Britney Spears tries to work around her children's school schedule.

The 'Hold it Against Me' hitmaker - who has just released a new album and is about to embark on a tour - is back in the spotlight after a two-year break and says she tries to fit her work commitments around Sean Preston, five, and four-year-old Jayden James' lessons.

She explained: "I'm usually pretty busy when I'm not working. I have two children, so I usually get them up in the morning, and I'm usually at the gym, and I help cook dinner sometimes ... a lot of the stuff that I do I do early in the morning when my boys are at school."

Speaking in new MTV documentary 'Britney Spears: I Am The Femme Fatale' - which follows the pop star as she shoots a new music video and returns to the stage - she also admitted to feeling nervous about performing live again.

She said: "I haven't been out (on stage) for a year . I have jitterbugs."

The 29-year-old singer also described the shoot for the video for 'Till the World Ends' as "grimy" and claims she worked so hard she wasn't even allowed a break to go to the toilet.

She explained: "It would cost about $1,000 of studio time.

"It was a little much. It was grimy and sweaty and it felt like there was poop everywhere, but it was just sweat. You work through it."