Jake Gyllenhaal worked out in a flak jacket before shooting one of his movies, as he wanted to get used to running in a heavy costume.

The actor sports a rippling physique in Prince of Persia: The Sands of Time, and spent hours pumping iron to develop his flat stomach and rippling biceps. Jake knew he had to wear a weighty costume for the role, so decided to don a special outfit whenever he exercised so it didn’t come as too much of a shock.

“I wore a flak jacket to work out and carried an extra 20lbs when I went on a run to simulate the armour, which is very heavy. Whenever I ran I’d also carry something in my hand to get used to running with a sword,” he explained. “It was six months of training. Everything I did was so I could do the same thing on set, not for aesthetics.”

The 29-year-old pushed himself hard for the part, and didn’t stop training even on set. He wanted to shoot as many of the action sequences as possible himself, meaning he didn’t get much free time while making the movie.

“I always want to do as much as I can myself,” he has explained. “And I’m a perfectionist when it comes to fight sequences. I want to get every move perfect and I refuse to accept anything less than that.”

Prince of Persia: The Sands of Time will be released on DVD later this month.