In an interview with The Guardian, Ben Foster admitted to taking performance-enhancing drugs under medical supervision to prepare for the role.
Foster admitted the emotional storyline about the disgraced cyclist took more a toll on him than the physical demands of the role.
The movie omits any reference to Paul Kimmage, the Irish journalist who writing for the Sunday Times did as much as David Walsh to expose Armstrong and who had even more sensational confrontations with the cheating cyclist than Walsh did.
Stephen Frears told The Hollywood Reporter that he cast Guillaume Canet - a French actor who barely speaks English, to play Italian doctor Michele Ferrari because he couldn't find an Italian actor who speaks English.
The film is based on Walsh's book "Seven Deadly Sins: My Pursuit of Lance Armstrong".