From Wikipedia :
“Ryan Gosling was only 17 when he was cast in the lead role. To train for the role, Ryan took intense martial arts classes by the same trainer who taught Lucy Lawless and Kevin Sorbo. He was so tall and thin that his costume had to be reworked to minimize the look of how thin he was. Original costume sketches showed a darker upper body costume. When Ryan was cast, the costume designers made the upper body of his costume lighter in color and broader in the chest to help create a more bulky look. Make-up was used on Ryan’s arms to help add muscle contours. Similar tricks were used for both Kevin Sorbo and Lucy Lawless for their characters.”
(Source: bickle)