In clinical settings, dynamic foot function is commonly inferred from static and passive foot measurements; however, there is little evidence that static foot structure can predict dynamic foot function during walking gait. Previous research seeking to find correlations between the two have focused primarily on sagittal plane midfoot angles even though the midfoot has triplanar motion, which misses potentially important information. Additionally, the focus on kinematics alone may miss the contributions that forces play in midfoot mechanics. To address the angle limitations, a novel Signed Helical Angle (SHA) was developed to capture the triplanar motion of the midfoot from a multi-segment foot model. This was combined with foot segmental force measurements and inverse dynamics to capture dynamic midfoot stiffness. The SHA method and static-dynamic analysis were evaluated on 40 healthy subjects walking at a controlled speed. Subjects were divided into three structural groups based on static arch height (high, normal, low) and stiffness (stiff, normal, flexible). One-way ANOVA was used to evaluate differences among groups in dynamic motion and stiffness and a multiple regression was employed to evaluate relationships across the sample. Calculating the SHA resulted in a greater range of motion (ROM) compared to the sagittal Euler angle commonly used, showing that the motion in the other planes are captured in the SHA. The Finite Helical Axis (FHAx) associated with the SHA also showed that on average the population had a clear distinction between pronation and supination during the stance phase, although individual subjects exhibited substantial variability. While there were visual distinctions in the SHA and the midfoot stiffness among the three stiffness groups and the three arch height groups, the differences were not statistically significant. The only measurement achieving statistical significance was the mean of the sagittal plane midfoot Euler angles among the three AHI groups (p = 0.015); however, this is a postural measure which simply confirms that a high arch will remain high and a low arch will remain low throughout the gait cycle. The lack of any relationships between static foot structure and dynamic foot function, despite advanced modeling and measurements, further confirms that other factors play a large role in foot mechanics. Future studies should focus on evaluating the role of the intrinsic foot musculature (e.g., muscle strength, activation, and redundancy) during gait, and replacing traditional shoe and orthotic recommendations.



College and Department

Mechanical Engineering



Date Submitted


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biomechanics, midfoot motion, stiffness, finite helical axis



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