Structure Of Muscle Fibers Research Articles

Resistance training of long duration modulates force and unloaded shortening velocity of single muscle fibres of young women

The aim of the present study was to clarify the impact of long term (1 year) resistance training (RT) on structure and function of single muscle fibres of vastus lateralis in young female subjects. Five young women (age: 25.4 ± 6.2 year) performed exercise sessions at 60% of single subject own repetition maximum (1 RM) 1 h twice a week. Maximum voluntary force was determined pre- and post-RT and was found to significantly increase post-RT ensuring a successful impact of RT on muscle performance in vivo. Needle muscle biopsy samples were obtained both pre- and post-RT and the following determinations were performed: myosin heavy chain isoform (MHC) distribution of the whole muscle samples by SDS–PAGE; cross sectional area (CSA), specific force (Po/CSA) and maximum shortening velocity ( Vo) of a large population ( n = 358) of single skinned muscle fibres classified on the basis of MHC isoform composition by SDS–PAGE. The results suggest that the long duration of RT can determine a significant increase in specific force (Po/CSA) and unloaded shortening velocity ( Vo) of single muscle fibres in female subjects, whereas no muscle fibre hypertrophy and no shift in MHC isoform content was observed.

Slaughter Performance of Four Different Turkey Strains, with Special Focus on the Muscle Fiber Structure and the Meat Quality of the Breast Muscle

The increase in human consumption of turkey meat and the shift in the poultry market from whole birds to further processed meat products increases the visibility of meat alterations (e.g., heterogenic color, drip loss, petechial hemorrhages) at retail. Changes in poultry meat quality have been related to the intensive growth of the current turkey strains. Considering this, the main objective of this investigation was to evaluate the meat quality and muscle structure of commercially available turkey strains with different growth properties but similar breast yields. Toms (n = 120) of 4 different turkey strains (British United Turkeys Big 6, Kelly Broad-Breasted Bronze, Kelly Wrolstad, Kelly Super Mini; n = 30 per strain) were reared in an experimental barn under similar environmental and feeding conditions and were slaughtered at 22 wk of age in a commercial slaughterhouse. The strains Big 6 and Broad-Breasted Bronze belong to the fast-growing (FG) turkey strain and the other 2 to the slow-growing (SG) turkey strain. The carcass weights, as estimated by video imaging, differed significantly (P < 0.05) between the SG and FG groups. The breast yields (percentage of carcass weight) of the investigated strains were similar. Except for the significantly (P < 0.05) greater protein concentration in the musculus pectoralis superficialis of the SG birds, the musculus pectoralis superficialis had nearly similar fat and ash contents. Plasma lactate concentrations were similar in the investigated turkey strains but the creatine kinase activities were greater in the FG turkeys at the time of slaughter. Determination of the different meat quality parameters [pH, electrical conductivity, color (L*a*b*), drip loss, shear force] did not result in clear differences between the SG and FG turkey strains. There were larger muscle fibers in the FG in comparison with the SG strains, but no differences could be determined in the capillary density and incidence of degenerated or giant fibers, except for a higher rate in the Wrolstad strain. The present results are contradictory to the opinion that turkeys with faster growth have worse meat quality.

Passive mechanical features of single fibers from human muscle biopsies – effects of storage

BackgroundThe purpose of this study was to investigate the effect of storage of human muscle biopsies on passive mechanical properties.MethodsStress-strain analysis accompanied by laser diffraction assisted sarcomere length measurement was performed on single muscle fibres from fresh samples and compared with single fibres from stored samples (-20°C, 4 weeks) with the same origin as the corresponding fresh sample. Basic morphological analysis, including cross sectional area (CSA) measurement, fibre diameter measurement, fibre occupancy calculation and overall morphology evaluation was done.ResultsStatistical analysis of tangent values in stress-strain curves, corresponding to the elastic modulus of single muscle fibres, did not differ when comparing fresh and stored samples from the same type of muscle. Regardless of the preparation procedure, no significant differences were found, neither in fibre diameter nor the relation between muscle fibres and extra-cellular matrix measured under light microscopy.ConclusionWe conclude that muscle fibre structure and mechanics are relatively insensitive to the storage procedures used and that the different preparations are interchangeable without affecting passive mechanical properties. This provides a mobility of the method when harvesting muscle biopsies away from the laboratory.

Beef sausage structure affected by sodium chloride and potassium lactate

A histological and ultrastructural study was conducted to characterize changes in the muscle fibre structure of three fresh sausage preparations, depending on meat composition, sodium chloride (NaCl) and potassium lactate (K-lactate) contents. After addition of 0.8% and 1.6% NaCl, 65% and 51%, respectively, of the area observed showed well preserved fibres (histological data). The altered regions presented a large disorganization of the myofilaments and a solubilization of the sarcolemma and of the Z lines. K-lactate addition had no marked effects on meat structure. The preparation containing some sheep meat was more sensitive to salt than the others containing only bovine meat. The level of alteration was much lower than those obtained in pork meat in another study. Technological conditions used to modify the internal muscle fibre structure during sausage processing depend on the species used. Therefore, the classification of the sausage preparation to “meat preparation” or “meat product” under the EU regulation (EC) No. 853/2004 (which assign meat preparations to meat if the product has undergone a process insufficient to modify the internal muscle fibre structure of the meat) must be systematically controlled when changing the meat sausage composition.

Structural and functional alterations of muscle fibres in the novel mouse model of facioscapulohumeral muscular dystrophy

We recently generated a mouse model of facioscapulohumeral muscular dystrophy (FSHD) by selectively overexpressing FRG1, a candidate gene for FSHD, in skeletal muscle. The muscles of the FRG-1 mice did not show any plasmamembrane defect suggesting a novel pathogenetic mechanism for FSHD. Here, we study structure and function of muscle fibres from three lines of mice overexpressing FRG1 at different levels: FRG1-low, FRG1-med, FRG1-high. Cross-sectional area (CSA), specific force (Po/CSA) and maximum shortening velocity (V(o)) of identified types of muscle fibres from FRG1-low and FRG1-med mice were analysed and found to be lower than in WT mice. Fast fibres and especially type 2B fibres (the fastest type) were preferentially involved in the dystrophic process showing a much larger force deficit than type 1 (slow) fibres. Consistent with the latter observation, the MHC isoform distribution of several muscles of the three FRG1 lines showed a shift towards slower MHC isoforms in comparison to WT muscle. Moreover, fast muscles showed a more evident histological deterioration, a larger atrophy and a higher percentage of centrally nucleated fibres than the soleus, the slowest muscle in mice. Interestingly, loss in CSA, Po/CSA and V(o) of single muscle fibres and MHC isoform shift towards a slower phenotype can be considered early signs of muscular dystrophy (MD). They were, in fact, found also in FRG1-low mice which did not show any impairment of function in vivo and of muscle size in vitro and in soleus muscles, which had a completely preserved morphology. This study provides a detailed characterization of structure and function of muscle fibres in a novel murine model of one of the main human MDs and suggests that fundamental features of the dystrophic process, common to most MDs, such as the intrinsic loss of contractile strength of muscle fibres, the preferential involvement of fast fibres and the shift towards a slow muscle phenotype can occur independently from obvious alterations of the plasma membrane.

Myopathies in the older patient

Myopathy is a convenient shorthand term meaning muscle disease or dysfunction. In other words, the myopathies are those conditions in which the patient's symptoms and signs can be attributed to a pathological process affecting either the structure of muscle fibres or their associated interstitial tissues, or to disturbance of the biochemical or electrophysiological function of those fibres. Myopathies are rare in all age ranges. They may be inherited or acquired. Onset of inherited myopathies in elderly people, not surprisingly, is uncommon, but some of these diseases are asymptomatic, or cause such minor symptoms that their significance is not appreciated by the patient, and thus they may not be recognized until late on in life. Their recognition may have implications for other, younger, family members. Many of the acquired myopathies afflicting older people are treatable, but the commonest, inclusion body myositis, is not, and incorrect diagnosis and inappropriate use of steroids may compound morbidity.

Tratamiento quirúrgico de la insuficiencia cardiaca. Restauración ventricular y cirugía de la válvula mitral

The efficiency of the heart as a pump is intimately linked to the structure and function of heart muscle fibers. The process of ventricular remodeling that occurs following myocardial damage must be regarded as an etiopathologic factor in heart failure. In this situation, the development of mitral regurgitation triggers symptoms and worsens prognosis. In recent years, the technique of surgical ventricular restoration has been introduced as a novel diagnostic and therapeutic approach in patients with heart failure. Magnetic resonance imaging has become the principle exploratory technique for diagnosis and follow-up in these patients. From a surgical point of view, we must adopt a three-pronged approach to these patients: the coronary vessels must be dealt with, the mitral valve must be repaired if there is at least moderate regurgitation, and ventricular volume must be reduced.

In vivo diffusion tensor imaging of the human calf muscle

To demonstrate the feasibility of in vivo calf muscle fiber tracking in human subjects. An EPI-based diffusion tensor imaging (DTI) sequence with six-direction diffusion gradient sensitization was implemented, and DT images were acquired at 3 Tesla on five subjects using an extremity coil. The mean diffusivity, fractional anisotropy (FA), and fiber angle (with respect to the magnet z-axis) were measured in different muscles, and fibers were tracked from several regions of interest (ROIs). The fiber orientations in the current DTI studies agree well with those determined in previous spectroscopic studies. The orientation angles ranged from 13.4 degrees in the lateral gastrocnemius to 48.5 degrees in the medial soleus. The diffusion ellipsoid in muscle tissue is anisotropic and approximates a prolate model, as shown by color maps of the anisotropy. Fibers were tracked from the different muscle regions, and the unipennate and bipennate structure of muscle fibers was visualized. The study clearly shows that in vivo fiber tracking of muscle fibers is feasible and could potentially be applied to study muscle structure function relationships.

S-myotrophin promotes the hypertrophy of skeletal muscle of mice in vivo

S-myotrophin is a newly discovered muscle growth factor. Effects of crude S-myotrophin injection on the growth and morphology of skeletal muscle of normal, ScN and mdx mice were investigated in the present study. Total dose of crude S-myotrophin was 100μg (100μg protein/ml×50μl×20 times).In the case of normal mice (Sea:ddY), body weight and the weight of M. gluteus major of crude S-myotrophin injected mice was significantly heavier than that of control (PBS-injected) mice after 5 weeks’ feeding. Antibody staining of laminin and dystrophin showed clear sarcolemmal and basement membrane structure surrounding each muscle fibre. The numbers of muscle fibres per 100μm2 was less in crude S-myotrophin-injected normal mice than in PBS-injected mice. Quite similar observations as in the case of normal mice were obtained in the case of ScN mice having heterogeneous gene of dystrophin.In the case of mdx mice, body weight and the weight of M. gluteus major of crude S-myotrophin injected mdx mice was significantly heavier than that of PBS-injected mdx mice. Antibody staining of laminin showed almost intact structure of the basement membrane containing laminin even in skeletal muscle of mdx mice subjected to crude S-myotrophin injection, while irregular and incompletely developed structure of muscle fibres or necrosis were observed in muscle fibres of PBS-injected mdx mice.In spite of crudeness of the preparation, the present animal experiments indicate that S-myotrophin has a strong growth promoting activity of muscle cells of normal and dystrophic mice.

Advances in radio frequency and ohmic heating of meats

Interest in both radio frequency (RF) and ohmic heating of foods has increased in recent years. In particular, their application to meat products has been investigated. A critical factor is the dielectric constants of the products being heated. These have been measured for meats. In particular, the dielectric constant ε′, dielectric loss factor ε″, thermal heat capacity c p , thermal conductivity k and thermal diffusivity α of two local comminuted meat products of differing diameters, both pork based, (pork luncheon roll PLR and white pudding WP) were measured between 5 and 85 °C. Radio frequency (RF) and microwave (MW) ε″ values varied across 5–85 °C ( P < 0.05). Microwave ε′ and ε″ values for WP tended to peak at 45 °C and decrease thereafter, whereas for PLR, ε′ and ε″ peaked at 65 °C which appeared to match potato starch gelatinisation within this product. WP and PLR had significantly higher c p values at 25 °C, which corresponded to the melting point of pork fat. At 85 °C, k values were higher ( P < 0.05) than at 5, 25 and 45 °C but were not higher than values at 65 °C. Thermal diffusivity α values increased with temperature ( P < 0.05). For ohmic heating, the electrical conductivity becomes the controlling variable. Efficacy of ohmic processing can be influenced by the conductivities of individual components within the food and their behaviour and interactions during the heating process. Conductivity measurements on pork cuts indicated that lean is highly conductive compared to fat and addition of fat to lean reduced the overall conductivity but the addition of fat over the range (i.e. 0–100%) was non-linear. Light microscopy suggested that differences in the conductivities of leg and shoulder lean (entire) (0.76 vs. 0.64 S m −1, respectively) could be due to the denser muscle fibre structure and/or higher intra-muscular fat in the shoulder vs. the leg meat. This could be of significance for ohmic processing of full muscle products. Of course, for both forms of heating, the quality of the heated product becomes the critical factor. The effect of radio frequency cooking, on the quality (assessed by cook yield, water holding capacity texture profile analysis, penetration test, Warner–Bratzler shear, colour and sensory evaluation) and cooking time of two types of pork products (leg ham and shoulder ham) were compared to steam cooked samples. RF cooking of the hams resulted in a shorter cooking time. Instrumental measurements indicated that RF heated samples had a higher cook yield ( P < 0.05), but a lower water holding capacity ( P < 0.05). Texture profile analysis indicated that RF cooked samples were harder ( P < 0.05), particularly for leg hams. A sensory panel also indicated that panellists could distinguish between radio frequency and steam cooked samples ( P < 0.05).

The Effect of Rate of Distraction Osteogenesis on Structure and Function of Anterior Digastric Muscle Fibers

The authors hypothesized that distraction at a rate of 3 mm/day, compared with mandibular distraction at a rate of 1 mm/day, would produce a maladaptive response in adjacent muscles of mastication. The authors further hypothesized that the maladaptive response would manifest at the single fiber level by means of increased sarcomeric heterogeneity, decreased maximum force output, and increased susceptibility to stretch-induced injury. In an ovine model, distraction osteogenesis of the right hemimandible was performed at either 1 mm/day for 21 days (n = 2) or 3 mm/day for 7 days (n = 2) to achieve a total distraction distance of 21 mm. The left hemimandibles served as controls. After a consolidation period of 2 days, the anterior digastric muscles were harvested; in six randomly selected single fibers from each muscle, maximum calcium-activated force (Po) was measured at optimal sarcomere length. The amount of damage to the sarcomeres in each fiber was assessed microscopically. To test susceptibility to contraction-induced injury, each fiber was given an activated stretch of 20 percent. Compared with control fibers and fibers distracted at 1 mm/day, maximum tetanic force (Po) was significantly lower in fibers distracted at 3 mm/day. Compared with control fibers, specific Po (Po/cross-sectional area) was lower in fibers distracted at 3 mm/day. The number of sarcomeres appearing damaged in fibers distracted at 3 mm/day was significantly higher than in control fibers or in fibers distracted at 1 mm/day. A greater deficit in Po was observed after a single activated stretch in fibers distracted at 3 mm/day than in control fibers or in fibers distracted at 1 mm/day. The authors conclude that distraction of the anterior digastric muscle in sheep at 3 mm/day produces a maladaptive response in the muscle fibers but a rate of 1 mm/day is tolerated by the muscle fibers. These data are consistent with the hypothesis that distraction of skeletal muscle at high rates results in increased heterogeneity of sarcomere lengths and that this increase in heterogeneity is the most likely potential mechanism resulting in whole muscle force deficits and in increased susceptibility to stretch-induced injury in distracted muscles.

Scanning electron microscopic study of the muscle fiber arrangement in the rat cricopharyngeal muscle

Conclusions. Myomyous junctions comprise a complex muscle fiber network, which is thought to synchronize the activity of the cricopharyngeal (CP) muscle fibers. Myomyous and myotendinous junctions explain the heterogeneity in muscle fiber length which contributes to the efficient behavior of the muscle. This scanning electron microscopy (SEM) study demonstrated the complex muscle fiber arrangement of the CP muscle and improved on the previous description of its morphological specificity. Objective. To examine the 3D ultrastructure of the inferior pharyngeal constrictor muscle fibers to obtain further knowledge of their morphological characteristics with regard to the specific functions of the muscle in deglutition. Material and methods. Six adult rats were used. Their CP and thyropharyngeal (TP) muscles were obtained and processed using the HCl hydrolysis method to remove i.m. connective tissue. The fine muscle fiber structure was observed by means of SEM. Results. Multifaceted muscle fiber interconnections (myomyous junctions) were identified in the CP muscle. The myomyous junctions were characterized by the tight connection of many finger-like processes at the ends of a lateral branch or bifurcating trunk of the muscle fibers. In addition, muscle fibers occasionally tapered and ended within the muscle belly, forming myotendinous junctions. The TP muscle lacked these structures.

Structural manifestations of mitochondrial dysfunction in skeletal muscles of early aging OXYS rats

Changes in the mitochondrial compartment are the central element in the morphogenesis of musculoskeletal abnormalities in early aging OXYS rats. Compensatory hyperplasia and hypertrophy with enlargement of the working surface area are seen in these organelles at the age of 2 months. The mitochondria are characterized by polymorphism, compact packing of cristae. By the age of 9 months destructive changes and sharp reduction of the mitochondrial compartment are observed is many myocytes. Disorders in the mitochondrial structure and function and oxidative stress can be among the causes of degenerative changes in the myofibrillar system and other structures of muscle fibers, including those resultant from activation of apoptosis.

Assessing the quality of mechanically and manually recovered chicken meat

The biochemical composition and histological characteristics of meat recovered mechanically by the auger/sieve (a/s) and the hollow drum/belt (hd/b) principles from two different chicken carcass parts were compared with meat recovered manually. The quality of meat recovered mechanically by the hollow drum/belt principle was equal to or higher than the quality of manually recovered meat. The degradation of muscle structure was highest in the meat recovered by the a/s principle and lowest in the manually recovered meat. For the biochemical measurements with the exception of collagen, determinations of a single sample were sufficient to achieve a repeatability of 0.9, whereas for the histological measurements at least 8 samples were necessary. It is suggested that a quality-grading scale based on biochemical composition and level of degradation of muscle fibre structure should be established for all types of minced meat regardless of whether the meat is obtained by mechanical or manual procedures and that legislation concerning the use of MRM should be based on such a scale.

Changes in diaphragm structure following prolonged mechanical ventilation in piglets.

Prolonged mechanical ventilation and inactivity negatively affect muscle function. The mechanisms for this dysfunction are unclear and clinical studies of respiratory muscle are difficult to carry out. An animal model simulating the critical care environment was used to investigate the effects of 5 days' mechanical ventilation and diaphragm inactivity on diaphragm muscle morphology. Twelve 2-4-month-old piglets weighing 23-30 kg were studied. Seven animals received controlled mechanical ventilation and sedation such that spontaneous breathing efforts were inhibited over 5 days. Five control animals were ventilated for only 4-6 h following surgical preparation. Diaphragm biopsies were obtained from the left costal region at the end of all experiments. Morphometric, morphologic, electron microscopic and enzyme histochemical examination of costal diaphragm biopsies was carried out. Contractile properties were studied over 5 days and the results have been previously reported. Cross-sectional area of alI fiber types was increased compared with controls. The proportion of type IIb/x fibers increased following inactivity (P < 0,05) and the proportion of type I and IIa fibers tended to decrease although not significantly. Focal areas of diaphragm fiber regeneration were found without signs of inflammation. Increased appearance of cytoplasmic vacuoles consisting of lipid accumulation was noted in type I fibers. Several study animals developed focal areas with weak myofibrillar ATPase activity and disrupted fiber organization. There were areas of myofibrillary destruction and loss of sarcomeric pattern, without evidence of selective thick filament loss or a change in the myosin to actin ratio. Five days' mechanical ventilation with sedation and complete diaphragm inactivity resulted in changes in muscle fiber structure. A causal relationship can not be concluded but the acute changes in fiber type distribution and structure suggest that previously reported diaphragm contractile impairment occurs at the level of muscle fibers.

Ohmic processing: Electrical conductivities of pork cuts

Efficacy of ohmic processing can be influenced by the conductivities of individual components within the food and their behaviour and interactions during the heating process. This study relates to the determination of electrical conductivities of a selection of pork meat cuts used in meat processing. Conductivity measurements of pork cuts indicated that lean is highly conductive compared to fat and addition of fat to lean reduced the overall conductivity but the addition of fat over the range (i.e. 0–100%) was non-linear. Light microscopy suggested that differences in the conductivities of leg and shoulder lean (entire) (0.76 vs. 0.64 S m −1, respectively) could be due to the denser muscle fibre structure and/or higher intra-muscular fat in shoulder vs. leg. This could be of significance for ohmic processing of full muscle products.

Three-dimensional measurement of ice crystals in frozen beef with a micro-slicer image processing system

A novel technique has been developed for measuring the three-dimensional (3-D) structure and distribution of ice crystals formed in frozen beef by using a micro-slicer image processing system (MSIPS). The system has functions to reconstruct the 3-D image based on the image data of exposed cross-sections obtained by multi-slicing of a frozen sample with the minimum thickness of 1 μm and to display the internal structure as well as an arbitrary cross-section of the sample choosing observation angles. The size and distribution of ice crystals can be determined from the 2-D quantitative information, such as the periphery and area of the crystals. The effects of freezing conditions on the morphology and distribution of the ice crystals were demonstrated quantitatively from the observations of raw beef stained by fluorescent indicator. For the samples frozen at −15 °C, the network structure of ice crystals were observed mainly at intercellular space, having approximately 100 μm in cross-sectional size, while that prepared at −120 °C showed the spherical crystals of 10–20 μm in diameter within the cells. The 3-D image of the sample demonstrated that the growth of ice columns was restricted by the intrinsic structure of muscle fibers. The proposed method provided a new tool to investigate the effects of freezing conditions on the size, morphology and distribution of ice crystals.

The effect of ageing and immobilization on structure and function of human skeletal muscle fibres

The effect of ageing and immobilization on structure and function of human skeletal muscle fibres

Effect of the fungal extracellular protease EPg222 on texture of whole pieces of pork loin

Proteolytic activity of the fungal protease EPg222 and its effect on texture has been investigated in a meat model system based on sterile pieces of pork loins incubated for 32 days. SDS-PAGE analysis of treated samples showed intense hydrolysis of the myofibrillar proteins H-meromyosin, T-troponin, tropomyosin and the proteins bands of 98, 89, 48, 39, 37 and 28 kDa after 17 days of incubation. Proteolytic activity of the enzyme led to a higher accumulation of NPN in treated than untreated samples. Microstructural analysis of muscle fibres showed loss of muscle fibre structure only in treated batch. The texture profile analysis reveals lower values in hardness, gumminess and chewiness in treated than control batch. This effect may be of great interest in dry-cured meat products to counterbalance the increase of hardness reported in these products as consequence of protein denaturation.

Inter-sarcomere dynamics in muscle fibres. A neglected subject?

The sarcomere is the functional unit of muscle, and all sarcomeres are connected in series in myofibrils within a muscle fibre. From this point of view of the structure a single model consisting of a contractile, a series and a parallel element can not account for the description of a real muscle fibre. Additionally, the titin protein filament needs to be considered as a passive visco-elastic element in parallel with the contractile apparatus. Therefore, the structure of a single muscle fibre is complex due mechanical elements ("motors") operating in series and in parallel. Moreover, variability does exist in the mechanical properties along a fibre and hence a multi-segmental model is more realistic and would give rise to many new insights. By attributing a segment model to each half-sarcomere, a fibre can be constructed through rigorous coupling of these units in series and parallel. The dynamics of such a multi-segmental model is much more complex, but it can explain a variety of effects reported in standard classical mechanics experiments. With a relatively simple mechanistic description we can show that the dynamics of such multi-sarcomere systems exhibit a variety of effects (relaxation phenomena, permanent extra-tension, biphasic force-velocity relation) and should therefore not be neglected in muscle fibre modelling. We have observed in single skinned fibre experiments that non-uniformities in sarcomere length changes are prominent during activation and relaxation.