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Concept: Sarcopenia

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Sarcopenia results from the progressive loss of skeletal muscle mass and reduced function in older age. It is likely to be associated with the well-documented reduction of motor unit numbers innervating limb muscles and the increase in size of surviving motor units via reinnervation of denervated fibres. However no evidence currently exists to confirm the extent of motor unit remodelling in sarcopenic individuals. The aim of the present study was to compare motor unit size and number between young (n = 48), non-sarcopenic old (n = 13), pre-sarcopenic (n = 53) and sarcopenic (n = 29) men. Motor unit potentials (MUPs) were isolated from intramuscular and surface electromyographic recordings. The motor unit numbers were reduced in all groups of old compared with young (all P < 0.001). Motor unit potentials were enlarged in non-sarcopenic and pre-sarcopenic men compared with young (P = 0.039 and 0.001 respectively), but not in the VL of sarcopenic old (P = 0.485). The results suggest that extensive motor unit remodelling occurs relatively early during ageing, exceeds the loss of muscle mass and precedes sarcopenia. Reinnervation of denervated muscle fibres likely expands the motor unit size in non-sarcopenic and pre-sarcopenic old, but not in the sarcopenic old. These findings suggest that a failure to expand the motor unit size distinguishes sarcopenic from pre-sarcopenic muscles. This article is protected by copyright. All rights reserved.

Concepts: Muscle, Cardiac muscle, Glycogen, Muscle atrophy, Sarcopenia, Myosin, Electromyography, Muscular system

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An operational definition of musculoskeletal decline in older people is needed to allow development of interventions for prevention or treatment, as was developed for the treatment of osteoporosis. Frailty and sarcopenia are linked, but distinct, correlates of musculoskeletal aging that have many causes, including age-related changes in body composition, inflammation, and hormonal imbalance. With the emergence of a number of exciting candidate therapies to retard the loss of muscle mass with aging, the derivation of a consensual definition of sarcopenia and physical frailty becomes an urgent priority. Although several consensual definitions have been proposed, these require clinical validation. An operational definition, which might provide a threshold for treatment/trial inclusion, should incorporate a loss of muscle mass as well as evidence of a decrease in muscle strength and/or physical activity. Evidence is required for a link between improvements in the measures of muscle strength and/or physical activity and clinical outcomes to allow development of interventions to improve clinical outcomes in frail older patients.

Concepts: Psychology, Metabolism, Energy, Muscle, Physical exercise, Definition, Muscle atrophy, Sarcopenia

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The balance between the rates of protein synthesis and protein degradation governs the maintenance of muscle mass in the body. The main purpose of this review is to highlight the latest understanding of the various pathways that maintain this balance between muscle atrophy and hypertrophy.

Concepts: Metabolism, Muscle, Actin, Muscle atrophy, Sarcopenia, Muscular system, Peptide synthesis, Atrophy

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This paper reviews the health implications of obesity, sarcopenia and sarcopenic obesity on CVD and mortality in older adults and discusses the obesity paradox seen in patients with CVD. Obesity is a major public health problem with increasing prevalence worldwide. It is an established risk factor for cardiovascular morbidity and mortality in adult populations. However, there is controversy surrounding the effects of obesity as measured by BMI in older people, and overweight and obesity (BMI ⩾ 25 kg/m2) are apparently associated with increased survival in those with CVD (obesity paradox). Ageing is associated with an increase in visceral fat and a progressive loss of muscle mass which have opposing effects on mortality. Thus BMI is not a good indicator of obesity in older adults. Sarcopenia, the age-associated loss of skeletal muscle mass, is a major concern in ageing populations and has been associated with metabolic impairment, CVD risk factors, physical disability and mortality. Sarcopenia often coexists with obesity. Sarcopenic obesity is a new category of obesity in older adults who have high adiposity coupled with low muscle mass. To fully understand the effect of obesity on mortality in the elderly it is important to take muscle mass into account. The evidence suggests that sarcopenia with obesity may be associated with higher levels of metabolic disorders and an increased risk of mortality than obesity or sarcopenia alone. Efforts to promote healthy ageing should focus on both preventing obesity and maintaining or increasing muscle mass.

Concepts: Epidemiology, Middle age, Obesity, Muscle, Muscle atrophy, Old age, Sarcopenia, Geriatrics

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By the sixth decade of life, nearly one quarter of the population has substantial muscle atrophy, or sarcopenia. Despite the creation of a standardized definition of sarcopenia by the European Working Group on Sarcopenia in Older People, variability may exist in the diagnostic criteria utilized for clinical sarcopenia research. The primary objectives of this review were to characterize diagnostic criteria used for measurement of sarcopenia in original studies, and to describe associations between sarcopenia and important clinical outcomes. We performed a literature review of the term “sarcopenia” in PubMed. Inclusion criteria were English language, original data, a clear and specific definition for diagnosing sarcopenia, and the analysis of sarcopenia’s effect on a clinical outcome. A total of 283 studies met inclusion criteria. More than half of the included sarcopenia investigations were level IV studies (54.1%), while 43.1% provided level II evidence. Under one third (27.6%) of studies examined sarcopenia with regard to surgical outcomes. In terms of diagnostic criteria for sarcopenia, 264 (93.3%) studies used measures of skeletal muscle mass, with dual energy X-ray absorptiometry (DEXA) being the most common modality (43.6%). Sarcopenia was found to be a consistent predictor of chronic disease progression, all-cause mortality, poorer functional outcomes, and postoperative complications. In conclusion, there is substantial evidence that sarcopenia impacts both medical and surgical outcomes. However, current research has utilized heterogeneous diagnostic criteria for sarcopenia. Further efforts to standardize the modalities used to diagnose sarcopenia in clinical research and practice will help strengthen our ability to study this important phenomenon.

Concepts: Osteoporosis, Medicine, Diagnosis, Muscle, Muscle atrophy, Sarcopenia, Clinical research, Atrophy

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Sarcopenia is the age-related loss of muscle mass, strength, and function. It is a common finding in older patients and is associated with decreased life expectancy and potentially higher susceptibility to chemotherapy toxicity. This study describes the prevalence of sarcopenia in older adults with early stage colorectal cancer.

Concepts: Cancer, Oncology, Energy, Chemotherapy, Muscle, Colorectal cancer, Muscle atrophy, Sarcopenia

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Low muscle mass and weakness are common and potentially disabling in older adults, but in order to become recognized as a clinical condition, criteria for diagnosis should be based on clinically relevant thresholds and independently validated. The Foundation for the National Institutes of Health Biomarkers Consortium Sarcopenia Project used an evidence-based approach to develop these criteria. Initial findings were presented at a conference in May 2012, which generated recommendations that guided additional analyses to determine final recommended criteria. Details of the Project and its findings are presented in four accompanying manuscripts.

Concepts: Muscle, Muscle atrophy, Sarcopenia, Muscular system, Clinical death, Illuminated manuscript

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Inadequate nutrition and physical inactivity are the mainstays of primary sarcopenia-physiopathology in older individuals. Gut microbiota composition is strongly dependent on both of these elements, and conversely, can also influence the host physiology by modulating systemic inflammation, anabolism, insulin sensitivity, and energy production. The bacterial metabolism of nutrients theoretically influences skeletal muscle cell functionality through producing mediators that drive all of these systemic effects. In this study, we review the scientific literature supporting the concept of the involvement of gut microbiota in primary sarcopenia physiopathology. First, we examine studies associating fecal microbiota alterations with physical frailty, i.e., the loss of muscle performance and normal muscle mass. Then, we consider studies exploring the effects of exercise on gut microbiota composition. Finally, we examine studies demonstrating the possible effects of mediators produced by gut microbiota on skeletal muscle, and intervention studies considering the effects of prebiotic or probiotic administration on muscle function. Even if there is no evidence of a distinct gut microbiota composition in older sarcopenic patients, we conclude that the literature supports the possible presence of a “gut-muscle axis”, whereby gut microbiota may act as the mediator of the effects of nutrition on muscle cells.

Concepts: Bacteria, Gut flora, Metabolism, Obesity, Muscle, Cardiac muscle, Glycogen, Sarcopenia

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The growing recognition of sarcopenia, the age-related loss of skeletal muscle mass and function, has highlighted the need to understand more about its etiology. Declines in muscle mass and strength are expected aspects of aging, but there is significant variability between individuals in rates of loss. Although some of these differences can be explained by fixed factors, such as sex, much of the remaining variation is unexplained. This has led to increasing interest in the influence of adult lifestyle, particularly in the effects of modifiable factors such as physical activity and diet, and in identifying intervention opportunities both to prevent and manage sarcopenia. A number of trials have examined the separate effects of increased exercise or dietary supplementation on muscle mass and physical performance of older adults, but less is known about the extent to which benefits of exercise training could be enhanced when these interventions are combined. In a comprehensive review of the literature, we consider 17 studies of older adults (≥65 years) in which combined nutrition and exercise interventions were used to increase muscle strength and/or mass, and achieve improvements in physical performance. The studies were diverse in terms of the participants included (nutritional status, degree of physical frailty), supplementation strategies (differences in nutrients, doses), exercise training (type, frequency), as well as design (duration, setting). The main message is that enhanced benefits of exercise training, when combined with dietary supplementation, have been shown in some trials - indicating potential for future interventions, but that existing evidence is inconsistent. Further studies are needed, particularly of exercise training combined with dietary strategies that increase intakes of a range of nutrients, as well as bioactive non-nutrients, to provide the evidence on which public health and clinical recommendations can be based.

Concepts: Nutrition, Energy, Obesity, Muscle, Physical exercise, Glycogen, Sarcopenia, Exercise physiology

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All proposed definitions of sarcopenia include the measurement of muscle mass, but the techniques and threshold values used vary. Indeed, the literature does not establish consensus on the best technique for measuring lean body mass. Thus, the objective measurement of sarcopenia is hampered by limitations intrinsic to assessment tools. The aim of this study was to review the methods to assess muscle mass and to reach consensus on the development of a reference standard.

Concepts: Metrology, Muscle, Educational psychology, Psychometrics, Muscle atrophy, Sarcopenia, Test method, 2006 albums