London, Jan 10 (Agencies): Actress-singer Jennifer Lopez is all set to sport a svelte look in her judging debut on 'American Idol' this month by shedding her curvaceous derriere.

The 41-year-old actress is being trained by Tracy Anderson, who is also the ex-fitness instructor of pop star Madonna. Anderson's celebrity clients include Hollywood actress Gwyneth Paltrow and Columbian singer Shakira.

"Jen is one of the hardest-working fitness fanatics in Hollywood and definitely has the discipline for Tracy's tough regime. She loves the difference Tracy's dance workout has already made," a friend said.

The 'Maid in Manhattan' star liked what Anderson did for Shakira and wanted the same. Earlier Madonna had to go through extreme workouts with the trainer.

Lopez previously worked out with Gunnar Peterson, who got her back into shape after she had twins.