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Assessment of a low skeletal muscle mass (SM) is important for diagnosis of ageing and disease-associated sarcopenia and is hindered by heterogeneous methods and terminologies that lead to differences in diagnostic criteria among studies and even among consensus definitions. The aim of this review was to analyze and summarize previously published cut-offs for SM applied in clinical and research settings and to facilitate comparison of results between studies. Multiple published reference values for discrepant parameters of SM were identified from 64 studies and the underlying methodological assumptions and limitations are compared including different concepts for normalization of SM for body size and fat mass (FM). Single computed tomography or magnetic resonance imaging images and appendicular lean soft tissue by dual X-ray absorptiometry (DXA) or bioelectrical impedance analysis (BIA) are taken as a valid substitute of total SM because they show a high correlation with results from whole body imaging in cross-sectional and longitudinal analyses. However, the random error of these methods limits the applicability of these substitutes in the assessment of individual cases and together with the systematic error limits the accurate detection of changes in SM. Adverse effects of obesity on muscle quality and function may lead to an underestimation of sarcopenia in obesity and may justify normalization of SM for FM. In conclusion, results for SM can only be compared with reference values using the same method, BIA- or DXA-device and an appropriate reference population. Limitations of proxies for total SM as well as normalization of SM for FM are important content-related issues that need to be considered in longitudinal studies, populations with obesity or older subjects.

This study aimed to investigate the gut microbial genera associated with skeletal muscle mass, using a large-scale survey from the standpoint of preventing sarcopenia. A total of 848 participants were included in the analysis. The mean (SD) ages of men (n = 353) and women (n = 495) were 50.0 (12.9) years and 50.8 (12.8) years, respectively. Body composition was assessed using appendicular skeletal muscle mass/body weight (ASM/BW), ASM, and BW. Additionally, the relationship between gut microbial genera and body composition was analyzed. The means (SD) of ASM/BW were 34.9 (2.4) % in men and 29.4 (2.9) % in women. Blautia and Bifidobacterium were positively associated with ASM/BW only in men (Blautia: β = 0.0003, Bifidobacterium: β = 0.0001). However, Blautia was negatively associated with BW (β = −0.0017). Eisenbergiella was positively associated with ASM/BW (β = 0.0209) and negatively associated with BW (β = −0.0769) only in women. Our results indicate that Blautia, Bifidobacterium and Eisenbergiella, which are positively associated with ASM/BW, might help increase skeletal muscle mass. ASM/BW may clarify the relationship between gut microbiota and skeletal muscle mass without being affected by obesity or excess body fat mass.

Background Skeletal muscle mass is subjected to constant changes and is considered a good predictor for outcome in various diseases. Bioelectrical‐impedance analysis (BIA) and magnetic resonance imaging (MRI) are approved methodologies for its assessment. However, muscle mass estimations by BIA may be influenced by excess intramuscular lipids and adipose tissue in obesity. The objective of this study was to evaluate the feasibility of quantitative assessment of skeletal muscle mass by MRI as compared with BIA. Methods Subjects from a population‐based cohort underwent BIA (50 kHz, 0.8 mA) and whole‐body MRI including chemical‐shift encoded MRI (six echo times). Abdominal muscle mass by MRI was quantified as total and fat‐free cross‐sectional area by a standardized manual segmentation‐algorithm and normalized to subjects' body height2 (abdominal muscle mass indices: AMMIMRI). Results Among 335 included subjects (56.3 ± 9.1 years, 56.1% male), 95 (28.4%) were obese (BMI ≥ 30 kg/m2). MRI‐based and BIA‐based measures of muscle mass were strongly correlated, particularly in non‐obese subjects [r < 0.74 in non‐obese (P < 0.001) vs. r < 0.56 in obese (P < 0.001)]. Median AMMITotal(MRI) was significantly higher in obese as compared with non‐obese subjects (3246.7 ± 606.1 mm2/m2 vs. 2839.0 ± 535.8 mm2/m2, P < 0.001, respectively), whereas the ratio AMMIFat‐free/AMMITotal (by MRI) was significantly higher in non‐obese individuals (59.3 ± 10.1% vs. 53.5 ± 10.6%, P < 0.001, respectively). No significant difference was found regarding AMMIFat‐free(MRI) (P = 0.424). In analyses adjusted for age and sex, impaired glucose tolerance and measures of obesity were significantly and positively associated with AMMITotal(MRI) and significantly and inversely with the ratio AMMIFat‐free(MRI)/AMMITotal(MRI) (P < 0.001). Conclusions MRI‐based assessment of muscle mass is feasible in population‐based imaging and strongly correlated with BIA. However, the observed weaker correlation in obese subjects may explain the known limitation of BIA in obesity and promote MRI‐based assessments. Thus, skeletal muscle mass parameters by MRI may serve as practical imaging biomarkers independent of subjects' body weight.

Sarcopenia is an evolving concept and the current definition of sarcopenia includes both a loss of muscle strength and loss of muscle mass. However, despite the increasing knowledge and improved technology, a worldwide operational definition of sarcopenia applicable across racial/ethnic groups and populations lacks consensus. As a result the prevalence of sarcopenia (8 to 40% of older people over 60 years) varies depending on the study sample (namely the age of the sample), the definition, and the assessment tool used. DXA is the main assessment method used to evaluate muscle mass, which is further adjusted to height, weight fat mass, or BMI to obtain an index of sarcopenia. Cross-sectional analyses seemed to prove an association between low muscle mass and functional decline, but these results were not consistent when analysed longitudinally over time. This inconsistency could be due to methodological issues as the selected populations in the cohorts where autonomous, community-dwelling, older people. In this highly active population decreases in muscle mass might be not as important as decreases in strength to predict functional decline. The aim of the present paper was to perform a comprehensive review of the literature on the epidemiology of sarcopenia and its consequences to be presented on November 13th and 14th 2008, at the Carla Workshop.

Background: Patients with type 2 diabetes mellitus (T2DM) have an increased risk of muscle mass reduction. However, the association between muscle mass and mortality in T2DM remains unknown. Methods: This was a historical cohort study with the endpoint of all-cause mortality. This study included 163 Japanese men and 141 postmenopausal women with T2DM whose body compositions were evaluated using dual-energy X-ray absorptiometry. Low muscle mass was defined as a skeletal muscle mass index (SMI) of <7.0 kg/m2 for men and <5.4 kg/m2 for women. Results: During the 6-year follow-up period, 32 men and 14 women died. In a Cox regression analysis adjusted for age, T2DM duration, glycated hemoglobin, serum creatinine, fasting C-peptide, body mass index, and lean body mass were associated with the risk of mortality in men [hazard ratio (HR) = 1.81, 95% confidence interval (CI) = 1.00–3.28 per standard deviation (SD) decrease, p = 0.049] and women (HR = 4.53, 95% CI = 1.14–17.96 per SD decrease, p = 0.032). Neither fat mass nor bone mineral content was associated with mortality. Low SMI was associated with increased mortality in women (HR = 5.97, 95% CI = 1.04–34.37, p = 0.045), while the association between low SMI and mortality was marginal in men (HR = 2.38, 95% CI = 0.92–6.14, p = 0.074). Conclusions: Low muscle mass was independently associated with all-cause mortality in patients with T2DM. The preservation of skeletal muscle mass is important to protect patients with T2DM from increased mortality risk.

The need for developing a simple and effective assessment tool for muscle mass has been increasing in a rapidly aging society. This study aimed to evaluate the feasibility of the surface electromyography (sEMG) parameters for estimating muscle mass. Overall, 212 healthy volunteers participated in this study. Maximal voluntary contraction (MVC) strength and root mean square (RMS) values of motor unit potentials from surface electrodes on each muscle (biceps brachii, triceps brachii, biceps femoris, rectus femoris) during isometric exercises of elbow flexion (EF), elbow extension (EE), knee flexion (KF), knee extension (KE) were acquired. New variables (MeanRMS, MaxRMS, and RatioRMS) were calculated from RMS values according to each exercise. Bioimpedance analysis (BIA) was performed to determine the segmental lean mass (SLM), segmental fat mass (SFM), and appendicular skeletal muscle mass (ASM). Muscle thicknesses were measured using ultrasonography (US). sEMG parameters showed positive correlations with MVC strength, SLM, ASM, and muscle thickness measured by US, but showed negative correlations with SFM. An equation was developed for ASM: ASM = −26.04 + 20.345 × Height + 0.178 × weight − 2.065 × (1, if female; 0, if male) + 0.327 × RatioRMS(KF) + 0.965 × MeanRMS(EE) (SEE = 1.167, adjusted R2 = 0.934). sEMG parameters in controlled conditions may represent overall muscle strength and muscle mass in healthy individuals.

Objectives: To examine the prevalence of sarcopenia and sarcopenic obesity (SO) as defined by different indices, including appendicular skeletal muscle mass (ASM)/height2, skeletal muscle mass index (SMI) and residuals for Korean adults, and to explore the association between SO and metabolic syndrome. Methods: Our study sample included 526 participants (328 women, 198 men) for whom complete data on body composition were collected using available dual X-ray absorptiometry. Modified National Cholesterol Education Program Adult Treatment Panel III criteria were used to identify the individuals with metabolic syndrome. Results: The prevalence of sarcopenia and SO is higher in older adults. Using two s.d. of ASM/height2 below reference values from young, healthy adults as a definition of sarcopenia, the prevalence of sarcopenia and SO was 6.3% and 1.3% in older (60 years) men and 4.1% and 0.8% in older women, respectively. The prevalence of sarcopenia using the residuals method was 15.4% in older men and 22.3% in older women. In addition, using two s.d. of SMI, the prevalence of sarcopenia and SO was 5.1% and 5.1%, respectively, in older men and 14.2% and 12.5%, respectively, in older women. Among women, SO subjects defined by the SMI had three times the risk of metabolic syndrome (odds ratios (OR)=3.24, 95% confidence interval (CI)=1.21-8.66) and non-sarcopenic obese subjects had approximately twice the risk of metabolic syndrome (OR=2.17, 95% CI=1.22-3.88) compared with normal subjects. Similar trends were observed in men. Conclusion: The prevalence and cutoff values of sarcopenia and SO in the Korean population were evaluated using different methods. Among the different indices of sarcopenia and SO, SO only defined using the SMI was associated with the risk of metabolic syndrome. As the Korean population gets older and more obese, the problematics of SO need to be elucidate.

•The high aspartate aminotransferase to alanine aminotransferase ratio was an independent adverse indicator for the presence of low muscle mass, except in the overweight population and patients with metabolic syndrome.•By multiple general linear regression analysis, a formula was constructed to calculate the skeletal muscle mass index.•When people with abnormal liver function were excluded, the aspartate aminotransferase to alanine aminotransferase ratio remained significantly associated with the prevalence of low muscle mass. The aspartate aminotransferase to alanine aminotransferase (AST/ALT) ratio, an indicator for liver fibrosis, could be easily detected in clinical practice. The aim of this study was to examine the association between the AST/ALT ratio and skeletal muscle mass among Chinese community adult residents. We enrolled 2644 participants, age ≥18 y, undergoing bioelectrical impedance analysis and liver function test. Univariate and multivariate logistic regression models were used to analyze the effect of the AST/ALT ratio on the presence of low muscle mass (LMM). Multiple linear regression analysis was used to assess the factors associated with the skeletal muscle mass index (SMI) and to construct a formula to calculate the SMI. When the AST/ALT ratio was regarded as a categorical variable, AST/ALT quartiles 9-2.19) kept independent effects on the presence of LMM status. When it was regarded as a continuous variable, each unit of the AST/ALT ratio was significantly associated with a 49% (P < 0.01) augment of the prevalence of LMM. By multiple general linear regression analysis, the formula was constructed with an adjusted R2 of 0.72: SMI (kg/m2) = –0.14 AST/ALT ratio + 1.35 sex (male: 1; female: 0) + 0.72 overweight status (yes: 1; no: 0) – 0.14 age (≤65: 0; >65: 1) + 6.26. In general, the high AST/ALT ratio was an independent adverse indicator of the presence of LMM.

•We developed and validated two equations to predict appendicular skeletal muscle mass.•The simpler equation used handgrip strength, body weight, and body height.•The more accurate equation used 24-h urinary creatinine excretion volume, handgrip strength, body weight, and body height.•The appendicular skeletal muscle mass estimated by these equations showed a strong correlation with the measured appendicular skeletal muscle mass.•The estimated skeletal muscle mass index accurately discriminated the sarcopenia cutoff value. Muscle mass is typically assessed by abdominal computed tomography, magnetic resonance imaging, and dual-energy x-ray absorptiometry. However, these tests are not routinely performed in patients with head and neck cancer (HNC), making sarcopenia assessment difficult. The aim of this study was to develop and validate equations for predicting appendicular skeletal muscle mass (ASM) from data obtained in daily medical practice, with bioelectrical impedance analysis (BIA)-measured appendicular skeletal muscle mass (BIA-ASM) as a reference. This cross-sectional study included 103 men with HNC who were randomly placed into development and validation groups. The prediction equations for BIA-ASM were developed by multiple regression analysis and validated by Bland–Altman analyses. The estimated skeletal muscle mass index (eSMI) was also statistically evaluated to discriminate the cutoff value for BIA-measured SMI according to the Asian Working Groups for Sarcopenia. Two practical equations, which included 24-h urinary creatinine excretion volume (24hUCrV), handgrip strength (HGS), body weight (BW), and body height (BHt), were developed: ASM (kg) = −39.46 + (3.557 × 24hUCrV [g]) + (0.08872 × HGS [kg]) + (0.1263 × BW [kg]) + (0.2661 × BHt [cm]) if available for 24hUCrV (adjusted R2 = 0.8905), and ASM (kg) = −42.60 + (0.1643 × HGS [kg]) + (0.1589 × BW [kg]) + (0.2807 × BHt [cm]) if not (adjusted R2 = 0.8589). ASM estimated by these two equations showed a significantly strong correlation with BIA-ASM (R > 0.900). Bland–Altman analyses showed a good agreement, and eSMI accuracy was high (>80%) in both equations. These two equations are a valid option for estimating ASM and diagnosing sarcopenia in patients with HNC in all facilities without special equipment.

As a widely distributed and natural existing antioxidant, ferulic acid and its functions have been extensively studied in recent decades. In the present study, hypertrophic growth of fast skeletal myofibers was observed in adult zebrafish after ferulic acid administration for 30 days, being reflected in increased body weight, body mass index (BMI), and muscle mass, along with an enlarged cross-sectional area of myofibers. qRT-PCR analyses demonstrated the up-regulation of relative mRNA expression levels of myogenic transcriptional factors (MyoD, myogenin and serum response factor (SRF)) and their target genes encoding sarcomeric unit proteins involved in muscular hypertrophy (skeletal alpha-actin, myosin heavy chain, tropomyosin, and troponin I). Western blot analyses detected a higher phosphorylated level of zTOR (zebrafish target of rapamycin), p70S6K, and 4E-BP1, which suggests an enhanced translation efficiency and protein synthesis capacity of fast skeletal muscle myofibers. These changes in transcription and translation finally converge and lead to higher protein contents in myofibers, as confirmed by elevated levels of myosin heavy chain (MyHC), and an increased muscle mass. To the best of our knowledge, these findings have been reported for the first time in vivo and suggest potential applications of ferulic acid as functional food additives and dietary supplements owing to its ability to promote muscle growth.