Britney Spears' is ''very happy'' with her body ahead of the start of her Las Vegas concert residency.

Award-winning trainer Tony Martinez has revealed the 'Work Bitch' hitmaker is really pleased with her level of fitness after working hard to get in shape for her two-year concert residency.

Britney has been working as hard as she can in the gym to ensure she can perform her 90-minute shows at the Planet Hollywood Resort & Casino, which kick-off on December 27.

Tony told RadarOnline.com: ''She is working as hard as she can, and it is paying off. She's using all her energy right now to get ready for her 90 minute Las Vegas show.

''She wants to be in the best shape possible, and she is very happy with her body right now. She is in a really good place, and I'm so proud of her.''

Tony has shown mother-of-two Britney how to use her time effectively through 40-minute workouts four-days-a-week to make sure she's ready for the demanding dance routines for 'Britney: Piece of Me'.

He added: ''My workout motto is work out smarter, not longer.

''There's no need to run on the treadmill for two hours. I've shown her ways to sculpt her body that take less than 20 minutes. Now she's loving these quick workouts.''