On-Line Algorithms of Stride-Parameter Estimation for in-Shoe Motion-Sensor System

We propose two on-line algorithms for stride parameter estimation for an in-shoe motion-sensor system (IMS) system: one for on-line stride segmentation based on stable foot-flat detection using foot-sole angle and the other for a three-dimensional zero-velocity-update for accurate stride parameterization. We developed a small and lightweight IMS device, which consists of an inertial measurement unit, micro control unit, and peripheral electrical components, integrated with an insole so that it can be placed inside a shoe at the arch of the foot. Stride parameters, i.e., stride length, walking speed, foot height, circumduction, peak foot sole angle in the dorsiflexion and plantarflexion directions, and toe-in $/$ out angle, that characterize a user’s foot motion are estimated. We recruited 30 healthy participants and evaluated the precision of our IMS system by comparing the stride parameters calculated with this system with those acquired from a motion-capture system. The results indicate the precision of the system in terms of the root mean square error for stride length of 0.069 m, walking speed of 0.094 $\text{m}/\text{s}$ , foot height of 1.5 cm, circumduction of 1.0 cm, peak foot-sole angle in the dorsiflexion of 3.3 deg. and in the plantarflexion directions of 5.9 deg., and toe-in $/$ out angle of 2.5 deg. Our IMS system has good precision regarding all parameters and high reliability and promises to contribute to personal health and wellness services and solutions by serving as a powerful and practical tool for objective gait assessment in real-world contexts.