INTRODUCTION AND OBJECTIVES: Healthy feet are important for overall health and well-being. Previous studies of older subjects showed that those with a lowered arch had an increased odds of having foot deformities, pain, and hyperpronation in gait. (1–3) No investigation to date has comprehensively characterized foot biomechanics in a large sample of healthy active young subjects.

METHODS: Foot structure, function, and arch height flexibility (AHF) were measured in 1,052 incoming cadets to the United States Military Academy. Based on the previously established standing arch height index (AHI), 70% of subjects exhibited planus foot structures. (4,5) To examine the effects of AHF on dynamic barefoot plantar pressure, 1,414 planus feet were further categorized by AHF. Those that fell within the highest and the lowest quintiles were defined as flexible and stiff AHF, respectively, while the middle 3 quintiles were categorized as referent.

RESULTS: Descriptive statistics and normality testing were performed using SPSS software version 22 (IBM, Chicago, IL, USA). A Generalized Linear Model with an identify link function was used to examine the effects of AHF category while accounting for potential dependence in bilateral data. The Wald Chi-square was calculated for each dependent variable with significance set at p < 0.05. Post hoc pairwise comparisons for all pairs were performed using the Generalized Chi Square test at P < 0.017.

CONCLUSIONS: A significant difference was found in Center of Pressure Excursion Index (CPEI) and Peak Pressure (PP). Post hoc pairwise comparisons showed a significant difference between flexible versus stiff AHF: those with flexible AHF exhibited reduced CPEI (greater hyperpronation) while those with stiff AHF showed elevated PP. Results suggest that, in addition to AHI, the arch flexibility may affect dynamic foot function. This was a part of larger study. Additional studies are needed to examine the effects of AHI and AHF on regional plantar loading and overuse injuries.

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