Jessica Simpson Shares Post-Workout Selfie -- and She's Looking Super Fit!

'Move move move for your own mental health.'

Jessica Simpson is working on her fitness in quarantine! The 39-year-old singer took to Instagram on Wednesday to share a post-workout mirror selfie.

In the sweaty shot, Simpson rocks a tie-dye sports bra with matching high-waisted shorts and a coordinating headband. The impressive pic shows off Simpson's toned abs, arms and legs.

"Woke up before all 3 kiddos to get my steps in and spend time with me, myself, and I," she wrote alongside the photo referencing her three kids, Maxwell, 8, Ace, 6, Birdie, 1. "Move move move for your own mental health."

A source close to Simpson tells ET that the star is walking outdoors and on her treadmill. "It’s the way she stays sane, so it’s as much for mental health as it is for physical wellness," the source shares. 

Simpson is also eating healthy, but in moderation. She's all about eating the things she likes, but using portion control. "There has definitely been a lot of baking going on with the kids and she doesn’t totally deny herself," the source says. 

Last year, ET caught up with Simpson's trainer, Harley Pasternak, who revealed how the mom of three lost 100 pounds after giving birth to Birdie.

"She lost the weight because of everything she did when she wasn't in the gym. Of the 168 hours of the week, she's only working out around three of those," he said, adding that Simpson makes it a point to walk 12,000 to 14,000 steps per day.

The weight loss came after Simpson struggled with body image issues for years. In fact, in her memoir, Open Book, Simpson revealed that she previously underwent two tummy tucks.

"I was so ashamed of my body at this point that I wouldn’t let Eric see me without a white T-shirt on," Simpson wrote of her husband, Eric Johnson. "I had sex with it on and even showered with it on. I couldn’t bear to look at myself."

When ET spoke with Simpson, she shared that the tummy tuck decision came after the births of her first two children.

"That was after I lost a ton of weight and I had skin and stretch marks because I had two babies back-to-back, 14 months apart," she said, adding that she had "gained so much weight" during her pregnancies.

Watch the video below for more on Simpson.