title: The evolution of compliance in the human lateral mid-foot.
abstract: Fossil evidence for longitudinal arches in the foot is frequently used to constrain the origins of terrestrial bipedality in human ancestors. This approach rests on the prevailing concept that human feet are unique in functioning with a relatively stiff lateral mid-foot, lacking the significant flexion and high plantar pressures present in non-human apes. This paradigm has stood for more than 70 years but has yet to be tested objectively with quantitative data. Herein, we show that plantar pressure records with elevated lateral mid-foot pressures occur frequently in healthy, habitually shod humans, with magnitudes in some individuals approaching absolute maxima across the foot. Furthermore, the same astonishing pressure range is present in bonobos and the orangutan (the most arboreal great ape), yielding overlap with human pressures. Thus, while the mean tendency of habitual mechanics of the mid-foot in healthy humans is indeed consistent with the traditional concept of the lateral mid-foot as a relatively rigid or stabilized structure, it is clear that lateral arch stabilization in humans is not obligate and is often transient. These findings suggest a level of detachment between foot stiffness during gait and osteological structure, hence fossilized bone morphology by itself may only provide a crude indication of mid-foot function in extinct hominins. Evidence for thick plantar tissues in Ardipithecus ramidus suggests that a human-like combination of active and passive modulation of foot compliance by soft tissues extends back into an arboreal context, supporting an arboreal origin of hominin bipedalism in compressive orthogrady. We propose that the musculoskeletal conformation of the modern human mid-foot evolved under selection for a functionally tuneable, rather than obligatory stiff structure.
authors: Department of Musculoskeletal Biology, Institute of Aging and Chronic Disease, University of Liverpool, Sherrington Buildings, Ashton St, Liverpool L69 3GE, UK. k.t.bates@liverpool.ac.uk
authors: Karl T
authors: KT
authors: Bates
authors: David
authors: D
authors: Collins
authors: Russell
authors: R
authors: Savage
authors: Juliet
authors: J
authors: McClymont
authors: Emma
authors: E
authors: Webster
authors: Todd C
authors: TC
authors: Pataky
authors: Kristiaan
authors: K
authors: D'Aout
authors: William I
authors: WI
authors: Sellers
authors: Matthew R
authors: MR
authors: Bennett
authors: Robin H
authors: RH
authors: Crompton
mesh_terms: D000328:Adult; D000368:Aged; D000818:Animals; D005075:Biological Evolution; D003187:Compliance; D005260:Female; D005528:Foot / Q000033:anatomy & histology / Q000502:physiology*; D005684:Gait; D006801:Humans; D008124:Locomotion; D008297:Male; D008875:Middle Aged; D019974:Pan paniscus / Q000033:anatomy & histology / Q000502:physiology*; D057079:Pongo / Q000033:anatomy & histology / Q000502:physiology*; D011312:Pressure; D055815:Young Adult
keywords: bipedalism; foot pressure; locomotion; mid-foot; topological analysis
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