Fiber Type Distribution Research Articles

Impact of Body Mass Index on Muscle Strength, Thicknesses, and Fiber Composition in Young Women.

High body mass index (BMI) may influence muscle strength, muscle thickness (Mtk), and fiber composition. We evaluated these parameters in 31 and 27 women grouped in non-oral contraceptive (non-OC) groups and OC groups, respectively, and further divided them into groups based on BMI: BMIlow, BMInorm, and BMIhigh. Maximum isometric force (Fmax), Mtk, and the relative percentage of muscle fiber composition (%) were examined in both groups. Fmax and Mtk values were significantly greater in the BMIhigh than the BMIlow within the OC group. However, there was no significant difference in the non-OC group. BMIlow and BMInorm groups showed a difference in the distribution of muscle fiber types 1 and 2 with almost the same proportions in both non-OC and OC groups. However, the BMIhigh group showed a difference in the distribution of muscle fiber types 1 and 2, with type 1 about 18.76% higher in the non-OC group. Contrastively, type 2 was about 34.35% higher in the OC group. In this study, we found that there was a significant difference in Fmax and Mtk according to the BMI level in the OC group, but no significant difference was found in the non-OC group. Moreover, the distribution of type 2 muscle fibers tended to be higher in the OC group of BMIhigh, although the sample size was small. Therefore, although no significant difference of Fmax and Mtk was found according to BMI level in the non-OC group in this study, the increase in BMI level appeared to be more associative of muscle strength in the OC group. Based on the present results, future studies are needed that consider the BMI level as well as the presence or absence of OC in future research about women’s muscle strength.

Satellite cell depletion does not affect diaphragm adaptations to hypoxia.

The diaphragm is the main skeletal muscle responsible for inspiration and is susceptible to age-associated decline in function and morphology. Satellite cells in diaphragm fuse into unperturbed muscle fibers throughout life, yet their role in adaptations to hypoxia in diaphragm is unknown. Given their continual fusion, we hypothesize that satellite cell depletion will negatively impact adaptations to hypoxia in the diaphragm, particularly with aging. We used the Pax7CreER/CreER:R26RDTA/DTA genetic mouse model of inducible satellite cell depletion to investigate diaphragm responses to hypoxia in adult (6 mo) and aged (22 mo) male mice. The mice were subjected to normobaric hypoxia at 10% [Formula: see text] or normoxia for 4 wk. We showed that satellite cell depletion had no effect on diaphragm muscle fiber cross-sectional area, fiber-type distribution, myonuclear density, or regulation of extracellular matrix in either adult or aged mice. Furthermore, we showed lower muscle fiber cross-sectional area with hypoxia and age (main effects), while extracellular matrix content was higher and satellite cell abundance was lower with age (main effect) in diaphragm. Lastly, a greater number of Pax3-mRNA+ cells was observed in diaphragm muscle of satellite cell-depleted mice independent of hypoxia (main effect), potentially as a compensatory mechanism for the loss of satellite cells. We conclude that satellite cells are not required for diaphragm muscle adaptations to hypoxia in either adult or aged mice.NEW & NOTEWORTHY Satellite cells show consistent fusion into diaphragm muscle fibers throughout life, suggesting a critical role in maintaining homeostasis. Here, we report identical diaphragm adaptations to hypoxia with and without satellite cells in adult and aged mice. In addition, we propose that the higher number of Pax3-positive cells in satellite cell-depleted diaphragm muscle acts as a compensatory mechanism.

High-throughput muscle fiber typing from RNA sequencing data

BackgroundSkeletal muscle fiber type distribution has implications for human health, muscle function, and performance. This knowledge has been gathered using labor-intensive and costly methodology that limited these studies. Here, we present a method based on muscle tissue RNA sequencing data (totRNAseq) to estimate the distribution of skeletal muscle fiber types from frozen human samples, allowing for a larger number of individuals to be tested.MethodsBy using single-nuclei RNA sequencing (snRNAseq) data as a reference, cluster expression signatures were produced by averaging gene expression of cluster gene markers and then applying these to totRNAseq data and inferring muscle fiber nuclei type via linear matrix decomposition. This estimate was then compared with fiber type distribution measured by ATPase staining or myosin heavy chain protein isoform distribution of 62 muscle samples in two independent cohorts (n = 39 and 22).ResultsThe correlation between the sequencing-based method and the other two were rATPas = 0.44 [0.13–0.67], [95% CI], and rmyosin = 0.83 [0.61–0.93], with p = 5.70 × 10–3 and 2.00 × 10–6, respectively. The deconvolution inference of fiber type composition was accurate even for very low totRNAseq sequencing depths, i.e., down to an average of ~ 10,000 paired-end reads.ConclusionsThis new method (https://github.com/OlaHanssonLab/PredictFiberType) consequently allows for measurement of fiber type distribution of a larger number of samples using totRNAseq in a cost and labor-efficient way. It is now feasible to study the association between fiber type distribution and e.g. health outcomes in large well-powered studies.

Mechanotherapy does not Enhance Recovery Following Muscle Disuse Atrophy in Female Rats

BackgroundRecovery from skeletal muscle atrophy is important for regaining function. We previously showed that mechanotherapy enhances regrowth of muscle in adult male rats by elevating protein synthesis.ObjectiveThe purpose of this study was to determine if female rats also respond to mechanotherapy during regrowth after disuse‐induced atrophy.HypothesisMechanotherapy in female rats augments muscle regrowth after atrophy by enhancing protein synthesis.MethodsAdult (10 month) F344/BN female rats were randomly assigned to one of four groups: weight‐bearing (WB; N=6), hindlimb suspension (HS; N=9), reambulation after HS without mechanotherapy (RA; N=9), or RA with mechanotherapy (RAM; N=10). HS lasted for 14 and RA for 7 days. Starting the day of RA, mechanotherapy was applied to the right gastrocnemius muscle at a load of 4.5N for 30 minutes every other day (4 bouts total). Rats received deuterium oxide (D2O) for determination of myofibrillar protein and RNA synthesis (Ksyn) and degradation (Kdeg). We analyzed gastrocnemius muscles for myonuclear number (dystrophin‐DAPI), satellite cell (SC) number (Pax7), and fiber type and cross‐sectional area (CSA; laminin‐myosin heavy chain). We used a one‐way ANOVA to determine statistical significance at p<0.05. Values are mean ± SD.ResultsMuscle wet weight (g) was lower with HS (933 ± 56) compared to WB (1140 ± 86) and greater in RA (1012 ± 64) and RAM (1030 ± 41) compared to HS. However, no difference was observed between RA and RAM. Mean fiber CSA (µm2) was significantly lower in HS (1877 ± 244) compared to WB (2395 ± 248), while RA (2124 ± 287) was not different from WB or HS. RAM CSA (2013 ± 182) was lower than WB and not different from HS or RA. Myofibrillar Ksyn (mg/day) was lower in HS (13 ± 2.1) compared to WB (22 ± 2.2). RA (32 ± 3.2) and RAM (30 ± 4.3) were higher than HS and WB, but no difference was observed between RA and RAM. Myofibrillar Kdeg (1/t) was greater in HS (0.03 ± 0.004) compared to WB (0.02 ± 0.005), and RA (0.04 ± 0.007) and RAM (0.04 ± 0.005) were higher than HS and WB, but not different from each other. RNA Ksyn (%/day) was not different between WB (2 ± 0.2) and HS (2 ± 0.3), whereas RE (3 ± 0.4) and REM (4 ± 0.6) were both higher that WB and HS, but not different from each other. There were no differences in fiber type distribution between the groups. CSA of all fiber types was lower with HS, whereas no differences were observed between RA, RAM and HS. We did not find a significant difference in myonuclear number or centrally located nuclei between the groups. The number of SCs (per/fiber) was lower in HS (0.03 ± 0.01) and RA (0.04 ± 0.01) compared to WB (0.05 ± 0.008) and was higher in RAM (0.05 ± 0.02) compared to HS.ConclusionMuscle recovery from atrophy in female rats occurs with reambulation and elevated protein turnover is the underlying anabolic mechanism. We therefore conclude that the additional load using mechanotherapy does not enhance muscle recovery in females, which is different than the response previously published for males.

Dog Faces Are Faster than Wolf Faces

Humans domesticated dogs with attention to the facial expressions that dogs produce, selecting for a suite of facial movement. Domestic dogs and humans are adept at accurately understanding one another’s facial expressions and movement around the eyes in dogs is highly valued by humans. This unique, mutual ability to accurately process facial expressions is part of the dog‐human bond. An accurate understanding of how dog and wolf faces differ from one another is fundamental to understanding the processes of animal domestication, evolution of the dog, and the origins of human behavior since the Upper Paleolithic. While we know that dogs have facial musculature that wolves do not regularly possess, our understanding of evolutionary muscle physiology between these two species is incomplete. The present study was designed to assess differential distribution of slow‐twitch (type I) and fast‐twitch (type II) myosin fibers in select facial muscles of dogs and wolves. We tested the hypothesis that dog facial muscle physiology would be more similar to humans than to wolves in terms of myosin fiber type distribution. We used samples from the orbicularis oris muscle (OOM) and the zygomaticus major muscle (ZM) from a range of domestic dog breeds (Canis familiaris) and gray wolves (Canis lupus) that were part of previous studies. Samples were processed for myosin immunohistochemistry (IHC) and we selected 3‐5 sections from each specimen stained for identification of each fiber type in both the OOM and ZM muscles. We created composite images of stained sections and assessed fiber type percentages using ImageJ. Percentage of fast‐twitch fibers in dog samples ranged from 66%‐95% and wolves averaged around 25%. Slow‐twitch fiber percentages in dogs averaged only 10% while wolves averaged 29%. The dog range of type II fibers mirrors the range found in human facial muscles, indicating that the domestication process in dogs also involved selection for rapid facial movement, similar to the movement seen in human faces.

Histomorphological and functional contralateral symmetry in the gastrocnemius muscles of the laboratory rat.

It is usual in anatomical and physiological research to assess the effects of some intervention on extremities (e.g., training programmes or injury recovery protocols) using one muscle for the intervention and its contralateral as control. However, the existence of laterality (left‐handedness or right‐handedness) in athletes of different specialities is widely recognized. In rats, gastrocnemius is one of the muscles most widely used because of its importance in locomotion and high relative limb mass. Since we have not found studies reporting laterality assessment on the morphology and function in rat gastrocnemius, our study aimed to evaluate the fibre histochemical, morphometrical and muscle force contractile properties between right and left gastrocnemius of the laboratory rat. Fibre‐type proportion, fibre morphometrical measurements, muscle capillarization and muscle force properties were analysed in the right and left gastrocnemius of six male rats. No statistically significant differences (p = 0.265) were found in gastrocnemius to body weight ratio (‰) between right (6.55 ± 0.40) and left (6.49 ± 0.40) muscles. The muscles analysed showed a great degree of heterogeneity in fibre type distribution, having three clearly distinguished regions named red, mixed and white. In the three regions, there were no statistical differences in fibre type proportions between right and left gastrocnemius, as is indicated by the p‐values (from 0.203 to 0.941) obtained after running t‐Student paired tests for each fibre type. When analysing fibre cross‐sectional area, individual fibre capillarization and fibre circularity, no significant differences between right and left gastrocnemius in any of these morphometrical parameters were found in any muscle region or fibre type. Most of the p‐values (70%) resulting from running t‐Student paired tests were higher than 0.400, and the lowest p‐value was 0.115. Seemingly, global capillary and fibre densities were not statistically different between right and left sides in all muscle regions with p‐values ranging from 0.337 to 0.812. Force parameters normalized to gastrocnemius mass (mN g−1) did not show any significant difference between right (PF = 74.0 ± 13.4, TF = 219.4 ± 13.0) and left (PF = 70.9 ± 10.7, TF = 213.0 ± 18.0) muscles with p = 0.623 (PF) and p = 0.514 (TF). Twitch time parameters (ms) also lacked significant differences between the two sides (CT: 43.4 ± 8.6 vs. 45.0 ± 14.3, p = 0.639; HRT: 77.6 ± 15.0 vs. 82.3 ± 25.3, p = 0.475). Finally, both muscles also showed similar (p = 0.718) fatigue properties. We did find an absence of laterality at the morphological and functional levels, which raises the possibility of using right and left gastrocnemius muscles interchangeably for experimental designs where one muscle is used to analyse data after a physiological intervention and its contralateral muscle plays the control role, thus allowing unbiased paired comparisons to derive accurate conclusions.

The Clinical, Myopathological, and Genetic Analysis of 20 Patients With Non-dystrophic Myotonia

IntroductionNon-dystrophic myotonias (NDMs) are skeletal muscle ion channelopathies caused by CLCN1 or SCN4A mutations. This study aimed to describe the clinical, myopathological, and genetic analysis of NDM in a large Chinese cohort.MethodsWe reviewed the clinical manifestations, laboratory results, electrocardiogram, electromyography, muscle biopsy, genetic analysis, treatment, and follow-up of 20 patients (from 18 families) with NDM.ResultsCases included myotonia congenita (MC, 17/20) and paramyotonia congenita (PMC, 3/20). Muscle stiffness and hypertrophy, grip and percussion myotonia, and the warm-up phenomenon were frequently observed in MC and PMC patients. Facial stiffness, eye closure myotonia, and cold sensitivity were more common in PMC patients and could be accompanied by permanent weakness. Nine MC patients and two PMC patients had cardiac abnormalities, mainly manifested as cardiac arrhythmia, and the father of one patient died of sudden cardiac arrest. Myotonic runs in electromyography were found in all patients, and seven MC patients had mild myopathic changes. There was no difference in muscle pathology between MC and PMC patients, most of whom had abnormal muscle fiber type distribution or selective muscle fiber atrophy. Nineteen CLCN1 variants were found in 17 MC patients, among which c.795T>G (p.D265E) was a new variant, and two SCN4A variants were found in three PMC patients. The patients were treated with mexiletine and/or carbamazepine, and the symptoms of myotonia were partially improved.ConclusionsMC and PMC have considerable phenotypic overlap. Genetic investigation contributes to identifying the subtype of NDM. The muscle pathology of NDM lacks specific changes.

Comparison of Meat Quality Characteristics and Proteolysis Trends associated with Muscle Fiber Type Distribution between Duck Pectoralis Major and Iliotibialis Muscles.

This study was conducted to evaluate the proteolysis trends and change in meat quality during 10 days of cold storage in duck M. pectoralis major (PM) and M. iliotibialis (IL). Duck IL had a higher pH and greater degree of lightness but lower cooking loss than PM (p<0.05). During the 10-day cold storage, the pH value of PM declined significantly (p<0.05), while the meat quality traits of IL were not affected by cold storage (p>0.05). In PM, the redness increased from day 1 to day 5, while cooking loss was lower on day 10 compared to day 5 (p<0.05). There were no significant differences in the activities of cathepsin B and proteasome 20S during cold storage (p>0.05). The activity of calpains declined gradually during 10 days of storage (p<0.05), and the activity of calpains in PM was higher than that in IL (p<0.05). A total of 5,155 peptides were detected and derived from 34 proteins of duck PM muscle, whereas 4,222 peptides derived from 32 proteins were detected from duck IL muscle. Duck PM muscle was composed only of fast type of muscle fiber, whereas IL muscle was composed of both slow and fast types. The proteins responsible for glycolysis or myofibrillar proteins were closely related to changes in meat color or water-holding capacity during cold storage. These results suggest that changes in meat quality characteristics during cold storage are closely related to protein degradation, which is also related to the distribution of muscle fiber types.

Improved impedance to maladaptation and enhanced VCAM-1 upregulation with resistance-type training in the long-lived Snell dwarf (Pit1dw/dw) mouse.

Snell dwarf mice with the Pit1dw/dw mutation are deficient in growth hormone, prolactin, and thyroid stimulating hormone and exhibit >40% lifespan extension. This longevity is accompanied by compromised muscular performance. However, research regarding young (3-month-old) Snell dwarf mice demonstrate exceptional responsivity to resistance-type training especially in terms of a shifted fiber type distribution and increased protein levels of vascular cell adhesion molecule-1 (VCAM-1), a possible mediator of such remodeling. In the present study, we investigated whether this responsiveness persists at 12 months of age. Unlike 12-month-old control mice, age-matched Snell dwarf mice remained resistant to training-induced maladaptive decreases in performance and muscle mass. This was accompanied by retainment of the remodeling capacity in muscles of Snell dwarf mice to increase VCAM-1 protein levels and a shift in myosin heavy chain (MHC) isoform distribution with training. Even decreasing training frequency for control mice, an alteration which protected muscles from maladaptation at 12 months of age, did not result in the overt remodeling observed for Snell dwarf mice. The results demonstrate a distinct remodeling response to resistance-type exercise operative in the context of the Pit1dw/dw mutation of long-lived Snell dwarf mice.

Overexpression of thioredoxin‐2 attenuates age‐related muscle loss by suppressing mitochondrial oxidative stress and apoptosis

AbstractBackgroundSkeletal muscle mass is regulated by intracellular anabolic and catabolic activities. Increased catabolic activity can shift the balance towards net protein breakdown and muscle atrophy. Mitochondrial oxidative stress activates catabolism and is linked to muscle loss. Reducing mitochondrial oxidative stress is thus a plausible approach to prevent muscle atrophy. We tested this concept in age‐dependent muscle atrophy by genetically overexpressing the mitochondrial antioxidant thioredoxin‐2 (TXN2).MethodsWe tested the functional role of TXN2 using ageing (n = 7–10 per group) and denervation (n = 3 per group) models in a transgenic mouse line that overexpresses TXN2. We investigated if overexpression of TXN2 blocks muscle loss in these models by examination of muscle weight, fibre size, and fibre number in young (~7 months) and aged (~26 months) TXN2‐transgenic mice and controls. We studied the underlying mechanisms by mRNA and protein assays including transcriptomic profiling, western blot analysis, immunostaining, as well as succinate dehydrogenase, dihydroethidium, and terminal deoxynucleotidyl transferase dUTP nick end labelling staining.ResultsOverexpression of TXN2 did not significantly alter the baseline skeletal muscle size, weight, fibre type distribution, or expression of mitochondrial respiratory chain components, but it did preserve muscle mass during ageing. The hindlimb muscle mass in aged TXN‐transgenic mice was ~21–24% greater (in tibialis anterior, gastrocnemius/soleus combined, and tibialis anterior/extensor digitorum longus combined) than in age‐matched controls (all P &lt; 0.05). The reduction in both muscle fibre number (872 ± 206 vs, 637 ± 256 fibres in extensor digitorum longus muscle, P &lt; 0.05) and muscle fibre size (1959 ± 296 vs. 1477 ± 564 μm2 in tibialis anterior muscle, P &lt; 0.05) seen in young vs. aged control muscles was not significant in young vs. aged TXN‐transgenic mice (both P &gt; 0.05). Transcriptomic analysis revealed that catabolic genes that are up‐regulated in ageing muscle, including those subserving apoptosis and the ubiquitin‐like conjugation system, were normalized by TXN2 overexpression. Further, overexpressing TXN2 suppressed oxidative stress and caspase‐9/3‐mediated apoptotic signalling in the aged muscle at the protein level. Although denervation and its effects have been considered a component of age‐related muscle atrophy, TXN2 overexpression failed to attenuate atrophy in an acute denervation model (TXN‐transgenic vs. control mice, P &gt; 0.05), despite preventing denervation‐induced oxidative stress and apoptosis.ConclusionsMitochondrial oxidative stress appears to play a crucial role in effecting chronic age‐dependent, but not acute neurogenic, muscle atrophy. Increased TXN2 protects muscle against oxidative stress‐associated catabolic activity in ageing muscle and thus is a potential therapeutic approach to attenuate age‐related muscle atrophy.

Skeletal Muscle Quality Of Nonagenarians And Centenarians

Skeletal muscle adipose tissue infiltration is hypothesized to lead to poorer muscle quality and function with aging. Indeed, skeletal muscle adiposity has emerged as a consistent, independent predictor of skeletal muscle strength, mobility, metabolic disorders, and survival among older adults. However, phenotypic features of skeletal muscle among the oldest-old remain poorly characterized. Herein, we evaluated the skeletal muscle characteristics of 54 nonagenarians and centenarians (mean age 98 years, range 90-110 years; 63% women) and 25 middle-aged individuals (mean age 54 years, range 40-59 years; 36% women) belonging to the Long Life Family Study (LLFS), an international, multicenter cohort of families with a clustering of longevity. Ultrasonography was used to measure echo intensity of the sternocleidomastoid muscle, which has a similar fiber type distribution to the rectus femoris. Greater echo intensity is indicative of lower muscle quality (greater adipose and fibrotic tissue). Current smoking, alcohol intake, and BMI were similar between the age groups. Nonagenarians and centenarians had lower grip strength (16.3 vs. 39 kg) and were less physically active (22.2% vs 66.7% exercised 1+ times per week) compared to younger individuals (P<0.001 for all). Mean±SE echo intensity, adjusted for gender, field center, BMI and physical activity was 52.1±1.7 among nonagenarians and centenarians compared to 44.2±2.4 among younger individuals (P=0.0098). Our preliminary findings suggest that nonagenarians and centenarians may have substantially lower skeletal muscle quality and strength compared to their younger aged counterparts. Additional research is needed to better understand the mechanisms leading to poorer muscle characteristics of the oldest-old.

Lower citrate synthase activity, mitochondrial complex expression, and fewer oxidative myofibers characterize skeletal muscle from growth-restricted fetal sheep.

Skeletal muscle from the late gestation sheep fetus with intrauterine growth restriction (IUGR) has evidence of reduced oxidative metabolism. Using a sheep model of placental insufficiency and IUGR, we tested the hypothesis that by late gestation, IUGR fetal skeletal muscle has reduced capacity for oxidative phosphorylation because of intrinsic deficits in mitochondrial respiration. We measured mitochondrial respiration in permeabilized muscle fibers from biceps femoris (BF) and soleus (SOL) from control and IUGR fetal sheep. Using muscles including BF, SOL, tibialis anterior (TA), and flexor digitorum superficialis (FDS), we measured citrate synthase (CS) activity, mitochondrial complex subunit abundance, fiber type distribution, and gene expression of regulators of mitochondrial biosynthesis. Ex vivo mitochondrial respiration was similar in control and IUGR muscle. However, CS activity was lower in IUGR BF and TA, indicating lower mitochondrial content, and protein expression of individual mitochondrial complex subunits was lower in IUGR TA and BF in a muscle-specific pattern. IUGR TA, BF, and FDS also had lower expression of type I oxidative fibers. Fiber-type shifts that support glycolytic instead of oxidative metabolism may be advantageous for the IUGR fetus in a hypoxic and nutrient-deficient environment, whereas these adaptions may be maladaptive in postnatal life.

Loss of Nup210 results in muscle repair delays and age-associated alterations in muscle integrity.

Nuclear pore complexes, the channels connecting the nucleus with the cytoplasm, are built by multiple copies of ∼30 proteins called nucleoporins. Recent evidence has exposed that nucleoporins can play cell type-specific functions. Despite novel discoveries into the cellular functions of nucleoporins, their role in the regulation of mammalian tissue physiology remains mostly unexplored because of a limited number of nucleoporin mouse models. Here we show that ablation of Nup210/Gp210, a nucleoporin previously identified to play a role in myoblast differentiation and Zebrafish muscle maturation, is dispensable for skeletal muscle formation and growth in mice. We found that although primary satellite cells from Nup210 knockout mice can differentiate, these animals show delayed muscle repair after injury. Moreover, Nup210 knockout mice display an increased percentage of centrally nucleated fibers and abnormal fiber type distribution as they age. Muscle function experiments also exposed that Nup210 is required for muscle endurance during voluntary running. Our findings indicate that in mammals, Nup210 is important for the maintenance of skeletal muscle integrity and for proper muscle function providing novel insights into the in vivo roles of nuclear pore complex components.

Comparison of muscle fiber characteristics and glycolytic potential between slow- and fast-growing broilers

Muscle fiber characteristics had beneficial effects on meat masses and meat quality in broilers. Its number is determined at birth and directly affects the growth and development of muscle fibers after birth. However, whether the muscle fiber characteristics in different types of chickens are different at birth has not been fully documented. In this study, the 1-day-old Xueshan chicken (slow-growing broiler) and Ross 308 broiler (fast-growing broiler) were selected, respectively, and the fiber type distribution, fiber density, and fiber size in the breast (pectoralis major, PM) and leg (gastrocnemius, GAS) muscles were detected. The results showed that the PM only made up of type IIB fibers regardless of breed, and that few type I fibers (approximately 17.55%) was identified in GAS of Ross 308 broiler. The PM muscles had significantly higher fiber density, lower cross-sectional area and diameter than those of GAS muscles in both 2 breeds (P < 0.05). The highest fiber density was observed in PM of Xueshan chicken. Furthermore, the muscle fiber characteristics were partly controlled by glycolytic potential (GP), and the GP was also invesgated. The GP in PM and GAS of Ross 308 broiler were higher than in Xueshan chicken (P < 0.05). Taken together, 1-day-old Xueshan chicken exhibited higher fiber density and lower GP compared to 1-day-old Ross 308 broiler, especially in PM, which could not only reveal the differences of muscle characteristics among different types of chickens, but also explore a new way to improve the masses and quality of poultry meat.

Moderate Intensity Exercise Training Improves Skeletal Muscle Performance in Symptomatic and Asymptomatic Statin Users

BackgroundThe combination of statin therapy and physical activity reduces cardiovascular disease risk in patients with hyperlipidemia more than either treatment alone. However, mitochondrial dysfunction associated with statin treatment could attenuate training adaptations. ObjectivesThis study determined whether moderate intensity exercise training improved muscle and exercise performance, muscle mitochondrial function, and fiber capillarization in symptomatic and asymptomatic statin users. MethodsSymptomatic (n = 16; age 64 ± 4 years) and asymptomatic statin users (n = 16; age 64 ± 4 years) and nonstatin using control subjects (n = 20; age 63 ± 5 years) completed a 12-week endurance and resistance exercise training program. Maximal exercise performance (peak oxygen consumption), muscle performance and muscle symptoms were determined before and after training. Muscle biopsies were collected to assess citrate synthase activity, adenosine triphosphate (ATP) production capacity, muscle fiber type distribution, fiber size, and capillarization. ResultsType I muscle fibers were less prevalent in symptomatic statin users than control subjects at baseline (P = 0.06). Exercise training improved muscle strength (P < 0.001), resistance to fatigue (P = 0.01), and muscle fiber capillarization (P < 0.01), with no differences between groups. Exercise training improved citrate synthase activity in the total group (P < 0.01), with asymptomatic statin users showing less improvement than control subjects (P = 0.02). Peak oxygen consumption, ATP production capacity, fiber size, and muscle symptoms remained unchanged in all groups following training. Quality-of-life scores improved only in symptomatic statin users following exercise training (P < 0.01). ConclusionsA moderate intensity endurance and resistance exercise training program improves muscle performance, capillarization, and mitochondrial content in both asymptomatic and symptomatic statin users without exacerbating muscle complaints. Exercise training may even increase quality of life in symptomatic statin users. (The Effects of Cholesterol-Lowering Medication on Exercise Performance [STATEX]; NL5972/NTR6346)

Eccentric Overload during Resistance Exercise: A Stimulus for Enhanced Satellite Cell Activation.

This study aimed to assess if one bout of concentric/eccentric exercise with damaging eccentric overload (CON/ECC+) provides a sufficient stimulus to induce SC activation, proliferation, and differentiation. Biopsies from the vastus lateralis muscle of recreationally active men were obtained in the rested condition and again from the contralateral leg 7 d after exhaustive concentric/eccentric (CON/ECC) (n = 15) or CON/ECC+ (n = 15) leg extension exercise and in a nonexercising control group (CG) (n = 10). Total SC number (Pax7+), activated (Pax7+/MyoD+), and differentiating (myogenin+) SCs, fiber type distribution, and myofibers expressing neonatal myosin heavy chain (MHCneo) were determined immunohistochemically. Creatine kinase and myoglobin were measured in venous blood. Isokinetic strength tests were repeatedly conducted. Significant increases in creatine kinase and myoglobin (P = 0.001) indicated myofiber damage, whereas maximal strength was not impaired. Only after CON/ECC+, SC content (P = 0.019) and SC related to type II fibers (P = 0.011) were significantly increased. A significant increase in the proportion of activated SCs occurred after CON/ECC+ only (P = 0.003), the increase being significantly (P < 0.05) different from the changes after CON/ECC and in CG. The number of differentiating SC and MHCneo remained unchanged. Eccentric overload during leg extension exercise induced significant SC activation, increases in SC content and in SC number related to type II myofibers. However, there were no signs of increased SC differentiation or formation of new myofibers.

W' Recovery Kinetics after Exhaustion: A Two-Phase Exponential Process Influenced by Aerobic Fitness.

The aims of this study were 1) to model the temporal profile of W' recovery after exhaustion, 2) to estimate the contribution of changing V˙O2 kinetics to this recovery, and 3) to examine associations with aerobic fitness and muscle fiber type (MFT) distribution. Twenty-one men (age = 25 ± 2 yr, V˙O2peak = 54.4 ± 5.3 mL·min-1·kg-1) performed several constant load tests to determine critical power and W' followed by eight trials to quantify W' recovery. Each test consisted of two identical exhaustive work bouts (WB1 and WB2), separated by a variable recovery interval of 30, 60, 120, 180, 240, 300, 600, or 900 s. Gas exchange was measured and muscle biopsies were collected to determine MFT distribution. W' recovery was quantified as observed W' recovery (W'OBS), model-predicted W' recovery (W'BAL), and W' recovery corrected for changing V˙O2 kinetics (W'ADJ). W'OBS and W'ADJ were modeled using mono- and biexponential fitting. Root-mean-square error (RMSE) and Akaike information criterion (∆AICC) were used to evaluate the models' accuracy. The W'BAL model (τ = 524 ± 41 s) was associated with an RMSE of 18.6% in fitting W'OBS and underestimated W' recovery for all durations below 5 min (P < 0.002). Monoexponential modeling of W'OBS resulted in τ = 104 s with RMSE = 6.4%. Biexponential modeling of W'OBS resulted in τ1 = 11 s and τ2 = 256 s with RMSE = 1.7%. W'ADJ was 11% ± 1.5% lower than W'OBS (P < 0.001). ∆AICC scores favored the biexponential model for W'OBS, but not for W'ADJ. V˙O2peak (P = 0.009) but not MFT distribution (P = 0.303) was associated with W'OBS. We showed that W' recovery from exhaustion follows a two-phase exponential time course that is dependent on aerobic fitness. The appearance of a fast initial recovery phase was attributed to an enhanced aerobic energy provision resulting from changes in V˙O2 kinetics.

Histopathological, Ultrastructural, and Immunohistochemical Findings in Radial Longitudinal Deficiency: A Prospective, Observational Study

To report the histopathological, electron microscopic, and immunohistochemical findings of tissue samples obtained from patients with radial longitudinal deficiency (RLD) and investigate the contribution of abnormality in soft tissues as a secondary driver of deformity in RLD. Specimens from radial-sided muscles and tendons were obtained at the time of surgery (either radialization or centralization) from 14 patients with 16 limbs affected with Bayne type 3 and type 4 RLD. The specimens were evaluated using light microscopy, electron microscopy, and immunohistochemical examination. Among the 16 frozen muscle specimens, 6 (37%) showed normal muscle, while 10 (63%) showed the presence of atrophic fibers. The 6 cases with normal muscle showed no abnormality in fiber type distribution. Six patients showed predominance of type 1 muscle fibers. None of the specimens had myofibroblasts; 4 of 16 specimens had mast cells, and 9 of 16 specimens showed the presence of platelet derived growth factor-positive cells. Features of myofibroblasts (the presence of basal lamina, intercellular junctions, or pinocytic vesicles) were not identified in any specimen on electron microscopy. The histopathological, electron microscopic, and immunohistochemical findings, in particular the absence of myofibroblasts, in tissue samples obtained from patients with RLD, do not support the assumption of abnormality in soft tissues as a secondary driver of deformity in RLD. This study provides a preliminary insight into a possible role of soft tissues in the development of the deformity in RLD.

Identifying achilles tendon structure differences by ultrasound tissue characterization in asymptomatic individuals.

Ultrasound Tissue Characterization (UTC) is a modality that can be utilized to characterize tendon tissue structure using ultrasonographic imaging paired with a computer algorithm to distinguish echo-types. Several studies have demonstrated UTCs ability to distinguish Achilles tendon morphology changes, but no study has established normative data of the Achilles tendon in the general population. The aim of this study was to determine UTC echo-type distribution in the Achilles tendon in an asymptomatic population. UTC scans were completed and analyzed on 508 participants without Achilles tendinopathy. Dedicated UTC-algorithms were used to distinguish and calculate echo-type percentages and the fiber type distribution was compared. The overall sample echo-type percentages demonstrated greater levels of Type I and II echo-types, 65.73% and 32.00%, respectively, and lower levels of Type III and IV echo-types, 1.74% and 0.57%, respectively. In addition, females had lower levels of Echo-type I compared to men and greater levels of echo-type II (p<0.001). We also found that African-Americans had significantly greater amounts of echo-type I and lesser amounts of echo-type II when compared to Caucasians (p<0.05). The results of this study create a normative data set for future UTC studies to utilize as a baseline for the evaluation of Achilles tendons. In addition, it demonstrated tendon type differences between sexes and races that need to be accounted for in future studies.

Effects of Encapsulated Methionine on Skeletal Muscle Growth and Development and Subsequent Feedlot Performance and Carcass Characteristics in Beef Steers.

Simple SummaryResearch investigating the effects of amino acids in growing and finishing beef cattle is not a new topic. Many studies suggest that in cattle fed a concentrate-based diet, lysine is the most limiting amino acid followed by methionine. When considering supplementing amino acids to growing-finishing beef cattle, the amino acids must be protected from ruminal microbial consumption for the beef animal to be able to absorb the amino acids in the small intestine. The regulation of skeletal muscle growth is a multifaceted, complex process controlled through many signaling cascades. One major process involved in muscle growth is the mammalian target of the rapamycin (mTOR) signaling pathway. The objectives of these studies were to investigate the role of encapsulated methionine on feedlot growth performance and carcass characteristics and to elucidate the role of methionine supplementation on the mTOR signaling pathway and skeletal muscle development in feedlot steers during the finishing phase.Two studies were conducted to evaluate the effect of encapsulated methionine on live performance, carcass characteristics, and skeletal muscle development in feedlot steers. In Experiment 1, 128 crossbred steers (body weight [BW] = 341 ± 36.7 kg) were used in a randomized complete block design and supplemented with 0, 4, 8, or 12 g/(head day [d]) of ruminally protected methionine (0MET, 4MET, 8MET, and 12MET, respectively) for 111 d or 139 d. In Exp. 2, 20 steers (BW = 457 ± 58 kg) were stratified by BW and randomly assigned to either the 0MET or 8MET treatment; longissimus muscle (LM) biopsies were collected on d 0, 14, 28, 42, and 56, and analyzed for mRNA and protein expression. Additionally, immunohistochemical analysis was performed to measure fiber type area and distribution as well as the density of muscle nuclei and satellite cells (Myf5, Pax7, and Myf5/Pax7). In Experiment 1, no significant differences were observed for live performance (p ≥ 0.09). There was, however, a linear relationship between LM area and methionine supplementation (p = 0.04), with a 9% increase in the area when steers were supplemented with 12MET compared to 0MET. In Exp. 2, There were no treatment × day interactions (p ≥ 0.10) for expression of mRNA or protein abundance. Although mRNA expression and protein abundance of all genes were influenced by day (p ≤ 0.04), methionine supplementation did not have a significant effect (p ≥ 0.08). There was a significant treatment × day interaction for distribution of MHC-I fibers (p = 0.03), where 8MET supplemented cattle had a greater proportion of MHC-I fibers after 56 d of supplementation than did 0MET steers. Cross-sectional area was increased over time regardless of fiber type (p < 0.01) but was unaffected by treatment (p ≥ 0.36). While nuclei density was not impacted by treatment (p = 0.55), the density of myonuclei increased nearly 55% in 8MET supplemented cattle (p = 0.05). The density of Myf5 positive satellite cells tended to decrease with methionine supplementation (p = 0.10), while the density of Pax7 expressing cells tended to increase (p = 0.09). These results indicate that encapsulated methionine supplementation may influence markers of skeletal muscle growth, and potential improvements in the LM area may exist.