updated 06/13/2012 AT 3:35 PM ET
•originally published 06/13/2012 AT 12:00 PM ET
Just six weeks after giving birth to daughter Maxwell Drew, Simpson stepped out in apparent workout gear on Tuesday and made her way to an L.A. gym. The new mom has also announced she will be working with Weight Watchers.
“I think anybody who’s gone through a pregnancy, after they have the baby, it’s like, ‘I need to do something about this,’ ” she told PEOPLE recently.
“For me, I really want to do something that is a lifestyle, because in the past,” she continued, “I’ve been known to yo-yo diet.”
– Evan Lambert