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

The purpose of this study was to determine if using similar walking velocities obtained from fractions of the Froude number (NFr) 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 1.16 m s−1 (VS2) and then at two similar velocities (VSim27 and VSim37) determined from two fractions of the NFr (0.27 and 0.37) so that the average group velocity remained unchanged in both conditions (image). NFr 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 NFr allows kinematic and plantar pressure similarities between subjects to be observed and leads to a lower inter-subject variability.