Britney Spears's continues to transform herself as she prepares for her upcoming world tour.

With her latest album Circus topping the charts, the singer has now been putting a lot of work into dance rehearsals with her crew. New exclusive rehearsal photos were posted to Spears's Web site.

Jamie King, who choreographed her 2000 tour, is working together on the new dance moves. The singer look toned in a tank top showing off her arms and abs.

The singer successfully shed 20 pounds in recent months, bringing her famous waistline back to what it was in her early days when she first broke out onto the scene.

Click here for more Britney Spears work out photos.

This was all part of a two-hour cardio-and-strength-training session three times a week (in addition to dance rehearsals), Us Weekly recently reported.