It's not a good sign when your workout makes other people laugh. But as Lexie launches into a series of side lunges at Essex Junction's HammerFit gym, she doesn't seem to mind when the person next to her erupts in giggles.

That's because it's her 7-month-old daughter, Jane, watching her mom from an infant car seat in a Tuesday morning session of "Baby Pump." Earlier this year, HammerFit owner Jessica Ebert Edelmann started the class as a way for moms to work out, bond with their new babies and meet new friends. A play on the popular Les Mills Body Pump classes, Baby Pump is a 45-minute non- to low-impact workout that uses hand weights, resistance bands and, yes, babies to tone and strengthen.

"At first, the moms are a bit nervous and proud that they just made it to class," says Edelmann. "Two to three times later, they're enjoying themselves, and the babies are happier because mom is radiating confidence."

Before a recent class, instructor Candice Allembert has a few moments to chat — moms with new babies tend to show up fashionably late. "Working out, you shouldn't feel guilty," she says. "It's not about getting to a size 0; it's about getting fit and having the energy to go up and down stairs with your children." There's even a chair in the back where moms can nurse.

Allembert then pops in a peppy soundtrack — the '80s hit The Safety Dance, and songs from The Lion King and The Muppets — as she leads four moms through a warm-up of stepping in place and stretching hamstrings and hip flexors. For now, the four babies are happily snug in their car seats or on soft blankets. Eleven-week-old Jack is sound asleep.

It's just the right tempo to allow near continual mother-and-child contact: Lexie laughs back at Jane; Megan plants a kiss on 5-month-old Olivia's forehead while holding plank position. I think back on how I used to set my 6-week-old daughter next to the treadmill and had to stop running every time she squirmed for fear of upsetting fellow gym members. This is a much better way to exercise with babies.

Allembert devised much of the routine from working out at home with her own children, now ages 14 and 17, when they were babies; indeed, many of the moves lend themselves to a living- room floor. Doing wide-leg squats while holding the baby, for example, is a no-brainer.

But staying home would mean missing out on the camaraderie, the compliments doled out by Allembert — "I love Olivia's pajamas!" she exclaims to Megan during a set — and all the other adorable babies. My children are 3 and 5 now, and being around all the oxytocin almost makes me want to have another — until a few of the infants squawk for more attention.

Everyone makes it to the end of the 45-minute session, but that's not always the case for new moms who must put their workout on hold for a few hours or a day. Says Allembert, "Sometimes you just have to surrender."