At Monday's Los Angeles premiere of the new Disney film, a lighthearted Gyllenhaal laughed away concerns about his grueling regimen, insisting that becoming buff was simply part of his job.
"It was so hard," Gyllenhaal told PEOPLE sarcastically. "Being an actor is so hard. Being in shape is so hard, too, and being paid to get into shape is even harder – and you can quote me on all of those."
When it comes to physical training, "I like the focus," he says. "I'm somebody who likes to kind of keep moving. When you're shooting a movie, the downtime is always the hardest thing, and when you get to be physical in between takes it's actually a good thing, I think, for any actor."
Gyllenhaal, 29, was, in fact, inspired by a veteran leading man better known for curling Oscar trophies: "I remember when I worked with Dustin Hoffman – as a wrap gift Dustin gave me a walker to do triceps push-ups on, because that's how he'd get his energy going. Every actor has different tricks, and I thought that it was a great thing. I would go run and jump and do what I could to get excited and ready for the next take and to stay in shape."
And while his shoulders currently aren't quite as big as they are in the movie posters, Gyllenhaal says he has kept up some of his Persia" physique. "You focus on it like an athlete would and it's kind of off-season, but I'm very much a physical and active person. So I like to maintain as much as I can."