If you have seen this picture of a shirtless Zac Efron, you know that he looks, well, scrawny, but he does not look that way anymore. What happened? Where did those biceps come from?

There is a rumor out there that Efron has been using steroids (Human Growth Hormone) to gain muscle mass, and that he is using something else that allows him to eat more calories – which he needs to gain muscle mass – without adding body fat, but I do not believe that.

Do not forget, Zac is only 20, he is young. And for a young, healthy guy like he is, it is not hard to gain muscle mass in a relatively short time, assuming he knows what he is doing in the gym and at the dinner table.

Zac Efron’s diet Zac has altered his diet. “He’s on a high-protein, low-carb diet to help build muscles,” says the source. “And Zac says he wants to bulk up fast.”

Zac Efron’s workout He does three-hour sessions with his personal trainer: cardio, free weights and weight machines.

And insider close to Zac says, “He wants to be really big and buff by the time he starts filming the remake of Footloose.”

Zac Efron big and buff? I do not know about that. His arms have clearly improved in size. His legs are still too skinny. Efron’s back and pecs need a lot more work.

The bottom line: It takes a lot of hard work and superior genetics “to be really big,” but Efron appears to be on the right track. Eat big, lift big, rest – that is the formula for getting h-u-g-e, can Zac pull it off? [sources: Star, OK!]