Foot morphology influences the change in arch index between standing and walking conditions

Human foot morphology has been of interest to anatomists, clinicians, and paleontologists for a century due to its importance in bipedal walking. Foot shape changes as forces move through it from the body to the substrate. Although the arch of the foot has been extensively evaluated, the role of foot morphology in the change of the arch height in walking is less explored. To remedy this lacuna, the Arch Indices (AIs) of the left and right feet of 77 people were calculated in double and single stance standing and walking (dynamic) conditions. The feet were categorized into clinical foot types (cavus, normal, planus). The change in static AI between double and single stance was used to predict dynamic AI and the difference between predicted and observed dynamic AI was examined. As expected, AIs increased (i.e., arch height decreased) with increasing load on the foot for the entire sample and each foot type (p's > .001), but the ability of change in static AIs to predict dynamic AI varied among foot types, implicating the possibility of variability in foot mechanics among foot types. While planus feet change stiffness during walking, presumably due to muscular action, cavus feet are more variable in their response to load. Static and dynamic AIs are effective in reflecting the changes in foot stiffness that occur in walking and future work should examine the role of extrinsic muscle activation in this stiffness change.