Changes in neuromuscular function after training by functional electrical stimulation

Effect of electrical stimulation training and detraining on abdominal muscle function

BACKGROUND

Electrical muscle stimulation (EMS) has been applied in many rehabilitation settings for muscle strengthening, facilitation of muscle contraction, re-education of muscle action, and maintenance of muscle strength and size during prolonged immobilization.

OBJECTIVE

The purpose of this study was to investigate effect of 8 weeks of EMS training on abdominal muscle function and to determine whether the training effect could be maintained after 4 weeks of EMS detraining.

METHODS

Twenty-five subjects performed EMS training for 8 weeks. Before and after 8 weeks of EMS training, and after 4 weeks of EMS detraining, muscle size (cross-sectional area [CSA] of the rectus abdominals [RA] and lateral abdominal wall [LAW]), strength, endurance, and lumbopelvic control (LC) were measured.

RESULTS

There were significant increases in CSA [RA (p< 0.001); LAW (p< 0.001)], strength [trunk flexor (p= 0.005); side-bridge (p< 0.05)], endurance [trunk flexor (p= 0.010); side-bridge (p< 0.05)], and LC (p< 0.05) after 8 weeks of EMS training. The CSA of the RA (p< 0.05) and the LAW (p< 0.001) were measured after 4 weeks of detraining and they were greater than that of the baseline. There were no significant differences in abdominal strength, endurance, and LC between baseline measurements and post-detraining.

CONCLUSION

The study indicates that there is less of a detraining effect on muscle size than on muscle strength, endurance, and LC.

A Prediction Model for Various Treatment Pathways of Upper Extremity in Tetraplegia

Upper extremity function is essential for the autonomy in patients with cervical spinal cord injuries and consequently a focus of the rehabilitation and treatment efforts. Routinely, an individualized treatment plan is proposed to the patient by an interprofessional team. It dichotomizes into a conservative and a surgical treatment pathway. To select an optimal pathway, it is important to define predictors that substantiate the treatment strategy. Apart from standard assessments (Standards for Neurological Classification of Spinal Cord Injury (ISNCSCI), the manual muscle test (MRC), and lower motoneuron integrity of key actuators for hand function performed by motor point (MP) mapping might serve as a possible predictor. Type of damage (upper motor neuron (UMN) or lower motor neuron (LMN) lesion) influences hand posture and thus treatment strategy as positioning and splinting of fingers, hands, arms, and surgical reconstructive procedures (muscle-tendon or nerve transfers) in choice and timing of intervention. For this purpose, an analysis of a database comprising 220 patients with cervical spinal cord injury is used. It includes ISNCSCI, MRC, and MP mapping of defined muscles at selected time points after injury. The ordinal regression analysis performed indicates that MP and ASIA impairment scale (AIS) act as predictors of muscle strength acquisition. In accordance with the innervation status defined by MP, electrical stimulation (ES) is executed either via nerve or direct muscle stimulation as a supplementary therapy to the traditional occupational and physiotherapeutic treatment methods. Depending on the objective, ES is applied for motor learning, strengthening, or maintenance of muscle contractile properties. By employing ES, hand and arm function can be predicted by MP and AIS and used as the basis for providing an individualized treatment plan.

A scoping review of the contralateral effects of unilateral peripheral stimulation on neuromuscular function

It is known that resistance exercise using one limb can affect motor function of both the exercised limb and the unexercised contralateral limb, a phenomenon termed cross-education. It has been suggested that cross-education has clinical implications, e.g. in rehabilitation for orthopaedic conditions or post-stroke paresis. Much of the research on the contralateral effect of unilateral intervention on motor output is based on voluntary exercise. This scoping review aimed to map the characteristics of current literature on the cross-education caused by three most frequently utilised peripheral neuromuscular stimulation modalities in this context: electrical stimulation, mechanical vibration and percutaneous needling, that may direct future research and translate to clinical practice. A systematic search of relevant databases (Ebsco, ProQuest, PubMed, Scopus, Web of Science) through to the end of 2020 was conducted following the PRISMA Extension for Scoping Review. Empirical studies on human participants that applied a unilateral peripheral neuromuscular stimulation and assessed neuromuscular function of the stimulated and/or the unstimulated side were selected. By reading the full text, the demographic characteristics, context, design, methods and major findings of the studies were synthesised. The results found that 83 studies were eligible for the review, with the majority (53) utilised electrical stimulation whilst those applied vibration (18) or needling (12) were emerging. Although the contralateral effects appeared to be robust, only 31 studies claimed to be in the context of cross-education, and 25 investigated on clinical patients. The underlying mechanism for the contralateral effects induced by unilateral peripheral stimulation remains unclear. The findings suggest a need to enhance the awareness of cross-education caused by peripheral stimulation, to help improve the translation of theoretical concepts to clinical practice, and aid in developing well-designed clinical trials to determine the efficacy of cross-education therapies.

Effects of Various Physical Interventions on Reducing Neuromuscular Fatigue Assessed by Electromyography: A Systematic Review and Meta-Analysis

Introduction: Various interventions have been applied to improve recovery from muscle fatigue based on evidence from subjective outcomes, such as perceived fatigue and soreness, which may partly contribute to conflicting results of reducing muscle fatigue. There is a need to assess the effectiveness of various intervention on reducing neuromuscular fatigue assessed by a quantitative outcome, such as electromyography (EMG). The objective of this review and meta-analysis was to evaluate the effectiveness of different interventions and intervention timing for reducing fatigue rates during exercise. Methods: The literature was searched from the earliest record to March 2021. Eighteen studies with a total of 87 data points involving 281 participants and seven types of interventions [i.e., active recovery (AR), compression, cooling, electrical stimulation (ES), light-emitting diode therapy (LEDT), massage, and stretching] were included in this meta-analysis. Results: The results showed that compression (SMD = 0.28; 95% CI = -0.00 to 0.56; p = 0.05; I ² = 58%) and LEDT (SMD = 0.49; 95% CI = 0.11 to 0.88; p = 0.01; I ² = 52%) have a significant recovery effect on reducing muscle fatigue. Additionally, compression, AR, and cooling have a significant effect on reducing muscle fatigue when conducted during exercise, whereas a non-effective trend when applied after exercise. Discussion: This meta-analysis suggests that compression and LEDT have a significant effect on reducing muscle fatigue. The results also suggest that there is a significant effect or an effective trend on reducing muscle fatigue when compression, AR, cooling, and ES are applied during exercise, but not after exercise.

Muscle Hypertrophy and Architectural Changes in Response to Eight-Week Neuromuscular Electrical Stimulation Training in Healthy Older People

Loss of muscle mass of the lower limbs and of the spine extensors markedly impairs locomotor ability and spine stability in old age. In this study, we investigated whether 8 w of neuromuscular electrical stimulation (NMES) improves size and architecture of the lumbar multifidus (LM) and vastus lateralis (VL) along with locomotor ability in healthy older individuals. Eight volunteers (aged 65 ≥ years) performed NMES 3 times/week. Eight sex- and age-matched individuals served as controls. Functional tests (Timed Up and Go test (TUG) and Five Times Sit-to-Stand Test (FTSST)), VL muscle architecture (muscle thickness (MT), pennation angle (PA), and fiber length (FL)), along with VL cross-sectional area (CSA) and both sides of LM were measured before and after by ultrasound. By the end of the training period, MT and CSA of VL increased by 8.6% and 11.4%, respectively. No significant increases were observed in FL and PA. LM CSA increased by 5.6% (left) and 7.1% (right). Interestingly, all VL architectural parameters significantly decreased in the control group. The combined NMES had a large significant effect on TUG (r = 0.50, p = 0.046). These results extend previous findings on the hypertrophic effects of NMES training, suggesting to be a useful mean for combating age-related sarcopenia.

Impact of transcutaneous neuromuscular electrical stimulation or resistance exercise on skeletal muscle mRNA expression in COPD

Background: Voluntary resistance exercise (RE) training increases muscle mass and strength in patients with chronic obstructive pulmonary disease (COPD). Nonvolitional transcutaneous neuromuscular electrical stimulation (NMES) may be an alternative strategy for reducing ambulatory muscle weakness in patients unable to perform RE training, but little comparative data are available. This study, therefore, investigated changes in muscle mRNA abundance of a number of gene targets in response to a single bout of NMES compared with RE. Methods: Twenty-six patients with stable COPD (15 male; FEV₁, 43±18% predicted; age, 64±8 years; fat free mass index, 16.6±1.8 kg/m²) undertook 30 minutes of quadriceps NMES (50 Hz, current at the limit of tolerance) or 5×30 maximal voluntary isokinetic knee extensions. Vastus lateralis muscle biopsies were obtained at rest immediately before and 24 hours after intervention. Expression of 384 targeted mRNA transcripts was assessed by real time TaqMan PCR. Significant change in expression from baseline was determined using the ΔΔC_T method with a false discovery rate (FDR) of <5%. Results: NMES and RE altered mRNA abundance of 18 and 68 genes, respectively (FDR <5%), of which 14 genes were common to both interventions and of the same magnitude of fold change. Biological functions of upregulated genes included inflammation, hypertrophy, muscle protein turnover, and muscle growth, whilst downregulated genes included mitochondrial and cell signaling functions. Conclusions: Compared with NMES, RE had a broader impact on mRNA abundance and, therefore, appears to be the superior intervention for maximizing transcriptional responses in the quadriceps of patients with COPD. However, if voluntary RE is not feasible in a clinical setting, NMES by modifying expression of genes known to impact upon muscle mass and strength may have a positive influence on muscle function.

Influence of Elbow Flexion and Stimulation Site on Neuromuscular Electrical Stimulation of the Biceps Brachii

Functional electrical stimulation (FES) can help individuals with physical disabilities by assisting limb movement; however, the change in muscle geometry associated with limb movement may affect the response to stimulation. The aim of this paper was to quantify the effects of elbow flexion and stimulation site on muscle torque production. Contraction torque about the elbow was measured in 12 healthy individuals using a custom elbow flexion testbed and a transcutaneous electrode array. Stimulation was delivered to six distinct sites along the biceps brachii over 11 elbow flexion angles. Flexion angle was found to significantly influence the optimal (i.e., torque-maximizing) stimulation site ( ), with post hoc analysis indicating a proximal shift in optimal stimulation site with increased flexion. Similarly, the biceps stimulation site was found to significantly influence the flexion angle at which peak torque occurred ( ), with post hoc analysis indicating an increase in peak-torque flexion angle as stimulation site is moved proximally up the biceps. Since maximizing muscle force per unit stimulation is a common goal in rehabilitative FES, future efforts could examine methods which compensate for the shift in optimal stimulation site during FES-induced limb movement.

Effects of electrical muscle stimulation early in the quadriceps and tibialis anterior muscle of critically ill patients

BACKGROUND

Electrical muscle stimulation (EMS) is applied to critically ill patients in order to improve their muscle strength, thereby preventing hypotrophy and promoting functional recovery.

OBJECTIVE

To assess the effects of early EMS on the range of movement of the ankle joint, and on thigh and leg circumference in critically ill patients.

METHODS

This is a prospective randomized clinical trial comprising 11 patients undergoing mechanical ventilation. Before and after EMS the thigh and leg circumference in both lower limbs and the goniometry of the tibiotarsal joint were measured. The angle of 90° on the goniometer was taken as the standard neutral position (NP), with the arm fixed on the lateral malleolus of the ankle joint. Other measurements, namely dorsiflexion and plantar flexion, referred to as mobile arm, were taken from the NP. These recordings were obtained following an active contraction of the patients' muscles.

RESULTS

Compared with the electrostimulated limb, a difference in dorsiflexion of the control limb was observed (96.2 ± 24.9 versus 119.9 ± 14.1°; p = 0.01). A girth of 10 cm of the leg was found in limb reduction when compared to the electrostimulated one (24.7 ± 3.1 versus 26.4 ± 4.0 cm; p = 0.03).

CONCLUSIONS

EMS used at low current intensity and for a short duration failed to prevent muscle atrophy in critically ill patients. However, we did find a significant improvement in active dorsiflexion of the ankle joint suggesting that it could help to prevent against stance plantar flexion in these patients.

An official American Thoracic Society/European Respiratory Society statement: key concepts and advances in pulmonary rehabilitation

BACKGROUND

Pulmonary rehabilitation is recognized as a core component of the management of individuals with chronic respiratory disease. Since the 2006 American Thoracic Society (ATS)/European Respiratory Society (ERS) Statement on Pulmonary Rehabilitation, there has been considerable growth in our knowledge of its efficacy and scope.

PURPOSE

The purpose of this Statement is to update the 2006 document, including a new definition of pulmonary rehabilitation and highlighting key concepts and major advances in the field.

METHODS

A multidisciplinary committee of experts representing the ATS Pulmonary Rehabilitation Assembly and the ERS Scientific Group 01.02, "Rehabilitation and Chronic Care," determined the overall scope of this update through group consensus. Focused literature reviews in key topic areas were conducted by committee members with relevant clinical and scientific expertise. The final content of this Statement was agreed on by all members.

RESULTS

An updated definition of pulmonary rehabilitation is proposed. New data are presented on the science and application of pulmonary rehabilitation, including its effectiveness in acutely ill individuals with chronic obstructive pulmonary disease, and in individuals with other chronic respiratory diseases. The important role of pulmonary rehabilitation in chronic disease management is highlighted. In addition, the role of health behavior change in optimizing and maintaining benefits is discussed.

CONCLUSIONS

The considerable growth in the science and application of pulmonary rehabilitation since 2006 adds further support for its efficacy in a wide range of individuals with chronic respiratory disease.

Age- and stroke-related skeletal muscle changes: a review for the geriatric clinician

Independently, aging and stroke each have a significant negative impact on skeletal muscle, but the potential cumulative effects of aging and stroke have not been explored. Optimal interventions for individuals post stroke may include those that specifically target skeletal muscle. Addressing changes in muscles may minimize activity limitations and enhance participation post stroke. This article reviews the impact of aging and stroke on muscle morphology and composition, including fiber atrophy, reductions in muscle cross-sectional area, changes in muscle fiber distributions, and increases in intramuscular fat. Relationships between changes in muscle structure, muscle function, and physical mobility are reviewed. Clinical recommendations that preserve and enhance skeletal muscle in the aging adult and individuals post stroke are discussed. Future research directions that include systematic comparison of the differences in skeletal muscle between younger and older adults who have sustained a stroke are suggested.

Muscle maintenance by volitional contraction against applied electrical stimulation

Muscle training exercises are needed for muscular endurance during spaceflight. This study was designed to investigate effects of volitional contraction against applied electrical stimulation on the muscular endurance of the proximal upper extremity. Thirteen healthy sedentary men were allocated into two groups. One group participated in a hybrid (HYB) exercise regimen in which the biceps brachii was stimulated as he volitionally extended his elbow, and the triceps brachii was stimulated as the volitionally flexed his elbow. The second group underwent a similar regimen in which the electrical stimulation (ELS) was alternatively delivered to the biceps brachii and then to the triceps brachii with the limb fixed. Forty-second surface electromyography (EMG) recordings at 50% maximum voluntary contraction (MVC) were made as baseline data at just before starting the training regimen, and again conclusion. The median frequency (MF) and mean power frequency (MPF) slopes with time were determined using power spectrum analysis. There were statistical significance only for the triceps in which the MF and MPF slopes in the HYB Group became less negative over the period of study (from -45.7+/-14.7 and -47.0+/-8.6%/min at baseline to -36.9+/-10.7 and -36.8+/-7.0%/min at the end of training, respectively). The corresponding values for these slopes in the ELS Group showed opposite tends with less marked changes of borderline significance for MF and of statistical significance for MPF. These results suggested that the HYB exercise regimen was capable of producing an improvement in triceps but not biceps brachii.

Central and peripheral contributions to fatigue after electrostimulation training

PURPOSE

We examined the effect of 4 (WK4) and 8 wk (WK8) of neuromuscular electrical stimulation (NMES) training on both endurance time and mechanisms contributing to task failure.

METHODS

Ten males performed a fatiguing isometric contraction with the knee extensor muscles at 20% of maximal voluntary contraction (MVC) until exhaustion before (B), at WK4, and at WK8 of NMES training. The electromyographic (EMG) activity and muscle activation obtained under MVC were recorded before and after the fatiguing task to assess central fatigue. Torque and EMG responses obtained under electrically evoked contractions were examined before and after the fatiguing task to analyze peripheral fatigue.

RESULTS

Knee extensor MVC torque increased significantly between B and WK4 (+16%), between WK4 and WK8 (+10%), and between B and WK8 (+26%), which meant that the average target torque sustained during the fatiguing contraction increased between the testing sessions. Endurance time decreased significantly over the three sessions (493+/-101 s at B, 408+/-159 s at WK4, and 338+/-126 s at WK8) despite a similar reduction in knee extensor MVC (approximately 25%). Negative correlations were found between endurance time absolute changes and target torque absolute gains. Average EMG activity of the knee extensor muscles was lower after training, but the mean rate of increase was similar over the three sessions. Single-twitch contractile properties were not affected by the task.

CONCLUSION

We conclude that the endurance time was shorter after 4 and 8 wk of NMES training, and this was associated with higher absolute contraction intensity. Despite endurance time reduction, NMES training did not affect the amount of fatigue at exhaustion nor the central and peripheral contributions to fatigue.

Neural drive preservation after detraining following neuromuscular electrical stimulation training

The purpose of the study was to investigate the behaviour of the central nervous system when 5 weeks of neuromuscular electrical stimulation (NMES) training was followed by 5 weeks of detraining. Nineteen males were divided into the neuromuscular electrostimulated group (EG, n=12) and the control group (CG, n=7). The training program consisted of 15 sessions of isometric NMES over a 5-week period. The EG subjects were tested before training (PRE), after 5 weeks of NMES training (POST) and after 5 weeks of detraining (DE) while CG subjects were only tested at PRE and at POST. Soleus (SOL) and gastrocnemii (GAS) maximal H-reflex and M-wave potentials were evoked at rest (i.e., H(max) and M(max), respectively) and during maximal voluntary contraction (MVC) (i.e., H(sup) and M(sup), respectively). SOL and GAS V-wave were recorded by supramaximal stimulation delivered during MVC. SOL and GAS electromyographic (EMG) activity as well as muscle activation were also assessed during MVC. After training, plantar flexor MVC increased significantly by 22% (P<0.001). Torque gains were associated with an increase in muscle activation (P<0.05), SOL and GAS normalized EMG activity (P<0.01 and P<0.05, respectively) and V/M(sup) ratios (P<0.01 and P<0.05, respectively). No significant changes occurred in any of these parameters between POST and DE. H(max)/M(max) and H(sup)/M(sup) ratios for both muscles were unchanged after both the training and detraining periods. In conclusion, the NMES training-induced neural adaptations were maintained after detraining, suggesting that neural changes are long-lasting and did not affect the elements of H-reflex pathways.

Late neural adaptations to electrostimulation resistance training of the plantar flexor muscles

The present study aimed to examine early and late neural adaptations to short-term electrostimulation training of the plantar flexor muscles. Changes in triceps surae muscle activation (twitch interpolation), maximal electromyographic (EMG) activity, H-reflex amplitudes and antagonist coactivation were investigated after electrostimulation training (4 weeks) and after 4 weeks of detraining in a group of ten young healthy men. Maximal voluntary contraction torque was significantly higher (P < 0.01) after training (+19.4%) and detraining (+17.2%) with respect to baseline. Activation level, soleus and lateral gastrocnemius EMG normalized to the maximal M-wave significantly increased as a result of training (P < 0.05), and these gains were preserved after detraining, excepted for soleus EMG. Maximal H reflex to maximal M wave ratio increased significantly between baseline and detraining for both soleus and lateral gastrocnemius muscles (P < 0.05). Tibialis anterior coactivation was unchanged after training but significantly decreased after the detraining period (P < 0.01). Short-term electrostimulation resistance training was accompanied by early (increased muscle activation and EMG activity) and late neural adaptations (increased spinal reflex amplitude and decreased coactivation), likely explaining the increase and then the preservation of the maximal voluntary strength. These effects may help in conceiving and programming effective electrostimulation therapy programs for both healthy and immobilized plantar flexor muscles.

Chronic electrostimulation after nerve repair by self-anastomosis: effects on the size, the mechanical, histochemical and biochemical muscle properties

This study tests the effects of chronic electrostimulation on denervated/reinnervated skeletal muscle in producing an optimal restoration of size and mechanical and histochemical properties. We compared tibialis anterior muscles in four groups of rats: in unoperated control (C) and 10 weeks following nerve lesion with suture (LS) in the absence of electrostimulation and in the presence of muscle stimulation with either a monophasic rectangular current (LSEm) or a biphasic modulated current (LSEb). The main results were (1) muscle atrophy was reduced in LSEm (-26%) while it was absent in LSEb groups (-8%); (2) the peak twitch amplitude decreased in LS and LSEm but not in LSEb groups, whereas the contraction time was shorter; (3) muscle reinnervation was associated with the emergence of type IIC fibers and proportions of types I, IIA and IIB fibers recovered in the superficial portion of LSEb muscles; (4) the ratio of oxidative to glycolytic activities decreased in the three groups with nerve injury and repair; however, this decrease was more accentuated in LSEm groups. We conclude that muscle electrostimulation following denervation and reinnervation tends to restore size and functional and histochemical properties during reinnervation better than is seen in unstimulated muscle.

Neural and muscular changes to detraining after electrostimulation training

We investigated the effects of 4 weeks of detraining subsequent to an 8-week electrostimulation (ES) training program on changes in muscle strength, neural and muscular properties of the knee extensor muscles. Nine male subjects followed the training program consisting of 32 sessions of isometric ES training over an 8-week period. All subjects were tested before and after 8 weeks of ES training, and were then retested after 4 weeks of detraining. Quadriceps muscle anatomical cross-sectional area (ACSA) was assessed by ultrasonography imaging. The electromyographic (EMG) activity and muscle activation (i.e., by means of the twitch interpolation technique) obtained during maximal voluntary contractions (MVC) were used to examine neural adaptations. After training, the knee extensor voluntary torque increased significantly by 26%. Torque gains were accompanied by an increase in vastii EMG activity normalized to respective M-wave (+43%), muscle activation (+6%) and quadriceps ACSA (+6%). After detraining, knee extensor MVC, vastii EMG activity, muscle activation and quadriceps ACSA decreased significantly by 9%, 20%, 5% and 3%, respectively. Also, the knee extensor MVC values remained significantly elevated (14%) above baseline levels at the end of the detraining period and this was associated with a larger quadriceps ACSA (+3%) but not with a higher neural activation. We concluded that the voluntary torque losses observed after detraining could be attributed to both neural and muscular alterations. Muscle size preservation could explain the higher knee extensor MVC values observed after the cessation of training compared to those obtained before training, therefore indicating that muscle size changes are slower than neural drive reduction.

Carbon dioxide depresses the F wave by a central, not peripheral, mechanism during isoflurane anesthesia

Carbon dioxide (CO(2)) has anesthetic properties and has been reported to depress the F wave of the evoked electromyogram; the F wave is thought to reflect motoneuron excitability. Anesthetics such as isoflurane also depress the F wave. Because CO(2) can depress muscle contractile function, as well as spinal cord neurons, it is unclear whether CO(2) depresses the F wave via a central or peripheral mechanism. We anesthetized rabbits with isoflurane (1.4%) and prepared for hindlimb bypass (with a membrane oxygenator) whereby the partial pressures of CO(2) in the hindlimb muscle and torso could be independently adjusted. The F wave was recorded from the hindlimb plantar muscles when the CO(2) was normal to the hindlimb and torso, and when it was increased (to approximately 90 mm Hg) in the hindlimb, the torso, or both. Increasing the CO(2) to just the hindlimb had no significant effect on the F-wave amplitude, but increasing the CO(2) to the torso depressed the F wave to 52% +/- 32% of control; adding CO(2) to the hindlimb during torso hypercarbia did not result in any additional depression of the F wave. CO(2) depressed the F wave via a central, not peripheral, mechanism, although the precise mechanism is unknown.