The influence of sagittal center of pressure offset on gait kinematics and kinetics

Abstract

Objectives

Kinetic patterns of the lower extremity joints have been shown to be influenced by modification of the location of the center of pressure (CoP) of the foot. The accepted theory is that a shifted location of the CoP alters the distance between the ground reaction force and the center of the joint, thereby modifying torques during gait. Various footwear designs have been reported to significantly alter the magnitude of sagittal joint torques during gait. However, the relationship between the CoP and the kinetic patterns in the sagittal plane has not been examined. The aim of this study was to evaluate the association between the sagittal location of the CoP and gait patterns during gait in healthy men.

Methods

A foot-worn biomechanical device which allows controlled manipulation of the CoP location was utilized. Fourteen healthy men underwent successive gait analysis with the device set to convey three different sagittal locations of the CoP: neutral, anterior offset and posterior offset.

Results

CoP translation in the sagittal plane (i.e., from posterior to anterior) significantly related with an ankle dorsiflexion torque and a knee extension torque shift throughout the stance phase. Likewise, an anterior translation of the CoP significantly reduced the extension torque at the hip during pre-swing.

Conclusions

The study results confirm a direct correlation between sagittal offset of the CoP and the magnitude of joint torques throughout the lower extremity.

Introduction

During the stance phase of the gait cycle, a force is applied to the ground which is coupled with a ground reaction force (GRF). The magnitude of the GRF is equal and its direction is opposite to the force the body exerts (Winter, 1984). Consequently, joint torques develop which are equivalent to the magnitude of the GRF and the perpendicular distance from the joint center to the force (Gronley and Perry, 1984; Winter, 1984). Theoretically, altering the instantaneous center of pressure (CoP) of the foot would influence the orientation of this force and the resulting joint torques and angles through the body segments.

This principle has been the focus of previous research which examined the utilization of footwear-derived biomechanical manipulation. Application of wedge insoles were found to shift the location of the CoP in the coronal plane, thereby altering joint torques from the foot proximally (Kakihana et al., 2005; Maly et al., 2002; Xu et al., 1999) and decreasing the load at the medial compartment of the knee joint in healthy and arthritic subjects (Crenshaw et al., 2000; Kakihana et al., 2005; Ogata et al., 1997; Yasuda and Sasaki, 1987). In a previous study (Haim et al., 2008), we examined the effect of controlled coronal plane CoP modulation at the foot. The magnitude of the knee adduction torque was found to significantly correlate with the coronal orientation of the CoP.

Several studies have investigated the effect of sagittal plane footwear modifications on kinematic and kinetic parameters of the lower extremities. Walking with different heel-height shoes has been reported to decrease stride length (de Lateur et al., 1991), to alter joint torques in the lower extremity (Snow and Williams, 1994), and to prolong midstance knee flexor torques during gait (Kerrigan et al., 2005). Missing-heel shoes were found to reduce walking speed and stride length, to increase cadence, and to considerably alter normal ankle joint function (Attinger-Benz et al., 1998). Gait analysis of negative heel rocker sole shoes showed an increase in cadence and a significant alteration of proximal joint metrics (Myers et al., 2006). Similarly, changes in CoP locus were reported with relation to rocker sole shoes (Xu et al., 1999). However, much of the above-mentioned research utilized footwear modifications that introduced considerable alterations to the normal functioning of the ankle.

The purpose of the current study was to assess the effect of the sagittal CoP position on kinetic and kinematic parameters of the lower extremities. Utilizing a novel foot-worn biomechanical device which allows controlled manipulation of the CoP, we hypothesized that translation of elements in the sagittal plane (i.e., from posterior to anterior) would result in a matching alteration of the magnitude of lower extremity sagittal joint torques and kinematic patterns during the stance phase.