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

FES-rowing in tetraplegia: a preliminary report

STUDY DESIGN

A training intervention study using functional electrical stimulation-rowing (FES-R) in a group of eight individuals with tetraplegia.

OBJECTIVES

To assess the feasibility of a structured progressive FES-R training programme in people with tetraplegia, and to explore the number and type of FES-training sessions required to enable continuous FES-R for 30 min.

SETTING

A fully integrated sports centre, elite rowing training centre and university sport science department.

METHODS

Eight participants with chronic complete and incomplete tetraplegia (C4 to C7, American Spinal Injury Association Impairment Scale A, B and C) who had not previously used any form of FES-assisted exercise, participated in the study. Participants completed a progressive FES-assisted training programme building to three continuous 30-min FES-R sessions per week at 60-80% of their predetermined peak power output. Thereafter, rowing performance was monitored for 12 months.

MAIN OUTCOME MEASURES

number and type of FES-training sessions required before achieving 30-min continuous FES-R, and FES-R average power output (POav) pre and post 12 months training. Participant feedback of perceived benefits was also documented.

RESULTS

All participants were able to continuously FES-row for 30 min after completing 13±7 FES-R training sessions. Each individual POav during 30 min FES-R increased over 12 months FES-training. FES-R was found safe and well tolerated in this group of individuals with tetraplegia.

CONCLUSION

Individuals with tetraplegia are able to engage in a progressive programme of FES-R training. Future research examining FES-R training as an adjunctive therapy in people with tetraplegia is warranted.

Cardiorespiratory responses during functional electrical stimulation cycling and electrical stimulation isometric exercise

STUDY DESIGN

Prospective experimental.

OBJECTIVES

To compare the cardiorespiratory responses with electrical stimulation (ES) producing either dynamic leg cycling or intermittent isometric leg contractions using the same ES protocol.

SETTING

Sydney, Australia.

METHODS

Eight paraplegics (T4-T11) performed ES exercise sessions on two separate days. On day 1, cardiorespiratory responses were measured during 5 min of rest followed by 35 min of cycling, and finally 15 min of intermittent isometric exercise using the same ES parameters. On the second day, after 5 min of rest, 35 min of isometric exercise was performed followed by 15 min of cycling.

RESULTS

There were no significant differences during the first 35 min of exercise on each day comparing the two modes of exercise for average rate of oxygen consumption (cycling, 534±128 ml min(-1); isometric 558±146 ml min(-1); P=0.451), the average heart rate (cycling, 93±15 b.p.m.; isometric 95±17 b.p.m.; P=0.264) or minute ventilation (cycling, 23.0±6.5 l min(-1); isometric 23.8±6.7 l min(-1); P=0.655). In addition, there were no significant differences between exercise modes for any peak cardiorespiratory values recorded during the initial 35 min of exercise or the following 15 min crossover exercise phase.

CONCLUSION

The current data found that intermittent ES leg isometric exercise elicited a similar cardiorespiratory response compared with functional ES leg cycling, suggesting it should be investigated as a viable alternative intervention for increasing whole body metabolic rate during sustained exercise training sessions for individuals with paralyzed muscles.

Functional electrical stimulation cycling in youth with spinal cord injury: A review of intervention studies

CONTEXT

Preliminary research suggests that functional electrical stimulation cycling (FESC) might be a promising intervention for youth with spinal cord injury (SCI).

OBJECTIVE

To review the evidence on FESC intervention in youth with SCI.

METHODS

Systematic literature searches were conducted during December 2012. Two reviewers independently selected titles, abstracts, and full-text articles. Of 40 titles retrieved, six intervention studies met inclusion criteria and were assessed using American Academy for Cerebral Palsy and Developmental Medicine Levels of Evidence and Conduct Questions for Group Design.

RESULTS

The study results were tabulated based on levels of evidence, with outcomes categorized according to the International Classification of Functioning, Disability, and Health framework. Evidence from the six included studies suggests that FESC is safe for youth with SCI, with no increase in knee/hip injury or hip displacement. Results from one level II randomized controlled trial suggest that a thrice weekly, 6-month FESC program can positively influence VO2 levels when compared with passive cycling, as well as quadriceps strength when compared with electrical stimulation and passive cycling.

CONCLUSIONS

FESC demonstrates limited yet encouraging results as a safe modality to mitigate effects of inactivity in youth with SCI. More rigorous research involving a greater number of participants is needed before clinicians can be confident of its effectiveness.

Exercise responses during functional electrical stimulation cycling in individuals with spinal cord injury

PURPOSE

This study compared acute exercise responses during arm cranking, functional electrical stimulation (FES)-assisted leg cycling, and combined arm and leg ("hybrid") cycling in individuals with spinal cord injury during maximal and submaximal exercise.

METHODS

Nine male subjects with long-standing neurological lesions from C7 to T12 were recruited. All subjects performed arm crank ergometry (ACE), FES leg cycle exercise (FES-LCE), combined ACE + FES-LCE, and cycling on a hybrid FES tricycle (HYBRID). They were assessed for their peak exercise responses in all four modalities. Subsequently, their submaximal heart rates (HR), cardiac outputs (Q), stroke volumes (SV), and arteriovenous oxygen extractions (Ca-Cv)O2 were measured at 40%, 60%, and 80% of mode-specific V˙O2peak.

RESULTS

Arm exercise alone and arm + leg exercise resulted in significantly higher V˙O2peak and HRpeak compared with FES-LCE (P < 0.05). Submaximal V˙O2 during FES-LCE was significantly lower than all other modalities across the range of exercise intensities (P < 0.05). ACE elicited 70%-94% higher steady-state V˙O2, and HYBRID evoked 99%-148% higher V˙O2 compared with FES-LCE. Steady-state FES-LCE also produced significantly lower Q, HR, and (Ca-Cv)O2. ACE evoked 31%-36% higher Q and 19%-47% greater HR than did FES-LCE. HYBRID elicited 31%-49% greater Q and 23%-56% higher HR than FES-LCE.

CONCLUSIONS

Combined arm and leg exercise can develop a higher oxygen uptake and greater cardiovascular demand compared with ACE or FES-LCE alone. These findings suggested that combined arm + leg FES training at submaximal exercise intensities may lead to greater gains of aerobic fitness than would arm exercise alone. These data also proffered that FES leg cycling exercise by itself may be insufficient to promote aerobic fitness in the spinal cord injury population.

Whole body oxygen uptake and evoked knee torque in response to low frequency electrical stimulation of the quadriceps muscles: V•O2 frequency response to NMES

Background

There is emerging evidence that isometric Neuromuscular Electrical Stimulation (NMES) may offer a way to elicit therapeutically significant increases in whole-body oxygen uptake in order to deliver aerobic exercise to patients unable to exercise volitionally, with consequent gains in cardiovascular health. The optimal stimulation frequency to elicit a significant and sustained pulmonary oxygen uptake has not been determined. The aim of this study was to examine the frequency response of the oxygen uptake and evoked torque due to NMES of the quadriceps muscles across a range of low frequencies spanning the twitch to tetanus transition.

Methods

Ten healthy male subjects underwent bilateral NMES of the quadriceps muscles comprising eight 4 minute bouts of intermittent stimulation at selected frequencies in the range 1 to 12 Hz, interspersed with 4 minutes rest periods. Respiratory gases and knee extensor torque were simultaneously monitored throughout. Multiple linear regression was used to fit the resulting data to an energetic model which expressed the energy rate in terms of the pulse frequency, the torque time integral and a factor representing the accumulated force developed per unit time.

Results

Additional oxygen uptake increased over the frequency range to a maximum of 564 (SD 114) ml min^-1 at 12 Hz, and the respiratory exchange ratio was close to unity from 4 to 12 Hz. While the highest induced torque occurred at 12 Hz, the peak of the force development factor occurred at 6 Hz. The regression model accounted for 88% of the variability in the observed energetic response.

Conclusions

Taking into account the requirement to avoid prolonged tetanic contractions and to minimize evoked torque, the results suggest that the ideal frequency for sustainable aerobic exercise is 4 to 5 Hz, which coincided in this study with the frequency above which significant twitch force summation occurred.

Functional electrical stimulation elliptical stepping versus cycling in spinal cord-injured individuals

BACKGROUND

The cardiorespiratory responses and mechanical efficiencies of two modalities of functional electrical stimulation augmented leg exercises - isokinetic cycling and isokinetic elliptical stepping - were compared amongst individuals with spinal cord injury.

METHODS

Five subjects performed seated isokinetic evoked cycling and elliptical stepping leg exercise at 10, 20 and 30rev·min(-1) pedal cadences. 3-D motion analysis and force transducers attached onto the foot pedals quantified the external forces and power outputs developed by each lower extremity. Hip, knee and ankle joints power were derived via inverse dynamics analysis. The subjects' cardiorespiratory responses during exercise were measured by respiratory gas analysis.

FINDINGS

Ensemble-averaged oxygen uptakes across pedal cadences were higher during stepping (448 (75) ml·min(-1)) compared to cycling (422 (54) ml·min(-1)). External power outputs and metabolic efficiencies during stepping (9.9 (8.3) W, 2.9 (3.2) %) were double those observed during cycling (5.3 (6.3) W, 1.6 (1.9) %). Cumulative internal and external leg joint powers during stepping were twice higher than cycling, but the stepping mechanical efficiencies derived from inverse dynamics analysis were comparable to cycling (76.3 (21.2) % and 63.6 (12.3) % respectively). Heart rate responses were similar between cycling and stepping, while carbon dioxide production and expired ventilation were slightly higher during elliptical stepping.

INTERPRETATION

Both exercise modalities could deliver appropriate training stimuli for improving the aerobic fitness and leg pedalling strength of spinal cord-injured individuals. However electrical stimulation-enhanced elliptical stepping might provide greater exercise dose-potency for leg muscle strengthening than electrically-enhanced cycling due to the higher power outputs observed.

Motor unit recruitment when neuromuscular electrical stimulation is applied over a nerve trunk compared with a muscle belly: quadriceps femoris

Neuromuscular electrical stimulation (NMES) can be delivered over a nerve trunk or muscle belly and both can generate contractions through peripheral and central pathways. Generating contractions through peripheral pathways is associated with a nonphysiological motor unit recruitment order, which may limit the efficacy of NMES rehabilitation. Presently, we compared recruitment through peripheral and central pathways for contractions of the knee extensors evoked by NMES applied over the femoral nerve vs. the quadriceps muscle. NMES was delivered to evoke 10 and 20% of maximum voluntary isometric contraction torque 2–3 s into the NMES (time1) in two patterns: 1) constant frequency (15 Hz for 8 s); and 2) step frequency (15–100-15 Hz and 25–100-25 Hz for 3–2-3 s, respectively). Torque and electromyographic activity recorded from vastus lateralis and medialis were quantified at the beginning (time1) and end (time2; 6–7 s into the NMES) of each pattern. M-waves (peripheral pathway), H-reflexes, and asynchronous activity (central pathways) during NMES were quantified. Torque did not differ regardless of NMES location, pattern, or time. For both muscles, M-waves were ∼7–10 times smaller and H-reflexes ∼8–9 times larger during NMES over the nerve compared with over the muscle. However, unlike muscles studied previously, neither torque nor activity through central pathways were augmented following 100 Hz NMES, nor was any asynchronous activity evoked during NMES at either location. The coefficient of variation was also quantified at time2to determine the consistency of each dependent measure between three consecutive contractions. Torque, M-waves, and H-reflexes were most variable during NMES over the nerve. In summary, NMES over the nerve produced contractions with the greatest recruitment through central pathways; however, considering some of the limitations of NMES over the femoral nerve, it may be considered a good complement to, as opposed to a replacement for, NMES over the quadriceps muscle for maintaining muscle quality and reducing contraction fatigue during NMES rehabilitation.

Use of the Case Western Reserve/Veterans Administration neuroprosthesis for exercise, standing and transfers by a paraplegic subject

Functional electric stimulation (FES) is a technology that may allow patients with spinal cord injury (SCI) to transfer stand and walk. This paper reports upon the use of the Case Western Reserve Neuroprosthesis by a T6 ASIA B paraplegic subject. The subject was able to stand for two minutes and 50 seconds. He could walk 35 feet with a swing to gait. Measurement of energy consumption showed that metabolic demand was only 2.1 metabolic equivalent units. The factors that limited the use of the device that need to be improved to make the technology practical for household or community ambulation are speed (5.8 m/min) of ambulation and fatigue of the stimulated muscles.

Acute energy cost of multi-modal activity-based therapy in persons with spinal cord injury

OBJECTIVE

To examine acute energy costs of multi-modal activity-based therapy (ABT) in men and women with spinal cord injury (SCI).

STUDY DESIGN

Descriptive case series.

SETTING

An outpatient center in California.

PARTICIPANTS

Seven men and women (age = 28.3 ± 11.6 years; duration of injury = 4.3 ± 2.5 years) with injury levels ranging from C5 to T8.

INTERVENTION

Activity-based therapy.

OUTCOME MEASURES

Oxygen uptake (VO(2)), energy expenditure (kcal/minute), SCI Metabolic Equivalent of Task (MET) (1 MET = 2.7 ml/kg/minute).

RESULTS

Oxygen uptake (VO(2)) during ABT ranged from 5.10 to 8.62 ml/kg/minute, with VO(2) consistently higher during modalities involving load bearing versus non-load bearing (P = 0.08). SCI MET values ranged from 1.89 to 3.24 and were significantly higher in subjects with mid-thoracic injury versus low-cervical injury (P = 0.01).

CONCLUSION

Data reveal that multi-modal ABT increases VO(2) in persons with SCI, but energy expenditure is relatively low. Strategies must be identified to optimize energy expenditure in the SCI to reduce health risks. Modalities involving load bearing seem to be superior to non-load-bearing activities. VO(2) was greater in response to load-bearing modalities than non-load-bearing modalities. It remains to be determined whether chronic ABT enhances cardiovascular fitness and reduces disease risks in this population.

Motor unit recruitment when neuromuscular electrical stimulation is applied over a nerve trunk compared with a muscle belly: triceps surae

Neuromuscular electrical stimulation (NMES) can be delivered over a nerve trunk or muscle belly and can generate contractions by activating motor (peripheral pathway) and sensory (central pathway) axons. In the present experiments, we compared the peripheral and central contributions to plantar flexion contractions evoked by stimulation over the tibial nerve vs. the triceps surae muscles. Generating contractions through central pathways follows Henneman's size principle, whereby low-threshold motor units are activated first, and this may have advantages for rehabilitation. Statistical analyses were performed on data from trials in which NMES was delivered to evoke 10–30% maximum voluntary torque 2–3 s into the stimulation (Time1). Two patterns of stimulation were delivered: 1) 20 Hz for 8 s; and 2) 20–100-20 Hz for 3–2-3 s. Torque and soleus electromyography were quantified at the beginning (Time1) and end (Time2; 6–7 s into the stimulation) of each stimulation train. H reflexes (central pathway) and M waves (peripheral pathway) were quantified. Motor unit activity that was not time-locked to each stimulation pulse as an M wave or H reflex (“asynchronous” activity) was also quantified as a second measure of central recruitment. Torque was not different for stimulation over the nerve or the muscle. In contrast, M waves were approximately five to six times smaller, and H reflexes were approximately two to three times larger during NMES over the nerve vs. the muscle. Asynchronous activity increased by 50% over time, regardless of the stimulation location or pattern, and was largest during NMES over the muscle belly. Compared with NMES over the triceps surae muscles, NMES over the tibial nerve produced contractions with a relatively greater central contribution, and this may help reduce muscle atrophy and fatigue when NMES is used for rehabilitation.

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.