There’s practically an entire industry devoted to returning new moms to their “pre-baby shape,” but there’s a good reason why it’s so hard to bounce back from a baby belly. It’s called relaxin, a hormone produced at high levels at the end of pregnancy with a name that’s true to its function. “It relaxes your muscles [and the] connective tissue,” says prenatal and postnatal Pilates instructor Joan Van Geison, who previously walked me through prenatal exercises
. Relaxin eases the birth process, but it can make new moms feel “mushy,” like they can’t build muscle tone no matter how hard they try—and the hormone can stick around for months after giving birth. “Oh! Nobody says that! Nobody ever told me that,” is the common refrain Joan hears after delivering this news.