"I have not been this sore in my entire life," she told Vegas Player magazine. "When I started working out, I was sore for like, three days. I could hardly move. I'm really challenging myself with the choreography."
Sources have told People that the Piece of Me show will have a "nightclub-like feel", and revealed that Britney plans to bring back many of her iconic looks for the show, which opens 27 December at Planet Hollywood Resort and Casino.
"Whenever I do a show, I'm really keen on making it a show," she said. "I love to dance and perform. Because it's Vegas, I want to do something different. This is the perfect place to bring it to the next level."
The 31-year-old also said she is looking forward to the stability Vegas will bring.
"When you tour, it's so hard on the body," she explained. "I look back and I don't know how I did it. Being in one place is cool. It's a more stable environment."
Britney is a mother of two boys, Sean, eight, and Jayden, seven, and she plans on bringing the boys, and her boyfriend David Lucardo, with her to Vegas.
"It's important to have a group of people around you who can keep you down to earth," she told the magazine. "It's a mind-altering experience when you become a pop star at such a young age.
"Some people are made for it and some people aren't. If you keep good friends around you and stay grounded, you'll be ok."
The Louisiana native described her early days in show business as "surreal".
"It was kind of like a dream,' Britney revealed. "I'm from a small town and I wasn't expecting anything. When it happened, it was kind of surreal. I got so busy travelling that I was oblivious to it all.
"I didn't even realise what was happening. It was like a dream that I never woke up from. It was pretty spectacular."
The Vegas stint isn't the only project Britney has been working on. Next month, she will also release her eight studio album, which, she has revealed, will feature a very special collaboration.
On Wednesday, the singer tweeted the track list for her upcoming album Britney Jean, which includes a duet with her 22-year-old sister Jamie Lynn Spears titled Chillin' With You.
Britney Jean is scheduled for release on 3 December, the day after Britney's 32nd birthday.