Christian Bale said that due to the improvisational directing style of Adam McKay, he had to do more research for this film than any other film he's done. In order to ad-lib in character, Bale not only needed to have Dick Cheney's mannerisms and vernacular down, but he also had to know which policies, their instances, and abbreviations the Vice President would be aware of at any given moment in his life.
Christian Bale gained 45 pounds, shaved his head, bleached his eyebrows and exercised to thicken his neck for his role as Cheney. Bale said he achieved his hefty physique for the film by eating a lot of pies.
As Cheney has had well-documented heart problems for most of his adult life, Christian Bale had to study heart attack prevention as part of his method--his tips ended up saving Adam McKay's life, as he suffered a heart attack during post-production.
Director Adam McKay suffered a mild heart attack during post-production. He decided to include black-and-white footage of the procedure to insert the stent in his heart, considering this to be his cameo. McKay attributed his heart attack to gaining weight and increasing his cigarette smoking under the pressure of the shoot, and resolved to quit smoking.
Sam Rockwell's biggest physical concern was George W. Bush's "lip forward" method of speaking. He requested prosthetic in the mouth region, in addition to the entirely prosthetic nose he wore for the film.