Muscle fiber size and function in elderly humans: a longitudinal study

Efficacy of whey protein supplementation on resistance exercise-induced changes in lean mass, muscle strength, and physical function in mobility-limited older adults

BACKGROUND

Whey protein supplementation may augment resistance exercise-induced increases in muscle strength and mass. Further studies are required to determine whether this effect extends to mobility-limited older adults. The objectives of the study were to compare the effects of whey protein concentrate (WPC) supplementation to an isocaloric control on changes in whole-body lean mass, mid-thigh muscle cross-sectional area, muscle strength, and stair-climbing performance in older mobility-limited adults in response to 6 months of resistance training (RT).

METHODS

Eighty mobility-limited adults aged 70-85 years were randomized to receive WPC (40g/day) or an isocaloric control for 6 months. All participants also completed a progressive high-intensity RT intervention. Sample sizes were calculated based on the primary outcome of change in whole-body lean mass to give 80% power for a 0.05-level, two-sided test.

RESULTS

Lean mass increased 1.3% and 0.6% in the WPC and control groups, respectively. Muscle cross-sectional area was increased 4.6% and 2.9% in the WPC and control groups, respectively, and muscle strength increased 16%-50% in WPC and control groups. Stair-climbing performance also improved in both groups. However, there were no statistically significant differences in the change in any of these variables between groups.

CONCLUSIONS

These data suggest that WPC supplementation at this dose does not offer additional benefit to the effects of RT in mobility-limited older adults.

Genomic and proteomic profiling reveals reduced mitochondrial function and disruption of the neuromuscular junction driving rat sarcopenia

Molecular mechanisms underlying sarcopenia, the age-related loss of skeletal muscle mass and function, remain unclear. To identify molecular changes that correlated best with sarcopenia and might contribute to its pathogenesis, we determined global gene expression profiles in muscles of rats aged 6, 12, 18, 21, 24, and 27 months. These rats exhibit sarcopenia beginning at 21 months. Correlation of the gene expression versus muscle mass or age changes, and functional annotation analysis identified gene signatures of sarcopenia distinct from gene signatures of aging. Specifically, mitochondrial energy metabolism (e.g., tricarboxylic acid cycle and oxidative phosphorylation) pathway genes were the most downregulated and most significantly correlated with sarcopenia. Also, perturbed were genes/pathways associated with neuromuscular junction patency (providing molecular evidence of sarcopenia-related functional denervation and neuromuscular junction remodeling), protein degradation, and inflammation. Proteomic analysis of samples at 6, 18, and 27 months confirmed the depletion of mitochondrial energy metabolism proteins and neuromuscular junction proteins. Together, these findings suggest that therapeutic approaches that simultaneously stimulate mitochondrogenesis and reduce muscle proteolysis and inflammation have potential for treating sarcopenia.

Increased ceramide content and NFκB signaling may contribute to the attenuation of anabolic signaling after resistance exercise in aged males

One of the most fundamental adaptive physiological events is the response of skeletal muscle to high-intensity resistance exercise, resulting in increased protein synthesis and ultimately larger muscle mass. However, muscle growth in response to contraction is attenuated in older humans. Impaired contractile-induced muscle growth may contribute to sarcopenia: the age-associated loss of muscle mass and function that is manifested by loss of strength, contractile capacity, and endurance. We hypothesized that the storage of ceramide would be increased in older individuals and this would be associated with increases in NFκB signaling and a decreased anabolic response to exercise. To test this hypothesis we measured ceramides at rest and anabolic and NFκB signaling after an acute bout of high-intensity resistance exercise in young and older males. Using lipidomics analysis we show there was a 156% increase in the accumulation of C16:0-ceramide (P < 0.05) and a 30% increase in C20:0-ceramide (P < 0.05) in skeletal muscle with aging, although there was no observable difference in total ceramide. C16:0-ceramide content was negatively correlated (P = 0.008) with lower leg lean mass. Aging was associated with a ~60% increase in the phosphorylation of the proinflammatory transcription factor NFκB in the total and nuclear cell fractions (P < 0.05). Furthermore, there was an attenuated activation of anabolic signaling molecules such as Akt (P < 0.05), FOXO1 (P < 0.05), and S6K1 (P < 0.05) after an acute bout of high-intensity resistance exercise in older males. We conclude that ceramide may have a significant role in the attenuation of contractile-induced skeletal muscle adaptations and atrophy that is observed with aging.

Workshop report: Can an understanding of the mechanisms underlying age-related loss of muscle mass and function guide exercise and other intervention strategies?

An international workshop was hosted by the University of Liverpool on 15-16 July 2011 to address at a basic level what is known about the fundamental mechanisms by which skeletal muscle mass and function are lost during aging and to examine the nature of interventions that might prevent these mechanistic changes. Of particular importance was to attempt to evaluate how different forms of exercise (or muscle contractile activity) influence these processes and how these effects can be best optimized to prevent or delay age-related loss of muscle function. The program took the form of a two-day meeting, comprising a series of invited talks and breakout sessions designed to identify key gaps in current knowledge and potential future research questions. The aims of this Workshop were two-fold: 1. To identify the current state-of-the-art in the understanding of the mechanisms that contribute to loss of skeletal muscle mass and function that occurs with aging and to address at a mechanistic level how, and to what extent, exercise and/or other interventions might prevent these changes. 2. To identify specific areas of research where information is sparse but which are likely to yield data that will impact on future strategies to manipulate age-related loss of muscle mass and function in older people. The areas discussed in detail were loss of functional motor units, reduced muscle stem cell activity, age-related changes in transcriptional responses of muscle to exercise and nutrition, age-related changes in protein homeostasis, mitochondrial function, altered cross-talk between muscle with immune cells and how the developments in basic science to understand mechanisms underlying age-related loss of muscle mass and function can be translated. Following each session three key areas where further studies are needed were identified.

Biomarkers of sarcopenia in clinical trials-recommendations from the International Working Group on Sarcopenia

Sarcopenia, the age-related skeletal muscle decline, is associated with relevant clinical and socioeconomic negative outcomes in older persons. The study of this phenomenon and the development of preventive/therapeutic strategies represent public health priorities. The present document reports the results of a recent meeting of the International Working Group on Sarcopenia (a task force consisting of geriatricians and scientists from academia and industry) held on June 7-8, 2011 in Toulouse (France). The meeting was specifically focused at gaining knowledge on the currently available biomarkers (functional, biological, or imaging-related) that could be utilized in clinical trials of sarcopenia and considered the most reliable and promising to evaluate age-related modifications of skeletal muscle. Specific recommendations about the assessment of aging skeletal muscle in older people and the optimal methodological design of studies on sarcopenia were also discussed and finalized. Although the study of skeletal muscle decline is still in a very preliminary phase, the potential great benefits derived from a better understanding and treatment of this condition should encourage research on sarcopenia. However, the reasonable uncertainties (derived from exploring a novel field and the exponential acceleration of scientific progress) require the adoption of a cautious and comprehensive approach to the subject.

Systemic vascular function is associated with muscular power in older adults

Age-associated loss of muscular strength and muscular power is a critical determinant of loss of physical function and progression to disability in older adults. In this study, we examined the association of systemic vascular function and measures of muscle strength and power in older adults. Measures of vascular endothelial function included brachial artery flow-mediated dilation (FMD) and the pulse wave amplitude reactive hyperemia index (PWA-RHI). Augmentation index (AIx) was taken as a measure of systemic vascular function related to arterial stiffness and wave reflection. Measures of muscular strength included one repetition maximum (1RM) for a bilateral leg press. Peak muscular power was measured during 5 repetitions performed as fast as possible for bilateral leg press at 40% 1RM. Muscular power was associated with brachial FMD (r = 0.43, P < 0.05), PWA-RHI (r = 0.42, P < 0.05), and AIx (r = -0.54, P < 0.05). Muscular strength was not associated with any measure of vascular function. In conclusion, systemic vascular function is associated with lower-limb muscular power but not muscular strength in older adults. Whether loss of muscular power with aging contributes to systemic vascular deconditioning or vascular dysfunction contributes to decrements in muscular power remains to be determined.

Force-generation capacity of single vastus lateralis muscle fibers and physical function decline with age in African green vervet monkeys

Previous studies on the contractile properties of human myofibrils reported increase, decrease, or no change with aging, perhaps due to the differences in physical activity, diet, and other factors. This study examined physical performance and contractile characteristics of myofibrils of vastus lateralis (VL) muscle in young adult and old African green vervet monkeys. Animals were offered the same diet and lived in the same enclosures during development, so we were able to examine skeletal muscle function in vivo and in vitro with fewer potential confounding factors than are typical in human research studies. Fiber atrophy alone did not account for the age-related differences in specific force and maximal power output. Regression modeling used to identify factors contributing to lower fiber force revealed that age is the strongest predictor. Our results support a detrimental effect of aging on the intrinsic force and power generation of myofilament lattice and physical performance in vervet monkeys.

Relationship between site-specific loss of thigh muscle and gait performance in women: the HIREGASAKI study

Sarcopenia is observed as a site-specific loss of skeletal muscle mass, however, it is unknown whether the site-specific sarcopenia is associated with development of physical disability. The purpose of this study was to examine the relationship between age-related thigh muscle loss and gait performance. Fifty-three women aged 52-83 years had their thigh muscle thickness (MTH) measured by ultrasound at five sites on the anterior (30%, 50%, and 70% of thigh length) and posterior (50% and 70% of thigh length) aspects of their thigh. Maximum and normal walking speeds, zig-zag walking time, and maximal voluntary isometric knee extension and flexion strength were measured. Age was inversely correlated to the anterior and posterior MTH ratio (e.g., anterior 50%:posterior 70% MTH ratio [r=-0.426, p=0.002]), thus the site-specific muscle loss of the thigh was observed in the present sample. There were no significant correlations between the anterior/posterior MTH ratio and maximum and normal walking speeds. However, the ratios of anterior 50%:posterior 70% MTH (r=-0.430) and anterior 30%:posterior 70% MTH (r=-0.444) were correlated (p=0.001) to zig-zag walking test. After adjusting for age, height and weight, the anterior 30%:posterior 70% MTH (r=-0.292, p=0.040) was inversely correlated to zig-zag walking performance. Isometric knee extension strength was also inversely correlated to zig-zag walking. Our results suggest that an age-related loss of adductor/quadriceps muscles may be associated with a decrease in a relatively difficult task performance such as zig-zag walking.

Mass spectrometry-based proteomic analysis of middle-aged vs. aged vastus lateralis reveals increased levels of carbonic anhydrase isoform 3 in senescent human skeletal muscle

The age-related loss of skeletal muscle mass and associated progressive decline in contractile strength is a serious pathophysiological issue in the elderly. In order to investigate global changes in the skeletal muscle proteome after the fifth decade of life, this study analysed total extracts from human vastus lateralis muscle by fluorescence difference in-gel electrophoresis. Tissue specimens were derived from middle-aged (47-62 years) vs. aged (76-82 years) individuals and potential changes in the protein expression profiles were compared between these two age groups by a comprehensive gel electrophoresis-based survey. Age-dependent alterations in the concentration of 19 protein spots were revealed and mass spectrometry identified these components as being involved in the excitation-contraction-relaxation cycle, muscle metabolism, ion handling and the cellular stress response. This indicates a generally perturbed protein expression pattern in senescent human muscle. Increased levels of mitochondrial enzymes and isoform switching of the key contractile protein, actin, support the idea of glycolytic-to-oxidative and fast-to-slow transition processes during muscle aging. Importantly, the carbonic anhydrase (CA)3 isoform displayed an increased abundance during muscle aging, which was independently verified by immunoblotting of differently aged human skeletal muscle samples. Since the CA3 isoform is relatively muscle-specific and exhibits a fibre type-specific expression pattern, this enzyme may represent an interesting new biomarker of sarcopenia. Increased levels of CA are indicative of an increased demand of CO₂-removal in senescent muscle, and also suggest age-related fibre type shifting to slower-contracting muscles during human aging.

Skeletal muscle power: a critical determinant of physical functioning in older adults

Muscle power declines earlier and more precipitously with advancing age compared with muscle strength. Peak muscle power also has emerged as an important predictor of functional limitations in older adults. Our current working hypothesis is focused on examining lower extremity muscle power as a more discriminant variable for understanding the relationships between impairments, functional limitations, and resultant disability with aging.

Age-related loss of muscle mass and strength

Age-related muscle wasting and increased frailty are major socioeconomic as well as medical problems. In the quest to extend quality of life it is important to increase the strength of elderly people sufficiently so they can carry out everyday tasks and to prevent them falling and breaking bones that are brittle due to osteoporosis. Muscles generate the mechanical strain that contributes to the maintenance of other musculoskeletal tissues, and a vicious circle is established as muscle loss results in bone loss and weakening of tendons. Molecular and proteomic approaches now provide strategies for preventing age-related muscle wasting. Here, attention is paid to the role of the GH/IGF-1 axis and the special role of the IGFI-Ec (mechano growth factor/MGF) which is derived from the IGF-I gene by alternative splicing. During aging MGF levels decline but when administered MGF activates the muscle satellite (stem) cells that “kick start” local muscle repair and induces hypertrophy.

Aging of human muscle: understanding sarcopenia at the single muscle cell level

The loss of muscle mass with age, also known as sarcopenia, is a major scientific and public health problem. Muscle atrophy is associated with the loss of functional capacity and poor health outcomes in elderly men and women. A detailed understanding of this problem in humans can be enhanced by the use of experiments with single muscle fibers. It is likely that both muscle atrophy and a decrease in muscle-fiber quality contribute to muscle dysfunction among the elderly. A better understanding of sarcopenia at the single-fiber level may lead to the design of more effective rehabilitative interventions.

Sarcopenia and predictors of the fat free mass index in community-dwelling and assisted-living older men and women

The purpose of this study was to assess the relationship of the fat free mass index (FFMI), an indicator of sarcopenia in older adults, to anthropometric, gait, balance, and strength measures. We hypothesized that strength, balance, and mobility measures will correlate, and could be used to predict FFMI in older adults. Thirty-three older adults (81.5±7.9 years) participated. Fat free mass (FFM) was measured using Air-Displacement Plethysmography (ADP). Anthropometric measures, maximum handgrip (MG) and quadriceps strength were quantified. Clinical tests included the Berg Balance Scale (BBS), Dynamic Gait Index (DGI), and the Timed-up and Go (TUG) test. Finally, variability measures in gait and balance were calculated. Means, standard deviations (SD), correlations and multiple linear regression statistical analyses were then performed using functional predictor variables for FFMI. In total, 54.5% males and 36.3% females in our population were classified sarcopenic. FFMI correlated only to waist circumference (Total population (Pop), R(2)=0.649 p<0.01; Sarcopenics (Sarc), R(2)=0.636, p<0.05) and maximum grip strength (Pop, R(2)=0.633, p<0.01; Sarc, R(2)=0.771, p<0.01), nullifying our hypothesis. Multiple linear regression analyses revealed waist circumference, maximum handgrip strength, greater variability of time spent in double support, and anterior-posterior balance variability predicted 70.7% of the variance within the population. Results demonstrate a successful predictor model for FFMI based on a combination of strength, circumference and gait/balance variance measures. The ability to predict FFMI based on these variables will facilitate the diagnosis of sarcopenia in older adults.

Subproteomic analysis of basic proteins in aged skeletal muscle following offgel pre-fractionation

The progressive loss of skeletal muscle mass is a serious pathophysiological problem in the elderly, which warrants detailed biochemical studies into the underlying mechanism of age-related fiber degeneration. Over the last few years, mass spectrometry (MS)-based proteomics has identified a considerable number of new biomarkers of muscle aging in humans and animal models of sarcopenia. However, interpretation of the proteomic findings is often complicated by technical and biological limitations. Although gel electrophoresis-based approaches represent a highly sensitive analytical way for the large-scale and high-throughput survey of global changes in skeletal muscle proteins during aging, often the presence of components with an isoelectric point in the basic range is underestimated. We, therefore, carried out a comparative subproteomic study of young versus aged rat muscle focusing on potential changes in muscle proteins with an alkaline isoelectric point, using a combination of offgel electrophoresis and two-dimensional (2D) slab gel electrophoresis. Offgel electrophoresis was successfully applied as a prefractionation step to enrich basic protein species from crude tissue extracts representing young adult versus senescent muscle specimens. Proteomics has demonstrated alterations in a small cohort of basic proteins during muscle aging. The mass spectrometric identification of altered proteins and immunoblotting revealed a decrease in the glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and a concomitant increase in mitochondrial creatine kinase (CK) and ubiquinol cytochrome-c reductase. This agrees with the idea of a glycolytic-to-oxidative shift during muscle aging, which is indicative of an overall fast-to-slow transition process in senescent rat muscle. Thus, alterations in the abundance of metabolic enzymes appear to play a central role in the molecular pathogenesis of age-dependent muscle wasting.

Effect of old age on human skeletal muscle force-velocity and fatigue properties

It is generally accepted that the muscles of aged individuals contract with less force, have slower relaxation rates, and demonstrate a downward shift in their force-velocity relationship. The factors mediating age-related differences in skeletal muscle fatigue are less clear. The present study was designed to test the hypothesis that age-related shifts in the force-velocity relationship impact the fatigue response in a velocity-dependent manner. Three fatigue protocols, consisting of intermittent, maximum voluntary knee extension contractions performed for 4 min, were performed by 11 young (23.5 ± 0.9 yr, mean ± SE) and 10 older (68.9 ± 4.3) women. The older group fatigued less during isometric contractions than the young group (to 71.1 ± 3.7% initial torque and 59.8 ± 2.5%, respectively; P = 0.02), while the opposite was true during contractions performed at a relatively high angular velocity of 270°·s(-1) (old: 28.0 ± 3.9% initial power, young: 52.1 ± 6.9%; P < 0.01). Fatigue was not different (P = 0.74) between groups during contractions at an intermediate velocity, which was selected for each participant based on their force-velocity relationship. There was a significant association between force-velocity properties and fatigue induced by the intermediate-velocity fatigue protocol in the older (r = 0.72; P = 0.02) and young (r = 0.63; P = 0.04) groups. These results indicate that contractile velocity has a profound impact on age-related skeletal muscle fatigue resistance and suggest that changes in the force-velocity relationship partially mediate this effect.

Non-invasive muscle contraction assay to study rodent models of sarcopenia

Background

Age-related sarcopenia is a disease state of loss of muscle mass and strength that affects physical function and mobility leading to falls, fractures, and disability. The need for therapies to treat age-related sarcopenia has attracted intensive preclinical research. To facilitate the discovery of these therapies, we have developed a non-invasive rat muscle functional assay system to efficiently measure muscle force and evaluate the efficacy of drug candidates.

Methods

The lower leg muscles of anesthetized rats are artificially stimulated with surface electrodes on the knee holders and the heel support, causing the lower leg muscles to push isometric pedals that are attached to force transducers. We developed a stimulation protocol to perform a fatigability test that reveals functional muscle parameters like maximal force, the rate of fatigue, fatigue-resistant force, as well as a fatigable muscle force index. The system is evaluated in a rat aging model and a rat glucocorticoid-induced muscle loss model

Results

The aged rats were generally weaker than adult rats and showed a greater reduction in their fatigable force when compared to their fatigue-resistant force. Glucocorticoid treated rats mostly lost fatigable force and fatigued at a higher rate, indicating reduced force from glycolytic fibers with reduced energy reserves.

Conclusions

The involuntary contraction assay is a reliable system to assess muscle function in rodents and can be applied in preclinical research, including age-related sarcopenia and other myopathy.

Muscle power failure in mobility-limited older adults: preserved single fiber function despite lower whole muscle size, quality and rate of neuromuscular activation

This study investigated the physiological and gender determinants of the age-related loss of muscle power in 31 healthy middle-aged adults (aged 40-55 years), 28 healthy older adults (70-85 years) and 34 mobility-limited older adults (70-85 years). We hypothesized that leg extensor muscle power would be significantly lower in mobility-limited elders relative to both healthy groups and sought to characterize the physiological mechanisms associated with the reduction of muscle power with aging. Computed tomography was utilized to assess mid-thigh body composition and calculate specific muscle power and strength. Surface electromyography was used to assess rate of neuromuscular activation and muscle biopsies were taken to evaluate single muscle fiber contractile properties. Peak muscle power, strength, muscle cross-sectional area, specific muscle power and rate of neuromuscular activation were significantly lower among mobility-limited elders compared to both healthy groups (P ≤ 0.05). Mobility-limited older participants had greater deposits of intermuscular adipose tissue (P < 0.001). Single fiber contractile properties of type I and type IIA muscle fibers were preserved in mobility-limited elders relative to both healthy groups. Male gender was associated with greater decrements in peak and specific muscle power among mobility-limited participants. Impairments in the rate of neuromuscular activation and concomitant reductions in muscle quality are important physiological mechanisms contributing to muscle power deficits and mobility limitations. The dissociation between age-related changes at the whole muscle and single fiber level suggest that, even among older adults with overt mobility problems, contractile properties of surviving muscle fibers are preserved in an attempt to maintain overall muscle function.

Component characteristics of thigh muscle volume in young and older healthy men

The purpose of this study was to compare the component characteristics of thigh muscle volume in Japanese young and older men. The subjects in both young (YM, n = 15) and older (OM, n = 13) men were physically active (performed aerobic-type exercise 1-3 times per week), but none of the subjects had regularly participated in resistance training for a minimum of 3 years prior to the study. Contiguous transverse magnetic resonance imaging (1.5-T scanner) images were obtained from the thigh, and total and individual (quadriceps, hamstrings and adductors) muscle volumes were calculated by multiplying the muscle cross-sectional area (CSA) by slice thickness and the total number of slices. Muscle length and average muscle CSA (muscle volume divided by muscle length) were determined for each muscle. Maximum voluntary isometric (MVC) knee extension and flexion strength were measured, and muscle quality was defined as MVC per unit average muscle CSA (MVC/CSA). Quadriceps muscle volume and average CSA were, respectively, 20% and 16% lower (P < 0.05) in the OM than in the YM, while hamstrings and adductors muscle volumes and average CSA were similar in both groups. Knee extension and flexion MVC were lower (P < 0.05) in the OM than in the YM. Knee extensor MVC/CSA was similar in the two groups, while knee flexor MVC/CSA was lower (P < 0.05) in the OM than in the YM. Our results suggest that age-related thigh muscle volume loss is muscle specific, in that greater quadriceps muscle loss was found in the older group.

The epidemiology of sarcopenia in community living older adults: what role does lifestyle play?

BACKGROUND: Sarcopenia, the age-related decline in skeletal muscle mass and function, is a relatively poorly understood process which may play an important role in the incidence of physical disability and falls in older adults. Evidence demonstrates that both genetic and environmental factors contribute to increased susceptibility for sarcopenia development, yet some of these factors may represent unavoidable consequences of ageing. METHODS: A review of literature, generally from epidemiological research, was performed to examine the influence that potentially modifiable lifestyle factors (general physical activity, dietary nutrient intake and sun exposure), as well as chronic disease and medication use, may have on sarcopenia progression. RESULTS: The review demonstrated that while physical activity, nutrient intake and sun exposure often decline during ageing, each may have important but differing benefits for the prevention of muscle mass and functional declines in older adults. Conversely, age-related increases in the prevalence of chronic diseases and the subsequent prescription of pharmacotherapy may exacerbate sarcopenia progression. CONCLUSIONS: The prevalence of poor physical activity, diet and sun exposure, as well as chronic disease and medication use, within older adult populations may be modifiable through simple lifestyle and health care interventions. As such, these factors may represent the most effective targets for sarcopenia prevention during the ageing process.

Effects of ageing on single muscle fibre contractile function following short-term immobilisation

Very little attention has been given to the combined effects of healthy ageing and short-term disuse on the contractile function of human single muscle fibres. Therefore, the present study investigated the effects of 2 weeks of lower limb cast immobilisation (i.e. disuse) on selected contractile properties of single muscle fibres (n = 378) from vastus lateralis of nine young (24 ± 1 years) and eight old (67 ± 2 years) healthy men with comparable levels of physical activity. Prior to immobilisation, MHC IIa fibres produced higher maximum Ca(2+)-activated force (approx. 32%) and specific force (approx. 33%) and had lower Ca(2+) sensitivity than MHC I fibres (P < 0.05), with no differences between young and old. After immobilisation, the decline in single fibre force (MHC I: young 21% and old 22%; MHC IIa: young 22% and old 30%; P < 0.05) as well as specific force (MHC I: young 14% and old 13%; MHC IIa: young 18% and old 25%; P < 0.05) was more pronounced in MHC IIa fibres compared to MHC I fibres (P < 0.05), with no differences between young and old. Notably, there was a selective decrease in Ca(2+) sensitivity in MHC IIa fibres of young (P < 0.05) and in MHC I fibres of old individuals (P < 0.05), respectively. In conclusion, 2 weeks of lower limb immobilisation caused greater impairments in single muscle fibre force and specific force in MHC IIa than MHC I fibres independently of age. In contrast, immobilisation-induced changes in Ca(2+) sensitivity that were dependent on age and MHC isoform.

Physical activity and sarcopenia

Physical activity can be a valuable countermeasure to sarcopenia in its treatment and prevention. In considering physical training strategies for sarcopenic subjects, it is critical to consider personal and environmental obstacles to access opportunities for physical activity for any patient with chronic disease. This article presents an overview of current knowledge of the effects of physical training on muscle function and the physical activity recommended for sarcopenic patients. So that this countermeasure strategy can be applied in practice, the authors propose a standardized protocol for prescribing physical activity in chronic diseases such as sarcopenia.

Human myotubes from myoblast cultures undergoing senescence exhibit defects in glucose and lipid metabolism

Adult stem cells are known to have a finite replication potential. Muscle biopsy-derived human satellite cells (SCs) were grown at different passages and differentiated to human myotubes in culture to analyze the functional state of various carbohydrate and lipid metabolic pathways. As the proliferative potential of myoblasts decreased dramatically with passage number, a number of cellular functions were altered: the capacity of myoblasts to fuse and differentiate into myotubes was reduced, and metabolic processes in myotubes such as glucose uptake, glycogen synthesis, glucose oxidation and fatty acid β-oxidation became gradually impaired. Upon insulin stimulation, glucose uptake and glycogen synthesis increased but as the cellular proliferative capacity became gradually exhausted, the response dropped concomitantly. Palmitic acid incorporation into lipids in myotubes decreased with passage number and could be explained by reduced incorporation into diacyl- and triacylglycerols. The levels of long-chain acyl-CoA esters decreased with increased passage number. Late-passage, non-proliferating, myoblast cultures showed strong senescence-associated β-galactosidase activity indicating that the observed metabolic defects accompany the induction of a senescent state. The main function of SCs is regeneration and skeletal muscle-build up. Thus, the metabolic defects observed during aging of SC-derived myotubes could have a role in sarcopenia, the gradual age-related loss of muscle mass and strength.

Proteomic Profiling of Mitochondrial Enzymes during Skeletal Muscle Aging

Mitochondria are of central importance for energy generation in skeletal muscles. Expression changes or functional alterations in mitochondrial enzymes play a key role during myogenesis, fibre maturation, and various neuromuscular pathologies, as well as natural fibre aging. Mass spectrometry-based proteomics suggests itself as a convenient large-scale and high-throughput approach to catalogue the mitochondrial protein complement and determine global changes during health and disease. This paper gives a brief overview of the relatively new field of mitochondrial proteomics and discusses the findings from recent proteomic surveys of mitochondrial elements in aged skeletal muscles. Changes in the abundance, biochemical activity, subcellular localization, and/or posttranslational modifications in key mitochondrial enzymes might be useful as novel biomarkers of aging. In the long term, this may advance diagnostic procedures, improve the monitoring of disease progression, help in the testing of side effects due to new drug regimes, and enhance our molecular understanding of age-related muscle degeneration.

Age-related, site-specific muscle loss in 1507 Japanese men and women aged 20 to 95 years

We investigated the relationship between age and muscle size in both the appendicular and trunk regions of 1507 Japanese men and women aged 20 to 95 years. Seven hundred twenty-two men (young [aged 20-39 years], n = 211; middle-aged [aged 40-59 years], n = 347; and old [aged 6095 years], n = 164) and 785 women (young, n = 207; middle-aged, n = 341; and old, n = 237) were recruited for this cross-sectional study. Muscle thickness (MTH) and subcutaneous fat thickness (FTH) were measured by ultrasound at 8 sites on the anterior and posterior aspects of the body. MTH was expressed in terms relative to limb length (MTH/L) or height (MTH/Ht). Percent body fat was estimated from FTH, and fat-free mass (FFM) was calculated. In men, a graded decrease in FFM was found in all age groups. In women, FFM was similar in the young and middle-aged groups, but was lower in the oldest group. Age was significantly and inversely correlated with FFM in men (r = - 0.358, p < 0.01), but not in women (r = -0.08). On the other hand, age was strongly and inversely correlated with quadriceps MTH/L (men, r = -0.529; women, r = -0.489; both p < 0.001) and abdomen MTH/Ht (men, r = -0.464; women, r = -0.446; both p < 0.001) in both men and women, while there were only weak correlations between age and other lower limb and trunk sites. Our results indicated that sarcopenia is observed as a site-specific loss of skeletal muscle mass, especially for the quadriceps and abdominal muscles, in Japanese men and women aged 20 to 95 years. Key pointsIt is not fully understood whether age-related changes in muscle size differ between the appendicular and trunk muscles and/or between muscle groups located in the anterior and posterior aspects of the body in a large population.Age-related muscle loss is observed as a site-specific, especially of the quadriceps and abdominal muscles, in Japanese men and women aged 20 to 95 years.The age-related muscle losses are not supported by the muscle activation pattern of normal daily activities evaluated by EMG activity.

The effects of stretching on the flexibility, muscle performance and functionality of institutionalized older women

Stretching has been widely used to increase the range of motion. We assessed the effects of a stretching program on muscle-tendon length, flexibility, torque, and activities of daily living of institutionalized older women. Inclusion/exclusion criteria were according to Mini-Mental State Examination (MMSE) (>13), Barthel Index (>13) and Lysholm Scoring Scale (>84). Seventeen 67 ± 9 year-old elderly women from a nursing home were divided into 2 groups at random: the control group (CG, N = 9) participated in enjoyable cultural activities; the stretching group (SG, N = 8) performed active stretching of hamstrings, 4 bouts of 1 min each. Both groups were supervised three times per week over a period of 8 weeks. Peak torque was assessed by an isokinetic method. Both groups were evaluated by a photogrammetric method to assess muscle-tendon length of uni- and biarticular hip flexors and hamstring flexibility. All measurements were analyzed before and after 8 weeks by two-way ANOVA with the level of significance set at 5%. Hamstring flexibility increased by 30% in the SG group compared to pre-training (76.5 ± 13.0° vs 59.5 ± 9.0°, P = 0.0002) and by 9.2% compared to the CG group (76.5 ± 13.0° vs 64.0 ± 12.0°, P = 0.0018). Muscle-tendon lengths of hip biarticular flexor muscles (124 ± 6.8° vs 118.3 ± 7.6°, 5.0 ± 7.0%, P = 0.031) and eccentric knee extensor peak torque were decreased in the CG group compared to pre-test values (-49.4 ± 16.8 vs -60.5 ± 18.9 Nm, -15.7 ± 20%, P = 0.048). The stretching program was sufficient to increase hamstring flexibility and a lack of stretching can cause reduction of muscle performance.

Regulation of skeletal muscle transcriptome in elderly men after 6 weeks of endurance training at lactate threshold intensity

A compromised muscle function due to aging, sarcopenia and reduced level of physical activity can lead to metabolic complications and chronic diseases. Endurance exercise counters these diseases by inducing beneficial adaptations whose molecular mechanisms remain unclear. We have investigated the transcriptomic changes following mild-intensity endurance training in skeletal muscle of elderly men. Seven healthy subjects followed an exercise program of cycle ergometer training at lactate threshold (LT) level for 60 min/day, five times/week during six weeks. Physiological and transcriptomic changes were analyzed before and after training. LT training decreased percentage body fat and fasting levels of plasma glucose, while increasing high-density lipoprotein cholesterol and lecithin-cholesterol acyltransferase levels. Transcriptomic analysis revealed fast-to-slow fiber type transition, increased amount of mtDNA encoded transcripts and modulation of 12 transcripts notably related to extracellular matrix (ECM), oxidative phosphorylation (OXPHOS), as well as partially characterized and novel transcripts. The training simultaneously induced the expression of genes related to slow fiber type transition, OXPHOS and ECM, which might contribute to the improvement of glucose and lipid metabolisms and whole body aerobic capacity.

Aberrant mitochondrial homeostasis in the skeletal muscle of sedentary older adults

The role of mitochondrial dysfunction and oxidative stress has been extensively characterized in the aetiology of sarcopenia (aging-associated loss of muscle mass) and muscle wasting as a result of muscle disuse. What remains less clear is whether the decline in skeletal muscle mitochondrial oxidative capacity is purely a function of the aging process or if the sedentary lifestyle of older adult subjects has confounded previous reports. The objective of the present study was to investigate if a recreationally active lifestyle in older adults can conserve skeletal muscle strength and functionality, chronic systemic inflammation, mitochondrial biogenesis and oxidative capacity, and cellular antioxidant capacity. To that end, muscle biopsies were taken from the vastus lateralis of young and age-matched recreationally active older and sedentary older men and women (N = 10/group; female symbol = male symbol). We show that a physically active lifestyle is associated with the partial compensatory preservation of mitochondrial biogenesis, and cellular oxidative and antioxidant capacity in skeletal muscle of older adults. Conversely a sedentary lifestyle, associated with osteoarthritis-mediated physical inactivity, is associated with reduced mitochondrial function, dysregulation of cellular redox status and chronic systemic inflammation that renders the skeletal muscle intracellular environment prone to reactive oxygen species-mediated toxicity. We propose that an active lifestyle is an important determinant of quality of life and molecular progression of aging in skeletal muscle of the elderly, and is a viable therapy for attenuating and/or reversing skeletal muscle strength declines and mitochondrial abnormalities associated with aging.

Functional consequences of sarcopenia and dynapenia in the elderly

PURPOSE OF REVIEW

The economic burden due to the sequela of sarcopenia (muscle wasting in the elderly) are staggering and rank similarly to the costs associated with osteoporotic fractures. In this article, we discuss the societal burden and determinants of the loss of physical function with advancing age, the physiologic mechanisms underlying dynapenia (muscle weakness in the elderly), and provide perspectives on related critical issues to be addressed.

RECENT FINDINGS

Recent epidemiological findings from longitudinal aging studies suggest that dynapenia is highly associated with both mortality and physical disability even when adjusting for sarcopenia indicating that sarcopenia may be secondary to the effects of dynapenia. These findings are consistent with the physiologic underpinnings of muscle strength, as recent evidence demonstrates that alterations in muscle quantity, contractile quality and neural activation all collectively contribute to dynapenia.

SUMMARY

Although muscle mass is essential for regulation of whole body metabolic balance, overall neuromuscular function seems to be a critical factor for maintaining muscle strength and physical independence in the elderly. The relative contribution of physiologic factors contributing to muscle weakness are not fully understood and further research is needed to better elucidate these mechanisms between muscle groups and across populations.

Impaired voluntary neuromuscular activation limits muscle power in mobility-limited older adults

BACKGROUND

Age-related alterations of neuromuscular activation may contribute to deficits in muscle power and mobility function. This study assesses whether impaired activation of the agonist quadriceps and antagonist hamstrings, including amplitude- and velocity-dependent characteristics of activation, may explain differences in leg extension torque and power between healthy middle-aged, healthy older, and mobility-limited older adults.

METHODS

Torque, power, and electromyography were recorded during maximal voluntary leg extension trials across a range of velocities on an isokinetic dynamometer.

RESULTS

Neuromuscular activation was similar between middle-aged and older healthy groups, with differences in torque and power explained predominantly by muscle size. However, the older mobility-limited group demonstrated marked impairment of torque, power, and agonist muscle activation, with the greatest deficits occurring at the fastest movement velocities. Agonist muscle activation was found to be strongly associated with torque output.

CONCLUSIONS

Similar neuromuscular activation between the middle-aged and older healthy groups indicates that impaired voluntary activation is not an obligatory consequence of aging. However, the finding that the mobility-limited group exhibited impaired activation of the agonist quadriceps and concomitant deficits in torque and power output suggests that neuromuscular activation deficits may contribute to compromised mobility function in older adults.

DIGE analysis of rat skeletal muscle proteins using nonionic detergent phase extraction of young adult versus aged gastrocnemius tissue

Contractile weakness and loss of muscle mass are critical features of the aging process in mammalians. Age-related fibre wasting has a profound effect on muscle metabolism, fibre type distribution and the overall physiological integrity of the neuromuscular system. This study has used mass spectrometry-based proteomics to investigate the fate of the aging rat muscle proteome. Using nonionic detergent phase extraction, this report shows that the aged gastrocnemius muscle exhibits a generally perturbed protein expression pattern in both the detergent-extracted fraction and the aqueous protein complement from senescent muscle tissue. In the detergent-extracted fraction, the expression of ATP synthase, isocitrate dehydrogenase, enolase, tropomyosin and beta-actin was increased. Different isoforms of creatine kinase and prohibitin showed differential changes. In the aqueous fraction, malate dehydrogenase, sulfotransferase, triosephosphate isomerase, aldolase, cofilin-2 and lactate dehydrogenase showed increased levels. Interestingly, differential effects on dissimilar 2-D spots of the same protein species were shown for Cu/Zn superoxide dismutase, albumin, annexin A4 and phosphoglycolate phosphatase. Mitochondrial Hsp60, Hsp71 and nucleoside diphosphate kinase B exhibited a reduced abundance in aged muscle. The majority of altered proteins were found to be involved in mitochondrial metabolism, glycolysis, metabolic transportation, regulatory processes, the cellular stress response, detoxification mechanisms and muscle contraction.

The impact of sarcopenia and exercise training on skeletal muscle satellite cells

It has been well-established that the age-related loss of muscle mass and strength, or sarcopenia, impairs skeletal muscle function and reduces functional performance at a more advanced age. Skeletal muscle satellite cells (SC), as precursors of new myonuclei, have been suggested to be involved in the development of sarcopenia. In accordance with the type II muscle fiber atrophy observed in the elderly, recent studies report a concomitant fiber type specific reduction in SC content. Resistance type exercise interventions have proven effective to augment skeletal muscle mass and improve muscle function in the elderly. In accordance, recent work shows that resistance type exercise training can augment type II muscle fiber size and reverse the age-related decline in SC content. The latter is supported by an increase in SC activation and proliferation factors that generally appear following exercise training. Present findings strongly suggest that the skeletal muscle SC control myogenesis and have an important, but yet unresolved, function in the loss of muscle mass with aging. This review discusses the contribution of skeletal muscle SC in the age-related loss of muscle mass and the efficacy of exercise training as a means to attenuate and/or reverse this process.

Muscle atrophy in immobilization and senescence in humans

PURPOSE OF REVIEW

Recent reports exploring the mechanisms thought to be responsible for the determination of muscle mass during health, ageing and immobilization in humans have presented findings that have wide ranging implications. This brief review highlights some of the more important findings.

RECENT FINDINGS

Contrary to expectations, recent findings suggest an apparent dissociation between muscle signalling pathways and their associated events in humans, particularly in relation to muscle protein synthesis. Although debate concerning the relative importance of muscle protein synthesis and degradation to muscle mass loss during immobilization continues, and the mechanisms responsible for this loss and its restoration during rehabilitation remain unclear, new evidence has emerged showing that anabolic resistance to protein nutrition develops during immobilization. This latter observation is in agreement with earlier evidence pointing to anabolic resistance of muscle to protein nutrition existing in the elderly, which is of clinical importance. Recent observations also suggest that a sex difference exists in the rate of muscle protein synthesis under postabsorptive conditions in the elderly and may explain why women lose muscle mass at a slower rate with age than men.

SUMMARY

These recent findings highlight our current lack of understanding of the mechanisms that regulate muscle mass in humans.

Determining physiological cross-sectional area of extensor carpi radialis longus and brevis as a whole and by regions using 3D computer muscle models created from digitized fiber bundle data

Architectural parameters and physiological cross-sectional area (PCSA) are important determinants of muscle function. Extensor carpi radialis longus (ECRL) and brevis (ECRB) are used in muscle transfers; however, their regional architectural differences have not been investigated. The aim of this study is to develop computational algorithms to quantify and compare architectural parameters (fiber bundle length, pennation angle, and volume) and PCSA of ECRL and ECRB. Fiber bundles distributed throughout the volume of ECRL (75+/-20) and ECRB (110+/-30) were digitized in eight formalin embalmed cadaveric specimens. The digitized data was reconstructed in Autodesk Maya with computational algorithms implemented in Python. The mean PCSA and fiber bundle length were significantly different between ECRL and ECRB (p < or = 0.05). Superficial ECRL had significantly longer fiber bundle length than the deep region, whereas the PCSA of superficial ECRB was significantly larger than the deep region. The regional quantification of architectural parameters and PCSA provides a framework for the exploration of partial tendon transfers of ECRL and ECRB.

Skeletal muscle fatigue in old age: whose advantage?

The results of recent studies indicate that in healthy men and women aged beyond approximately 65 years, the energy-producing pathways in skeletal muscle may combine with changes in motor unit behavior and muscle contractile properties to provide a unique environment for resisting muscle fatigue under some conditions.

Improvements in whole muscle and myocellular function are limited with high-intensity resistance training in octogenarian women

Advanced sarcopenia is prevalent among octogenarian women; yet little is known about myocellular quality and plasticity in this cohort. The aim of this investigation was to examine single muscle fiber contractile function and whole muscle characteristics before and after 12 wk of high-intensity progressive resistance training (PRT) in very old (85 +/- 1 yr) women (OW, n = 6). Young women [YW (21 +/- 2 yr old), n = 9] were included as a control group. Whole muscle strength [1 repetition maximum (RM)] and size (CT scans) were assessed before and after PRT. Functional experiments (size, peak force, velocity, and power) were performed on vastus lateralis myosin heavy chain (MHC) I and IIa muscle fibers before and after PRT. With PRT, 1-RM strength increased (P < 0.05) in YW (36%) and OW (26%). Thigh muscle cross-sectional area increased (5%) in YW (P < 0.05), but thigh muscle did not hypertrophy in OW. Before PRT, there were no differences in single-fiber parameters between YW and OW. With PRT, MHC IIa fiber size (28%), peak force (31%), and power (28%) improved, but no changes were observed in MHC I fibers, in YW (P < 0.05). There were no improvements in MHC I or IIa single-fiber function in OW. These data show that the myocellular functional profile in OW is similar to that in YW but that OW have a blunted hypertrophic response to PRT at the whole muscle and myocellular level. The limited myocellular plasticity in OW with PRT contrasts with that in YW and previous PRT studies in elderly women only a decade younger. These data suggest that attempts to greatly enhance skeletal muscle mass and function should begin before 80 yr of age.

Trait-specific tracking and determinants of body composition: a 7-year follow-up study of pubertal growth in girls

BACKGROUND

Understanding how bone (BM), lean (LM) and fat mass (FM) develop through childhood, puberty and adolescence is vital since it holds key information regarding current and future health. Our study aimed to determine how BM, LM and FM track from prepuberty to early adulthood in girls and what factors are associated with intra- and inter-individual variation in these three tissues.

METHODS

The study was a 7-year longitudinal cohort study. BM, LM and FM measured using dual-energy X-ray absorptiometry, self-reported dietary information, leisure time physical activity (LTPA) and other factors were assessed one to eight times in 396 girls aged 10 to 13 years (baseline), and in 255 mothers once.

RESULTS

The location of a girl's BM, LM and FM in the lower, middle or upper part of the sample distribution was established before puberty and tracked in its percentile of origin over 7 years (r = 0.72 for BM, r = 0.61 for LM, and r = 0.65 for FM all p < 0.001 first vs. last measurements' ranking). Seventy-three percent of those in the lowest quartile for BM and 69% for LM, and 79% of those in the highest quartile for FM at baseline remained in their quartile at 7-year follow-up. Heritability was estimated to contribute 69% of the total variance of the BM, 50% of the LM, and 57% of the FM. Besides body size, diet index (explaining 9% of variance), breast feeding duration (6%) and mother's BM (9%) predicted high BM. Diet index and high LTPA predicted high LM (24% and 14%, respectively), and low FM (25% and 12%, respectively), and low level of parental education predicted high FM (4%).

CONCLUSION

Individual levels of BM, LM and FM are established before puberty and track in a trait-specific manner until early adulthood. Girls who are prone to develop low BM and LM and high FM in adulthood can be identified in prepuberty. The developments of three components of body composition are inter-related during growth. BM was the most heritable trait while LM the most environmentally modifiable. Diet and physical activity played an important role in increasing LM and preventing the accumulation of excessive FM.

Anaerobic performance in masters athletes

With increasing age, it appears that masters athletes competing in anaerobic events (10–100 s) decline linearly in performance until 70 years of age, after which the rate of decline appears to accelerate. This decline in performance appears strongly related to a decreased anaerobic work capacity, which has been observed in both sedentary and well-trained older individuals. Previously, a number of factors have been suggested to influence anaerobic work capacity including gender, muscle mass, muscle fiber type, muscle fiber size, muscle architecture and strength, substrate availability, efficiency of metabolic pathways, accumulation of reaction products, aerobic energy contribution, heredity, and physical training. The effects of sedentary aging on these factors have been widely discussed within literature. Less data are available on the changes in these factors in masters athletes who have continued to train at high intensities with the aim of participating in competition. The available research has reported that these masters athletes still demonstrate age-related changes in these factors. Specifically, it appears that morphological (decreased muscle mass, type II muscle fiber atrophy), muscle contractile property (decreased rate of force development), and biochemical changes (changes in enzyme activity, decreased lactate production) may explain the decreased anaerobic performance in masters athletes. However, the reduction in anaerobic work capacity and subsequent performance may largely be the result of physiological changes that are an inevitable result of the aging process, although their effects may be minimized by continuing specific high-intensity resistance or sprint training.