Skeletal muscle fibre type transformation following spinal cord injury

Cervical spinal cord stimulation for treatment of upper limb paralysis: a narrative review

Recent advances in cervical spinal cord stimulation (SCS) have demonstrated improved efficacy as a therapeutic intervention for restoring hand functions in individuals with spinal cord injuries or stroke. Accumulating evidence consistently shows that cervical SCS yields significant improvements in grip force, proximal arm strength and muscle activation, with both immediate and sustained effects. This review synthesizes the evidence that electrical stimulations modulate the spinal and supraspinal organization of uninjured descending motor tracts, primarily the residual corticospinal tract, reticulospinal tract and propriospinal network of neurons, as well as increasing the sensitivity of spinal interneurons at the stimulated segments to these inputs. Additionally, we examine contemporary strategies aimed at achieving more precise patterned stimulations, including intraspinal microstimulation, ventral cord stimulation and closed-loop neuromodulation, and discuss the potential benefits of incorporating cervical SCS into a multimodal treatment paradigm.Level of evidence: V.

Muscle Fibrosis, NF-B, and TGF- Are Differentially Altered in Two Models of Paralysis (Botox Versus Neurectomy)

Objective: Volumetric muscle loss results in intramuscular axotomy, denervating muscle distal to the injury and leading to paralysis, denervation, and loss of muscle function. Once the nerve is damaged, paralyzed skeletal muscle will atrophy and accumulate noncontractile connective tissue. The objective of this study was to determine differences in connective tissue, atrophy, and inflammatory signaling between two paralysis models, botulinum toxin (Botox), which blocks acetylcholine transmission while keeping nerves intact, and neurectomy, which eliminates all nerve-to-muscle signaling. Approach: Twenty male Sprague Dawley rats were randomized and received a sciatic-femoral neurectomy (SFN), Botox-induced muscle paralysis of the proximal femur muscles, quadriceps femoris, hamstrings, and calf muscles (BTX), or sham. Muscle force was measured 52 days postsurgery, and samples were collected for histology, protein, and mRNA assays. Results: SFN and BTX decreased twitch and tetanic force, decreased fiber size by twofold, and increased myogenic expression compared with controls. SFN increased the levels of all major extracellular matrix proteins correlating with fibrosis [e.g., laminin, fibronectin, and collagen type(s) I, III, VI]. SFN also increased profibrotic and proinflammatory mRNA compared with BTX and controls. Innovation: SFN and BTX were similar in gross morphology and functional deficiencies. However, SFN exhibited a higher amount of fibrosis in histological sections and immunoblotting. The present study shows evidence that nerve signaling changes NF-κB and TGF-β signaling, warranting future studies to determine the mechanisms involved. Conclusion: These data indicate that nerve signaling may influence fibrogenesis following denervation, but the mechanisms involved may differ as a function of the method of paralysis.

Neurogenic Aging After Spinal Cord Injury: Highlighting the Unique Characteristics of Aging After Spinal Cord Injury

Emanating from several decades of study into the effects of the aging process after spinal cord injury (SCI), "accelerated aging" has become a common expression as the SCI accelerates the onset of age-related pathologies. However, the aging process follows a distinct trajectory, characterized by unique patterns of decline that differ from those observed in the general population without SCI. Aging brings significant changes to muscles, bones, and hormones, impacting overall physical function. Muscle mass and strength begin to decrease with a reduction in muscle fibers and impaired repair mechanisms. Bones become susceptible to fractures as bone density decreases. Hormonal changes combined with decreased physical activity accelerate the reduction of muscle mass and increase in body fat. Muscle atrophy and skeletal muscle fiber type transformation occur rapidly and in a unique pattern after SCI. Bone loss develops more rapidly and results in an increased risk of fractures in body regions unique to individuals with SCI. Other factors, such as excessive adiposity, decreased testosterone and human growth hormone, and increased systemic inflammation, contribute to a higher risk of neuropathically driven obesity, dyslipidemia, glucose intolerance, insulin resistance, and increasing cardiovascular disease risk. Cardiorespiratory changes after SCI result in lower exercise heart rates, decreased oxygenation, and mitochondrial dysfunction. While it is important to acknowledge the accelerated aging processes after SCI, it is essential to recognize the distinct differences in the aging process between individuals without physical disabilities and those with SCI. These differences, influenced by neuropathology, indicate that it may be more accurate to describe the aging process in individuals with chronic SCI as neurogenic accelerated aging (NAA). Research should continue to address conditions associated with NAA and how to ameliorate the accelerated rate of premature age-related conditions. This review focuses on the NAA processes and the differences between them and the aging process in those without SCI. Recommendations are provided to help slow the development of premature aging conditions.

The Effect of Lower Limb Combined Neuromuscular Electrical Stimulation on Skeletal Muscle Cross-Sectional Area and Inflammatory Signaling

In individuals with a spinal cord injury (SCI), rapid skeletal muscle atrophy and metabolic dysfunction pose profound rehabilitation challenges, often resulting in substantial loss of muscle mass and function. This study evaluates the effect of combined neuromuscular electrical stimulation (Comb-NMES) on skeletal muscle cross-sectional area (CSA) and inflammatory signaling within the acute phase of SCI. We applied a novel Comb-NMES regimen, integrating both high-frequency resistance and low-frequency aerobic protocols on the vastus lateralis muscle, to participants early post-SCI. Muscle biopsies were analyzed for CSA and inflammatory markers pre- and post-intervention. The results suggest a potential preservation of muscle CSA in the Comb-NMES group compared to a control group. Inflammatory signaling proteins such as TLR4 and Atrogin-1 were downregulated, whereas markers associated with muscle repair and growth were modulated beneficially in the Comb-NMES group. The study's findings suggest that early application of Comb-NMES post-SCI may attenuate inflammatory pathways linked to muscle atrophy and promote muscle repair. However, the small sample size and variability in injury characteristics emphasize the need for further research to corroborate these results across a more diverse and extensive SCI population.

Functional Sitting Balance and Anthropometric Measures Are Related to Inspiratory Muscle Performance in People with Spinal Cord Injury

Background

Respiratory complications are a leading cause of mortality post spinal cord injury (SCI). Along with breathing, respiratory muscles have a role in maintaining seated balance. Postinjury breathing influences respiratory muscle function. Preliminary evidence indicates a relation between respiratory muscle function and seated balance in people with chronic SCI dwelling in the community, but the relationship between balance and body habitus has not been explored.

Objectives

To explore the relationships among inspiratory muscle function, functional seated balance (FSB), and body habitus in people with SCI.

Methods

A convenience sample of inpatients with SCI (C5-T12) aged 18 to 60 years who were using a wheelchair was recruited from November 2022 to March 2023. Those with additional neurological disorders or respiratory support were excluded. Respiratory muscle function measures included maximal inspiratory pressure (MIP), sustained MIP (SMIP), and Fatigue Index Test (FIT). FSB was scored using the Function in Sitting Test (FIST). Body habitus was assessed using the axillary: umbilical (A:U) ratio. Spearman correlations explored the relationships.

Results

Thirty-eight of 42 screened participants were eligible and participated (male, 32). Levels of injury ranged from C5 to T12. The mean (SD) age and duration of injury of the sample was 25.61 (6.68) years and 31.03 (28.69) months, respectively. SMIP and FIT correlated significantly with FSB (r s= .441, p = .01, and r s= .434, p = .006, respectively). A significant correlation between SMIP and A:U ratio (r s= -.330, p = .043) was observed.

Conclusion

We observed a significant correlation between inspiratory pressure parameters and both functional seated balance and body habitus, adding to evidence on postural role of respiratory muscles.

Time-dependent reduction in oxidative capacity among cultured myotubes from spinal cord injured individuals

BACKGROUND

Skeletal muscle adapts in reaction to contractile activity to efficiently utilize energy substrates, primarily glucose and free fatty acids (FA). Inactivity leads to atrophy and a change in energy utilization in individuals with spinal cord injury (SCI). The present study aimed to characterize possible inactivity-related differences in the energy metabolism between skeletal muscle cells cultured from satellite cells isolated 1- and 12-months post-SCI.

METHODS

To characterize inactivity-related disturbances in spinal cord injury, we studied skeletal muscle cells isolated from SCI subjects. Cell cultures were established from biopsy samples from musculus vastus lateralis from subjects with SCI 1 and 12 months after the injury. The myoblasts were proliferated and differentiated into myotubes before fatty acid and glucose metabolism were assessed and gene and protein expressions were measured.

RESULTS

The results showed that glucose uptake was increased, while oleic acid oxidation was reduced at 12 months compared to 1 month. mRNA expressions of PPARGC1α, the master regulator of mitochondrial biogenesis, and MYH2, a determinant of muscle fiber type, were significantly reduced at 12 months. Proteomic analysis showed reduced expression of several mitochondrial proteins.

CONCLUSION

In conclusion, skeletal muscle cells isolated from immobilized subjects 12 months compared to 1 month after SCI showed reduced fatty acid metabolism and reduced expression of mitochondrial proteins, indicating an increased loss of oxidative capacity with time after injury.

Handcycling with concurrent lower body low-frequency electromyostimulation significantly increases acute oxygen uptake in elite wheelchair basketball players: an acute crossover trial

OBJECTIVE

Wheelchair basketball (WCB) demands high-intensity training due to its intermittent nature. However, acute oxygen uptake (V˙O2) in handcycling is restricted. Combining handcycling with low-frequency electromyostimulation (LF-EMS) may enhance V˙O2 in elite WBC athletes.

DESIGN

Randomized crossover trail.

SUBJECTS

Twelve German national team WCB players (age: 25.6 [5.6] years, height: 1.75 [0.16] m, mass: 74.0 [21.7] kg, classification: 2.92 [1.26]).

METHOD

Participants underwent 2×5 min of handcycling (60 rpm, ¾ bodyweight resistance in watts) (HANDCYCLE) and 2×5 min of handcycling with concurrent LF-EMS (EMS_HANDCYCLE). LF-EMS (4Hz, 350µs, continuous stimulation) targeted gluteal, quadriceps, and calf muscles, adjusted to individual pain thresholds (buttocks: 69.5 [22.3] mA, thighs: 66.8 [20.0] mA, calves: 68.9 [31.5] mA).

RESULTS

Significant mode-dependent differences between HANDCYCLE and EMS_HANDCYCLE were found in V˙O2 (17.60 [3.57] vs 19.23 [4.37] ml min-1 kg-1, p = 0.001) and oxygen pulse (16.69 [4.51] vs 18.41 [5.17] ml, p = 0.002). ΔLactate was significantly lower in HANDCYCLE (0.04 [0.28] vs 0.31 [0.26] mmol l-1). Although perceived effort did not differ (p = 0.293), discomfort was rated lower in HANDCYCLE (1.44 [1.28] vs 3.94 [2.14], p = 0.002).

CONCLUSION

LF-EMS applied to the lower extremities increases oxygen demand during submaximal handcycling. Thus, longitudinal application of LF-EMS should be investigated as a potential training stimulus to improve aerobic capacity in wheelchair athletes.

Clustering index analysis on EMG-Torque relation-based representation of complex neuromuscular changes after spinal cord injury

Spinal cord injury (SCI) resulting in complex neuromuscular pathology is not sufficiently well understood. To better quantify neuromuscular changes after SCI, this study uses a clustering index (CI) method for surface electromyography (sEMG) clustering representation to investigate the relation between sEMG and torque in SCI survivors. The sEMG signals were recorded from 13 subjects with SCI and 13 gender-age matched able-bodied subjects during isometric contraction of the biceps brachii muscle at different torque levels using a linear electrode array. Two torque representations, maximum voluntary contraction (MVC%) and absolute torque, were used. CI values were calculated for sEMG. Regression analyses were performed on CI values and torque levels of elbow flexion, revealing a strong linear relationship. The slopes of regressions between SCI survivors and control subjects were compared. The findings indicated that the range of distribution of CI values and slopes was greater in subjects with SCI than in control subjects (p < 0.05). The increase or decrease in slope was also observed at the individual level. This suggests that the CI and its sEMG clustering-torque relation may serve as valuable quantitative indicators for determining neuromuscular lesions after SCI, contributing to the development of effective rehabilitation strategies for improving motor performance.

Aster glehni Extract, Including Caffeoylquinic Acids as the Main Constituents, Induces PPAR β/δ-Dependent Muscle-Type Change and Myogenesis in Apolipoprotein E Knockout Mice

To probe the functions of Aster glehni (AG) extract containing various caffeoylquinic acids on dyslipidemia, obesity, and skeletal muscle-related diseases focused on the roles of skeletal muscle, we measured the levels of biomarkers involved in oxidative phosphorylation and type change of skeletal muscle in C2C12 cells and skeletal muscle tissues from apolipoprotein E knockout (ApoE KO) mice. After AG extract treatment in cell and animal experiments, western blotting, immunohistochemistry, and enzyme-linked immunosorbent assay (ELISA) were used to estimate the levels of proteins that participated in skeletal muscle type change and oxidative phosphorylation. AG extract elevated protein expression of peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α), phosphorylated 5'-AMP-activated protein kinase (p-AMPK), peroxisome proliferator-activated receptor beta/delta (PPARβ/δ), myoblast determination protein 1 (MyoD), and myoglobin in skeletal muscle tissues. Furthermore, it elevated the ATP concentration. However, protein expression of myostatin was decreased by AG treatment. In C2C12 cells, increments of MyoD, myoglobin, myosin, ATP-producing pathway, and differentiation degree by AG were dependent on PPARβ/δ and caffeoylquinic acids. AG extract can contribute to the amelioration of skeletal muscle inactivity and sarcopenia through myogenesis in skeletal muscle tissues from ApoE KO mice, and function of AG extract may be dependent on PPARβ/δ, and the main functional constituents of AG are trans-5-O-caffeoylquinic acid and 3,5-O-dicaffeoylquinic acid. In addition, in skeletal muscle, AG has potent efficacies against dyslipidemia and obesity through the increase of the type 1 muscle fiber content to produce more ATP by oxidative phosphorylation in skeletal muscle tissues from ApoE KO mice.

Differences in Skeletal Muscle Fiber Characteristics Between Affected and Nonaffected Limbs in Individuals With Stroke: A Scoping Review

OBJECTIVE

The objective of this scoping review was to characterize and identify knowledge gaps about the changes in skeletal muscle fiber type proportion and cross-sectional area (CSA) after stroke.

METHODS

This scoping review followed previously proposed frameworks. A systematic search was conducted for articles examining muscle fiber type proportion and CSA in individuals with stroke in EMBASE, MEDLINE, PsycINFO, CINAHL, SPORTDiscus, and Web of Science databases from inception to December 20, 2022. Two independent authors screened and extracted the data. Results were discussed using theories proposed by the authors of the included studies.

RESULTS

Of 13 studies (115 participants), 6 (46%) were case studies or case series, 6 (46%) were cross-sectional studies, and 1 (8%) was an experimental study. Studies had small sample sizes (1-23 participants) and various muscle sampling sites (6 different muscles). All 13 studies examined muscle fiber type distributions, and 6 (46%) examined CSA. Ten (77%) studies examined differences between paretic and nonparetic muscles, and 5 (38%) compared people with stroke to people without stroke. Results from 9 of 13 studies (69%) supported a greater proportion of type II muscle fibers in the paretic limb. Of those, 4 studies (42 participants), 3 studies (17 participants), and 1 study (1 participant) saw no differences, preferential type II and type I CSA loss between limbs, respectively.

CONCLUSION

Of the limited available evidence, stroke appears to result in a shift to a higher proportion of type II muscle fibers in the paretic muscles. There are mixed results for effects on muscle fiber CSA, but there is some evidence of specific atrophy of type II muscle fibers.

IMPACT

Changes in paretic skeletal muscle fibers of individuals with stroke may explain, in part, the substantial losses in strength and power in this population. Interventions to restore type II muscle fiber size may benefit people with stroke.

Temporary diaphragm pacing for patients at risk of prolonged mechanical ventilation after extensive aortic repair

Objective

Prolonged mechanical ventilation (MV) after extensive aortic reconstructive surgery is common. Studies have demonstrated that diaphragm pacing (DP) improves lung function in patients with unilateral diaphragm paralysis. The goal of this study is to determine whether this technology can be applied to complex aortic repair to reduce prolonged MV and other respiratory sequelae.

Methods

A retrospective review was performed of patients who underwent temporary DP after extensive aortic reconstructive surgery between 2019 and 2022. The primary end point was prolonged MV incidence. Other measured end points included diaphragm electromyography improvement, length of hospitalization, duration of intensive care unit stay, and reintubation rates.

Results

Fourteen patients deemed at high risk of prolonged MV based on their smoking and respiratory history underwent DP after extensive aortic repair. The mean age was 70.2 years. The indications for aortic repair were a thoracoabdominal aortic aneurysm (n = 8, including 2 ruptured, 2 symptomatic, and 1 mycotic), a perivisceral aneurysm (n = 4), and a perivisceral coral reef aorta (n = 2). All patients had a significant smoking history (active or former) or other risk factors for ventilator-induced diaphragmatic dysfunction and prolonged MV. The mean total duration of MV postoperatively was 31.9 hours (range, 8.1-76.5 hours). The total average pacing duration was 4.4 days. Two patients required prolonged MV, with an average of 75.4 hours. Two patients required reintubation. No complications related to DP wire placement or removal occurred.

Conclusions

DP is safe and feasible for patients at high risk of pulmonary insufficiency after extensive aortic reconstructive surgery.

Saponin extract from Achyranthes bidentata Blume alleviates disuse-induced muscle atrophy through PI3K/Akt signaling pathway

ETHNOPHARMACOLOGICAL RELEVANCE

The roots of Achyranthes bidentata Blume are one of the regularly used herbal drugs in Chinese medicine, and has been applied for strengthening the muscle and bone for a long time. However, its effect on muscle remains unclear.

AIM OF THE STUDY

This paper aims to explore the anti-muscle atrophy effect of A. bidentata, and to clarify the possible signaling pathways involved.

MATERIALS AND METHODS

The saponin extract of the roots of A. bidentata (ABSE) was prepared and analyzed, and its activity on myoblast differentiation was assayed with C2C12 cell culture. ABSE was then orally administered at dosage of 35, 70 and 140 mg/kg/day to disuse-induced muscle atrophy mice. The studies on mice body weight and muscle quality were conducted, and Western blot was used for exploring the possible signaling pathways involved in the muscle protective action aided with transcriptome analysis.

RESULTS

The total saponin content of ABSE was 59.1%. ABSE promoted the C2C12 cells differentiation to myotube in C2C12 differentiation assay. Further study with disuse-induced muscle atrophy mice model demonstrated that ABSE significantly increased muscle fiber diameter as well as the proportion of slow muscle fibers. Possible mechanism study aided with transcriptome analysis revealed that ABSE alleviated muscle atrophy at least through activation of PI3K/Akt pathway in vivo & vitro.

CONCLUSIONS

The saponin extract of the root of A. bidentata (ABSE) has a protective effect on muscle atrophy, and showed a considerable potential in prevention and treatment of muscle atrophy.

Slow or fast: Implications of myofibre type and associated differences for manifestation of neuromuscular disorders

Many neuromuscular disorders can have a differential impact on a specific myofibre type, forming the central premise of this review. The many different skeletal muscles in mammals contain a spectrum of slow- to fast-twitch myofibres with varying levels of protein isoforms that determine their distinctive contractile, metabolic, and other properties. The variations in functional properties across the range of classic 'slow' to 'fast' myofibres are outlined, combined with exemplars of the predominantly slow-twitch soleus and fast-twitch extensor digitorum longus muscles, species comparisons, and techniques used to study these properties. Other intrinsic and extrinsic differences are discussed in the context of slow and fast myofibres. These include inherent susceptibility to damage, myonecrosis, and regeneration, plus extrinsic nerves, extracellular matrix, and vasculature, examined in the context of growth, ageing, metabolic syndrome, and sexual dimorphism. These many differences emphasise the importance of carefully considering the influence of myofibre-type composition on manifestation of various neuromuscular disorders across the lifespan for both sexes. Equally, understanding the different responses of slow and fast myofibres due to intrinsic and extrinsic factors can provide deep insight into the precise molecular mechanisms that initiate and exacerbate various neuromuscular disorders. This focus on the influence of different myofibre types is of fundamental importance to enhance translation for clinical management and therapies for many skeletal muscle disorders.

Comparison of static and dynamic symmetry between masseter-innervated and dual-innervated free multivector serratus anterior muscle transfer for complete facial paralysis

PURPOSE

In this study, facial symmetry was compared between the masseter-innervated and dual-innervated free multivector serratus anterior muscle transfer (FMSAMT) methods.

METHODS

Eighteen patients with unilateral complete facial paralysis underwent facial reanimation surgery between April 2006 and July 2019. The masseter-innervated FMSAMT group (Group M, n = 8) underwent end-to-end coaptation with the ipsilateral masseter nerve in one stage. The dual-innervated FMSAMT group (Group D, n = 10) underwent end-to-end coaptation with the masseter nerve and end-to-side coaptation with the contralateral facial nerve via cross-face nerve graft. They were further divided into the one-stage (Group D1, n = 5) and two-stage (Group D2, n = 5) subgroups. The durations of periods until the first visible muscle contraction with clenching, first spontaneous smile, and the completion of resting tone were evaluated. The possibility of a spontaneous smile and symmetry of the midline and horizontal deviation at rest and during voluntary smiling were compared between each group.

RESULTS

Groups M and D differed significantly in the possibility of a spontaneous smile and improvement rate of midline deviation and horizontal deviation at rest (p < 0.001, p < 0.001, and p = 0.001, respectively) but not in the improvement rate of midline and horizontal deviation during voluntary smiling. The duration of the period until the completion of resting tone was significantly shorter in Group D1 than in Group D2 (p = 0.048); however, the possibility of a spontaneous smile and the improvement rate of midline and horizontal deviation were not significantly different.

CONCLUSIONS

Dual-innervated FMSAMT was effective in guaranteeing a symmetrical resting tone, voluntary smiling, and reproducing a spontaneous smile.

SHRSP5/Dmcr rats fed a high-fat and high-cholesterol diet develop disease-induced sarcopenia as nonalcoholic steatohepatitis progresses

BACKGROUND

Secondary sarcopenia develops as a result of a bedridden state and illnesses, such as cachexia, liver disease, and diabetes. However, there is a lack of animal models to investigate the underlying mechanisms and potential treatments for secondary sarcopenia. Recently, secondary sarcopenia has been associated with the prognosis of nonalcoholic steatohepatitis. This study aimed to investigate whether stroke-prone spontaneously hypertensive rat 5 (SHRSP5/Dmcr) which developed severe nonalcoholic steatohepatitis by a high-fat and high-cholesterol (HFC; containing 2% cholic acid) diet is a useful model of secondary sarcopenia.

METHODS

SHRSP5/Dmcr rats were divided into 6 groups fed with a Stroke-Prone (SP: normal chow) or HFC diets for different periods (4, 12, and 20 weeks), and WKY/Izm rats were divided into 2 groups fed an SP or HFC diet. Body weight, food intake, and muscle force were measured weekly for all rats. After the end of the diet period, skeletal muscle strength evoked by electrical stimulation was recorded, blood was collected, and organ weight was measured. The sera were used for biochemical analysis and the organs were used for histopathological analysis.

RESULTS

SHRSP5/Dmcr rats fed an HFC diet developed nonalcoholic steatohepatitis, and their skeletal muscles, especially fast muscles, showed atrophy, indicating that muscle atrophy is aggravated by the progression of nonalcoholic steatohepatitis. In contrast, WKY/Izm rats fed an HFC diet did not exhibit sarcopenia.

CONCLUSIONS

This study suggests that SHRSP5/Dmcr rats could be a useful novel model for investigate the mechanism of secondary sarcopenia disorder associated with nonalcoholic steatohepatitis.

Human and African ape myosin heavy chain content and the evolution of hominin skeletal muscle

Humans are unique among terrestrial mammals in our manner of walking and running, reflecting 7 to 8 Ma of musculoskeletal evolution since diverging with the genus Pan. One component of this is a shift in our skeletal muscle biology towards a predominance of myosin heavy chain (MyHC) I isoforms (i.e. slow fibers) across our pelvis and lower limbs, which distinguishes us from chimpanzees. Here, new MyHC data from 35 pelvis and hind limb muscles of a Western gorilla (Gorilla gorilla) are presented. These data are combined with a similar chimpanzee dataset to assess the MyHC I content of humans in comparison to African apes (chimpanzees and gorillas) and other terrestrial mammals. The responsiveness of human skeletal muscle to behavioral interventions is also compared to the human-African ape differential. Humans are distinct from African apes and among a small group of terrestrial mammals whose pelvis and hind/lower limb muscle is slow fiber dominant, on average. Behavioral interventions, including immobilization, bed rest, spaceflight and exercise, can induce modest decreases and increases in human MyHC I content (i.e. -9.3% to 2.3%, n = 2033 subjects), but these shifts are much smaller than the mean human-African ape differential (i.e. 31%). Taken together, these results indicate muscle fiber content is likely an evolvable trait under selection in the hominin lineage. As such, we highlight potential targets of selection in the genome (e.g. regions that regulate MyHC content) that may play an important role in hominin skeletal muscle evolution.

Preservation of functional descending input to paralyzed upper extremity muscles in motor complete cervical spinal cord injury

OBJECTIVE

Spinal cord injury (SCI) is classified as complete or incomplete depending on the extent of sensorimotor preservation below the injury level. However, individuals with complete SCIs can voluntarily activate paralyzed lower limb muscles alone or by engaging non-paralyzed muscles during neurophysiological assessments, indicating presence of residual pathways across the injury. However, similar phenomena have not been explored for the upper extremity (UE) muscles following cervical SCIs.

METHODS

Eighteen individuals with motor complete cervical SCI (AIS A or B) and five age-matched non-injured (NI) individuals performed various UE events against manual resistance during functional neurophysiological assessment (FNPA), and electromyographic (EMG) activity was recorded from UE muscles.

RESULTS

Our findings demonstrated i) voluntary activation of clinically paralyzed muscles as evident from EMG readouts, ii) increased activity in these muscles during events engaging muscles above the injury level, iii) reduced spectral properties of paralyzed muscles in SCI compared to NI participants.

CONCLUSIONS

Functional EMG activity in clinically paralyzed muscles indicate presence of residual pathways across the injury establishing supralesional control over the sublesional neural circuitry.

SIGNIFICANCE

The findings may help explain the neurophysiological basis for UE recovery and can be exploited in designing rehabilitation techniques to facilitate UE recovery following cervical SCIs.

Systemic inflammation after spinal cord injury: A review of biological evidence, related health risks, and potential therapies

Individuals with chronic traumatic spinal cord injury (SCI) develop progressive multi-system health problems that result in clinical illness and disability. Systemic inflammation is associated with many of the common medical complications and acquired diseases that accompany chronic SCI, suggesting that it contributes to a number of comorbid pathological conditions. However, many of the mechanisms that promote persistent systemic inflammation and its consequences remain ill-defined. This review describes the significant biological factors that contribute to systemic inflammation, major organ systems affected, health risks, and the potential treatment strategies. We aim to highlight the need for a better understanding of inflammatory processes, and to establish appropriate strategies to address inflammation in SCI.

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.

C. Moreira M, D. M. Pinheiro L, R. Pereira T, G. Carmona G, P. D. Freire J, A. I. Bastos J, Padilha Lanari Bo A. User-centered design and spatially-distributed sequential electrical stimulation in cycling for individuals with paraplegia

Background

In this work, we share the enhancements made in our system to take part in the CYBATHLON 2020 Global Edition Functional Electrical Stimulation (FES) Bike Race. Among the main improvements, firstly an overhaul, an overhaul of the system and user interface developed with User-centered design principles with remote access to enable telerehabilitation. Secondly, the implementation and experimental comparison between the traditional single electrode stimulation (SES) and spatially distributed sequential stimulation (SDSS) applied for FES Cycling.

Methods

We report on the main aspects of the developed system. To evaluate the user perception of the system, we applied a System Usability Scale (SUS) questionnaire. In comparing SDSS and SES, we collected data from one subject in four sessions, each simulating one race in the CYBATHLON format.

Results

User perception measured with SUS indicates a positive outcome in the developed system. The SDSS trials were superior in absolute and average values to SES regarding total distance covered and velocity. We successfully competed in the CYBATHLON 2020 Global Edition, finishing in 6th position in the FES Bike Race category.

Conclusions

The CYBATHLON format induced us to put the end-user in the center of our system design principle, which was well perceived. However, further improvements are required if the intention is to progress to a commercial product. FES Cycling performance in SDSS trials was superior when compared to SES trials, indicating that this technique may enable faster and possibly longer FES cycling sessions for individuals with paraplegia. More extensive studies are required to assess these aspects.

Physical Fitness and Inflammatory Response to the Training Load of Wheelchair Rugby Players

The aim of the study was the evaluation of the hormonal response of wheelchair rugby participants under the half-year training cycle. The study sample included 11 members of the Polish national wheelchair rugby team with spinal cord injury at the cervical level, ranging in age from 21 to 41 years, body weight (72.2 ± 11.53 kg), and body height (182.3 ± 6.11 cm). The disabled individuals with spinal cord injury subjected to the study constitute a homogeneous group in terms of age, body height, weight, and injury level. The study was carried out at the beginning and at the end of a 6-month training period. In the first and second examination, measurements of the peak oxygen uptake (peakVO₂) and blood biochemical analysis were performed (Lactate dehydrogenase (LDH) activity and concentration of creatinine (Cr), total testosterone (TT), free testosterone (FT), and cortisol (C)). A significant change was observed in the concentration of C in the Wheelchair Rugby players’ blood between two research periods (p < 0.05 (ES:0.76)) and a correlation between the post-training change in FT/C concentration and the change in Cr concentration (r = −0.6014, p < 0.05). The 6-month training period did not result in overloads within the group of players. However, due to the significant loss of the capacity of the spinal cord injury (SCI) and the possibility of a life-threatening trend, the anabolic/catabolic status of the players should be monitored using blood biochemical indices.

A High-Intensity Warm-Up Increases Thermal Strain But Does Not Affect Repeated Sprint Performance in Athletes With a Cervical Spinal Cord Injury

PURPOSE

To compare the effects of typical competition versus high-intensity intermittent warm-up (WU) on thermoregulatory responses and repeated sprint performance during wheelchair rugby game play.

METHODS

An intermittent sprint protocol (ISP) simulating the demands of wheelchair rugby was performed by male wheelchair rugby players (7 with cervical spinal cord injury [SCI] and 8 without SCI) following 2 WU protocols. These included a typical competition WU (control) and a WU consisting of high-intensity efforts (INT). Core temperature (Tcore), thermal sensation, and thermal comfort were recorded. Wheelchair performance variables associated to power, speed, and fatigue were also calculated.

RESULTS

During the WU, Tcore was similar between conditions for both groups. During the ISP, a higher Tcore was found for SCI compared to NON-SCI (38.1 [0.3] vs 37.7 [0.3] °C: P = .036, d = 0.75), and the SCI group experienced a higher peak Tcore for INT compared with control (39.0 [0.4] vs 38.6 [0.6] °C; P = .004). Peak Tcore occurred later in the ISP for players with SCI (96 [5.8] vs 48 [2.7] min; P < .001). All players reported a higher thermal sensation and thermal comfort following INT (P < .001), with no differences between conditions throughout the ISP. No significant differences were found in wheelchair performance variables during the ISP between conditions (P ≥ .143).

CONCLUSIONS

The high-INT WU increased thermal strain in the SCI group during the ISP, potentially due to increased metabolic heat production and impaired thermoregulation, while not impacting on repeated sprint performance. It may be advisable to limit high-INT bouts during a WU in players with SCI to mitigate issues related to hyperthermia in subsequent performance.

Physiological Considerations to Support Podium Performance in Para-Athletes

The twenty-first century has seen an increase in para-sport participation and the number of research publications on para-sport and the para-athlete. Unfortunately, the majority of publications are case reports/case series or study single impairment types in isolation. Indeed, an overview of how each International Paralympic Committee classifiable impairment type impact athlete physiology, health, and performance has not been forthcoming in the literature. This can make it challenging for practitioners to appropriately support para-athletes and implement evidence-based research in their daily practice. Moreover, the lack of a cohesive publication that reviews all classifiable impairment types through a physiological lens can make it challenging for researchers new to the field to gain an understanding of unique physiological challenges facing para-athletes and to appreciate the nuances of how various impairment types differentially impact para-athlete physiology. As such, the purpose of this review is to (1) summarize how International Paralympic Committee classifiable impairments alter the normal physiological responses to exercise; (2) provide an overview of "quick win" physiological interventions targeted toward specific para-athlete populations; (3) discuss unique practical considerations for the para-sport practitioner; (4) discuss research gaps and highlight areas for future research and innovation, and (5) provide suggestions for knowledge translation and knowledge sharing strategies to advance the field of para-sport research and its application by para-sport practitioners.

Neither Postabsorptive Resting Nor Postprandial Fat Oxidation Are Related to Peak Fat Oxidation in Men With Chronic Paraplegia

The peak rate of fat oxidation (PFO) achieved during a graded exercise test is an important indicator of metabolic health. In healthy individuals, there is a significant positive association between PFO and total daily fat oxidation (FO). However, conditions resulting in metabolic dysfunction may cause a disconnect between PFO and non-exercise FO. Ten adult men with chronic thoracic spinal cord injury (SCI) completed a graded arm exercise test. On a separate day following an overnight fast (≥ 10 h), they rested for 60 min before ingesting a liquid mixed meal (600 kcal; 35% fat, 50% carbohydrate, 15% protein). Expired gases were collected and indirect calorimetry data used to determine FO at rest, before and after feeding, and during the graded exercise test. Participants had “good” cardiorespiratory fitness (VO_2peak: 19.2 ± 5.2 ml/kg/min) based on normative reference values for SCI. There was a strong positive correlation between PFO (0.30 ± 0.08 g/min) and VO_2peak (r = 0.86, p = 0.002). Additionally, postabsorptive FO at rest was significantly and positively correlated with postprandial peak FO (r = 0.77, p = 0.01). However, PFO was not significantly associated with postabsorptive FO at rest (0.08 ± 0.02 g/min; p = 0.97), postprandial peak FO (0.10 ± 0.03 g/min; p = 0.43), or incremental area under the curve postprandial FO (p = 0.22). It may be advantageous to assess both postabsorptive FO at rest and PFO in those with SCI to gain a more complete picture of their metabolic flexibility and long-term metabolic health.

Selective neural stimulation methods improve cycling exercise performance after spinal cord injury: a case series

BACKGROUND

Exercise after paralysis can help prevent secondary health complications, but achieving adequate exercise volumes and intensities is difficult with loss of motor control. Existing electrical stimulation-driven cycling systems involve the paralyzed musculature but result in rapid force decline and muscle fatigue, limiting their effectiveness. This study explores the effects of selective stimulation patterns delivered through multi-contact nerve cuff electrodes on functional exercise output, with the goal of increasing work performed and power maintained within each bout of exercise.

METHODS

Three people with spinal cord injury and implanted stimulation systems performed cycling trials using conventional (S-Max), low overlap (S-Low), low duty cycle (C-Max), and/or combined low overlap and low duty cycle (C-Low) stimulation patterns. Outcome measures include total work (W), end power (Pend), power fluctuation indices (PFI), charge accumulation (Q), and efficiency (η). Mann-Whitney tests were used for statistical comparisons of W and Pend between a selective pattern and S-Max. Welch's ANOVAs were used to evaluate differences in PFIs among all patterns tested within a participant (n ≥ 90 per stimulation condition).

RESULTS

At least one selective pattern significantly (p < 0.05) increased W and Pend over S-Max in each participant. All selective patterns also reduced Q and increased η compared with S-Max for all participants. C-Max significantly (p < 0.01) increased PFI, indicating a decrease in ride smoothness with low duty cycle patterns.

CONCLUSIONS

Selective stimulation patterns can increase work performed and power sustained by paralyzed muscles prior to fatigue with increased stimulation efficiency. While still effective, low duty cycle patterns can cause inconsistent power outputs each pedal stroke, but this can be managed by utilizing optimized stimulation levels. Increasing work and sustained power each exercise session has the potential to ultimately improve the physiological benefits of stimulation-driven exercise.

Functional electrical stimulation cycling exercise after spinal cord injury: a systematic review of health and fitness-related outcomes

OBJECTIVES

The objective of this review was to summarize and appraise evidence on functional electrical stimulation (FES) cycling exercise after spinal cord injury (SCI), in order to inform the development of evidence-based clinical practice guidelines.

METHODS

PubMed, the Cochrane Central Register of Controlled Trials, EMBASE, SPORTDiscus, and CINAHL were searched up to April 2021 to identify FES cycling exercise intervention studies including adults with SCI. In order to capture the widest array of evidence available, any outcome measure employed in such studies was considered eligible. Two independent reviewers conducted study eligibility screening, data extraction, and quality appraisal using Cochranes' Risk of Bias or Downs and Black tools. Each study was designated as a Level 1, 2, 3 or 4 study, dependent on study design and quality appraisal scores. The certainty of the evidence for each outcome was assessed using GRADE ratings ('High', 'Moderate', 'Low', or 'Very low').

RESULTS

Ninety-two studies met the eligibility criteria, comprising 999 adults with SCI representing all age, sex, time since injury, lesion level and lesion completeness strata. For muscle health (e.g., muscle mass, fiber type composition), significant improvements were found in 3 out of 4 Level 1-2 studies, and 27 out of 32 Level 3-4 studies (GRADE rating: 'High'). Although lacking Level 1-2 studies, significant improvements were also found in nearly all of 35 Level 3-4 studies on power output and aerobic fitness (e.g., peak power and oxygen uptake during an FES cycling test) (GRADE ratings: 'Low').

CONCLUSION

Current evidence indicates that FES cycling exercise improves lower-body muscle health of adults with SCI, and may increase power output and aerobic fitness. The evidence summarized and appraised in this review can inform the development of the first international, evidence-based clinical practice guidelines for the use of FES cycling exercise in clinical and community settings of adults with SCI. Registration review protocol: CRD42018108940 (PROSPERO).

The role of chronic muscle (in)activity on carnosine homeostasis: a study with spinal cord-injured athletes

To examine the role of chronic (in)activity on muscle carnosine (MCarn) and how chronic (in)activity affects MCarn responses to β-alanine supplementation in spinal cord-injured athletes, 16 male athletes with paraplegia were randomized (2:1 ratio) to receive β-alanine (n = 11) or placebo (PL, n = 5). They consumed 6.4 g/day of β-alanine or PL for 28 days. Muscle biopsies of the active deltoid and the inactive vastus lateralis (VL) were taken before and after supplementation. MCarn in the VL was also compared with the VL of a group of individuals without paraplegia (n = 15). MCarn was quantified in whole muscle and in pools of individual fibers by high-performance liquid chromatography. MCarn was higher in chronically inactive VL vs. well-trained deltoid (32.0 ± 12.0 vs. 20.5 ± 6.1 mmol/kg DM; P = 0.018). MCarn was higher in inactive vs. active VL (32.0 ± 12.0 vs. 21.2 ± 7.5 mmol/kg DM; P = 0.011). In type-I fibers, MCarn was significantly higher in the inactive VL than in the active deltoid (38.3 ± 4.7 vs. 27.3 ± 11.8 mmol/kg DM, P = 0.014). MCarn increased similarly between inactive VL and active deltoid in the β-alanine group (VL: 68.9 ± 55.1%, P = 0.0002; deltoid: 90.5 ± 51.4%, P < 0.0001), with no changes in the PL group. MCarn content was higher in the inactive VL than in the active deltoid and the active VL, but this is probably a consequence of fiber type shift (type I to type II) that occurs with chronic inactivity. Chronically inactive muscle showed an increase in MCarn after BA supplementation equally to the active muscle, suggesting that carnosine accretion following β-alanine supplementation is not influenced by muscle inactivity.

Ultrasound Imaging as a Diagnostic Tool to Assess the Functional Status of Muscles after a Spinal Cord Injury

The aim of this study was to evaluate the use of ultrasound imaging (USI) as a diagnostic tool to assess muscle function after a spinal cord injury (SCI). Ultrasound videos of the gastrocnemius medialis muscle were recorded both at rest and during attempted maximum voluntary contraction (MVC) for fifteen participants with a SCI and fifteen able-bodied controls. Measurements were repeated at monthly intervals for participants in the SCI group during their inpatient stay. Differences in muscle echogenicity and thickness were detected between both able-bodied and SCI groups and subgroups of SCI participants, suggesting USI can detect and monitor changes in muscle structure which are characteristic of atrophy. Decreased muscle movement in the SCI groups was also detected during attempted MVC. The ability of USI to distinguish between different levels of function demonstrates the potential of USI as a quantitative tool to assess muscles.

Cardiometabolic risks and atherosclerotic disease in ApoE knockout mice: Effect of spinal cord injury and Salsalate anti-inflammatory pharmacotherapy

OBJECTIVE

To test in mice with a double mutation of the ApoE gene (ApoE-/-) whether spinal cord injury (SCI) hastens the native trajectory of, and established component risks for, atherosclerotic disease (AD), and whether Salsalate anti-inflammatory pharmacotherapy attenuates the impact of SCI.

METHODS

ApoE-/- mice were anesthetized and underwent a T9 laminectomy. Exposed spinal cords were given a contusion injury (70 k-dynes). Sham animals underwent all surgical procedures, excluding injury. Injured animals were randomized to 2 groups: SCI or SCI+Salsalate [120 mg/Kg/day i.p.]. Mice were serially sacrificed at 20-, 24-, and 28-weeks post-SCI, and body mass was recorded. At sacrifice, heart and aorta were harvested intact, fixed in 10% buffered formalin, cleaned and cut longitudinally for en face preparation. The aortic tree was stained with oil-red-O (ORO). AD lesion histomorphometry was calculated from the proportional area of ORO. Plasma total cholesterol, triglycerides and proatherogenic inflammatory cytokines (PAIC's) were analyzed.

RESULTS

AD lesion in the aortic arch progressively increased in ApoE-/-, significant at 24- and 28-weeks. AD in SCI is significantly greater at 24- and 28-weeks compared to time-controlled ApoE-/-. Salsalate treatment attenuates the SCI-induced increase at these time points. Body mass in all SCI groups are significantly reduced compared to time-controlled ApoE-/-. Cholesterol and triglycerides are significantly higher with SCI by 24- and 28-weeks, compared to ApoE-/-, and Salsalate reduces the SCI-induced effect on cholesterol. PAIC's interleukin-1β (IL-1β), interleukin-6 (IL-6), tumor necrosis factor α (TNFα), monocyte chemoattractant protein-1 (MCP-1), and chemokine (C-C motif) ligand 5 (CCL-5) are significantly greater with SCI compared to ApoE-/- at varying timepoints. Salsalate confers a marginal reducing effect on PAIC's by 28-weeks compared to SCI. Regression models determine that each PAIC is a significant and positive predictor of lesion. (p's <0.05).

CONCLUSIONS

SCI accelerates aortic AD and associated risk factors, and anti-inflammatory treatment may attenuate the impact of SCI on AD outcomes. PAIC's IL-1β, IL-6, TNFα, MCP-1, and CCL-5 may be effective predictors of AD.

Direct evidence for decreased presynaptic inhibition evoked by PBSt group I muscle afferents after chronic SCI and recovery with step-training in rats

KEY POINTS

Presynaptic inhibition is modulated by supraspinal centres and primary afferents in order to filter sensory information, adjust spinal reflex excitability, and ensure smooth movement. After spinal cord injury (SCI), the supraspinal control of primary afferent depolarization (PAD) interneurons is disengaged, suggesting an increased role for sensory afferents. While increased H-reflex excitability in spastic individuals indicates a possible decrease in presynaptic inhibition, it remains unclear whether a decrease in sensory-evoked PAD contributes to this effect. We investigated whether the PAD evoked by hindlimb afferents contributes to the change in presynaptic inhibition of the H-reflex in a decerebrated rat preparation. We found that chronic SCI decreases presynaptic inhibition of the plantar H-reflex through a reduction in PAD evoked by posterior biceps-semitendinosus (PBSt) muscle group I afferents. We further found that step-training restored presynaptic inhibition of the plantar H-reflex evoked by PBSt, suggesting the presence of activity-dependent plasticity of PAD pathways activated by flexor muscle group I afferents.

ABSTRACT

Spinal cord injury (SCI) results in the disruption of supraspinal control of spinal networks and an increase in the relative influence of afferent feedback to sublesional neural networks, both of which contribute to enhancing spinal reflex excitability. Hyperreflexia occurs in ∼75% of individuals with a chronic SCI and critically hinders functional recovery and quality of life. It is suggested that it results from an increase in motoneuronal excitability and a decrease in presynaptic and postsynaptic inhibitory mechanisms. In contrast, locomotor training decreases hyperreflexia by restoring presynaptic inhibition. Primary afferent depolarization (PAD) is a powerful presynaptic inhibitory mechanism that selectively gates primary afferent transmission to spinal neurons to adjust reflex excitability and ensure smooth movement. However, the effect of chronic SCI and step-training on the reorganization of presynaptic inhibition evoked by hindlimb afferents, and the contribution of PAD has never been demonstrated. The objective of this study is to directly measure changes in presynaptic inhibition through dorsal root potentials (DRPs) and its association with plantar H-reflex inhibition. We provide direct evidence that H-reflex hyperexcitability is associated with a decrease in transmission of PAD pathways activated by posterior biceps-semitendinosus (PBSt) afferents after chronic SCI. More precisely, we illustrate that the pattern of inhibition evoked by PBSt group I muscle afferents onto both L4-DRPs and plantar H-reflexes evoked by the distal tibial nerve is impaired after chronic SCI. These changes are not observed in step-trained animals, suggesting a role for activity-dependent plasticity to regulate PAD pathways activated by flexor muscle group I afferents.

Cosine tuning determines plantarflexors' activities during human upright standing and is affected by incomplete spinal cord injury

Plantarflexors such as the soleus (SOL) and medial gastrocnemius (MG) play key roles in controlling bipedal stance; however, how the central nervous system controls the activation levels of these plantarflexors is not well understood. Here we investigated how the central nervous system controls the plantarflexors' activation level during quiet standing in a cosine tuning manner where the maximal activation is achieved in a preferred direction (PD). Furthermore, we investigated how spinal cord injury affects these plantarflexors' activations. Thirteen healthy adults (AB) and thirteen individuals with chronic, incomplete spinal cord injury (iSCI) performed quiet standing trials. Their body kinematics and kinetics as well as electromyography signals from the MG and SOL were recorded. In the AB group, we found that the plantarflexors followed the cosine tuning manner during quiet standing. That is, MG was most active when the ratio of plantarflexion torque to knee extension torque was ~2:-3, whereas SOL was most active when the ratio was ~2:1. This suggests that the SOL muscle, despite being a monoarticular muscle, is sensitive to both ankle plantarflexion and knee extension during quiet standing. The difference in the PDs accounts for the phasic activity of MG and for the tonic activity of SOL. Unlike the AB group, the MG's activity was similar to the SOL's activity in the iSCI group, and the SOL PDs were similar to those in the AB group. This result suggests that chronic iSCI affects the control strategy, i.e., cosine tuning, for MG, which may affect standing balance in individuals with iSCI.NEW & NOTEWORTHY Soleus muscle shows a tonic activity whereas medial gastrocnemius muscle shows a phasic activity during quiet standing. Cosine tuning and their preferred direction account for the different muscle activation patterns between these two muscles. In individuals with chronic incomplete spinal cord injury, the preferred direction of gastrocnemius medial head is affected, which may result in their deteriorated standing balance.

Human skeletal muscle fiber type percentage and area after reduced muscle use: A systematic review and meta-analysis

The main objective of this systematic review was to examine the effect of reduced muscle activity on the relative number of type 1 muscle fibers (%) in the human vastus lateralis muscle. Other objectives were changes in type 2A and 2X percentages and muscle fiber cross-sectional area. We conducted systematic literature searches in eight databases and included studies assessing type 1 fiber percentage visualized by ATPase or immunohistochemical staining before and after a period (≥14 days) of reduced muscle activity. The reduced muscle activity models were detraining, leg unloading, and bed rest. Forty-two studies comprising 451 participants were included. Effect sizes were calculated as the mean difference between baseline and follow-up and Generic Inverse Variance tests with random-effects models were used for the weighted summary effect size. Overall, the mean type 1 muscle fiber percentage was significantly reduced after interventions (-1.94%-points, 95% CI [-3.37, -0.51], P = .008), with no significant differences between intervention models (P = .86). Meta-regression showed no effect of study duration on type 1 fiber percentage (P = .98). Conversely, the overall type 2X fiber percentage increased after reduced muscle activity (P < .001). The CSA of the muscle fiber types decreased after the study period (all P-values < 0.001) with greater reductions in type 2 than type 1 fibers (P < .001). The result of this meta-analysis display that the type 1 muscle fiber percentage decrease as a result of reduced muscle activity, although the effect size is relatively small.

Mechanomyography-based assessment during repetitive sit-to-stand and stand-to-sit in two incomplete spinal cord-injured individuals

Standing up and sitting down movements are important prerequisites to achieve functional independence in everyday life of spinal cord injury (SCI) patients. Thus, mechanomyography (MMG) was proposed as a safe monitoring tool to evaluate muscle function performance of these activities. Two incomplete SCI participants performed repetitive sit-to-stand (SitTS) and stand-to-sit (StandTS) until fatigued challenge. Three sets of these activities were completed with MMG sensors attached over the quadriceps muscles of both legs. A 5-min rest was allocated between each set, totalling 399 trials of SitTS and StandTS activities. There was a significant difference between MMG’s mean root mean square maximum (RMSmax) in SitTS and StandTS activities (p = 0.014). The mean values of RMSmax and root mean square average (RMSave) on the right leg were detected to be significantly higher compared to those of the left leg during these activities (p < 0.05). In the frequency domain, MMG’s mean power frequency (MPF) proved to be significantly higher at the beginning compared to the end of the three sets of both activities (p = 0.000). These muscle performances during both activities can be verified based on the analysis of MMG behaviour in time and frequency domains. Furthermore, this study indicated that MMG can be used as a monitoring tool to identify muscle fatigue throughout a prolonged event.

Sum of phase-shifted sinusoids stimulation prolongs paralyzed muscle output

Neuroprostheses that activate musculature of the lower extremities can enable standing and movement after paralysis. Current systems are functionally limited by rapid muscle fatigue induced by conventional, non-varying stimulus waveforms. Previous work has shown that sum of phase-shifted sinusoids (SOPS) stimulation, which selectively modulates activation of individual motor unit pools (MUPs) to lower the duty cycle of each while maintaining a high net muscle output, improves joint moment maintenance but introduces greater instability over conventional stimulation. In this case study, implementation of SOPS stimulation with a real-time feedback controller successfully decreased joint moment instability and further prolonged joint moment output with increased stimulation efficiency over open-loop approaches in one participant with spinal cord injury. These findings demonstrate the potential for closed-loop SOPS to improve functionality of neuroprosthetic systems.

Quantifying muscle coactivation in individuals with incomplete spinal cord injury using wavelets

BACKGROUND

Individuals with incomplete spinal cord injury often have decreased gait function and coactivation of antagonistic muscle pairs. Common ways of quantifying coactivation using electromyographic signals do not consider frequency information in the signal. As electromyographic signals from different motor unit types have different frequency components and muscle fiber type can change in individuals with spinal cord injury, it may be beneficial to consider frequency components. The aims were to demonstrate the utility of using a method which considers temporal and frequency components of the electromyographical signal to quantify coactivation in lower extremity muscles in individuals with incomplete spinal cord injury through 1) comparison with able-bodied individuals and 2) comparison before and after body weight supported treadmill training.

METHODS

Frequency decomposition techniques were applied to electromyographical signals to consider the temporal and frequency components of the electromyographical signals to quantify coactivation over a range of frequencies.

RESULTS

Our main findings show that correlation coefficients between total EMG intensities of rectus femoris-biceps femoris and medial gastrocnemius-tibialis anterior were significantly different between able-bodied individuals and those with incomplete spinal cord injury (p = 0006, p = 0.01). The correlation spectra of medial gastrocnemius-tibialis anterior of the spinal cord injury group were substantially different than those the able-bodied group, while the EMG normalcy score was significantly different (p = 0.002). We also found that there was a change in coactivation of ankle muscles after body weight supported treadmill training.

INTERPRETATION

Our findings indicate that there may be frequency specific differences in muscle coactivation between able-bodied individuals and those with incomplete spinal cord injury. Changes in coactivation were also observed before and after body weight supported treadmill training. These differences may reflect the changes in recruitment patterns of different motor unit types.

Feasibility of overnight electrical stimulation-induced muscle activation in people with a spinal cord injury. A Pilot study

Study Design

We investigated whether overnight ES is a feasible method to activate gluteal, quadriceps, and hamstrings muscles in a two-week experiment. Electrical stimulation (ES) induced muscle contractions have proven positive effects on risk factors for developing pressure ulcers in people with a spinal cord injury (SCI). Therefore prolonged overnight ES-induced muscle activation is interesting, but has never been studied.

Objective

To study feasibility of ES-induced leg muscle activation. In eight participants with motor complete SCI gluteal, hamstrings and quadriceps muscles were activated with a 2-weeks overnight stimulation protocol, 8 h per night, using specially developed ES-shorts.

Setting

The Netherlands.

Methods

Muscle fatigue was determined with a muscle contraction sensor. Questionnaires on sleep quality (SQ) and the ES-shorts usability were taken.

Results

After 8 h of activation muscles still contracted, although fatigue occurred, and mean contraction size was lower at the end of a cycle (p = 0.03). SQ (0-100) after intervention was 75, and 66 after 4 weeks without overnight ES (p = 0.04) indicating ES improves sleep quality. The usability of the ES-shorts was good.

Conclusions

This study shows that overnight ES-induced muscle activation using ES-shorts in SCI is a new, feasible method that does not interfere with sleep. The nightly use of the ES-shorts might be considered as an important part of the daily routine in SCI.

A Tool to Select FES Parameters for chronic SCI

Functional electrical stimulation has been used in rehabilitation programs for patients with chronic spinal cord injury. When used correctly it is able to improve the well-being of patients. However, when the stimulus is not adequate it can accelerate the process of fatigue, reducing the time available for training the programmed motor activity. To optimize the configuration of the stimulatory parameters, we developed a tool capable of simulating the muscle strength performance in response to different stimulatory profiles. The tool was able to reproduce the behavior of motoneurons in chronic spinal cord injury and to estimate the muscular strength resulting from the application of different stimuli. We consider that this FES Simulator is a promising tool to design and simulate different profiles of electrical stimulation, optimizing the decision process of the stimulation parameters.

Medial gastrocnemius muscles fatigue but do not atrophy in paralyzed cat hindlimb after long-term spinal cord hemisection and unilateral deafferentation

This study of medial gastrocnemius (MG) muscle and motor units (MUs) after spinal cord hemisection and deafferentation (HSDA) in adult cats, asked 1) whether the absence of muscle atrophy and unaltered contractile speed demonstrated previously in HSDA-paralyzed peroneus longus (PerL) muscles, was apparent in the unloaded HSDA-paralyzed MG muscle, and 2) how ankle unloading impacts MG muscle and MUs after dorsal root sparing (HSDA-SP) with foot placement during standing and locomotion. Chronic isometric contractile forces and speeds were maintained for up to 12 months in all conditions, but fatigability increased exponentially. MU recordings at 8-11½ months corroborated the unchanged muscle force and speed with significantly increased fatigability; normal weights of MG muscle confirmed the lack of disuse atrophy. Fast MUs transitioned from fatigue resistant and intermediate to fatigable accompanied by corresponding fiber type conversion to fast oxidative (FOG) and fast glycolytic (FG) accompanied by increased GAPDH enzyme activity in absolute terms and relative to oxidative citrate synthase enzyme activity. Myosin heavy chain composition, however, was unaffected. MG muscle behaved like the PerL muscle after HSDA with maintained muscle and MU contractile force and speed but with a dramatic increase in fatigability, irrespective of whether all the dorsal roots were transected. We conclude that reduced neuromuscular activity accounts for increased fatigability but is not, in of itself, sufficient to promote atrophy and slow to fast conversion. Position and relative movements of hindlimb muscles are likely contributors to sustained MG muscle and MU contractile force and speed after HSDA and HSDA-SP surgeries.

Interdisciplinary bodyweight management program for persons with SCI

Objective: Persons with spinal cord injury (SCI) have a higher prevalence of being overweight than the general population, which is thought to be due to a variety of metabolic, physiologic and psychological changes. The quality improvement project described in this work was designed to help overweight persons with SCI lose bodyweight through nutrition, exercise, and behavioral management strategies.Methods: Eighteen persons with SCI who were overweight were enrolled in a 12-week interdisciplinary weight management program. Participants were limited to persons at least one-year post-acute SCI with an established overweight status. Measurements, including a person's weight, body mass index, and waist circumference (WaC), were taken at the program's start, at its end, and six months post program.Results: Seventeen out of 18 participants experienced weight loss, (WaC) decreased (P < 0.001), and the program was effective at reducing weight (P < 0.001). Six months following participation in the program participants did experience a significant change in weight or waist size six months post program, thus indicating that subjects did not regain weight after completion of the program.Conclusion: This quality improvement project provided indications of the benefits of an SCI-specific interdisciplinary weight management program. Clinical research evaluating methods for helping persons with SCI achieve a healthy bodyweight is indicated.

Ventilator-induced diaphragm dysfunction: translational mechanisms lead to therapeutical alternatives in the critically ill

Mechanical ventilation [MV] is a life-saving technique delivered to critically ill patients incapable of adequately ventilating and/or oxygenating due to respiratory or other disease processes. This necessarily invasive support however could potentially result in important iatrogenic complications. Even brief periods of MV may result in diaphragm weakness [i.e., ventilator-induced diaphragm dysfunction [VIDD]], which may be associated with difficulty weaning from the ventilator as well as mortality. This suggests that VIDD could potentially have a major impact on clinical practice through worse clinical outcomes and healthcare resource use. Recent translational investigations have identified that VIDD is mainly characterized by alterations resulting in a major decline of diaphragmatic contractile force together with atrophy of diaphragm muscle fibers. However, the signaling mechanisms responsible for VIDD have not been fully established. In this paper, we summarize the current understanding of the pathophysiological pathways underlying VIDD and highlight the diagnostic approach, as well as novel and experimental therapeutic options.

Non-invasive, Brain-controlled Functional Electrical Stimulation for Locomotion Rehabilitation in Individuals with Paraplegia

Spinal cord injury (SCI) impairs the flow of sensory and motor signals between the brain and the areas of the body located below the lesion level. Here, we describe a neurorehabilitation setup combining several approaches that were shown to have a positive effect in patients with SCI: gait training by means of non-invasive, surface functional electrical stimulation (sFES) of the lower-limbs, proprioceptive and tactile feedback, balance control through overground walking and cue-based decoding of cortical motor commands using a brain-machine interface (BMI). The central component of this new approach was the development of a novel muscle stimulation paradigm for step generation using 16 sFES channels taking all sub-phases of physiological gait into account. We also developed a new BMI protocol to identify left and right leg motor imagery that was used to trigger an sFES-generated step movement. Our system was tested and validated with two patients with chronic paraplegia. These patients were able to walk safely with 65-70% body weight support, accumulating a total of 4,580 steps with this setup. We observed cardiovascular improvements and less dependency on walking assistance, but also partial neurological recovery in both patients, with substantial rates of motor improvement for one of them.

Mechanomyography responses characterize altered muscle function during electrical stimulation-evoked cycling in individuals with spinal cord injury

BACKGROUND

Investigation of muscle fatigue during functional electrical stimulation (FES)-evoked exercise in individuals with spinal cord injury using dynamometry has limited capability to characterize the fatigue state of individual muscles. Mechanomyography has the potential to represent the state of muscle function at the muscle level. This study sought to investigate surface mechanomyographic responses evoked from quadriceps muscles during FES-cycling, and to quantify its changes between pre- and post-fatiguing conditions in individuals with spinal cord injury.

METHODS

Six individuals with chronic motor-complete spinal cord injury performed 30-min of sustained FES-leg cycling exercise on two days to induce muscle fatigue. Each participant performed maximum FES-evoked isometric knee extensions before and after the 30-min cycling to determine pre- and post- extension peak torque concomitant with mechanomyography changes.

FINDINGS

Similar to extension peak torque, normalized root mean squared (RMS) and mean power frequency (MPF) of the mechanomyography signal significantly differed in muscle activities between pre- and post-FES-cycling for each quadriceps muscle (extension peak torque up to 69%; RMS up to 80%, and MPF up to 19%). Mechanomyographic-RMS showed significant reduction during cycling with acceptable between-days consistency (intra-class correlation coefficients, ICC = 0.51-0.91). The normalized MPF showed a weak association with FES-cycling duration (ICC = 0.08-0.23). During FES-cycling, the mechanomyographic-RMS revealed greater fatigue rate for rectus femoris and greater fatigue resistance for vastus medialis in spinal cord injured individuals.

INTERPRETATION

Mechanomyographic-RMS may be a useful tool for examining real time muscle function of specific muscles during FES-evoked cycling in individuals with spinal cord injury.

Effects of ursolic acid on sub-lesional muscle pathology in a contusion model of spinal cord injury

Spinal Cord Injury (SCI) results in severe sub-lesional muscle atrophy and fiber type transformation from slow oxidative to fast glycolytic, both contributing to functional deficits and maladaptive metabolic profiles. Therapeutic countermeasures have had limited success and muscle-related pathology remains a clinical priority. mTOR signaling is known to play a critical role in skeletal muscle growth and metabolism, and signal integration of anabolic and catabolic pathways. Recent studies show that the natural compound ursolic acid (UA) enhances mTOR signaling intermediates, independently inhibiting atrophy and inducing hypertrophy. Here, we examine the effects of UA treatment on sub-lesional muscle mTOR signaling, catabolic genes, and functional deficits following severe SCI in mice. We observe that UA treatment significantly attenuates SCI induced decreases in activated forms of mTOR, and signaling intermediates PI3K, AKT, and S6K, and the upregulation of catabolic genes including FOXO1, MAFbx, MURF-1, and PSMD11. In addition, UA treatment improves SCI induced deficits in body and sub-lesional muscle mass, as well as functional outcomes related to muscle function, motor coordination, and strength. These findings provide evidence that UA treatment may be a potential therapeutic strategy to improve muscle-specific pathological consequences of SCI.

Nutritional Health Considerations for Persons with Spinal Cord Injury

Chronic spinal cord injury (SCI) often results in morbidity and mortality due to all-cause cardiovascular disease (CVD) and comorbid endocrine disorders. Several component risk factors for CVD, described as the cardiometabolic syndrome (CMS), are prevalent in SCI, with the individual risks of obesity and insulin resistance known to advance the disease prognosis to a greater extent than other established risks. Notably, adiposity and insulin resistance are attributed in large part to a commonly observed maladaptive dietary/nutritional profile. Although there are no evidence-based nutritional guidelines to address the CMS risk in SCI, contemporary treatment strategies advocate more comprehensive lifestyle management that includes sustained nutritional guidance as a necessary component for overall health management. This monograph describes factors in SCI that contribute to CMS risks, the current nutritional profile and its contribution to CMS risks, and effective treatment strategies including the adaptability of the Diabetes Prevention Program (DPP) to SCI. Establishing appropriate nutritional guidelines and recommendations will play an important role in addressing the CMS risks in SCI and preserving optimal long-term health.

Paralytic and nonparalytic muscle adaptations to exercise training versus high-protein diet in individuals with long-standing spinal cord injury

This study compares the effects of an 8-wk isocaloric high-protein (HP) diet versus a combination exercise (Comb-Ex) regimen on paralytic vastus lateralis (VL) and nonparalytic deltoid muscle in individuals with long-standing spinal cord injury (SCI). Fiber-type distribution, cross-sectional area (CSA), levels of translation initiation signaling proteins (Erk-1/2, Akt, p70S6K1, 4EBP1, RPS6, and FAK), and lean thigh mass were analyzed at baseline and after the 8-wk interventions. A total of 11 participants (C5-T12 levels, 21.8 ± 6.3 yr postinjury; 6 Comb-Ex and 5 HP diet) completed the study. Comb-Ex training occurred 3 days/wk and consisted of upper body resistance training (RT) in addition to neuromuscular electrical stimulation (NMES)-induced-RT for paralytic VL muscle. Strength training was combined with high-intensity arm-cranking exercises (1-min intervals at 85-90%, V̇o2peak) for improving cardiovascular endurance. For the HP diet intervention, protein and fat each comprised 30%, and carbohydrate comprised 40% of total energy. Clinical tests and muscle biopsies were performed 24 h before and after the last exercise or diet session. The Comb-Ex intervention increased Type IIa myofiber distribution and CSA in VL muscle and Type I and IIa myofiber CSA in deltoid muscle. In addition, Comb-Ex increased lean thigh mass, V̇o2peak, and upper body strength ( P < 0.05). These results suggest that exercise training is required to promote favorable changes in paralytic and nonparalytic muscles in individuals with long-standing SCI, and adequate dietary protein consumption alone may not be sufficient to ameliorate debilitating effects of paralysis. NEW & NOTEWORTHY This study is the first to directly compare the effects of an isocaloric high-protein diet and combination exercise training on clinical and molecular changes in paralytic and nonparalytic muscles of individuals with long-standing spinal cord injury. Our results demonstrated that muscle growth and fiber-type alterations can best be achieved when the paralyzed muscle is sufficiently loaded via neuromuscular electrical stimulation-induced resistance training.

Contribution of Neuromuscular Factors to Quadriceps Asymmetry After Anterior Cruciate Ligament Reconstruction

CONTEXT

  To quantify quadriceps weakness after anterior cruciate ligament reconstruction (ACLR), researchers have often analyzed only peak torque. However, analyzing other characteristics of the waveform, such as the rate of torque development (RTD), time to peak torque (TTP), and central activation ratio (CAR), can lend insight into the underlying neuromuscular factors that regulate torque development.

OBJECTIVE

  To determine if interlimb neuromuscular asymmetry was present in patients with ACLR at the time of clearance to return to activity.

DESIGN

  Cross-sectional study.

SETTING

  Laboratory.

PATIENTS OR OTHER PARTICIPANTS

  A total of 10 individuals serving as controls (6 men, 4 women; age = 23.50 ± 3.44 years, height = 1.73 ± 0.09 m, mass = 71.79 ± 9.91 kg) and 67 patients with ACLR (43 men, 24 women; age = 21.34 ± 5.73 years, height = 1.74 ± 0.11 m, mass = 77.85 ± 16.03 kg, time postsurgery = 7.52 ± 1.36 months) participated.

MAIN OUTCOME MEASURE(S)

  Isokinetic (60°/s) and isometric quadriceps strength were measured. Peak torque, TTP, and RTD were calculated across isometric and isokinetic trials, and CAR was calculated from the isometric trials via the superimposed burst. Repeated-measures analyses of variance were used to compare limbs in the ACLR and control groups.

RESULTS

  No between-limbs differences were detected in the control group ( P > .05). In the ACLR group, the involved limb demonstrated a longer TTP for isokinetic strength ( P = .04; Cohen d effect size [ES] = 0.18; 95% confidence interval [CI] = -0.16, 0.52), lower RTD for isometric ( P < .001; Cohen d ES = 0.73; 95% CI = 0.38, 1.08) and isokinetic ( P < .001; Cohen d ES = 0.84; 95% CI = 0.49, 1.19) strength, lower CAR ( P < .001; Cohen d ES = 0.37; 95% CI = 0.03, 0.71), and lower peak torque for isometric ( P < .001; Cohen d ES = 1.28; 95% CI = 0.91, 1.65) and isokinetic ( P < .001; Cohen d ES = 1.15; 95% CI = 0.78, 1.52) strength.

CONCLUSIONS

  Interlimb asymmetries at return to activity after ACLR appeared to be regulated by several underlying neuromuscular factors. We theorize that interlimb asymmetries in isometric and isokinetic quadriceps strength were associated with changes in muscle architecture. Reduced CAR, TTP, and RTD were also present, indicating a loss of motor-unit recruitment or decrease in firing rate.

Effect of tendon vibration during wide-pulse neuromuscular electrical stimulation (NMES) on muscle force production in people with spinal cord injury (SCI)

Background

Neuromuscular electrical stimulation (NMES) is commonly used in skeletal muscles in people with spinal cord injury (SCI) with the aim of increasing muscle recruitment and thus muscle force production. NMES has been conventionally used in clinical practice as functional electrical stimulation (FES), using low levels of evoked force that cannot optimally stimulate muscular strength and mass improvements, and thus trigger musculoskeletal changes in paralysed muscles. The use of high intensity intermittent NMES training using wide-pulse width and moderate-intensity as a strength training tool could be a promising method to increase muscle force production in people with SCI. However, this type of protocol has not been clinically adopted because it may generate rapid muscle fatigue and thus prevent the performance of repeated high-intensity muscular contractions in paralysed muscles. Moreover, superimposing patellar tendon vibration onto the wide-pulse width NMES has been shown to elicit further increases in impulse or, at least, reduce the rate of fatigue in repeated contractions in able-bodied populations, but there is a lack of evidence to support this argument in people with SCI.

Methods

Nine people with SCI received two NMES protocols with and without superimposing patellar tendon vibration on different days (i.e. STIM and STIM+vib), which consisted of repeated 30 Hz trains of 58 wide-pulse width (1000 μs) symmetric biphasic pulses (0.033-s inter-pulse interval; 2 s stimulation train; 2-s inter-train interval) being delivered to the dominant quadriceps femoris. Starting torque was 20% of maximal doublet-twitch torque and stimulations continued until torque declined to 50% of the starting torque. Total knee extensor impulse was calculated as the primary outcome variable.

Results

Total knee extensor impulse increased in four subjects when patellar tendon vibration was imposed (59.2 ± 15.8%) but decreased in five subjects (− 31.3 ± 25.7%). However, there were no statistically significant differences between these sub-groups or between conditions when the data were pooled.

Conclusions

Based on the present results there is insufficient evidence to conclude that patellar tendon vibration provides a clear benefit to muscle force production or delays muscle fatigue during wide-pulse width, moderate-intensity NMES in people with SCI.

Trial registration

ACTRN12618000022268. Date: 11/01/2018. Retrospectively registered.

Injection of high dose botulinum-toxin A leads to impaired skeletal muscle function and damage of the fibrilar and non-fibrilar structures

Botulinum-toxin A (BoNT/A) is used for a wide range of conditions. Intramuscular administration of BoNT/A inhibits the release of acetylcholine at the neuromuscular junction from presynaptic motor neurons causing muscle-paralysis. The aim of the present study was to investigate the effect of high dose intramuscular BoNT/A injections (6 UI = 60 pg) on muscle tissue. The gait pattern of the rats was significantly affected 3 weeks after BoNT/A injection. The ankle joint rotated externally, the rats became flat footed, and the stride length decreased after BoNT/A injection. Additionally, there was clear evidence of microstructural changes on the tissue level by as evidenced by 3D imaging of the muscles by Synchrotron Radiation X-ray Tomographic Microscopy (SRXTM). Both the fibrillar and the non-fibrillar tissues were affected. The volume fraction of fibrillary tissue was reduced significantly and the non-fibrillar tissue increased. This was accompanied by a loss of the linear structure of the muscle tissue. Furthermore, gene expression analysis showed a significant upregulation of COL1A1, MMP-2, TGF-b1, IL-6, MHCIIA and MHCIIx in the BoNT/A injected leg, while MHVIIB was significantly downregulated.

IN CONCLUSION

The present study reveals that high dose intramuscular BoNT/A injections cause microstructural damage of the muscle tissue, which contributes to impaired gait.