With her Las Vegas show set to open next month, the mother of two is getting her body in serious shape – so much so, in fact, that she's had moments where she could barely move.
"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."
Multiple sources have told PEOPLE that Spears's Piece of Me show will have a "nightclub-like" feel, something Spears wanted in order to keep the energy up. She even plans on bringing back many of her iconic looks for the show, set to open Dec. 27 at Planet Hollywood Resort and Casino.
"Whenever I do a show, I'm really keen on making it a show. I love to dance and perform," she told the magazine. "Because it's Vegas, I want to do something different. This is the perfect place to bring it to the next level."
It's also the perfect place for stability, she said. Vegas? Stable?
"When you tour, it's so hard on the body," she explains. "I look back and I don't know how I did it. Being in one place is cool. It's a more stable environment."