Muscle Functional Properties Research Articles

SMASH - semi-automatic muscle analysis using segmentation of histology: a MATLAB application.

BackgroundHistological assessment of skeletal muscle tissue is commonly applied to many areas of skeletal muscle physiological research. Histological parameters including fiber distribution, fiber type, centrally nucleated fibers, and capillary density are all frequently quantified measures of skeletal muscle. These parameters reflect functional properties of muscle and undergo adaptation in many muscle diseases and injuries. While standard operating procedures have been developed to guide analysis of many of these parameters, the software to freely, efficiently, and consistently analyze them is not readily available. In order to provide this service to the muscle research community we developed an open source MATLAB script to analyze immunofluorescent muscle sections incorporating user controls for muscle histological analysis.ResultsThe software consists of multiple functions designed to provide tools for the analysis selected. Initial segmentation and fiber filter functions segment the image and remove non-fiber elements based on user-defined parameters to create a fiber mask. Establishing parameters set by the user, the software outputs data on fiber size and type, centrally nucleated fibers, and other structures. These functions were evaluated on stained soleus muscle sections from 1-year-old wild-type and mdx mice, a model of Duchenne muscular dystrophy. In accordance with previously published data, fiber size was not different between groups, but mdx muscles had much higher fiber size variability. The mdx muscle had a significantly greater proportion of type I fibers, but type I fibers did not change in size relative to type II fibers. Centrally nucleated fibers were highly prevalent in mdx muscle and were significantly larger than peripherally nucleated fibers.ConclusionsThe MATLAB code described and provided along with this manuscript is designed for image processing of skeletal muscle immunofluorescent histological sections. The program allows for semi-automated fiber detection along with user correction. The output of the code provides data in accordance with established standards of practice. The results of the program have been validated using a small set of wild-type and mdx muscle sections. This program is the first freely available and open source image processing program designed to automate analysis of skeletal muscle histological sections.

Whey Proteins Are More Efficient than Casein in the Recovery of Muscle Functional Properties following a Casting Induced Muscle Atrophy

The purpose of this study was to investigate the effect of whey supplementation, as compared to the standard casein diet, on the recovery of muscle functional properties after a casting-induced immobilization period. After an initial (I0) evaluation of the contractile properties of the plantarflexors (isometric torque-frequency relationship, concentric power-velocity relationship and a fatigability test), the ankle of 20 male adult rats was immobilized by casting for 8 days. During this period, rats were fed a standard diet with 13% of casein (CAS). After cast removal, rats received either the same diet or a diet with 13% of whey proteins (WHEY). A control group (n = 10), non-immobilized but pair-fed to the two other experimental groups, was also studied and fed with the CAS diet. During the recovery period, contractile properties were evaluated 7 (R7), 21 (R21) and 42 days (R42) after cast removal. The immobilization procedure induced a homogeneous depression of average isometric force at R7 (CAS: − 19.0±8.2%; WHEY: − 21.7±8.4%; P<0.001) and concentric power (CAS: − 26.8±16.4%, P<0.001; WHEY: − 13.5±21.8%, P<0.05) as compared to I0. Conversely, no significant alteration of fatigability was observed. At R21, isometric force had fully recovered in WHEY, especially for frequencies above 50 Hz, whereas it was still significantly depressed in CAS, where complete recovery occurred only at R42. Similarly, recovery of concentric power was faster at R21 in the 500−700°/s range in the WHEY group. These results suggest that recovery kinetics varied between diets, the diet with the whey proteins promoting a faster recovery of isometric force and concentric power output as compared to the casein diet. These effects were more specifically observed at force level and movement velocities that are relevant for functional abilities, and thus natural locomotion.

Changes in strength, endurance, and fatigue during a resistance-training program for the triceps brachii muscle.

As a result of the adaptation process, some functional properties show different functions over time during strength training. Muscle strength and fatigue may show different adaptation patterns in reaching the improvement plateau after several weeks of training. To follow muscle endurance and fatigue values during resistance training of the elbow extensors in young nonathletes. Descriptive laboratory study. Controlled laboratory. Nineteen healthy young nonathletes (age = 21.0 ± 1.1 years; body mass index = 25.2 ± 2.9 kg/m(2)). Triceps brachii resistance training was performed on the isoacceleration dynamometer for 10 weeks (frequency = 5 times a week, 5 sets of 10 maximal elbow extensions, 1-minute resting period between sets). Measurements of endurance strength and fatigability were conducted using the same equipment, and endurance strength (ES), fatigue rate (FR), and decrease in strength (DS) were defined. All measured values for triceps brachii strength changed after training (ES increased by 57%, FR decreased by 68%, and DS improved by 59%; P < .001). No correlation was found between ES and the fatigability values-FR and DS (r(2) = 0.37 for FR and r(2) = 0.04 for DS; P > .05). The FR and DS trends showed specific functions, which reached a plateau after 4 weeks of training, and we found no further weekly changes in these values as the training continued. As an adaptation to exercise, ES showed a continuous, yet not linear, increase. Fatigability in the triceps brachii decreased in the first 4 weeks of training. After that period, muscle functional properties improved as a result of increased endurance.

Bradykinin type 2 receptor -9/-9 genotype is associated with triceps brachii muscle hypertrophy following strength training in young healthy men

BackgroundBradykinin type 2 receptor (B2BRK) genotype was reported to be associated with changes in the left-ventricular mass as a response to aerobic training, as well as in the regulation of the skeletal muscle performance in both athletes and non-athletes. However, there are no reports on the effect of B2BRK 9-bp polymorphism on the response of the skeletal muscle to strength training, and our aim was to determine the relationship between the B2BRK SNP and triceps brachii functional and morphological adaptation to programmed physical activity in young adults.MethodsIn this 6-week pretest-posttest exercise intervention study, twenty nine healthy young men (21.5 ± 2.7 y, BMI 24.2 ± 3.5 kg/m2) were put on a 6-week exercise protocol using an isoacceleration dynamometer (5 times a week, 5 daily sets with 10 maximal elbow extensions, 1 minute rest between sets). Triceps brachii muscle volumes were assessed by using magnetic resonance imaging before and after the strength training. Bradykinin type 2 receptor 9 base pair polymorphism was determined for all participants.ResultsFollowing the elbow extensors training, an average increase in the volume of both triceps brachii was 5.4 ± 3.4% (from 929.5 ± 146.8 cm3 pre-training to 977.6 ± 140.9 cm3 after training, p<0.001). Triceps brachii volume increase was significantly larger in individuals homozygous for −9 allele compared to individuals with one or two +9 alleles (−9/-9, 8.5 ± 3.8%; vs. -9/+9 and +9/+9 combined, 4.7 ± 4.5%, p < 0.05). Mean increases in endurance strength in response to training were 48.4 ± 20.2%, but the increases were not dependent on B2BRK genotype (−9/-9, 50.2 ± 19.2%; vs. -9/+9 and +9/+9 combined, 46.8 ± 20.7%, p > 0.05).ConclusionsWe found that muscle morphological response to targeted training – hypertrophy – is related to polymorphisms of B2BRK. However, no significant influence of different B2BRK genotypes on functional muscle properties after strength training in young healthy non athletes was found. This finding could be relevant, not only in predicting individual muscle adaptation capacity to training or sarcopenia related to aging and inactivity, but also in determining new therapeutic strategies targeting genetic control of muscle function, especially for neuromuscular disorders that are characterized by progressive adverse changes in muscle quality, mass, strength and force production (e.g., muscular dystrophy, multiple sclerosis, Parkinson’s disease).

Fiber‐type composition in the perivertebral musculature of lizards: Implications for the evolution of the diapsid trunk muscles

The perivertebral musculature of lizards is critical for the stabilization and the mobilization of the trunk during locomotion. Some trunk muscles are also involved in ventilation. This dual function of trunk muscles in locomotion and ventilation leads to a biomechanical conflict in many lizards and constrains their ability to breathe while running ("axial constraint") which likely is reflected by their high anaerobic scope. Furthermore, different foraging and predator-escape strategies were shown to correlate with the metabolic profile of locomotor muscles in lizards. Because knowledge of muscle's fiber-type composition may help to reveal a muscle's functional properties, we investigated the distribution pattern of muscle fiber types in the perivertebral musculature in two small lizard species with a generalized body shape and subjected to the axial constraint (Dipsosaurus dorsalis, Acanthodactylus maculatus) and one species that circumvents the axial constraint by means of gular pumping (Varanus exanthematicus). Additionally, these species differ in their predator-escape and foraging behaviors. Using refined enzyme-histochemical protocols, muscle fiber types were differentiated in serial cross-sections through the trunk, maintaining the anatomical relationships between the skeleton and the musculature. The fiber composition in Dipsosaurus and Acanthodactylus showed a highly glycolytic profile, consistent with their intermittent locomotor style and reliance on anaerobic metabolism during activity. Because early representatives of diapsids resemble these two species in several postcranial characters, we suggest that this glycolytic profile represents the plesiomorphic condition for diapsids. In Varanus, we found a high proportion of oxidative fibers in all muscles, which is in accordance with its high aerobic scope and capability of sustained locomotion.

Muscle excursion does not correlate with increased serial sarcomere number after muscle adaptation to stretched tendon transfer

Chronic skeletal muscle stretch typically increases serial muscle fiber sarcomere number. Since serial sarcomere number correlates with functional excursion in normal muscle, observed changes in sarcomere number are often extrapolated to their new assumed function. However, this has not been well demonstrated experimentally. Thus, we measured the functional properties of muscles stretched due to tendon transfer surgery. Muscle active and passive length-tension curves were measured 1 week and 4 weeks after surgery, and then each muscle was further examined to determine structural adaptation as well as single fiber and fiber bundle passive mechanical properties. We found a disconnect between the functional and structural muscle properties. Specifically, muscle excursion was significantly lower in the transferred muscle compared to controls, even though serial sarcomere number had increased. Furthermore, maximum tetanic tension was significantly reduced, though the two groups had similar physiological cross sectional areas. Passive tension increased in the transferred muscle, which was deemed to be due to proliferation of extracellular matrix. These data are the first to report that muscle morphological adaptation after chronic stretch does not accurately predict the muscle's functional properties. These data have significant implications for examining muscle physiological properties under surgical interventions.

Genetic Variation of the Human ACE and ACTN3 Genes and Their Association With Functional Muscle Properties in Lithuanian Elite Athletes

Based on the results of many studies, the angiotensin-converting enzyme (ACE) and the α-actinin-3 (ACTN3) genes are considered strong candidate genes associated with human physical performance. On the other hand, the data regarding the association of the ACE I/D and ACTN3 R/X polymorphisms with human physical performance in different populations have been conflicting. The objective of our research was to evaluate the significance of these genetic variants on muscle performance phenotype in Lithuanian athletes. The study involved 193 Lithuanian elite athletes and 250 controls from the general Lithuanian population. Genotyping was performed by polymerase chain reaction and/or restriction fragment length polymorphism analysis. Anthropometric measurements and muscle strength (grip strength and vertical jump) were measured. It was determined that ACE I/I and I/D genotypes were more frequent in the athlete group compared with the general Lithuanian population. The results of grip strength and vertical jump were better in the athletes with the ACE I/I and ACTN3 X/X genotype compared with the athletes with ACE D/D and ACTN3 R/R, respectively. The ACE I and ACTN3 X alleles determine speed and power for Lithuanian athletes. In line with other researchers, it can be confirmed that the absence of a functional ACTN3 in fast-twitch muscle fibers is compensated. Lithuanian athletes who are carriers of the ACE I/I and I/D as well as ACTN3 X/X and R/X genotypes have the potential to achieve better results in power-requiring sports; therefore, the analyzed polymorphisms of these genes might be used as the criteria for the sport type selection.

Material Properties of Caenorhabditis elegans Swimming at Low Reynolds Number

Undulatory locomotion, as seen in the nematode Caenorhabditis elegans, is a common swimming gait of organisms in the low Reynolds number regime, where viscous forces are dominant. Although the nematode's motility is expected to be a strong function of its material properties, measurements remain scarce. Here, the swimming behavior of C. elegans is investigated in experiments and in a simple model. Experiments reveal that nematodes swim in a periodic fashion and generate traveling waves that decay from head to tail. The model is able to capture the experiments' main features and is used to estimate the nematode's Young's modulus E and tissue viscosity η. For wild-type C. elegans, we find E ≈ 3.77 kPa and η ≈ −860 Pa·s; values of η for live C. elegans are negative because the tissue is generating rather than dissipating energy. Results show that material properties are sensitive to changes in muscle functional properties, and are useful quantitative tools with which to more accurately describe new and existing muscle mutants.

A novel muscle biopsy clamp yields accurate in vivo sarcomere length values

The measurement of in vivo muscle sarcomere length facilitates the definition of in vivo muscle functional properties and comparison of muscle designs amongst functional muscle groups. In vivo sarcomere lengths are available for just a handful of human muscles, largely due to the technical challenges associated with their measurement. The purpose of this report was to develop and test a muscle biopsy clamp that can quickly and accurately measure in vivo muscle sarcomere length. To test the device, muscle biopsies ( n=23) were removed from the tibialis anterior muscles of New Zealand White rabbits immediately after sarcomere length measurements were made using laser diffraction. The muscle biopsy contained within the clamp was immediately fixed in Formalin for subsequent sarcomere length measurement. Comparisons of clamp-based and diffraction-based sarcomere lengths demonstrated excellent agreement between the two techniques, especially when the biopsy was obtained at relatively long lengths (above 2.6 μm). Given the intraoperative speed and simplicity of this technique and the relatively low-cost of the biopsy clamp, this method of measuring muscle sarcomere length should help investigators generate much-needed in vivo muscle structural and functional data.

CHANGES IN QUALITY OF MINCED MEAT FROM GOAT DUE TO GAMMA IRRADIATION

ABSTRACT Thigh muscles from aged (3–4 years) goat were minced, packed in polyethylene bags (250 g each), gamma irradiated with a dosage of 4 kGy and the packets held at 3 ± 1C for 8 days. Nonirradiated muscle mince packed and stored similarly were treated as control. Both irradiated and nonirradiated muscle mince were sampled on 0, 5 and 8 days of storage and analyzed for physicochemical, microbiological and sensory quality attributes. Irradiation resulted in lower (P ≤ 0.05) muscle pH (3.5–5.1%), water holding capacity (4.5–6.7%), thiobarbituric acid values (19.4–34.9%) and higher (P ≤ 0.05) free fatty acid (26.9–61.0%) and Hunter a* (3.3–17.3%) values compared with nonirradiated control muscle samples. A reduction (P ≤ 0.05) of 2 log cfu/g in total aerobic bacteria and psychrotrophs, and 1 log cfu/g in total staphylococci, yeast and molds were also observed in irradiated samples while enterococci, Escherichia coli and Staphylococcus aureus could not be detected in irradiated and stored muscles. Sensory quality scores on a 9‐point hedonic scale decreased from 7.5–8.3 to 7.1–7.9 during storage at 3 ± 1C for 8 days and were marginally influenced by irradiation. The results establish that a 4‐kGy dosage is appropriate for irradiation to maintain fresh meat quality under chilled condition.PRACTICAL APPLICATIONSMuscles are highly perishable primarily because high microbial load and irradiation effectively reduces the microbial counts and helps extension of shelf life of muscle foods. Production and retention of free radicals produced by irradiation cause changes in, apart from bacterial counts, proteins and lipids which in turn may affect functional properties such as water holding capacity and emulsion and sensory characteristics. Many muscle foods, such as sausages, burgers, loaves, kebabs, etc., are emulsion‐type products, a quality that is dependent on functional properties of muscles' proteins/lipids. These products are industrially produced and are marketed in India and abroad. The industry is aware of the beneficial effect of irradiation in reducing the microbial load but has an apprehension that irradiation may adversely affect the functional properties and sensory characteristics of muscle foods. The study reported in this paper overcomes that apprehension when meat was irradiated with a permitted dosage of 4 kGy.

Functional and evolutionary relationships of troponin C

Striated muscle contraction is initiated when, following membrane depolarization, Ca(2+) binds to the low-affinity Ca(2+) binding sites of troponin C (TnC). The Ca(2+) activation of this protein results in a rearrangement of the components (troponin I, troponin T, and tropomyosin) of the thin filament, resulting in increased interaction between actin and myosin and the formation of cross bridges. The functional properties of this protein are therefore critical in determining the active properties of striated muscle. To date there are 61 known TnCs that have been cloned from 41 vertebrate and invertebrate species. In vertebrate species there are also distinct fast skeletal muscle and cardiac TnC proteins. While there is relatively high conservation of the amino acid sequence of TnC homologs between species and tissue types, there is wide variation in the functional properties of these proteins. To date there has been extensive study of the structure and function of this protein and how differences in these translate into the functional properties of muscles. The purpose of this work is to integrate these studies of TnC with phylogenetic analysis to investigate how changes in the sequence and function of this protein, integrate with the evolution of striated muscle.

Differential responses of serum and salivary interleukin-6 to acute strenuous exercise

Physical exercise is associated with elevation of serum levels of interleukin-6 (IL-6) because of its production in the muscles. The use of IL-6 measurements in saliva has been proposed in the field of immunopathology, mainly involving salivary gland disease. We evaluated the responses of serum and salivary IL-6 in two different groups of athletes submitted to different types of controlled strenuous exercise (spinning activity and maximal isokinetic test). Serum and salivary samples for IL-6 measurements, and serum samples for lactate and myoglobin determination before and after exercise, were obtained. Salivary IL-6 was measured by ELISA after dilution experiments and compared with results obtained by immunoradiometric assay. Spinning activity elicited significant increases in all the variables, and no correlation was found among the respective variations. A significant response to the isokinetic exercise was observed for serum IL-6, lactate and myoglobin only; no correlation was found between serum and salivary IL-6. Our study demonstrated that serum and salivary IL-6 responses to exercise are dissociated, possibly in relation to the lack of relationships between the systemic/muscular and the salivary routes of IL-6 production. Analytical issues that concern IL-6 measurement in saliva deserve attention, notably regarding the collection method used to absorb saliva. Concomitant monitoring of serum markers of inflammation, muscle metabolism and damage can provide information about muscle function properties and adaptations to physical effort in different types of athletes.

Muscle function in 164 men and women aged 20--84 yr.

The purpose of the present study was to investigate the effect of aging in men and women on muscle functional properties, i.e., muscle force and force per unit of cross-sectional area (force/CSA). A total of 164 volunteers participated in this study and were divided into five groups according to their chronological age as follows: 20s (20--39 yr old), 40s, 50s, 60s, and 70s (70--84 yr old). Isokinetic (0, 60, 180, and 300 degrees.s(-1)) knee extensor and flexor peak torque, and CSA of the quadriceps femoris (QF) muscle of the mid-thigh were measured. Peak torque during knee extension and flexion was inversely related to age in both men and women. This was the case irrespective of the speed of contraction in both genders (men: r = -0.797 to -0.756, all P < 0.001, women: r = -0.639 to -0.530, all P < 0.001). A significant correlation was observed between CSA of QF and peak torque during isometric knee extension in men (r = 0.827, P < 0.001) and women (r = 0.657, P < 0.001). During isometric contraction, the force/CSA exhibited a significant decrease with increasing age in men (r = -0.518, P < 0.001) but not in women (r = -0.207, NS). These results thus suggest that muscle strength losses would be mainly due to a decline in muscle mass in both genders, whereas age-related decline in muscle function in men may also be the result of neural factors, such as muscle recruitment and/or specific tension.

From Molar Unit to Whole Muscle Properties During Locomotor Movements

Over the last century, progress has been made in understanding the basic structure and function of muscle. The emphasis on muscle research has become increasingly focused at the molecular level, and startling advances have been made. Surprisingly, at the whole muscle level significant questions remain unanswered. The details of how muscles are actually used in locomotion are lacking. The foregoing sections have discussed some basic muscle properties and then reviewed instances in which they have been directly measured during locomotor movements. Although most of the basic functional properties of muscle are known, some simple questions such as what the preferred operating point is on the F-L and F-V curves remain unanswered. Design principles of muscle structure and their control by the CNS have yet to be illuminated. Most in vivo techniques to study muscle function are difficult to use. This precludes their use on all but a small number of specialized muscles. With the exception of photography and electromyography, at best a small number of muscles can be studied at a time. The technique of measuring some muscle properties in vivo and then duplicating the conditions in an isolated muscle for further measurements seems promising. Combinations of mathematical models and careful experimental verification will also be necessary.

Effect of Antemortem Electrical Stunning on Functional Properties of Turkey Muscle

Muscle samples were collected from two groups of turkeys, one group electrically stunned before exsanguination and the other group nonstunned. Sampling was done at 0, 4, 8, and 24 h postmortem. Examination of muscle samples for glycogen, pH, adenosine triphosphate (ATP), R value (ratio of inosine nucleotides to adenosine nucleotides), and extractable protein demonstrated that glycolysis was delayed by electrical stunning. Muscle myofibrils, however, showed no effect of stunning on Mg + +-ATPase, sulfhydryls, or sodium dodecylsulfate-polyacrylamide gel electrophoresis patterns. Functional properties of the muscle as measured by emulsion stability evaluations showed greater stability in prerigor muscle but no significant effect of stunning. The results indicate that although electrical stunning delayed glycolysis, the overall effect was not great enough to be a significant factor in improvement of functional properties of muscle for further processing.

Circulatory response to static muscle contractions in three different muscle groups

Summary. The circulatory responses to static contractions of three different muscle groups were compared. Contractions at 15 and 25–30 % MVC of forearm muscles (hand‐grips) were compared to quadriceps muscle contractions in eleven male subjects, and in 10 subjects the response to hand‐grip contractions and foot plantar flexion was studied.All contractions at 15% MVC induced slight but significant changes in heart rate (HR); intra‐arterial blood pressure (BP) changes were more marked. 25–30 % MVC intensities always elicited a greater HR ‐and BP response than 15 % intensity in the same muscle group.Stroke volume (measured during hand‐grips and quadriceps contractions) was unchanged at all exercise intensities; hence, HR was a reliable measure of changes in cardiac output (Q). The circulation became hyperkinetic during exercise, since the rise in oxygen uptake was very slight despite a moderate increase in Q.Quadriceps contractions always elicited a larger HR, BP and Q response at a given time than hand‐grip contractions and the HR and BP at foot plantar flexion was always least marked. HR at exhaustion followed the same pattern. It is suggested that differences in functional properties of muscles are partly responsible for the magnitude of the reflex cardiovascular response during static contractions, but muscle strength and size may also influence the results.

Functional properties of muscles transplanted between normal and dystrophic mice

Tibialis anterior muscles were transplanted between 12-week-old normal and dystrophic mice with intact or polydimethyl silicone-capped peroneal nerve. After 150 days the transplants were removed and their isometric twitch contraction properties were studied in vitro at 20 C. Intact normal and dystrophic muscles of equivalent age were used as controls. Dystrophic muscles developed lower twitch and tetanus tension than normal muscles and showed prolonged half relaxation time. The contraction time and twitch/tetanus ratio of both types of muscle were similar. Of all transplantations performed, only those in normal mice with intact nerve responded upon stimulation. Both normal and dystrophic transplants in normal hosts showed similar isometric properties. Although intact dystrophic muscles and viable dystrophic transplants in normal hosts were similar in weight, the transplants developed about three to four times more tension. In addition, dystrophic transplants showed relaxation times similar to normal muscles. It is suggested that the dystrophic lesion in mice may have a neural origin.