Gwyneth Paltrow has finally sorted out her "sagging a*s".

The Oscar-winning actress - who has two children, Apple, five, and three-year-old Moses, with husband Chris Martin - has been working hard with celebrity trainer Tracy Anderson and is amazed how much she has helped change her appearance.

She wrote on her GOOP website: "She has kicked my formerly sagging a*s into shape, and I will be forever grateful."

The 37-year-old beauty also posted a video of the trainer's "little arms series", which Gwyneth used when preparing herself for action movie 'Iron Man'.

Talking about the lower arm exercises, she excitedly wrote: "It works wonders, especially for the batwing problem."

Tracy has become a huge hit among Hollywood stars and counts Jennifer Aniston, Madonna and Courteney Cox-Arquette among her clients.

'Cougar Town' star Courteney is full of praise for Tracy, saying: "I heard about Tracy through friends who had seen fantastic results. I have seen amazing results that I never thought were possible. My butt has lifted, my arms are sculpted, and my skin is tight and actually clings to the muscle again."