Jake Gyllenhaal's Grueling Physical Transformation for 'Southpaw'

Jake Gyllenhaal says he fully committed himself for six months to get into shape for 'Southpaw'. (Photo: Southpaw).

While actors will often jump from one demanding role to the next with very little downtime, it's generally not the case that the physical demands required for each are so completely at the opposite ends of the spectrum. Such is the case with Jake Gyllenhaal — who went from portraying a gaunt crime reporter in the drama "Nightcrawler," to less than a year later bulking up to play a ripped prizefighter in "Southpaw."

"We literally turned him into a beast," director Antoine Fuqua told Deadline last year. "Jake, my God, he’s a very electric, powerful fighter in this movie, and a guy who fights for his daughter. I’m confident that this will change how people see Jake, as a leading man."

To achieve that look, Gyllenhaal’s trainer, former professional boxer Terry Claybon, set out to immerse the 34-year-old actor in the world of boxing. For the first two months, the actor hit the gym three hours daily, splitting the time between mornings and evenings. The remaining four months found Gyllenhaal boxing for three hours in the morning and working out for three hours at night. Claybon tells Yahoo! movies that a gradual build-up in sit-ups culminated in the actor being able to pull off more than 2,000 daily.

As for diet, because of the grueling workout schedule, Gyllenhaal didn't need to be particularly careful of the foods he was consuming. Claybon says it came down to carbs in the morning and protein in the evening. As a result, he quickly regained the 30 pounds he lost for "Nightcrawler," adding an additional 15 pounds of muscle to his frame.

"I lived in [the competitive fighting] world for six months," Gyllenhaal told Men's Journal, saying that he sparred in the ring with real pros, attended high-profile boxing matches, and basically forced himself to become one with the sport.

"I could talk for hours about it," he added. "It's so wonderful for the mind and especially for youth, to understand how to express your physical power. I think especially, talking as a man, to know you are capable of a certain power and to know that you don't have to use it."

Check out a trailer for the film below. "Southpaw" hits theaters July 25.