Britney Spears desperate to slim down as she prepares to reprise role on TV sitcom

Britney Spears was back at the gym yesterday in a desperate effort to shape up for a second appearance on the TV sitcom How I Met Your Mother.

The singer worked out on a treadmill and did sit-ups at Bally's Fitness Center in Studio City, Los Angeles for the second time in as many weeks following the news she is set to return to the show.

Scroll down for more...

Back on the treadmill: Britney, who is trying to get back in shape, was spotted at her local gym in LA yesterday

Britney's appearance on the hit US program last month drew the series' highest ever ratings.

A source told People magazine: "The show is ecstatic and so is Britney. She had so much fun the first time around she really wanted to come back."

Spears' reinstated manager Larry Rudolph said: "It was a really positive experience for her. She talked about it quite a bit the last time I saw her... She wants to do it again."

Earlier, a tanned and healthy-looking Britney enjoyed some precious quality time with her children.

Scroll down for more...

Looking up: the singer, with her sons in LA yesterday, is putting her troubles behind her

Clutching youngest son Jayden James, 19 months, closely to her hip, she smiled broadly at elder son Sean Preston, 2, who giggled at his mother as he runs ahead with his nanny.

As they took a stroll around the streets near her Hollywood home, Britney, 26, looked content for the first time in ages as she continues to battle to regain full custody of her sons.

Scroll down for more...

Babe in arms: Britney cradles her son, Jayden James

It was the first time in months that Britney, 26, has been allowed unsupervised visits with her sons, a far cry from the scenes the world witnessed in January when she barricaded herself inside her home and refused to hand them back to ex-husband Kevin Federline.

It is a dramatic turnaround for the troubled star who has avoided nightclubs and showbiz parties in the past couple of months, preferring to spend quiet nights at home instead.

Scroll down for more...

Working girl: last month Britney plays a flirtatious receptionist in an upcoming episode of US sitcom How I Met Your Mother. She is set to make a second appearance on the show

As another custody hearing approaches, she'll be hoping to turn her back on a turbulent year which saw her shave all her hair off, charged with an alleged hit-and-run, hospitalised and held in a psychiatric ward.

On May 6, Britney and her father Jamie, who has been in control of her assets and her estate since February, will go before Los Angeles County Superior Court Commissioner Scott Gordon to ask for more overnight visits with her sons.

If she succeeds, Britney will be allowed one evening a week with her children for the first time since January.

A source close to the star said: "Britney wants her kids back. And she will do everything in her power to make that goal a reality."