Effects of sporadic inclusion body myositis on skeletal muscle fibre type specific morphology and markers of regeneration and inflammation.

Sporadic inclusion body myositis (sIBM) is a subgroup of idiopathic inflammatory myopathies characterised by progressive muscle weakness and skeletal muscle inflammation. Quantitative data on the myofibre morphology in sIBM remains scarce. Further, no previous study has examined fibre type association of satellite cells (SC), myonuclei number, macrophages, capillaries, and myonuclear domain (MD) in sIBM patients. Muscle biopsies from sIBM patients (n = 18) obtained previously (NCT02317094) were included in the analysis for fibre type-specific myofibre cross-sectional area (mCSA), SCs, myonuclei and macrophages, myonuclear domain, and capillarisation. mCSA (p < 0.001), peripheral myonuclei (p < 0.001) and MD (p = 0.005) were higher in association with type 1 (slow-twitch) than type 2 (fast-twitch) fibres. Conversely, quiescent SCs (p < 0.001), centrally placed myonuclei (p = 0.03), M1 macrophages (p < 0.002), M2 macrophages (p = 0.013) and capillaries (p < 0.001) were higher at type 2 fibres compared to type 1 fibres. In contrast, proliferating (Pax7+/Ki67+) SCs (p = 0.68) were similarly associated with each fibre type. Type 2 myofibres of late-phase sIBM patients showed marked signs of muscle atrophy (i.e. reduced mCSA) accompanied by higher numbers of associated quiescent SCs, centrally placed myonuclei, macrophages and capillaries compared to type 1 fibres. In contrast, type 1 fibres were suffering from pathological enlargement with larger MDs as well as fewer nuclei and capillaries per area when compared with type 2 fibres. More research is needed to examine to which extent different therapeutic interventions including targeted exercise might alleviate these fibre type-specific characteristics and countermeasure their consequences in impaired functional performance.

The impact of life-long strength versus endurance training on muscle fiber morphology and phenotype composition in older men.

Aging is typically associated with decreased muscle strength and rate of force development (RFD), partly explained by motor unit remodeling due to denervation, and subsequent loss of fast-twitch type II myofibers. Exercise is commonly advocated to counteract this detrimental loss. However, it is unclear how life-long strength versus endurance training may differentially affect markers of denervation and reinnervation of skeletal myofibers and, in turn, affect the proportion and morphology of fast-twitch type II musculature. Thus, we compared fiber type distribution, fiber type grouping, and the prevalence of atrophic myofibers (≤1,494 µm2) in strength-trained (OS) versus endurance-trained (OE) master athletes and compared the results to recreationally active older adults (all >70 yr, OC) and young habitually active references (<30 yr, YC). Immunofluorescent stainings were performed on biopsy samples from vastus lateralis, along with leg press maximal strength and RFD measurements. OS demonstrated similar type II fiber distribution (OS: 52.0 ± 16.4%; YC: 51.1 ± 14.4%), fiber type grouping, maximal strength (OS: 170.0 ± 18.9 kg, YC: 151.0 ± 24.4 kg), and RFD (OS: 3,993 ± 894 N·s-1, YC: 3,470 ± 1,394 N·s-1) as young, and absence of atrophic myofibers (OS: 0.2 ± 0.7%; YC: 0.1 ± 0.4%). In contrast, OE and OC exhibited more atrophic fibers (OE: 1.2 ± 1.0%; OC: 1.1 ± 1.4%), more grouped fibers, and smaller proportion of type II fibers (OE: 39.3 ± 11.9%; OC: 35.0 ± 12.4%) than OS and YC (all P < 0.05). In conclusion, strength-trained master athletes were characterized by similar muscle morphology as young, which was not the case for recreationally active or endurance-trained old. These results indicate that strength training may preserve type II fibers with advancing age in older men, likely as a result of chronic use of high contractile force generation.NEW & NOTEWORTHY Aging is associated with loss of fast-twitch type II myofibers, motor unit remodeling, and grouping of myofibers. This study reveals, for the first time, that strength training preserves neural innervation of type II fibers, resulting in similar myofiber type distribution and grouping in life-long strength-trained master athletes as young moderately active adults. In contrast, life-long endurance-trained master athletes and recreationally active old adults demonstrated higher proportion of type I fibers accompanied by more marked grouping of type I myofibers, and more atrophic fibers compared with strength-trained master athletes and young individuals. Thus, strength training should be utilized as a training modality for preservation of fast-twitch musculature, maximal muscle strength, and rapid force capacity (RFD) with advancing age.

Lack of muscle stem cell proliferation and myocellular hypertrophy in sIBM patients following blood-flow restricted resistance training.

Sporadic inclusion body myositis (sIBM) is characterised by skeletal muscle inflammation, progressive muscle loss and weakness, which is largely refractory to immunosuppressive treatment. Low-load blood-flow restricted (BFR) training has been shown to evoke gains in myofibre cross sectional area (mCSA) in healthy adults. This could partially be due to the activation and integration of muscle satellite cells (SC) resulting in myonuclei addition. Consequently, this study investigated the effect of 12-weeks lower limb low-load BFR resistance training in sIBM patients on SC and myonuclei content, myofibre size and capillarization. Muscle biopsies from sIBM patients randomised to 12-weeks of low-load BFR resistance training (n = 11) or non-exercising controls (CON) (n = 9) were analysed for SC and myonuclei content, myofibre size and capillarization using three-colour immunofluorescence microscopy and computerised quantification procedures. No between-group differences (time-by-group interactions) or within-groups changes were observed for resident SCs (Pax7+/Six1+), proliferating SCs (Pax7+/ Ki67+), myonuclei (Six1+), type 1 mCSA or capillary number (CD31+). However, a time-by-group interaction for type 2 mCSA was observed (p = 0.04). Satellite cell content, myonuclei number, mCSA and capillary density remained unaffected following 12-weeks low-load BFR resistance training, indicating limited myogenic capacity and satellite cell plasticity in long-term sIBM patients.

Supplementation of Specific Collagen Peptides Following High-Load Resistance Exercise Upregulates Gene Expression in Pathways Involved in Skeletal Muscle Signal Transduction.

Previous evidence suggests that resistance training in combination with specific collagen peptides (CP) improves adaptive responses of the muscular apparatus. Although beneficial effects have been repeatedly demonstrated, the underlying mechanisms are not well understood. Therefore, the primary objective of the present randomized trial was to elucidate differences in gene expression pathways related to skeletal muscle signal transduction following acute high-load resistance exercise with and without CP intake. Recreationally active male participants were equally randomized to high-load leg extension exercise in combination with 15 g CP or placebo (PLA) supplementation. Muscle biopsies from the vastus lateralis muscle were obtained at baseline as well as 1, 4 and 24 h post exercise to investigate gene expression using next generation sequencing analysis. Several important anabolic pathways including PI3K-Akt and MAPK pathways were significantly upregulated at 1 and 4 h post-exercise. Significant between-group differences for both pathways were identified at the 4 h time point demonstrating a more pronounced effect after CP intake. Gene expression related to the mTOR pathway demonstrated a higher visual increase in the CP group compared to PLA by trend, but failed to achieve statistically significant group differences. The current findings revealed a significantly higher upregulation of key anabolic pathways (PI3K-Akt, MAPK) in human skeletal muscle 4 h following an acute resistance training combined with intake of 15 g of specific collagen peptides compared to placebo. Further investigations should examine potential relationships between upregulated gene expression and changes in myofibrillar protein synthesis as well as potential long-term effects on anabolic pathways on the protein level.

Effects of blood-flow restricted resistance training on mechanical muscle function and thigh lean mass in sIBM patients.

Sporadic inclusion body myositis (sIBM) is an idiopathic inflammatory muscle disease associated with skeletal muscle inflammation and a parallel progressive decline in muscle strength and physical function. Eventually, most sIBM patients require use of wheelchair after about 10 years of diagnosis and assistance to perform activities of daily living. This study presents data from a randomized controlled intervention trial (NCT02317094) that examined the effect of 12 weeks low-load blood-flow restricted (BFR) resistance training on maximal muscle strength, power, rate of force development (RFD), thigh lean mass (TLM), and voluntary muscle activation (VA) in sIBM patients. A time-by-group interaction in knee extensor strength was observed in the stronger leg (p ≤ 0.033) but not the weaker leg. Within-group changes were observed with BFR training (BFR) manifested by increased knee extensor strength in the strongest leg (+13.7%, p = 0.049), whereas non-exercising patients (CON) showed reduced knee extensor strength (-7.7%, p = 0.018). Maximal leg extensor power obtained for the stronger leg remained unchanged following BFR training (+9.5%, p = 0.37) while decreasing in CON (-11.1%, p = 0.05). No changes in TLM were observed. VA declined post-training (p = 0.037) in both BFR (-6.3% points) and CON (-7.5% points). The present data indicate that BFR resistance training can attenuate the rate of decline in mechanical muscle function typically experienced by sIBM patients. The preservation of muscle mass and mechanical muscle function with BFR resistance training may be considered of high clinical importance in sIBM patients to countermeasure the disease-related decline in physical function.

Changes in systemic GDF15 across the adult lifespan and their impact on maximal muscle power: the Copenhagen Sarcopenia Study.

BACKGROUND: Although growth differentiation factor 15 (GDF15) is known to increase with disease and is associated with low physical performance, the role of GDF15 in normal ageing is still not fully understood. Specifically, the influence of circulating GDF15 on impairments in maximal muscle power (a major contributor to functional limitations) and the underlying components has not been investigated. METHODS: Data from 1305 healthy women and men aged 20 to 93 years from The Copenhagen Sarcopenia Study were analysed. Circulating levels of GDF15 and markers of inflammation (tumor necrosis factor-alpha, interleukin-6, and high-sensitivity C-reactive protein) were measured by ELISA (R&D Systems) and multiplex bead-based immunoassays (Bio-Rad). Relative (normalized to body mass), allometric (normalized to height squared), and specific (normalized to leg muscle mass) muscle power were assessed by the Nottingham power rig [leg extension power (LEP)] and the 30 s sit-to-stand (STS) muscle power test. Total body fat, visceral fat, and leg lean mass were assessed by dual energy X-ray absorptiometry. Leg skeletal muscle index was measured as leg lean mass normalized to body height squared. RESULTS: Systemic levels of GDF15 increased progressively as a function of age in women (1.1 ± 0.4 pg·mL-1 ·year-1 ) and men (3.3 ± 0.6 pg·mL-1 ·year-1 ) (both P < 0.05). Notably, GDF15 increased at a faster rate from the age of 65 years in women (11.5 ± 1.2 pg·mL-1 ·year-1 , P < 0.05) and 70 years in men (19.3 ± 2.3 pg·mL-1 ·year-1 , P < 0.05), resulting in higher GDF15 levels in men compared with women above the age of 65 years (P < 0.05). Independently of age and circulatory markers of inflammation, GDF15 was negatively correlated to relative STS power (P < 0.05) but not LEP, in both women and men. These findings were mainly explained by negative associations of GDF15 with specific STS power in women and men (both P < 0.05). CONCLUSIONS: A J-shaped relationship between age and systemic GDF15 was observed, with men at older age showing steeper increases and elevated GDF15 levels compared with women. Importantly, circulating GDF15 was independently and negatively associated with relative STS power, supporting the potential role of GDF15 as a sensitive biomarker of frailty in older people.

Assessment of functional sit-to-stand muscle power: Cross-sectional trajectories across the lifespan.

BACKGROUND: The 30-s sit-to-stand (STS) muscle power test is a valid test to assess muscle power in older people; however, whether it may be used to assess trajectories of lower-limb muscle power through the adult lifespan is not known. This study evaluated the pattern and time course of variations in relative, allometric and specific STS muscle power throughout the lifespan. METHODS: Subjects participating in the Copenhagen Sarcopenia Study (729 women and 576 men; aged 20 to 93 years) were included. Lower-limb muscle power was assessed with the 30-s version of the STS muscle power test. Allometric, relative and specific STS power were calculated as absolute STS power normalized to height squared, body mass and leg lean mass as assessed by DXA, respectively. RESULTS: Relative STS muscle power tended to increase in women (0.08 ±â€¯0.05 W·kg-1·yr-1; p = 0.082) and increased in men (0.14 ±â€¯0.07 W·kg-1·yr-1; p = 0.046) between 20 and 30 years, followed by a slow decline (-0.05 ±â€¯0.05 W·kg-1·yr-1 and -0.06 ±â€¯0.08 W·kg-1·yr-1, respectively; both p > 0.05) between 30 and 50 years. Then, relative STS power declined at an accelerated rate up to oldest age in men (-0.09 ±â€¯0.02 W·kg-1·yr-1) and in women until the age of 75 (-0.09 ±â€¯0.01 W·kg-1·yr-1) (both p < 0.001). A lower rate of decline was observed in women aged 75 and older (-0.04 ±â€¯0.02 W·kg-1·yr-1; p = 0.039). Similar age-related patterns were noted for allometric and specific STS power. CONCLUSIONS: The STS muscle power test appears to provide a feasible and inexpensive tool to monitor cross-sectional trajectories of muscle power throughout the lifespan.

Exercise-induced fluid shifts are distinct to exercise mode and intensity: a comparison of blood flow-restricted and free-flow resistance exercise.

MRI can provide fundamental tools in decoding physiological stressors stimulated by training paradigms. Acute physiological changes induced by three diverse exercise protocols known to elicit similar levels of muscle hypertrophy were evaluated using muscle functional magnetic resonance imaging (mfMRI). The study was a cross-over study with participants (n = 10) performing three acute unilateral knee extensor exercise protocols to failure and a work matched control exercise protocol. Participants were scanned after each exercise protocol; 70% 1 repetition maximum (RM) (FF70); 20% 1RM (FF20); 20% 1RM with blood flow restriction (BFR20); free-flow (FF) control work matched to BFR20 (FF20WM). Post exercise mfMRI scans were used to obtain interleaved measures of muscle R2 (indicator of edema), R2' (indicator of deoxyhemoglobin), muscle cross sectional area (CSA) blood flow, and diffusion. Both BFR20 and FF20 exercise resulted in a larger acute decrease in R2, decrease in R2', and expansion of the extracellular compartment with slower rates of recovery. BFR20 caused greater acute increases in muscle CSA than FF20WM and FF70. Only BFR20 caused acute increases in intracellular volume. Postexercise muscle blood flow was higher after FF70 and FF20 exercise than BFR20. Acute changes in mean diffusivity were similar across all exercise protocols. This study was able to differentiate the acute physiological responses between anabolic exercise protocols. Low-load exercise protocols, known to have relatively higher energy contributions from glycolysis at task failure, elicited a higher mfMRI response. Noninvasive mfMRI represents a promising tool for decoding mechanisms of anabolic adaptation in muscle.NEW & NOTEWORTHY Using muscle functional MRI (mfMRI), this study was able to differentiate the acute physiological responses following three established hypertrophic resistance exercise strategies. Low-load exercise protocols performed to failure, with or without blood flow restriction, resulted in larger changes in R2 (i.e. greater T2-shifts) with a slow rate of return to baseline indicative of myocellular fluid shifts. These data were cross evaluated with interleaved measures of macrovascular blood flow, water diffusion, muscle cross sectional area (i.e. acute macroscopic muscle swelling), and intracellular water fraction measured using MRI.

Subcellular localization- and fibre type-dependent utilization of muscle glycogen during heavy resistance exercise in elite power and Olympic weightlifters.

AIM: Glycogen particles are found in different subcellular localizations, which are utilized heterogeneously in different fibre types during endurance exercise. Although resistance exercise typically involves only a moderate use of mixed muscle glycogen, the hypothesis of the present study was that high-volume heavy-load resistance exercise would mediate a pattern of substantial glycogen depletion in specific subcellular localizations and fibre types. METHODS: 10 male elite weightlifters performed resistance exercise consisting of four sets of five (4 × 5) repetitions at 75% of 1RM back squats, 4 × 5 at 75% of 1RM deadlifts and 4 × 12 at 65% of 1RM rear foot elevated split squats. Muscle biopsies (vastus lateralis) were obtained before and after the exercise session. The volumetric content of intermyofibrillar (between myofibrils), intramyofibrillar (within myofibrils) and subsarcolemmal glycogen was assessed by transmission electron microscopy. RESULTS: After exercise, biochemically determined muscle glycogen decreased by 38 (31:45)%. Location-specific glycogen analyses revealed in type 1 fibres a large decrement in intermyofibrillar glycogen, but no or only minor changes in intramyofibrillar or subsarcolemmal glycogen. In type 2 fibres, large decrements in glycogen were observed in all subcellular localizations. Notably, a substantial fraction of the type 2 fibres demonstrated near-depleted levels of intramyofibrillar glycogen after the exercise session. CONCLUSION: Heavy resistance exercise mediates a substantial utilization of glycogen from all three subcellular localization in type 2 fibres, while mostly taxing intermyofibrillar glycogen stores in type 1 fibres. Thus, a better understanding of the impact of resistance training on myocellular metabolism and performance requires a focus on compartmentalized glycogen utilization.

Physiological responses of human skeletal muscle to acute blood flow restricted exercise assessed by multimodal MRI.

Important physiological quantities for investigating muscle hypertrophy include blood oxygenation, cell swelling, and changes in blood flow. The purpose of this study was to compare the acute changes of these parameters in human skeletal muscle induced by low-load (20% 1-RM) blood flow-restricted (BFR-20) knee extensor exercise compared with free-flow work-matched (FF-20WM) and free-flow 50% 1-RM (FF-50) knee extensor exercise using multimodal magnetic resonance imaging (MRI). Subjects (n = 11) completed acute exercise sessions for each exercise mode in an MRI scanner, where interleaved measures of muscle R2 (indicator of edema), [Formula: see text] (indicator of deoxyhemoglobin), macrovascular blood flow, and diffusion were performed before, between sets, and after the final set for each exercise protocol. BFR-20 exercise resulted in larger acute decreases in R2 and greater increases in cross-sectional area than FF-20WM and FF-50 (P < 0.01). Blood oxygenation decreased between sets during BFR-20, as indicated by a 13.6% increase in [Formula: see text] values (P < 0.01)), whereas they remained unchanged for FF-20WM and decreased during FF-50 exercise. Quadriceps blood flow between sets was highest for the heavier load (FF-50), averaging 305 mL/min, and lowest for BFR-20 at 123 ± 73 mL/min until post-exercise cuff release, where blood flow rates in BFR-20 exceeded both FF protocols (P < 0.01). Acute changes in diffusion rates were similar for all exercise protocols. This study was able to differentiate the acute exercise response of selected physiological factors associated with skeletal muscle hypertrophy. Marked differences in these parameters were found to exist between BFR and FF exercise conditions, which contribute to explain the anabolic potential of low-load blood flow restricted muscle exercise.NEW & NOTEWORTHY Acute changes in blood flow, diffusion, blood oxygenation, cross-sectional area, and the "T2 shift" are evaluated in human skeletal muscle in response to blood flow-restricted (BFR) and conventional free-flow knee extensor exercise performed in an MRI scanner. The acute physiological response to exercise was dependent on the magnitude of load and the application of BFR. Physiological variables changed markedly and established a steady state rapidly after the first of four exercise sets.

Skeletal Muscle Microvascular Changes in Response to Short-Term Blood Flow Restricted Training-Exercise-Induced Adaptations and Signs of Perivascular Stress.

Aim: Previous reports suggest that low-load muscle exercise performed under blood flow restriction (BFR) may lead to endurance adaptations. However, only few and conflicting results exist on the magnitude and timing of microvascular adaptations, overall indicating a lack of angiogenesis with BFR training. The present study, therefore, aimed to examine the effect of short-term high-frequency BFR training on human skeletal muscle vascularization. Methods: Participants completed 3 weeks of high-frequency (one to two daily sessions) training consisting of either BFR exercise [(BFRE) n = 10, 22.8 ± 2.3 years; 20% one-repetition maximum (1RM), 100 mmHg] performed to concentric failure or work-matched free-flow exercise [(CON) n = 8, 21.9 ± 3.0 years; 20% 1RM]. Muscle biopsies [vastus lateralis (VL)] were obtained at baseline, 8 days into the intervention, and 3 and 10 days after cessation of the intervention to examine capillary and perivascular adaptations, as well as angiogenesis-related protein signaling and gene expression. Results: Capillary per myofiber and capillary area (CA) increased 21-24 and 25-34%, respectively, in response to BFRE (P < 0.05-0.01), while capillary density (CD) remained unchanged. Overall, these adaptations led to a consistent elevation (15-16%) in the capillary-to-muscle area ratio following BFRE (P < 0.05-0.01). In addition, evaluation of perivascular properties indicated thickening of the perivascular basal membrane following BFRE. No or only minor changes were observed in CON. Conclusion: This study is the first to show that short-term high-frequency, low-load BFRE can lead to microvascular adaptations (i.e., capillary neoformation and changes in morphology), which may contribute to the endurance effects previously documented with BFR training. The observation of perivascular membrane thickening suggests that high-frequency BFRE may be associated with significant vascular stress.

Age- and Sex-Specific Changes in Lower-Limb Muscle Power Throughout the Lifespan.

BACKGROUND: Our main goal was to evaluate the pattern and time course of changes in relative muscle power and its constituting components throughout the life span. METHODS: A total of 1,305 subjects (729 women and 576 men; aged 20-93 years) participating in the Copenhagen Sarcopenia Study took part. Body mass index (BMI), leg lean mass assessed by dual-energy X-ray absorptiometry (DXA), and leg extension muscle power (LEP) assessed by the Nottingham power rig were recorded. Relative muscle power (normalized to body mass) and specific muscle power (normalized to leg lean mass) were calculated. Segmented regression analyses were used to identify the onset and pattern of age-related changes in the recorded variables. RESULTS: Relative muscle power began to decline above the age of 40 in both women and men, with women showing an attenuation of the decline above 75 years. Relative muscle power decreased with age due to (i) the loss of absolute LEP after the fourth decade of life and (ii) the increase in BMI up to the age of 75 years in women and 65 years in men. The decline in absolute LEP was caused by a decline in specific LEP up to the age of 75 in women and 65 in men, above which the loss in relative leg lean mass also contributed. CONCLUSIONS: Relative power decreased (i) above 40 years by the loss in absolute power (specific power only) and the increase in body mass, and (ii) above ~70 years by the loss in absolute power (both specific power and leg lean mass).

The immune system in sporadic inclusion body myositis patients is not compromised by blood-flow restricted exercise training.

BACKGROUND: Sporadic inclusion body myositis (sIBM) is clinically characterised by progressive proximal and distal muscle weakness and impaired physical function while skeletal muscle tissue displays abnormal cellular infiltration of T cells, macrophages, and dendritic cells. Only limited knowledge exists about the effects of low-load blood flow restriction exercise in sIBM patients, and its effect on the immunological responses at the myocellular level remains unknown. The present study is the first to investigate the longitudinal effects of low-load blood flow restriction exercise on innate and adaptive immune markers in skeletal muscle from sIBM patients. METHODS: Twenty-two biopsy-validated sIBM patients were randomised into either 12 weeks of low-load blood flow restriction exercise (BFRE) or no exercise (CON). Five patients from the control group completed 12 weeks of BFRE immediately following participation in the 12-week control period leading to an intervention group of 16 patients. Muscle biopsies were obtained from either the m. tibialis anterior or the m. vastus lateralis for evaluation of CD3-, CD8-, CD68-, CD206-, CD244- and FOXP3-positive cells by three-colour immunofluorescence microscopy and Visiopharm-based image analysis quantification. A linear mixed model was used for the statistical analysis. RESULTS: Myocellular infiltration of CD3-/CD8+ expressing natural killer cells increased following BFRE (P < 0.05) with no changes in CON. No changes were observed for CD3+/CD8- or CD3+/CD8+ T cells in BFRE or CON. CD3+/CD244+ T cells decreased in CON, while no changes were observed in BFRE. Pronounced infiltration of M1 pro-inflammatory (CD68+/CD206-) and M2 anti-inflammatory (CD68+/CD206+) macrophages were observed at baseline; however, no longitudinal changes in macrophage content were observed for both groups. CONCLUSIONS: Low-load blood flow restriction exercise elicited an upregulation in CD3-/CD8+ expressing natural killer cell content, which suggests that 12 weeks of BFRE training evokes an amplified immune response in sIBM muscle. However, the observation of no changes in macrophage or T cell infiltration in the BFRE-trained patients indicates that patients with sIBM may engage in this type of exercise with no risk of intensified inflammatory activity.

The Copenhagen Sarcopenia Study: lean mass, strength, power, and physical function in a Danish cohort aged 20-93 years.

BACKGROUND: Despite no international consensus on the diagnostic criteria for sarcopenia, low lean mass, muscle strength, and physical function are important risk factors for disability, frailty, and mortality in older individuals, as well as in a wide range of patients with muscle loss. Here, we provide a population-based reference material of total and regional lean body mass, muscle strength/power parameters, and physical function in a healthy cohort of Danish men and women across the lifespan. METHODS: Volunteers aged 20-93 years from the Copenhagen City Heart Study were invited to establish a Danish reference material (Copenhagen Sarcopenia Study) on lean mass characteristics [appendicular lean mass (ALM), iDXA, GE Lunar], muscle function [handgrip strength (HGS), Jamar dynamometer and leg extension power (LEP), Nottingham Power Rig], and physical function [30 s sit-to-stand test (STS), 10-m maximal and habitual gait speed (GS)]. RESULTS: A total of 1305 participants [729 women (age: 56.4 ± 18.9 years, height: 1.66 ± 0.01 m, body mass index: 24.6 ± 4.3 kg/m2 and 576 men, age: 57.0 ± 17.5 years, height: 1.80 ± 0.07 m, body mass index: 26.0 ± 3.9 kg/m2 ] completed all measurements and were included in the present analysis. Lean mass characteristics (TLM, ALM, and ALM/h2 ) decreased with increasing age in both men and women (P < 0.001). Men demonstrated larger absolute and relative total ALM and higher HGS and LEP compared with women at all age intervals (P < 0.001). HGS and LEP decreased progressively with age in both men and women (P < 0.01); 30 s STS performance, habitual GS, and maximal GS decreased at an accellerated rate of decline with increasing age in both men and women (P < 0.001). Habitual GS was reduced in men and women aged ≥70 years, while maximal GS was reduced from the age of ≥60 years compared with young adults (P < 0.001). Regardless of sex, 30 s STS was reduced from the age of ≥50 years compared with the young reference group (P < 0.001) CONCLUSIONS: While the power-based measurements (LEP and 30 s STS) started to decline already at age +50 years, less power-based parameters (GS and HGS) and lean mass characteristics (TLM, ALM, and ALM/h2 ) remained unaltered until after the age of +70 years. Notably, the cut-off thresholds derived in the present study differed from earlier reference data, which underlines the importance of obtaining updated and local reference materials.

Fundamental constraints in synchronous muscle limit superfast motor control in vertebrates.

Superfast muscles (SFMs) are extremely fast synchronous muscles capable of contraction rates up to 250 Hz, enabling precise motor execution at the millisecond time scale. SFM phenotypes have been discovered in most major vertebrate lineages, but it remains unknown whether all SFMs share excitation-contraction coupling pathway adaptations for speed, and if SFMs arose once, or from independent evolutionary events. Here, we demonstrate that to achieve rapid actomyosin crossbridge kinetics bat and songbird SFM express myosin heavy chain genes that are evolutionarily and ontologically distinct. Furthermore, we show that all known SFMs share multiple functional adaptations that minimize excitation-contraction coupling transduction times. Our results suggest that SFM evolved independently in sound-producing organs in ray-finned fish, birds, and mammals, and that SFM phenotypes operate at a maximum operational speed set by fundamental constraints in synchronous muscle. Consequentially, these constraints set a fundamental limit to the maximum speed of fine motor control.

Blood flow restricted training leads to myocellular macrophage infiltration and upregulation of heat shock proteins, but no apparent muscle damage.

KEY POINTS: Muscular contractions performed using a combination of low external loads and partial restriction of limb blood flow appear to induce substantial gains in muscle strength and muscle mass. This exercise regime may initially induce muscular stress and damage; however, the effects of a period of blood flow restricted training on these parameters remain largely unknown. The present study shows that short-term, high-frequency, low-load muscle training performed with partial blood flow restriction does not induce significant muscular damage. However, signs of myocellular stress and inflammation that were observed in the early phase of training and after the training intervention, respectively, may be facilitating the previously reported gains in myogenic satellite cell content and muscle hypertrophy. The present results improve our current knowledge about the physiological effects of low-load muscular contractions performed under blood flow restriction and may provide important information of relevance for future therapeutic treatment of muscular atrophy. ABSTRACT: Previous studies indicate that low-load muscle contractions performed under local blood flow restriction (BFR) may initially induce muscle damage and stress. However, whether these factors are evoked with longitudinal BFR training remains unexplored at the myocellular level. Two distinct study protocols were conducted, covering 3 weeks (3 wk) or one week (1 wk). Subjects performed BFR exercise (100 mmHg, 20% 1RM) to concentric failure (BFRE) (3 wk/1 wk), while controls performed work-matched (LLE) (3 wk) or high-load (HLE; 70% 1RM) (1 wk) free-flow exercise. Muscle biopsies (3 wk) were obtained at baseline (Pre), 8 days into the intervention (Mid8), and 3 and 10 days after training cessation (Post3, Post10) to examine macrophage (M1/M2) content as well as heat shock protein (HSP27/70) and tenascin-C expression. Blood samples (1 wk) were collected before and after (0.1-24 h) the first and last training session to examine markers of muscle damage (creatine kinase), oxidative stress (total antibody capacity, glutathione) and inflammation (monocyte chemotactic protein-1, interleukin-6, tumour necrosis factor α). M1-macrophage content increased 108-165% with BFRE and LLE at Post3 (P < 0.05), while M2-macrophages increased (163%) with BFRE only (P < 0.01). Membrane and intracellular HSP27 expression increased 60-132% at Mid8 with BFRE (P < 0.05-0.01). No or only minor changes were observed in circulating markers of muscle damage, oxidative stress and inflammation. The amplitude, timing and localization of the above changes indicate that only limited muscle damage was evoked with BFRE. This study is the first to show that a period of high-frequency, low-load BFR training does not appear to induce general myocellular damage. However, signs of tissue inflammation and focal myocellular membrane stress and/or reorganization were observed that may be involved in the adaptation processes evoked by BFR muscle exercise.

Physical function and muscle strength in sporadic inclusion body myositis.

INTRODUCTION: In this study, self-reported physical function, functional capacity, and isolated muscle function were investigated in sporadic inclusion body myositis (sIBM) patients. METHODS: The 36-item Short Form (SF-36) Health Survey and 2-min walk test (2MWT), timed up & go test (TUG), and 30-s chair stand performance were evaluated. In addition, patients were tested for knee extensor muscle strength (isokinetic dynamometer) and leg extension power (Nottingham power rig). RESULTS: TUG performance was the strongest predictor of self-reported physical function (r2 = 0.56, P < 0.05). Knee extension strength and between-limb strength asymmetry were the strongest multi-regression indicators of TUG performance (r2 = 0.51, P < 0.05). Strength asymmetry showed the strongest single-factor (negative) association with 2MWT performance (r2 = 0.49, P < 0.05). DISCUSSION: TUG assessment appears to sensitively predict self-perceived physical function in sIBM patients. Notably, between-limb asymmetry in lower limb muscle strength had a substantial negative impact on motor tasks involving gait function. Muscle Nerve 56: E50-E58, 2017.

Delayed Effect of Blood Flow-restricted Resistance Training on Rapid Force Capacity.

PURPOSE: The aim of the present study was to investigate the effect and time course of high-frequent low-load blood flow-restricted (BFR) resistance training on rapid force capacity (i.e., rate of torque development [RTD]). MATERIALS AND METHODS: Ten male subjects (22.8 ± 2.3 yr) performed four sets of knee extensor exercise (20% one-repetition maximum) to concentric failure during concurrent BFR of the thigh (100 mm Hg), and eight work-matched controls (21.9 ± 3.0 yr) trained without BFR (CON). Twenty-three training sessions were performed within 19 d. Maximal slow and fast knee joint velocity muscle strength and rapid force capacity (e.g., RTD) and evoked twitch contractile parameters were assessed before (Pre) and 5 and 12 d after (Post5 and Post12) training. Muscle biopsies were obtained Pre, after 8 d (Mid8), and 3 and 10 d after (Post3 and Post10) training to examine changes in myofiber area and expression of myocellular proteins known to be modified by cellular stress (CaMKII, annexin A6, SNO-CYS). RESULTS: RTD remained unchanged after BFR training at Post5, while increasing 15%-20% Post12 (P < 0.01). Evoked muscle twitch parameters showed a general decline Post5 (P < 0.01) while returning to baseline levels at Post12. All contractile parameters essentially remained unchanged in CON. Elevated CaMKII was observed with BFR training at Post3 (57%) and Post10 (71%) (P < 0.05), whereas SNO-CYS increased in CON at Mid8 (P < 0.05). CONCLUSION: This study is the first to show that low-load resistance exercise performed with BFR leads to marked increases in rapid force capacity (RTD). However, a general delayed adaptive response was observed for voluntary contractile parameters (including RTD) in parallel with a decline and subsequent recovery in evoked contractile properties, suggesting the delayed gain in rapid force capacity mainly have a peripheral origin.

Effects of a multi-component camp-based intervention on inflammatory markers and adipokines in children: A randomized controlled trial.

OBJECTIVE: To examine the effects of a multi-component camp-based intervention on inflammatory markers and adipokines in children. METHODS: One hundred and fifteen children were recruited in Odense, Denmark (2012-2014). The participants were randomly allocated to either the day camp intervention arm (DCIA) or the standard intervention arm (SIA). The intervention for the DCIA consisted of a 6-week camp-based intervention and a 46-week family-based intervention. The SIA was offered one weekly physical activity session for 6 weeks and one educational meeting. C-reactive protein (CRP), monocyte chemoattractant protein-1 (MCP1), leptin, and adiponectin were measured in serum at baseline, 6 weeks and 52 weeks. RESULTS: In comparison with the SIA, the reductions in CRP (P=0.003) and leptin (p<0.001) were larger in the DCIA at 6 weeks. The intervention effects on leptin were significantly mediated by the changes in body fat mass. No intervention effects on CRP and leptin were seen at 52 weeks. No between-group differences in changes in MCP1 and adiponectin were observed at 6 weeks or 52 weeks. CONCLUSIONS: The 6-week camp intervention resulted in reductions in CRP and leptin. The intervention effects did not persist to 52 weeks. The intervention effect on leptin was explained by changes in body fat mass.

Carbohydrate restricted recovery from long term endurance exercise does not affect gene responses involved in mitochondrial biogenesis in highly trained athletes.

The aim was to determine if the metabolic adaptations, particularly PGC-1α and downstream metabolic genes were affected by restricting CHO following an endurance exercise bout in trained endurance athletes. A second aim was to compare baseline expression level of these genes to untrained. Elite endurance athletes (VO2max 66 ± 2 mL·kg(-1)·min(-1), n = 15) completed 4 h cycling at ~56% VO2max. During the first 4 h recovery subjects were provided with either CHO or only H2O and thereafter both groups received CHO. Muscle biopsies were collected before, after, and 4 and 24 h after exercise. Also, resting biopsies were collected from untrained subjects (n = 8). Exercise decreased glycogen by 67.7 ± 4.0% (from 699 ± 26.1 to 239 ± 29.5 mmol·kg(-1)·dw(-1)) with no difference between groups. Whereas 4 h of recovery with CHO partly replenished glycogen, the H2O group remained at post exercise level; nevertheless, the gene expression was not different between groups. Glycogen and most gene expression levels returned to baseline by 24 h in both CHO and H2O. Baseline mRNA expression of NRF-1, COX-IV, GLUT4 and PPAR-α gene targets were higher in trained compared to untrained. Additionally, the proportion of type I muscle fibers positively correlated with baseline mRNA for PGC-1α, TFAM, NRF-1, COX-IV, PPAR-α, and GLUT4 for both trained and untrained. CHO restriction during recovery from glycogen depleting exercise does not improve the mRNA response of markers of mitochondrial biogenesis. Further, baseline gene expression of key metabolic pathways is higher in trained than untrained.