The antithesis of plan-to-the-nth-degree businesswomen, Amansala spa owners Melissa Perlman and Erica Gragg have pretty much winged it professionally—so far with spectacular results. After moving from New York City to Tulum, Mexico, five years ago with just "a suitcase full of sheets," the longtime friends splashed onto the scene with their Bikini Boot Camp. In no time, the likes of Sienna Miller, Jade Jagger, and Maggie Gyllenhaal were heading to the eco-chic resort on the Mayan Riviera, 80 miles south of Cancún.

With its mix of intensive fitness (tons of cardio, resistance training, and yoga), field trips to nearby ruins, and sun-drenched R&R, the program has been such a hit that Perlman has added an offspring: After-the-Baby Boot Camp, a weeklong postpartum shape-up that moms can attend with their babies. It takes place at the newly renovated Casa Magna, just 10 minutes down the beach from Amansala.

making connections

Perlman, a new mom herself—her son, Dylan, was born last May—tapped into her own needs while formulating the After-the-Baby program. It definitely mimics Bikini Boot Camp in one key area: major bonding. "Bikini isn't just exercise—it's about women joining together and having a spirit of community," she says. "And After-the-Baby is like that, too. Before I had my son, I never understood it when new moms would talk about their experiences—that whole 'Did you have a C-section? How's your relationship now?' exchange. Those are conversations women who haven't had children yet can't really relate to."

Now that she's in the trenches herself, Perlman considers new-mother networking essential. "There's something nice about having the support of other women who can sympathize with you," she says. "Especially if they're also trying to fit back into their skinny jeans."

focusing on fitness

About those skinny jeans: To facilitate slimming down enough to slide back into the pre-pregnancy J Brands, After-the-Baby offers a hefty dose of exercise, much of it outdoors and starting soon after sunrise (guests' babies—those other crack-of-dawn creatures—are attended to by staff nannies).

A typical spa day begins with a stretch and a beach walk, followed by a light breakfast and yoga. Although Amansala hosts plenty of intensive yoga retreats, After-the-Baby is less om-centric. "We're not doing three-hour sessions," says Perlman. "But we'll do an hour and a half. In the morning, we'll do a power-flow class. If we hold a class in the afternoon—after a hard bike ride, say—it's more restorative." Core toning is incorporated into virtually every fitness activity, from African tribal-dance classes to stability-ball workouts to swimming. "For new moms," says Perlman, "ab strength is a big part of getting back in shape."

Next Page: Planning a trip to Boot Camp