The relationship between foot stiffness and loading rate at heel contact in running

Abstract

The purpose of this study was to propose a simplified foot stiffness evaluation method, and to clarify the influence of the foot stiffness on loading rate at heel contact in the practical running. Thirteen male heel contact strikers participated in this study, and the navicular height and vertical ground reaction force in the seated and standing conditions by using of a motion capture system and a force plate, respectively. Foot Stiffness is calculated as vertical ground reaction force change divided by change of navicular height ratio from seated to standing condition, and Simplified Foot Stiffness is calculated as 38.575 percent body weight, which is calculated as subtracting 11.7% body weight (determinated by segment mass of foot, shank and thigh and mass center position of thigh) form 50% body weight (standing condition), divided by change of navicular height ratio. In addition, maximum loading rate of each subject was measured in the practical running in the speed of 3.3 m/s by use of a force plate. The results are as follows : (1) Simplified Foot Stiffness corresponded to Foot Stiffness and (2) there is significant positive correlation between Simplified Foot Stiffness and maximum loading rate (r=0.889, p<0.01). These results indicate that loading rate in practical running can be predicted by evaluation of change of navicular height without vertical force measurement.