Realization and validation of a piezoresistive textile-based insole for gait-related measurements.

The measurement of gait-related parameters is required in several application fields, such as experimental biomechanics and robotics. To enhance the wearability, smart textile-based sensors are always more widespread. In this context, we proposed an innovative insoles sensorized with piezoresistive textile able to gather information related to gait phase duration and center of pressure. An experimental protocol involved five healthy people was carried out to validate the gait-related measurements by using two force platforms as reference system. A total of 80 strides has been used for the validation procedure. The on/ off status of the piezoresistive sensors placed on toe and heel has been analyzed by applying a threshold-based procedure in order to compute the duration of the stride, as well the stance and swing phase. As for the center of pressure (CoP), the sensor outputs were post-processed to carry put the displacement of the CoP during the stride. The absolute error (AE) and the median absolute error (MAE) have been computed to evaluate the accuracy of the insole to measure the gait events and the gait phase duration in comparison of force platform outputs. Moreover, the correlation between the CoP displacements computed through the two sensor systems was computed, as well the root mean square error (RMSE). The gait phase duration was associated with a MAE lower than 0.05 s both considering the stance and the swing; vice versa a MAE up to 0.16 s was found for the identification of the events. Considering the CoP, the average correlation coefficient was found equal to 0.92; with a RMSE up to 3.2 cm. These findings allow us to assess the ability of the realized insole in the measurement of the gait phases duration; whereas the CoP measurement should be considered viable only if it is sufficient to know the trend of the displacement rather than the accurate value. Considering the achievement, such insole could be used for robotic application when seeking to develop control system for lower limb exoskeleton.