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

<b>Aim</b><p></p> The energy efficiency of FES-cycling in spinal cord injured subjects is very much lower than that of normal cycling, and efficiency is dependent upon the parameters of muscle stimulation. We investigated measures which can be used to evaluate the effect on cycling performance of changes in stimulation parameters, and which might therefore be used to optimise them. We aimed to determine whether oxygen cost and stimulation cost measurements are sensitive enough to allow discrimination between the efficacy of different activation ranges for stimulation of each muscle group during constant-power cycling. <p></p> <b>Methods</b><p></p> We employed a custom FES-cycling ergometer system, with accurate control of cadence and stimulated exercise workrate. Two sets of muscle activation angles (“stimulation patterns”), denoted “P1” and “P2”, were applied repeatedly (eight times each) during constant-power cycling, in a repeated measures design with a single paraplegic subject. Pulmonary oxygen uptake was measured in real time and used to determine the oxygen cost of the exercise. A new measure of stimulation cost of the exercise is proposed, which represents the total rate of stimulation charge applied to the stimulated muscle groups during cycling. A number of energy-efficiency measures were also estimated. <p></p> <b>Results</b><p></p> Average oxygen cost and stimulation cost of P1 were found to be significantly lower than those for P2 (paired <i>t</i>-test, <i>p</i> < 0.05): oxygen costs were 0.56 ± 0.03 l min<sup>−1</sup> and 0.61 ± 0.04 l min<sup>−1</sup>(mean ± S.D.), respectively; stimulation costs were 74.91 ± 12.15 mC min<sup>−1</sup> and 100.30 ± 14.78 mC min<sup>−1</sup> (mean ± S.D.), respectively. Correspondingly, all efficiency estimates for P1 were greater than those for P2. <p></p> <b>Conclusion</b><p></p> Oxygen cost and stimulation cost measures both allow discrimination between the efficacy of different muscle activation patterns during constant-power FES-cycling. However, stimulation cost is more easily determined in real time, and responds more rapidly and with greatly improved signal-to-noise properties than the ventilatory oxygen uptake measurements required for estimation of oxygen cost. These measures may find utility in the adjustment of stimulation patterns for achievement of optimal cycling performance. <p></p&gt

Amplifier design for EMG recording from stimulation electrodes during functional electrical stimulation leg cycling ergometry

Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.Functional electrical stimulation leg cycle ergometry (FESLCE), which is often used as exercise for people with spinal cord injury (SCI), has recently been applied in the motor rehabilitation of stroke patients. Recently completed studies show controversial results, but with a tendency to positive training effects. Current technology is identical to that used in FES-LCE for SCI, whereas the pathology of stroke differs strongly. Most stroke patients with hemiparesis are able to drive an ergometer independently. Depending on the degree of spasticity, the paretic leg will partially support or hinder movements. Electrical stimulation increases muscle force and endurance and both are prerequisites for restoring gait. However, the effect of FES-LCE on improving impaired motor coordination is unclear. To measure motor coordination during FES-LCE, an EMG-amplifier design has been investigated which suppresses stimulation artifacts and allows detection of volitional or reflex induced muscle activity. Direct measurement of EMG from stimulation electrodes between stimulation pulses is an important asset of this amplifier. Photo-MOS switches in front of the preamplifier are utilized to achieve this. The technology presented here can be used to monitor the effects of FES-LCE to adapt the stimulation strategy or to realize EMG-biofeedback training.BMBF, 01EZ0766, Verbundprojekt RehaRobES: Regelungsverfahren für endeffektor-basierte Reha-Robotik in Kombination mit Elektrischer Stimulation in der Gangtherapie nach Schlaganfall - Teilprojekt Fahrradergometer etc

Evidence for complex integration and dynamic neural regulation of skeletal muscle recruitment during exercise in humans

A model is proposed in which the development of physical exhaustion is a relative rather than an absolute event and the sensation of fatigue is the sensory representation of the underlying neural integrative processes. Furthermore, activity is controlled as part of a pacing strategy involving active neural calculations in a “governor” region of the brain, which integrates internal sensory signals and information from the environment to produce a homoeostatically acceptable exercise intensity. The end point of the exercise bout is the controlling variable. This is an example of a complex, non-linear, dynamic system in which physiological systems interact to regulate activity before, during, and after the exercise bout

A functional electrical stimulation system for human walking inspired by reflexive control principles

This study presents an innovative multichannel functional electrical stimulation gait-assist system which employs a well-established purely reflexive control algorithm, previously tested in a series of bipedal walking robots. In these robots, ground contact information was used to activate motors in the legs, generating a gait cycle similar to that of humans. Rather than developing a sophisticated closed-loop functional electrical stimulation control strategy for stepping, we have instead utilised our simple reflexive model where muscle activation is induced through transfer functions which translate sensory signals, predominantly ground contact information, into motor actions. The functionality of the functional electrical stimulation system was tested by analysis of the gait function of seven healthy volunteers during functional electrical stimulation–assisted treadmill walking compared to unassisted walking. The results demonstrated that the system was successful in synchronising muscle activation throughout the gait cycle and was able to promote functional hip and ankle movements. Overall, the study demonstrates the potential of human-inspired robotic systems in the design of assistive devices for bipedal walking

Sensory electrical stimulation during cycling for the rehabilitation of muscle coordination

Gait (a person’s way of walking) is highly complex and involves the musculoskeletal and nervous systems to achieve coordinated movement. Gait is key in daily life, and its impairment greatly reduces the quality of life, personal freedom and self-esteem of afected people. Gait alterations arise from disruption of neuromuscular coordination mechanisms, either due to injury or degeneration (ictus, spinal cord injury...). The long term goal of the line of research that is started with the work presented in this Thesis is to build and validate a neurorehabilitation platform that uses biologically-inspired mechanisms in order to en- hance muscle coordination of walking in neurologically injured patients. As a frst step towards this ambitious goal, this Bachelor’s Thesis involved the design, development and technical validation of the neurorehabilitation platform that combines cycling with sensory electrical stimulation. Furthermore, a pilot study was conducted in order to assess the performance and usability of the neurorehabilitation platform. Prelim- inary results were encouraging, which gives the confdence toward the future applications of the platform. The present Bachelor’s Thesis has developed the necessary setups for performing a variety of experiments related with cycling and electrical stimulation. Future work should focus in further developing the experimental technique used for assessment of muscle coordina- tion, and using the developed neurorehabilitation platform for conducting broader studies with more subjects, both healthy and neurologically injured, with a variety of modali- ties and diverse stimulation patterns. Eventually, and based on the acquired knowledge about stimulation and neurorehabilitation, a commercial neurorehabilitation device could be created and distributed in order to enable low-cost walking rehabilitation for neurolog- ically injured patients.Ingeniería Biomédic

Down-Conditioning of Soleus Reflex Activity using Mechanical Stimuli and EMG Biofeedback

Spasticity is a common syndrome caused by various brain and neural injuries, which can severely impair walking ability and functional independence. To improve functional independence, conditioning protocols are available aimed at reducing spasticity by facilitating spinal neuroplasticity. This down-conditioning can be performed using different types of stimuli, electrical or mechanical, and reflex activity measures, EMG or impedance, used as biofeedback variable. Still, current results on effectiveness of these conditioning protocols are incomplete, making comparisons difficult. We aimed to show the within-session task- dependent and across-session long-term adaptation of a conditioning protocol based on mechanical stimuli and EMG biofeedback. However, in contrast to literature, preliminary results show that subjects were unable to successfully obtain task-dependent modulation of their soleus short-latency stretch reflex magnitude