As a woman who describes herself — matter-of-factly, not self-hatingly — as shaped like a cello, I’m deeply pleased by this fascinating marathon-season report from our friends over at Boston University’s Research Website, headlined “In Defense of Wide Hips.” Re-posted with their permission:
By Kate Becker
What can you learn from a pelvis? Among the qualities that make humans unique are two physical features: our way of walking and running upright on two legs, and our newborn babies’ very large heads. Those two traits of humanity meet at the pelvis, a set of bones that includes the ilium, ischium, pubis, and sacrum.
For more than 50 years, anthropologists thought that the human pelvis was shaped by an evolutionary tug-of-war between the competing demands of bipedalism and childbirth. Now, a team of scientists that includes Kristi Lewton, an assistant professor in the department of anatomy and neurobiology at Boston University School of Medicine, and colleagues at Harvard University and Hunter College has shown that this so-called “obstetric dilemma” might not be a dilemma at all.
They found no connection at all between hip width and efficiency: wide-hipped runners moved just as well as their narrow-hipped peers.
Humans give birth to very large (“ginormous!”) newborns, says Lewton. While chimps and other nonhuman primate babies emerge from the birth canal with room to spare, human infants must perform a complicated series of rotations to make their way into the world, and the pelvic opening is just barely big enough. If something goes wrong, the lives of both mother and baby are at risk. So, why hasn’t the human body evolved a wider pelvis? Anthropologists have long believed that an evolutionary trade-off was at work; they assumed that a wide pelvis was “bad for bipedalism,” says Lewton. Yet, until now, no one had rigorously tested this assumption.
Lewton and her colleagues set out to discover whether wide hips really do make running and walking less efficient. They recruited 38 undergraduates, including both men and women, and had them walk and run on a treadmill while gauging how hard they were working by measuring their oxygen consumption. While the participants exercised, their motion was tracked by eight cameras trained on infrared markers attached to the participants’ hips, knees, ankles, thighs, and shanks. Lewton and her colleagues estimated the subjects’ hip width using the results from the infrared trackers, and later combined their data with results from a Washington University in St. Louis research team that used MRI to get a direct measure of hip width. (True hip width is defined as the distance between the hip joints, points out Lewton, and is different from what you would measure with a tailor’s tape.)
If the basic assumptions of the obstetric dilemma are right, says Lewton, participants with wider hips should run and walk less efficiently than those with narrow ones. But that wasn’t what Lewton and her team found. Continue reading