Arnold Schwarzenegger in The Expendables 2: "At 65, I'm exercising on a Boris ... - Telegraph.co.uk

But he admitted: "It is tougher as you get older. Your metabolism slows down. Your muscles don’t respond in exactly the same way any more. When you do action scenes and fight scenes and run around you take longer to recuperate, but so what? It doesn’t matter. It’s not like we don’t get paid for it.”

Speaking ahead of the London premiere, Schwarzenegger said he had been keeping fit by pedalling around the city on a “Boris bike”. The former governor of California is a friend of Boris Johnson, the Mayor of London.

“I’m addicted to exercising and I have to do something every day. Here in London it’s been fun because they have the Boris bikes so I’ve been bicycle riding and sightseeing at the same time,” he said.

The actor said there was competition on set with his co-stars. “Everyone on the set was very helpful. I’d been out of the movies for eight years so they actually went a bit overboard thinking that I don’t know how to hold a gun any more.

“But at the same time we were very competitive. Because of watching them, I tried to step it up. We were always competing about who has the most defined muscles, who has the best body, who has the least amount of body fat, who has the biggest gun, who kills the most people, who kills in the most unique way...”

Jet Li, Bruce Willis, Jason Statham, Scott Adkins, Liam Hemsworth and Chuck Norris also appear in the sequel, while tennis player Novak Djokovic has an unlikely cameo.

Van Damme plays a villain in the film about a gang of mercenaries who reunite for one more mission.

The Muscles from Brussels thanked Stallone, co-writer of the film, for rescuing him from a life of straight-to-DVD movies.

"You know, when I walk in the street or the airport people come up to me and say, 'Hey, when’s the next movie?'

"Thanks to him, I'm going back to the big screen because I’ve got these good eyes, good face, but you don’t see that on DVD because you have to over-exaggerate. So thank you, Mr Stallone," Van Damme laughed.

Stallone, 66, said he kept in shape for the film by employing "scientific methods and equipment they use for Olympians today".

He sustained various injuries during the first Expendables film but said he was determined to come back for more.

“I had my neck fused in the last one because of a stunt that went bad. I had two back operations, a shoulder operation, an Achilles operation. It took its toll. And the doctor said don’t take a rough fall, let the stunt fellow do it.

“But sometimes you just have to do it and throw common sense out of the window. There were some tough scenes in this one but I can’t help myself.”

Stallone was asked to name the best and worst lines he had spoken during his 40-year career.

The Rocky star replied: “I guess my best is ‘Yo, Adrian!’. It’s one thing you just can’t criticise.

"The worst would have to be all my dialogue in Stop! Or My Mom Will Shoot. Every line.”