Properties Of Muscle Cells Research Articles

A deep learning-based approach for fully automated segmentation and quantitative analysis of muscle fibers in pig skeletal muscle

Muscle fiber properties exert a significant influence on pork quality, with cross-sectional area (CSA) being a crucial parameter closely associated with various meat quality indicators, such as shear force. Effectively identifying and segmenting muscle fibers in a robust manner constitutes a vital initial step in determining CSA. This step is highly intricate and time-consuming, necessitating an accurate and automated analytical approach. One limitation of existing methods is their tendency to perform well on high signal-to-noise ratio images of intact, healthy muscle fibers but their lack of validation on more complex image datasets featuring significant morphological changes, such as the presence of ice crystals. In this study, we undertake the fully automatic segmentation of muscle fiber microscopic images stained with myosin adenosine triphosphate (mATPase) activity using a deep learning architecture known as SOLOv2. Our objective is to efficiently derive accurate measurements of muscle fiber size and distribution. Tests conducted on actual images demonstrate that our method adeptly handles the intricate task of muscle fiber segmentation, yielding quantitative results amenable to statistical analysis and displaying reliability comparable to manual analysis.

Discriminant canonical analysis as a tool for genotype traceability testing based on turkey meat and carcass traits.

The present study aims to develop a statistical tool for turkey breed traceability testing based on meat and carcass quality characteristics. To this end, a comprehensive meta-analysis was performed, collecting data from a total of 75 studies approaching meat and carcass attributes of 37 turkey strains and landraces since the late 1960s. A total of 22 meat and carcass traits were considered variables, grouped in the following clusters: carcass dressing traits, muscle fiber properties, pH, colorimetry, water-capacity traits, texture-related attributes, and nutritional composition of the meat. Once the multicollinearity analysis allowed the deletion of redundant variables, cold carcass weight, slaughter weight, muscle fiber diameter, sex-female, carcass/piece weight, meat redness, ashes, pH24, meat lightness, moisture, fat, and water-holding capacity showed explanatory properties in the discriminating analysis (p < 0.05). In addition, strong positive and negative correlations were found among those variables studied. Carcass traits were positively associated, particularly slaughter weight and cold carcass weight (+0.561). Among meat physical traits, pH showed positive correlations with drip loss (+0.490) and pH24 (+0.327), and water-holding capacity was positively associated with cholesterol (+0.434) and negatively associated with collagen (-0.398). According to nutritional traits, fat and ash showed a strong correlation (+0.595), and both were negatively associated with moisture (-0.375 and -0.498, respectively). Strong negative correlations were found as well between meat protein and fat (-0.460) and between collagen and cholesterol (-0.654). Finally, the Mahalanobis distance suggested a clustering pattern based on meat and carcass characteristics that report information about interbreeding and variety proximity. This study establishes a departure point in the development of a tool for breed traceability guaranteeing aimed at enhancing distinguished, local breed-based turkey meat.

Muscle Fiber, Connective Tissue and Meat Quality Characteristics of Pork from Low Birth Weight Pigs as Affected by Diet-Induced Increased Fat Absorption and Preferential Muscle Marbling.

This study investigated how birth weight differences in piglets affected carcass and muscle fiber properties as well as meat quality at slaughter. Within litters, piglets were grouped according to their birth weight as either normal (NBW; 1.62-1.73 kg) or low (LBW; 1.18-1.29 kg). At 5 weeks of age, NBW piglets were randomly transitioned to control (C) or isocaloric high fat diets derived from non-dairy (HF), while LBW piglets were randomly transitioned to high fat diets derived from non-dairy (HF) or dairy sources (HFHD). Piglets were reared in individual pens under standardized housing and feeding conditions. Live weight was recorded weekly, and pigs were slaughtered at 12 weeks of age. Hot carcass weights, dressing percentages, lean meat yield, and primal cut proportions were determined. The m. longissimus thoracis was collected from the right side of the carcass for measurement of physical and chemical properties of meat and muscle fiber characteristics. Results indicated that LBW pigs compensated for their live weight compared to NBW pigs at 6 weeks of age. The mean muscle fiber diameter of LBW-HFHD group is significantly higher than NBW-C and NBW-HF group, and the type I muscle fiber diameter is significantly higher than NBW-C group. Dairy fat inclusion in LBW pig diet reduced carcass back fat thickness. This increased the calculated lean meat yield to be comparable to that of NBW pigs fed a commercial diet. Incorporating dairy-sourced high-fat into LBW pigs' diets appears to be an effective strategy for producing carcasses equivalent to NBW pigs.

MYH13, a superfast myosin expressed in extraocular, laryngeal and syringeal muscles.

MYH13 is a unique type of sarcomeric myosin heavy chain (MYH) first detected in mammalian extraocular (EO) muscles and later also in vocal muscles, including laryngeal muscles of some mammals and syringeal muscles of songbirds. All these muscles are specialized in generating very fast contractions while producing relatively low force, a design appropriate for muscles acting against a much lower load than most skeletal muscles inserting into the skeleton. The definition of the physiological properties of muscle fibres containing MYH13 has been complicated by the mixed fibre type composition of EO muscles and the coexistence of different MYH types within the same fibre. A major advance in this area came from studies on isolated recombinant myosin motors and the demonstration that the affinity of actin-bound human MYH13 for ADP is much weaker than those of fast-type MYH1 (type 2X) and MYH2 (type 2A). This property is consistent with a very fast detachment of myosin from actin, a major determinant of shortening velocity. The MYH13 gene arose early during vertebrate evolution but was characterized only in mammals and birds and appears to have been lost in some teleost fish. The MYH13 gene is located at the 3' end of the mammalian fast/developmental gene cluster and in a similar position to the orthologous cluster in syntenic regions of the songbird genome. MYH13 gene regulation is controlled by a super-enhancer in the mammalian locus and deletion of the neighbouring fast MYH1 and MYH4 genes leads to abnormal MYH13 expression in mouse leg muscles.

The effect of breed and body weight at slaughter on histochemical muscle fiber characteristics and meat quality of longissimus lumborum and semitendinosus lamb muscles

Abstract. The skeletal muscles of mammals are composed of fibers of different morphological, metabolic and functional characteristics. The properties of muscle fibers may be determined genetically as well as by environmental factors such as the age of the animals, their physical activity, the level of nutrition, or the selection intensity. The present study was conducted to determine the influence of genotype (Polish Lowland vs. Polish Heath) and body weight at slaughter (23–25 kg vs. 35–40 kg) of lambs on histological characteristics of muscle fibers in musculus longissimus lumborum (LL) and musculus semitendinosus (ST) skeletal muscles and their impact on chosen meat quality features. Three types of muscle fibers were identified: slow-twitch oxidative (STO), fast-twitch oxidative (FTO) and fast-twitch glycolytic (FTG). Differences in the diameters of individual fiber types between the LL and ST muscles have been found in both investigated genotypes. The diameters of the analyzed types of fibers were usually larger in the ST muscle compared to the LL muscle. The lambs of the more primitive Polish Heath breed were characterized by a smaller diameter of all fiber types, especially in the LL muscle. The higher proportion of STO fibers and the lower proportion of FTO fibers have been found in the LL muscle of Polish Heath lambs in the group with lower body weight. The breed of lambs, muscle type and slaughter body weight had an impact on some meat quality characteristics, especially color, intramuscular fat content and expressed juice.

Study of Meat and Carcass Quality-Related Traits in Turkey Populations through Discriminant Canonical Analysis.

The present research aimed to determine the main differences in meat and carcass quality traits among turkey genotypes worldwide and describe the clustering patterns through the use of a discriminant canonical analysis (DCA). To achieve this goal, a comprehensive meta-analysis of 75 documents discussing carcass and meat characteristics in the turkey species was performed. Meat and carcass attributes of nine different turkey populations were collected and grouped in terms of the following clusters: carcass dressing traits, muscle fiber properties, pH, color-related traits, water-retaining characteristics, texture-related traits, and meat chemical composition. The Bayesian ANOVA analysis reported that the majority of variables statistically differed (p < 0.05), and the multicollinearity analysis revealed the absence of redundancy problems among variables (VIF < 5). The DCA reported that cold carcass weight, slaughter weight, sex-male, carcass/piece weight, and the protein and fat composition of meat were the traits explaining variability among different turkey genotypes (Wilks' lambda: 0.488, 0.590, 0.905, 0.906, 0.937, and 0.944, respectively). The combination of traits in the first three dimensions explained 94.93% variability among groups. Mahalanobis distances cladogram-grouped populations following a cluster pattern and suggest its applicability as indicative of a turkey genotype's traceability.

Structural Adaptation of the Excitation-Contraction Coupling Apparatus in Calsequestrin1-Null Mice during Postnatal Development.

The precise arrangement and peculiar interaction of transverse tubule (T-tubule) and sarcoplasmic reticulum (SR) membranes efficiently guarantee adequate contractile properties of skeletal muscle fibers. Fast muscle fibers from mice lacking calsequestrin 1 (CASQ1) are characterized by the profound ultrastructural remodeling of T-tubule/SR junctions. This study investigates the role of CASQ1, an essential component of calcium release units (CRUs), in the postnatal development of muscle fibers. By using CASQ1-knockout mice, we examined the maturation of CRUs and the involvement of different junctional proteins in the juxtaposition of the membrane system. Our morphological investigation of both wild-type (WT) and CASQ1-null extensor digitorum longus (EDL) fibers, from 1 week to 4 months of age, yielded noteworthy findings. Firstly, we observed that the absence of CASQ1 hindered the full maturation of CRUs, despite the correct localization of key junctional components (ryanodine receptor, dihydropyridine receptor, and triadin) to the junctional SR in adult animals. Furthermore, analysis of protein expression profiles related to T-tubule biogenesis and organization (junctophilin 1, amphiphysin 2, caveolin 3, and mitsugumin 29) demonstrated delayed progression in their expression during postnatal development in the absence of CASQ1, suggesting the impaired maturation of CRUs. The absence of CASQ1 directly impacts the proper assembly of CRUs during development and influences the expression and coordination of other proteins involved in T-tubule biogenesis and organization.

Hip and Knee Joint Kinematics Predict Quadriceps Hyperreflexia in People with Post-stroke Stiff-Knee Gait.

Wearable assistive technology for the lower extremities has shown great promise towards improving gait function in people with neuromuscular injuries. But common secondary impairments, such as hypersensitive stretch reflexes or hyperreflexia, have been often neglected. Incorporation of biomechanics into the control loop could improve individualization and avoid hyperreflexia. However, adding hyperreflexia prediction to the control loop would require expensive or complex measurement of muscle fiber characteristics. In this study, we explore a clinically accessible biomechanical predictor set that can accurately predict rectus femoris (RF) reaction after knee flexion assistance in pre-swing by a powered orthosis. We examined a total of 14 gait parameters based on gait kinematic, kinetic, and simulated muscle-tendon states from 8 post-stroke individuals with Stiff-Knee gait (SKG) wearing a knee exoskeleton robot. We independently performed both parametric and non-parametric variable selection approaches using machine learning regression techniques. Both models revealed the same four kinematic variables relevant to knee and hip joint motions were sufficient to effectively predict RF hyperreflexia. These results suggest that control of knee and hip kinematics may be a more practical method of incorporating quadriceps hyperreflexia into the exoskeleton control loop than the more complex acquisition of muscle fiber properties.

Effects of Probiotics Supplementation on the Intestinal Metabolites, Muscle Fiber Properties, and Meat Quality of Sunit Lamb.

The development of animal husbandry is closely related to the meat quality of small ruminants. Intestinal metabolites and the muscle fiber types of lambs are important factors that affect their meat quality, but few studies have examined the regulation of the "intestinal muscle axis" by probiotics. In this study, 12 Sunit lambs were divided into a control group (C) and a probiotics group (P). The gene expressions of the myosin heavy chain, metabolic enzyme activity, and short-chain fatty acids in the intestines were analyzed using gas chromatography-mass spectrometry (GC-MS) and quantitative real-time PCR. The results showed that levels of propionic acid and butyric acid in the intestines of group P were significantly higher than in group C (p < 0.05). In addition, probiotics increased the number and area ratio of type I muscle fibers. They also increased the mRNA expression of MyHC IIA and the activity of malate dehydrogenase (MDH) and succinate dehydrogenase (SDH). Propionic acid was negatively correlated with the number ratio of type IIB muscle fibers. Butyric acid was found to be significantly positively correlated with the number ratio of type IIA muscle fibers. Cooking loss, pH24h, and shear force decreased significantly in group P. In conclusion, intestinal metabolites (SCFAs) altered the activity of oxidative-myofibril-metabolizing enzymes and the expression of myosin heavy-chain type IIA, reduced the meat shear values, and improved meat tenderness. This study provides a new basis for improving the production and meat quality of small ruminants.

Passive constitutive theory of a single muscle fiber for the potential diagnosis of muscle diseases at the molecular level

Titins are mainly responsible for passive mechanical properties of a single muscle fiber, which, however, can be compromised by the change in molecular structures of titins occurring in some muscle-related diseases. Based on molecular structures of titins within a sarcomere unit, we have developed a constitutive theory for the passive elasticity of a single muscle fiber with the utilization of the virtual work principal. The number density of titins, domain composition of titins, the kinetics of folded domains within titins, the interaction between the water and molecular chains, the sarcomere length, etc., can all be considered in the theory. The predicted stress-strain curves based on the theory are in agreement with experiment. We also demonstrate that abnormal structural parameters of titins from patients with chronic obstructive pulmonary disease or muscle atrophy caused by long-term disuse can be extracted with the theory. We then suggest that this constitutive theory may potentially facilitate the molecular diagnosis of muscle diseases exhibiting abnormality in the passive elasticity .

Calcium and strontium contractile activation properties of single skinned skeletal muscle fibres from elderly women 66–90 years of age

The single freshly skinned muscle fibre technique was used to investigate Ca2+- and Sr2+-activation properties of skeletal muscle fibres from elderly women (66–90 years). Muscle biopsies were obtained from the vastus lateralis muscle. Three populations of muscle fibres were identified according to their specific Sr2+-activation properties: slow-twitch (type I), fast-twitch (type II) and hybrid (type I/II) fibres. All three fibre types were sampled from the biopsies of 66 to 72 years old women, but the muscle biopsies of women older than 80 years yielded only slow-twitch (type I) fibres. The proportion of hybrid fibres in the vastus lateralis muscle of women of circa 70 years of age (24%) was several-fold greater than in the same muscle of adults (< 10%), suggesting that muscle remodelling occurs around this age. There were no differences between the Ca2+- and Sr2+-activation properties of slow-twitch fibres from the two groups of elderly women, but there were differences compared with muscle fibres from young adults with respect to sensitivity to Ca2+, steepness of the activation curves, and characteristics of the fibre-type dependent phenomenon of spontaneous oscillatory contractions (SPOC) (or force oscillations) occurring at submaximal levels of activation. The maximal Ca2+ activated specific force from all the fibres collected from the seven old women use in the present study was significantly lower by 20% than in the same muscle of adults. Taken together these results show there are qualitative and quantitative changes in the activation properties of the contractile apparatus of muscle fibres from the vastus lateralis muscle of women with advancing age, and that these changes need to be considered when explaining observed changes in women’s mobility with aging.

Computational modeling of damage in the hierarchical microstructure of skeletal muscles

One of the skeletal muscle’s exceptional properties is its high damage tolerance in terms of its high toughness, which allows the muscle to withstand cracks of millimeter length while maintaining most of its strength (Taylor et al., 2012). In skeletal muscles, damage occurs on different hierarchical levels of the microstructure. We analyze the damage behavior on hierarchy levels 3 (muscle fiber) and 4 (fascicle) on which the most common serious muscle injuries occur. Our model captures damage initiation and rupture of activated muscle fibers resulting from eccentric contractions. We consider the interaction between muscle fibers and endomysium and investigate the influence of the components titin and endomysium on the mechanical behavior in pre-damaged fascicles. Endomysium generally transmits contractile forces. Our results show that high strains in pre-damaged fiber regions are not transferred by the endomysium and, thus, adjacent undamaged fibers are well protected. Moreover, the results show titin’s extraordinary stabilization properties of pre-damaged muscle fibers, so that macroscopic strains of fascicles are hardly reduced in case of strongly pre-damaged fibers and intact titin.

Dysfunctional paraspinal muscles in adult spinal deformity patients lead to increased spinal loading.

PurposeDecreased spinal extensor muscle strength in adult spinal deformity (ASD) patients is well-known but poorly understood; thus, this study aimed to investigate the biomechanical and histopathological properties of paraspinal muscles from ASD patients and predict the effect of altered biomechanical properties on spine loading.Methods68 muscle biopsies were collected from nine ASD patients at L4–L5 (bilateral multifidus and longissimus sampled). The biopsies were tested for muscle fiber and fiber bundle biomechanical properties and histopathology. The small sample size (due to COVID-19) precluded formal statistical analysis, but the properties were compared to literature data. Changes in spinal loading due to the measured properties were predicted by a lumbar spine musculoskeletal model.ResultsSingle fiber passive elastic moduli were similar to literature values, but in contrast, the fiber bundle moduli exhibited a wide range beyond literature values, with 22% of 171 fiber bundles exhibiting very high elastic moduli, up to 20 times greater. Active contractile specific force was consistently less than literature, with notably 24% of samples exhibiting no contractile ability. Histological analysis of 28 biopsies revealed frequent fibro-fatty replacement with a range of muscle fiber abnormalities. Biomechanical modelling predicted that high muscle stiffness could increase the compressive loads in the spine by over 500%, particularly in flexed postures.DiscussionThe histopathological observations suggest diverse mechanisms of potential functional impairment. The large variations observed in muscle biomechanical properties can have a dramatic influence on spinal forces. These early findings highlight the potential key role of the paraspinal muscle in ASD.

Administration of Branched-Chain Amino Acids in the Pre- or Post-Hatch Period Improves the Fiber Characteristics of Pectoralis major Muscle in Turkey Poults Subjected to Early or Delayed Feeding

Poultry meat quality is controlled by muscle fiber properties associated with body weight gain in the immediate pre- or post-hatch period. This study aimed to determine the effect of administration of branched-chain amino acids blend (BCAAb, 3 L-leucine:1 L-isoleucine:2 L-valine) in the pre- or post-hatch period on the growth performance and fiber characteristics of the Pectoralis major (PM) muscle in turkey poults subjected to early or delayed feeding. Newly hatched poults from eggs injected in ovo with BCAAb or received no injection were used in a 21-d study. Poults (n=192) produced without injection of BCAAb received a starter diet supplemented (BCAA) or not (C) with the BCAAb (2 g/kg) immediately or with a delay of 48 h (48BCAA and 48C) after hatching. Poults (n=36) produced with (IOBCAA) in ovo injection of BCAAb (2 mg /ml) received the diet and water immediately. The BCAA and IOBCAA poults had higher body weight than those of the C, 48C, and 48BCAA birds. The body weight of the C poults was higher than those of the 48C and 48BCAA birds. The BCAA poults had higher PM muscle weight than those of the C and 48C poults, while that of the IOBCAA poults was higher than that of the 48C poults. The IOBCAA treatment increased the protein content of the PM muscle meat, compared with the C and 48C treatments. The 48C treatment increased the type IIB fiber area and the type I and type IIA fiber percentages but decreased the type IIB fiber, compared with other treatments. The numbers of type IIB and total fibers in the IOBCAA poults were higher than those of the 48C birds. In conclusion, administering BCAAb in ovo or in a starter diet enhanced early growth performance and improved the fiber characteristics of the PM muscle in turkey poults.

Single skeletal muscle fiber mechanical properties: a muscle quality biomarker of human aging.

Skeletal muscle strength, mass, and function should be carefully monitored for signs of decline with advanced adult age. An understanding of the pathophysiology and severity of sarcopenia can be improved with the exploration of changes in muscle fiber properties. Furthermore, although functional decline with increase age is a well-known phenomenon, the mechanisms underlying this decline, and the features that characterize it, are complex and variable. The age-related decline of muscle function is a result of not only a decrease of muscle mass but also a decline in the intrinsic properties of muscle fibers that are independent of size. We believe it is important to understand changes in muscle quality (force adjusted for size), and not to focus solely on muscle mass, because muscle quality is closely related to measurements of function and could potentially predict clinical outcomes such as morbidity, disability, and mortality. Neurological and metabolic mechanisms contribute to muscle quality, but the intrinsic properties of muscle cells are central to the maintenance of force-generating capacity. Muscle quality can be evaluated with the assessment of morphological, physiological, and mechanical properties in single permeabilized or skinned fibers. This approach excludes the influence of the nervous system, tendons, and the extracellular matrix. In this review, we summarized the changes in active and passive mechanical properties at the single muscle cell level in older skeletal muscles. We argue that intrinsic mechanical changes in human single muscle fibers are useful biomarkers and indicators of muscle quality.

Excitability properties of mouse and human skeletal muscle fibres compared by muscle velocity recovery cycles

Mouse models of skeletal muscle channelopathies are not phenocopies of human disease. In some cases (e.g. Myotonia Congenita) the phenotype is much more severe, whilst in others (e.g. Hypokalaemic periodic paralysis) rodent physiology is protective. This suggests a species’ difference in muscle excitability properties. In humans these can be measured indirectly by the post-impulse changes in conduction velocity, using Muscle Velocity Recovery Cycles (MVRCs). We performed MVRCs in mice and compared their muscle excitability properties with humans. Mouse Tibialis Anterior MVRCs (n = 70) have only one phase of supernormality (increased conduction velocity), which is smaller in magnitude (p = 9 × 10−21), and shorter in duration (p = 3 × 10−24) than human (n = 26). This abbreviated supernormality is followed by a period of late subnormality (reduced velocity) in mice, which overlaps in time with the late supernormality seen in human MVRCs. The period of late subnormality suggests increased t-tubule Na+/K+-pump activity. The subnormal phase in mice was converted to supernormality by blocking ClC-1 chloride channels, suggesting relatively higher chloride conductance in skeletal muscle. Our findings help explain discrepancies in phenotype between mice and humans with skeletal muscle channelopathies and potentially other neuromuscular disorders. MVRCs are a valuable new tool to compare in vivo muscle membrane properties between species and will allow further dissection of the molecular mechanisms regulating muscle excitability.

A Roadmap to Reconstructing Muscle Architecture from CT Data.

Skeletal muscle is responsible for voluntary force generation across animals, and muscle architecture largely determines the parameters of mechanical output. The ability to analyze muscle performance through muscle architecture is thus a key step towards better understanding the ecology and evolution of movements and morphologies. In pennate skeletal muscle, volume, fiber lengths, and attachment angles to force transmitting structures comprise the most relevant parameters of muscle architecture. Measuring these features through tomographic techniques offers an alternative to tedious and destructive dissections, particularly as the availability of tomographic data is rapidly increasing. However, there is a need for streamlined computational methods to access this information efficiently. Here, we establish and compare workflows using partially automated image analysis for fast and accurate estimation of animal muscle architecture. After isolating a target muscle through segmentation, we evaluate freely available and proprietary fiber tracing algorithms to reconstruct muscle fibers. We then present a script using the Blender Python API to estimate attachment angles, fiber lengths, muscle volume, and physiological cross-sectional area. We apply these methods to insect and vertebrate muscle and provide guided workflows. Results from fiber tracing are consistent compared to manual measurements but much less time-consuming. Lastly, we emphasize the capabilities of the open-source three-dimensional software Blender as both a tool for visualization and a scriptable analytic tool to process digitized anatomical data. Across organisms, it is feasible to extract, analyze, and visualize muscle architecture from tomography data by exploiting the spatial features of scans and the geometric properties of muscle fibers. As digital libraries of anatomies continue to grow, the workflows and approach presented here can be part of the open-source future of digital comparative analysis.

Investigating the active contractile function of the rat paraspinal muscles reveals unique cross-bridge kinetics in the multifidus

Various aspects of paraspinal muscle anatomy, biology, and histology have been studied; however, information on paraspinal muscle contractile function is almost nonexistent, thus hindering functional interpretation of these muscles in healthy individuals and those with low back disorders. The aim of this study was to measure and compare the contractile function and force-sarcomere length properties of muscle fibers from the multifidus (MULT) and erector spinae (ES) as well as a commonly studied lower limb muscle (Extensor digitorum longus (EDL)) in the rat. Single muscle fibers (n = 77 total from 6 animals) were isolated from each of the muscles and tested to determine their active contractile function; all fibers used in the analyses were type IIB. There were no significant differences between muscles for specific force (sFo) (p = 0.11), active modulus (p = 0.63), average optimal sarcomere length (p = 0.27) or unloaded shortening velocity (Vo) (p = 0.69). However, there was a significant difference in the rate of force redevelopment (ktr) between muscles (p = < 0.0001), with MULT being significantly faster than both the EDL (p = < 0.0001) and ES (p = 0.0001) and no difference between the EDL and ES (p = 0.41). This finding suggests that multifidus has faster cross-bridge turnover kinetics when compared to other muscles (ES and EDL) when matched for fiber type. Whether the faster cross-bridge kinetics translate to a functionally significant difference in whole muscle performance needs to be studied further.

Rehabilitation of Older Adults with Sarcopenia: From Cell to Functioning.

ABSTRACTThe 20th and 21st centuries have witnessed a substantial increase in human life expectancy and in the number of men and women aged 60 years and older. Aging is associated with a large number of health conditions, including sarcopenia, which has been the subject of important research in the past 30 years. Sarcopenia is characterized by an age-related loss of muscle mass, weakness, and impaired physical performance. The condition can be diagnosed with a combination of measurements of these three elements. The precise definition of sarcopenia and the selection of optimal assessment methods have changed significantly in the past 20 years; nonetheless, the prevalence of sarcopenia in the general older population is in the range of 5–15%. Molecular and cellular events at the muscle cell level impact the size and quality of muscles (force adjusted for size). The active and passive mechanical properties of single muscle fibers are altered by changes in the structure and function of various cellular elements. Systemic factors such as inflammation, loss of hormonal influence, and deleterious lifestyle choices also contribute to sarcopenia. The consequences of sarcopenia include many adverse effects such as impairments in activities of daily living, falls, loss of independence, and increased mortality. Several rehabilitative interventions have been tested, and the safest and most effective is the use of progressive resistance exercise. An increase in dietary protein intake has synergistic effects. Future research should focus on a consensus definition of sarcopenia, identification of the best assessment methods, understanding of biological mechanisms, and testing of innovative interventions.

Evaluating Sexual Dimorphism of the Muscle Spindles and Intrafusal Muscle Fibers in the Medial Gastrocnemius of Male and Female Rats.

This study sought to investigate the sexual dimorphism of muscle spindles in rat medial gastrocnemius muscle. The muscles were cut transversely into 5–10 and 20 μm thick serial sections and the number, density, and morphometric properties of the muscle spindles were determined. There was no significant difference (p > 0.05) in the number of muscle spindles of male (14.45 ± 2.77) and female (15.00 ± 3.13) rats. Muscle mass was 38.89% higher in males (1.08 vs. 0.66 g in females), making the density of these receptors significantly higher (p < 0.01) in females (approximately one spindle per 51.14 mg muscle mass vs. one per 79.91 mg in males). There were no significant differences between the morphometric properties of intrafusal muscle fibers or muscle spindles in male and female rats (p > 0.05): 5.16 ± 2.43 and 5.37 ± 2.27 μm for male and female intrafusal muscle fiber diameter, respectively; 5.57 ± 2.20 and 5.60 ± 2.16 μm for male and female intrafusal muscle fiber number, respectively; 25.85 ± 10.04 and 25.30 ± 9.96 μm for male and female shorter muscle spindle diameter, respectively; and 48.99 ± 20.73 and 43.97 ± 16.96 μm for male and female longer muscle spindle diameter, respectively. These findings suggest that sexual dimorphism in the muscle spindles of rat medial gastrocnemius is limited to density, which contrasts previous findings reporting differences in extrafusal fibers diameter.