Transcript for Becoming 'Superman': Henry Cavill's Formula for Fitness
Moving on our "heat index" this morning, the workout plan that turned henry cavill into the man of steel. It's a training regimen. But not just about exercise. It's also about eating. Abc's abbie boudreau has the steely details. Reporter: Superman and his man of steel strength. On the big screen. And in real life. Superhuman to superhero. British actor, henry cavill, reveals the secret to his bulging biceps in that body suit. Mark is one of the most incredible people I've met. He opened my eyes to seeing past what I saw with my own. Reporter: He trained cavill and russell crowe, who dropped 40 pounds for his part. There must be a secret behind the transformation. So, what is it? The secret is -- it's a well-kept secret, called commitment and self-discipline. Reporter: Cavill's transformation began by packing on 20 pounds. What was he eating? We didn't care. If he decided, I can get an extra 1,000 calories by eating pizza, that was fine. Reporter: Then, the workout, five or six days a week, for 11 months. We're trying to use physical means to basically repair a person or change them in a psycho/physical way, so they can play a role, in this context. You need a guy to look like superman. It will be better if he feels super, in order to transmit that message. Reporter: How did it change him? I would say henry turned into a man on this show. And not only in terms of, you know, physically he made enormous changes. But in the way that he carried himself. And in the way he -- I could see him relating and adapting to other people. Reporter: He took me through some super moves. Push your heels to the floor. Reporter: Clearly, I'm no wonder woman. But then again, even superman had to start somewhere. For "good morning america," abbie boudreau, abc news, los angeles.
This transcript has been automatically generated and may not be 100% accurate.