Evaluation of instrumented shoes for ambulatory assessment of ground reaction forces

Liedtke C, Fokkenrood SA, Menger JT, van der Kooij H, Veltink PH. Biomedical Signals and Systems, University of Twente, Faculty of Electrical Engineering, Mathematics and Computer Science, Institute for Biomedical Technology (BMTI), P.O. Box 217, 7500 AE Enschede, The Netherlands. Currently, force plates or pressure sensitive insoles are the standard tools to measure ground reaction forces and centre of pressure data during human gait. Force plates, however, impose constraints on foot placement, and the available pressure sensitive insoles measure only one component of force. In this study, shoes instrumented with two force transducers measuring forces and moments in three dimensions were evaluated. Technical performance was assessed by comparing force measurement and centre of pressure reconstructions of the instrumented shoes against a force plate. The effect of the instrumented shoes on gait was investigated using an optical tracking system and a force plate. Instrumented shoes were compared against normal shoes and weighted shoes. The ground reaction force measured with force plate and instrumented shoes differed by 2.2+/-0.1% in magnitude and by 3.4+/-1.3 degrees in direction. The horizontal components differed by 9.9+/-3.8% in magnitude and 26.9+/-10.0 degrees in direction. Centre of pressure location differed by 13.7+/-2.4mm between measurement systems. A MANOVA repeated measures analysis on data of seven subjects, revealed significant differences in gait pattern between shoe types (p</=0.05). A subsequent univariate analysis showed significant differences only in maximum ground reaction force but these could not be attributed to specific shoe types by pair-wise comparison. This study indicates that shoes instrumented with force transducers can be a valuable alternative to current measurement systems if accurate sensing of position and orientation of the force transducers is improved. They are applicable in ambulatory settings and suitable for inverse dynamics analysis.