The Influence of the Parameters of the Vertical Runner Model on Ground Reaction Force in Different Running Styles

Abstract

The purpose of this study is to analyze the differences in two running styles: rear-foot strike (RFS), in which the heel lands first and fore-foot strike (FFS), in which the ball of the foot lands before the heel comes down. These running styles were compared in term of vertical mathematical model parameters and motion-analyzed data. The ground reaction forces were measured by force platform with the same subjects performing each style of running at various velocities ranging from 2.23 m/s to 4.47 m/s. A unique set of parameters of the model for each trial was computed by nonlinear programming to minimize the sum of the relative standard error of the ground reaction force and the relative error of rebound velocity. Motion-analyzed data was measured by a high-speed motion capture system. The differences in running styles were considered by using results from parameters of a multi-degree-of-freedom model and motion analysis. The results of this study indicate that the FFS needs less energy than RFS because of the contact style and the impulse as internal forces. And it also indicates that the ratio of the upper to lower mass of the vertical mathematical model is higher in FFS than in RFS. A previous study also showed that the effective mass related to the first peak of ground reaction force was smaller in FFS than that in RFS. For this reason, FFS may reduce the risk of running injuries such as injuries to the hip, knee and ankle joints by reducing the impact to the body.