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Gotta get her body back in shape for warmer months! And for that Vegas gig too...

On Thursday Britney Spears went to the gym in Calabasas, and not only are we loving her newly dyed brunette locks, but it looks like she's really been busting her booty on the treadmill!

Earlier this month it was reported that the 31-year-old pop superstar was still deciding between Caesars Palace and Planet Hollywood, but her camp has yet to confirm which one she'll go with. But one thing is for sure: Her long-term concert deal will be worth more than $100 million!