Froude number fractions to increase walking pattern dynamic similarities: Application to plantar pressure study in healthy subjects

Abstract 

The purpose of this study was to determine if using similar walking velocities obtained from fractions of the Froude number (N_Fr) and leg length can lead to kinematic and kinetic similarities and lower variability. Fifteen male subjects walked on a treadmill at 0.83 (VS₁) and 1.16ms⁻¹ (VS₂) and then at two similar velocities (V_Sim27 and V_Sim37) determined from two fractions of the N_Fr (0.27 and 0.37) so that the average group velocity remained unchanged in both conditions (). N_Fr can theoretically be used to determine walking velocities proportional to leg lengths and to establish dynamic similarities between subjects. This study represents the first attempt at using this approach to examine plantar pressure. The ankle and knee joint angles were studied in the sagittal plane and the plantar pressure distribution was assessed with an in-shoe measurement device. The similarity ratios were computed from anthropometric parameters and plantar pressure peaks. Dynamically similar conditions caused a 25% reduction in leg joint angles variation and a 10% significant decrease in dimensionless pressure peak variability on average of five footprint locations. It also lead to heel and under-midfoot pressure peaks proportional to body mass and to an increase in the number of under-forefoot plantar pressure peaks proportional to body mass and/or leg length. The use of walking velocities derived from N_Fr allows kinematic and plantar pressure similarities between subjects to be observed and leads to a lower inter-subject variability.

In-shoe pressure measurements have proven to be valuable for the understanding of lower extremity function. Set walking velocities used for clinical assessment mask the effects of body size and individual gait mechanics. The anthropometric scaling of walking velocities (fraction of N_Fr) should improve identification of unique walking strategies and pathological foot functions.

Keywords: Walking, Froude number, Dynamic similarity, Joint angles, Plantar pressure