David Corenswet is taking on one of the biggest challenges of his career. The 31-year-old actor is taking on "Superman," a character that, while beloved and storied, is a challenging one to adapt to the screen.

Corenswet prepares to leave his relative anonymity behind as he steps into the red boots of the most popular superhero of all time.

Corenswet's physical trainer breaks down the routine that helped the formerly svelte actor put on 40 pounds of muscle—and how he got Nicholas Hoult prepped for Lex Luthor.