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Jennifer Lopez

HOW SHE DID IT
She gained nearly 50 lbs. while pregnant with twins Max and Emme, but Lopez didn't rush back to the gym after their February arrival. "I'm supposed to be relaxing for the first six weeks," Lopez, 38, told PEOPLE in March. Now she's slowly getting back into shape with thrice weekly workouts with trainer Gunnar Peterson. Pairing 20-30 minute walks with varying sets of push-ups and lunges, "[the workout] has to increase her strength and stamina. This can't wipe her out," says Peterson, who calls Lopez "hands-on" with her twins. "She looks great. If you're in terrific shape to start with, it's easier to get back into shape post-pregnancy."

Halle Berry

HOW SHE DID IT
Since giving birth to daughter Nahla Ariela in March, Berry has been sticking to a diet of lean proteins, complex carbs and vegetables. She has also ramped up her exercise regimen: After relying on low-impact activities such as swimming while pregnant, Berry, 41, is now hitting the gym five days a week with trainer Ramona Braganza. Her hour-long sessions are broken out into three separate cardio routines: the elliptical, kickboxing and a stair or hill climb. In between, Berry does core work, such as abdominal and pelvic exercises, as well as strength training, with a leg workout every session.

Christina Aguilera

HOW SHE DID IT
Although son Max Liron arrived in January, Aguilera didn't start exercising again until mid-March. "I'm slowly and surely getting into it," says the 27-year-old singer, who delivered her son via C-section. Now back to working out with trainer Tee Sorge, "I do the treadmill, I box, and I do a lot of weights," Aguilera says. "I feel so much better when I work out. I want to feel healthy and strong." She also credits breast-feeding for helping her burn calories, and the fact that, while pregnant, "I never felt my weight get out of hand." But there has been one hard part to getting back in shape, she admits: "Trying to peel myself away from Max!"

Salma Hayek

HOW SHE DID IT
The actress hit the books and the gym to get back her famous hourglass figure after welcoming daughter Valentina Paloma last September. "It's been really hard work, studying what I can eat that's healthy for me [and] healthy for her!" Hayek, 41, told Oprah Winfrey in April. Though she is also working out regularly, Hayek has learned to keep her weight-loss goals realistic. "I thought, I'm just going to lose all the weight superfast because I'm going to breast-feed, and everybody tells you that if you breast-feed, it's going to come off like this. It's a lie!" she said. But "I'm proud of the weight that I've lost, and the rest is going to go when it's time to go."

  • Contributors:
  • CONTRIBUTORS Michelle Tan,
  • With Bethany Lye,
  • Jenny Sundel,
  • Ulrica Wihlborg.