Vertical unloading produced by electrically evoked withdrawal reflexes during gait: Preliminary results

Abstract

The objective of this study was to investigate the capability of Force Sensitive Resistors (FSR) to characterize perturbations of gait produced by electrically evoked withdrawal reflexes. Reflexes were evoked by cutaneous electrical stimulation at 4 locations on the sole of the left foot and delivered at 3 different phases in early swing. Force changes were measured by 4 FSR's attached to each foot. The vertical ground reaction force was estimated by summing the force signals for each foot separately. Response measures were mean peak force and peak slope evaluated in 5 gait sub-phases immediately after the stimulus: 1st double support, 1st right single support, 2nd double support, 1st left single support and 3rd double support. The results showed that perturbation of gait could be detected by the selected features and that stimulation led to a weight shift from the ipsilateral to contralateral leg starting with a more rapid unloading of the ipsilatteral leg, supported by a rapid loading of the contralateral leg in the 1st double support. This is followed by a 48N higher peak force for the contralateral leg and 34N lower peak force for the ipsilateral leg in 1st right single support and in the 2nd double support phases. Further, the peak force in the 1st right single support shows a significant dependency with the stimulation phase.