Meeting Abstract

73.5  Tuesday, Jan. 6  Different functional mechanisms of foot-footpad complex for plantigrade and digitigrade mammals in the context of locomotion CHI, K. -J.*; SCHMITT, D.; ROTH, V. L.; Duke University and National Chung-Hsing University, Taiwan; Duke University; Duke University kjchi@phys.nchu.edu.tw

All terrestrial mammals have footpads and, as the first point of contact between foot and substrate, footpads must often serve multiple mechanical roles. To meet competing (and sometimes opposite) functional demands the structure or material of the footpad may need to have different mechanical properties for each of various functions during locomotion: Pads must be compliant to cushion impact, but stiff to effectively transmit force; damped for stable foot-ground contact, but resilient to return elastic energy. To explore how these competing needs are met, this study compares kinematics of the foot-footpad complex in plantigrade humans and digitigrade dogs. The results show that humans and dogs use different mechanisms to meet the multiple functional demands placed on the footpad. A single heel pad of plantigrade humans can accommodate both compressive and shear force through mechanical anisotropy. In digitigrades dogs, by contrast, the compressive force is accommodated mainly in the footpads, while the shear is through the bar-linkage system of the paw. One adaptive explanation for the decoupling of compression and shear in the foot-footpad complex of digitigrade animals is that, by removing the requirement of accommodating shear within the pads, the digitigrade footpads can have higher compressive stiffness through the incorporation of additional tensile material. This may compensate for any increase of tissue stress due to greater plantar pressure produced in the evolutionary transition in some mammalian lineages from plantigrady to digitigrady.