Increased Aerobic Fitness After Neuromuscular Electrical Stimulation Training in Adults With Spinal Cord Injury

Neuromuscular electrical stimulation for the treatment of diabetic sensorimotor polyneuropathy: A prospective, cohort, proof-of-concept study

OBJECTIVE

To assess a potential efficacy signal, safety and feasibility of neuromuscular electrical stimulation (NMES) therapy as an adjunct to standard care in patients with diabetic sensorimotor polyneuropathy (DSPN).

METHODS

In this single-centre, prospective, cohort, proof-of-concept study, 25 patients with DSPN consented to at least one daily 30-minute NMES therapy session (Revitive® IX) for 10 weeks, with 20 patients completing the study. The primary outcome measure was nerve conductivity assessed using a nerve conduction study of the sural, superficial peroneal, common peroneal and tibial nerves at 10 weeks compared to baseline. Secondary outcomes included superficial femoral artery (SFA) haemodynamics during NMES therapy compared to rest and quality-of-life at 10 weeks compared to baseline.

RESULTS

At 10 weeks, there were significant increases in sural sensory nerve action potential amplitude and conduction velocity (p < 0.001), superficial peroneal sensory nerve action potential amplitude (p = 0.001) and conduction velocity (p = 0.002), common peroneal nerve conduction velocity (p = 0.004) and tibial nerve compound muscle action potential amplitude (p = 0.002) compared to baseline. SFA volume flow and time-averaged mean velocity significantly increased (p ≤ 0.003) during NMES compared to rest. Patient-reported Michigan Neuropathy Screening Instrument scores significantly decreased (p = 0.028) at 10 weeks compared to baseline. Three unrelated adverse events occurred, and 15 participants adhered to treatment.

CONCLUSIONS

NMES therapy as an adjunct to standard care for 10 weeks significantly increased lower limb nerve conductivity in patients with DSPN and may be beneficial in the treatment of DSPN.

Optimization of Protocols Using Neuromuscular Electrical Stimulation for Paralyzed Lower-Limb Muscles to Increase Energy Expenditure in People With Spinal Cord Injury

OBJECTIVE

The aim of this study was to evaluate whether using surface neuromuscular electrical stimulation (NMES) for paralyzed lower-limb muscles results in an increase in energy expenditure and whether the number of activated muscles and duty cycle affect the potential increase.

DESIGN

This was a cross-sectional study.

RESULTS

Energy expenditure during all NMES protocols was significantly higher than the condition without NMES (1.2 ± 0.2 kcal/min), with the highest increase (+51%; +0.7 kcal/min, 95% confidence interval, 0.3-1.2) for the protocol with more muscles activated and the duty cycle with a shorter rest period. A significant decrease in muscle contraction size during NMES was found with a longer stimulation time, more muscles activated, or the duty cycle with a shorter rest period.

CONCLUSION

Using NMES for paralyzed lower-limb muscles can significantly increase energy expenditure compared with sitting without NMES, with the highest increase for the protocol with more muscles activated and the duty cycle with a shorter rest period. Muscle fatigue occurred significantly with the more intense NMES protocols, which might cause a lower energy expenditure in a longer protocol. Future studies should further optimize the NMES parameters and investigate the long-term effects of NMES on weight management in people with SCI.

Does aerobic exercise benefit persons with tetraplegia from spinal cord injury? A systematic review

CONTEXT

This review synthesizes the findings of previous research studies on the cardiovascular and metabolic benefits of aerobic exercise for individuals with tetraplegia secondary to spinal cord injury. They are often less active due to muscular paralysis, sensory loss, and sympathetic nervous system dysfunction that result from injury. Consequently, these persons are at higher risk for exercise intolerance and secondary health conditions.

OBJECTIVE

To evaluate the evidence concerning efficacy of aerobic exercise training for improving health and exercise performance in persons with tetraplegia from cervical injury.

METHODS

The search engines PubMed and Google Scholar were used to locate published research. The final 75 papers were selected on the basis of inclusion criteria. The studies were then rank-ordered using Physiotherapy Evidence Database.

RESULTS

Studies combining individuals with tetraplegia and paraplegia show that voluntary arm-crank training can increase mean peak power output by 33%. Functional electrical stimulation leg cycling was shown to induce higher peak cardiac output and stroke volume than arm-crank exercise. A range of peak oxygen uptake (VO_2peak) values have been reported (0.57-1.32 L/min). Both VO_2peak and cardiac output may be enhanced via increased muscle pump in the legs and venous return to the heart. Hybrid exercise (arm-crank and functional electrical stimulation leg cycling) can result in greater peak oxygen uptake and cardiovascular responses.

CONCLUSION

Evidence gathered from this systematic review of literature is inconclusive due to the lack of research focusing on those with tetraplegia. Higher power studies (level 1-3) are needed with the focus on those with tetraplegia.

Recovery Off-Kinetics Following Exhaustive Upper Body Exercise in Spinal Cord Injury

Background

People with spinal cord injury (SCI) present with impaired autonomic control when the lesion is above T6. This could lead to delayed cardiorespiratory recovery following vigorous physical activity.

Objectives

To characterize and compare gas exchange off-kinetics following exhaustive exercise in individuals with SCI and an apparently healthy control group.

Methods

Participants were 19 individuals with SCI who presented with the inability to voluntarily lift their legs against gravity (age, 44.6 ± 14.2 years; AIS A, n = 5; AIS B, n = 7; AIS C, n = 7; paraplegia, n = 14; tetraplegia, n = 5) and 10 healthy comparisons (COM; age, 30.5 ± 5.3 years). All participants performed an arm ergometer cardiopulmonary exercise test (aCPET) to volitional exhaustion followed by a 10-minute passive recovery. O₂ uptake (V̇o₂ ) and CO₂ output (V̇co₂ ) off-kinetics was examined using a mono-exponential model in which tau off (τ_off ) and mean response time (MRT) were determined. The off-kinetics transition constant (Kt_off ) was calculated as ΔV̇o₂ /MRT. Student t tests were used to compare SCI versus COM group means.

Results

COM had a significantly higher relative peak V̇o₂ compared to SCI (1.70 ± 0.55 L/min vs 1.19 ± 0.51 L/min, p = .019). No difference was observed for τ_off between the groups, however Kt_off for both V̇o₂ and V̇co₂ was significantly lower in the SCI compared to the COM group.

Conclusion

A reduced Kt_off during recovery may suggest inefficiencies in replenishing muscle ATP stores and lactate clearance in these participants with SCI. These findings may contribute to the observed lower cardiorespiratory fitness and greater fatigability typically reported in individuals with SCI.

Cardiac, Autonomic, and Cardiometabolic Impact of Exercise Training in Spinal Cord Injury: A QUALITATIVE REVIEW

INTRODUCTION

Direct and indirect effects of spinal cord injury lead to important cardiovascular (CV) complications that are further increased by years of injury and the process of "accelerated aging." The present review examines the current evidence in the literature for the potential cardioprotective effect of exercise training in spinal cord injury.

REVIEW METHODS

PubMed and Web of Science databases were screened for original studies investigating the effect of exercise-based interventions on aerobic capacity, cardiac structure/function, autonomic function, CV function, and/or cardiometabolic markers. We compared the effects in individuals <40 yr with time since injury <10 yr with those in older individuals (≥40 yr) with longer time since injury (≥10 yr), reasoning that the two can be considered individuals with low versus high CV risk factors.

SUMMARY

Studies showed similar exercise effects in both groups (n = 31 in low CV risk factors vs n = 15 in high CV risk factors). The evidence does not support any effect of exercise training on autonomic function but does support an increased peripheral blood flow, improved left ventricular mass, higher peak cardiac output, greater lean body mass, better antioxidant capacity, and improved endothelial function. In addition, some evidence suggests that it can result in lower blood lipids, systemic inflammation (interleukin-6, tumor necrosis factor α, and C-reactive protein), and arterial stiffness. Training intensity, volume, and frequency were key factors determining CV gains. Future studies with larger sample sizes, well-matched groups of subjects, and randomized controlled designs will be needed to determine whether high-intensity hybrid forms of training result in greater CV gains.

Energy Expenditure, Cardiorespiratory Fitness, and Body Composition Following Arm Cycling or Functional Electrical Stimulation Exercises in Spinal Cord Injury: A 16-Week Randomized Controlled Trial

Background: Physical deconditioning and inactivity following spinal cord injury (SCI) are associated with multiple cardiometabolic risks. To mitigate cardiometabolic risk, exercise is recommended, but it is poorly established whether arm cycling exercise (ACE) or functional electrical stimulation (FES) leg cycling yields superior benefits. Objectives: To determine the adaptations of 16 weeks of FES cycling and ACE on exercise energy expenditure (EEE), cardiorespiratory fitness (CRF), and obesity after SCI. Methods: Thirteen physically untrained individuals were randomly assigned to FES (n = 6) or ACE (n = 7) exercise 5 days/week for 16 weeks. Pre- and post-intervention EEE, peak oxygen consumption (absolute and relative VO2Peak), and work were assessed using indirect calorimetry, while body composition was measured by dual-energy x-ray absorptiometry. Results: Main effects were found for peak power (p < .001), absolute (p = .046) and relative (p = .042) VO2Peak, and peak work (p = .013). Compared to baseline, the ACE group increased in EEE (+85%, p = .002), peak power (+307%, p < .001), VO2Peak (absolute +21%, relative +22%, p ≤ .024), peak work (19% increase, p = .003), and total body fat decreased (-6%, p = .05). The FES group showed a decrease in percentage body fat mass (-5%, p = .008). The ACE group had higher EEE (p = .008), peak power (p < .001), and relative VO2Peak (p = .025) compared to postintervention values in the FES group. Conclusion: In the current study, ACE induced greater increases in EEE and CRF, whereas ACE and FES showed similar results on body fat. Exercise promotional efforts targeting persons with SCI should use both FES and ACE to reduce sedentary behavior and to optimize different health parameters after SCI.

Development of a battery-free ultrasonically powered functional electrical stimulator for movement restoration after paralyzing spinal cord injury

BACKGROUND

Functional electrical stimulation (FES) is used to restore movements in paretic limbs after severe paralyses resulting from neurological injuries such as spinal cord injury (SCI). Most chronic FES systems utilize an implantable electrical stimulator to deliver a small electric current to the targeted muscle or nerve to stimulate muscle contractions. These implanted stimulators are generally bulky, mainly due to the size of the batteries. Furthermore, these battery-powered stimulators are required to be explanted every few years for battery replacement which may result in surgical failures or infections. Hence, a wireless power transfer technique is desirable to power these implantable stimulators.

METHODS

Conventional wireless power transduction faces significant challenges for safe and efficient energy transfer through the skin and deep into the body. Inductive and electromagnetic power transduction is generally used for very short distances and may also interfere with other medical measurements such as X-ray and MRI. To address these issues, we have developed a wireless, ultrasonically powered, implantable piezoelectric stimulator. The stimulator is encapsulated with biocompatible materials.

RESULTS

The stimulator is capable of harvesting a maximum of 5.95 mW electric power at an 8-mm depth under the skin from an ultrasound beam with about 380 mW/cm2 of acoustic intensity. The stimulator was implanted in several paraplegic rats with SCI. Our implanted stimulator successfully induced several hindlimb muscle contractions and restored leg movement.

CONCLUSIONS

A battery-free miniature (10 mm diameter × 4 mm thickness) implantable stimulator, developed in the current study is capable of directly stimulating paretic muscles through external ultrasound signals. The required cost to develop the stimulator is relatively low as all the components are off the shelf.

The efficacy and prescription of neuromuscular electrical stimulation (NMES) in adult cancer survivors: a systematic review and meta-analysis

PURPOSE

This study aims to (1) summarise and critically evaluate the effects of neuromuscular electrical stimulation (NMES) on indices of health and quality of life (QoL) in adult cancer survivors, (2) assess the safety of NMES as a rehabilitation method in this population, and (3) identify commonly used NMES treatment parameters and describe treatment progression.

METHODS

A systematic search of four electronic databases targeted studies evaluating the effects of NMES on physical function, aerobic fitness, muscle strength, body composition, and health-related quality of life (HR-QoL) in adult cancer survivors, published through March 2018. Two reviewers independently reviewed and appraised the risk of bias of each study.

RESULTS

Nine studies were included. Meta-analyses found that the overall pooled effect favoured NMES for improving muscle strength, but the standardised mean difference was not significant (0.36; 95% CI - 0.25, 0.96). Further meta-analyses indicated that NMES significantly improved HR-QoL (0.36; 95% CI 0.10, 0.62), with notable gains identified under the subcategories QoL Function (0.87; 95% CI 0.32, 1.42). Current NMES prescription is not standardised and NMES is prescribed to target secondary complications of treatment. Risk of bias was high for most studies.

CONCLUSIONS

NMES use in adult cancer survivors is an emerging field and current literature is limited by studies of poor quality and a lack of adequately powered RCTs. Existing evidence suggests that NMES is safe and may be more effective than usual care for improving HR-QoL. Prescription and progression should be tailored for the individual based on functional deficits.

Reliability of measurements for sub-painful and painful perception on artificial electrical stimulations

Artificial electrical stimulation is a common type of stimulus to induce sub-painful and painful sensation in clinical or neuroscience experiments. The Numerical Rating Scale (NRS) is often used to evaluate subjective perception due to external stimulations. Yet the relationship between the intensity levels of electrical stimulations and self-perception has seldom been examined. The aim of the study was to obtain evidence on the reliability and accuracy of sub-painful and painful perceptions of healthy participants using the NRS under different levels of electrical stimulus. A total of 72 pain-free healthy volunteers (female=44) were recruited. In the first experiment, each participant was given different levels of a non-nociceptive or nociceptive electrical stimulus and then asked to give a perception rating based on an 11-point NRS. In the second experiment, each participant was asked to memorize 5 levels of sub-nociceptive or nociceptive stimuli and to recognize the level of stimulus given each time. For the NRS rating task, intraclass coefficients (ICCs) reached satisfactory level for sub-nociceptive (0.85<ICC<0.93) and nociceptive stimulation (0.90<ICC<0.96). The ICCs were the highest for the weakest sub-nociceptive and nociceptive stimuli. For the stimulus recognition task, accuracy was also found to be highest for the weakest sub-nociceptive stimulus (κ=0.67) and lowest for the strongest nociceptive stimulus (κ=0.34). The results suggest that, with adequate training, NRS can be a reliable measurement tool for both sub-painful and painful rating due to electrical stimulation.

An Energetic Model of Low Frequency Isometric Neuromuscular Electrical Stimulation

The objective of this study was to evaluate whether an adapted Hill-type model of muscle energetics could account for the relatively high energy turnover observed during low frequency isometric Neuromuscular Electrical Stimulation (NMES). A previously validated Hill-based model was adapted to estimate the energy consumption due to muscle activation, force maintenance and internal shortening of the muscle during isometric NMES. Quadriceps muscle model parameters were identified for 10 healthy subjects based on the experimentally measured torque response to isometric stimulation at 8 Hz. Model predictions of torque and energy consumption rates across the stimulation range 1-12 Hz were compared with experimental data recorded from the same subjects. The model provided estimates in close agreement with the experimental values for the group mean energy consumption rate across the frequency range tested, (R adj (2) = 0.98), although prediction of individual data points for all frequencies and all subjects was more variable, (R adj (2) = 0.70). The model suggests that approximately one-third of the energy between 4 and 6 Hz is due to shortening heat. The model provides a means of identifying optimal therapeutic stimulation patterns for sustained incremental oxygen uptake at minimum torque output for a given muscle and provides insight into the energetic components involved.

The reliability of hand-held dynamometry for strength assessment during electrically induced muscle contractions

OBJECTIVES

To determine inter- and intra-tester reliability of strength measurements during maximal electrically induced contractions (MEIC) using a hand-held dynamometer (HHD).

METHODS

Thirty-seven healthy young female adults, mean age (SD) 23.4 (2.4) years, were tested by two examiners during two sessions, with order of examiners randomized. Biphasic pulses (phase duration--300 µs; pulse frequency--75 Hz) were employed in order to induce contractions of the quadriceps femoris muscle at a maximally tolerated current level. Strength of maximal voluntary isometric contractions (MVIC) and of MEIC was recorded with a HHD utilizing a stabilization belt.

RESULTS

Good to excellent inter- and intra-tester reliability were determined with intra-class correlation coefficients ranging between 0.8 and 0.9, and no bias in the Bland-Altman plots. The 95% repeatability ranged between 8.7 and 13.0 kg for the MVIC and MEIC, and between 20.7 and 25.6% for the % MVIC.

CONCLUSION

Our results confirm previous findings indicating good to excellent reliability of quadriceps femoris muscle MVIC assessment with a HHD. However, a high 95% repeatability range indicates the HHD is not sufficiently reliable as an indicator of the force level attained during electrically induced contractions. Other methods need to be investigated to assist in determining whether MEIC have reached therapeutic levels.

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.

Whole body oxygen uptake and evoked torque during subtetanic isometric electrical stimulation of the quadriceps muscles in a single 30-minute session

OBJECTIVE

To evaluate the time course of fatigue in torque output and oxygen uptake during isometric subtetanic neuromuscular electrical stimulation (NMES) to facilitate the design of NMES-based rehabilitation protocols that can accumulate a defined aerobic exercise volume within a given time period.

DESIGN

Single-arm intervention study with within-subject comparisons.

SETTING

University research laboratory.

PARTICIPANTS

Volunteer sample of healthy men (N=11; mean age, 34.2 ± 11.5 y; range, 19-53 y; body mass, 79.1 ± 11.7 kg; range, 58-100 kg).

INTERVENTION

A single 30-minute session of continuous bilateral isometric quadriceps NMES at 4 Hz evoking a mean twitch amplitude of 12% of the maximum voluntary contraction.

MAIN OUTCOME MEASURES

Whole body oxygen consumption rate (V˙o2), and evoked torque were measured simultaneously throughout.

RESULTS

Mean increment in V˙o2 was 596 ± 238 mL/min, and average exercise intensity during the session was 3 ±.47 metabolic equivalents. The V˙o2 and torque declined slowly at a rate of -.54%±.31% and -.47%±.57% per minute, respectively.

CONCLUSIONS

Despite having a higher incremental V˙o2, the observed fatigue rate was considerably less than that previously reported during intermittent isometric tetanic stimulation, suggesting that subtetanic isometric NMES is more sustainable for exercise interventions aimed at accumulating a therapeutic aerobic exercise volume.

Low force contractions induce fatigue consistent with muscle mRNA expression in people with spinal cord injury

Spinal cord injury (SCI) is associated with muscle atrophy, transformation of muscle fibers to a fast fatigable phenotype, metabolic inflexibility (diabetes), and neurogenic osteoporosis. Electrical stimulation of paralyzed muscle may mitigate muscle metabolic abnormalities after SCI, but there is a risk for a fracture to the osteoporotic skeletal system. The goal of this study was to determine if low force stimulation (3 Hz) causes fatigue of chronically paralyzed muscle consistent with selected muscle gene expression profiles. We tested 29 subjects, nine with a SCI and 20 without and SCI, during low force fatigue protocol. Three SCI and three non-SCI subjects were muscle biopsied for gene and protein expression analysis. The fatigue index (FI) was 0.21 ± 0.27 and 0.91 ± 0.01 for the SCI and non-SCI groups, respectively, supporting that the low force protocol physiologically fatigued the chronically paralyzed muscle. The post fatigue potentiation index (PI) for the SCI group was increased to 1.60 ± 0.06 (P <0.001), while the non-SCI group was 1.26 ± 0.02 supporting that calcium handling was compromised with the low force stimulation. The mRNA expression from genes that regulate atrophy and fast properties (MSTN, ANKRD1, MYH8, and MYCBP2) was up regulated, while genes that regulate oxidative and slow muscle properties (MYL3, SDHB, PDK2, and RyR1) were repressed in the chronic SCI muscle. MSTN, ANKRD1, MYH8, MYCBP2 gene expression was also repressed 3 h after the low force stimulation protocol. Taken together, these findings support that a low force single twitch activation protocol induces paralyzed muscle fatigue and subsequent gene regulation. These findings suggest that training with a low force protocol may elicit skeletal muscle adaptations in people with SCI.

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.