Pilot randomized trial of progressive resistance exercise augmented by neuromuscular electrical stimulation for people with multiple sclerosis who use walking aids.

OBJECTIVE: To investigate the feasibility and preliminary outcomes of a home progressive resistance training (PRT) program augmented by neuromuscular electrical stimulation (NMES). DESIGN: Randomized controlled pilot trial. SETTING: Participant homes. PARTICIPANTS: People with multiple sclerosis (MS) (N=37) who use a walking aid. INTERVENTIONS: A 12-week home PRT program or the same program augmented by NMES. MAIN OUTCOME MEASURES: Strength using hand-held dynamometry; repeated sit to stand test; Berg Balance Scale; timed Up & Go test; 12-Item Multiple Sclerosis Walking Scale; Multiple Sclerosis Impact Scale-29, version 2; and Modified Fatigue Impact Scale (MFIS). The NMES group also completed a device usability questionnaire. RESULTS: Only change in MFIS score was significantly greater in the NMES group than the PRT group (P=.012). The NMES group improved significantly in quadriceps endurance (median of change, 8.5; P=.043), balance (median of change, 3.5; P=.001), physical impact of MS (median of change, -8.3; P=.001), and impact of fatigue (median of change, -17; P=.001). Participants rated the device as highly usable. CONCLUSIONS: This pilot study suggests that a home PRT program with NMES is feasible, and the neuromuscular electrical stimulation device is usable by this population. Only reduction in impact of fatigue was greater in the NMES than the PRT group.

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.

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.

Neuromuscular electrical stimulation can elicit aerobic exercise response without undue discomfort in healthy physically active adults.

Recent studies have suggested that subtetanic neuromuscular electrical stimulation (NMES) protocols applied to the quadriceps and hamstrings may have potential as an alternative aerobic exercise modality. However, its tolerability and effectiveness in the physically active population has been questioned. The primary purpose of this study was to measure physiological and subjective responses to a modified subtetanic NMES protocol in a physically active adult population. Furthermore, the effect of habituation to stimulation on tolerability, the repeatability of response on separate days, and the differences in male and female responses to stimulation were assessed. Oxygen uptake (V[Combining Dot Above]O(2)), heart rate (HR), blood lactate (BLa), rate of perceived exertion, and subjective discomfort were measured in 16 participants (8 men and 8 women) throughout a subtetanic NMES protocol performed at incremental intensities to subjective comfort threshold on 2 separate days, before and after 9 NMES habituation sessions. Peak physiological responses observed at subjective comfort threshold were consistent with therapeutic aerobic exercise intensities (51.5 ± 10.9% V[Combining Dot Above]O(2)max; 72.0 ± 10.9% HRmax; 4.7 ± 2.7 mMol BLa). Peak V[Combining Dot Above]O(2) and current intensity achieved were significantly higher (p < 0.05), yet perceived discomfort was unchanged, after the period of habituation. However, physiological and subjective responses at equivalent stimulation intensities remained unchanged on different days. Male participants showed higher values than female participants. These results suggest that subtetanic NMES can elicit a consistent aerobic exercise response without undue discomfort and could be considered as an alternative exercise modality.

Design considerations for the development of neuromuscular electrical stimulation (NMES) exercise in cancer rehabilitation.

AIM: The aim of this narrative review is to explore design considerations for effective neuromuscular electrical stimulation exercise prescription in cancer rehabilitation, with simultaneous consideration for fundamental principles of exercise training and the current state of the art in neuromuscular electrical stimulation technologies and application methodologies. METHOD: Narrative review. RESULTS: First, we consider the key neuromuscular electrical stimulation exercise design considerations, with a focus on training objectives and individual training requirements and constraints for individuals with cancer. Here, we contend that concurrent, low and high frequency neuromuscular electrical stimulation exercise, individually prescribed and progressed may be optimal for enhancing physical function. Second, we review the appropriate literature to identify the most appropriate stimulation parameters (pulse frequency, intensity, duration and duty cycle) to deliver effective neuromuscular electrical stimulation in cancer rehabilitation. CONCLUSIONS: We propose an informed and innovative neuromuscular electrical stimulation exercise intervention design and provide practical information for clinicians and practitioners who may work with and implement neuromuscular electrical stimulation exercise in cancer.Implications for rehabilitationNeuromuscular electrical stimulation is an emerging technology in cancer rehabilitation to help provide an aerobic and muscle strengthening exercise stimulus.Neuromuscular electrical stimulation may help improve aerobic exercise capacity, muscle strength and augment quality of life.Current prescription in cancer lacks adherence to the fundamental principles of exercise training, which may negatively affect adherence.

Transcutaneous spinal cord stimulation and motor responses in individuals with spinal cord injury: A methodological review.

BACKGROUND: Transcutaneous spinal cord stimulation (tSCS) is a non-invasive modality in which electrodes can stimulate spinal circuitries and facilitate a motor response. This review aimed to evaluate the methodology of studies using tSCS to generate motor activity in persons with spinal cord injury (SCI) and to appraise the quality of included trials. METHODS: A systematic search for studies published until May 2021 was made of the following databases: EMBASE, Medline (Ovid) and Web of Science. Two reviewers independently screened the studies, extracted the data, and evaluated the quality of included trials. The electrical characteristics of stimulation were summarised to allow for comparison across studies. In addition, the surface electromyography (EMG) recording methods were evaluated. RESULTS: A total of 3753 articles were initially screened, of which 25 met the criteria for inclusion. Studies were divided into those using tSCS for neurophysiological investigations of reflex responses (n = 9) and therapeutic investigations of motor recovery (n = 16). The overall quality of evidence was deemed to be poor-to-fair (10.5 ± 4.9) based on the Downs and Black Quality Checklist criteria. The electrical characteristics were collated to establish the dosage range across stimulation trials. The methods employed by included studies relating to stimulation parameters and outcome measurement varied extensively, although some trends are beginning to appear in relation to electrode configuration and EMG outcomes. CONCLUSION: This review outlines the parameters currently employed for tSCS of the cervicothoracic and thoracolumbar regions to produce motor responses. However, to establish standardised procedures for neurophysiological assessments and therapeutic investigations of tSCS, further high-quality investigations are required, ideally utilizing consistent electrophysiological recording methods, and reporting common characteristics of the electrical stimulation administered.

A performance comparison of neuromuscular electrical stimulation protocols for isolated quadriceps contraction versus co-contraction of quadriceps and hamstrings.

A Neuromuscular Electrical Stimulation (NMES) protocol that incorporates co-contraction of the quadriceps and hamstrings may provide greater functional benefits for knee rehabilitation. It is unclear if the addition of a co-contraction will affect the desired torque outputs of one or two of the involved muscle groups. Due to the proposed functional benefits of co-contraction, it may be beneficial to test the addition of a co-contraction electrical muscle stimulation. In this study we recruited 14 participants with whom we compared two NMES protocols; isolated quadriceps contraction (k-NMES) versus co-contraction of quadriceps and hamstrings (co-NMES). We examined peak knee extension evoked torque, current intensities required to produce given torque outputs, and self-reported discomfort levels at given torques. At maximum tolerable intensity peak torque output was similar in k-NMES versus co-NMES. To achieve specific submaximal levels of torque output as percentages of maximum voluntary contraction (MVC), a higher current intensity was required for co-NMES yet with no greater level of discomfort. Results suggest that clinicians who wish to achieve a co-contraction of quadriceps and hamstrings as part of a rehabilitation programme can use co-NMES without having to sacrifice the strength of contraction achieved in the quadriceps. This could lead to better functional outcomes, though more work is required to confirm this.

Self directed home based electrical muscle stimulation training improves exercise tolerance and strength in healthy elderly.

Advancing age is associated with a gradual decline in muscle strength, exercise tolerance and subsequent capacity for activities of daily living. It is important that we develop effective strategies to halt this process of gradual decline in order to enhance functional ability and capacity for independent living. To achieve this, we must overcome the challenge of sustaining ongoing engagement in physical exercise programmes in the sedentary elderly population, particularly those who experience barriers to exercise participation. Recent developments in electrical muscle stimulation technology could provide a potential solution. In this pilot case-control study we investigated the effects of a self-directed home based programme of electrical muscle stimulation training on muscle strength and exercise tolerance in a group of 16 healthy elderly volunteers (10f, 6m). Study participants completed 30 separate 1-hour electrical muscle stimulation sessions at home over a 6-week period. We observed significant improvements in quadriceps muscle strength and 6-minute walk distance, suggesting that this form of electrical muscle stimulation training has promise as an exercise modality in the elderly population.

The effectiveness of supplementing a standard rehabilitation program with superimposed neuromuscular electrical stimulation after anterior cruciate ligament reconstruction: a prospective, randomized, single-blind study.

BACKGROUND: Rehabilitation after anterior cruciate ligament reconstruction is a key determinant affecting patient return to usual activity levels. Neuromuscular electrical stimulation is a treatment that can counteract strength loss and serve as an adjunct to conventional therapy. PURPOSE: To compare the effect of adding traditional neuromuscular electrical stimulation (Polystim) or a novel garment-integrated neuromuscular electrical stimulation (Kneehab) to a standard postoperative rehabilitation program (control). STUDY DESIGN: Randomized controlled trial; Level of evidence, 1. METHODS: Ninety-six patients, of a total enrolled cohort of 131 patients randomized to 1 of 3 intervention groups, completed a standard rehabilitation program. In addition, the 2 neuromuscular electrical stimulation groups underwent 20-minute sessions of neuromuscular electrical stimulation 3 times a day, 5 days a week, for 12 weeks, in which stimulation was superimposed on isometric volitional contractions. Outcome measures including isokinetic strength of the knee extensors of the injured and uninjured leg at 90 and 180 deg/s, along with functional tests of proprioception, were assessed at baseline and at 6 weeks, 12 weeks, and 6 months postoperatively. RESULTS: The Kneehab group achieved significantly better results at each time point compared with the Polystim and control groups (P < .001). Extensor strength of the Kneehab group at speeds of 90 and 180 deg/s increased by 30.2% and 27.8%, respectively, between the preoperative measurements and the 6-month follow-up point in the injured leg. The corresponding changes for Polystim were 5.1% and 5%, whereas for the control group they were 6.6% and 6.7%, respectively. The mean single-legged hop test hop score of the Kneehab group improved by 50% between the 6-week and 6-month follow-up, whereas the corresponding changes for the Polystim and control groups were 26.3% and 26.2%, respectively. Although there was no significant difference between the groups with respect to the Tegner score and the International Knee Documentation Committee 2000 knee examination score, the Kneehab group showed a significant difference in mean improvement for the baseline corrected Lysholm score compared with the control group (P = .01; 95% confidence interval, 1.12-8.59) and with the Polystim group (P < .001; 95% confidence interval, 1.34-9.09) with no significant difference evident between Polystim and control groups (P = .97; 95% confidence interval, -4.23 to 3.51). CONCLUSION: Intensive garment-integrated stimulation combined with standard rehabilitation is effective at accelerating recovery after knee surgery.

Clinical application of neuromuscular electrical stimulation induced cardiovascular exercise.

We need to find novel ways of increasing exercise participation, particularly in those populations who find it difficult to participate in voluntary exercise. In recent years researchers have started to investigate the potential for using electrical stimulation to artificially stimulate a pattern of muscle activity that would induce a physiological response consistent with cardiovascular exercise. Work to date has indicated that this is best achieved by using a stimulation protocol that results in rapid rhythmical isometric contractions of the large leg muscle groups at sub tetanic frequencies. Studies completed by our group indicate that this technique can serve as a viable alternative to voluntary cardiovascular exercise. Apart from being able to induce a cardiovascular exercise effect in patient populations (e.g. heart failure, COPD, spinal cord injury, obesity), this approach may also have value in promotion of exercise activity in a microgravity environment.

Neuromuscular electrical stimulation training results in enhanced activation of spinal stabilizing muscles during spinal loading and improvements in pain ratings.

Low back pain is associated with dysfunction in recruitment of muscles in the lumbopelvic region. Effective rehabilitation requires preferential activation of deep stabilizing muscle groups yet training these muscles poses challenges in a clinical setting. This study was carried out in order to quantify the response of deep stabilizing muscles (transverses abdominis and deep fibres of multifidus) to a period of training using a novel neuromuscular electrical stimulation (NMES) application in a group of patients with chronic low back pain. Analysis of results revealed clinically and statistically significant improvements in indicators of both muscle groups' performance, as evidenced by ultrasound evaluation of activation during voluntary activity. These improvements were associated with significant improvements in self reported pain levels, suggesting that NMES has an important role to play in CLBP rehabilitation.

Effect of subcutaneous fat thickness and surface electrode configuration during neuromuscular electrical stimulation.

The effect of subcutaneous fat thickness, electrode size and inter-electrode distance on the minimum stimulus current necessary for fiber excitation was examined in an attempt to improve the efficacy of neuromuscular electrical stimulation (NMES) in obese populations. A three-dimensional finite element model of the human thigh was developed and used to calculate the potential along a myelinated nerve fiber due to NMES. The activating function was used to examine alterations in the excitation of the fiber due to fat thickness, electrode size and inter-electrode distance. The finite element model was coupled to a neural model to examine the stimulus current required for action potential propagation. The stimulus current required to evoke 10% of the maximum M-wave amplitude was measured experimentally. Both experimental and modeling studies indicated that the stimulus current required to reach the threshold for muscle activation increased with fat thickness, electrode size, and inter-electrode distance. However, as fat thickness increased, the threshold for muscle activation became less sensitive to inter-electrode distance and electrode size. These results suggest that by using larger electrodes above regions of high subcutaneous fat thickness, the efficacy of NMES could be maintained while reducing the current density at the skin and the associated subject discomfort.

Neuro-muscular electrical stimulation training enhances maximal aerobic capacity in healthy physically active adults.

Previous research has shown that a novel form of neuro-muscular electrical stimulation (NMES) can be used to bring about aerobic training effects in sedentary adults and in patients with heart failure. However, it is not clear whether this form of NMES could induce a significantly strong cardiovascular exercise effect in a more active group where a greater stimulus is required for training. In this study we investigated the aerobic training effects of repeated exposure to low frequency NMES in a group of physically active healthy adults. Results demonstrated a clinically and statistically significant training response following 18 trainings sessions, suggesting that this form of NMES has a role to play in cardiovascular exercise training in a physically active healthy population.

Electrical muscle stimulation for deep stabilizing muscles in abdominal wall.

Low back pain is associated with dysfunction in recruitment of muscles in the lumbopelvic region. Effective rehabilitation requires preferential activation of deep stabilizing muscle groups. This study was carried out in order to quantify the response of deep stabilizing muscles (transverses abdominis) and superficial muscle in the abdominal wall (external oblique) to electrical muscle stimulation (EMS). Results demonstrate that EMS can preferentially stimulate contractions in the deep stabilizers and may have significant potential as a therapeutic intervention in this area, pending further refinements to the technology.

The effect of subcutaneous fat thickness on the efficacy of transcutaneous electrical stimulation.

Transcutaneous electrical stimulation is a widely used technique to relieve the symptoms of various neuromuscular disorders and to improve muscle strength. It is currently being investigated in the treatment of obesity to physically enable and encourage increased levels of voluntary exercise. Due to the high resistivity of subcutaneous fat tissue, higher stimulus currents are required to evoke muscle contraction in obese subjects than in subjects of a healthy weight, which can lead to patient discomfort. In this study, a three-dimensional finite element model of the human thigh, including skin, fat, muscle and bone, was developed to examine the relationship between fat thickness and evoked muscle activation. The effects of fat thickness, electrode size and inter-electrode distance on the activating function were investigated during monopolar and bipolar stimulation. The amplitude of the activating function was found to reduce as electrode size increased, however, this effect was relatively less at higher fat thicknesses. The activating function was also less sensitive to inter-electrode distance as fat thickness increased. These results indicate that by increasing electrode size, the current density at the skin surface can be reduced, thereby reducing patient discomfort while maintaining the efficacy of the electrical stimulation in obese patient populations.

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.