Cardiovascular responses during submaximal electrical stimulation-induced leg cycling in individuals with paraplegia

Mechanomyography reflects the changes in oxygenated hemoglobin during electrically evoked cycling in individuals with spinal cord injury

BACKGROUND

Functional electrical stimulation (FES) cycling has been reported to enhance muscle strength and improve muscle fatigue resistance after spinal cord injury (SCI). Despite its proposed benefits, the quantification of muscle fatigue during FES cycling remains poorly documented. This study sought to quantify the relationship between the vibrational performance of electrically-evoked muscles measured through mechanomyography (MMG) and its oxidative metabolism through near-infrared spectroscopy (NIRS) characteristics during FES cycling in fatiguing paralyzed muscles in individuals with SCI.

METHODS

Six individuals with SCI participated in the study. They performed 30 min of FES cycling with MMG and NIRS sensors on their quadriceps throughout the cycling, and the signals were analyzed.

RESULTS

A moderate negative correlation was found between MMG root mean square (RMS) and oxyhaemoglobin (O2Hb) [r = -0.38, p = 0.003], and between MMG RMS and total hemoglobin (tHb) saturation [r = -0.31, p = 0.017]. Statistically significant differences in MMG RMS, O2Hb, and tHb saturation occurred during pre- and post-fatigue of FES cycling (p < 0.05).

CONCLUSIONS

MMG RMS was negatively associated with O2Hb and muscle oxygen derived from NIRS. MMG and NIRS sensors showed good inter-correlations, suggesting a promising use of MMG for characterizing metabolic fatigue at the muscle oxygenation level during FES cycling in individuals with SCI.

Impact of subtetanic neuromuscular electrical stimulation on cardiac autonomic nervous system in young individuals

BACKGROUND

Although subtetanic neuromuscular electrical stimulation (NMES) has been proposed as an exercise training and/or rehabilitation tool, the impact of NMES on the autonomic nervous system (ANS) is unclear. Thus, we hypothesized that NMES would alter ANS, i.e., increase sympathetic activity and decrease parasympathetic activity, in young individuals.

METHODS

Eighteen healthy young individuals (16 males, mean age: 22 [SD: 4] years, Body Mass Index: 21.7 [2.2] kg/m2) volunteered. Blood pressure (BP), heart rate (HR), and R-R intervals were recorded during 6-minute resting, NMES, and recovery conditions. Short-term heart rate variability analysis of R-R intervals was performed for the frequency and time domains during each condition. Time domain indices included the root mean square of successive R-R interval differences (RMSSD), and the percentage of successive R-R intervals differing by more than 50ms (pRR50%). Frequency domain indices (fast Fourier transform) of R-R intervals included total power (TP), low-frequency (LF) power (0.04-0.15 Hz), and high-frequency (HF) power (0.15-0.4 Hz).

RESULTS

BP was not altered but HR was significantly increased during NMES (P<0.001), and it returned to the resting level at recovery. RMSSD and pRR50 decreased from resting to NMES and returned at recovery conditions (P<0.05, respectively). TP and HF decreased from resting to NMES and returned at recovery conditions (P<0.05, respectively). LF increased from NMES to recovery (P<0.05). The LF/HF ratio showed no significant differences between conditions (P=0.210).

CONCLUSIONS

Cardiac ANS fluctuated by subtetanic NMES without BP elevation in healthy young individuals. Parasympathetic but not sympathetic activity was affected by NMES stimulation.

Functional electrical stimulation: cardiorespiratory adaptations and applications for training in paraplegia

Regular exercise can be broadly beneficial to health and quality of life in humans with spinal cord injury (SCI). However, exercises must meet certain criteria, such as the intensity and muscle mass involved, to induce significant benefits. SCI patients can have difficulty achieving these exercise requirements since the paralysed muscles cannot contribute to overall oxygen consumption. One solution is functional electrical stimulation (FES) and, more importantly, hybrid training that combines volitional arm and electrically controlled contractions of the lower limb muscles. However, it might be rather complicated for therapists to use FES because of the wide variety of protocols that can be employed, such as stimulation parameters or movements induced. Moreover, although the short-term physiological and psychological responses during different types of FES exercises have been extensively reported, there are fewer data regarding the long-term effects of FES. Therefore, the purpose of this brief review is to provide a critical appraisal and synthesis of the literature on the use of FES for exercise in paraplegic individuals. After a short introduction underlying the importance of exercise for SCI patients, the main applications and effects of FES are reviewed and discussed. Major findings reveal an increased physiological demand during FES hybrid exercises as compared with arms only exercises. In addition, when repeated within a training period, FES exercises showed beneficial effects on muscle characteristics, force output, exercise capacity, bone mineral density and cardiovascular parameters. In conclusion, there appears to be promising evidence of beneficial effects of FES training, and particularly FES hybrid training, for paraplegic individuals.

The effect of using variable frequency trains during functional electrical stimulation cycling

Objectives.  This paper describes an experimental investigation of variable frequency stimulation patterns as a means of increasing torque production and, hence, performance in cycling induced by functional electrical stimulation. Materials and Methods.  Experiments were conducted on six able-bodied subjects stimulating both quadriceps during isokinetic trials. Constant-frequency trains (CFT) with 50-msec interpulse intervals and four catchlike-inducing trains (CIT) were tested. The CITs had an initial, brief, high-frequency burst of two pulses at the onset of or within a subtetanic low-frequency stimulation train. Each stimulation train consisted of the same number of pulses. The active torques produced by each train were compared. Parametric main effect ANOVA tests were performed on the active torque-time integral (TTI), on the active torque peaks and on the time needed to reach those peaks (T2P). Results.  The electrical stimulation of the quadriceps produced active torques with mean peak values in the range of 1.6-3.5 Nm and a standard error below 0.2 Nm. CITs produced a significant increase of TTI and torque peaks compared with CFTs in all the experimental conditions. In particular, during the postfatigue trials, the CITs with the doublet placed in the middle of the train produced TTIs and torque peaks about 61% and 28% larger than the CFT pattern, respectively. In addition, the CITs showed the lowest reduction of the performance between prefatigue and postfatigue conditions. Conclusions.  The use of CITs improves the functional electrical stimulation cycling performance compared with CFT stimulation. This application might have a relevant clinical importance for individuals with stroke where the residual sensation is still present and thus the maximization of the performance without an excessive increase of the stimulation intensity is advisable. Therefore, exercise intensity can be increased yielding a better muscle strength and endurance that may be beneficially for later gait training in individuals with stroke.

Early poststroke rehabilitation using a robotic tilt-table stepper and functional electrical stimulation

Background. Stroke frequently leaves survivors with hemiparesis. To prevent persistent deficits, rehabilitation may be more effective if started early. Early training is often limited because of orthostatic reactions. Tilt-table stepping robots and functional electrical stimulation (FES) may prevent these reactions. Objective. This controlled convenience sample study compares safety and feasibility of robotic tilt-table training plus FES (ROBO-FES) and robotic tilt-table training (ROBO) against tilt-table training alone (control). A preliminary assessment of efficacy is performed. Methods. Hemiparetic ischemic stroke survivors (age 58.3 ± 1.2 years, 4.6 ± 1.2 days after stroke) were assigned to 30 days of ROBO-FES (n = 38), ROBO (n = 35), or control (n = 31) in addition to conventional physical therapy. Impedance cardiography and transcranial doppler sonography were performed before, during, and after training. Hemiparesis was assessed using the British Medical Research Council (MRC) strength scale. Results. No serious adverse events occurred; 8 patients in the tilt-table group prematurely quit the study because of orthostatic reactions. Blood pressure and CBFV dipped <10% during robot training. In 52% of controls mean arterial pressure decreased by ≥20%. ROBO-FES increased leg strength by 1.97 ± 0.88 points, ROBO by 1.50 ± 0.85 more than control (1.03 ± 0.61, P < 0.05). CBFV increased in both robotic groups more than in controls (P < 0.05). Conclusions. Robotic tilt-table exercise with or without FES is safe and may be more effective in improving leg strength and cerebral blood flow than tilt table alone.

Electrical muscle stimulation for chronic heart failure: an alternative tool for exercise training?

Conventional exercise training has been shown conclusively to improve exercise capacity, quality of life, and even reduce mortality in chronic heart failure. Unfortunately, not all heart failure patients are suitable for conventional exercise programs for various reasons. The exciting new technique of electrical muscle stimulation (EMS) of large groups of muscles has been shown to produce a physiologic response consistent with cardiovascular exercise at mild to moderate intensities by increasing peak oxygen consumption, carbon dioxide production, ventilatory capacity, and heart rate. Additionally, there is improvement in muscle strength. The handful of small studies that exist of home-based EMS training of leg muscles in heart failure show that EMS produces similar benefits to conventional exercise in improving exercise capacity, making EMS an alternative to aerobic exercise training in those that cannot undertake conventional exercise. The improvement seen in leg muscle strength promises also to improve mobility in this sedentary population.

A randomized controlled trial on the effects of cycling with and without electrical stimulation on cardiorespiratory and vascular health in children with spinal cord injury

OBJECTIVE

To examine the cardiorespiratory/vascular effects of cycling with and without functional electrical stimulation (FES) in children with spinal cord injury (SCI).

DESIGN

Randomized controlled trial.

SETTING

Pediatric referral hospital.

PARTICIPANTS

Children with SCI (N=30), ages 5 to 13 years, with injury levels from C4 to T11, and American Spinal Injury Association grades A, B, or C.

INTERVENTIONS

Children were randomly assigned to 1 of 3 groups: FES leg cycling exercise, passive leg cycling, or noncycling control group receiving electrical stimulation therapy. After receiving instruction on the use of the equipment, children exercised for 1 hour 3 times per week for 6 months at home with parental supervision.

MAIN OUTCOME MEASURES

Oxygen uptake (Vo(2)) during an incremental arm ergometry test, resting heart rate, forced vital capacity, and a fasting lipid profile.

RESULTS

There were no differences (P>.05) between groups after 6 months of exercise when comparing pre- and postvalues. However, there were differences between groups for some variables when examining percent change. The FES cycling group showed an improvement (P=.035) in Vo(2) (16.2%+/-25.0%) as compared with the passive cycling group (-28.7%+/-29.1%). For lipid levels, the electrical stimulation-only group showed declines (P=.032) in cholesterol levels (-17.1%+/-8.5%) as compared with the FES cycling group (4.4%+/-20.4%).

CONCLUSIONS

Cycling with FES led to gains in Vo(2), whereas electrical stimulation alone led to improvements in cholesterol.

Activity-based restorative therapies: concepts and applications in spinal cord injury-related neurorehabilitation

Physical rehabilitation following spinal cord injury-related paralysis has traditionally focused on teaching compensatory techniques, thus enabling the individual to achieve day-to-day function despite significant neurological deficits. But the concept of an irreparable central nervous system (CNS) is slowly being replaced with evidence related to CNS plasticity, repair, and regeneration, all related to persistently maintaining appropriate levels of neurological activity both below and above the area where the damage occurred. It is now possible to envision functional repair of the nervous system by implementing rehabilitative interventions. Making the transition from "bench to bedside" requires careful analysis of existing basic science evidence, strategic focus of clinical research, and pragmatic implementation of new therapeutic tools. Activity, defined as both function specific motor task and exercise appears to be a necessity for optimization of functional, metabolic, and neurological status in chronic paralysis. Crafting a comprehensive rehabilitative intervention focused on functional improvement through neurological gains seems logical. The terms activity-based restorative therapies, activity-based therapies, and activity-based rehabilitation have been coined in the last 10 years to describe a new fundamental approach to deficits induced by neurological paralysis. The goal of this approach is to achieve activation of the neurological levels located both above and below the injury level using rehabilitation therapies. This article reviews basic and clinical science evidence pertaining to implementation of physical activity and exercise as a therapeutic tool in the management of chronic spinal cord-related neurological paralysis.

A systematic review of the management of orthostatic hypotension after spinal cord injury

OBJECTIVE

To review systematically the evidence for the management of orthostatic hypotension (OH) in patients with spinal cord injuries (SCIs).

DATA SOURCES

A key word literature search was conducted of original and review articles as well as practice guidelines using Medline, CINAHL, EMBASE, and PsycInfo, and manual searches of retrieved articles from 1950 to July 2008, to identify literature evaluating the effectiveness of currently used treatments for OH.

STUDY SELECTION

Included randomized controlled trials (RCTs), prospective cohort studies, case-control studies, pre-post studies, and case reports that assessed pharmacologic and nonpharmacologic intervention for the management of OH in patients with SCI.

DATA EXTRACTION

Two independent reviewers evaluated the quality of each study, using the Physiotherapy Evidence Database score for RCTs and the Downs and Black scale for all other studies. Study results were tabulated and levels of evidence assigned.

DATA SYNTHESIS

A total of 8 pharmacologic and 21 nonpharmacologic studies were identified that met the criteria. Of these 26 studies (some include both pharmacologic and nonpharmacologic interventions), only 1 pharmacologic RCT was identified (low-quality RCT producing level 2 evidence), in which midodrine was found to be effective in the management of OH after SCI. Functional electrical stimulation was one of the only nonpharmacologic interventions with some evidence (level 2) to support its utility.

CONCLUSIONS

Although a wide array of physical and pharmacologic measures are recommended for the management of OH in the general population, very few have been evaluated for use in SCI. Further research needs to quantify the efficacy of treatment for OH in subjects with SCI, especially of the many other pharmacologic interventions that have been shown to be effective in non-SCI conditions.

Oxygen consumption during functional electrical stimulation-assisted exercise in persons with spinal cord injury: implications for fitness and health

A lesion in the spinal cord leads in most cases to a significant reduction in active muscle mass, whereby the paralysed muscles cannot contribute to oxygen consumption (VO2) during exercise. Consequently, persons with spinal cord injury (SCI) can only achieve high VO2 values by excessively stressing the upper body musculature, which might increase the risk of musculoskeletal overuse injury. Alternatively, the muscle mass involved may be increased by using functional electrical stimulation (FES). FES-assisted cycling, FES-cycling combined with arm cranking (FES-hybrid exercise) and FES-rowing have all been suggested as candidates for cardiovascular training in SCI. In this article, we review the levels of VO2 (peak [VO2peak] and sub-peak [VO2sub-peak]) that have been reported for SCI subjects using these FES exercise modalities. A systematic literature search in MEDLINE, EMBASE, AMED, CINAHL, SportDiscus and the authors' own files revealed 35 studies that reported on 499 observations of VO2 levels achieved during FES-exercise in SCI. The results show that VO2peak during FES-rowing (1.98 L/min, n = 17; 24.1 mL/kg/min, n = 11) and FES-hybrid exercise (1.78 L/min, n = 67; 26.5 mL/kg/min, n = 35) is considerably higher than during FES-cycling (1.05 L/min, n = 264; 14.3 mL/kg/min, n = 171). VO2sub-peak values during FES-hybrid exercise were higher than during FES-cycling. FES-exercise training can produce large increases in VO2peak; the included studies report average increases of +11% after FES-rowing training, +12% after FES-hybrid exercise training and +28% after FES-cycling training. This review shows that VO2 during FES-rowing or FES-hybrid exercise is considerably higher than during FES-cycling. These observations are confirmed by a limited number of direct comparisons; larger studies to test the differences in effectiveness of the various types of FES-exercise as cardiovascular exercise are needed. The results to date suggest that FES-rowing and FES-hybrid are more suited for high-intensity, high-volume exercise training than FES-cycling. In able-bodied people, such exercise programmes have shown to result in superior health and fitness benefits. Future research should examine whether similar high-intensity and high-volume exercise programmes also give persons with SCI superior fitness and health benefits. This kind of research is very timely given the high incidence of physical inactivity-related health conditions in the aging SCI population.

What are the electrical stimulation design parameters for maximum VO2 aimed at cardio-pulmonary rehabilitation?

Electrical Stimulation (ES) is increasingly being considered as a means to improve cardio-pulmonary performance in patients with reduced exercise capacity. This short review considers the ES signal parameters and protocols used in studies that have included a measurement of oxygen uptake during the session. It suggests that the tetanic signal parameters normally used for muscle strengthening are not suitable for producing a sustained increase in oxygen uptake. Instead, very low frequencies are preferred, perhaps because there is less fatigue of the type 1 muscle fibers.

Energetics of paraplegic cycling: a new theoretical framework and efficiency characterisation for untrained subjects

Complete lower-limb paralysis resulting from spinal cord injury precludes volitional leg exercise, leading to muscle atrophy and physiological de-conditioning. Cycling can be achieved using phased stimulation of the leg muscles. With training there are positive physiological adaptations and health improvement. Prior to training, however, power output may not be sufficient to overcome losses involved in rotating the legs and little is known about the energetics of untrained paralysed muscles. Here we propose efficiency measures appropriate to subjects with severe physical impairment performing cycle ergometry. These account for useful internal work (i.e. muscular work done in moving leg mass) and are applicable even for very low work rates. Experimentally, we estimated total work efficiency of ten untrained subjects with paraplegia to be 7.6 +/- 2.1% (mean +/- SD). This is close to values previously reported for anaesthetised able-bodied individuals performing stimulated cycling exercise, but is less than 1/3 of that of able-bodied subjects cycling volitionally. Correspondingly, oxygen cost of the work (38.8 +/- 13.9 ml min(-1) W(-1)) was found to be approximately 3.5 times higher. This indicates the need, for increased power output from paralysed subjects, to maximise muscle strength through training, and to improve efficiency by determining better methods of stimulating the individual muscles involved in the exercise.

Muscle oxygenation during prolonged electrical stimulation-evoked cycling in paraplegics

This study investigated cardiorespiratory responses and muscle oxygenation during prolonged electrical stimulation (ES)-evoked leg cycling in individuals with paraplegia (PARA). Four PARA and 6 able-bodied (AB) persons participated in this study. Subjects performed 10 min of passive cycling and 40 min of active cycling (PARA, ES cycling; AB, voluntary cycling) at workloads selected to elicit an equivalent oxygen uptake between groups. Cycling power output, cardiorespiratory responses, mechanical efficiency, and quadriceps muscle oxygenation (measured with near-infrared spectroscopy) were measured over the duration of the exercise. Oxygen uptake was similar in both groups during active cycling (PARA, 737 ± 177 mL·min–1; AB, 840 ± 90 mL·min–1). The cycling power output for PARA individuals commenced at 8.8 W, but varied considerably over 40 min. PARA individuals demonstrated markedly lower gross mechanical efficiency (~1.3%) during ES cycling compared with AB individuals performing voluntary exercise (~12.6%). During ES cycling, muscle oxygen saturation (SO2) decreased to approximately 72 ± 19%, whereas SO2 during volitional cycling was unaltered from resting levels. Muscle oxygenated haemoglobin initially decreased (–23%) during ES cycling, but returned to resting levels after 10 min. Deoxygenated haemoglobin initially rose during the first 5 min of ES cycling, and remained elevated by 28% thereafter. Upon cessation of ES cycling, lower-limb muscle oxygenation increased (+93%), suggesting reactive hyperaemia in PARA individuals after such exercise. During ES cycling, muscle oxygenation followed a different pattern to that observed in AB individuals performing voluntary cycling at an equivalent VO2. Equilibrium between oxygen demand and oxygen delivery was reached during prolonged ES cycling, despite the lack of neural adjustments of leg vasculature in the paralyzed lower limbs.

Ambulatory impedance cardiography: a systematic review

BACKGROUND

Standard noninvasive impedance cardiography has been used to examine the cardiovascular responses of individuals to a wide range of stimuli in critical care and laboratory settings. It has been shown to be a reliable alternative to invasive thermodilution techniques and an acceptable alternative to the use of a pulmonary artery catheter. Ambulatory impedance cardiography provides a similar assessment of cardiac function to standard noninvasive impedance cardiography, but it does so while individuals engage in activities of daily living. It offers portability and the option of managing complex patients in outpatient settings.

OBJECTIVE

To critically examine through a literature analysis the validity, reliability, and sensitivity of ambulatory impedance cardiography for the assessment of cardiac performance during activities of daily living.

METHODS

The Cochrane Database of Systematic Reviews (CDSR), The Cochrane Database of Methodology Reviews (CDMR), The Cochrane Central Register of Controlled Trials (CENTRAL), Database of Abstracts of Reviews of Effects (DARE), National Health Service Economic Evaluation Database (NHS EED), Health Technology Assessment (HTA), and The Cochrane Methodology Register (CMR; 1966-2005); MEDLINE (1950-2005); and CINAHL (1982-2005) were searched using the following terms: ambulatory cardiac performance, impedance cardiac performance, AIM cardiac performance monitor, thoracic electrical bio-impedance, impedance cardiography, ambulatory impedance monitor, bio-impedance technology, ambulatory impedance cardiography, bio-electric impedance; also included were reference lists of retrieved articles. Studies were selected if they used an ambulatory impedance monitor to examine one or more of the following cardiovascular responses: pre-ejection period (PEP), left ventricular ejection time (LVET), stroke volume (SV), or a combination of these.

RESULTS

Studies have been predominantly descriptive and have been focused on a young, male population with a normal body mass index (BMI; 25-29 kg/m). Inconsistencies in determining specific markers of cardiac function (e.g., PEP and SV) across studies necessitated that results be reported by outcome for each study separately.

DISCUSSION

Ambulatory impedance monitors are valid and reliable instruments used for the physiologic measurement of cardiac performance. Sensitivity is established utilizing within-individual measurements of relative change. This is especially important in light of an aging population and technical advances in healthcare. Further research is warranted using nursing interventions that focus on an older, female population who have a BMI greater than 30 kg/m. Availability of noninvasive ambulatory measures of cardiac function has the potential to improve care for a variety of patient populations, including those with hypertension, heart failure, pain, anxiety, and depressive symptoms.

Electrical stimulation of unloaded muscles causes cardiovascular exercise by increasing oxygen demand

BACKGROUND

The development of new strategies to encourage increased levels of physical activity can help to reduce the incidence of cardiovascular disease. A new system of electrical muscle stimulation (EMS) has been developed that attempts to cause an increase in energy expenditure by mimicking the action of shivering in the body. The purpose of this study was to show that this form of EMS is capable of eliciting a cardiovascular exercise response in healthy adults.

DESIGN

An observational study.

METHODS

Ten healthy volunteers completed a maximal treadmill test and four EMS sessions using a hand-held EMS device that delivered current to the body via five silicone rubber electrodes on each leg. At each session subjects completed 3 min stimulation at each of four stimulation outputs (10, 20, 30 and 40% of maximum output) while cardiopulmonary gas exchange and heart rate (HR) were measured. Physiological responses at increasing levels of stimulation were evaluated.

RESULTS

Average (+/-SD) HR and oxygen consumption (VO2) levels of 67+/-11 bpm and 4.7+/-1.2 ml/kg per min at rest, respectively, were increased to 186+/-10 bpm and 44.9+/-9.8 ml/kg per min at peak exercise intensity on treadmill testing. The electrical stimulation was generally well tolerated by the subjects. Subjects demonstrated statistically significant increases in all physiological variables measured with successive increases in stimulation intensity. Peak HR and VO2 at 40% stimulation intensity were 101+/-12 bpm and 14.9+/-4.3 ml/kg per min, respectively.

CONCLUSIONS

These results demonstrate that this form of EMS is capable of producing a physiological response consistent with cardiovascular exercise at mild to moderate intensities. It achieves this without producing gross movement of the limbs or loading of the joints. This EMS-induced cardiovascular exercise response could be used to promote increased levels of physical activity in populations unable to participate in voluntary exercise.

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

AIM

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.

METHODS

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.

RESULTS

Average oxygen cost and stimulation cost of P1 were found to be significantly lower than those for P2 (paired t-test, p<0.05): oxygen costs were 0.56+/-0.03l min-1 and 0.61+/-0.04l min-1 (mean+/-S.D.), respectively; stimulation costs were 74.91+/-12.15 mC min-1 and 100.30+/-14.78 mC min-1 (mean+/-S.D.), respectively. Correspondingly, all efficiency estimates for P1 were greater than those for P2.

CONCLUSION

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.