The 82nd Annual Meeting of the American Association of Physical Anthropologists (2013)

Effects of bipedal infant-carrying on thoracic and pelvic rotations in walking gait


Anthropology, University of Cincinnati

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Pedal grasping was likely lost in association with the evolution of hominin bipedalism; therefore, like humans, hominin mothers had to actively carry their infants. While it is known that infant-carrying is energetically expensive, its effects on maternal gait kinematics have been largely unexplored. In this study, I test the hypothesis that carrying an infant constrains normal rotations of the thorax and pelvis. Significant limitations in segmental motion are indicative of disrupted gait and may therefore contribute to the tremendous energetic cost associated with infant-carrying. By establishing the relationship between infant-carrying and human movement, we can employ a comparative approach to understand how early hominin mothers may have kinematically coped with the challenge of transporting their infants.

Multi-plane angular excursions of the thorax and pelvis were calculated from 3D kinematic data acquired from 1202 strides, taken from three subjects walking with and without a simulated infant on a treadmill at varying speeds. Wilcoxon/Kruskal-Wallis tests were used to detect significant differences in segmental rotations between normal and infant-carrying conditions.

As predicted, axial rotation of the thorax and pelvis decreased significantly when carrying an infant. Similarly, infant-carrying resulted in significantly decreased sagittal excursion of the thorax. In contrast to expectations, thoracic and pelvic obliquity, as well as anterior pelvic tilt, increased significantly when carrying an infant. While infant-carrying constrains thoracic motion more than pelvic motion, both segments undergo marked kinematic changes when carrying an infant. This deviation from normal gait suggests that infant-carrying may reduce stability, contributing to its high energetic cost.

University of Cincinnati and the Charles Phelps Taft Research Center at the University of Cincinnati

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