Britney Spears' trim and toned physique is down to "hard work".

The singer - who is mother to Sean Preston, four, and three-year-old Jayden James - recently revealed her body transformation, and her former personal trainer has admitted she didn't get her chiseled figure by sitting back and doing nothing.

Marc Corliss - who helped the 'Toxic' hitmaker tone up in Los Angeles a couple of years ago - explained: "There are no shortcuts to anything. Britney goes after what she wants. She's a hard worker. Plus, I'm sure her diet is on point as well."

The diet and exercise expert said he is a big advocate of balancing strength training and cardio exercise, and advises people who want a body like Britney's to train for 45 minutes, five days a week.

He added to gossip website HollywoodLife.com: "It obviously has to be a combo of all of it. You can't have success if you're missing a piece of the puzzle. The best thing to do is interval training, like a quick sprint and then go back to resistance training, like push ups or squats.

"Five days a week is pretty active. If you're going at maximum effort, you only need to put in about 45 minutes."