Gwyneth Paltrow was not afraid to show some skin when she walked the red carpet for the premiere of Iron Man 3. The sheer dress gave viewers a peek at the star's backside, which Gwyneth credits to trainer Tracy Anderson. Tracy helped transform Gwyneth's self-described saggy and square-shaped butt into a lifted, rounded, and shapely backside. We learned three of Gwyneth's favorite butt-toning moves directly from her trainer — just in time to help you rock your skinny jeans. Add these exercises to your workout to feel the burn and see the lift!