Muscle Fiber Type Research Articles

Effects of Free-Range Systems on Muscle Fiber Characteristics and Welfare Indicators in Geese

Recently, free-range poultry production has increased with notable benefits for animal welfare and meat quality traits. Geese, the third-most productive poultry species, have not been studied extensively. This study investigated the effects of different free-range systems on muscle fiber characteristics and welfare status (feather quality, walking ability, and behavioral changes) in Yangzhou geese. A total of 180 male geese, aged 28 days, were randomly assigned to either a long-distance pasture system (LDPS, approximately 200 m from the geese house) or a short-distance pasture system (SDPS, approximately 50 m from the geese house). The indoor system (IS) treatment was used as a control. And all geese were equipped with pedometers. Daily step counts revealed that the geese took an average of 5777 and 4520 steps in the LDPS and SDPS, respectively, whereas only 2736 steps in the IS. Although no significant differences were observed in the muscle fiber types among the three systems, free-range systems contributed to more developed muscle fibers than the IS. In addition, thicker muscle fibers in the extensor digitorum longus and gastrocnemius muscles were observed in the LDPS group than in the SDPS group. Additionally, feather cleanliness and damage were evaluated. LDPS resulted in significantly cleaner feathers on the chest, abdomen, and back than the IS. Furthermore, geese in the free-range systems had less feather damage than those in the IS. Notably, pasture systems allowed for natural behaviors, such as single-foot standing, feather pecking, and walking, regardless of grazing distance. Taken together, these results show that the muscle fibers of geese in the free-range system were more developed. Simultaneously, increasing the amount of exercise for geese will improve their welfare, which is beneficial to their health, growth, and development, and provides a technical reference for the free-range breeding system for geese.

MOTS-c Impact on Muscle Cell Differentiation and Metabolism Across Fiber Types.

MOTS-c belongs to a group of mitochondrial peptides involved in metabolic processes in the body. This peptide has garnered increasing attention since its discovery in 2015 because of its potential to ameliorate metabolic parameters in animals with diabetes or insulin resistance. MOTS-c is involved in muscle metabolism; however, little is known about its role in fiber differentiation. We conducted a study to explore the effect of MOTS-c on cellular processes using the C2C12 and L6 cell lines, representing different metabolic types of muscle fibers. The research methods were real-time PCR, Western blot, and lipid accumulation measurement. Notably, our investigations revealed that MOTS-c increased the survival of C2C12 cells at doses of 10 and 100 nM (p<0.01) and stimulated the phosphorylation of extracellular signal-regulated kinase within 5 min of incubation (p<0.05). Remarkably, these effects were not observed in L6 cells; however, both cell lines showed a reduced rate of proliferation. Furthermore, MOTS-c promotes the differentiation of C2C12 cells by increasing the expression of muscle regulatory factors, but it does not produce such an effect in L6 cells. Additionally, cells were treated with physiological concentrations of free fatty acids and MOTS-c, unveiling an augmentation in lipid accumulation observed in L6 cells and a decrease in lipid accumulation in C2C12 cells. In conclusion, our findings have suggested a diverse response to MOTS-c depending on the type of muscle fibers, particularly in the domains of survival, cell differentiation, and lipid accumulation.

A comparison of seasonal flexibility in pectoralis muscle fiber type and enzyme activity in migratory and resident sparrow species

The pectoralis muscle in birds is important for flight and thermogenesis. In migratory songbirds this muscle exhibits seasonal flexibility in size, but whether this flexibility reflects changes in muscle fiber type has not been well documented. We investigated how seasonal changes in photoperiod affected pectoralis muscle fiber type and metabolic enzymes, comparing among three closely-related sparrow species: two seasonal migrants and one year-round, temperate climate resident. We quantified fast oxidative glycolytic (FOG) and fast glycolytic (FG) fibers histologically, and measured activities of citrate synthase (CS) and lactate dehydrogenase (LDH) in the pectoralis muscle of the three species that were acclimated to long- or short-daylight length conditions. In all species FOG was the predominant fiber type, but song sparrows had FG fibers regardless of daylight length. By contrast, Lincoln's sparrows incorporated FG fibers only under short-daylight length onditions, and house sparrows did not significantly express FG fibers, regardless of conditions. Both migratory species increased LDH activity in short-daylight conditions, but did not alter CS activity. In contrast, resident house sparrows did not alter CS or LDH activity with changes in daylight length. Our findings suggest that the presence of FG fibers is important for seasonal flexibility in LDH activity. Additionally, migratory species exhibited seasonal flexibility in muscle fiber type and enzyme activity, presumably to support migratory flight, while the resident species did not exhibit such seasonal flexibility, suggesting that this consistent phenotype is important year-round, despite changing thermogenic requirements.

Relationship between muscle power, muscle volume and limb length in healthy male and female adolescents.

Muscle power is essential for the activities of daily living. Muscle power production depends on numerous factors such as muscle size and length, muscle architecture and fiber type and varies with age during growth. The association between muscle power output during a jump and lower limb muscle volume and length in adolescents is largely unknown. This study determined the relationships between muscle power developed during a countermovement jump with lower limb muscle volume and length in adolescents aged between 16 and 19 years. Forty healthy adolescent males (n = 20) and females (n = 20) aged 16 to 19 years underwent a counter-movement jump (CMJ) test. Muscle power (MP) during the jump was calculated using the Gomez-Bruton equation. Lower limb muscle volume (MV) and length were calculated in both sexes using anthropometric methods. Pearson correlation was used to assess the associations between variables. Independent-sample t-tests were used to compare anthropometric and muscle performance data between males and females. Cohen's d was used to determine the size of the differences. There were differences in all anthropometric variables between males and females (p < 0.001). CMJ height (d = 4.45; p = 0.001) and MP (d = 4.74; p = 0.001) were greater in males than in females (p < 0.001). These differences persisted when jump performance was normalized to the MV (d = 1.05; p = 0.01) and length (d = 4.07; p = 0.001). There were correlations between MV and MP for males and females, with a significant correlation between limb length and MP for males (r = 0.55; p = 0.002). This study indicates that MV and length are associated with MP production during a CMJ in adolescents aged between 16 and 19 years, suggesting that these factors may be important determining factors for vertical jumping performance during adolescence. The sex-differences in jump performance variables persisted after normalization by MV and length, suggesting that MV and length did not entirely explain the sex difference in muscle power output during a CMJ.

Musashi-2 regulates skeletal muscle fiber type and energy metabolism

Musashi-2 regulates skeletal muscle fiber type and energy metabolism

Genome-Wide Association Study of Myofiber Type Composition Traits in a Yellow-feather Broiler Population

Meat quality is a key factor determining the economic viability of the broiler industry, particularly in native broiler breeds. Skeletal muscles contain a mixture of muscle fibers, each possessing unique physicochemical properties; the composition of myofiber types within these muscles is closely linked to meat quality. However, comprehension of the regulatory mechanisms governing this trait remains limited. Therefore, we conducted a genome-wide association study (GWAS) with a population of 400 yellow-feather broilers to explore genetic variations associated with myofiber-type composition at the genomic level. Whole-genome resequencing was employed to detect genetic variations and immunohistochemistry was used for muscle fiber typing in the sartorius muscle. We identified 1 and 18 single-nucleotide polymorphisms (SNPs) significantly and potentially associated with the proportion of slow muscle fibers, respectively, and 1 and 12 SNPs significantly and potentially associated with the area proportion of slow muscle fibers, respectively. We annotated several candidate genes, including DMD, KLF7, CREB1, EFCAB11, GADD45A, GSTT1, and GSTT1L, which are related to myofiber type composition. We also demonstrated that myofiber composition traits exhibit low-to-medium heritability, indicating potential for enhancement through genetic selection. These findings provide a crucial reference for further studies on the regulatory mechanisms of poultry meat quality and for advancing the breeding of superior-quality broiler chickens.

No detectable loss of myonuclei from human muscle fibers after 6 wk of immobilization following an Achilles tendon rupture.

Muscle disuse has rapid and debilitating effects on muscle mass and overall health, making it an important issue from both scientific and clinical perspectives. However, the myocellular adaptations to muscle disuse are not yet fully understood, particularly those related to the myonuclear permanence hypothesis. Therefore, in this study, we assessed fiber size, number of myonuclei, satellite cells, and capillaries in human gastrocnemius muscle after a period of immobilization following an Achilles tendon rupture. Six physically active patients (5 males/1 female, 43 ± 15 yr) were recruited to participate after sustaining an acute unilateral Achilles tendon rupture. Muscle biopsies were obtained from the lateral part of the gastrocnemius before and after 6 wk of immobilization using a plaster cast and orthosis. Muscle fiber characteristics were analyzed in tissue cross-sections and isolated single fibers using immunofluorescence and high-resolution microscopy. Immobilization did not change muscle fiber type composition nor cross-sectional area of type I or type II fibers, but muscle fiber volume tended to decline by 13% (P = 0.077). After immobilization, the volume per myonucleus was significantly reduced by 20% (P = 0.008). Myonuclei were not lost in response to immobilization but tended to increase in single fibers and type II fibers. No significant changes were observed for satellite cells or capillaries. Myonuclei were not lost in the gastrocnemius muscle after a prolonged period of immobilization, which may provide support to the myonuclear permanence hypothesis in human muscle. Capillaries remained stable throughout the immobilization period, whereas the response was variable for satellite cells, particularly in type II fibers.NEW & NOTEWORTHY The impact of prolonged immobilization on muscle fiber characteristics is difficult to study in humans and therefore remains poorly understood. We analyzed cross-sections and single fibers from gastrocnemius before and after 6 wk of immobilization due to an Achilles tendon rupture. Our data suggest that myonuclei are not lost in response to such stimuli, thus lending support to the hypothesis of myonuclear permanency in human muscle.

Progress and prospects of the effects and mechanisms of myokines in regulating fiber type transition of skeletal muscle

The fiber type transition of skeletal muscle is an intricate and essential physiological process in the body, significantly influencing both the function and metabolism of skeletal muscle. This phenomenon is not only affected by external environmental changes but also intricately regulated by internal physiological mechanisms. Therefore, exploring the physiological process of muscle fiber type transition holds considerable significance for the treatment of human neuromuscular disorders and the improvement of meat quality in livestock and poultry. It has been discovered that the cytokines secreted by skeletal muscle, i.e., myokines, play a role in the fiber type transition of skeletal muscle. Myokines mainly act on skeletal muscle in autocrine and paracrine forms to participate in signal transduction and regulate the fiber type transition of skeletal muscle. This paper reviews the functional differences among various muscle fiber types, expounds the effects and mechanisms of myokines in regulating the transition processes of these fiber types, and prospects the future research directions in this field. This review is expected to provide theoretical support for enhancing the meat quality of livestock and poultry and treating skeletal muscle-related diseases.

Aging-induced changes in lymphatic muscle cell transcriptomes are associated with reduced pumping of peripheral collecting lymphatic vessels in mice.

Lymphatic muscle cells (LMCs) within the wall of collecting lymphatic vessels exhibit tonic and autonomous phasic contractions, which drive active lymph transport to maintain tissue-fluid homeostasis and support immune surveillance. Damage to LMCs disrupts lymphatic function and is related to various diseases. Despite their importance, knowledge of the gene transcriptional signatures in LMCs and how they relate to lymphatic function in normal and disease contexts is largely missing. We have generated a comprehensive transcriptional single-cell atlas-including LMCs-of peripheral collecting lymphatic vessels from mice across the lifespan. We identified genes that distinguish LMCs from other types of muscle cells, characterized the phenotypical and transcriptomic changes in LMCs in aged vessels, and identified a proinflammatory microenvironment that suppresses the contractile apparatus in LMCs from advanced-aged mice. Our findings provide a valuable resource to accelerate future research for the identification of potential drug targets on LMCs to improve lymphatic vessel function.

Arginase-II gene deficiency reduces skeletal muscle aging in mice.

Age-associated sarcopenia decreases mobility and is promoted by cell senescence, inflammation, and fibrosis. The mitochondrial enzyme arginase-II (Arg-II) plays a causal role in aging and age-associated diseases. Therefore, we aim to explore the role of Arg-II in age-associated decline of physical activity and skeletal muscle aging in a mouse model. Young (4-6 months) and old (20-24 months) wild-type (wt) mice and mice deficient in arg-ii (arg-ii-/-) of both sexes are investigated. We demonstrate a decreased physical performance of old wt mice, which is partially prevented in arg-ii-/- animals, particularly in males. The improved phenotype of arg-ii-/- mice in aging is associated with reduced sarcopenia, cellular senescence, inflammation, and fibrosis, whereas age-associated decline of microvascular endothelial cell density, satellite cell numbers, and muscle fiber types in skeletal muscle is prevented in arg-ii-/- mice. Finally, we demonstrate an increased arg-ii gene expression level in aging skeletal muscle and found Arg-II protein expression in endothelial cells and fibroblasts, but not in skeletal muscle fibers, macrophages, and satellite cells. Our results suggest that increased Arg-II in non-skeletal muscle cells promotes age-associated sarcopenia, particularly in male mice.

Anatomical and histological analyses of ankle plantar flexors: insights into connective tissue composition and muscle architecture.

The tibialis posterior (TP), flexor digitorum longus (FDL), and flexor hallucis longus (FHL) are muscles that contribute to the stability of foot and ankle movements, playing a crucial role in achieving optimal gait. However, a comprehensive examination of the anatomical characteristics and histological variances of each muscle has not been conclusively established. A total of 10 un-embalmed cadavers were dissected, and muscles from each cadaver were consistently harvested from the musculotendon junction. The ratio of collagen and elastic fibers was assessed through three immunohistological analyses, focusing on distinct histological characteristics in type I (slow twitch) and type II (fast twitch) fibers. Additionally, Ultrasonography was utilized to compare and analyze the thickness, fascicle angle, and muscle fiber length of each muscle. Concerning the relative proportion of elastic fibers to collagen, the TP exhibited the highest collagen content (21.9 ± 0.30%, mean ± standard deviation), while the FHL had the highest elastic fiber proportion (48.4 ± 0.44%). The TP predominantly comprised slow type muscle fibers (36.88 ± 0.83%), whereas the FHL contained a higher density of fast type muscle fibers (32.46 ± 4.02%). US analysis indicated that the thickness of the TP was relatively greater (2.0 ± 0.2mm) compared to the FDL (1.2 ± 0.1mm) and FHL (1.1 ± 0.1mm). Additionally, the fascicle length was notably longer in the TP (25.6 ± 4.1mm). Our anatomical and histological findings indicate that the tibialis posterior (TP) is the thickest with a significant physiological angle and a high collagen content. This characteristic enables the TP to provide stability by transmitting a constant force to the calf. On the other hand, the flexor hallucis longus (FHL) exhibits the highest elastic fiber content, confirming its ability to exert instantaneous, swift, and powerful force.

Transcriptomic Profiling Reveals Differences in Slow-Twitch and Fast-Twitch Muscles of a Cigarette Smoke-Exposed Rat Model.

Cigarette smoking is known to affect muscle function and exercise capacity, including muscle fatigue resistance. Most studies showed diminished cross-sectional area and fibre type shifting in slow-twitch muscles such as the soleus, while effects on fast-twitch muscles were seldom reported and the differential responses between muscle types in response to exposureto cigarette smoke (CS) were largely unknown. This study aimed to elucidate the histomorphological, biochemical and transcriptomic changes induced by CS on both slow-twitch and fast-twitch muscles. Male Sprague-Dawley rats were randomly divided into two groups: sham air (SA) and CS. The rats were exposed to CS for 8 weeks using an exposure chamber system to mimic smoking conditions. Histomorphological analyses on muscle fibre type and cross-sectional area were determined in soleus and extensor digitorum longus (EDL). Transcriptomic profiles were investigated for identifying differentially expressed genes (DEGs) and potential mechanistic pathways involved. Inflammatory responses in terms of the macrophage population and the level of inflammatory cytokines were measured. Markers for muscle-specific proteolysis were also examined. Soleus muscle, but not in EDL, exhibited a significant increase in Type IIa fibres (SA: 9.0 ± 3.3%; CS: 19.8 ± 2.4%, p = 0.002) and decrease in Type I fibres (SA: 90.1 ± 3.6%; CS: 77.9 ± 3.3%, p = 0.003) after CS exposure. RNA sequencing revealed 165 identified DEGs in soleus including upregulation of 'Cd68', 'Ccl2' and 'Ucp2' as well as downregulation of 'Ucp3', etc. Pathways enrichment analysis revealed that the upregulated pathways in soleus were related to immune system and cellular response, while the downregulated pathways were related to oxidative metabolism. Only 10 DEGs were identified in EDL with less enriched pathways. The soleus also showed elevated pro-inflammatory cytokines, and the total macrophage marker CD68 was significantly higher in soleus of CS compared to the SA group (CD68+/no. of fibre: SA = 60.3 ± 39.3%; CS = 106.5 ± 27.2%, p = 0.0039), while the two groups in EDL muscle showed no significant difference. The expression of E3 ubiquitin ligase atrogin-1 associated with muscle degradation pathways was 1.63-fold higher in the soleus after CS, while no significant differences were observed in the EDL. The CS-induced inflammatory responses on soleus muscle are likely mediated via targeting mitochondrial-related signalling, resulting in mitochondrial dysfunction and impaired oxidative capacity. The presumably less active mitochondrial-related signalling in EDL renders it less susceptible to changes towards CS, accounting for differential impacts between muscle types.

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.

Delphinidin induces a fast-to-slow muscle fiber type shift through the AMPK signaling pathway in C2C12 myotubes

Delphinidin, a plant anthocyanidin, suppresses disuse muscle atrophy in mice. However, its effect on muscle fiber type shift is unclear. To examine whether delphinidin affects skeletal muscle fiber type, differentiated C2C12 cells were treated with delphinidin. Results revealed that delphinidin upregulated the mRNA expression of myosin heavy chain type I (MyHCI), troponin C1, troponin I1, and MyHCIIx and increased slow MyHC protein level in C2C12 myotubes. Delphinidin also enhanced succinic dehydrogenase (SDH) activities and suppressed lactate dehydrogenase (LDH) activity. Adenosine monophosphate–activated protein kinase (AMPK) inhibition attenuated delphinidin-induced MyHCI upregulation and MyHCIIb downregulation. We investigated the effect of delphinidin on the upstream factors involved in AMPK activation. Delphinidin increased liver kinase B1 (LKB1) phosphorylation and nuclear respiratory factor 1 (NRF1) and calcium/calmodulin-dependent protein kinase 2 (CaMKK2) protein levels. In conclusion, delphinidin induced muscle fiber type conversion from fast-twitch to slow-twitch muscles through the AMPK signaling pathway.

Modelling Skeletal Muscle Motor Unit Recruitment Contributions to Contractile Function: Part 3 - Substrate Oxidation of Phosphagen, Lipid, and Carbohydrate Metabolism

This study aimed to apply and expand a prior model of motor unit recruitment of the vastus lateralis muscle (VL) to explore theoretical motor unit-specific substrate oxidation. The model utilized repeated contractions of varied frequency and fraction of motor unit recruitment, and four different genetic expressions of motor unit proportions. The study applied prior modelled data of the vastus lateralis (VL) motor unit contractile power and turnover of adenosine triphosphate (ATPto) based on non-linear functions of estimated percentage contributions of different energy systems across various muscle fibre types and contraction frequencies. Using LabVIEW™ programming, the model then used the prior data of ATPto and known ATPto coefficients for substrate oxidation for the energy systems of phosphagen, glycolytic, and mitochondrial respiration from fatty acid and carbohydrate to calculate total and fibre type (motor unit) specific creatine phosphate catabolism, glycogenolysis, glycolytic glucose oxidation, fatty acid oxidation in mitochondrial respiration, glucose oxidation in mitochondrial respiration, and lactate production. Results revealed that for the phosphagen system, substrate turnover was far larger than research-based expressions of decreasing concentrations of creatine phosphate and ATP. This is to be expected for modelled research involving temporal summation of metabolism. Creatine phosphate is continually broken down and partially replenished during low intensity exercise, with such partial replenishment sustained during more intense exercise thanks to the creatine kinase shuttle. For carbohydrate oxidation, mitochondrial respiration accounted for greatest substrate oxidation in type I, and I-IIa motor units, where glycolysis accounted for most substrate oxidation in type IIa, IIab and IIb motor units. Fatty acid oxidation was larger for lower motor unit recruitment conditions, and highest for type I-IIa and IIa motor units. This result is logical based on the larger net muscle fibre recruitment for contraction conditions necessitating progression to fast twitch motor units causing higher substrate oxidation. Such findings reinforce the need for more research on fibre type specific substrate oxidation during different exercise intensities and durations.

Influence of Bovine Myosin Heavy Chain Isoforms and Muscle Fiber Cross-Sectional Are&lt;em&gt;a o&lt;/em&gt;n the Eating Quality and Connective Tissue Characteristics of 11 Different Beef Muscles

The objective of this study was to determine the impact of muscle fiber type, cross-sectional area (CSA), and diameter on the eating quality of 11 different beef muscles. Eleven different beef muscles were utilized in 2 separate studies. In the 2 studies, triceps brachii, rectus abdominus, rectus femoris, supraspinatus, gluteus medias, pectoralis profundi, semitendinosus, longissimus thoracis, longissimus lumborum, tensor fascia latae, and gastrocnemius were collected from 10 USDA Choice carcasses (N = 110). To determine muscle fiber type, myofibrillar proteins were extracted and separated via gel electrophoresis and immunoblot, while muscle fiber CSA and diameter were determined using a dystrophin antibody stain via fluorescence microscopy. Pearson correlation analysis was performed to determine the relationship between muscle fiber type, CSA, diameter, and the eating quality of the 11 beef cuts from previously reported studies. Muscles from both studies showed distinct differences in the relative percentage of type I and type IIA muscle fiber types, CSA, and diameter (P &amp;lt; 0.05). Correlation analysis from study 1 demonstrated positive correlations between type I fibers and many positive attributes of eating quality such as tenderness, juiciness, and lipid flavor intensity, while negative correlations were found between type IIA fibers and those attributes (P &amp;lt; 0.01). Interestingly, results from study 2 showed that increasing type I fiber percentage may also contribute to greater connective tissue content and collagen crosslink density (P &amp;lt; 0.01). Finally, a negative correlation was found between muscle fiber CSA and diameter with connective tissue amount (P &amp;lt; 0.05), and a positive correlation was found between muscle fiber CSA and diameter with tenderness measurements (P &amp;lt; 0.05) in both studies. Overall, muscles with greater type I fiber % delivered a more favorable eating experience than those with more glycolytic metabolism. Notably, increased CSA and fiber diameter did not diminish eating quality and were found to have a muscle-specific relationship with tenderness.

Multi-channel EMG manifestations of upper-extremity muscle coordination imbalance among community-dwelling sarcopenic seniors

BackgroundSarcopenia is an age-related, insidious, crippling but curable degenerative disease if diagnosed and treated early. However, no accessible and accurate early screening method is available for community settings that does not require specialized personnel. One of the hallmarks of sarcopenia is the pathological changes of muscle fiber type composition and motor unit firing patterns. Surface electromyography (sEMG) may serve as an effective tool for detecting differences between healthy and sarcopenic individuals due to its superior wearability and accessibility compared to other screening methods such as medical imaging and bioimpedance measurements, making it ideal for community-based sarcopenic screening. Our study aims to explore sEMG biomarkers that can be used for screening or diagnosis of sarcopenia.ResultsWe collected multi-channel sEMG signals from six forearm muscles of 98 healthy and 55 sarcopenic community-dwelling older adults. Participants performed grasp tasks at 20% and 50% of maximum voluntary contraction (MVC). Hexagons created by various EMG features, normalized with respect to respective MVC, and symmetry analyses were performed to estimate multi-muscle coordination patterns. An innovative index, namely incenter–circumcenter distance of muscle coordination (ICDMC), is proposed to discriminate between the healthy and sarcopenic groups. We utilized non-parametric tests to compare the ICDMC between the two groups, considering a p-value less than 0.05 statistically significant. The results showed that at 20% MVC, ICDMCs from root mean square (RMS), mean absolute value (MAV), slope sign changes (SSC) and wavelength (WL) showed statistically significant differences. More insights of this sEMG manifestation of sarcopenia were revealed by gender- and age-stratifications analyses.ConclusionsOur results demonstrated that there are clear sEMG manifestations of altered muscle coordination in sarcopenic patients. More consistent force generation patterns were observed in the sarcopenic group, especially at lower contraction intensities. The novel ICDMC can quantify differences between sarcopenic and healthy muscle. These results warrant further research to further develop more accessible sarcopenia screening strategies in community settings based on electrophysiological measurements such as sEMG.

Skeletal muscle cell transformation and its influencing factors

Abstract. The composition of muscle fiber type is closely related to pork quality, and the pork quality with high proportion of slow muscle fiber is relatively good. In the study, various regulatory factors were found to act on key genes that determine the type of skeletal muscle fibers. The results show that there are many transcription factors affecting the transformation of muscle fiber types, including calcineurin-NFAT signaling pathway, MEF2-HDACs signaling, AMPK-PGC1 and nuclear receptor PPAR /PPAR . However, the underlying mechanism of individual regulators is still unclear. The mechanism of action of PGC-1 , MicroRNA and PPAR () and the synergistic effects of MEF2 and PPAR with PGC-1 and PPAR () and ERR were analyzed. Relevant results were obtained such as PGC-1 gene expression can induce the conversion of type IIx muscle fibers to type I muscle fibers, and miR-133a regulates the conversion of slow muscle fibers to fast muscle fibers by targeting TEAD1; MiR-208b regulates the transformation of slow muscle fibers by targeting and inhibiting METTL8. PPAR () drives the formation of functional type I muscle fibers. In this paper, there is still a gap in the deep molecular mechanism, in the follow-up study, we can further clarify the factors of the key genes to determine the type of muscle fibers, as well as the deep influence mechanism between each factor. Future research and exploration can focus on the regulation factor proposed in this paper.

Single-nucleus RNA sequencing reveals midgut cellular heterogeneity and transcriptional profiles in Bombyx mori cytoplasmic polyhedrosis virus infection.

The gut is not only used by insects as an organ for the digestion of food and absorption of nutrients but also as an important barrier against the invasion and proliferation of pathogenic microorganisms. Bombyx mori cytoplasmic polyhedrosis virus (BmCPV), an insect-specific virus, predominantly colonizes the midgut epithelial cells of the silkworm, thereby jeopardizing its normal growth. However, there is limited knowledge of the cellular immune responses to viral infection and whether the infection is promoted or inhibited by different types of cells in the silkworm midgut. In this study, we used single-nucleus RNA sequencing to identify representative enteroendocrine cells, enterocytes, and muscle cell types in the silkworm midgut. In addition, by analyzing the transcriptional profiles of various subpopulations in the infected and uninfected groups, we found that BmCPV infection suppresses the response of the antiviral pathways and induces the expression of BmHSP70, which plays a role in promoting BmCPV replication. However, certain immune genes in the midgut of the silkworm, such as BmLebocin3, were induced upon viral infection, and downregulation of BmLEB3 using RNA interference promoted BmCPV replication in the midgut of B. mori. These results suggest that viral immune evasion and active host resistance coexist in BmCPV-infected silkworms. We reveal the richness of cellular diversity in the midgut of B. mori larvae by single-nucleus RNA sequencing analysis and provide new insights into the complex interactions between the host and the virus at the single-cell level.

Morphological Evidence for a Unique Neuromuscular Functional Unit of the Human Vocalis Muscle.

Human vocalization is a complex process that is still only partially understood. Previous studies have suggested the possibility of a localized neuromuscular network of the larynx. Here we investigate this structure in human dissection specimens using multiple immunofluorescence and transmission electron microscopy (TEM). In the area of the pars interna of the thyroarytenoid muscle, muscle fibers are present that are clearly differentiated from skeletal or cardiac muscle cells and show an intermediate ultrastructure. In addition, intramuscular neurons are present that are detectable by both electron and fluorescence microscopy and may have a sensory function in a local neuronal network. Also, several types of sensory and motor synapses are detectable and distributed throughout the pars interna of the thyroarytenoid muscle, with multisynaptic muscle fibers being a common feature. These findings suggest the existence of a previously unrecognized type of muscle fiber coupled to an intramuscular neuronal network, the presence of which could explain functional peculiarities at the laryngeal level.