Changes In Muscle Morphology Research Articles

Macrophage depletion impairs skeletal muscle regeneration: The roles of regulatory factors for muscle regeneration.

Though macrophages are essential for skeletal muscle regeneration, which is a complex process, the roles and mechanisms of the macrophages in the process of muscle regeneration are still not fully understood. The objective of this study is to explore the roles of macrophages and the mechanisms involved in the regeneration of injured skeletal muscle. One hundred and twelve C57BL/6 mice were randomly divided into muscle contusion and macrophages depleted groups. Their gastrocnemius muscles were harvested at the time points of 12 h, 1, 3, 5, 7, 14 d post-injury. The changes in skeletal muscle morphology were assessed by hematoxylin and eosin (HE) stain. The gene expression was analyzed by real-time polymerase chain reaction. The data showed that CL-liposomes treatment did affect the expression of myogenic regulatory factors (MyoD, myogenin) after injury. In addition, CL-liposomes treatment decreased the expression of regulatory factors of muscle regeneration (HGF, uPA, COX-2, IGF-1, MGF, FGF6) and increased the expression of inflammatory cytokines (TGF-β1, TNF-α, IL-1β, RANTES) in the late stage of regeneration. Moreover, there were significant correlations between macrophages and some regulatory factors (such as HGF, uPA) for muscle regeneration. These results suggested that macrophages depletion impairs skeletal muscle regeneration and that the regulatory factors for muscle regeneration may play important roles in this process.

Reduced skeletal muscle satellite cell number alters muscle morphology after chronic stretch but allows limited serial sarcomere addition

Muscles add sarcomeres in response to stretch, presumably to maintain optimal sarcomere length. Clinical evidence from patients with cerebral palsy, who have both decreased serial sarcomere number and reduced satellite cells (SCs), suggests a hypothesis that SCs may be involved in sarcomere addition. A transgenic Pax7-DTA mouse model underwent conditional SC depletion, and their soleii were then stretch-immobilized to assess the capacity for sarcomere addition. Muscle architecture, morphology, and extracellular matrix (ECM) changes were also evaluated. Mice in the SC-reduced group achieved normal serial sarcomere addition in response to stretch. However, muscle fiber cross-sectional area was significantly smaller and was associated with hypertrophic ECM changes, consistent with fibrosis. While a reduced SC population does not hinder serial sarcomere addition, SCs play a role in muscle adaptation to chronic stretch that involves maintenance of both fiber cross-sectional area and ECM structure. Muscle Nerve 55: 384-392, 2017.

Altered expression of pectoral myosin heavy chain isoforms corresponds to migration status in the white-crowned sparrow (Zonotrichia leucophrys gambelii).

Birds undergo numerous changes as they progress through life-history stages, yet relatively few studies have examined how birds adapt to both the dynamic energetic and mechanical demands associated with such transitions. Myosin heavy chain (MyHC) expression, often linked with muscle fibre type, is strongly correlated with a muscle's mechanical power-generating capability, thus we examined several morphological properties, including MyHC expression of the pectoralis, in a long-distance migrant, the white-crowned sparrow (Zonotrichia leucophrys gambelii) throughout the progression from winter, spring departure and arrival on breeding grounds. White-crowned sparrows demonstrated significant phenotypic flexibility throughout the seasonal transition, including changes in prealternate moult status, lipid fuelling, body condition and flight muscle morphology. Pectoral MyHC expression also varied significantly over the course of the study. Wintering birds expressed a single, newly classified adult fast 2 isoform. At spring departure, pectoral isoform expression included two MyHC isoforms: the adult fast 2 isoform along with a smaller proportion of a newly present adult fast 1 isoform. By spring arrival, both adult fast isoforms present at departure remained, yet expression had shifted to a greater relative proportion of the adult fast 1 isoform. Altering pectoral MyHC isoform expression in preparation for and during spring migration may represent an adaptation to modulate muscle mechanical output to support long-distance flight.

TAZ Activator Is Involved in IL-10-Mediated Muscle Responses in an Animal Model of Traumatic Brain Injury.

The transcriptional coactivator with PDZ-binding motif (TAZ) functions as a downstream regulatory target in the Hippo signaling pathway that plays various roles. We previously developed a cell-based assay and identified the TAZ activator IBS008738 as a potential therapeutic target for glucocorticoid-induced atrophy. To further explore the application of IBS008738 in various muscle-related diseases, we examined the function of IBS008738 in inflammatory cytokine-mediated mouse muscle responses after traumatic brain injury (TBI). Preliminary screening suggested that IBS008738 treatments increased the levels of IL-10 in C2C12 cells. In TBI and sham control mice, we compared the effect of IBS008738 treatments on TNF α, IL-6, and IL-10 mRNA levels, muscle morphologic changes, and macrophage phenotype changes. Our findings support that the TAZ activator IBS008738 decreases muscle wasting by upregulating IL-10 and inhibiting TNF α and IL-6, and this process is implemented by changing the macrophage phenotypes. These results indicate a new mechanism of the TAZ activator as a potential therapy for atrophy.

Identification of morphological markers of sarcopenia at early stage of aging in skeletal muscle of mice

The gastrocnemius muscle (GM) of young (3months) and aged (12months) female wild-type C57/BL6 mice was examined by light and electron microscopy, looking for the presence of structural changes at early stage of the aging process. Morphometrical parameters including body and gastrocnemius weights, number and type of muscle fibers, cross section area (CSA), perimeter, and Feret's diameter of single muscle fiber, were measured. Moreover, lengths of the sarcomere, A-band, I-band, H-zone, and number and CSA of intermyofibrillar mitochondria (IFM), were also determined. The results provide evidence that 12month-old mice had significant changes on skeletal muscle structure, beginning with the reduction of gastrocnemius weight to body weight ratio, compatible with an early loss of skeletal muscle function and strength. Moreover, light microscopy revealed increased muscle fibers size, with a significant increase on their CSA, perimeter, and diameter of both type I and type II muscle fibers, and a reduction in the percentage of muscle area occupied by type II fibers. Enhanced connective tissue infiltrations, and the presence of centrally nucleated muscle fibers, were also found in aged mice. These changes may underlie an attempt to compensate the loss of muscle mass and muscle fibers number. Furthermore, electron microscopy discovered a significant age-dependent increase in the length of sarcomeres, I and H bands, and reduction on the overlapped actin/myosin length, supporting contractile force loss with age. Electron microscopy also showed an increased number and CSA of IFM with age, which may reveal more endurance at 12months of age. Together, mice at early stage of aging already show significant changes in gastrocnemius muscle morphology and ultrastructure that are suggestive of the onset of sarcopenia.

The injury of marginal mandibular branch unexpectedly promotes the repair of buccal branch of facial nerve in a rat model

Conclusions: The results indicate that the injury of the marginal mandibular branch improved the recovery of the buccal branch in a rat model.Objective: The aim of this study was to investigate whether the injury or intactness of the marginal mandibular branch affects the regeneration of the facial nerve buccal branch in a rat model.Methods: This experiment was conducted on 30 adult rats, which were randomly and equally divided into two groups. The buccal branch of the facial nerve was transected and reconstructed, with the marginal mandibular branch damaged (group A) or intact (group B). The vibrissae movement of rats was assessed since the 4th week after operation. At the 8th and 12th week, compound muscle action potentials (CMAPs) and morphological changes of injured buccal branches were evaluated.Results: After the operation, vibrissae movement of rats was eliminated in group A, but it was similar to the health side in group B. CMAPs were recorded from regenerated buccal branches in group A since the 8th week, but no CMAPs could be recorded in group B at each time point. Additionally, the diameter of nerve fibers, the thickness of myelin sheath, and the density of regenerated fibers in group A were significantly larger than those in group B (p < 0.05).

Interleukin-13 Receptor α1-Dependent Responses in the Intestine Are Critical to Parasite Clearance.

Nematode infection upregulates interleukin-4 (IL-4) and IL-13 and induces STAT6-dependent changes in gut function that promote worm clearance. IL-4 and IL-13 activate the type 2 IL-4 receptor (IL-4R), which contains the IL-13Rα1 and IL-4Rα chains. We used mice deficient in IL-13Rα1 (IL-13Rα1(-/-)) to examine the contribution of IL-13 acting at the type 2 IL-4R to immune and functional responses to primary (Hb1) and secondary (Hb2) infections with the gastrointestinal nematode parasite Heligmosomoides bakeri There were differences between strains in the IL-4 and IL-13 expression responses to Hb1 but not Hb2 infection. Following Hb2 infection, deficient mice had impaired worm expulsion and higher worm fecundity despite normal production of Th2-derived cytokines. The upregulation of IL-25 and IL-13Rα2 in Hb1- and Hb2-infected wild-type (WT) mice was absent in IL-13Rα1(-/-)mice. Goblet cell numbers and resistin-like molecule beta (RELM-β) expression were attenuated significantly in IL-13Rα1(-/-)mice following Hb2 infections. IL-13Rα1 contributes to the development of alternatively activated macrophages, but the type 1 IL-4R is also important. Hb1 infection had no effects on smooth muscle function or epithelial permeability in either strain, while the enhanced mucosal permeability and changes in smooth muscle function and morphology observed in response to Hb2 infection in WT mice were absent in IL-13Rα1(-/-)mice. Notably, the contribution of claudin-2, which has been linked to IL-13, does not mediate the increased mucosal permeability following Hb2 infection. These results show that activation of IL-13Rα1 is critical for key aspects of the immune and functional responses to Hb2 infection that facilitate expulsion.

Time-dependent gene expression analysis after mouse skeletal muscle contusion

BackgroundThough the mechanisms of skeletal muscle regeneration are deeply understood, those involved in muscle contusion, one of the most common muscle injuries in sports medicine clinics, are not. The objective of this study is to explore the mechanisms involved in muscle regeneration after contusion injury. MethodsIn this study, a total of 72 mice were used. Eight of them were randomly chosen for the control group, while the rest were subjected to muscle contusion. Subsequently, their gastrocnemius muscles were harvested at different time points. The changes in muscle morphology were assessed by hematoxylin and eosin (HE) stain. In addition, the gene expression was analyzed by real-time polymerase chain reaction. ResultsThe data showed that the expression of many genes, i.e., specific markers of immune cells and satellite cells, regulatory factors for muscle regeneration, cytokines, and chemokines, increased in the early stages of recovery, especially in the first 3 days. Furthermore, there were strict rules in the expression of these genes. However, almost all the genes returned to normal at 14 days post-injury. ConclusionThe sequence of immune cells invaded after muscle contusion was neutrophils, M1 macrophages and M2 macrophages. Some CC (CCL2, CCL3, and CCL4) and CXC (CXCL10) chemokines may be involved in the chemotaxis of these immune cells. HGF may be the primary factor to activate the satellite cells after muscle contusion. Moreover, 2 weeks are needed to recover when acute contusion happens as used in this study.

Muscle histopathology in children with spastic cerebral palsy receiving botulinum toxin type A.

Botulinum toxin A (BoNTA) is routine treatment for hypertonicity in children with cerebral palsy (CP). This single-blind, prospective, cross-sectional study of 10 participants (mean age 11 years 7 months) was done to determine the relationship between muscle histopathology and BoNTA in treated medial gastrocnemius muscle of children with CP. Open muscle biopsies were taken from medial gastrocnemius muscle and vastus lateralis (control) during orthopedic surgery. Neurogenic atrophy in the medial gastrocnemius was seen in 6 participants between 4 months and 3 years post-BoNTA. Type 1 fiber loss with type 2 fiber predominance was significantly related to the number of BoNTA injections (r = 0.89, P < 0.001). The impact of these changes in muscle morphology on muscle function in CP is not clear. It is important to consider rotating muscle selection or injection sites within the muscle or allowing longer time between injections.

The impact of obesity on skeletal muscle strength and structure through adolescence to old age.

Obesity is associated with functional limitations in muscle performance and increased likelihood of developing a functional disability such as mobility, strength, postural and dynamic balance limitations. The consensus is that obese individuals, regardless of age, have a greater absolute maximum muscle strength compared to non-obese persons, suggesting that increased adiposity acts as a chronic overload stimulus on the antigravity muscles (e.g., quadriceps and calf), thus increasing muscle size and strength. However, when maximum muscular strength is normalised to body mass, obese individuals appear weaker. This relative weakness may be caused by reduced mobility, neural adaptations and changes in muscle morphology. Discrepancies in the literature remain for maximal strength normalised to muscle mass (muscle quality) and can potentially be explained through accounting for the measurement protocol contributing to muscle strength capacity that need to be explored in more depth such as antagonist muscle co-activation, muscle architecture, a criterion valid measurement of muscle size and an accurate measurement of physical activity levels. Current evidence demonstrating the effect of obesity on muscle quality is limited. These factors not being recorded in some of the existing literature suggest a potential underestimation of muscle force either in terms of absolute force production or relative to muscle mass; thus the true effect of obesity upon skeletal muscle size, structure and function, including any interactions with ageing effects, remains to be elucidated.

Skeletal muscle ultrastructure and function in statin-tolerant individuals.

Statins have well-known benefits on cardiovascular mortality, though up to 15% of patients experience side effects. With guidelines from the American Heart Association, American College of Cardiology, and American Diabetes Association expected to double the number of statin users, the overall incidence of myalgia and myopathy will increase. We evaluated skeletal muscle structure and contractile function at the molecular, cellular, and whole tissue levels in 12 statin tolerant and 12 control subjects. Myosin isoform expression, fiber type distributions, single fiber maximal Ca(2+) -activated tension, and whole muscle contractile force were similar between groups. No differences were observed in myosin-actin cross-bridge kinetics in myosin heavy chain I or IIA fibers. We found no evidence for statin-induced changes in muscle morphology at the molecular, cellular, or whole tissue levels. Collectively, our data show that chronic statin therapy in healthy asymptomatic individuals does not promote deleterious myofilament structural or functional adaptations.

Skeletal muscle morphology in sarcopenia defined using the EWGSOP criteria: findings from the Hertfordshire Sarcopenia Study (HSS).

BackgroundSarcopenia is defined as the loss of muscle mass and function with age and is associated with decline in mobility, frailty, falls and mortality. There is considerable interest in understanding the underlying mechanisms. Our aim was to characterise muscle morphology changes associated with sarcopenia among community dwelling older men.MethodsOne hundred and five men aged 68–76 years were recruited to the Hertfordshire Sarcopenia Study (HSS) for detailed characterisation of muscle including measures of muscle mass, strength and function. Muscle tissue was obtained from a biopsy of the vastus lateralis for 99 men and was processed for immunohistochemical studies to determine myofibre distribution and area, capillarisation and satellite cell (SC) density.ResultsSix (6 %) men had sarcopenia as defined by the European Working Group on Sarcopenia in Older People (EWGSOP) criteria. These men had lower SC density (1.7 cells/mm2 vs 3.8 cells/mm2, p = 0.06) and lower SC/fibre ratio (0.02 vs 0.06, p = 0.06) than men without sarcopenia. Although men with sarcopenia tended to have smaller myofibres and lower capillary to fibre ratio, these relationships were not statistically significant.ConclusionWe have shown that there may be altered muscle morphology parameters in older men with sarcopenia. These results have the potential to help identify cell and molecular targets for therapeutic intervention. This work now requires extension to larger studies which also include women.

Live imaging of muscles in Drosophila metamorphosis: Towards high-throughput gene identification and function analysis

Time-lapse microscopy in developmental biology is an emerging tool for functional genomics. Phenotypic effects of gene perturbations can be studied non-invasively at multiple time points in chronological order. During metamorphosis of Drosophila melanogaster, time-lapse microscopy using fluorescent reporters allows visualization of alternative fates of larval muscles, which are a model for the study of genes related to muscle wasting. While doomed muscles enter hormone-induced programmed cell death, a smaller population of persistent muscles survives to adulthood and undergoes morphological remodeling that involves atrophy in early, and hypertrophy in late pupation. We developed a method that combines in vivo imaging, targeted gene perturbation and image analysis to identify and characterize genes involved in muscle development. Macrozoom microscopy helps to screen for interesting muscle phenotypes, while confocal microscopy in multiple locations over 4–5days produces time-lapse images that are used to quantify changes in cell morphology. Performing a similar investigation using fixed pupal tissues would be too time-consuming and therefore impractical. We describe three applications of our pipeline. First, we show how quantitative microscopy can track and measure morphological changes of muscle throughout metamorphosis and analyze genes involved in atrophy. Second, our assay can help to identify genes that either promote or prevent histolysis of abdominal muscles. Third, we apply our approach to test new fluorescent proteins as live markers for muscle development. We describe mKO2 tagged Cysteine proteinase 1 (Cp1) and Troponin-I (TnI) as examples of proteins showing developmental changes in subcellular localization. Finally, we discuss strategies to improve throughput of our pipeline to permit genome-wide screens in the future.

Gaze strategies while negotiating obstacles in a virtual environment with distractors

s / Gait & Posture 42S (2015) S1–S27 S3 Table 1 Morphological and structural features in CP and TD children. Age [years] Muscle volume [cm3] Muscle length [cm] MTU [cm] Average muscle area [cm2] Normalized Muscle volume [cm2] Mean EI of muscle CP 8.6±2.3 32.4±13.8 16.2±3.9 33.5±6.0 2.1±0.5 1.1±0.3 101.0±9.7 TD 9.2±2.3 52.2±19.0 17.3±2.7 34.0±4.9 2.9±0.7 1.5±0.4 129.2±20.3 t-Test (p-value) 0.740 0.103 0.331 0.566 0.018* 0.040* 0.006* volume (=volume/MTU length) were calculated. In addition, the mean EI value (expressed in a grey-scale of 256 values), was also evaluated. Comparisons were made using the Student t-test (unpaired). Statistical significance (*) was set to p 0.79, p>0.01), but with a lower slope in CP (5.2 vs. 7.8 cm3/years). In CP, a significant negative correlation was found between EI and average muscle area (R2 =0.60, p=0.04). Discussion: We found a smaller muscle volume in CP children, as previously reported [2]. Interestingly, as a CP child ages, slower muscle growth occurs than in the TD children. Averaged muscle area was found to be more sensitive to distinguish between TD and CP children. Furthermore, the MG was hyper-echoic in the CP group relative to the TD group, supporting our hypothesis. Combining EI and average muscle area shows potential in estimating the amount of fibrotic changes occurring within a muscle. Utilising the new approach for 3D reconstruction offers an objective and efficient manner to diagnose muscle and tendon morphological and structural changes in the clinical environment.

New continuous-flow total artificial heart and vascular permeability

BackgroundWe tested the short-term effects of completely nonpulsatile versus pulsatile circulation after ventricular excision and replacement with total implantable pumps in an animal model on peripheral vascular permeability. MethodsTen calves underwent cardiac replacement with two HeartMate III continuous-flow rotary pumps. In five calves, the pump speed was rapidly modulated to impart a low-frequency pulse pressure in the physiologic range (10–25 mm Hg) at a rate of 40 pulses per minute (PP). The remaining five calves were supported with a pulseless systemic circulation and no modulation of pump speed (NP). Skeletal muscle biopsies were obtained before cardiac replacement (baseline) and on postoperative days (PODs) 1, 7, and 14. Skeletal muscle-tissue water content was measured, and morphologic alterations of skeletal muscle were assessed. VE-cadherin, phospho–VE-cadherin, and CD31 were analyzed by immunohistochemistry. ResultsThere were no significant changes in tissue water content and skeletal muscle morphology within group or between groups at baseline, PODs 1, 7, and 14, respectively. There were no significant alterations in the expression and/or distribution of VE-cadherin, phospho–VE-cadherin, and CD31 in skeletal muscle vasculature at baseline, PODs 1, 7, and 14 within each group or between the two groups, respectively. Although continuous-flow total artificial heart (CFTAH) with or without a pulse pressure caused slight increase in tissue water content and histologic damage scores at PODs 7 and 14, it failed to reach statistical significance. ConclusionsThere was no significant adherens-junction protein degradation and phosphorylation in calf skeletal muscle microvasculature after CFTAH implantation, suggesting that short term of CFTAH with or without pulse pressure did not cause peripheral endothelial injury and did not increase the peripheral microvascular permeability.

Cervical Intervertebral Disc Heights and Paraspinal Muscle Morphology Changes Following Long-term Spaceflight and 30-Day Recovery

Exposure to microgravity during long-duration spaceflights lengthens the spine is associated with a 5-fold greater incidence of herniated nucleus pulposus (HNP), particularly in the cervical region, compared with age-matched ground controls. Concurrent muscle atrophy or deconditioning may also contribute to increased HNP risk. PURPOSE: To evaluate cervical IVD height change and associated paraspinal muscle change following a 6-month International Space Station (ISS) mission and a 30-day post-flight recovery period. METHODS: Cervical spine MRI images were conducted pre-flight, immediate post-flight and 30-to-45 days post-flight recovery of 3 astronauts. IVD heights were measured at the anterior, middle and posterior sections from the upper C2-C3 to lower C7-T1 disc levels. Functional cross-sectional area measurements of the axial cervical paraspinal muscles at the C5-C6 level were performed. The fractional portion of lean muscle area was measured from a standardized region of interest within the posterior cervical extensors. Student-T tests were used to determine significant changes at p<0.05. RESULTS: Cervical IVD heights increased 0.35±0.42mm during the 6-month exposure to microgravity and recovered an average of 0.08±0.37mm over 30 days. The posterior aspect of the IVD heights was significantly decreased during recovery (0.30±0.36mm) while the anterior and middle segments remained swollen (Table 1). An average 9.9±17.8% decrease in cervical lean muscle tissue was measured post flight with a 30-day recovery of 2.2±3.8%. CONCLUSIONS: In the 30 days following ISS missions, there was significant reduction of the posterior cervical IVD heights associated with decreased lean muscle mass of posterior extensors. Supported by NASA grants NNX10AM18G and NNX13AM89G.

Quadriceps And Hamstring Muscle Volume Following Anterior Cruciate Ligament Reconstruction Using An Allograft

Impaired muscle function of the quadriceps and hamstring muscles is commonly observed following anterior cruciate ligament reconstruction (ACLR), which makes these muscles primary targets during post-ACLR rehabilitation. The changes in quadriceps and hamstrings muscle morphology, however, have not been investigated following ACLR using an allograft in which the donor site morbidity accompanied with autografts is avoided. PURPOSE: To examine muscle volume of the quadriceps and hamstring muscles in females following ACLR using an allograft. METHODS: Seven females (mean age: 25.1 ± 2.6 years) with unilateral ACLR using an allograft participated. The average time from surgery was 30.3 ± 18.7 months. All subjects had completed rehabilitation and had been cleared to return to full activity by their orthopaedic surgeons. Magnetic resonance images were used to quantify volumes of the quadriceps, hamstrings, and subcutaneous fat for the distal two-thirds of both thighs, starting from the base of the patella. Differences between the injured and uninjured limbs were examined using Wilcoxon signed-rank tests. RESULTS: The overall quadriceps muscle volume of the reconstructed limb was 7.3 ± 6.4 % (p = 0.043) smaller when compared to the uninjured limb. The lower quadriceps volume of the reconstructed limb was a result of a smaller volume of the vastus lateralis (smaller by 7.9 ± 8.2 %, p = 0.043) and vastus medialis (smaller by 10.3 ± 9.1 %, p = 0.043) when compared to the uninjured limb. No differences between the two limbs were observed for the entire or individual hamstring muscles. While subcutaneous fat volume of the reconstructed limb was 2.7 ± 3.6 % greater compared to the uninjured limb, this difference was not statically significant (p = 0.063). CONCLUSION: Females who have undergone ACLR using an allograft do not demonstrate a change in the hamstring muscle volume as previously reported in individuals with ACLR using a semitendinosus-gracilis autograft. However, our findings of selective atrophy in the vastus lateralis and vastus medialis suggest that factors other than donor tissue integrity (e.g., unloading, muscle inhibition, etc.) may be responsible for the impaired quadriceps muscle function following ACLR using an allograft.

Characterization and bioactivities of a novel purified polysaccharide from Endothelium corneum gigeriae Galli

In the present study, characterization and cardioprotective activities in vivo of a novel purified polysaccharide (PECGp) from Endothelium corneum gigeriae Galli were investigated. The results found that PECGp had a 96kDa molecular weight. The backbone chains were composed of α-d-Glc and α-l-Rha linked by (1→4) glycosidic bonds. (1→4, 6) linked α-d-Glc and (1→2, 4) linked α-l-Rha in backbone chains with branches consisting of (1→4) linked α-d-Glc and terminal α-d-Glc-6-COOH. The assay of cardioprotective activities demonstrated that PECGp could significantly reduce the ST-segment elevation, prevented abnormal changes of heart muscle morphology, reverse abnormal hemodynamic and hemorheological parameters, rectify disorganized superoxide dismutase, nitric oxide synthase, nitric oxide, malondialdehyde, creatine kinase, creatine kinase MB fraction and lactate dehydrogenase levels. The results suggested that PECGp could be considered as a potential candidate for developing novel cardioprotective agents.

Superior Indices of Neuromuscular Function in Elite Octogenarian Masters Athletes

Aging is associated with a progressive deterioration of muscle mass and function that leads to greatest clinical impact in those 蠅80 y of age. Conversely, elite octogenarian masters athletes (MA) retain a remarkable degree of physical function. Because aging muscle is profoundly impacted by neuromuscular changes, we hypothesized that muscle of MAs would have attenuated changes in muscle morphology and neuromuscular function compared to non-athlete (NA) controls. Muscle biopsies of vastus lateralis muscle were obtained for analysis of fiber type grouping and fiber size in NA (n = 14, age: 81 ± 4 y) and elite MAs (n = 15, age: 80 ± 5 y). Motor unit number estimate, compound muscle action potential, and strength were conducted in the tibialis anterior muscle. Quadriceps area (QA) and strength (QS), and functional capacity (chair stand and stand-up & go) were also measured. Elite MAs exhibited greater QA (p = 0.015), QS (p = 0.013), and functional performance (p < 0.01) compared to NA. MAs had greater fiber size (p = 0.024), lower percentage of small fibers (< 2500µm; p = 0.031) and more fiber type grouping (p = 0.029) compared to NA. Furthermore, MAs had significantly greater motor unit number estimate and compound muscle action potential than NA. Consistent with our hypothesis, elite MAs exhibited not only superior indices of functional performance and muscle strength, but also better preserved muscle morphology and neuromuscular function including 1) fewer small fibers, 2) increased fiber type grouping (suggesting superior reinnervation), and 3) better retention of motor unit numbers versus NA.

Comparison of Training Intensity Versus Training Volume on Endocrine and Muscle Growth Changes in Trained Men

Changes in muscle morphology and the endocrine response to 8‐weeks of resistance training were examined in 29 resistance‐trained men. Changes in lean body (LBM) and leg mass (LM) were assessed by dual energy X‐ray absorptiometry. Ultrasound images were used to assess muscle thickness (MT) and cross‐sectional area (CSA) in the Vastus Lateralis (VL) and Rectus Femoris (RF). Participants were randomly assigned to either a high volume (VOL, n = 14, 4 x 10‐12RM, 1min rest) or high intensity (INT, n = 15, 4 x 3‐5RM, 3min rest) resistance training program. Blood samples were collected at baseline, immediately post, 30 min post, and 60 min post‐exercise prior to and following the 8‐week program, and tested for testosterone, growth hormone (GH), insulin‐like growth factor 1 (IGF1), cortisol (C), and insulin. Area under the curve (AUC) analysis revealed a greater response in GH (36.6%, p = 0.007) and C (20.6%, p &lt; 0.001) for VOL compared to INT at WK3. No other differences in the hormonal response were noted at WK3. At WK10, AUC analysis indicated that C was greater for VOL (13.8%, p = 0.008) compared to INT. Compared to WK3, WK10 showed a reduced (p &lt; 0.05) response in GH (43.2 ± 24.8%) and C (13.1 ± 17.8%) for VOL and IGF1 (5.3 ± 6.8%) for INT. Though no (group x time) interactions were found, INT experienced increases (p &lt; 0.05) in LBM (1.5 ± 1.8kg), LM (0.5 ± 0.9kg), VL MT (0.2 ± 0.3cm), and VL CSA (3.8 ± 5.5cm2). No changes were noted in any of these variables in VOL. INT appears to provide a significant stimulus for training induced muscle growth and lean mass accruement in trained men.