The efficacy of carbon fiber insoles to enhance mechanical leverage during walking does not vary with navicular drop-derived foot mobility.

Abstract

Many age-related gait changes (i.e., shorter steps, slower speeds, higher metabolic rate, instability) may be precipitated at least in part by reduced push-off intensity and a diminished ability to regulate foot-ankle leverage during walking. Carbon fiber insoles (CFIs) have been shown to improve foot-ankle leverage in younger and older adults in group average comparisons. The purpose of this study in n = 20 younger adults and n = 20 older adults was to determine whether the efficacy of CFIs to enhance foot-ankle leverage during walking depends on passive structural midfoot mobility, measured here using the sit-to-stand navicular drop test (NDT). We hypothesized that greater NDT values, indicative of greater passive midfoot mobility, would correlate with greater increases in foot-ankle leverage when walking with CFIs versus standardized footwear. We defined the change in foot-ankle leverage using that of the peak external moment arm of the ground reaction force (ΔR_ext) and peak ankle moment (ΔM_ank) and examined two CFI stiffnesses (i.e., k_med and k_high). In contrast to our hypothesis, we found no statistically significant associations (p > 0.05) between passive midfoot mobility (i.e., NDT values) and enhanced leverage outcomes (ΔR_ext and ΔM_ank) induced by CFIs. This apparent lack of individual specificity suggests either that: (i) personalized prescription may require dynamic evaluation of midfoot mobility or (ii) generalized prescription of CFIs, without the requisite need for personalized stiffness construction, may improve foot-ankle leverage to mitigate age-related gait changes.