The relationship between static arch height and arch stiffness

Foot type, and particularly arch height is an intrinsic injury risk factor which has received much attention within the literature (Cowan et al. 1993). However, the relationship between foot type and injury is somewhat unclear. In addition to arch height, arch stiffness may be important in trying to relate foot type to injury. It is commonly thought that high arches tend to be more rigid, and lower arches more flexible. Furthermore, it is suggested that more flexible feet with lower arches may serve as more effective natural shock absorbers than more rigid foot types. A higher incidence of shock related bony injuries has been reported in high arched runners (Williams et al. 2001). Zifchock et al. (2006) measured the foot structure of 145 individuals in both 10% and 50% of weight bearing, with relative arch deformation between conditions used as a means of assessing arch stiffness. Although a relationship between variables was observed, only 9% of the variance in arch stiffness could be explained by arch height (Zifchock et al. 2006). During shod running, vertical ground reaction forces can reach 2-3 times body weight. Assessing arch characteristics in loaded conditions closer to those seen during running may provide insight into dynamic arch stiffness and its potential relationship to injury. The aim of the present study was to assess the relationship between arch height and arch stiffness in 10% and 90% of weight bearing. It is suggested that calculating arch stiffness between these conditions may give a better indication of foot function in loaded conditions, such as gait.