Ground reaction force and plantar pressure reduction in an incremental weight bearing system

INTRODUCTION:: With increasing frequency, harness-supported treadmill ambulation has been advocated in patient use in order to provide reduction in weight-bearing to healing tissues and as a method which reduces the energy cost of treadmill ambulation. The purpose of this study was to analyse the ability of one of these devices (Zuni Exercise System) to support a percentage of a subject's body weight during walking and running and to explore the relationship of unloading to pressure reduction in selected plantar surface regions of the foot. METHODS:: Ten healthy male volunteers with no known foot pathology participated in this study. In-shoe plantar pressure (PEDAR) and vertical ground reaction force (GRF) were measured during walking and running at full body weight and at a 20% body[Figure: see text][Figure: see text] weight supported setting. Statistical evaluation used a one way ANOVA and a post-hoc paired t-test with significance set at p < 0.05. RESULTS:: Walking with a setting of 20% body weight supported was achieved with a reduction of the first and second vertical force peaks of 23.8+/-7.3% and 27.2+/-4.1% respectively, somewhat greater than the selected setting (Figure 1). The total force time integral during walking unloaded was 22.8+/-3.3%, which was only slightly greater than the selected 20% reduction. During running the active vertical force peak and total force time integral were reduced by 19.9+/-6.0% and 20.0+/-3.3% respectively during the unloaded condition (Figure 2). Plantar pressures were reduced from 6.8 - 27.8% during body weight supported conditions. The reduction in plantar pressure was variable across different regions of the foot with the toes in walking and the medial forefoot region in running being the least unloaded. DISCUSSION AND CONCLUSIONS:: The Zuni Exercise System appears to be a valid device to predictably reduce the vertical component of the GRF during walking and running with 20% body weight supported. Plantar pressures were reduced during body weight supported conditions but the reduction varied at different regions of the foot. However, the variability of the reduction across subjects was substantial, implying that a given regional pressure may not be as predictably reduced during a body weight supported condition. This highlights the difficulty a practitioner has in the ability to confidently reduce pressure by a set amount in a selected foot region by using assistive devices without direct in-shoe measurements.