At the first brick and mortar gym for new moms and moms-to-be, students receive instruction on how to exercise their changing bodies–and experience a sense of community. “Pretend these two 8-pound weights are newborn twins,” commands my fitness instructor as she hoists dumbbells above her head. Between a few huffs and puffs, she ups the ante, adding, “Your baby will want to be held all the time, so get used to it.