Sigourney Weaver at the Premiere of the film 'Snow Cake' at the Edinburgh International Film Festival. Edinburgh, Scotland - 15.08.06

The 56-year-old actress was filming a scene in which she had to jump on a trampoline when the accident occurred.

She says, "They had to shoot that scene really fast, and there was no time to warm up. I hurt both knees and I've been in physical therapy for months.

"Having to take a year off from working out was tough. I've missed it. I've put on eight pounds, which I'm looking forward to losing.

"You have to learn what not to do with your knees."

Source: WENN