Sylvester Stallone says filming 'Rambo' was so "tough" it made 'Rocky Balboa' seem like ballet.

The 61-year-old Hollywood hard man - who reprises the role of Vietnam war veteran John Rambo for the blockbuster movie - claims the fourth installment is the "most difficult action movie" he has ever made.

Stallone, who was speaking at the U.K. premiere of 'Rambo' at London's Leicester Square yesterday, said: "I thought after filming all the hard boxing scenes in 'Rocky Balboa' in 2006, 'What could be tougher?' But it was like the 'The Nutcracker' ballet compared to 'Rambo'.

"This was the most difficult action movie I have ever made, and I've made a few."

Stallone, who also directed the movie, revealed his unique tips for combating the aging process.

When asked how he coped with the arduous action scenes Stallone added to BANG Showbiz: "Fish, fish and more fish. I try to ignore the skepticism about my age and just get on with making films. The stunts in 'Rambo' were pretty hard but I still did all but one of them myself. I feel like I am 20 again but with arthritis."

"I've done four 'Rambo' films now but I really hope there will be more to come."

'Rambo' sees the war hero take a group of mercenaries up into Myanmar via the Salween River in search of missing Christian aid workers.