The variability of the centre of pressure pattern

Abstract

INTRODUCTION:: The centre of pressure pattern (COPP), or force line, has been used to describe abnormal foot movement during gait and as a method to assess foot orthoses effectiveness. The purpose, therefore, of this study was to measure the between-trial variability of the COPP as well as explore possible differences between shoe-floor and within-shoe measurements. METHODS:: Ten healthy individuals from a pool of 110 volunteers were selected for this study based upon their willingness to participate and the presence of a forefoot and/or rearfoot valgus or varus deformity. An EMED-SF pressure platform was used to collect COPP data at the shoe-floor interface. The EMED PEDAR insole pressure system was used to collect COPP data within-the-shoe. Ten trials of COPP were recorded simultaneously using the two systems as the subjects walked over ground in standardized footwear and two different types of foot orthoses. The footwear used consisted of the Reebok Boston Road running shoe. The two types of orthoses studied were a rigid orthotic with forefoot and/or rearfoot posts and soft orthotic without any posts. Quantification of the COPP was achieved by calculating its absolute integral. RESULTS:: The result of a one-way repeated measuresANOVA and subsequent post-hoc analysis showed that the rigid orthoses condition was significantly different from the soft orthoses or no orthosis conditions. Analysis of the between-trial reliability for COPP integral calculation, however, indicated that there was 43.4 to 48.6% variability. The intraclass correlation coefficients were found to be less than 0.504. DISCUSSION:: While the results showed that the within-shoe shoe only condition and the soft orthoses condition caused the greatest decrease in the COPP integral, the COPP integral was extremely inconsistent, whether measured at the shoe-floor interface or within-the-shoe. CONCLUSION:: The results of this investigation indicate that COPP is highly variable when measured either at the shoe-floor interface or within-the-shoe over multiple trials. Based upon these findings, the COPP, as measured by its absolute integral, would be a poor representation of foot movement and, as such, would not be an acceptable method for the assessment of foot orthoses effectiveness.