The issue of baby weight hangs heavy on the minds of many postpartum women, with images of famous moms like the impossibly fit model Gisele Bündchen, who had her second child last year, seared into their brains.

But more women and health professionals are turning their attention to changes beyond weight. Pregnancy and labor cause significant strain on muscle and bone structures. Some research shows that stretched, weakened or torn muscles and misaligned bones may seem simply annoying at first, but can develop into debilitating...