C.C. Monaghan

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

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.

The effect of FES of the tibial nerve on physiological activation of leg muscles during gait

The effects of surface functional electrical stimulation (FES) of the tibial nerve of healthy subjects were evaluated. The FES was applied at three different times during gait: early, mid and late stances. The purpose of this work is to understand the effect of unilateral stimulation on the bilateral activation patterns of leg muscles, because FES is used in practice to improve gait, while associated neuromuscular change is not often measured. The experimental protocol presented here will be transferred to stroke subjects, who could benefit from improved push-off during gait. Results show that FES of the tibial nerve changes the offset timing of the tibialis anterior muscle on the stimulated side and the on- and offset timings of the tibialis anterior muscle of the leg contralateral to stimulation. Additionally, activity levels of the semitendinosus ipsilateral and tibialis anterior contralateral to the stimulated leg significantly decreased, with respect to the non-stimulated condition. For the semitendinosus, this was a difference of 6-7microV, with p<0.05. For the tibialis anterior, this was a difference of 7-15microV, with a significance of p=0.00, respectively. This information is important for future applications of stimulation as it means that stimulation not only affects the stimulated muscle but also the physiological motor control by the CNS.

Interaction of Artificial and Physiological Activation of the Gastrocnemius During Gait

Objectives.u2002 The purpose of this research was to understand the effects of surface functional electrical stimulation (FES) of the tibial nerve on the activation of the gastrocnemius medialis of the stimulated side.

Functional electrical stimulation of the triceps surae during gait

Every year stroke affects approximately 15 million people worldwide. It is the leading cause of disability in the western world. Gait relearning has high priority for stroke survivors. One of the most commonly treated effects of stroke gait is drop-foot (the inability to raise the toes during the swing). However, push-off is also severely diminished during stroke gait. Electromyography (EMG) results show that all muscles of the affected (paretic) side have decreased physiological activation. Reduction and premature activation of the triceps surae leads to poor push-off. Our goal was to stimulate the triceps surae using functional electrical stimulation to increase the activation of this muscle group. EMG of the stimulated muscle and other leg muscles of legs was measured, simultaneously. The aim was to evaluate how stimulation influences the activation patterns of the stimulated and non-stimulated muscles. Tests were first carried out on healthy subjects. Surface stimulation was applied to the tibial nerve, which activates the triceps surae. Stimulation timing was controlled using a uniaxial gyroscope on the lateral shank. Stimulation bursts of 300ms duration, 50Hz was applied at each step. EMG of the medial gastrocnemius, tibialis anterior, semitendinosus and rectus femoris of both legs was measured at 2048Hz. Responses between each stimulation pulse were analysed, for motor and reflexive signals. Additionally, the amplitude changes and the on and offset times of EMG bursts were analysed. Results: While FES influenced the activation patterns of healthy and stroke subjects on the stimulated and non-stimulated sides, the effects were considerably varied. Motor and or reflexive responses in the stimulated gastrocnemius were observed in healthy and stroke. In healthy subjects, responses were also observed in the tibilais anterior of the stimulated side. Less clear changes were seen in the physiological on and offset timings. Future studies should involve a larger test group with more strictly defined patient criteria. Using percutaneous or implantable stimulation electrodes, stimulation levels can be reduced; by-passing cutaneous sensation and preventing recruitment instability since the electrode would be in direct contact with the nerve. Finally, subjects should undergo a training program to facilitate gait while using FES.