitting a 7-iron 175 yards. "That's why I like to work with younger people," Dunn says. "I like to work with everyone, but young people learn faster."

If he knows, or cares, that he's talking to a movie star, he hasn't given the first indication.

"What's your first name?"

"Zac."

"Zac. I'll remember that. I don't have many Zacs."

After a few minutes and the arrival of his actual student, Dunn nods provisional approval of the "It's a start" kind. Efron pays him for the half lesson and promises to remember what he's heard.

Teen-dream stardom can go a number of ways, most of which are down. Imagine a half-formed 18-year-old version of yourself, in all its rubbery fumbling or furious egomania or bruised shyness, and give it VIP access to the globe and the eardrum-destroying adoration of millions of fans. Then imagine thinking, just years removed, "I should definitely take that job where I train like a Marine."

This goes some way in explaining what Efron is doing in The Lucky One. Based on a book by chick-lit specialist Nicholas Sparks, the film stars Efron as a Marine back from Iraq. The man has ghosts in his head and a hole in his heart shaped like bombshell costar Taylor Schilling, whose character is officially American cinema's all-time hottest dog-kennel owner. Efron's performance is restrained, his speech crisp and tentative. He cut his hair. There's no singing.

The Lucky One required becoming not just a leading man but also a believable Marine. "I didn't feel like I was the type of guy to actually portray them accurately," Efron says during a break from the tee. There was a lot I'd have to learn."

Fortunately, he learns quickly. Efron and director Scott Hicks first decamped to Marine Corps Base Camp Pendleton in California, where in his first meetings with Marines who were back from two or three tours, the seriousness of the role hit home—as did the mountain of physical and mental preparation he had ahead. "They were my age," Efron says, "23, 24, even younger. And most of the staff sergeants were not huge guys. They were about my height, 5'9", 5'10", some shorter, but all very stocky. And I'm there in a backward hat and Vans, walking around like I'm still in college."

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He pauses for a long time.

"It's much different from the lifestyle I'm living over here," he says. Where do you start the conversation? I didn't know what to say, what questions were inaccurate."

Efron trained at a simulated firing range; he was taught how, in full kit on 110-degree Santa Clarita afternoons, to clear empty cabins and sheds. That wasn't even the hardest part. He also needed to whip himself into Marine shape, a task he would accomplish with a surfeit of protein and the help of trainer Logan Hood, a former Navy SEAL.

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Efron was 145 pounds, lean and cardio fit, when he began training for the film. By the time The Lucky One wrapped 4 months later, he'd gained 18 1/2 pounds. "Substantially bigger," Hood says. On a guy with a slight frame like Efron's, 18 1/2 pounds makes a big difference. "You don't really have to be 6 feet and 225 pounds to look big on camera."

For 4 months, 5 days a week, Efron's day began at 5:30 a.m. with protein ("a shake and, you know, an eight-egg omelet," he says), a drive to Long Beach, and a workout on a full stomach. "I got used to it at the time, but I wouldn't recommend it," he says. "It's not practical to do for a long period of time. You feel this debilitating soreness. This kind of stuff, going golfing, you can't do." He wound up eating six to eight times a day and sucking down shakes between meals, with a daily target of 3,500 calories.

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Still, the results spoke for themselves: Efron was lifting weights he'd never been able to lift before. "You get this strange sense of power as those weights increase," Efron says. "By the end of the movie I didn't recognize myself. You hear about guys like Christian Bale who dive into it and are really able to transform. I've always wondered if I had the willpower to actually do it. And I'll always have pride around the sense that I can."

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“You want to get lunch?” Efron asks, and then I'm following him through Los Angeles in a rented car that's not as nice as his. He's suggested Hugo's, a fine place next to a gas station and full of beautiful people, aggressively healthy foods (sauteed leafy greens, black bean cakes, quinoa, and a green juice that has "a lot of chlorophyll in it"). The parking lot is full, so we head one block west and park in front of someone's house. We walk back through the residential neighborhood, seemingly the only two pedestrians in the city of Los Angeles.

For someone making the tricky and paparazzi-stalked transition from young-adult actor to leading man, Efron seems to travel with a disarming lack of self-destructive behaviors. He was born north of here, in San Luis Obispo, to active, grounded parents; as a youth he attended public schools and stuck to sports, surfing, skateboarding, and BMX. But he always seemed to be pushing himself. "We would go bowling and everyone else would be having fun, and me, my dad, and my little brother wanted to actually learn how to bowl. Even to this day I have trouble just going bowling. I want to win. It's horrible sometimes," he says with a laugh.

Apparently, occasional bouts of bowling-based insanity are the extent of Efron's debauchery. He's "frugal" with his money and doesn't ingest anything with a lengthy list of chemicals. His biggest controversy entailed dropping a condom on the ground at a movie premiere, which is a funny sort of controversy to have, since it actually suggests that the guy is responsible.

When he begins working on a movie, Efron says he tells his friends he'll be "MIA for a while," and between projects he sticks mostly to the Valley. "The city's a strange spot," he says once we've been seated. "I don't feel like I fit in there." He has no Twitter account, and when he talks about himself he tries to make sure "it's about the work."

There's plenty of it. He lent his voice to Dr. Seuss' The Lorax, an animated film released in March; the weekend before our interview, he'd completed filming on The Paperboy, a death-row drama with John Cusack, Nicole Kidman, and Matthew McConaughey. He has his own production company. He's finished shooting a movie with filmfest favorite Ramin Bahrani. He's been having dinner lately with Warren Beatty, a master with wisdom to share.

"Look, I was just a musical-theater guy," Efron says. "I would have been happy to do that for the rest of my life. But there's something about me that's always searching for the more challenging route, and the actors that I really admire are always picking things out of their comfort zones, trying to stretch to see where they can go. It just seems like the road less traveled."

Jacked like Zac
Look like a Marine in 4 short months

Zac Efron's trainer, Logan Hood of Epoch Training, used these four principles in transforming the young actor's physique.

Control the variables
Building a Marine-caliber body calls for a comprehensive approach. "Training is only one piece of the puzzle," Hood says. "Sleep is huge. Stress is huge. Fuel you're putting in your body is an enormous component. But nobody brags about having followed a regimented diet for 4 months." You have to decide what's more important: eating that entire pizza or having the body you want.

Opt for quality over quantity
Efron worked out 5 days a week, about an hour each time. "That's another misconception," Hood says. "If you're eating appropriately and getting enough rest, you don't need to train all day. All the work's happening when you're outside of the gym."

Go old-school
You don't need fancy equipment. Hood put Efron through a regimen of "typical old powerlifting stuff": squats, dead-lifts, heavy overhead presses, weighted pullups—simple exercises that over time allow for heavier and heavier weights.

Stick with the plan
Efron didn't bulk up overnight. Nobody can: "It's months and months of process and diet," Hood says. "What people see on the screen is a guy who basically immersed himself into a training process over a period of time. It's more than just doing exercise and taking more protein."