2020 Volume 25 Pages 139-148
Shock absorption is considered the primary function of the normal foot arch however the difference between the low arch foot and normal arch foot in terms of this shock-absorbing function remains unclear. Therefore to clarify this difference, the shock absorbing characteristics of low arch and normal arch foot were quantitatively compared based on mechanical characteristic values. In the present study, the participants were classified into the normal arch foot and low arch foot-groups, and the spring constant and load transmission were calculated from the measurements. Compared with the normal arch foot, the low-arch foot exhibited a firm spring, and the vertical load applied to the lower thigh stendid to be supported by the upper thigh. Thereafter, we attempted to express the dynamic characteristics of the response as mathematical models when a load was applied to the lower thigh. The spring constant and settling time were compared using the load responses obtained in the experiment. No significant differences in spring constant were observed between the low arch and normal arch foot groups. However, a significantly longer settling time was detected for the low arch foot. Based on the complexity of the load responses, a mathematical piecewise linear dynamic model consisting of inertia, viscosity, and stiffness was identified. The identified model closely estimated the load responses of the lower thigh. Comparison of the dynamic characteristics of the identified models revealed the shock-absorbing characteristics of the low arch foot relative to those of the normal arch foot. For ensuring that the shock-absorbing characteristics of the low arch foot is similar to those of the normal arch foot, an identification model that captures individual characteristics is required to provide the basis for the design of a plantar insert.
