Zac Efron packed on 18 pounds of muscle for his role as a troubled Marine in the Nicholas Sparks drama The Lucky One -- no easy feat for the 24-year-old actor.

"By the end of the movie I didn't recognize myself," Efron, who weighed 145 pounds when production began, tells the May issue of Men's Health. "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."

Efron -- who first rose to fame as basketball heartthrob Troy Bolton in the High School Musical movies -- has always challenged himself to do more. "I could pick up almost anything. If you put it in front of me, I could always find a way to tackle it," he says of his rigorous training regimen. "I was never a natural at anything, but I could always outwork everybody."

To build muscle, Efron began each day at 5:30 a.m. with a high-protein meal ("a shake and, you know, an eight-egg omelet," he says) followed by a morning workout. By day's end, he aimed to consume 3,500 calories.

Efron also worked with Logan Hood of Epoch Training, and he was soon able to lift more than ever before. "You get this strange sense of power as those weights increase," he tells Men's Health. Efron worked out five days a week, about an hour each time. "If you're eating appropriately and getting enough rest, you don't need to train all day," Hood explains. "All the work's happening when you're outside of the gym."

Efron's new movie, The Lucky One, is in theaters April 20.

滬江娛樂快訊：小帥哥扎克·埃夫隆為了電影《幸運(yùn)兒》瘋狂健身，增重18磅——當(dāng)然全是壯壯的肌肉啦！不是每個(gè)人增重減重都像克里斯蒂安貝爾那樣輕輕松松——蝙蝠俠為了藝術(shù)忽悠自己的體重可不是一回兩回了——扎克接受專業(yè)的健身訓(xùn)練，吃超級多的蛋白質(zhì)，完了以后狂鍛煉，每周五天，木有間斷。“當(dāng)電影結(jié)束拍攝的時(shí)候，我都不認(rèn)識自己啦！”