Keeping on top of her workout regimen, Nicole Richie took to the Tracy Anderson gym in Los Angeles, California for a heart-pumping cardio session this afternoon (September 29).

The House of Harlow designer looked ready to work up a sweat as she arrived to the fitness center, sporting a loose black t-shirt, cropped spandex pants and a pair of running shoes.

Meanwhile, according to an Us Weekly insider, both Nicole and actress Kate Hudson have recently underwent a breast augmentation from Beverly Hills plastic surgeon, Garth Fisher.

"Kate makes jokes about her boobs, but her chest has always been one of her biggest insecurities," a source previously told of Hudson's decision to go forward with the cosmetic procedure.

Nicole, on the other hand, is said to have blamed motherhood as her reason for going under the knife this summer, with an insider dishing, "In the past, she said she wanted a lift, though we never thought she was serious," adding, "The pregnancies took a toll. She said breast-feeding killed what boobs she did have!"

Enjoy the pictures of Nicole Richie at Tracy Anderson gym in Los Angeles, California (September 29).

Photo Credit: SplashNewsOnline.com, Wenn.com