Modeling of vertical ground reaction forces during double stance phase of the gait cycle for real-time treadmill measurements

An important aspect of gait analysis is the measurement and interpretation of the Ground Reaction Force (GRF) characteristics. These measurements are important for the calculation and analysis of joint moments and forces, in addition to its assistance in natural and artificial walk control. Usually, a force platform, requiring a large space, is used to obtain these measurements but only few steps could be analyzed. To carry out continuous GRF measurements for long time walking, a force platform embedded in a single-belt treadmill can be used. The difficulty of such systems arises from the fact that the resultant GRF of the two feet is obtained during double stance phase of the walk cycle. The present study proposes the use of a mathematical model to develop a method for the separation of these superimposed vertical GRF from the center of pressure (CoP) profile. Gait events were detected in order to specify the regions of double stance and to specify the GRF model during these periods. The performance of different mathematical functions in modeling the vertical GRF was examined. The results show that a model utilizing a hyperbolic tangent function (sigmoid) represents the best fit to the vertical GRF data. Our model is highly recommended for real-time monitoring of continuous GRF treadmill measurements that would facilitate and speed up the gait analysis and diagnosis done by physicians.