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Madonna has admitted that she is an "adrenaline junkie".

In backstage footage from her 'Sticky & Sweet' tour, the singer explained that she does not think she will ever retire.

According to the News of the World, she said: "I am a gypsy at heart. I can't imagine that I will ever stop touring. People call me an adrenaline junkie - I am about to prove them right."

Madonna also revealed that she is always working on new material so that she doesn't get bored.

"Whenever I'm working on old songs, even new ones, I am inevitably bored and sick of them already," she explained. "I have to reinvent it to make it exciting for myself."

Madonna's 'Sticky & Sweet' Concert will be released on CD, DVD and Blu-Ray on March 29.