title: Surprising trunk rotational capabilities in chimpanzees and implications for bipedal walking proficiency in early hominins.
abstract: Human walking entails coordinated out-of-phase axial rotations of the thorax and pelvis. A long-held assumption is that this ability relies on adaptations for trunk flexibility present in humans, but not in chimpanzees, other great apes, or australopithecines. Here we use three-dimensional kinematic analyses to show that, contrary to current thinking, chimpanzees walking bipedally rotate their lumbar and thoracic regions in a manner similar to humans. This occurs despite differences in the magnitude of trunk motion, and despite morphological differences in truncal 'rigidity' between species. These results suggest that, like humans and chimpanzees, early hominins walked with upper body rotations that countered pelvic rotation. We demonstrate that even if early hominins walked with pelvic rotations 50% larger than humans, they may have accrued the energetic and mechanical benefits of out-of-phase thoracic rotations. This would have allowed early hominins to reduce work and locomotor cost, improving walking efficiency early in hominin evolution.
authors.affiliation: Department of Anatomical Sciences, Stony Brook University, Health Sciences Center T8-040, Stony Brook, New York 11794-8081, USA.
authors.forename: Nathan E
authors.initials: NE
authors.lastname: Thompson
authors.affiliation: Department of Anatomical Sciences, Stony Brook University, Health Sciences Center T8-040, Stony Brook, New York 11794-8081, USA.
authors.forename: Brigitte
authors.initials: B
authors.lastname: Demes
authors.affiliation: Department of Basic Medical Sciences, University of Arizona College of Medicine, Phoenix, Health Sciences Education Building, Phoenix, Arizona 85004-2157, USA.
authors.forename: Matthew C
authors.initials: MC
authors.lastname: O'Neill
authors.affiliation: Interdepartmental Doctoral Program in Anthropological Sciences, Stony Brook University, Social &Behavioral Sciences Building, Stony Brook, New York 11794-4364, USA.
authors.forename: Nicholas B
authors.initials: NB
authors.lastname: Holowka
authors.affiliation: Department of Anatomical Sciences, Stony Brook University, Health Sciences Center T8-040, Stony Brook, New York 11794-8081, USA.
authors.forename: Susan G
authors.initials: SG
authors.lastname: Larson
mesh_terms: D000328:Adult; D000818:Animals; D001696:Biomechanical Phenomena; D005260:Female; D005684:Gait / Q000502:physiology*; D015186:Hominidae; D006801:Humans; D008297:Male; D002679:Pan troglodytes; D010388:Pelvis / Q000502:physiology; D016059:Range of Motion, Articular / Q000502:physiology; D012399:Rotation; D013131:Spine / Q000502:physiology*; D013909:Thorax / Q000502:physiology; D060726:Torso / Q000502:physiology*; D016138:Walking / Q000502:physiology*; D055815:Young Adult