Control strategies for integration of electric motor assist and functional electrical stimulation in paraplegic cycling: utility for exercise testing and mobile cycling

Abstract

Abstract-Aim:The aim of this study was to investigate feedback control strategies for integration of electric motor assist and functional electrical stimulation (FES) for paraplegic cycling, with particular focus on development of a testbed for exercise testing in FES cycling, in which both cycling cadence and workrate are simultaneously well controlled and contemporary physiological measures of exercise performance derived. A second aim was to investigate the possible benefits of the approach for mobile, recreational cycling.Methods: A recumbent tricycle with an auxiliary electric motor is used, which is adapted for paraplegic users, and instrumented for stimulation control. We propose a novel integrated control strategy which simultaneously provides feedback control of leg power output (via automatic adjustment of stimulation intensity) and cycling cadence (via electric motor control). Both loops are designed using system identification and analytical (model-based) feedback design methods. Ventilatory and pulmonary gas exchange response profiles are derived using a portable system for real-time breath-by-breath acquisition.Results: We provide indicative results from one paraplegic subject in which a series of feedback-control tests illustrate accurate control of cycling cadence, leg power control, and external disturbance rejection. We also provide physiological response profiles from a submaximal exercise step test and a maximal incremental exercise test, as facilitated by the control strategy. Conclusion: The integrated control strategy is effective in facilitating exercise testing under conditions of well-controlled cadence and power output. Our control approach significantly extends the achievable workrate range and enhances exercise-test sensitivity for FES cycling, thus allowing a more stringent characterization of physiological response profiles and estimation of key parameters of aerobic function. We further conclude that the control approach can significantly improve the overall performance of mobile recreational cycling.Index Terms-Cardiopulmonary exercise testing, control systems, functional electrical stimulation (FES), lower limb cycling, spinal-cord injury (SCI) rehabilitation.

Long‐term intensive electrically stimulated cycling by spinal cord–injured people: Effect on muscle properties and their relation to power output

“…Exercise tests were carried out using a feedback control system with motor assistance that allowed accurate quantification of PO, particularly at low levels (below that necessary to turn the pedals). 20 A progressive incremental exercise test was performed at 50 rpm, while the work rate was increased by 1-2 W every minute until it failed to increase (i.e., 100% stimulation intensity). PO during cycling was calculated from the cadence and torque measured at the crankshaft (SRM Powermeter; Schoberer Rad Messtechnik GmbH, Germany).…”

Comparison of stimulation patterns for FES-cycling using measures of oxygen cost and stimulation cost

“…We utilized a recumbent tricycle (Inspired Cycle Engineering Ltd., UK), adapted for paraplegic FES-cycling and arranged for static ergometry [26] (see figure 1). The tricycle is equipped with an electric motor, connected through gearing to a rear drive wheel, and coupled to the cranks at the front of the tricycle.…”

“…Full technical details of these feedback control systems and a discussion of the utility of the system for exercise testing are given in [26].…”

Comparison of Muscle Stimulation Groups for Simplified Practical FES Cycling Control with Cycling Wheelchair: An Experimental Test with Healthy Subjects

“…Mobile cycling with FES has been studied to develop locomotion device mainly for paraplegic subjects [4]- [7]. Integration of electric motor assist and FES has also been studied for this purpose [8], [9]. In addition to using the FES cycling as a mobility device, application of FES cycling to motor rehabilitation has been studied [10]- [12].…”

“…In oder to achieve widespread use of FES cycling, an FES cycling system easy to use for a user is desired. Current systems for FES mobile cycling use mainly a recumbent tricycle with ankle orthosis, and with or without electric power assist [6], [8]. Cycling wheelchairs incorporated a rotary encoder [10] or a motor assistance with an encoder [9] was also developed as experimental systems.…”