Progressive loss of skeletal muscle mass with aging (sarcopenia) forms a global health concern. It has been suggested that an impaired capacity to increase muscle protein synthesis rates in response ...to protein intake is a key contributor to sarcopenia. We assessed whether differences in post-absorptive and/or post-prandial muscle protein synthesis rates exist between large cohorts of healthy young and older men.
We performed a cross-sectional, retrospective study comparing in vivo post-absorptive muscle protein synthesis rates determined with stable isotope methodologies between 34 healthy young (22±1 y) and 72 older (75±1 y) men, and post-prandial muscle protein synthesis rates between 35 healthy young (22±1 y) and 40 older (74±1 y) men.
Post-absorptive muscle protein synthesis rates did not differ significantly between the young and older group. Post-prandial muscle protein synthesis rates were 16% lower in the older subjects when compared with the young. Muscle protein synthesis rates were >3 fold more responsive to dietary protein ingestion in the young. Irrespective of age, there was a strong negative correlation between post-absorptive muscle protein synthesis rates and the increase in muscle protein synthesis rate following protein ingestion.
Aging is associated with the development of muscle anabolic inflexibility which represents a key physiological mechanism underpinning sarcopenia.
Ageing is accompanied by a progressive loss of skeletal muscle mass and strength, leading to the loss of functional capacity and an increased risk for developing chronic metabolic diseases such as ...diabetes. The age-related loss of skeletal muscle mass results from a chronic disruption in the balance between muscle protein synthesis and degradation. As basal muscle protein synthesis rates are likely not different between healthy young and elderly human subjects, it was proposed that muscles from older adults lack the ability to regulate the protein synthetic response to anabolic stimuli, such as food intake and physical activity. Indeed, the dose-response relationship between myofibrillar protein synthesis and the availability of essential amino acids and/or resistance exercise intensity is shifted down and to the right in elderly human subjects. This so-called 'anabolic resistance' represents a key factor responsible for the age-related decline in skeletal muscle mass. Interestingly, long-term resistance exercise training is effective as a therapeutic intervention to augment skeletal muscle mass, and improves functional performance in the elderly. The consumption of different types of proteins, i.e. protein hydrolysates, can have different stimulatory effects on muscle protein synthesis in the elderly, which may be due to their higher rate of digestion and absorption. Current research aims to elucidate the interactions between nutrition, exercise and the skeletal muscle adaptive response that will define more effective strategies to maximise the therapeutic benefits of lifestyle interventions in the elderly.
Abstract Purpose This study aimed to (1) document patterns of quadriceps muscle wasting in the first 10 days of admission and (2) determine the relationship between muscle ultrasonography and ...volitional measures. Materials and methods Twenty-two adults ventilated for more than 48 hours were included. Sequential quadriceps ultrasound images were obtained over the first 10 days and at awakening and intensive care unit (ICU) discharge. Muscle strength and function were assessed at awakening and ICU discharge. Results A total of 416 images were analyzed. There was a 30% reduction in vastus intermedius (VI) thickness, rectus femoris (RF) thickness, and cross-sectional area within 10 days of admission. Muscle echogenicity scores increased for both RF and VI muscles by + 12.7% and + 25.5%, respectively (suggesting deterioration in muscle quality). There was a strong association between function and VI thickness ( r = 0.82) and echogenicity ( r = − 0.77). There was a moderate association between function and RF cross-sectional area ( r = 0.71). Conclusions Muscle wasting occurs rapidly in the ICU setting. Ultrasonography is a useful surrogate measure for identifying future impairment. Vastus intermedius may be an important muscle to monitor in the future because it demonstrated the greatest change in muscle quality and had the strongest relationship to volitional measures.
1 Department of Human Movement Sciences, Nutrition, and Toxicology Research Institute Maastricht, Maastricht University, Maastricht, The Netherlands; and 2 Basic and Clinical Myology Laboratory, ...Department of Physiology, The University of Melbourne, Melbourne, Victoria, Australia
ABSTRACT
Aging is accompanied by a progressive loss of skeletal muscle mass and strength, leading to the loss of functional capacity and an increased risk of developing chronic metabolic disease. The age-related loss of skeletal muscle mass is attributed to a disruption in the regulation of skeletal muscle protein turnover, resulting in an imbalance between muscle protein synthesis and degradation. As basal (fasting) muscle protein synthesis rates do not seem to differ substantially between the young and elderly, many research groups have started to focus on the muscle protein synthetic response to the main anabolic stimuli, i.e., food intake and physical activity. Recent studies suggest that the muscle protein synthetic response to food intake is blunted in the elderly. The latter is now believed to represent a key factor responsible for the age-related decline in skeletal muscle mass. Physical activity and/or exercise stimulate postexercise muscle protein accretion in both the young and elderly. However, the latter largely depends on the timed administration of amino acids and/or protein before, during, and/or after exercise. Prolonged resistance type exercise training represents an effective therapeutic strategy to augment skeletal muscle mass and improve functional performance in the elderly. The latter shows that the ability of the muscle protein synthetic machinery to respond to anabolic stimuli is preserved up to very old age. Research is warranted to elucidate the interaction between nutrition, exercise, and the skeletal muscle adaptive response. The latter is needed to define more effective strategies that will maximize the therapeutic benefits of lifestyle intervention in the elderly.
sarcopenia; nutrition; exercise training; muscle hypertrophy
Address for reprint requests and other correspondence: L. J. C. van Loon, Dept. of Human Movement Sciences, Maastricht Univ., PO Box 616, 6200 MD Maastricht, The Netherlands (e-mail: L.vanLoon{at}HB.unimaas.nl )
Sarcopenia describes the age-related loss of skeletal muscle mass and associated muscle weakness. Sarcopenia is a major global health problem given that the number and proportion of older people in ...the population is escalating worldwide and represent the fastest growing segment of society. The loss of muscle mass compromises physical capacity, increases susceptibility to falls, and impacts on an individual's functional independence and quality of life. Tackling sarcopenia sensibly and effectively will identify strategies that will enable older adults to age well and age productively. The underlying causes of sarcopenia are complex and multifactorial and will likely require combinatorial therapies to address its symptoms. Nutrition, particularly protein intake, is a more easily modifiable factor, especially when combined with structured (resistance) exercise programs. The relative success of protein feeding strategies for sarcopenia, is limited by a so-called anabolic resistance in older people. Meat contains essential amino acids and nutritive compounds of high quality, and even a moderate intake can increase muscle protein synthesis in older men and women. However, health risks have been identified with the consumption of different meats, with high intake of processed meats increasing the risk for cardiovascular disease and different cancers. Risks for fresh white and red meat are considerably less and modest consumption is encouraged as part of a healthy eating plan for many older adults to ensure adequate protein intake. Other nutritive strategies of relevance for sarcopenia involve fortifying the nutrient value of different meats. Studies on muscle cells and animal models of muscle wasting, have identified the therapeutic potential of the amino acid, glycine, to reduce inflammation, attenuate muscle atrophy, and re-sensitize muscle to anabolic stimuli. Glycine supplementation or feeding animal products with a high glycine content (e.g. gelatin), could represent simple and effective nutritional strategies as part of a suite of therapies to attenuate sarcopenia.
Background: Sarcopenia seems to be attributed to a blunted muscle protein synthetic response to food intake and exercise. This blunted response could be the result of impaired protein digestion and ...absorption kinetics and lead to lower postprandial plasma amino acid availability.
Objective: The objective was to compare in vivo dietary protein digestion and absorption kinetics and subsequent postprandial muscle protein synthesis rates at rest and after exercise between young and elderly men.
Design: Young and elderly men consumed a 20-g bolus of intrinsically l-1-13Cphenylalanine-labeled protein at rest or after exercise. Continuous infusions with l-ring-2H5phenylalanine were applied, and blood and muscle samples were collected to assess in vivo protein digestion and absorption kinetics and subsequent postprandial muscle protein synthesis rates.
Results: Exogenous phenylalanine appearance rates expressed over time did not differ between groups. No differences were observed in plasma phenylalanine availability between the young (51 ± 2%) and elderly (51 ± 1%) men or between the rest (52 ± 1%) and exercise (49 ± 1%) conditions. Muscle protein synthesis rates calculated from the oral tracer were 0.0620 ± 0.0065%/h and 0.0560 ± 0.0039%/h for the rest condition and 0.0719 ± 0.0057%/h and 0.0727 ± 0.0040%/h for the exercise condition in young and elderly men, respectively (age effect: P = 0.62; exercise effect: P < 0.05; interaction of age and exercise: P = 0.52).
Conclusions: Dietary protein digestion and absorption kinetics are not impaired after exercise or at an older age. Exercising before protein intake allows for a greater use of dietary protein–derived amino acids for de novo muscle protein synthesis in both young and elderly men. This trial was registered at clinicaltrials.gov as NCT00557388.
Purpose
To identify measures used to evaluate the broad constructs of functional impairment and limitations in the critically ill across the continuum of recovery, and to evaluate, synthesise and ...compare the clinimetric properties of the measures identified.
Methods
A systematic review of articles was carried out using the databases Medline (1950–2014), CINAHL (1982–2014), EMBASE (1980–2014), Cochrane Library (2014) and Scopus (1960–2014). Additional studies were identified by searching personal files. Eligibility criteria for selection: Search 1: studies which assessed muscle mass, strength or function using objective non-laboratory measures; Search 2: studies which evaluated a clinimetric property (reliability, measurement error, validity or responsiveness) for one of the measures identified in search one. Two independent reviewers assessed articles for inclusion and assessed risk of bias using the consensus-based standards for selection of health status measurement instruments checklist.
Results
Thirty-three measures were identified; however, only 20 had established clinimetric properties. Ultrasonography, dynamometry, physical function in intensive care test scored and the Chelsea critical care physical assessment tool performed the strongest for the measurement of impairment of body systems (muscle mass and strength) and activity limitations (physical function), respectively.
Conclusions
There is considerable variability in the type of measures utilized to measure physical impairments and limitations in survivors of critical illness. Future work should identify a core set of standardized measures, which can be utilized across the continuum of critical illness recovery embedded within the International Classification of Functioning framework. This will enable improved comparisons between future studies, which in turn will assist in identifying the most effective treatment strategies to ameliorate the devastating longer-term outcomes of a critical illness.
Age-Related Changes in Skeletal Muscle Iron Homeostasis Alves, Francesca M; Ayton, Scott; Bush, Ashley I ...
The journals of gerontology. Series A, Biological sciences and medical sciences,
01/2023, Letnik:
78, Številka:
1
Journal Article
Recenzirano
Sarcopenia is an age-related condition of slow, progressive loss of muscle mass and strength, which contributes to frailty, increased risk of hospitalization and mortality, and increased health care ...costs. The incidence of sarcopenia is predicted to increase to >200 million affected older adults worldwide over the next 40 years, highlighting the urgency for understanding biological mechanisms and developing effective interventions. An understanding of the mechanisms underlying sarcopenia remains incomplete. Iron in the muscle is important for various metabolic functions, including oxygen supply and electron transfer during energy production, yet these same chemical properties of iron may be deleterious to the muscle when either in excess or when biochemically unshackled (eg, in ferroptosis), it can promote oxidative stress and induce inflammation. This review outlines the mechanisms leading to iron overload in muscle with aging and evaluates the evidence for the iron overload hypothesis of sarcopenia. Based on current evidence, studies are needed to (a) determine the mechanisms leading to iron overload in skeletal muscle during aging; and (b) investigate whether skeletal muscles are functionally deficient in iron during aging leading to impairments in oxidative metabolism.
Summary Background and aims The non-essential amino acid, glycine, is often considered biologically neutral, but some studies indicate that it could be an effective anti-inflammatory agent. Since ...inflammation is central to the development of cancer cachexia, glycine supplementation represents a simple, safe and promising treatment. We tested the hypothesis that glycine supplementation reduces skeletal muscle inflammation and preserves muscle mass in tumor-bearing mice. Methods To induce cachexia, CD2F1 mice received a subcutaneous injection of PBS (control, n = 12) or C26 tumor cells ( n = 32) in accordance with the protocols developed by Murphy et al. Murphy KT, Chee A, Trieu J, Naim T, Lynch GS. Importance of functional and metabolic impairments in the characterization of the C-26 murine model of cancer cachexia. Dis Models Mech 2012;5(4):533–545.. Subcutaneous injections of glycine ( n = 16) or PBS ( n = 16) were administered daily for 21 days and at the conclusion of treatment, selected muscles, tumor and adipose tissue were collected and prepared for Real-Time RT-PCR or western blot analysis. Results Glycine attenuated the loss of fat and muscle mass, blunted increases in markers of inflammation (F4/80, P = 0.01 & IL-6 mRNA, P = 0.01) and atrophic signaling (MuRF, P = 0.047; atrogin-1, P = 0.04; LC3B, P = 0.06 and; BNIP3, P = 0.10) and tended to attenuate the loss of body mass ( P = 0.07), muscle function ( P = 0.06), and oxidative stress (GSSG/GSH, P = 0.06 and DHE, P = 0.07) seen in tumor-bearing mice. Preliminary studies that compared the effect of glycine administration with isonitrogenous doses of alanine or citrulline showed that the observed protective effect was specific to glycine. Conclusions Glycine protects skeletal muscle from cancer-induced wasting and loss of function, reduces the oxidative and inflammatory burden, and reduces the expression of genes associated with muscle protein breakdown in cancer cachexia. Importantly, these effects were glycine specific.
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