Henry Cavill refused to take steroids to muscle up for the role. He also refused any digital touch-ups or enhancement to his body in his shirtless scenes. He said it would have been dishonest of him to use trickery while playing Superman, and he wanted to push his body to the limits, to develop his physique into one that was worthy of the character.
Henry Cavill said that the most difficult part of making the movie was definitely his two shirtless scenes. He had been training for months prior to filming, but for his shirtless scenes, he went on an extremely difficult diet and training regimen in which his calorie intake was cut from five thousand to nearly fifteen hundred for six weeks. After six weeks, he reached a body fat level of just seven percent, the level achieved by professional body-builders during competitions. Henry said he did this because he wanted to make his abs as pronounced and his muscles as defined as humanly possible, to create the best possible Superman physique. Cavill returned to a more manageable routine after the scenes were shot, but felt his effort was rewarded when audiences and critics alike praised his physique for the true embodiment of what Superman would look like. After he had shot his shirtless scenes, director Zack Snyder gave him pizza and a tub of ice cream to reward him for his Herculean effort for the shirtless scenes.
Henry Cavill naturally has a hairy chest, and left it untouched for the shoot of this movie. He insisted that Superman has chest hair in this film; he rejected the notion that just because you are muscular, you should not have chest hair, and cited the Superman comic book "The Death Of Superman" as being an iconic representation in which Superman had a hairy chest.
Henry Cavill and Russell Crowe had met years prior to playing father and son when Henry was an extra in Rapimento e riscatto (2000), and received words of encouragement to pursue acting, and an autographed picture from Crowe, who was his favorite actor.
Several scenes and concepts are taken from the comic book Superman: Birthright (2003-04), written by Mark Waid and drawn by Leinil Yu, such as:
- Superman's "S" shield meaning "hope" in the Kryptonian language.
- Superman flying over a herd of zebra.
- Jonathan Kent's line, "You're the answer to, 'are we alone in the universe?'" (though in the comic, the line is spoken by Martha).
Aaron Smolinski: As a communications officer. He previously played one of the ages of baby Clark Kent in Superman (1978).