Control of triceps surae stimulation based on shank orientation using a uniaxial gyroscope during gait

Abstract

This article presents a stimulation control method using a uniaxial gyroscope measuring angular velocity of the shank in the sagittal plane, to control functional electrical stimulation of the triceps surae to improve push-off of stroke subjects during gait. The algorithm is triggered during each swing phase of gait when the angular velocity of the shank is relatively high. Subsequently, the start of the stance phase is detected by a change of sign of the gyroscope signal at approximately the same time as heel strike. Stimulation is triggered when the shank angle reaches a preset value since the beginning of stance. The change of angle is determined by integrating angular velocity from the moment of change of sign. The results show that the real-time reliability of stimulation control was at least 95% for four of the five stroke subjects tested, two of which were 100% reliable. For the remaining subject, the reliability was increased from 50% found during the experiment, to 99% during offline processing. Our conclusion is that a uniaxial gyroscope on the shank is a simple, more reliable alternative to the heel switch for the purpose of restoring push-off of stroke subjects during gait.

Fig. 1

Healthy subject data. a Shank angular velocity. b Integrated angular velocity (shank angle)

Fig. 2

Flow chart depicting the main steps involved in the stimulation control algorithm

Fig. 3

Subject donned with equipment for FES experiments

Fig. 4

Patient Data. a Angular velocity [deg/s] of stroke subject number 5 during gait. Uppermost, horizontal dashed line is T _sw, parallel to this, along zero is the zero line. The vertical lines indicate zero crossing. b Integrated angular velocity (change in angle in [deg] vs. time [s]) since negative crossing through zero