BSPEARS4AM0124PART2_01.jpgBritney Spears BSPEARS4AM0124PART2_03.jpg Wondering why Britney only wore a tank top out to dance practice last night?

Simple - those are probably her gym clothes!

Yes, the pop princess' venue of choice for practicing her moves was closed last night when she got the urge to shake it - meaning Britney Spears had to go to 24 Hour Fitness to get down!

That's what happens when the desire to dance seizes you in the middle of the night!