Fiber Cross-sectional Area Research Articles

Resistance training diminishes mitochondrial adaptations to subsequent endurance training in healthy untrained men.

We investigated the effects of performing a period of resistance training (RT) on the performance and molecular adaptations to a subsequent period of endurance training (ET). Twenty-five young adults were divided into an RT+ET group (n=13), which underwent 7weeks of RT followed by 7weeks of ET, and an ET-only group (n=12), which performed 7weeks of ET. Body composition, endurance performance and muscle biopsies were collected before RT (T1, baseline for RT+ET), before ET (T2, after RT for RT+ET and baseline for ET) and after ET (T3). Immunohistochemistry was performed to determine fibre cross-sectional area (fCSA), myonuclear content, myonuclear domain size, satellite cell number and mitochondrial content. Western blots were used to quantify markers of mitochondrial remodelling. Citrate synthase activity and markers of ribosome content were also investigated. RT improved body composition and strength, increased vastus lateralis thickness, mixed and type II fCSA, myonuclear number, markers of ribosome content, and satellite cell content (P<0.050). In response to ET, both groups similarly decreased body fat percentage (P<0.0001) and improved endurance performance (e.g. , and speed at which the onset of blood lactate accumulation occurred, P<0.0001). Levels of mitochondrial complexes I-IV in the ET-only group increased 32-66%, while those in the RT+ET group increased 1-11% (time, P<0.050). Additionally, mixed fibre relative mitochondrial content increased 15% in the ET-only group but decreased 13% in the RT+ET group (interaction, P=0.043). In conclusion, RT performed prior to ET had no additional benefits to ET adaptations. Moreover, prior RT seemed to impair mitochondrial adaptations to ET. KEY POINTS: Resistance training is largely underappreciated as a method to improve endurance performance, despite reports showing it may improve mitochondrial function. Although several concurrent training studies are available, in this study we investigated the effects of performing a period of resistance training on the performance and molecular adaptations to subsequent endurance training. Prior resistance training did not improve endurance performance and impaired most mitochondrial adaptations to subsequent endurance training, but this effect may have been a result of detraining from resistance training.

Asynchrony Injures Lung and Diaphragm in Acute Respiratory Distress Syndrome.

Patient-ventilator asynchrony is often observed during mechanical ventilation and is associated with higher mortality. We hypothesized that patient-ventilator asynchrony causes lung and diaphragm injury and dysfunction. Prospective randomized animal study. University research laboratory. Eighteen New Zealand White rabbits. Acute respiratory distress syndrome (ARDS) model was established by depleting surfactants. Each group (assist control, breath stacking, and reverse triggering) was simulated by phrenic nerve stimulation. The effects of each group on lung function, lung injury (wet-to-dry lung weight ratio, total protein, and interleukin-6 in bronchoalveolar lavage), diaphragm function (diaphragm force generation curve), and diaphragm injury (cross-sectional area of diaphragm muscle fibers, histology) were measured. Diaphragm RNA sequencing was performed using breath stacking and assist control (n = 2 each). Inspiratory effort generated by phrenic nerve stimulation was small and similar among groups (esophageal pressure swing ≈ -2.5 cm H2O). Breath stacking resulted in the largest tidal volume (>10 mL/kg) and highest inspiratory transpulmonary pressure, leading to worse oxygenation, worse lung compliance, and lung injury. Reverse triggering did not cause lung injury. No asynchrony events were observed in assist control, whereas eccentric contractions occurred in breath stacking and reverse triggering, but more frequently in breath stacking. Breath stacking and reverse triggering significantly reduced diaphragm force generation. Diaphragmatic histology revealed that the area fraction of abnormal muscle was ×2.5 higher in breath stacking (vs assist control) and ×2.1 higher in reverse triggering (vs assist control). Diaphragm RNA sequencing analysis revealed that genes associated with muscle differentiation and contraction were suppressed, whereas cytokine- and chemokine-mediated proinflammatory responses were activated in breath stacking versus assist control. Breath stacking caused lung and diaphragm injury, whereas reverse triggering caused diaphragm injury. Thus, careful monitoring and management of patient-ventilator asynchrony may be important to minimize lung and diaphragm injury from spontaneous breathing in ARDS.

Exercise mitigates Dapagliflozin-induced skeletal muscle atrophy in STZ-induced diabetic rats

BackgroundSodium-glucose cotransporter 2 inhibitors (SGLT2i) are commonly used in the management of type 2 diabetes mellitus (T2DM) and have been found to worsen the reduction of skeletal muscle mass in individuals with T2DM. This study aims to examine the potential of exercise in mitigating the skeletal muscle atrophy induced by SGLT2i treatment.MethodsA rat model of T2DM (40 male Sprague-Dawley rats; T2DM induced by a combination of high-fat diet and streptozotocin) was used to examine the effects of six-week treatment with Dapagliflozin (DAPA, SGLT2i) in combination with either aerobic exercise (AE) or resistance training (RT) on skeletal muscle. T2DM-eligible rats were randomized into the T2DM control group (CON, n = 6), DAPA treatment group (DAPA, n = 6), DAPA combined with aerobic exercise intervention group (DAPA + AE, n = 6), and DAPA combined with resistance training intervention group (DAPA + RT, n = 6). To assess the morphological changes in skeletal muscle, myosin ATPase and HE staining were performed. mRNA expression levels of Atrogin-1, MuRF1, and Myostatin were determined using quantitative PCR. Furthermore, protein expression levels of AKT, p70S6K, mTOR, FoXO1/3A, NF-κB, and MuRF1 were examined through western blotting.ResultsBoth the administration of DAPA alone and the combined exercise intervention with DAPA resulted in significant reductions in blood glucose levels and body weight in rats. However, DAPA alone administration led to a decrease in skeletal muscle mass, whereas RT significantly increased skeletal muscle mass and muscle fiber cross-sectional area. The DAPA + RT group exhibited notable increases in both total protein levels and phosphorylation levels of AKT and p70S6K in skeletal muscle. Moreover, the DAPA, DAPA + AE, and DAPA + RT groups demonstrated downregulation of protein expression (FoXO1/3A) and mRNA levels (Atrogin-1, MuRF1, and Myostatin) associated with muscle atrophy.ConclusionsOur findings provide support for the notion that dapagliflozin may induce skeletal muscle atrophy through mechanisms unrelated to protein metabolism impairment in skeletal muscle, as it does not hinder protein metabolic pathways while reduces muscle atrophy-related genes. Additionally, our observations reveal that RT proves more effective than AE in enhancing skeletal muscle mass and muscle fiber cross-sectional area in rats with T2DM by stimulating protein anabolism within the skeletal muscle.

Effects of Acupotomy on Immobilization-Induced Gastrocnemius Contracture and Fibrosis in Rats via Wnt/β-Catenin Signaling.

To determine whether acupotomy ameliorates immobilization-induced muscle contracture and fibrosis via Wnt/β-catenin signaling pathway. Thirty Wistar rats were randomly divided into 5 groups (n=6) by a random number table, including control, immobilization, passive stretching, acupotomy, and acupotomy 3 weeks (3-w) groups. The rat model of gastrocnemius contracture was established by immobilizing the right hind limb in plantar flexion for 4 weeks. Rats in the passive stretching group received passive stretching at gastrocnemius, a daily series of 10 repetitions for 30 s each at 30-s intervals for 10 consecutive days. Rats in the acupotomy and acupotomy 3-w groups received acupotomy once and combined with passive stretching at gastrocnemius a daily series of 10 repetitions for 30 s each at 30-s intervals for 10 consecutive days. Additionally, rats in the acupotomy 3-w group were allowed to walk freely for 3 weeks after 10-day therapy. After treatment, range of motion (ROM), gait analysis [i.e., paw area, stance/swing and maximum ratio of paw area to paw area duration (Max dA/dT)], gastrocnemius wet weight and the ratio of muscle wet weight to body weight (MWW/BW) were tested. Gastrocnemius morphometric and muscle fiber cross-sectional area (CSA) were assessed by hematoxylin-eosin staining. Fibrosis-related mRNA expressions (i.e., Wnt 1, β-catenin, axin-2, α-smooth muscle actin, fibronectin, and types I and III collagen) were measured using real-time quantitative polymerase chain reactions. Wnt 1, β-catenin and fibronectin concentrations were measured by enzyme-linked immunosorbent assay. Types I and III collagen in the perimysium and endomysium were analyzed using immunofluorescence. Compared with the control group, ROM, gait function, muscle weight, MWW/BW and CSA were significantly decreased in the immobilization group (all P<0.01), while protein levels of types I and III collagen, Wnt 1, β-catenin, fibronectin and mRNA levels of fibrosis-related genes were obviously increased (all P<0.01). Treatment with passive stretching or acupotomy restored ROM and gait function and increased muscle wet weight, MWW/BW and CSA (all P<0.05), while protein expression levels of Wnt 1, β-catenin, fibronectin, types I and III collagen and mRNA levels of fibrosis-related genes were remarkably declined compared with the immobilization group (all P<0.05). Compared with passive stretching group, ROM, gait function, MWW was remarkably restored (all P<0.05), and mRNA levels of fibrosis-related genes as well as protein expression levels of Wnt 1, β-catenin, fibronectin, types I and III collagen in the acupotomy group were obviously decreased (all P<0.05). Compared with the acupotomy group, ROM, paw area, Max dA/dT, and MWW were restored (all P<0.05), and mRNA levels of fibrosis-related genes along with protein levels of Wnt 1, β-catenin, fibronectin, types I and III collagen in the acupotomy 3-w group were decreased (P<0.05). Improvements in motor function, muscle contractures, and muscle fibrosis induced by acupotomy correlates with the inhibition of Wnt/β-catenin signaling pathway.

Sex differences in skeletal muscle fiber types: A meta-analysis.

Biopsies have been acquired from living men and women to determine proportions of Type I (slow-twitch) and II (fast-twitch) skeletal muscle fibers since the 1970s. Sex differences have been assumed but the literature has not been submitted to meta-analysis. Here, the aim was to generate effect sizes of sex differences in muscle fiber cross-sectional areas, distribution percentages, and area percentages. Data from 2875 men and 2452 women, who participated in 110 studies, were analyzed. Myofibrillar adenosine triphosphatase histochemistry was used in 71.8% of studies to classify fibers as Type I, II, IIA, and/or IIX; immunohistochemistry, immunofluorescence, or sodium dodecyl sulfate-polyacrylamide gel electrophoresis were used in 35.4% of studies to similarly classify myosin heavy chain (MHC) isoform content. Most studies involved biopsies from vastus lateralis (79.1%) in healthy individuals (92.7%) between 18 and 59 years old (80.9%). Men exhibited greater cross-sectional areas for all fiber types (g = 0.40-1.68); greater distribution percentages for Type II, MHC II, IIA, IIX fibers (g = 0.26-0.34); greater area percentages for Type II, IIA, MHC IIA, IIX fibers (g = 0.39-0.93); greater Type II/I and Type IIA/I fiber area ratios (g = 0.63, 0.94). Women exhibited greater Type I and MHC I distribution percentages (g = -0.13, -0.44); greater Type I and MHC I area percentages (g = -0.53, -0.69); greater Type I/II fiber area ratios (g = -1.24). These data, which represent the largest repository of comparative muscle fiber type data from living men and women, can inform discussions about biological sex and its impact on pathologies and sports performance (e.g., explaining sex differences in muscle strength and muscle endurance).

Morphological and functional changes in the skeletal muscles of the hind limbs in rats under enforced anaerobic physical exertion and allogeneic biomaterial application

Exhausting physical activity leads to sarcomere overstrain, destruction of the cell membrane, hydrolysis of structural proteins, thus, resulting in irreversible damage to muscle fibers. Allogeneic biomaterial (AB) is applied to regenerate various tissues and organs. The aim of the study was to identify morphofunctional features of the skeletal muscle tissue after physical exertion and under AB application. Material and methods. This experimental study involved male Wistar rats. Anaerobic physical exertion was simulated using the Porsolt test with a load equal 10 % of the body weight for 30 days. After training, animals of the main group (n = 10) were injected AB suspension: 4 ml of a 0.2 % solution into the muscles of the fore and hind limbs totally. Animals of the control group (n = 10) received physiological saline into similar zones. Tolerant load was investigated in 5 and 21 days after injection. Then the animals were withdrawn from the experiment, and muscles of the hind limbs were studied histologically, the total number, the average cross-sectional area of muscle fibers, and the number of necrotic fibers were measured. Results. In 5 and 21 days animals from the control group manifested dystrophic changes in muscle fibers: type III, IV contractures, microcirculation disorders, mosaic necrosis of muscle fibers, inflammatory cell infiltration, and a decreased tolerant load. In 21 days fibrosis was detected. The AB introduction provided rhabdomyogenesis as soon as in 5 days. Inflammatory cell infiltration decreased, the polygonality of muscle fiber profiles was restored, and edematous phenomena were leveled. There was hyperplasia of muscle fibers, a decreased number of necrotic muscle fibers, inhibited fibrosis, and an increased tolerant load. AB further biodegraded. Conclusion. AB contributed to the reduced manifestations of dystrophic changes in muscle fibers, strengthened actoprotective mechanism, and restored physical activity in the early stages.

Muscle fiber characteristics and expression level of Troponin T3, Toll-like receptor 2, and Toll-like receptor 4 genes in chicken meat with white striping.

The poultry industry faces an emerging muscular defect in chicken meat called white striping (WS). The biological processes associated with WS myopathy are immune system activation, angiogenesis, hypoxia, cell death, and striated muscle contraction. We examined the Troponin T3 (TNNT3), Toll-like receptor 2 (TLR2), and Toll-like receptor 4 (TLR4) genes based on their functions related to muscle contraction and the innate immune system. This study aimed to determine the muscle fiber characteristics (MFCs) and expression level of TNNT3, TLR2, and TLR4 genes in white striping chicken meat (WSCM). A total of 428 breast samples were randomly collected from a commercial poultry processing plant. The samples were classified into four levels: 0 (normal), 1 (moderate WS), 2 (severe WS), and 3 (extreme WS). Five samples per group were selected to evaluate MFCs, including total number of muscle fibers, muscle fiber diameter, cross-sectional area, endomysium thickness, and perimysium thickness. Five samples per group were selected for ribonucleic acid (RNA) isolation to evaluate the messenger RNA (mRNA) expression levels of TNNT3, TLR2, and TLR4 genes related to WS. Statistical analysis revealed that the total number of fibers, endomysium thickness, and perimysium thickness significantly differed between groups (p < 0.05). Muscle fiber diameter and cross-sectional area did not significantly differ (p > 0.05). The expression of the TNNT3 gene did not significantly differ among groups (p > 0.05). Toll-like receptor 2 and TLR4 mRNA expression significantly differed among groups (p < 0.05). These detailed MFCs will provide baseline information to observe WS in chicken meat. Toll-like receptor 2 and TLR4 genes may play a role in the occurrence of WS in chicken meat through non-specific immune reactions.

Poster 101: Evaluation of Novel Treatment Agents on Rotator Cuff Tendon and Muscle Pathology in a Murine Subacromial Impingement Model

Poster 101: Evaluation of Novel Treatment Agents on Rotator Cuff Tendon and Muscle Pathology in a Murine Subacromial Impingement Model

An electrical stimulation intervention protocol to prevent disuse atrophy and muscle strength decline: an experimental study in rat

BackgroundSkeletal muscle is negatively impacted by conditions such as spaceflight or prolonged bed rest, resulting in a dramatic decline in muscle mass, maximum contractile force, and muscular endurance. Electrical stimulation (ES) is an essential tool in neurophysiotherapy and an effective means of preventing skeletal muscle atrophy and dysfunction. Historically, ES treatment protocols have used either low or high frequency electrical stimulation (LFES/HFES). However, our study tests the use of a combination of different frequencies in a single electrical stimulation intervention in order to determine a more effective protocol for improving both skeletal muscle strength and endurance.MethodsAn adult male SD rat model of muscle atrophy was established through 4 weeks of tail suspension (TS). To investigate the effects of different frequency combinations, the experimental animals were treated with low (20 Hz) or high (100 Hz) frequency before TS for 6 weeks, and during TS for 4weeks. The maximum contraction force and fatigue resistance of skeletal muscle were then assessed before the animals were sacrificed. The muscle mass, fiber cross-sectional area (CSA), fiber type and related protein expression were examined and analyzed to gain insights into the mechanisms by which the ES intervention protocol used in this study regulates muscle strength and endurance.ResultsAfter 4 weeks of unloading, the soleus muscle mass and fiber CSA decreased by 39% and 58% respectively, while the number of glycolytic muscle fibers increased by 21%. The gastrocnemius muscle fibers showed a 51% decrease in CSA, with a 44% decrease in single contractility and a 39% decrease in fatigue resistance. The number of glycolytic muscle fibers in the gastrocnemius also increased by 29%. However, the application of HFES either prior to or during unloading showed an improvement in muscle mass, fiber CSA, and oxidative muscle fibers. In the pre-unloading group, the soleus muscle mass increased by 62%, while the number of oxidative muscle fibers increased by 18%. In the during unloading group, the soleus muscle mass increased by 29% and the number of oxidative muscle fibers increased by 15%. In the gastrocnemius, the pre-unloading group showed a 38% increase in single contractile force and a 19% increase in fatigue resistance, while in the during unloading group, a 21% increase in single contractile force and a 29% increase in fatigue resistance was observed, along with a 37% and 26% increase in the number of oxidative muscle fibers, respectively. The combination of HFES before unloading and LFES during unloading resulted in a significant elevation of the soleus mass by 49% and CSA by 90%, with a 40% increase in the number of oxidative muscle fibers in the gastrocnemius. This combination also resulted in a 66% increase in single contractility and a 38% increase in fatigue resistance.ConclusionOur results indicated that using HFES before unloading can reduce the harmful effects of muscle unloading on the soleus and gastrocnemius muscles. Furthermore, we found that combining HFES before unloading with LFES during unloading was more effective in preventing muscle atrophy in the soleus and preserving the contractile function of the gastrocnemius muscle.

Fatty infiltration of the multifidus muscle independently increases osteoporotic vertebral compression fracture risk

BackgroundVertebral compression fractures decrease daily life activities and increase economic and social burdens. Aging decreases bone mineral density (BMD), which increases the incidence of osteoporotic vertebral compression fractures (OVCFs). However, factors other than BMD can affect OVCFs. Sarcopenia has been a noticeable factor in the aging health problem. Sarcopenia, which involves a decrease in the quality of the back muscles, influences OVCFs. Therefore, this study aimed to evaluate the influence of the quality of the multifidus muscle on OVCFs.MethodsWe retrospectively studied patients aged 60 years and older who underwent concomitant lumbar MRI and BMD in the university hospital database, with no history of structurally affecting the lumbar spine. We first divided the recruited people into a control group and a fracture group according to the presence or absence of OVCFs, and further divided the fracture group into an osteoporosis BMD group and an osteopenia BMD group based on the BMD T-score of -2.5. Using images of lumbar spine MRI, the cross-sectional area and percentage of muscle fiber (PMF) of the multifidus muscle were obtained.ResultsWe included 120 patients who had visited the university hospital, with 45 participants in the control group and 75 in the fracture group (osteopenia BMD: 41, osteoporosis BMD: 34). Age, BMD, and the psoas index significantly differed between the control and fracture groups. The mean cross-sectional area (CSA) of multifidus muscles measured at L4-5 and L5-S1, respectively, did not differ among the control, P-BMD, and O-BMD groups. On the other hand, the PMF measured at L4-5 and L5-S1 showed a significant difference among the three groups, and the value of the fracture group was lower than that of the control group. Logistic regression analysis showed that the PMF value, not the CSA, of the multifidus muscle at L4-5 and L5-S1 affected the risk of OVCFs, with and without adjusting for other significant factors.ConclusionsHigh percentage of fatty infiltration of the multifidus muscle increases the spinal fracture risk. Therefore, preserving the quality of the spinal muscle and bone density is essential for preventing OVCFs.

The effects of exercise training on body composition in postmenopausal women: a systematic review and meta-analysis.

We conducted a systematic review and meta-analysis to investigate the effect of exercise training on body composition outcomes in postmenopausal women. PubMed, Web of Science, CINAHL, and Medline were searched to identify the randomized controlled trials which evaluated effect of exercise training versus control in postmenopausal women. Standardized mean differences (SMD), weighted mean differences (WMD) and 95% confidence intervals (95% CIs) were calculated using random effects model. One hundred and one studies involving 5,697 postmenopausal women were included in the meta-analysis. Results indicated that exercise training effectively increased muscle mass/ volume, muscle and fiber cross-sectional area and fat-free mass, and decreased fat mass, body fat percentage, waist circumference and visceral fat. Furthermore, subgroup analyses results revealed that aerobic and combined training had greater beneficial effects on fat mass outcomes, whereas resistance and combined training had greater beneficial effects on muscle mass outcomes. Overall, our results revealed that exercise training is effective for improving body composition in postmenopausal women. To be specific, aerobic training is effective on fat loss, whereas resistance training is effective on muscle gain. However, combination of aerobic and resistance trainings may be considered a viable strategy to improve body composition in postmenopausal women. https://www.crd.york.ac.uk/prospero/, identifier CRD42021283425.

Rice Germ Attenuates Chronic Unpredictable Mild Stress-Induced Muscle Atrophy.

Chronic stress leads to hypothalamic-pituitary-adrenal axis dysfunction, increasing cortisol levels. Glucocorticoids (GCs) promote muscle degradation and inhibit muscle synthesis, eventually causing muscle atrophy. In this study, we aimed to evaluate whether rice germ supplemented with 30% γ-aminobutyric acid (RG) attenuates muscle atrophy in an animal model of chronic unpredictable mild stress (CUMS). We observed that CUMS raised the adrenal gland weight and serum adrenocorticotropic hormone (ACTH) and cortisol levels, and these effects were reversed by RG. CUMS also enhanced the expression of the GC receptor (GR) and GC-GR binding in the gastrocnemius muscle, which were attenuated by RG. The expression levels of muscle degradation-related signaling pathways, such as the Klf15, Redd-1, FoxO3a, Atrogin-1, and MuRF1 pathways, were enhanced by CUMS and attenuated by RG. Muscle synthesis-related signaling pathways, such as the IGF-1/AKT/mTOR/s6k/4E-BP1 pathway, were reduced by CUMS and enhanced by RG. Moreover, CUMS raised oxidative stress by enhancing the levels of iNOS and acetylated p53, which are involved in cell cycle arrest, whereas RG attenuated both iNOS and acetylated p53 levels. Cell proliferation in the gastrocnemius muscle was reduced by CUMS and enhanced by RG. The muscle weight, muscle fiber cross-sectional area, and grip strength were reduced by CUMS and enhanced by RG. Therefore, RG attenuated ACTH levels and cortisol-related muscle atrophy in CUMS animals.

Myosin Heavy-Chain Messenger Ribonucleic Acid (mRNA) Expression and Fibre Cross-Sectional Area in Masseter, Digastric, Gastrocnemius and Soleus Muscles of Young and Adult Rats.

Different demands on the muscles of mastication may influence their functional profile (size and distribution of muscle fibre types), which may change during growth and maturation, potentially influencing craniofacial growth. The aim of this study was to evaluate mRNA expression and cross-sectional area of masticatory muscle fibres compared with limb muscles in young and adult rats. Twenty-four rats were sacrificed at two different ages, namely 12 at 4 weeks (young) and 12 at 26 weeks (adult). The masseter, digastric, gastrocnemius and soleus muscles were dissected. Gene expression of myosin heavy-chain isoforms Myh7 (MyHC-I), Myh2 (MyHC-IIa), Myh4 (MyHC-IIb) and Myh1 (MyHC-IIx) in the muscles was measured using qRT-PCR RNA analysis, and immunofluorescence staining was performed to measure the cross-sectional area of different muscle fibre types. Different muscle types and ages were compared. Significant differences were found in the functional profile between masticatory and limb muscles. For the masticatory muscles, there was an increase in Myh4 expression with age, and this change was more intense for the masseter muscles, which also presented an increase in Myh1 expression, similarly to limb muscles. The fibre cross-sectional area of the masticatory muscles was generally smaller in young rats; however, this difference was less pronounced than in limb muscles.

Supplemental Clostridium butyricum modulates skeletal muscle development and meat quality by shaping the gut microbiota of lambs

This study evaluated the contributions of Clostridium butyricum on skeletal muscle development, gastrointestinal flora and meat quality of lambs. Eighteen Dorper (♂) × Small Tailed Han sheep (♀) crossed ewe lambs of similar weight (27.43 ± 1.94 kg; age, 88 ± 5 days) were divided into two dietary treatments. The control group was fed the basal diet (C group), and the probiotic group was supplemented with C. butyricum on the basis of the C group (2.5 × 108 cfu/g, 5 g/day/lamb; P group) for 90 d. The results showed that dietary C. butyricum elevated growth performance, muscle mass, muscle fiber diameter and cross-sectional area, and decreased the shear force value of meat (P < 0.05). Moreover, C. butyricum supplementation accelerated protein synthesis by regulating the gene expression of IGF-1/Akt/mTOR pathway. We identified 54 differentially expressed proteins that regulated skeletal muscle development through different mechanisms by quantitative proteomics. These proteins were associated with ubiquitin-protease, apoptosis, muscle structure, energy metabolism, heat shock, and oxidative stress. The metagenomics sequencing results showed that Petrimonas at the genus level and Prevotella brevis at the species level in the rumen, while Lachnoclostridium, Alloprevotella and Prevotella at the genus level in the feces, were significantly enriched in the P group. Also, butyric acid and valeric acid levels were elevated in both rumen and feces of the P group. Overall, our results support the idea that C. butyricum could change gastrointestinal flora, and affect skeletal muscle development and meat quality of lambs by modulating gut-muscle axis.

A novel mitochondrial complex I ROS inhibitor partially improves muscle regeneration in adult but not old mice

It is unclear whether mitochondrial dysfunction and redox stress contribute to impaired age-related muscle regenerative capacity. Here we characterized a novel compound, BI4500, that inhibits the release of reactive oxygen species (ROS) from the quinone site in mitochondrial complex I (site IQ). We tested the hypothesis that ROS release from site IQ contributes to impaired regenerative capacity in aging muscle. Electron transfer system site-specific ROS production was measured in adult and aged mouse isolated muscle mitochondria and permeabilized gastrocnemius fibers. BI4500 inhibited ROS production from site IQ in a concentration-dependent manner (IC50 = ∼985 nM) by inhibiting ROS release without impairing complex I-linked respiration. In vivo BI4500 treatment decreased ROS production from site IQ. Muscle injury and sham injury were induced using barium chloride or vehicle injection to the tibialis anterior (TA) muscle in adult and aged male mice. On the same day as injury, mice began a daily gavage of 30 mg/kg BI4500 (BI) or placebo (PLA). Muscle regeneration (H&E, Sirius Red, Pax7) was measured at 5 and 35 days after injury. Muscle injury increased centrally nucleated fibers (CNFs) and fibrosis with no treatment or age effect. There was a significant age by treatment interaction for CNFs at 5- and 35-days post injury with significantly more CNFs in BI adults compared to PLA adults. Muscle fiber cross-sectional area (CSA) recovered significantly more in adult BI mice (−89 ± 365 μm2) compared to old PLA (−599 ± 153 μm2) and old BI (−535 ± 222 μm2, mean ± SD). In situ TA force recovery was measured 35 days after injury and was not significantly different by age or treatment. Inhibition of site IQ ROS partially improves muscle regeneration in adult but not old muscle demonstrating a role for CI ROS in the response to muscle injury. Site IQ ROS does not contribute to impaired regenerative capacity in aging.

Meta-Regression Analysis of Relationships between Fibre Type and Meat Quality in Beef and Pork-Focus on Pork.

This meta-regression analysis was conducted to identify the relationship between fibretype cross-sectional area (CSA) and frequency (%) and meat quality traits, especially tenderness (sensory and Warner-Bratzler Shear Force, WBSF). Literature searches were conducted using specific keywords which resulted in 32 peer-reviewed manuscripts that contained averages and correlation coefficients for fibre type (frequency and CSA) and quality traits of longissimus muscle for beef and pork (7 and 25 studies respectively). Correlations were analysed in meta-regression using R-Studio and linear regression was also conducted. For the combined beef and pork analysis, only pH, WBSF, and drip loss were associated with fibre type frequency and CSA (p < 0.05 for all). Limiting the analysis to pork, the key results were frequency of type I fibres were associated with decreased drip loss, increased cook loss, decreased lightness (L*) and increased sensory tenderness whereas frequency of type IIb fibres were associated with increased drip loss (p < 0.05 for all). In addition, the CSA of type I and IIb fibres was associated with colour traits lightness and redness (p < 0.05 for all). Future research should focus on fibre type across breeds and muscles to further understand the impacts of fibre type frequency and CSA on quality.

Physical exercise attenuates age-related muscle atrophy and exhibits anti-ageing effects via the adiponectin receptor 1 signalling.

Although the adiponectin signalling exerts exercise-mimicking effects, whether this pathway contributes to the anti-ageing benefits of physical exercise has not been established yet. Swim exercise training and wheel running were used to measure lifespan in the nematode Caenorhabditis elegans and skeletal muscle quality in mice, respectively. Muscle weight, muscle fibre cross-sectional area (CSA) and myonuclei number were used to evaluate muscle mass. RNA sequencing (RNA-Seq) analysis of skeletal muscle in exercised mice was used to study the underlying mechanisms. Western blot and immunofluorescence were performed to explore autophagy- and senescence-related markers. The C.elegans adiponectin receptor PAQR-1/AdipoR1, but not PAQR-2/AdipoR2, was activated (3.55-fold and 3.48-fold increases in p-AMPK on Days 1 and 6, respectively, P<0.001), which was involved in lifespan extension in exercised worms. Exercise training increased skeletal muscle mass index (1.29-fold, P<0.01), muscle weight (1.75-fold, P<0.001), myonuclei number (1.33-fold, P<0.05), muscle fibre CSA (1.39-fold, P<0.05) and capillary abundance (2.19-fold, P<0.001 for capillary density; 1.58-fold, P<0.01 for capillary number) in aged mice. Physical exercise reduced protein (2.94-fold, P<0.001) and mRNA levels (1.70-fold, P<0.001) of p16INK4a , a marker for cellular senescence, in skeletal muscle of aged mice. These beneficial effects of exercise on skeletal muscle of mice were dependent on AdipoR1. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis for differentially expressed genes in skeletal muscle between exercised mice with and without AdipoR1 knockdown by RNA-Seq analysis revealed that several KEGG pathways, such as 'AMPK signalling pathway' (P<0.001), 'FOXO signalling pathway' (P<0.001) and 'autophagy' (P<0.001) were overrepresented. Knockdown of FoxO3a inhibited exercise-mediated beneficial effects on skeletal muscle quality of mice by inhibiting autophagy/mitophagy (3.81-fold reduction in LC3-II protein, P<0.001; 1.53-fold reduction in BNIP3 protein, P<0.05). Knockdown of daf-16, the FoxO homologue in C.elegans, reduced autophagy (2.77-fold and 2.06-fold reduction in GFP::LGG-1 puncta in seam cells and the intestine, respectively, P<0.05) and blocked lifespan extension by exercise in worms. Our findings provide insights into how the AdipoR1 pathway has an impact on the anti-ageing benefits of exercise and implicate that activation of the AdipoR1 signalling may represent a potential therapeutic strategy for reducing age-related loss of skeletal muscle.

Experimental tensile tests on carbon fibre cords with bond-type anchorages

Despite the potential interest for civil engineering structural applications, few studies have explored the feasibility of employing carbon fibre cords as prestressed elements in strengthening systems. This research presents a large experimental campaign to investigate the tensile behaviour of straight carbon fibre cords connected to a bond-type anchorage. Specifically, 78 tensile tests have been performed varying several parameters: anchorage geometry, resin type, cord cross sectional area, and fibre free-length and treatment (unimpregnated or impregnated with resin). The results shed light on their role on the structural response, and highlight the existence of size effects regarding fibre free-length and cross sectional area of the cord. These phenomena are magnified in unimpregnated specimens, and, de facto, may prevent their use in full-scale post-tensioned applications.

Revisiting specific force loss in human permeabilised single skeletal muscle fibres obtained from older individuals.

Specific force (SF) has been shown to be reduced in some but not all studies of human ageing using chemically skinned single muscle fibres. This may be due in part to the health status/physical activity levels of different older cohorts, but also from methodological differences in studying skinned fibres. The aim of the present study was to compare SF in fibres from older hip fracture patients (HFP), healthy master cyclists (MC) and healthy non-trained young adults (YA) using two different activating solutions. Quadriceps muscle samples and 316 fibres were obtained from HFPs (74.6±4 years, n=5), MCs (74.8±1, n=5) and YA (25.5±2, n=6). Fibres were activated (pCa 4.5, 15oC) in solutions containing either 60 mM TES or 20 mM imidazole. SF was determined by normalising force to fibre CSA assuming either an elliptical or circular shape and to fibre myosin heavy chain content. Activation in TES resulted in significantly higher MHC-I SF in all groups and YA MHC-IIA fibres, irrespective of normalisation method. Whilst there were no differences in SF between the participant groups, the ratio of SF between the TES and imidazole solutions was lower in HFPs compared to YAs (MHC-I p<0.05; MHC-IIA p=0.055). Activating solution composition, as opposed to donor characteristics, had a more notable effect on single fibre SF. However, this two-solution approach revealed an age-related difference in sensitivity in HFPs which was not shown in MCs. This suggests further novel approaches may be required to probe age/activity-related differences in muscle contractile quality.

Association of variants and expression levels of MYOD1 gene with carcass and muscle characteristic traits in domestic pigeons

This study was to investigate the correlations of myogenic differentiation 1 (MYOD1) gene polymorphisms with carcass traits and its expression with breast muscle development in pigeons. Four SNPs were found in the pigeon MYOD1 gene. Correlation analysis showed that individuals with AA genotype at both SNPs g.2967A > G (p < .01) and g.3044G > A (p < .05) have significantly higher live weight (LW), carcass weight (CW), semi-eviscerated weight (SEW), eviscerated weight (EW) and breast muscle weight (BMW). Moreover, the two SNPs also had the same significant effects on MYOD1 mRNA expression levels in breast muscle of pigeons, ie, the AA genotype showed higher MYOD1 mRNA expression levels. The diameter and cross-section area of muscle fibers continuously increased from 0w to 4w (p < .05), accompanied with the increasing expression of MYOD1 gene, while the density decreased (p < .05) dramatically from 0w to 1w and continuously fell over in the next few weeks (p > .05). What’s more, the expression level of MYOD1 gene was positively correlated with a diameter (r = 0.937, p < .05) and cross-sectional area (r = 0.956, p < .01) of myofiber, and negatively correlated with density (r = −0.769, p < .01). The results showed that individuals with AA genotype at both SNPs g.2967A > G and g.3044G > A have showed higher carcass traits (LW, CW, SEW, EW, and BMW) and higher MYOD1 mRNA expression level in breast muscle than AB and BB genotypes. Moreover, the expression level of MYOD1 gene was closely correlated with muscle characteristic traits, indicating variants of MYOD1 gene was closely related to muscle development and could be a potential candidate gene in marker-assisted selection of pigeons.