Feedback control of electrical stimulation electrode arrays

Toward a wearable monitor of local muscle fatigue during electrical muscle stimulation using tissue Doppler imaging

Electrical muscle stimulation (EMS) is widely used in rehabilitation and athletic training to generate involuntary muscle contractions. However, EMS leads to rapid muscle fatigue, limiting the force a muscle can produce during prolonged use. Currently available methods to monitor localized muscle fatigue and recovery are generally not compatible with EMS. The purpose of this study was to examine whether Doppler ultrasound imaging can assess changes in stimulated muscle twitches that are related to muscle fatigue from electrical stimulation. We stimulated five isometric muscle twitches in the medial and lateral gastrocnemius of 13 healthy subjects before and after a fatiguing EMS protocol. Tissue Doppler imaging of the medial gastrocnemius recorded muscle tissue velocities during each twitch. Features of the average muscle tissue velocity waveforms changed immediately after the fatiguing stimulation protocol (peak velocity: -38%, p = .022; time-to-zero velocity: +8%, p = .050). As the fatigued muscle recovered, the features of the average tissue velocity waveforms showed a return towards their baseline values similar to that of the normalized ankle torque. We also found that features of the average tissue velocity waveform could significantly predict the ankle twitch torque for each participant (R2 = 0.255-0.849, p < .001). Our results provide evidence that Doppler ultrasound imaging can detect changes in muscle tissue during isometric muscle twitch that are related to muscle fatigue, fatigue recovery, and the generated joint torque. Tissue Doppler imaging may be a feasible method to monitor localized muscle fatigue during EMS in a wearable device.

Functional electrical stimulation for home-based upper-limb stroke rehabilitation

Functional electrical stimulation (FES) therapies have shown effectiveness in restoring movement post-stroke, especially when applied functionally to assist participants’ voluntary intention during repeated, motivating tasks. Recent development in non-contact sensors allows feedback to advanced controllers that precisely adjust FES via an electrode array to assist functional reach and grasp tasks. This has given rise to significant reduction in impairment, as measured in clinical trials. This paper describes the recent developments of a compact system suitable for transference to patients’ homes, with the intention of reducing upper-limb impairment following chronic stroke.