The singer admitted that she hired a personal trainer to get her in shape for her 'Part of Me' visual, which sees her join the US marines after coming out of an adulterous relationship.
Perry told MTV: "I got on a meal plan. I'm still on that meal plan, although I cheat a little bit - I have to live!
"I got a fantastic person to work me out and get me into really good shape. On the actual base, I did a lot of things. I flipped girls, I learned how to fireman-carry. I know how to carry my weight a little bit more."
However, the star confessed that there was one stunt she was unable to master and the director had to edit that particular shot in the video.
Perry said: "One thing I can't do, and I hope that there are other people out there that feel the same way, is climb a rope.
"Oh my gosh, it's so hard to climb rope! It's all about grip and arms. I tried five or six times on set, but I had to cheat that shot. My hands were shaking."
Perry's 'Part of Me' has reached number one on the US Hot 100 and is currently on course to top the UK chart this Sunday.
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Watch the music video for Katy Perry's 'Part of Me' below: