Josh Hartnett was determined to "prove" himself as an action star in his 40s.

The 46-year-old actor stars in the new action-comedy movie 'Fight or Flight' and explained that he was desperate to do all of his own stunts for the flick.

Speaking to Us Weekly, Josh said: "I was like, 'Can I do this? I wanna see if I can.'

"I wanted to prove something to myself, physically, but also just give somebody pure popcorn entertainment in the best way possible, which is with a lot of humour and a lot of physicality and over-the-top, unexpected surprises. I'm very proud of it."

The 'Pearl Harbor' star was allowed to perform every stunt bar one and found it pretty "demanding" working on the movie.

Josh explained: "I had a wonderful stunt double who helped preface all of the fights. And he did one stunt for me that I wasn't allowed to do. So aside from that one stunt, I did everything else.

"That was the one where the character's thrown into the bar. Because the glass was not breakaway enough for production and they were worried that I was gonna get cut badly and then we'd have to stop production. So that was the only thing that I wasn't allowed to do. But the rest of it's me. And it was pretty demanding."

'Fight or Flight' was filmed in just 25 days and Hartnett recalled how he repeatedly bumped his head during the making of the picture that features combat scenes on board an aircraft.

He said: "There'd be so many times I hit my head on these f****** baggage compartments there at head height - like, there's no room on a plane to fight. And I was getting pummelled into those things in every single scene.

"The blooper reel would just be me. Like, Oh, my neck 'cause it just kept hitting that thing. But we didn't have any time to reset or to recalibrate or to recover. We had to keep going and we had 25 days to shoot the whole thing.

"So it was just one after the other, after the other. Sometimes shooting two different scenes and two different sequences at the same time, or working one out while we were shooting the other one."