The story of Captain America is well covered in comic book lore: a scrawny, bullied orphan named Steve Rogers is chosen for a top secret government project during World War II in which he becomes a test subject for a super serum.
The serum transforms him into a strong and able soldier named Captain America, and he leads the U.S. Army in its fight against the Nazis.
Actor Chris Evans, who plays the title character in Friday's release of "Captain America: The First Avenger," put on 15 lbs. of muscle to play the role.
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The problem: he got too big for Steve Rodgers. Solution: "Skinny Steve."
Having literally built Evans into what the film's director Joe Johnston called "the perfect human specimen," the movie makers had to figure out how the 6 ft. tall actor with the muscled-up physique could convincingly portray the pre-serum Steve Rogers, a scrawny kid of a mere 90-something lbs.
Hollywood has dealt with on screen body changes in many ways over the years. The cast and crew of the 2000 film "Cast Away" took a year-long break so its star, Tom Hanks -- who first gained 50 lbs. for the role -- could drop weight to look like he'd been stranded on a tropical island for years.
One option for "Captain America" was to superimpose Evans' head on a skinny body double, much like the technology employed by filmmaker David Fincher in "The Curious Case of Benjamin Button" when Brad Pitt had to age backward.
Last year Fincher employed the same technique in "The Social Network," in which Armie Hammer played Tyler Winklevoss and identical twin brother Cameron Winklevoss, which meant digitally putting Hammer's head on actor Josh Pence's body.
On "Captain America," there was no way to take a year off because its backers at Marvel Studios have been on a tight schedule rolling out their superheroes one by one -- including the recent "Thor" -- so audiences will be familiar with most of them when they join forces in next summer's "The Avengers."
Like Fincher in "Social Network," director Johnston initially hired a body double and used the head replacement system in a scene where Steve Rogers was lying on a table. But he quickly realized it wouldn't work for other sequences.
"Chris moves in such a unique way; he doesn't move like anybody else," Johnston told Reuters. "The body double could not move like him. As hard as he tried to watch Chris and duplicate the movements, it just wasn't the same."
That was perfectly fine with Evans, who was not keen on having another actor involved in creating the iconic role.
"The beginning part of the movie is so crucial to get the audience invested in who Steve is, I didn't want to share that part of the performance with another actor," Evans, 30, told Reuters. "I talked to Joe about it and thankfully, he agreed."
Instead of the body double/superimposed head, the filmmakers used a "shrinking" technique and computers to basically erase portions of Evans' strong physique on screen.
"We filmed over 250 shots of Chris and used digital technology to 'shrink' him down to what we called 'Skinny Steve,'" said Johnston.
"It's pretty amazing," added Evans. "They took shape out of my jaw line, they shrunk my skeleton and they made my shoulders less broad."
While it may sound easy, it wasn't. Each time Evans' body went through the digital nips and tucks, it created empty space in the background which needed to be filled in.
Multiple shots had to be filmed with green screens just to superimpose the scenery that would normally have been there had bulky Evans really been little, scrappy Steve Rogers.
"It was a very arduous process," said Johnston. "It took all of pre-production and most of production to do all 250 shots."