At sweet 16 I was taller than my first boyfriend and my feet were “number nine.” Madly in love and desperate not to lose my surfer boy, I began slouching and cramming my feet into smaller and smaller shoes, eventually fitting into size 7 1/2. Willing to suffer blisters, calluses, and painful “Haglund’s deformity” at the back of my heels, nothing mattered except how cool my diminutive feet looked.

That memory fades into another snapshot of me sunbathing on my back in my bikini, feeling a sense of satisfaction that my hip bones were jutting two inches above my sunken brown belly.

Fast-forward a few years to early motherhood, and every trace of my natural childhood posture had vanished. My belly was still as flat as when I was a teenager on the beach, but my shoulders were now rounded, my chest sunken, and my head hanging in front of my body.

Shoe styles are even more restrictive today, and “sucked and tucked” posture is as ubiquitous among...