Estimation of Centre of Pressure from Wearable Intertial Sensors

Conventionally, centre of pressure (COP) measurements are acquired using force plate systems or instrumented treadmill devices. Despite their accuracy, these standard measuring techniques are restricted to laboratory settings, expensive equipment, and may not replicate normal outdoor walking, thus imposing some constraints on the ability to measure human movement. In this study, we propose a new method to estimate foot COP during walking, using exclusive information from wearable inertial sensors located in different parts of body. The dynamic relationship between the inertial sensor information (i.e. accelerations, angular velocities and quaternion orientation) and the measured COP using two-foot pressure insole sensors has been identified using a nonlinear autoregressive moving average with exogenous input (NARMAX) model. The results show that the COP movement can be estimated with high accuracy using only a single inertial sensor attached to the left ankle. The relative prediction errors were around 2.7% in the anterior-posterior direction (x-axis, forward and backward), and 7.6% in the medial-lateral direction (y-axis, side-to-side) for the left ankle sensor, which are comparable to 2.5% and 7.1% in the anterior-posterior and medial-lateral directions, respectively, when all six sensors were used. The proposed approach provides a promising low-cost method for COP estimation and continuous monitoring of gait characteristics in daily life applications.