Hollywood star Jake Gyllenhaal has revealed he didn't use a body double for his boxing scenes in his new movie.

For his role as boxer Billy Hope in Southpaw, he stepped into the ring himself and drastically transformed his body.

"I had a double but he never worked in the fights, I had no interest in that," he said, "I trained for as long as I did so that I could actually fight. I trained like I would be prepared to get hit. I sparred and did get hit, and our pact to each other, me and Antoine (director Antoine Fuqua), was that if you do get hit, even in training, or up close to training, or even in the fights themselves, then we would just use it."

Gyllenhaal is believed to have done around 2,000 sit-ups and around five hours of training a day to get in shape for the role.

"I think there is a positive but also a very animalistic side to getting into shape like that," he explained.

Growing up he got into a few fight's, but never won them and didn't know how to box before he signed up for the role.

He said: "There was a part of me that was nervous whether I could pull it off, which I think is why I ended up training as intensely as I did, and really trying to fight for real.

"I think part of it is, when you haven't done it since you were a kid or you don't feel as confident or know a whole lot about it, I think it's, for me personally, you know you have to pull it off in the way I knew Antoine wanted to shoot the movie, which was as realistically as possible."

Southpaw is released in cinemas on 24 July.