JGL was required to become fit for his role in Don Jon but this was no simple kind of being fit. His role required him to pump weights till his body became a complete muscle structure so that he could portray a perfect role of "Don Jon".
JGL was trained by Arin Babaian, who made the transformation possible. According to AskMen, Arin provided that JGL lived the real character of "Don Jon" by working out at the gym on a regular basis. He said that he was able to connect with the character more by living it in the real world. He worked out throughout the day focusing on each part of his body which is called the aesthetic based training.
JGL was required to look into the mirror while training, which was another reason to bring his character to life. However the mirror was also required to that JGL could train more efficiently through the aesthetic process. He was also required to eat weight-gaining food because he previously had an average structure. After having a good meal, he had to transform that fat into muscles by working out.
Examiner also provided that the character of "Don Jon" in the comedy film required Joseph to understand the importance of working out since he did not like the concept of working out in real life. He provided that working out is not his thing but since his work required him to do so, he gave it his 100 percent. He said he put on 12 pounds and used this fat for his muscle building.
He also provided that he did not enjoy training for this movie since it was very rigid and demanding however he did enjoy training for some of his previous movies where he was required to be a muscle man as well. With Joseph being the writer and director of the movie, he says that he took it as a challenge so that the viewers could get the most out of the movie.