The 24-year-old says he was impressed with his own will power. "By the end of the movie, I didn't recognise myself," Efron told Men's Health magazine, reports usmagazine.com.
"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 will power to actually do it. And I'll always have pride around the sense that I can," he added.
Efron thinks his willingness to work hard pays and has played a huge part in his successful career. "I could pick up almost anything. If you put it in front of me, I could always find a way to tackle it.
"While training for 'The Lucky One', I'd get this strange sense of power as those weights increased. I was never a natural at anything, but I could always outwork everybody," he added.