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OTRC: Britney Spears shows bikini body: How she keeps in shape (Photo)

Britney Spears appears in photos posted on her Twitter and Instagram pages on Sept. 8 and Sept. 7, 2013. They were shot on the set of her new music video, 'Work B----.' (twitter.com/britneyspears/status/376846154090045440/photo/1 pic.twitter.com/pxLgSm6hif / http://instagram.com/p/d_O8ywm8A3/)

Britney Spears recently posted a photo of herself on Twitter showcasing a trim, toned bikini body on the set of her new music video, "Work B----."

Following positive reactions online, the mother of two and pop star's personal trainer Tony Martinez has shared several of her workout secrets, one of which is timely. Spears, who is 31 and has two children from a previous marriage, has maintained a trim figure throughout the past couple of years but has appeared out of shape at times.

Spears, he told E! Online, exercises for about 40 minutes a day and does "Olympic-style," "hard-core" workouts, many of which incorporate sports such as football, basketball, boxing and tennis.

"She loves tennis. She likes to serve. She was serving the ball like Serena Williams!" the outlet on Monday quoted him as saying, a day after the tennis star won her fifth US Open title.

Martinez said Spears has been "using all sports right now to get ready for her 90-minute Las Vegas show." The singer is reportedly set to headline her own show at Planet Hollywood Resort & Casino in the city, although this has not been confirmed officially.

In addition to the bikini photo, which appears to have been taken inside a trailer, Spears also shared a picture on her Instagram page that shows her dancing on a video set in a black and gold bustier and black elbow-length gloves.

The official release date for "Work B----" has not been confirmed. Spears' website features a countdown below the title "All Eyes on Me" that is set to end on Sept. 17.

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