Britney Spears shows off her underbum

Britney Spears shows off her underbum in extremely brief shorts

She has been working up a major sweat in dance rehearsals in preparation for her new music and residency at Planet Hollywood in Las Vegas this winter. 

And Britney Spears seemed keen to show off the results of her hard work. 

The 31-year-old singer was seen arriving on the set of her new video in very brief tasselled shorts showing plenty of 'underbum'.

Britney's back! Spears posted a photograph of herself looking stunning in a turquoise bikini and platform heels on Sunday 

  

Keeping it brief: Britney stepped out on the set of her new music video in a pair of extremely short hot pants and jacket 

It wasn't a particularly flattering look for the singer - especially as she was wearing flip-flops, but a tweeted picture showed her in a more svelte light.

Britney also posted a snapshot of herself looking particularly svelte in a turquoise bikini on her Instagram account on Sunday. 

'Gonna get my tan on in the desert in between shots on the #WorkB***h set today,' she wrote in an  accompanying caption. 'It's HOT out here people!!!! #desert #heatwave #WorkB****hDay2

The star teamed her brightly coloured two piece with a pair of glittering platform heels for the picture and appeared to be inside some kind of trailer. 

Just 24 hours earlier, the star tweeted another sexy still from her video shoot which featured her sporting a yellow and black lacy bra set and elbow length leather gloves

Tease: Britney posted a sneak peek from her upcoming music video rumoured to be titled Work B***h, on Saturday

Fuller figured: Britney now looks slimmer than in previous years, pictured here in 2010

In the snapshot, Spears can be seen seductively holding her arms over her head in a sultry pose, showing off her incredibly toned midriff.

'Hot day on set… ;) A little dirty, little flirty, danced my A** off. Stoked for tomorrow!” she wrote next to the picture.

The new shots are a stark contrast to just two years ago when Britney was displaying a somewhat fuller figure.

She has been on a rigorous fitness schedule this year, doing three day a week hour long cardio workouts and daily yoga sessions according to Shape magazine. 

'The (Vegas) performances won’t be simple,' she told the publication back in May. 'They’ll be a massive party from start to finish. And to pull this off, I have to be in top condition and running at full speed.'

Britney is back with the hotly anticipated new single due out on September 17.

The rumoured title for her song is believed to be inspired by RuPaul’s Supermodel (You Better Work).

And many people believe that Britney will even be sampling the tune for her comeback single.

Spears has been posting the title as a hashtag for weeks now, which initially sparked the rumours, and RuPaul tweeted the blonde star on Friday: ‘Werk B***h! @BritneySpears’. 

Everything about the new album and single has been kept under wraps.

Last month the singer's official website went black with only a ticker counting down the days, hours, minutes and seconds until her comeback release on September 17.

The information, besides the countdown ticker, was a simple message stating: 'All Eyes On Me'.

In training: The 31-year-old pop star has been in constant rehearsals for her comeback performances, pictured on Friday in Thousand Oaks, California