Intermuscular fat: a review of the consequences and causes

Role of Epicardial Adipose Tissue in Health and Disease: A Matter of Fat?

Epicardial adipose tissue (EAT) is a small but very biologically active ectopic fat depot that surrounds the heart. Given its rapid metabolism, thermogenic capacity, unique transcriptome, secretory profile, and simply measurability, epicardial fat has drawn increasing attention among researchers attempting to elucidate its putative role in health and cardiovascular diseases. The cellular crosstalk between epicardial adipocytes and cells of the vascular wall or myocytes is high and suggests a local role for this tissue. The balance between protective and proinflammatory/profibrotic cytokines, chemokines, and adipokines released by EAT seem to be a key element in atherogenesis and could represent a future therapeutic target. EAT amount has been found to predict clinical coronary outcomes. EAT can also modulate cardiac structure and function. Its amount has been associated with atrial fibrillation, coronary artery disease, and sleep apnea syndrome. Conversely, a beiging fat profile of EAT has been identified. In this review, we describe the current state of knowledge regarding the anatomy, physiology and pathophysiological role of EAT, and the factors more globally leading to ectopic fat development. We will also highlight the most recent findings on the origin of this ectopic tissue, and its association with cardiac diseases. © 2017 American Physiological Society. Compr Physiol 7:1051-1082, 2017.

Comparison between Different Measures of Body Fat with Kidney Function Decline and Incident CKD

BACKGROUND AND OBJECTIVES

Although anthropometric measures of body fat are associated with development of CKD, they may not be able to distinguish between various forms of fat and therefore may be less accurate than computed tomography (CT) measures. We compared the association of CT and anthropometric measures of obesity with kidney outcomes in the Health Aging and Body Composition Study.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Participants were recruited from March of 1997 through July of 1998. CT measures included visceral abdominal fat (VAT), subcutaneous adipose tissue (SAT), and intermuscular fat area (IMAT), whereas anthropometric measures included waist circumference (WC) and body mass index (BMI). Kidney outcomes included kidney function (KF) decline (30% decrease in eGFRcysC in follow-up at either year 3 or 10) or incident CKD (follow-up eGFRcysC≤60 ml/min per 1.73 m2 in individuals with baseline GFR>60 ml/min per 1.73 m2). Multivariable logistic regression models and Poisson regression models were used to evaluate the association with decline in KF and incident kidney disease, respectively. We also assessed for the independent associations among the exposure measures by including them in the same model.

RESULTS

Two-thousand four-hundred and eighty-nine individuals were included. Mean age was 74±3 years, 49% were men, 39% were black, 59% were hypertensive, and 15% were diabetic. KF decline occurred in 17% of the population, whereas incident CKD also occurred in 17% of those at risk. In continuous models, SAT, VAT, IMAT, BMI, and WC (per SD increase) were all significantly associated with KF decline. There was a significant interaction between VAT and CKD with regard to KF decline (P=0.01). Only VAT, BMI, and WC were associated with incident CKD. Only VAT remained a significant risk factor for incident CKD when other exposure variables were included in the same model. There was no association between any measure of obesity and kidney outcomes when creatinine values at years 3 and 10 were used to estimate changes in eGFR.

CONCLUSIONS

Anthropometric measures of body fat appear to provide as consistent estimates of KF decline risk as CT measures in elders.

Intermuscular Adipose Tissue Content and Intramyocellular Lipid Fatty Acid Saturation Are Associated with Glucose Homeostasis in Middle-Aged and Older Adults

BACKGROUND

Insulin resistance is associated with the higher content of intermuscular adipose tissue (IMAT) and the saturation of intramyocellular lipid (IMCL), but a paucity of data exist in humans. This study examined associations among IMAT content, IMCL saturation, and fasting glucose concentration in middle-aged and older adults with overweight or obesity.

METHODS

Seventy-five subjects (26 males, 49 females) were recruited and thigh muscle and IMAT were assessed using magnetic resonance imaging. Vastus lateralis tissue was acquired from a subset of nine subjects and IMCL content and saturation were assessed using nonlinear dual complex microscopy.

RESULTS

The characteristics of the 75 subjects were as follows: age 59±11 years, body mass index 30±5 kg/m², fasting glucose concentration 5.2±0.5 mmol/L, fasting insulin concentration 12.2±7.3 μU/mL, fasting homeostatic model assessment of insulin resistance (HOMA-IR) 2.9±2.0 (mean±SD). IMAT to muscle tissue (MT) volume ratio was positively associated with the saturated fatty acid to unsaturated fatty acid ratio in IMCL. IMAT:MT was positively associated with fasting glucose concentration and HOMA-IR. IMCL saturation was positively associated with fasting glucose concentration while muscle cell area, IMCL area, and % IMCL in muscle cell were not associated with fasting glucose concentration.

CONCLUSION

These results indicate that higher intermuscular fat content and IMCL saturation may impact fasting glucose concentration in middle-aged and older adults with overweight or obesity. The centralization of adipose tissue in the appendicular region of the body may promote insulin resistance.

Early body composition, but not body mass, is associated with future accelerated decline in muscle quality

BACKGROUND

Muscle quality (MQ) or strength-to-mass ratio declines with aging, but the rate of MQ change with aging is highly heterogeneous across individuals. The identification of risk factors for accelerated MQ decline may offer clues to identity the underpinning physiological mechanisms and indicate targets for prevention and treatment. Using data from the Baltimore Longitudinal Study of Aging, we tested whether measures of body mass and body composition are associated with differential rates of changes in MQ with aging.

METHODS

Participants included 511 men and women, aged 50 years or older, followed for an average of 4 years (range: 1-8). MQ was operationalized as ratio between knee-extension isokinetic strength and CT-thigh muscle cross-sectional area. Predictors included body mass and body composition measures: weight (kg), body mass index (BMI, kg/m² ), dual-energy x-ray absorptiometry-measured total body fat mass (TFM, kg) and lean mass (TLM, kg), and body fatness (TFM/weight). Covariates were baseline age, sex, race, and body height.

RESULTS

Muscle quality showed a significant linear decline over the time of the follow up (average rate of decline 0.02 Nm/cm² per year, P < .001). Independent of covariates, neither baseline body weight (P = .756) nor BMI (P = .777) was predictive of longitudinal rate of decline in MQ. Instead, higher TFM and lower TLM at baseline predicted steeper longitudinal decline in MQ (P = .036 and P < .001, respectively). In particular, participants with both high TFM and low TLM at baseline experienced the most dramatic decline compared with those with low TFM and high TLM (about 3% per year vs. 0.5% per year, respectively). Participants in the higher tertile of baseline body fatness presented a significantly faster decline of MQ than the rest of the population (P = .021). Similar results were observed when body mass, TFM, and TLM were modeled as time-dependent predictors.

CONCLUSIONS

Body composition, but not weight nor BMI, is associated with future MQ decline, suggesting that preventive strategies aimed at maintaining good MQ with aging should specifically target body composition features.

Geriatric syndromes: new frontiers in HIV and sarcopenia

: HIV infection, in many circumstances, can now be managed as a chronic disease due to the marked increase in life expectancy since the introduction of combination antiretroviral therapy (ART). As the patients who first had access to combination ART age into their 50s and 60s, the effects of chronic HIV infection on health have become an important research focus in HIV infection. People living with HIV appear to exhibit an earlier occurrence of some aging-related conditions compared to people without HIV, in part due to higher rates of comorbidities, high-risk behaviors (e.g. smoking, substance use), chronic immune activation, inflammation, and ART-specific factors. Some studies have even suggested an earlier-than-expected appearance of the 'geriatric syndromes,' which are complex medical syndromes of older adults that are associated with morbidity and mortality. The geriatric syndromes include a wide variety of disease processes ranging from incontinence and dementia to impairments in physical function. This review will focus on one geriatric syndrome, sarcopenia, in older HIV-infected populations, and its relation to other aging syndromes, including frailty and falls. The contribution of HIV itself, ART exposure, and specific comorbidities, and the importance of early recognition and prevention of these aging syndromes will be highlighted.

Macronutrient and alcohol intake is associated with intermuscular adipose tissue in a randomly selected group of younger and older men and women

BACKGROUND

Alcohol and macronutrient intake have been found to be related to general and central body fat distribution. Intermuscular adipose tissue (IMAT) is a small ectopic fat depot located within the muscle bundles. IMAT is important for muscle function, mobility and energy homeostasis and also associated with cardiovascular- and diabetes-related risk factors.

AIM

To test the hypothesis that macronutrient and alcohol intake is associated with IMAT.

METHODS

50 men and 50 women, randomly selected from the general population formed height- and weight-representative age groups of 50 younger (27-31 years) and 50 older (57-61 years) subjects. A dietary questionnaire was used to estimate habitual intake of foods and beverages. Body composition including IMAT was measured with computed tomography.

RESULTS

Energy percent (E%) carbohydrates were negatively associated with IMAT in men (β: -0.6234, P < 0.05) and in younger subjects (β: -0.792, P < 0.05). E% alcohol was positively associated with IMAT in women (β: 2.3663, P < 0.01) and in older subjects (β: 1.232, P < 0.01). In younger individuals, E% protein was positively associated with IMAT (β: 1.840, P < 0.05). Centralized and general body fat distributions were positively associated with IMAT. S- (serum) cholesterol was positively associated with IMAT in men (β: 0.05177, P < 0.01) and younger individuals (β: 0.06701, P < 0.01).

CONCLUSIONS

These cross-sectional analyses showed associations between measures of body fat distribution and IMAT as well as associations between macronutrient- and alcohol intake and IMAT. Since IMAT is situated within the energy demanding striated muscles, our data could suggest that changes in dietary energy intake and macronutrient distribution may induce changes in IMAT in both normal weight and obese subjects.

Sarcopenic obesity or obese sarcopenia: A cross talk between age-associated adipose tissue and skeletal muscle inflammation as a main mechanism of the pathogenesis

Sarcopenia, an age-associated decline in skeletal muscle mass coupled with functional deterioration, may be exacerbated by obesity leading to higher disability, frailty, morbidity and mortality rates. In the combination of sarcopenia and obesity, the state called sarcopenic obesity (SOB), some key age- and obesity-mediated factors and pathways may aggravate sarcopenia. This review will analyze the mechanisms underlying the pathogenesis of SOB. In obese adipose tissue (AT), adipocytes undergo hypertrophy, hyperplasia and activation resulted in accumulation of pro-inflammatory macrophages and other immune cells as well as dysregulated production of various adipokines that together with senescent cells and the immune cell-released cytokines and chemokines create a local pro-inflammatory status. In addition, obese AT is characterized by excessive production and disturbed capacity to store lipids, which accumulate ectopically in skeletal muscle. These intramuscular lipids and their derivatives induce mitochondrial dysfunction characterized by impaired β-oxidation capacity and increased reactive oxygen species formation providing lipotoxic environment and insulin resistance as well as enhanced secretion of some pro-inflammatory myokines capable of inducing muscle dysfunction by auto/paracrine manner. In turn, by endocrine manner, these myokines may exacerbate AT inflammation and also support chronic low grade systemic inflammation (inflammaging), overall establishing a detrimental vicious circle maintaining AT and skeletal muscle inflammation, thus triggering and supporting SOB development. Under these circumstances, we believe that AT inflammation dominates over skeletal muscle inflammation. Thus, in essence, it redirects the vector of processes from "sarcopenia→obesity" to "obesity→sarcopenia". We therefore propose that this condition be defined as "obese sarcopenia", to reflect the direction of the pathological pathway.

The use of magnetic resonance imaging to characterize abnormal body composition phenotypes in youth with Prader-Willi syndrome

INTRODUCTION

Magnetic resonance imaging (MRI) provides detailed assessment of body composition compartments. No studies have employed state-of-the-art MRI methods to accurately examine abdominal adipose tissue (AT) and skeletal muscle in youth with Prader-Willi syndrome (PWS). Therefore, this study aimed to describe AT distribution and skeletal muscle in the abdominal region of youth with PWS using MRI.

METHODS

Anthropometric measures and whole-abdominal T1-weighted MRI were performed in sixteen (5 males and 11 females) youth diagnosed with PWS, and seventeen (10 males and 7 females) youth who did not have PWS (controls). Volume of subcutaneous, visceral, intermuscular, and total AT, and skeletal muscle in the abdominal region were quantified using a semiautomatic procedure. Results were summarized using median and interquartile range (IQR, 25th-75th), and ANCOVA test was used (with age and sex as covariates) to examine differences in body composition compartments between PWS and control group.

RESULTS

PWS group had similar age (10.5, 6.6-13.9 vs. 12.8, 10.0-14.4years; P=0.14) and BMI z-score (0.5, 0.2-1.3 vs. 0.2, -0.3 to 1.0; P=0.33) when compared with controls. Significant differences were observed in absolute volumes of total AT (PWS: 4.1, 2.0-6.6L; control: 2.9, 2.0-4.5L; P=0.01), subcutaneous AT (PWS: 2.8, 1.4-4.8L; control: 1.8, 1.1-3.2L; P=0.01), and intermuscular AT (PWS: 0.3, 0.1-0.4L; control: 0.3, 0.2-0.3L; P<0.005). Visceral AT/subcutaneous AT was lower in PWS (0.4, 0.3-0.5) compared to controls (0.5, 0.4-0.6), P=0.01. In addition, skeletal muscle volume was lower in PWS (1.5, 1.0-2.6L) compared to controls (3.1, 1.6-3.9L), P=0.03. Ratios of abdominal AT compartments to skeletal muscle were all higher in PWS compared to controls (all P<0.005).

CONCLUSIONS

PWS youth have greater abdominal adiposity, particularly subcutaneous AT and intermuscular AT, and lower volume of skeletal muscle compared to controls. The decreased ratio of visceral AT/subcutaneous AT in youth with PWS suggests an improved metabolic profile for the level of adiposity present; however, elevated ratios of AT to skeletal muscle suggest a sarcopenic obesity-like phenotype, which could lead to worse health outcomes.

Relationships between fatty infiltration in the thigh and calf in women with knee osteoarthritis

BACKGROUND

In individuals with knee osteoarthritis (OA), fatty infiltration into thigh muscle is associated with poor physical performance and strength. However, it is not known whether this also occurs in the calf and if this impacts physical function.

AIMS

We investigated the relationships between volumes of intramuscular fat (intraMF), intermuscular fat (IMF), subcutaneous fat (SCF), lean muscle and muscle adiposity, in the thighs compared to the calves of women with knee OA.

METHODS

MRI scans of the thigh and calf were acquired from 20 women over 55 years with knee OA (3.0T Discovery MR750, GE Healthcare). Axial IDEAL (iterative decomposition of water and fat with echo asymmetry and least-squares estimation) fat-separated images were segmented to quantify intraMF, IMF, SCF and lean muscle volumes (SliceOmatic 5.0, Tomovision). Correlation and linear regression analyses were run.

RESULTS

We found a positive relationship between thigh and calf intraMF (R ² = 0.592; B = 5.49; p = 0.001), muscle adiposity (R ² = 0.539; B = 0.567; p = 0.001), and SCF volume (R ² = 0.699; B = 12.847; p = 0.001), controlling for waist-to-hip ratio. Relationships between thigh and calf IMF (R ² = 0.239; B = 7.743; p = 0.061), lean muscle (R ² = 0.245; B = 4.149; p = 0.047) and combined intraMF and IMF volume (R ² = 0.242; B = 6.162; p = 0.044) were not significant.

DISCUSSION

Although a correlation exists between thigh and calf muscle adiposity, intraMF and SCF, this does not hold true for IMF or lean muscle. A greater amount of intraMF infiltration occurs in the thigh compared to the calf of women with knee OA.

CONCLUSION

The calf and thigh may both be involved in pathologic changes in muscle composition in knee OA.

Quantification of whole-body and segmental skeletal muscle mass using phase-sensitive 8-electrode medical bioelectrical impedance devices

Background/Objectives:

Bioelectrical impedance analysis (BIA) provides noninvasive measures of skeletal muscle mass (SMM) and visceral adipose tissue (VAT). This study (i) analyzes the impact of conventional wrist-ankle vs segmental technology and standing vs supine position on BIA equations and (ii) compares BIA validation against magnetic resonance imaging (MRI) and dual X-ray absorptiometry (DXA).

Subjects/Methods:

One hundred and thirty-six healthy Caucasian adults (70 men, 66 women; age 40±12 years) were measured by a phase-sensitive multifrequency BIA (seca medical body composition analyzers 515 and 525). Multiple stepwise regression analysis was used to generate prediction equations. Accuracy was tested vs MRI or DXA in an independent multiethnic population.

Results:

Variance explained by segmental BIA equations ranged between 97% for total SMM_MRI, 91–94% for limb SMM_MRI and 80–81% for VAT with no differences between supine and standing position. When compared with segmental measurements using conventional wrist-ankle technology. the relationship between measured and predicted SMM was slightly deteriorated (r=0.98 vs r=0.99, P<0.05). Although BIA results correctly identified ethnic differences in muscularity and visceral adiposity, the comparison of bias revealed some ethnical effects on the accuracy of BIA equations. The differences between LST_DXA and SMM_MRI at the arms and legs were sizeable and increased with increasing body mass index.

Conclusions:

A high accuracy of phase-sensitive BIA was observed with no difference in goodness of fit between different positions but an improved prediction with segmental compared with conventional wrist-ankle measurement. A correction factor for certain ethnicities may be required. When compared with DXA MRI-based BIA equations are more accurate for predicting muscle mass.

Systemic inflammation, body composition, and physical performance in old community-dwellers

BACKGROUND

Chronic inflammation, changes in body composition, and declining physical function are hallmarks of the ageing process. The aim of the present study was to provide a preliminary characterisation of the relationship among these age-related phenomena via multivariate modelling.

METHODS

Thirty-five old adults (OAs) and 17 young adults (YAs) were enrolled. The volume of skeletal muscle, subcutaneous adipose tissue (SAT), and intermuscular adipose tissue (IMAT) of the thigh was quantified by three-dimensional magnetic resonance imaging. Muscle strength was measured by knee extension strength testing. In OAs, physical performance was further assessed via the Short Physical Performance Battery (SPPB). Multi-block partial least squares-discriminant analysis (PLS-DA) was employed to explore the relationship among inflammatory profiles and functional and imaging parameters. Double cross-validation procedures were used to validate the predictive ability of the PLS-DA model.

RESULTS

The optimal complexity of the PLS-DA model was found to be two latent variables. The proportion of correct classification was 92.3% in calibration (94.1% in YAs and 91.4% in OAs), 84.6% in internal validation (95.3% in YAs and 78.5% in OAs), and 82.6% in external validation (94% in YAs and 76.9% in OAs). Relative to YAs, OAs were characterised by smaller muscle volume, greater IMAT volume, lower muscle strength, and higher levels of myeloperoxidase, P-selectin, soluble intercellular adhesion molecule 1, and vascular cell adhesion molecule 1. Compared with OAs with SPPB >8, those scoring ≤8 were characterised by smaller muscle volume, greater SAT volume, lower muscle strength, and higher levels of interleukin 1 beta, 6, 10, 12, 13, tumour necrosis factor alpha, and granulocyte-macrophage colony-stimulating factor.

CONCLUSIONS

Multi-block PLS-DA identified distinct patterns of relationships among circulating cytokines and functional and imaging parameters in persons of different ages and varying levels of physical performance. The longitudinal implementation of such an innovative strategy could allow for the tracking of health status over time, the early detection of deviations in health trajectories, and the monitoring of response to treatments.

Impact of Mediterranean diet on metabolic syndrome, cancer and longevity

Obesity symbolizes a major public health problem. Overweight and obesity are associated to the occurrence of the metabolic syndrome and to adipose tissue dysfunction. The adipose tissue is metabolically active and an endocrine organ, whose dysregulation causes a low-grade inflammatory state and ectopic fat depositions. The Mediterranean Diet represents a possible therapy for metabolic syndrome, preventing adiposopathy or "sick fat" formation.The Mediterranean Diet exerts protective effects in elderly subjects with and without baseline of chronic diseases. Recent studies have demonstrated a relationship between cancer and obesity. In the US, diet represents amount 30-35% of death causes related to cancer. Currently, the cancer is the second cause of death after cardiovascular diseases worldwide. Furthermore, populations living in the Mediterranean area have a decreased incidence of cancer compared with populations living in Northern Europe or the US, likely due to healthier dietary habits. The bioactive food components have a potential preventive action on cancer. The aims of this review are to evaluate the impact of Mediterranean Diet on onset, progression and regression of metabolic syndrome, cancer and on longevity.

Lifestyle guidelines for managing adverse effects on bone health and body composition in men treated with androgen deprivation therapy for prostate cancer: an update

Background:

Men treated with androgen deprivation therapy (ADT) for prostate cancer are prone to multiple treatment-induced adverse effects, particularly with regard to a deterioration in bone health and altered body composition including decreased lean tissue mass and increased fat mass. These alterations may partially explain the marked increased risk in osteoporosis, falls, fracture and cardiometabolic risk that has been observed in this population.

Methods:

A review was conducted that assessed standard clinical guidelines for the management of ADT-induced adverse effects on bone health and body composition in men with prostate cancer.

Results:

Currently, standard clinical guidelines exist for the management of various bone and metabolic ADT-induced adverse effects in men with prostate cancer. However, an evaluation of the effectiveness of these guidelines into routine practice revealed that men continued to experience increased central adiposity, and, unless pharmacotherapy was instituted, accelerated bone loss and worsening glycaemia occurred.

Conclusions:

This review discusses the current guidelines and some of the limitations, and proposes new recommendations based on emerging evidence regarding the efficacy of lifestyle interventions, particularly with regard to exercise and nutritional factors, to manage ADT-related adverse effects on bone health and body composition in men with prostate cancer.

A novel method for the quantification of fatty infiltration in skeletal muscle

BACKGROUND

Fatty infiltration of the skeletal muscle is a common but poorly understood feature of many myopathies. It is best described in human muscle, where non-invasive imaging techniques and representative histology have been optimized to view and quantify infiltrating fat. However, human studies are limited in their ability to identify cellular and molecular mechanisms regulating fatty infiltration, a likely prerequisite to developing targeted interventions. As mechanistic investigations move to small animals, studies may benefit from new or adapted imaging tools optimized for high resolution and whole muscle quantification.

RESULTS

Here, we describe a novel method to evaluate fatty infiltration, developed for use with mouse muscle. In this methodology, muscle cellular membranes and proteins are removed via decellularization, but fatty infiltrate lipid is spared, trapped in its native distribution in a transparent extracellular matrix construct. This lipid can then be stained with visible or fluorescent dyes and imaged. We present three methods to stain and evaluate lipid in decellularized muscles which can be used individually or combined: (1) qualitative visualization of the amount and 3D spatial distribution of fatty infiltration using visible lipid soluble dye Oil Red O (ORO), (2) quantitative analysis of individual lipid droplet metrics (e.g., volume) via confocal imaging of fluorescent lipid soluble dye boron-dipyrromethene (BODIPY), and (3) quantitative analysis of total lipid content by optical density reading of extracted stained lipid. This methodology was validated by comparing glycerol-induced fatty infiltration between two commonly used mouse strains: 129S1/SvlmJ (129S1) and C57BL/6J (BL/6J). All three methods were able to detect a significant increase in fatty infiltrate volume in the 129S1 muscle compared with that in BL/6J, and methods 1 and 2 additionally described a difference in the distribution of fatty infiltrate, indicating susceptibility to glycerol-induced fatty infiltration is strain-specific.

CONCLUSIONS

With more mechanistic studies of fatty infiltration moving to small animal models, having an alternative to expensive non-invasive imaging techniques and selective representative histology will be beneficial. In this work, we present a method that can quantify both individual adipocyte lipids and whole muscle total fatty infiltrate lipid.

Quantification of intermuscular and intramuscular adipose tissue using magnetic resonance imaging after neurodegenerative disorders

Ectopic adiposity has gained considerable attention because of its tight association with metabolic and cardiovascular health in persons with spinal cord injury (SCI). Ectopic adiposity is characterized by the storage of adipose tissue in non-subcutaneous sites. Magnetic resonance imaging (MRI) has proven to be an effective tool in quantifying ectopic adiposity and provides the opportunity to measure different adipose depots including intermuscular adipose tissue (IMAT) and intramuscular adipose tissue (IntraMAT) or intramuscular fat (IMF). It is highly important to distinguish and clearly define these compartments, because controversy still exists on how to accurately quantify these adipose depots. Investigators have relied on separating muscle from fat pixels based on their characteristic signal intensities. A common technique is plotting a threshold histogram that clearly separates between muscle and fat peaks. The cut-offs to separate between muscle and fat peaks are still not clearly defined and different cut-offs have been identified. This review will outline and compare the Midpoint and Otsu techniques, two methods used to determine the threshold between muscle and fat pixels on T1 weighted MRI. The process of water/fat segmentation using the Dixon method will also be outlined. We are hopeful that this review will trigger more research towards accurately quantifying ectopic adiposity due to its high relevance to cardiometabolic health after SCI.

Skeletal muscle quality as assessed by CT-derived skeletal muscle density is associated with 6-month mortality in mechanically ventilated critically ill patients

Background

Muscle quantity at intensive care unit (ICU) admission has been independently associated with mortality. In addition to quantity, muscle quality may be important for survival. Muscle quality is influenced by fatty infiltration or myosteatosis, which can be assessed on computed tomography (CT) scans by analysing skeletal muscle density (SMD) and the amount of intermuscular adipose tissue (IMAT). We investigated whether CT-derived low skeletal muscle quality at ICU admission is independently associated with 6-month mortality and other clinical outcomes.

Methods

This retrospective study included 491 mechanically ventilated critically ill adult patients with a CT scan of the abdomen made 1 day before to 4 days after ICU admission. Cox regression analysis was used to determine the association between SMD or IMAT and 6-month mortality, with adjustments for Acute Physiological, Age, and Chronic Health Evaluation (APACHE) II score, body mass index (BMI), and skeletal muscle area. Logistic and linear regression analyses were used for other clinical outcomes.

Results

Mean APACHE II score was 24 ± 8 and 6-month mortality was 35.6%. Non-survivors had a lower SMD (25.1 vs. 31.4 Hounsfield Units (HU); p < 0.001), and more IMAT (17.1 vs. 13.3 cm²; p = 0.004). Higher SMD was associated with a lower 6-month mortality (hazard ratio (HR) per 10 HU, 0.640; 95% confidence interval (CI), 0.552–0.742; p < 0.001), and also after correction for APACHE II score, BMI, and skeletal muscle area (HR, 0.774; 95% CI, 0.643–0.931; p = 0.006). Higher IMAT was not significantly associated with higher 6-month mortality after adjustment for confounders. A 10 HU increase in SMD was associated with a 14% shorter hospital length of stay.

Conclusions

Low skeletal muscle quality at ICU admission, as assessed by CT-derived skeletal muscle density, is independently associated with higher 6-month mortality in mechanically ventilated patients. Thus, muscle quality as well as muscle quantity are prognostic factors in the ICU.

Trial registration

Retrospectively registered (initial release on 06/23/2016) at ClinicalTrials.gov: NCT02817646.

Ectopic Fat Depots and Coronary Artery Calcium in South Asians Compared With Other Racial/Ethnic Groups

Background

South Asians have a low body mass index and high prevalence of cardiovascular disease (CVD) relative to other racial/ethnic groups. Radiographically detected ectopic fat distribution is better associated with CVD than body mass index. We assessed whether differences in ectopic fat depots explained differences in the prevalence/severity of coronary artery calcium (CAC), a predictor of incident CVD events, among South Asians compared with other racial/ethnic groups.

Methods and Results

We examined the associations of radiographically detected visceral, intermuscular, intrahepatic, and pericardial fat with CAC among adults without baseline CVD. We compared 803 South Asians in the Mediators of Atherosclerosis in South Asians Living in America to 4 racial/ethnic groups in the Multi‐Ethnic Study of Atherosclerosis: 2622 whites, 1893 blacks, 1496 Latinos, and 803 Chinese Americans. We adjusted for body mass index and known CVD risk factors. South Asians had the highest intrahepatic fat and lowest pericardial fat volume (PFV). There was a positive graded association between ectopic fat and higher CAC scores in all the groups with the strongest associations observed with PFV. PFV was independently associated with CAC severity in South Asians (P=0.01) and blacks (P=0.05) and borderline in whites (P=0.06). PFV partially explained the higher CAC burden in South Asians compared with blacks, but not the other racial/ethnic groups.

Conclusions

Differences in PFV explain a small fraction of the higher CAC burden in South Asians. Our findings suggest that ectopic fat depots may not explain the elevated CAC risk in South Asians.

The effect of obesity on the contractile performance of isolated mouse soleus, EDL, and diaphragm muscles

Obesity affects the major metabolic and cellular processes involved in skeletal muscle contractility. Surprisingly, the effect of obesity on isolated skeletal muscle performance remains unresolved. The present study is the first to examine the muscle-specific changes in contractility following dietary-induced obesity using an isolated muscle work-loop (WL) model that more closely represents in vivo muscle performance. Following 16-wk high-calorific feeding, soleus (SOL), extensor digitorum longus (EDL), and diaphragm (DIA) were isolated from female (CD-1) mice, and contractile performance was compared against a lean control group. Obese SOL produced greater isometric force; however, isometric stress (force per unit muscle area), absolute WL power, and normalized WL power (watts per kilogram muscle mass) were unaffected. Maximal isometric force and absolute WL power of the EDL were similar between groups. For both EDL and DIA, isometric stress and normalized WL power were reduced in the obese groups. Obesity caused a significant reduction in fatigue resistance in all cases. Our findings demonstrate a muscle-specific reduction in contractile performance and muscle quality that is likely related to in vivo mechanical role, fiber type, and metabolic profile, which may in part be related to changes in myosin heavy chain expression and AMP-activated protein kinase activity. These results infer that, beyond the additional requirement of moving a larger body mass, functional performance and quality of life may be further limited by poor muscle function in obese individuals. As such, a reduction in muscle performance may be a substantial contributor to the negative cycle of obesity.

NEW & NOTEWORTHY

The effect of obesity on isolated muscle function is surprisingly underresearched. The present study is the first to examine the effects of obesity on isolated muscle performance using a method that more closely represents real-world muscle function. This work uniquely establishes a muscle-specific profile of mechanical changes in relation to underpinning mechanisms. These findings may be important to understanding the negative cycle of obesity and in designing interventions for improving weight status.

Bilateral changes in muscle architecture of physically active people with chronic stroke: A quantitative muscle ultrasound study

OBJECTIVE

Changes in muscle architecture after stroke are usually assessed by investigating inter-limb differences. As a result bilateral changes of muscle architecture might be missed. Our aim was to investigate whether bilateral architectural changes in skeletal muscle can be detected in chronic, physically active stroke patients using quantitative muscle ultrasound (QMUS).

METHODS

Twenty-eight patients (mean time since stroke 5.2years, median Brunnström stage 4) were recruited. QMUS images were obtained bilaterally from 2 arm and 4 leg muscles. Corrected echogenicity (muscle ultrasound grayvalue) and muscle thickness were compared to reference values obtained from healthy subjects. Correlations of muscle changes with demographic, clinical and neurophysiological characteristics were explored.

RESULTS

Out of 6 muscles, a significant increase in mean echogenicity was found in 4 paretic and 3 non-paretic side muscles. Significant decreases in mean muscle thickness were found in 2 paretic side muscles and 1 non-paretic side muscle. Echogenicity of the medial gastrocnemius correlated moderately with walking speed (inversely) and time since stroke.

CONCLUSIONS

This study showed that QMUS is a feasible technique to investigate architectural changes in skeletal muscles in the chronic phase of stroke and that abnormalities can be found in muscles on both the hemiparetic and non-paretic side.

SIGNIFICANCE

Intriguing data on bilateral changes in muscles of people with stroke is presented. Directions for future research are provided.

Role of Hip Abductor Muscle Composition and Torque in Protective Stepping for Lateral Balance Recovery in Older Adults

OBJECTIVES

To examine differences in hip abductor strength and composition between older adults who primarily use medial step versus cross-step recovery strategies to lateral balance perturbations.

DESIGN

Cross-sectional.

SETTING

University research laboratory.

PARTICIPANTS

Community-dwelling older adults (N=40) divided into medial steppers (n=14) and cross-steppers (n=26) based on the first step of balance recovery after a lateral balance perturbation.

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

Computed tomography scans to quantify lean tissue and intramuscular adipose tissue (IMAT) areas in the hip abductor, hip abductor isokinetic torque, and first step length.

RESULTS

Medial steppers took medial steps in 71.1% of trials versus 4.6% of trials with cross-steps. The cross-steppers when compared with medial steppers, had lower hip abductor IMAT (24.7±0.7% vs 29.9±2.8%; P<.05), greater abductor torque (63.3±3.6Nm vs 48.4±4.1Nm; P<.01), and greater normalized first step length (.75±.03 vs .43±.08; P<.001). There was no difference in hip abductor lean tissue between the groups (P>.05).

CONCLUSIONS

Our findings suggest that older adults who initially use a medial step to recover lateral balance have lower hip abductor torque and may be less able to execute a biomechanically more stable cross-step. This may be related to increased IMAT levels. Assessments and interventions for enhancing balance and decreasing fall risk should take the role of the hip abductor into account.

Sonographic Measurement of the Quadriceps Muscle in Patients With Chronic Obstructive Pulmonary Disease: Functional and Clinical Implications

OBJECTIVES

The purpose of this study was to determine the association between functionality as assessed by the 6-minute walking test (6MWT), maximal voluntary contraction of the quadriceps (MVCQ), and quadriceps thickness and echo intensity as measured by sonography, in patients with chronic obstructive pulmonary disease (COPD).

METHODS

Maximal voluntary contraction of the quadriceps and the thickness and echo intensity of the rectus femoris and vastus intermedius were evaluated in 20 patients with COPD. Functionality was assessed by the 6MWT. Differences between the evaluated muscles were determined by the Student t test. Pearson and Spearman rank correlation coefficients were used to analyze relationships between variables of interest, according to data characteristics. Finally, multivariate regression models were applied.

RESULTS

There was a positive correlation between MVCQ and rectus femoris and vastus intermedius thickness (r = 0.427; P = .030; r = 0.469; P= .018, respectively) and a negative correlation between MVCQ and rectus femoris and vastus intermedius echo intensity (r= -0.500; P= .012; r= -0.482; P= .016). No correlation was found between MVCQ and the 6MWT (r = 0.319; P = .085). Multivariate regression analysis showed that the rectus femoris echo intensity, vastus intermedius echo intensity, and vastus intermedius thickness explained 70% of the variance in the distance walked during the 6MWT.

CONCLUSIONS

These results indicate that, in patients with COPD, both quadriceps force and exercise capacity are associated with quantitative (thickness) and qualitative (echo intensity) characteristics of the quadriceps. Consequently, comprehensive assessments of peripheral muscles should simultaneously include both measurements.

Automated quantification of abdominal adiposity by magnetic resonance imaging

OBJECTIVES

To develop a fully-automated algorithm to process axial magnetic resonance imaging (MRI) slices for quantifying abdominal visceral, subcutaneous and total adipose tissues, i.e., VAT, SAT, and TAT, without human intervention or prior knowledge.

MATERIALS AND METHODS

Fat regions in single MRI slice or sequence (20 slices) were identified with image processing techniques including region-growing, inhomogeneity correction, fuzzy c-means clustering, and active contours segmentation. The MR images of 85 subjects (60 males and 25 females), whose body mass index (BMI) values ranged from 19.96 to 40.35 kg/m2 , were analyzed using the fully-automated algorithm-the automatic method developed in the research and the widely used semi-automated software (sliceOmatic® Tomovision, Inc.)-the reference method.

RESULTS

The proposed automated method showed good performance against the reference method to quantify adipose tissues in both single umbilical slice and MRI sequence. The square of the Pearson correlation coefficients (R2 ) based on the results generated from the two methods for VAT/SAT/TAT were 0.977/0.998/0.997 for single slice data and 0.995/0.999/0.999 for volumetric data. The intra-class correlation of visceral adipose tissue (VAT) between the three operators was 0.939 in the reference method, which was improved to 0.999 in the automatic method. The adipose tissue measurements in the slice at Lumbar 3 vertebra have the highest correlation with the total fat volumes across the entire abdomen.

CONCLUSION

The fully-automated algorithm presented in the paper provides an accurate and reliable assessment of abdominal fat without human intervention. Am. J. Hum. Biol. 28:757-766, 2016. © 2016Wiley Periodicals, Inc.

Longitudinal bone, muscle and adipose tissue changes in physically active subjects - sex differences during adolescence and maturity

OBJECTIVES

To explore changes in bone, muscle and adipose tissue composition in athletes with high physical activity levels at different stages of life.

METHODS

Thigh MRIs were acquired at baseline and 2-year follow-up for 20 young (16±1 years) and 20 mature (46±5 years) athletes (10 males, 10 females, respectively). Longitudinal changes in cross-sectional areas (CSAs) of femoral bone, quadriceps muscle, and thigh subcutaneous (SCF) and intermuscular (IMF) adipose tissue were evaluated.

RESULTS

Adolescent males displayed significant muscle (+5.0%, 95%CI: 0.8, 9.2) and bone growth (+2.9%, 95%CI: 1.3, 4.5), whereas adolescent females did not (muscle: +0.8%, 95%CI: -2.2, 3.8; bone: +1.9%, 95%CI: -2.1, 5.6). Adolescent and mature females showed significant SCF increases (+11.0%, 95%CI: 0.9, 21.1 and +6.0%, 95%CI: 0.6, 11.4, respectively), whereas adolescent and mature males did not (+7.2%, 95%CI: -8.0, 22.5 and +1.5%, 95%CI: -9.7, 11.8, respectively). Muscle and bone changes were highly correlated in adolescent males (r=0.66), mature males (r=0.75) and mature females (r=0.68) but not in adolescent females (r=-0.11).

CONCLUSIONS

The results suggest sex-specific patterns of age-related change in bone, muscle and adipose tissue, and tight coupling of bone and muscle growth. Sex-specific bone-muscle-adipose tissue relationships may have implications for understanding sex differences in fracture risk.

Thermogenic profiling using magnetic resonance imaging of dermal and other adipose tissues

Dermal white adipose tissue (dWAT) was recently recognized for its potential to modify whole body metabolism. Here, we show that dWAT can be quantified using a high-resolution, fat-specific magnetic resonance imaging (MRI) technique. Noninvasive MRI has been used to describe adipocyte depots for many years; the MRI technique we describe uses an advanced fat-specific method to measure the thickness of dWAT, together with the total volume of WAT and the relative activation/fat depletion of brown adipose tissues (BAT). Since skin-embedded adipocytes may provide natural insulation, they provide an important counterpoint to the activation of thermogenic brown and beige adipose tissues, whereby these distinct depots are functionally interrelated and require simultaneous assay. This method was validated using characterized mouse cohorts of a lipodystrophic, dWAT-deficient strain (syndecan-1 KO) and 2 obese models (diet-induced obese mice and genetically obese animals, ob/ob). Using a preliminary cohort of normal human subjects, we found the thickness of skin-associated fat varied 8-fold, from 0.13-1.10 cm; on average, this depot is calculated to weigh 8.8 kg.

Recovery from volumetric muscle loss injury: A comparison between young and aged rats

Termed volumetric muscle loss (VML), the bulk loss of skeletal muscle tissue either through trauma or surgery overwhelms the capacity for repair, leading to the formation of non-contractile scar tissue. The myogenic potential, along with other factors that influence wound repair are known to decline with age. In order to develop effective treatment strategies for VML injuries that are effective across a broad range of patient populations, it is necessary to understand how the response to VML injury is affected by aging. Towards this end, this study was conducted to compare the response of young and aged animal groups to a lower extremity VML injury. Young (3months, n=12) and aged (18months, n=8) male Fischer 344 rats underwent surgical VML injury of the tibialis anterior muscle. Three months after VML injury it was found that young TA muscle was on average 16% heavier than aged muscle when no VML injury was performed and 25% heavier when comparing VML treated young and aged animals (p<0.0001, p<0.0001). Peak contractile force for both the young and aged groups was found to decrease significantly following VML injury, producing 65% and 59% of the contralateral limbs' peak force, respectively (p<0.0001). However, there were no differences found for peak contractile force based on age, suggesting that VML affects muscle's ability to repair, regardless of age. In this study, we used the ratio of collagen I to MyoD expression as a metric for fibrosis vs. myogenesis. Decreasing fiber cross-sectional area with advancing age (p<0.005) coupled with the ratio of collagen I to MyoD expression, which increased with age, supports the thought that regeneration is impaired in the aged population in favor of fibrosis (p=0.0241). This impairment is also exacerbated by the contribution of VML injury, where a 77-fold increase in the ratio of collagen I to MyoD was observed in the aged group (p<0.0002). The aged animal model described in this study provides a tool for investigators exploring not only the development of VML injury strategies but also the effect of aging on muscle regeneration.

Intermuscular adipose tissue and thigh muscle area dynamics during an 18-month randomized weight loss trial

It remains unclear whether intermuscular adipose tissue (IMAT) has any metabolic influence or whether it is merely a marker of abnormalities, as well as what are the effects of specific lifestyle strategies for weight loss on the dynamics of both IMAT and thigh muscle area (TMA). We followed the trajectory of IMAT and TMA during 18-mo lifestyle intervention among 278 sedentary participants with abdominal obesity, using magnetic resonance imaging. We measured the resting metabolic rate (RMR) by an indirect calorimeter. Among 273 eligible participants (47.8 ± 9.3 yr of age), the mean IMAT was 9.6 ± 4.6 cm(2) Baseline IMAT levels were directly correlated with waist circumference, abdominal subdepots, C-reactive protein, and leptin and inversely correlated with baseline TMA and creatinine (P < 0.05 for all). After 18 mo (86.3% adherence), both IMAT (-1.6%) and TMA (-3.3%) significantly decreased (P < 0.01 vs. baseline). The changes in both IMAT and TMA were similar across the lifestyle intervention groups and directly corresponded with moderate weight loss (P < 0.001). IMAT change did not remain independently associated with decreased abdominal subdepots or improved cardiometabolic parameters after adjustments for age, sex, and 18-mo weight loss. In similar models, 18-mo TMA loss remained associated with decreased RMR, decreased activity, and with increased fasting glucose levels and IMAT (P < 0.05 for all). Unlike other fat depots, IMAT may not represent a unique or specific adipose tissue, instead largely reflecting body weight change per se. Moderate weight loss induced a significant decrease in thigh muscle area, suggesting the importance of resistance training to accompany weight loss programs.

Why and How Limb Muscle Mass and Function Should Be Measured in Patients with Chronic Obstructive Pulmonary Disease

Impaired limb muscle function is a common occurrence in patients with chronic obstructive pulmonary disease (COPD), and it negatively influences exercise tolerance, quality of life, and even survival. Assessment of limb muscle mass and function in COPD is highly encouraged; it should include the quadriceps muscle, but other lower and upper limb muscles may also be evaluated to provide valuable information. Quantification of muscle mass as well as assessment of muscle strength and endurance are suggested. Bioelectrical impedance and dual-energy X-ray absorption can be realistically used in the clinical environment to monitor body composition. Although sophisticated computerized dynamometers provide the most accurate assessment, simple exercise and testing equipment are valid alternatives and they should help in implementing limb muscle function assessment in clinical settings. Isometric measurements, using strain-gauges or hand-held dynamometers, should be favored for their simplicity, availability, and quality of information provided. This perspective provides a rationale for the evaluation of limb muscle mass and function in COPD in routine clinical practice. In addition, measurement techniques used to assess limb muscle mass, strength, endurance, and fatigue in various clinical settings are discussed.

Abdominal obesity and hip fracture: results from the Nurses' Health Study and the Health Professionals Follow-up Study

Abdominal obesity might increase fracture risk. We studied the prospective associations between waist circumference, waist-to-hip ratio, and hip fracture. The indicators of abdominal obesity were associated with increased hip fracture risk in women, but not in men. The increased risk was restricted to women with low physical activity.

INTRODUCTION

Low weight is an established risk factor for osteoporosis and hip fracture. However, the association between fat tissue, muscle, and bone is complex, and abdominal obesity might increase fracture risk. We studied the prospective associations between indicators of abdominal obesity and hip fracture in two large US cohorts.

METHODS

At baseline in 1986 and through biennial follow-up, information on hip fracture and potential risk factors was collected in 61,677 postmenopausal women and 35,488 men above age 50. Waist and hip circumferences were reported at baseline and updated twice.

RESULTS

During follow-up, 1168 women and 483 men sustained a hip fracture. After controlling for known risk factors, there was a significant association in women between increasing waist circumference and hip fracture (RR per 10-cm increase 1.13 (95 % CI 1.04-1.23) and between increasing waist-to-hip ratio and hip fracture (RR per 0.1 unit increase 1.14 (95 % CI 1.04-1.23), but these associations were not seen in men. In women, both measures interacted with physical activity. Those in the highest (≥0.90) versus lowest (<0.75) category of waist-to-hip ratio had increased risk of hip fracture if their activity was less than the population median (RR = 1.61, 95 % CI 1.18-2.19) but not if their activity was higher (RR = 1.00, 95 % CI 0.72-1.40). A similar pattern was found for waist circumference.

CONCLUSION

Indicators of abdominal obesity were associated with increased hip fracture risk after controlling for BMI in women. The increased risk was restricted to women with low physical activity. In men, no significant associations were found.

Immunobiological factors aggravating the fatty infiltration on tendons and muscles in rotator cuff lesions

Rotator cuff lesions (RCLs) are a common cause of shoulder pain and dysfunction. The rotator cuff tendons can degenerate and/or tear from the greater tuberosity of the humerus, which is associated with several anatomical, physiological, biochemical, and molecular changes in tendon and muscle. In this article, these pathways are critically reviewed and discussed with various management strategies of RCLs. The article also highlights the immunobiological responses following the RCL and the inherent repair mechanisms elicited by the body. The greatest difficulty in treating this pathology is that the muscle can undergo irreversible fatty infiltration in the setting of chronic tears that is associated with poor surgical outcomes. The article also investigates the key molecular pathways of the muscle homeostasis (mTOR, Rho kinase, AMPK, and Ca(2+)) with the energy metabolism to propose a possible mechanism for fatty infiltration. Future research is warranted to target the key players of these pathways in the management of fatty infiltration and thus RCL.

Body composition and functional assessment of nutritional status in adults: a narrative review of imaging, impedance, strength and functional techniques

The accurate and valid assessment of body composition is essential for the diagnostic evaluation of nutritional status, identifying relevant outcome measures, and determining the effectiveness of current and future nutritional interventions. Developments in technology and our understanding of the influences of body composition on risk and outcome will provide practitioners with new opportunities to enhance current practice and to lead future improvements in practice. This is the second of a two-part narrative review that aims to critically evaluate body composition methodology in diverse adult populations, with a primary focus on its use in the assessment and monitoring of under-nutrition. Part one focused on anthropometric variables [Madden and Smith (2016) J Hum Nutr Diet 29: 7-25] and part two focuses on the use of imaging techniques, bioelectrical impedance analysis, markers of muscle strength and functional status, with particular reference to developments relevant to practice.

Muscle wasting and aging: Experimental models, fatty infiltrations, and prevention

Identification of cost-effective interventions to maintain muscle mass, muscle strength, and physical performance during muscle wasting and aging is an important public health challenge. It requires understanding of the cellular and molecular mechanisms involved. Muscle-deconditioning processes have been deciphered by means of several experimental models, bringing together the opportunities to devise comprehensive analysis of muscle wasting. Studies have increasingly recognized the importance of fatty infiltrations or intermuscular adipose tissue for the age-mediated loss of skeletal-muscle function and emphasized that this new important factor is closely linked to inactivity. The present review aims to address three main points. We first mainly focus on available experimental models involving cell, animal, or human experiments on muscle wasting. We next point out the role of intermuscular adipose tissue in muscle wasting and aging and try to highlight new findings concerning aging and muscle-resident mesenchymal stem cells called fibro/adipogenic progenitors by linking some cellular players implicated in both FAP fate modulation and advancing age. In the last part, we review the main data on the efficiency and molecular and cellular mechanisms by which exercise, replacement hormone therapies, and β-hydroxy-β-methylbutyrate prevent muscle wasting and sarcopenia. Finally, we will discuss a potential therapeutic target of sarcopenia: glucose 6-phosphate dehydrogenase.

Automated assessment of thigh composition using machine learning for Dixon magnetic resonance images

OBJECTIVES

To develop and validate a machine learning based automated segmentation method that jointly analyzes the four contrasts provided by Dixon MRI technique for improved thigh composition segmentation accuracy.

MATERIALS AND METHODS

The automatic detection of body composition is formulized as a three-class classification issue. Each image voxel in the training dataset is assigned with a correct label. A voxel classifier is trained and subsequently used to predict unseen data. Morphological operations are finally applied to generate volumetric segmented images for different structures. We applied this algorithm on datasets of (1) four contrast images, (2) water and fat images, and (3) unsuppressed images acquired from 190 subjects.

RESULTS

The proposed method using four contrasts achieved most accurate and robust segmentation compared to the use of combined fat and water images and the use of unsuppressed image, average Dice coefficients of 0.94 ± 0.03, 0.96 ± 0.03, 0.80 ± 0.03, and 0.97 ± 0.01 has been achieved to bone region, subcutaneous adipose tissue (SAT), inter-muscular adipose tissue (IMAT), and muscle respectively.

CONCLUSION

Our proposed method based on machine learning produces accurate tissue quantification and showed an effective use of large information provided by the four contrast images from Dixon MRI.

Wearable sensors and Mobile Health (mHealth) technologies to assess and promote physical activity in stroke: a narrative review

Stroke is a leading cause of disability worldwide, with approximately one third of people left with permanent deficits impacting on their function. This may contribute to a physically inactive lifestyle and further associated health issues. Current research suggests that people after stroke are not meeting the recommended levels of physical activity, and are less active than people with other chronic illnesses. Thus, it is important to understand how to support people after stroke to uptake and maintain physical activity. Wearable sensors and mobile health (mHealth) technologies are a potential platform to measure and promote physical activity. Some of these technologies may incorporate behaviour change techniques such as real-time feedback. Although wearable activity trackers and smartphone technology are widely available, the feasibility and applicability of these technologies for people after stroke is unclear. This article reviews the devices available for assessment of physical activity in stroke and discusses the potential for advances in technology to promote physical activity in this population.

Muscle function and fat content in relation to sarcopenia, obesity and frailty of old age--An overview

BACKGROUND AND AIM

In western countries, the proportion of people over age 60 is increasing faster than any other group. This is linked to higher rates of obesity. Older age, co-morbidities and obesity are all associated with frailty syndrome. In the core of both frailty and sarcopenia there are dysfunction and deterioration of the muscle and the fat tissues. This overview interlinks the phenotypes presented in older adults such as sarcopenia and frailty-alone and with relation to obesity, muscle function and fat tissue accumulation.

RECENT FINDINGS

Observational studies have well described the loss of muscle mass and strength through the years of adult life, both components of frailty and sarcopenia. They have shown that these changes are associated with dysmetabolism and functional deterioration, independent of common explanatory variables. In the metabolic mechanism core of this link, insulin resistance and higher ectopic fat accumulation may play a role. Basic experiments have partially validated this hypothesis. Whether there is a synergistic effect of obesity and frailty phenotype on morbidity risk is still questionable and currently under investigation; however, few cohort studies have shown that the frail-obese or sarcopenic-obese group have higher probability for metabolic complications.

SUMMARY

Muscle mass loss and fat accumulation in the muscle in the elderly, with or without the presence of obesity, may explain some of the functional and metabolic defects shown in the frail, sarcopenic population.

Muscle Quality and Myosteatosis: Novel Associations With Mortality Risk: The Age, Gene/Environment Susceptibility (AGES)-Reykjavik Study

Muscle composition may affect mortality risk, but prior studies have been limited to specific samples or less precise determination of muscle composition. We evaluated associations of thigh muscle composition, determined using computed tomography imaging, and knee extension strength with mortality risk among 4,824 participants aged 76.4 (standard deviation (SD), 5.5) years from the Age, Gene/Environment Susceptibility (AGES)-Reykjavik Study (2002-2006). Cox proportional hazards models were used to estimate hazard ratios. After 8.8 years of follow-up, there were 1,942 deaths. For men, each SD-increment increase in muscle lean area, muscle quality, and strength was associated with lower mortality risk, with decreases ranging between 11% and 22%. Each SD-increment increase in intermuscular adipose tissue and intramuscular adipose tissue was associated with higher mortality risk (hazard ratio (HR) = 1.13 (95% confidence interval (CI): 1.06, 1.22) and HR = 1.23 (95% CI: 1.15, 1.30), respectively). For women, each SD-increment increase in muscle lean area, muscle quality, and strength was associated with lower mortality risk, with decreases ranging between 12% and 19%. Greater intramuscular adipose tissue was associated with an 8% higher mortality risk (HR = 1.08, 95% CI: 1.01, 1.16). This study shows that muscle composition is associated with mortality risk. These results also show the importance of improving muscle strength and area and lowering muscle adipose tissue infiltration.

Prediction of Cardiorespiratory Fitness by the Six-Minute Step Test and Its Association with Muscle Strength and Power in Sedentary Obese and Lean Young Women: A Cross-Sectional Study

Impaired cardiorespiratory fitness (CRF) is a hallmark characteristic in obese and lean sedentary young women. Peak oxygen consumption (VO_2peak) prediction from the six-minute step test (6MST) has not been established for sedentary females. It is recognized that lower-limb muscle strength and power play a key role during functional activities. The aim of this study was to investigate cardiorespiratory responses during the 6MST and CPX and to develop a predictive equation to estimate VO_2peak in both lean and obese subjects. Additionally we aim to investigate how muscle function impacts functional performance. Lean (LN = 13) and obese (OB = 18) women, aged 20–45, underwent a CPX, two 6MSTs, and isokinetic and isometric knee extensor strength and power evaluations. Regression analysis assessed the ability to predict VO_2peak from the 6MST, age and body mass index (BMI). CPX and 6MST main outcomes were compared between LN and OB and correlated with strength and power variables. CRF, functional capacity, and muscle strength and power were lower in the OB compared to LN (<0.05). During the 6MST, LN and OB reached ~90% of predicted maximal heart rate and ~80% of the VO_2peak obtained during CPX. BMI, age and number of step cycles (NSC) explained 83% of the total variance in VO_2peak. Moderate to strong correlations between VO_2peak at CPX and VO_2peak at 6MST (r = 0.86), VO_2peak at CPX and NSC (r = 0.80), as well as between VO_2peak, NSC and muscle strength and power variables were found (p<0.05). These findings indicate the 6MST, BMI and age accurately predict VO_2peak in both lean and obese young sedentary women. Muscle strength and power were related to measures of aerobic and functional performance.

Intramuscular adipose tissue determined by T1-weighted MRI at 3T primarily reflects extramyocellular lipids

PURPOSE

The purpose of this study was to assess relationships between intramuscular adipose tissue (IntraMAT) content determined by MRI and intramyocellular lipids (IMCL) and extramyocellular lipids (EMCL) determined by (1)H magnetic resonance spectroscopy ((1)H MRS) or echo intensity determined by B-mode ultrasonography of human skeletal muscles.

METHODS

Thirty young and elderly men and women were included. T1-weighted MRI was taken from the right mid-thigh to measure IntraMAT content of the vastus lateralis (VL) and biceps femoris (BF) using a histogram shape-based thresholding technique. IMCL and EMCL were measured from the VL and BF at the right mid-thigh using (1)H MRS. Ultrasonographic images were taken from the VL and BF of the right mid-thigh to measure echo intensity based on gray-scale level for quantitative analysis.

RESULTS

There was a significant correlation between IntraMAT content by MRI and EMCL of the VL and BF (VL, r=0.506, P<0.01; BF, r=0.591, P<0.001) and between echo intensity and EMCL of the VL and BF (VL, r=0.485, P<0.05; BF, r=0.648, P<0.01). IntraMAT content was also significantly correlated with echo intensity of the VL and BF (VL, r=0.404, P<0.05; BF, r=0.493, P<0.01).

CONCLUSION

Our study suggests that IntraMAT content determined by T1-weighted MRI at 3T primarily reflects extramyocellular lipids, not intramyocellular lipids, in human skeletal muscles.

Less favorable body composition and adipokines in South Asians compared with other US ethnic groups: results from the MASALA and MESA studies

Background

Small studies have shown that South Asians (SAs) have more total body, subcutaneous, visceral and hepatic fat and abnormal adipokine levels compared to Whites. However, comprehensive studies of body composition and adipokines in SAs compared to other ethnic groups are lacking.

Methods

Using harmonized data, we performed a cross-sectional analysis of two community-based cohorts: Mediators of Atherosclerosis of South Asians Living in America (MASALA, n=906) and Multi-Ethnic Study of Atherosclerosis (MESA which included 2,622 Whites; 803 Chinese Americans; 1,893 African Americans; and 1,496 Latinos). General linear models were developed to assess ethnic differences in ectopic fat (visceral, intermuscular, and pericardial fat; and hepatic attenuation), lean muscle mass, and adipokines (adiponectin and resistin). Models were adjusted for age, sex, site, alcohol use, smoking, exercise, education, household income and BMI. Ectopic fat models were additionally adjusted for hypertension, diabetes, HDL, and triglycerides. Adipokine models were adjusted for subcutaneous, visceral, intermuscular, and pericardial fat; and hepatic attenuation.

Results

Compared to all ethnic groups in MESA (Whites, Chinese Americans, African Americans, and Latinos), SAs had greater intermuscular fat (pairwise comparisons to each MESA group, p < 0.01), lower hepatic attenuation (p < 0.001), and less lean mass (p < 0.001). SAs had greater visceral fat compared to Chinese Americans, African Americans and Latinos (p < 0.05) and greater pericardial fat compared to African Americans (p < 0.001). SAs had lower adiponectin levels compared to other ethnic groups (p < 0.01; except Chinese Americans) and higher resistin levels than all groups (p < 0.001), even after adjusting for differences in body composition.

Conclusion

There are significant ethnic differences in ectopic fat, lean mass, and adipokines. A less favorable body composition and adipokine profile in South Asians may partially explain the increased predisposition to cardiometabolic disease. The mechanisms that underlie these differences warrant further investigation.

Associations of calf inter- and intra-muscular adipose tissue with cardiometabolic health and physical function in community-dwelling older adults

OBJECTIVES

To determine associations of inter- and intra-muscular adipose tissue (IMAT) with cardiometabolic health and physical function in older adults.

METHODS

48 community-dwelling older adults aged ⋝65 years (mean 71.6±4.8 years; 52% women) underwent whole-body dual-energy X-ray absorptiometry, to assess appendicular lean mass (ALM), and peripheral quantitative computed tomography (pQCT; 66% tibia), to assess calf IMAT cross-sectional area ([CSA]; cm2) and muscle density (mg/cm(3); higher values indicate lower fat infiltration). Fasting glucose, lipids, triglycerides and C-reactive protein (CRP) were analysed. Physical function was assessed by postural sway (computerised posturography; N=41), and gait analysis (GAITRite Electronic Walkway; N=40).

RESULTS

Higher IMAT CSA and muscle density were associated with significantly higher (B=0.85 95%CI [0.34, 1.36]) and lower (-2.14 [-4.20, -0.08]) CRP and higher (0.93 [0.56, 1.30]) and lower postural sway (-3.12 [-4.74, -1.50]), respectively, after adjustment for age, sex and ALM/BMI. Higher IMAT CSA was associated with slower gait speed and cadence, and greater step time and step width (all P<0.03), while higher muscle density was associated with smaller step width (P<0.01) only.

CONCLUSIONS

Older adults with higher calf IMAT have poorer balance, mobility and inflammatory status. Interventions aimed at improving physical function in older adults should incorporate strategies to reduce IMAT.

Quantification of mass fat fraction in fish using water-fat separation MRI

Selection of fish with appropriate fat content and anatomic distribution is searched in fish industry. This necessitates fast and accurate measurements of mass fat fraction maps on a large number of fish. The objective of this work is to assess the relevance of MRI water-fat separation for this purpose. For the separation of the water and fat images we rely on a single T2(⁎) and a multiple peak fat spectrum model, the parameters of which are estimated using the "Varpro" method. The difference of proton density between fat and water and the lack of the signal from the macromolecules are taken into account to convert the obtained proton density fat fraction into mass fat fraction. We used 0.23T NMR to validate the method on 30 salmon steaks. The fat fraction values were in the range of 5% to 25%. Very good accordance was found between 1.5T MRI and NMR although MRI slightly overestimated the mass fat fraction. The R(2) of the linear regression was equal to 0.96 (P<10(-5)), the slope to 1.12 (CI.95=0.03). These results demonstrate that a good accuracy can be achieved. We also show that high throughput can be achieved since the measurements do not depend on the position and we conclude that, for example, it is feasible to quantify the mass fat fraction in fish steaks within about one minute per sample.

Adipogenic progenitors from obese human skeletal muscle give rise to functional white adipocytes that contribute to insulin resistance

BACKGROUND/OBJECTIVES

Recent reports indicate that inter/intramuscular adipose tissue (IMAT), composed by adipocytes underneath the deep fascia of the muscles, is positively correlated with aging, obesity and insulin resistance in humans. However, no molecular/cellular evidence is available to support these interactions. The current study aimed to better characterize human skeletal muscle-derived adipogenic progenitors obtained from obese volunteers and investigate the impact of derived adipocytes on insulin action in primary skeletal muscle cells.

METHODS

Primary cultured stroma-vascular fraction (SVF) obtained from vastus lateralis muscle biopsies of middle-aged obese subjects was immunoseparated (magnetic beads or flow cytometry). The characteristics and/or metabolic phenotype of CD56(+), CD56(-) and CD56(-)CD15(+) cellular fractions were investigated by complementary approaches (flow cytometry, cytology, quantitative PCR and metabolic assays). The effects of conditioned media from CD56(-)CD15(+) cells differentiated into adipocytes on insulin action and signaling in human primary myotubes was also examined.

RESULTS

Our data indicate that CD56(+) and CD56(-) cellular fractions isolated from cultured SVF of human muscle contain two distinct committed progenitors: CD56(+) cells (that is, satellite cells) as myogenic progenitors and CD15(+) cells as adipogenic progenitors, respectively. CD56(-)CD15(+)-derived adipocytes display the phenotype and metabolic properties of white adipocytes. Secretions of CD56(-)CD15(+) cells differentiated into functional white adipocytes reduced insulin-mediated non-oxidative glucose disposal (P=0.0002) and insulin signaling.

CONCLUSIONS

Using in-vitro models, we show for the first time that secretions of skeletal muscle adipocytes are able to impair insulin action and signaling of muscle fibers. This paracrine effect could explain, at least in part, the negative association between high levels of IMAT and insulin sensitivity in obesity and aging.

Measuring Abdominal Circumference and Skeletal Muscle From a Single Cross-Sectional Computed Tomography Image: A Step-by-Step Guide for Clinicians Using National Institutes of Health ImageJ

Diagnostic computed tomography (CT) scans provide numerous opportunities for body composition analysis, including quantification of abdominal circumference, abdominal adipose tissues (subcutaneous, visceral, and intermuscular), and skeletal muscle (SM). CT scans are commonly performed for diagnostic purposes in clinical settings, and methods for estimating abdominal circumference and whole-body SM mass from them have been reported. A supine abdominal circumference is a valid measure of waist circumference (WC). The valid correlation between a single cross-sectional CT image (slice) at third lumbar (L3) for abdominal SM and whole-body SM is also well established. Sarcopenia refers to the age-associated decreased in muscle mass and function. A single dimensional definition of sarcopenia using CT images that includes only assessment of low whole-body SM has been validated in clinical populations and significantly associated with negative outcomes. However, despite the availability and precision of SM data from CT scans and the relationship between these measurements and clinical outcomes, they have not become a routine component of clinical nutrition assessment. Lack of time, training, and expense are potential barriers that prevent clinicians from fully embracing this technique. This tutorial presents a systematic, step-by-step guide to quickly quantify abdominal circumference as a proxy for WC and SM using a cross-sectional CT image from a regional diagnostic CT scan for clinical identification of sarcopenia. Multiple software options are available, but this tutorial uses ImageJ, a free public-domain software developed by the National Institutes of Health.

Adiposity and spinal cord injury

The drastic changes in body composition following spinal cord injury (SCI) have been shown to play a significant role in cardiovascular and metabolic health. The pattern of storage and distribution of different types of adipose tissue may impact metabolic health variables similar to carbohydrate, lipid and bone metabolism. The use of magnetic resonance imaging provides insights on the interplay among different regional adipose tissue compartments and their role in developing chronic diseases. Regional adipose tissue can be either distributed centrally or peripherally into subcutaneous and ectopic sites. The primary ectopic adipose tissue sites are visceral, intramuscular and bone marrow. Dysfunction in the central nervous system following SCI impacts the pattern of distribution of adiposity especially between tetraplegia and paraplegia. The current editorial is focused primarily on introducing different types of adipose tissue and establishing scientific basis to develop appropriate dietary, rehabilitation or pharmaceutical interventions to manage the negative consequences of increasing adiposity after SCI. We have also summarized the clinical implications and future recommendations relevant to study adiposity after SCI.