Live strong and prosper: the importance of skeletal muscle strength for healthy ageing

Incretin-Based Weight Loss Pharmacotherapy: Can Resistance Exercise Optimize Changes in Body Composition?

This narrative review highlights the degree to which new antiobesity medications based on gut-derived nutrient-stimulated hormones (incretins) cause loss of lean mass, and the importance of resistance exercise to preserve muscle. Glucagon-like peptide 1 receptor agonists (GLP-1RA) induce substantial weight loss in randomized trials, effects that may be enhanced in combination with glucose-dependent insulinotropic polypeptide (GIP) receptor agonists. Liraglutide and semaglutide (GLP-1RA), tirzepatide (GLP-1 and GIP receptor dual agonist), and retatrutide (GLP-1, GIP, and glucagon receptor triple agonist) are peptides with incretin agonist activity that induce ∼15-24% weight loss in adults with overweight and obesity, alongside beneficial impacts on blood pressure, cholesterol, blood glucose, and insulin. However, these agents also cause rapid and significant loss of lean mass (∼10% or ∼6 kg), comparable to a decade or more of aging. Maintaining muscle mass and function as humans age is crucial to avoiding sarcopenia and frailty, which are strongly linked to morbidity and mortality. Studies indicate that supervised resistance exercise training interventions with a duration >10 weeks can elicit large increases in lean mass (∼3 kg) and strength (∼25%) in men and women. After a low-calorie diet, combining aerobic exercise with liraglutide improved weight loss maintenance compared with either alone. Retaining lean mass during incretin therapy could blunt body weight (and fat) regain on cessation of weight loss pharmacotherapy. We propose that tailored resistance exercise training be recommended as an adjunct to incretin therapy to optimize changes in body composition by preserving lean mass while achieving fat loss.

Muscle and tendon morphology of a world strongman and deadlift champion

This study compared the muscle and tendon morphology of an extraordinarily strong individual, a World's Strongest Man and deadlift champion (WSM), with that of various other athletic, trained, and untrained populations. The WSM completed the following: 1) 3.0-T MRI scans, to determine the volume of 22 individual lower limb muscles, 5 functional muscle groups, patellar tendon (PT) cross-sectional area (CSA), and PT moment arm; and 2) countermovement jumps (CMJ) and isometric midthigh pull (IMTP) contractions. The WSM was compared with previously assessed groups from our laboratory (muscle and tendon) and the wider research literature (CMJ and IMTP). The WSM's CMJ peak power (9,866 W) and gross (9,171 N) and net (7,480 N) IMTP peak forces were higher than any previously published values. The WSM's overall measured leg muscle volume was approximately twice that of untrained controls (+96%) but with pronounced anatomical variability in the extent of muscular development. The plantar flexor group (+120%) and the guy rope muscles (sartorius, gracilis, and semitendinosus: +140% to +202%), which stabilize the pelvis and femur, demonstrated the largest differences relative to that of untrained controls. The WSM's pronounced quadriceps size (greater than or equal to twofold vs. untrained) was accompanied by modest PT moment arm differences and, notably, was not matched by an equivalent difference in PT CSA (+30%). These results provide novel insight into the musculotendinous characteristics of an extraordinarily strong individual, which may be toward the upper limit of human variation, such that the WSM's very pronounced lower limb muscularity also exhibited distinct anatomical variability and with muscle size largely uncoupled from tendon size.NEW & NOTEWORTHY Lower-body muscle size of an extraordinarily strong individual, a World's Strongest Man and deadlift champion (WSM), was approximately twice that of controls but was underpinned by pronounced anatomical variability in the extent of muscular development (+23-202%): the plantar flexor group and guy rope muscles demonstrating the largest differences. The WSM's quadriceps size (more than or equal to twice that of controls) contrasted with modest differences in patella tendon moment arm (+18%) and was uncoupled from patellar tendon size (+30%).

Does high-frequency resistance exercise offer additional benefits to older adults? learnings from a randomized controlled trial

OBJECTIVE

Resistance exercise is an effective strategy to improve muscle strength in older adults. A limited-load resistance would be flexible and suitable for community-based training. It was unclear whether high-frequency resistance exercise offer additional benefits to older adults. Here, we aimed to examine the effect of limited-load resistance exercise among different frequency on muscle parameters in older adults.

METHODS

The current study was a single-blind, randomized controlled trial comparing the effectiveness of different-frequency resistance exercise in older adults. Change in skeletal muscle was estimated with a multi-frequency bioelectrical impedance analyzer. Demographics, physical examination, nutritional assessment, prealbumin and lymphocytes were also measured. Fisher's precision probability test and baseline-adjusted generalized linear models were applied accordingly to analyze the influence of dose-different exercise on prevalence of sarcopenia, muscle parameters and body composition. A two-sided p value of < 0.05 was defined statistical significance.

RESULTS

The participants had a mean age of 71.96 years and close gender ratio. One hundred and twenty-seven participants (control 40; low-dose 46; high-dose 41) completed the 6-month exercise intervention. In contrast to control group, only high-dose exercise groups experienced improvements in muscle mass (0.66 kg, p < 0.001) and max grip strength (+ 2.17 kg, p < 0.001). There were significant dose-response effects of muscle mass (index), fat mass (index), max grip strength, 5-times sit to stand test, 6-minute walking test and visceral fat area (all ptrend <0.01).

CONCLUSIONS

As the proved dose-dependent effect, current findings supported high-frequency limited-load resistance exercise applied and extended among older adults in community.

TRIAL REGISTRATION

This study was registered at Chinese Clinical Trial Registry Network (ChiCTR2200062007, Registered on 19 July 2022).

Non invasive techniques for direct muscle quality assessment after exercise intervention in older adults: a systematic review

BACKGROUND

The aging process induces neural and morphological changes in the human musculoskeletal system, leading to a decline in muscle mass, strength and quality. These alterations, coupled with shifts in muscle metabolism, underscore the essential role of physical exercise in maintaining and improving muscle quality in older adults. Muscle quality's morphological domain encompasses direct assessments of muscle microscopic and macroscopic aspects of muscle architecture and composition. Various tools exist to estimate muscle quality, each with specific technical requirements. However, due to the heterogeneity in both the studied population and study methodologies, there is a gap in the establishment of reference standards to determine which are the non-invasive and direct tools to assess muscle quality after exercise interventions. Therefore, the purpose of this review is to obtain an overview of the non-invasive tools used to measure muscle quality directly after exercise interventions in healthy older adults, as well as to assess the effects of exercise on muscle quality.

MAIN TEXT

To address the imperative of understanding and optimizing muscle quality in aging individuals, this review provides an overview of non-invasive tools employed to measure muscle quality directly after exercise interventions in healthy older adults, along with an assessment of the effects of exercise on muscle quality.

RESULTS

Thirty four studies were included. Several methods of direct muscle quality assessment were identified. Notably, 2 studies harnessed CT, 20 utilized US, 9 employed MRI, 2 opted for TMG, 2 adopted myotonometry, and 1 incorporated BIA, with several studies employing multiple tests. Exploring interventions, 26 studies focus on resistance exercise, 4 on aerobic training, and 5 on concurrent training.

CONCLUSIONS

There is significant diversity in the methods of direct assessment of muscle quality, mainly using ultrasound and magnetic resonance imaging; and a consistent positive trend in exercise interventions, indicating their efficacy in improving or preserving muscle quality. However, the lack of standardized assessment criteria poses a challenge given the diversity within the studied population and variations in methodologies.. These data emphasize the need to standardize assessment criteria and underscore the potential benefits of exercise interventions aimed at optimizing muscle quality.

Association of body mass index with muscle strength and cardiorespiratory fitness: A cross-sectional study based on Chinese adolescents

BACKGROUND

Muscle strength and cardiorespiratory fitness are important components of physical fitness and are important for the physical and mental health development of university students. However, obesity is also an important factor affecting physical fitness, and there are few studies on how body mass index (BMI), which reflects obesity, is associated with muscle strength and cardiorespiratory fitness among Chinese university students. Therefore, this study analyzed the association between BMI and muscle strength and cardiorespiratory fitness among Chinese university students in order to provide a reference and basis for promoting the development of physical fitness among Chinese university students.

METHODS

A stratified whole-group sampling method was used to test physical fitness items in 27 973 (15 527 boys, 55.51%) university students in 800 first- to fourth-year university classes in Anhui, Fujian, Xinjiang, Shanghai, and Jiangxi, China. The physical fitness items included height, weight, standing long jump, 1000 m running (boys), and 800 m running (girls) items. Curvilinear regression analysis was used to analyze the correlations that existed between BMI and standing long jump and VO2max.

RESULTS

The BMI of Chinese 19-22 years old university students was (21.14 ± 2.92) kg/m2. The mean standing long jump score was (197.31 ± 34.07) cm. In general, the BMI reached the highest point of 207.92 cm when the BMI was 26.25 kg/m2, and then showed a decreasing trend with the increase of BMI. The overall relationship between BMI and vertical jump showed an inverted "U"-shaped curve. In terms of VO2max, the overall trend of VO2max increased gradually with the increase of BMI, and when BMI reached 40 kg/m2, VO2max was 4.34 L-kg-1-min-1.

CONCLUSION

Chinese university students showed an inverted "U" curve relationship between BMI and standing long jump in general, while VO2max showed a gradual increase with increasing BMI. Compared with the cardiorespiratory fitness of Chinese university students, the effect of BMI changes on muscle strength was greater.

Skeletal muscle dysfunction with advancing age

As a result of advances in medical treatments and associated policy over the last century, life expectancy has risen substantially and continues to increase globally. However, the disconnect between lifespan and 'health span' (the length of time spent in a healthy, disease-free state) has also increased, with skeletal muscle being a substantial contributor to this. Biological ageing is accompanied by declines in both skeletal muscle mass and function, termed sarcopenia. The mechanisms underpinning sarcopenia are multifactorial and are known to include marked alterations in muscle protein turnover and adaptations to the neural input to muscle. However, to date, the relative contribution of each factor remains largely unexplored. Specifically, muscle protein synthetic responses to key anabolic stimuli are blunted with advancing age, whilst alterations to neural components, spanning from the motor cortex and motoneuron excitability to the neuromuscular junction, may explain the greater magnitude of function losses when compared with mass. The consequences of these losses can be devastating for individuals, their support networks, and healthcare services; with clear detrimental impacts on both clinical (e.g., mortality, frailty, and post-treatment complications) and societal (e.g., independence maintenance) outcomes. Whether declines in muscle quantity and quality are an inevitable component of ageing remains to be completely understood. Nevertheless, strategies to mitigate these declines are of vital importance to improve the health span of older adults. This review aims to provide an overview of the declines in skeletal muscle mass and function with advancing age, describes the wide-ranging implications of these declines, and finally suggests strategies to mitigate them, including the merits of emerging pharmaceutical agents.

Bidirectional Relationships between Sarcopenia and Pelvic Floor Disorders

Sarcopenia and pelvic floor disorders (PFDs) are prevalent and often cooccurring conditions in the aging population. However, their bidirectional relationship and underlying mechanisms remain underexplored. This narrative review aims to elucidate this relationship by exploring potential causative interplays, shared pathophysiological mechanisms, and common risk factors. A comprehensive literature search was conducted to identify relevant studies focusing on epidemiological associations, interaction mechanisms, and implications for patient care. While epidemiological studies demonstrate associations between sarcopenia and PFDs, our findings reveal a cyclical relationship where sarcopenia may exacerbate PFDs through mechanisms such as decreased muscle strength and mobility. Conversely, the presence of PFDs often leads to reduced physical activity due to discomfort and mobility issues, which in turn exacerbate the muscle atrophy associated with sarcopenia. Additionally, shared risk factors such as physical inactivity, nutritional deficiencies, metabolic syndrome, and menopausal hormonal changes likely contribute to the onset and progression of both conditions. These interactions underscore the importance of concurrently integrated care approaches that address both conditions. Effective management requires comprehensive screening, the recognition of contributing factors, and tailored exercise regimens supported by a multidisciplinary approach. Future research should focus on longitudinal studies tracking disease progression and evaluating the efficacy of multidisciplinary care models in optimizing patient outcomes.

Timing of TORC1 inhibition dictates Pol III involvement in Caenorhabditis elegans longevity

Organismal growth and lifespan are inextricably linked. Target of Rapamycin (TOR) signalling regulates protein production for growth and development, but if reduced, extends lifespan across species. Reduction in the enzyme RNA polymerase III, which transcribes tRNAs and 5S rRNA, also extends longevity. Here, we identify a temporal genetic relationship between TOR and Pol III in Caenorhabditis elegans, showing that they collaborate to regulate progeny production and lifespan. Interestingly, the lifespan interaction between Pol III and TOR is only revealed when TOR signaling is reduced, specifically in adulthood, demonstrating the importance of timing to control TOR regulated developmental versus adult programs. In addition, we show that Pol III acts in C. elegans muscle to promote both longevity and healthspan and that reducing Pol III even in late adulthood is sufficient to extend lifespan. This demonstrates the importance of Pol III for lifespan and age-related health in adult C. elegans.

Evaluation of Factors Influencing Handgrip Strength Asymmetry in Older Peruvian Adults

BACKGROUND

Sarcopenia is a musculoskeletal disease involving the reduction of muscle mass, strength, and performance. Handgrip strength (HGS) measurements included in frailty assessments are great biomarkers of aging and are related to functional deficits. We assessed the association between potential influencing factors and HGS asymmetry in older Peruvian adults.

METHODS

We used a database of the Peruvian Naval Medical Center "Cirujano Santiago Távara" located in Callao, Peru. All the patients included were ≥60 years old and had an HGS measurement in the dominant and non-dominant hand.

RESULTS

From a total of 1,468 patients, 74.66% had HGS asymmetry. After adjustment, calf circumference weakness (adjusted prevalence ratio [aPR]=1.08; 95% confidence interval [CI], 1.01-1.15), falls risk (aPR = 1.08; 95% CI, 1.02-1.16), and an altered Lawton index (aPR=0.92; 95% CI, 0.84-0.99) were associated with HGS asymmetry.

CONCLUSION

Our findings suggest that HGS asymmetry should be measured along with other geriatric assessments used to evaluate health outcomes in the elderly to enhance health promotion and prevention aimed at preserving muscle strength to curb functional limitations in the elderly.

Delineating the contribution of ageing and physical activity to changes in mitochondrial characteristics across the lifespan

Ageing is associated with widespread physiological changes prominent within all tissues, including skeletal muscle and the brain, which lead to a decline in physical function. To tackle the growing health and economic burdens associated with an ageing population, the concept of healthy ageing has become a major research priority. Changes in skeletal muscle mitochondrial characteristics have been suggested to make an important contribution to the reductions in skeletal muscle function with age, and age-related changes in mitochondrial content, respiratory function, morphology, and mitochondrial DNA have previously been reported. However, not all studies report changes in mitochondrial characteristics with ageing, and there is increasing evidence to suggest that physical activity (or inactivity) throughout life is a confounding factor when interpreting age-associated changes. Given that physical activity is a potent stimulus for inducing beneficial adaptations to mitochondrial characteristics, delineating the influence of physical activity on the changes in skeletal muscle that occur with age is complicated. This review aims to summarise our current understanding and knowledge gaps regarding age-related changes to mitochondrial characteristics within skeletal muscle, as well as to provide some novel insights into brain mitochondria, and to propose avenues of future research and targeted interventions. Furthermore, where possible, we incorporate discussions of the modifying effects of physical activity, exercise, and training status, to purported age-related changes in mitochondrial characteristics.

Does Aerobic Exercise Increase Skeletal Muscle Mass in Female and Male Adults?

INTRODUCTION

It is uncertain whether aerobic exercise in the form of walking contributes to the preservation or increase in total or regional skeletal muscle mass (SMM).

PURPOSE

This study aimed to determine the effects of aerobic exercise on total and regional (upper body verses leg SMM) in male ( n = 105) and female ( n = 133) adults with overweight and obesity.

METHODS

A retrospective analysis of data from four randomized controlled trials. Participants included those who completed the given trial (control, n = 63; intervention, n = 175) and with complete magnetic resonance imaging (MRI) measured adipose tissue and SMM pre- and postintervention. Macronutrient intake was assessed for a subsample of participants. Supervised exercise was performed by walking on a treadmill for durations ranging from 12 to 24 wk at intensities between 50% and 75% of V̇O 2peak .

RESULTS

All MRI-measured adipose tissue depots were reduced, and cardiorespiratory fitness was increased by aerobic exercise compared with controls ( P < 0.001). Independent of baseline SMM, aerobic exercise was associated with a small reduction (estimated mean difference ± standard error) in whole-body SMM (-0.310 ± 0.150 kg, P = 0.039) and upper body SMM (-0.273 ± 0.121 kg, P = 0.025) compared with control. No between-group difference was observed for change in leg SMM ( P > 0.10). A negative association was observed between the relative change in body weight and change in total ( R2 = 0.37, P < 0.001), upper body ( R2 = 0.21, P < 0.001), and leg SMM ( R2 = 0.09, P = 0.701). The SMM-to-adipose tissue ratio increased in response to aerobic exercise and was positively associated with weight loss ( P < 0.001). Change in SMM was not associated with dietary protein intake ( P > 0.10).

CONCLUSIONS

Aerobic exercise performed while walking preserves, but does not increase, SMM in exercising muscle of adults. SMM not directly targeted by aerobic exercise may not be maintained.

Body mass composition analysis as a predictor of overweight and obesity in children and adolescents

Introduction

Body mass composition is directly related to health and its disorders are correlated with diseases such as obesity, diabetes, osteoporosis and sarcopenia. The purpose of this study was to analyze body mass composition among traditional elementary school students and ballet school students.

Methods

A total of 340 students participated in the study, 95 of whom attended ballet school and 245 elementary school students. A Tanita BC-418 MA analyzer was used to analyze body mass composition. Such body composition indices as BMI (Body Mass Index), muscle mass, fat mass, lean body mass and water content were evaluated.

Results

The results show statistical significance for BMI between high school ballet students and elementary school ballet students, as well between high school ballet students and elementary school students. Comparisons in relation to gender and schools BMI, statistical significance was obtained for: BHSw (ballet high school women) and EBSw (elementary ballet school women), BHSw and ESw (elementary school women), BHSm (ballet high school men) and EBSm (elementary ballet school men), and between BHSm and ESw. Comparing muscle mass index (kg) between ballet high school and elementary school, between ballet high school and elementary school, and between ballet high school and elementary school - statistical significance was obtained for all comparisons. Analyzing in pairwise comparisons by gender and school achieved a statistically significant difference for: BHSw and EBSw, BHSm and EBSw, EBSw and ESm. Comparing the fat mass index (kg), no significant differences were observed between the analyzed schools and the school and gender of the children studied. The value of the lean body mass index differed significantly between groups by school and gender. Comparing the water content index, statistically significant differences were obtained for school and gender.

Discussion

The body mass composition of ballet school students differs from that of standard school students.

Epigenome-wide association study identifies DNA methylation loci associated with handgrip strength in Chinese monozygotic twins

Background: The decline in muscle strength and function with aging is well recognized, but remains poorly characterized at the molecular level. Here, we report the epigenetic relationship between genome-wide DNA methylation and handgrip strength (HGS) among Chinese monozygotic (MZ) twins. Methods: DNA methylation (DNAm) profiling was conducted in whole blood samples through Reduced Representation Bisulfite Sequencing method. Generalized estimating equation was applied to regress the DNAm of each CpG with HGS. The Genomic Regions Enrichment of Annotations Tool was used to perform enrichment analysis. Differentially methylated regions (DMRs) were detected using comb-p. Causal inference was performed using Inference about Causation through Examination of Familial Confounding method. Finally, we validated candidate CpGs in community residents. Results: We identified 25 CpGs reaching genome-wide significance level. These CpGs located in 9 genes, especially FBLN1, RXRA, and ABHD14B. Many enriched terms highlighted calcium channels, neuromuscular junctions, and skeletal muscle organ development. We identified 21 DMRs of HGS, with several DMRs within FBLN1, SLC30A8, CST3, and SOCS3. Causal inference indicated that the DNAm of 16 top CpGs within FBLN1, RXRA, ABHD14B, MFSD6, and TYW1B might influence HGS, while HGS influenced DNAm at two CpGs within FBLN1 and RXRA. In validation analysis, methylation levels of six CpGs mapped to FLBN1 and one CpG mapped to ABHD14B were negatively associated with HGS weakness in community population. Conclusion: Our study identified multiple DNAm variants potentially related to HGS, especially CpGs within FBLN1 and ABHD14B. These findings provide new clues to the epigenetic modification underlying muscle strength decline.

Sarcopenia risk, sarcopenia-related quality of life, and associated factors in people living with human immunodeficiency virus (HIV): A web-based survey

OBJECTIVES

We aimed to screen for the risk of sarcopenia and sarcopenia-related quality of life and associated factors of people living with HIV (PLWH).

RESEARCH METHODS AND PROCEDURES

This nonprobabilistic web-based survey evaluated PLWH. The participants were invited directly from a university-based inpatient clinic and responded to a web questionnaire that included the SARC-F and SarQoL to screen people at risk of sarcopenia and their quality of life. People at risk of sarcopenia were defined by the proposed cutoff points for SARC-F (≥ 4 points), and SarQoL overall score was categorized according to the median. Moreover, we performed a logistic regression to investigate associations between HIV-, lifestyle-, and health-associated factors (i.e., physical activity, dietary pattern, sleep quality, gastrointestinal symptoms, HIV diagnosis, type, combinations, and duration of ART, smoking, drinking, BMI, and weight loss), and outcomes (SARC-F and SarQoL).

RESULTS

The sample comprised 202 PLWH, mainly middle-aged (50.6-60.5 y; n = 101). Only 5.9% (n = 12) are at risk of sarcopenia according to SARC-F, and only 17.3% (n = 35) exhibited lower sarcopenia-related quality of life according to SarQoL. In the multiple models, only the gastrointestinal symptoms increased the odds of sarcopenia risk (OR: 1.058; P = 0.01) and poor sarcopenia-associated quality of life (OR: 1.041; P = 0.013).

CONCLUSIONS

We verified that only 5.9% and 17.3% of PLWH are at risk of sarcopenia and presented lower sarcopenia-related quality of life, respectively. Only the gastrointestinal symptoms were associated with a risk of sarcopenia and lower sarcopenia-related quality of life, without significant differences between age groups.

Health literacy mediates the relationships of cognitive and physical functions with health-related quality of life in older adults

Background

Declining cognitive function (CF) and physical function (PF) relate to poorer health-related quality of life (HRQoL) in older adults. As health literacy (HL) facilitates health information utilization, it may mediate links between functionality and HRQoL appraisals. This study examined HL as an intermediary between joint CF and PF contributions and HRQoL in Hong Kong older adults.

Methods

490 older adults aged 50-80 years completed assessments from March to July 2021. Health Literacy Survey Questionnaire Short Form 12 questions (HLS-SF12), Montreal Cognitive Assessment (MoCA), Senior Fitness Test (SFT) and 12-Item Short-Form Health Survey version 2 (SF-12v2) were used to assess HL, CF, PF and HRQoL, respectively. Path analysis tested a model with HL mediating CF/PF predictors and HRQoL outcome.

Results

Results for direct effects indicated that CF significantly associated with PF (β = 0.115, SE = 0.012, p < 0.001), PF significantly connected to HL (β = 0.101, SE = 0.022, p < 0.001), and HL significantly related to HRQoL (β = 0.457, SE = 0.049, p < 0.001). Meanwhile, PF significantly linked to HRQoL directly (β = 0.156, SE = 0.025, p < 0.001) as well as indirectly (β = 0.046, 95% CI [0.028, 0.067]). Significant mediating effect of HL was found on the relationship of PF and HRQoL.

Conclusion

Findings confirm CF and PF joint impacts on HL and HRQoL in older adults, elucidating HL's mediating role in translating functionality levels into HRQoL. Fostering enduring health knowledge access may thus buffer effects of age-related declines on well-being. Results can inform interventions leveraging this pathway to promote resilient trajectories.

A novel imaging method (FIM-ID) reveals that myofibrillogenesis plays a major role in the mechanically induced growth of skeletal muscle

An increase in mechanical loading, such as that which occurs during resistance exercise, induces radial growth of muscle fibers (i.e. an increase in cross-sectional area). Muscle fibers are largely composed of myofibrils, but whether radial growth is mediated by an increase in the size of the myofibrils (i.e. myofibril hypertrophy) and/or the number of myofibrils (i.e. myofibrillogenesis) is not known. Electron microscopy (EM) can provide images with the level of resolution that is needed to address this question, but the acquisition and subsequent analysis of EM images is a time- and cost-intensive process. To overcome this, we developed a novel method for visualizing myofibrils with a standard fluorescence microscope (fluorescence imaging of myofibrils with image deconvolution [FIM-ID]). Images from FIM-ID have a high degree of resolution and contrast, and these properties enabled us to develop pipelines for automated measurements of myofibril size and number. After extensively validating the automated measurements, we used both mouse and human models of increased mechanical loading to discover that the radial growth of muscle fibers is largely mediated by myofibrillogenesis. Collectively, the outcomes of this study offer insight into a fundamentally important topic in the field of muscle growth and provide future investigators with a time- and cost-effective means to study it.

YTHDF2 governs muscle size through a targeted modulation of proteostasis

The regulation of proteostasis is fundamental for maintenance of muscle mass and function. Activation of the TGF-β pathway drives wasting and premature aging by favoring the proteasomal degradation of structural muscle proteins. Yet, how this critical post-translational mechanism is kept in check to preserve muscle health remains unclear. Here, we reveal the molecular link between the post-transcriptional regulation of m6A-modified mRNA and the modulation of SMAD-dependent TGF-β signaling. We show that the m6A-binding protein YTHDF2 is essential to determining postnatal muscle size. Indeed, muscle-specific genetic deletion of YTHDF2 impairs skeletal muscle growth and abrogates the response to hypertrophic stimuli. We report that YTHDF2 controls the mRNA stability of the ubiquitin ligase ASB2 with consequences on anti-growth gene program activation through SMAD3. Our study identifies a post-transcriptional to post-translational mechanism for the coordination of gene expression in muscle.

Postprandial amino acid response after the ingestion of pea protein, milk protein, casein and a casein-pea blend, in healthy older adults

To identify the potential anabolic properties of a dairy-plant protein blend as compared to single plant-based and single dairy protein, the postprandial amino acid (AA) response of pea protein, milk protein, micellar casein, and a casein-pea protein blend was investigated in healthy older adults (age 72.3 ± 3.4 years, BMI 25.3 ± 2.9 kg/m2). Plasma AA levels were measured, before and up to 5 h after ingestion of each 20 g protein. Blending casein-pea in a 60/40 mixture resulted in improved plasma AA availability, i.e. area under the curve (AUC) and peak height, of total (essential) AA and of key AAs methionine and leucine compared to pea only, while preserving the higher availability of arginine. The casein/pea blend clearly showed an AA response that was in between that of its single constituents, indicating that blending could be a solution to improve a lower quality (plant) protein, which could be of relevance for older adults.

Determining the feasibility of characterising cellular senescence in human skeletal muscle and exploring associations with muscle morphology and physical function at different ages: findings from the MASS_Lifecourse Study

Cellular senescence may be associated with morphological changes in skeletal muscle and changes in physical function with age although there have been few human studies. We aimed to determine the feasibility of characterising cellular senescence in skeletal muscle and explored sex-specific associations between markers of cellular senescence, muscle morphology, and physical function in participants from the MASS_Lifecourse Study. Senescence markers (p16, TAF (Telomere-Associated DNA Damage Foci), HMGB1 (High Mobility Group Box 1), and Lamin B1) and morphological characteristics (fibre size, number, fibrosis, and centrally nucleated fibres) were assessed in muscle biopsies from 40 men and women (age range 47-84) using spatially-resolved methods (immunohistochemistry, immunofluorescence, and RNA and fluorescence in situ hybridisation). The associations between senescence, morphology, and physical function (muscle strength, mass, and physical performance) at different ages were explored. We found that most senescence markers and morphological characteristics were weakly associated with age in men but more strongly, although non-significantly, associated with age in women. Associations between senescence markers, morphology, and physical function were also stronger in women for HMGB1 and grip strength (r = 0.52); TAF, BMI, and muscle mass (r > 0.4); Lamin B1 and fibrosis (r =  - 0.5); fibre size and muscle mass (r ≥ 0.4); and gait speed (r =  - 0.5). However, these associations were non-significant. In conclusion, we have demonstrated that it is feasible to characterise cellular senescence in human skeletal muscle and to explore associations with morphology and physical function in women and men of different ages. The findings require replication in larger studies.

The mediating role of inflammaging between mitochondrial dysfunction and sarcopenia in aging: a review

Sarcopenia, characterized by the insidious reduction of skeletal muscle mass and strength, detrimentally affects the quality of life in elderly cohorts. Present therapeutic strategies are confined to physiotherapeutic interventions, signaling a critical need for elucidation of the etiological underpinnings to facilitate the development of innovative pharmacotherapies. Recent scientific inquiries have associated mitochondrial dysfunction and inflammation with the etiology of sarcopenia. Mitochondria are integral to numerous fundamental cellular processes within muscle tissue, including but not limited to apoptosis, autophagy, signaling via reactive oxygen species, and the maintenance of protein equilibrium. Deviations in mitochondrial dynamics, coupled with compromised oxidative capabilities, autophagic processes, and protein equilibrium, result in disturbances to muscular architecture and functionality. Mitochondrial dysfunction is particularly detrimental as it diminishes oxidative phosphorylation, escalates apoptotic activity, and hinders calcium homeostasis within muscle cells. Additionally, deleterious feedback loops of deteriorated respiration, exacerbated oxidative injury, and diminished quality control mechanisms precipitate the acceleration of muscular senescence. Notably, mitochondria exhibiting deficient energetic metabolism are pivotal in precipitating the shift from normative muscle aging to a pathogenic state. This analytical review meticulously examines the complex interplay between mitochondrial dysfunction, persistent inflammation, and the pathogenesis of sarcopenia. It underscores the imperative to alleviate inflammation and amend mitochondrial anomalies within geriatric populations as a strategy to forestall and manage sarcopenia. An initial overview provides a succinct exposition of sarcopenia and its clinical repercussions. The discourse then progresses to an examination of the direct correlation between mitochondrial dysfunction and the genesis of sarcopenia. Concomitantly, it accentuates potential synergistic effects between inflammatory responses and mitochondrial insufficiencies during the aging of skeletal muscle, thereby casting light upon emergent therapeutic objectives. In culmination, this review distills the prevailing comprehension of the mitochondrial and inflammatory pathways implicated in sarcopenia and delineates extant lacunae in knowledge to orient subsequent scientific inquiry.

A Novel Imaging Method (FIM-ID) Reveals that Myofibrillogenesis Plays a Major Role in the Mechanically Induced Growth of Skeletal Muscle

An increase in mechanical loading, such as that which occurs during resistance exercise, induces radial growth of muscle fibers (i.e., an increase in cross-sectional area). Muscle fibers are largely composed of myofibrils, but whether radial growth is mediated by an increase in the size of the myofibrils (i.e., myofibril hypertrophy) and/or the number of myofibrils (i.e., myofibrillogenesis) is not known. Electron microscopy (EM) can provide images with the level of resolution that is needed to address this question, but the acquisition and subsequent analysis of EM images is a time- and cost-intensive process. To overcome this, we developed a novel method for visualizing myofibrils with a standard fluorescence microscope (FIM-ID). Images from FIM-ID have a high degree of resolution and contrast, and these properties enabled us to develop pipelines for automated measurements of myofibril size and number. After extensively validating the automated measurements, we used both mouse and human models of increased mechanical loading to discover that the radial growth of muscle fibers is largely mediated by myofibrillogenesis. Collectively, the outcomes of this study offer insight into a fundamentally important topic in the field of muscle growth and provide future investigators with a time- and cost-effective means to study it.

Impact of Environmental Factors on the ACL Injury Risk in Recreational Alpine Skiing

In recreational alpine skiing, an ACL injury represents the most common injury. Skiing is a complex activity where the skier interacts with the environment, such as weather, snow conditions, temperature, etc. Thus, the aim of this study was to evaluate the potential impact of environmental factors on ACL injury risk in recreational alpine skiers. Among a cohort of 392 ACL-injured skiers and 392 uninjured controls matched for sex and skiing skill, environmental factors were collected by questionnaire. Factors included weather conditions, snow conditions, perceived temperature, and slope difficulty at the time-point of the accident (ACL-injured skiers) or of questioning during the ski day (uninjured controls).Multiple logistic regression revealed that in addition to age, five environmental factors were significantly predictive of an ACL injury: fresh snow (OR 10.5), grippy snow (OR 7.8), icy slope condition (OR 12.4), very cold/cold perceived temperature (OR 1.6), and skiing on easy slopes (OR 6.9). In conclusion, besides age, environmental factors such as fresh and grippy snow, icy slope conditions, low temperatures, and flat slopes are associated with an increased ACL injury risk in recreational alpine skiing. Those factors are at least partly modifiable and should be taken into consideration for preventive strategies.

Hallmarks of ageing in human skeletal muscle and implications for understanding the pathophysiology of sarcopenia in women and men

Ageing is a complex biological process associated with increased morbidity and mortality. Nine classic, interdependent hallmarks of ageing have been proposed involving genetic and biochemical pathways that collectively influence ageing trajectories and susceptibility to pathology in humans. Ageing skeletal muscle undergoes profound morphological and physiological changes associated with loss of strength, mass, and function, a condition known as sarcopenia. The aetiology of sarcopenia is complex and whilst research in this area is growing rapidly, there is a relative paucity of human studies, particularly in older women. Here, we evaluate how the nine classic hallmarks of ageing: genomic instability, telomere attrition, epigenetic alterations, loss of proteostasis, deregulated nutrient sensing, mitochondrial dysfunction, cellular senescence, stem cell exhaustion, and altered intercellular communication contribute to skeletal muscle ageing and the pathophysiology of sarcopenia. We also highlight five novel hallmarks of particular significance to skeletal muscle ageing: inflammation, neural dysfunction, extracellular matrix dysfunction, reduced vascular perfusion, and ionic dyshomeostasis, and discuss how the classic and novel hallmarks are interconnected. Their clinical relevance and translational potential are also considered.

Handgrip strength and work limitations: A prospective cohort study of 70,820 adults aged 50 and older

The purpose of the study was to investigate the association between handgrip strength and the incidence of work limitations in European adults aged 50 and older. We conducted a prospective cohort study among adults aged 50 and older from 27 European countries and Israel. Data were collected from the Survey of Health, Ageing and Retirement in Europe (SHARE) waves 1, 2, 4, 5, 6, and 7. Handgrip strength was measured using a hand dynamometer (Smedley, S Dynamometer, TTM) and participants replied to questions about work limitations. Cox regression was conducted for statistical analyses. A total of 70,820 older adults (mean age 61 ± 7.7 years; 54.3 % women) were followed during a mean of 3.8 ± 2.9 years. The fully adjusted model showed that participants with low handgrip strength (<16 kg in women and <27 kg in men) had a significantly higher risk of work limitations compared with participants with normal values of handgrip strength (hazard ratio: 1.36; 95 % confidence interval: 1.28-1.44). Kaplan-Meier trajectories revealed that the survival probability to experience work limitations in the normal handgrip category was 20 % lower than in the low handgrip category in most of the follow-up period. We identified low level of handgrip strength as a risk factor for work limitations in adults aged 50 years or older. This could be used as an accessible measure to screen workers at risk of developing work limitations.

Associations between physical activity, physical fitness, and body composition in adults living in Germany: A cross-sectional study

BACKGROUND & AIMS

Body composition (BC) changes with age and is associated with morbidity and mortality. A physically active lifestyle influences BC and represents an important predictor of successful aging. To emphasize this, the World Health Organization established activity recommendations for all age groups. We describe BC during adulthood using a cross-sectional sample from a German community and investigate the associations between physical activity (PA), physical fitness (PF), and BC.

METHODS

Data from 329 men and women aged 35 to 86 years were analyzed. PA was measured by questionnaire and classified into sport activity and habitual activity. PF was measured through physical performance tests and BC by bioelectrical impedance analysis. Fat mass index (FMI) and fat-free mass index (FFMI) were calculated to represent height-adjusted BC. Associations between PA, PF, and BC were analyzed using linear regression models.

RESULTS

For both sexes, strength was positively associated with FFMI (♂: ß = 0.313; ♀: ß = 0.213) and phase angle (♂: ß = 0.357; ♀: ß = 0.409). For FMI, a significant negative association with strength was found only in women (ß = -0.189). Cardiorespiratory fitness showed a negative association with FMI (ß = -0.312) and FFMI (ß = -0.201) for men, while in women a positive association was found for FFMI (ß = 0.186). For coordination, a significant association with FMI was observed only in women (ß = -0.190). Regarding PA only one significant relationship between sport activity and FMI among women (ß = -0.170) was found.

CONCLUSIONS

In our sample, PF was closer related to BC than PA. Strength and cardiorespiratory fitness were the strongest predictors for BC. This supports the World Health Organization's activity recommendations to include both resistance and endurance training in the weekly sports program to maintain a healthy BC.

Prediction equations to estimate muscle mass using anthropometric data: a systematic review

CONTEXT

Reduced muscle mass is linked to poor outcomes in both inpatients and outpatients, highlighting the importance of muscle mass assessment in clinical practice. However, laboratory methods to assess muscle mass are not yet feasible for routine use in clinical practice because of limited availability and high costs.

OBJECTIVE

This work aims to review the literature on muscle mass prediction by anthropometric equations in adults or older people.

DATA SOURCES

The following databases were searched for observational studies published until June 2022: MEDLINE, Embase, Scopus, SPORTDiscus, and Web of Science.

DATA EXTRACTION

Of 6437 articles initially identified, 63 met the inclusion criteria for this review. Four independent reviewers, working in pairs, selected and extracted data from those articles.

DATA ANALYSIS

Two studies reported new equations for prediction of skeletal muscle mass: 10 equations for free-fat mass and lean soft tissue, 22 for appendicular lean mass, 7 for upper-body muscle mass, and 7 for lower-body muscle mass. Twenty-one studies validated previously proposed equations. This systematic review shows there are numerous equations in the literature for muscle mass prediction, and most are validated for healthy adults. However, many equations were not always accurate and validated in all groups, especially people with obesity, undernourished people, and older people. Moreover, in some studies, it was unclear if fat-free mass or lean soft tissue had been assessed because of an imprecise description of muscle mass terminology.

CONCLUSION

This systematic review identified several feasible, practical, and low-cost equations for muscle mass prediction, some of which have excellent accuracy in healthy adults, older people, women, and athletes. Malnourished individuals and people with obesity were understudied in the literature, as were older people, for whom there are only equations for appendicular lean mass.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO registration number CRD42021257200.

Which trunk muscle parameter is the best predictor for physical function in older adults?

Background

Despite preliminary evidence demonstrating the relevance of trunk muscle strength for physical function in older adults, it is not clear which muscle-related trunk parameter is the best predictor for physical functions. Therefore, this study aimed to compare trunk muscle morphology or strength parameters regarding their predictive ability for physical functions.

Methods

Seventy-four older adults (38 men, 36 women, mean age 76.85 years) were tested for maximum absolute and relative isokinetic trunk flexion and extension strength, trunk lean mass, and trunk muscle quality. Functional assessment included normal and fast walking speed, repeated sit-to-stand transfer, timed up and go, and postural sway during a closed-feet and a semi-tandem stance adjusted for body height. Pearson's correlations were used to compare relationship between trunk strength adjusted and unadjusted for body weight to physical functions. Linear regression analysis including sex and age as co-variables was performed between trunk muscle and functional test parameters.

Results

Relative back extension strength was the most consistent significant predictor for all physical function tests (p = 0.004-0.04) except for postural sway. Relative trunk flexion strength was related to normal walking speed (p = 0.024). Trunk lean mass was related to timed up and go performance (p = 0.024).

Conclusion

Relative back extension strength is associated with better performance in nearly all standard tests for physical function in older adults, while trunk flexion strength and lean mass seem to play a minor role. Our findings emphasize the importance of trunk muscle strength, especially the back extensor muscles, for physical function in older adults.

A focus on leucine in the nutritional regulation of human skeletal muscle metabolism in ageing, exercise and unloading states

Muscle protein synthesis (MPS) and muscle protein breakdown (MPB) are influenced through dietary protein intake and physical (in)activity, which it follows, regulate skeletal muscle (SKM) mass across the lifespan. Following consumption of dietary protein, the bio-availability of essential amino acids (EAA), and primarily leucine (LEU), drive a transient increase in MPS with an ensuing refractory period before the next MPS stimulation is possible (due to the "muscle full" state). At the same time, MPB is periodically constrained via reflex insulin actions. Layering exercise on top of protein intake increases the sensitivity of SKM to EAA, therefore extending the muscle full set-point (∼48 h), to permit long-term remodelling (e.g., hypertrophy). In contrast, ageing and physical inactivity are associated with a premature muscle full set-point in response to dietary protein/EAA and contractile activity. Of all the EAA, LEU is the most potent stimulator of the mechanistic target of rapamycin complex 1 (mTORC1)-signalling pathway, with the phosphorylation of mTORC1 substrates increasing ∼3-fold more than with all other EAA. Furthermore, maximal MPS stimulation is also achieved following low doses of LEU-enriched protein/EAA, negating the need for larger protein doses. As a result, LEU supplementation has been of long term interest to maximise muscle anabolism and subsequent net protein accretion, especially when in tandem with resistance exercise. This review highlights current knowledge vis-à-vis the anabolic effects of LEU supplementation in isolation, and in enriched protein/EAA sources (i.e., EAA and/or protein sources with added LEU), in the context of ageing, exercise and unloading states.

Age-Related Differences between Old and Very Old Men in Performance and Fatigability Are Evident after Cycling but Not Isometric or Concentric Single-Limb Tasks

PURPOSE

This study aimed to compare performance and fatigability between young (n = 13; 18-30 yr), old (n = 13; 60-80 yr), and very old (n = 12; >80 yr) men during a single-joint isometric (ISO) and concentric (CON) task performed on an isokinetic dynamometer and a cycling (BIKE) task.

METHODS

Participants randomly performed incremental tasks consisting of stages of 75 contractions (i.e., 120 s, 0.8 s on/0.8 s off) for ISO and CON and 120 s at 37.5 rpm (similar duty cycle) for BIKE. Increments were set as a percentage of body weight. Knee extensor maximal force, voluntary activation, and twitch amplitude were measured at baseline, after each stage, and at task failure (five out of eight contractions below the target force or 6 s in a row at a cadence <37.5 rpm).

RESULTS

Compared with young men, performance (number of stages) was 24% and 40% lower in old and very old men in ISO, 54% and 59% lower in CON, and 36% and 60% lower in BIKE (all P < 0.05). Performance of old and very old differed only in BIKE (P < 0.01). For the last common stages performed, compared with young, force loss was greater for very old men in ISO and for old and very old men in BIKE (all P < 0.05). Overall, for the last common stage performed and task failure, old and very old men presented similar force loss, alterations in voluntary activation, and twitch amplitude.

CONCLUSIONS

Our findings reveal that, with workloads relative to body weight, differences in performance between old and very old men could only be observed during BIKE (i.e., the more ecologically valid task). Results from isometric or concentric conditions might not be transferable to dynamic exercise with large muscle masses.

Relationship between Euthyroidism and Muscle Mass and Strength: A Systematic Review

Thyroid hormones play a crucial role in skeletal muscle development, suggesting that thyroid function may influence muscle mass and muscle strength, which are both fundamental health-related indicators of several age-related consequences. However, whether there is a relationship between thyroid hormones, muscle mass, and muscle strength in individuals without thyroid dysfunctions is still unknown. Therefore, this systematic review aims to investigate whether thyroid hormones are related to muscle mass and strength parameters in euthyroid individuals. Three databases were searched (PubMed, Scopus, Web of Science) up to February 14, 2022, for peer-reviewed papers published in English. The search results were conducted independently by two different reviewers. The review included 13 studies with a total of 241,044 participants. All studies were observational: twelve studies measured thyroid stimulating hormone, ten and thirteen studies measured free triiodothyronine and free thyroxine, four studies analyzed the thyroid hormone ratio. The assessment methods for muscle mass were computed tomography, dual-energy X-ray absorptiometry and bioimpedance analysis, whereas hand dynamometer for muscle strength. Low levels within the normal range of free triiodothyronine, high levels within the normal range of free thyroxine, and lower thyroid hormone ratio may contribute to a reduced muscle function, which seems more evident in older males.

Super-Resolution Imaging Reveals the Nanoscale Distributions of Dystroglycan and Integrin Itga7 in Zebrafish Muscle Fibers

Cell signaling is determined partially by the localization and abundance of proteins. Dystroglycan and integrin are both transmembrane receptors that connect the cytoskeleton inside muscle cells to the extracellular matrix outside muscle cells, maintaining proper adhesion and function of muscle. The position and abundance of Dystroglycan relative to integrins is thought to be important for muscle adhesion and function. The subcellular localization and quantification of these receptor proteins can be determined at the nanometer scale by FPALM super-resolution microscopy. We used FPALM to determine localizations of Dystroglycan and integrin proteins in muscle fibers of intact zebrafish (Danio rerio). Results were consistent with confocal imaging data, but illuminate further details at the nanoscale and show the feasibility of using FPALM to quantify interactions of two proteins in a whole organism.

Effect of sodium-glucose transporter 2 inhibitors on sarcopenia in patients with type 2 diabetes mellitus: a systematic review and meta-analysis

Objective

Sarcopenia has been recognized as the third category of disabling complications in patients with type 2 diabetes mellitus(T2DM), in addition to micro- and macrovascular complications. Sodium-glucose co-transporter 2 (SGLT2) inhibitors are innovative glucose-lowering treatments that have been shown to reduce body weight and enhance cardiovascular and renal outcomes. However, there is vigilance that SGLT2 inhibitors should be taken cautiously because they target skeletal muscle and may raise the risk of sarcopenia. Herein, we conducted a meta-analysis of randomized controlled trials to evaluate the effects of SGLT2 inhibitors on sarcopenia in patients with T2DM.

Method

Relevant studies were obtained from PubMed, Embase, Medicine, Cochrane, and Web of Science databases to determine eligible studies until February 2023, without any language restrictions. A random effects model was utilized irrespective of heterogeneity, and the I² statistic was used to evaluate study heterogeneity. The differences in results were measured using the weighted average difference (WMD) of the continuous data, along with a 95% confidence interval (CI).

Results

A total of 25 randomized controlled trials with 2,286 participants were included. SGLT2 inhibitors significantly reduced weight-related changes and fat-related changes, including body weight(BW) (WMD= -2.74, 95% CI: -3.26 to -2.23, P<0.01), body mass index(BMI) (WMD= -0.72, 95% CI: -0.95 to -0.49, P<0.01), waist circumference(WC) (WMD= -1.60, 95% CI: -2.99 to -0.22, P=0.02), fat mass(FM)(WMD= -1.49, 95% CI: -2.18 to -0.80, P<0.01), percentage body fat(PBF) (WMD= -1.28, 95% CI: -1.83 to -0.74, P<0.01), visceral fat area(VFA)(WMD= -19.52, 95% CI: -25.90 to -13.14, P<0.01), subcutaneous fat area(SFA)(WMD= -19.11, 95% CI: -31.18 to -7.03, P=0.002), In terms of muscle-related changes, lean mass(LM)(WMD= -0.80, 95% CI: -1.43 to -0.16, P=0.01), and skeletal muscle mass(SMM) (WMD= -0.38, 95% CI: -0.65 to -0.10, P=0.007), skeletal muscle index(SMI) (WMD= -0.12, 95% CI: -0.22 to -0.02, P=0.02)were also significantly reduced. In addition, body water likewise decreased significantly (WMD=-0.96, 95% CI: -1.68 to -0.23, P=0.009).

Conclusions

As one of the most widely used hypoglycemic, SGLT2 inhibitors have beneficial effects on FM and BW weight loss in T2DM, such as BW, BMI, WC, FM, PBF, VFA, and SFA. However, the negative influence on muscle mass paralleled the reduction in FM and BW, and the consequent increased risk of sarcopenia warrants high attention, especially as patients are already predisposed to physical frailty.

Clinical Trial Registration

https://www.crd.york.ac.uk/prospero/#myprospero, identifier PROSPERO (No.CRD 42023396278).

Acute Cardiopulmonary Response of High-Intensity Interval Training with Elastic Resistance vs. High-Intensity Interval Training on a Treadmill in Healthy Adults

This study aims to describe and compare cardiopulmonary and subjective responses during high-intensity interval training with elastic resistance (EL-HIIT) and traditional high-intensity interval training (HIIT) sessions. Twenty-two healthy adults (27.6 ± 4.4 years) performed an EL-HIIT and a HIIT protocol consisting of 10 × 1 min at ~85% V·O2max prescribed by cardiopulmonary-specific tests. Pulmonary parameters, heart rate (HR), blood lactate, and rate of perceived exertion (RPE) were measured during exercise. Paired t-test and Cohen's d effect size were used to compare peak and average values. Two-way repeated measures ANOVA and mixed model with Bonferroni's post hoc test were used to compare each bout during the session. The EL-HIIT session showed higher peak and average values of HR, ventilation (V·E), relative and absolute oxygen uptake (V·O2), carbon dioxide production (V·CO2), and RPE than HIIT (p < 0.05). The effect size (ES) comparing HIIT and EL-HIIT was large for HR, V·E, and lactate (≥0.8) in peak values. Comparing each bout between HIIT and EL-HIIT, no difference was found in peak values (p > 0.05) during the session (excluding baseline, warm-up, and recovery). EL-HIIT presented a more pronounced cardiopulmonary and subjective response than HIIT.

Association of personal and equipment-related factors on ACL injury risk in alpine skiers with cautious or risk-taking behaviour: A case-control study

Background

In recreational alpine skiing ACL injury risk depends on the interaction of individual characteristics and behaviours as well as on equipment-related factors.

Aim

to evaluate if and to what extent personal characteristics and equipment-related parameters are associated with ACL injury risk in cautious and risk-taking recreational alpine skiers.

Methods

A retrospective questionnaire-based, case-control study of ACL-injured and uninjured in a cohort of cautious as well as risk-taking recreational skiers was conducted. Participants self-reported their demographics, skiing skill level, and risk-taking behaviour. Ski length, side-cut radius, widths of the tip, waist, and tail were recorded from each participant's skis. Standing heights at the front and rear components of the ski binding were measured with a digital sliding caliper, and a standing height ratio between the front and rear components was calculated. Ski boot sole abrasion at the toe and heel pieces was also measured with the digital sliding caliper.

Results

In total, 1068 recreational skiers (50.8% females) with a mean age of 37.8 ± 12.3 years participated, of whom 193 (22.0%) sustained an ACL injury, and 330 (30.9%) participants reported a risk-taking behaviour. Results of the multiple logistic regression analyses revealed that a higher age, a lower skill level, a higher standing height ratio, and greater ski boot sole abrasion at the toe as well as heel pieces were independently associated with an increased ACL injury risk in both the cautious and the risk-taking group. Among cautious skiers, a longer ski length was an additional significant risk factor for sustaining an ACL injury. In conclusion, the same personal and equipment related characteristics contribute to an increase in the ACL injury risk regardless of risk-taking behaviour, with the only difference that longer skis represent an additional risk factor in cautious skiers.

Are dietary intake and nutritional status of specific polyunsaturated fatty acids correlated with sarcopenia outcomes in community-dwelling older adults with sarcopenia? - Exploratory results from ENHANce

AIMS

To explore the relationship between dietary polyunsaturated fatty acids (PUFAs) intake, nutritional PUFAs status and sarcopenia outcomes in sarcopenic older adults.

METHODS

The Exercise and Nutrition for Healthy AgeiNg (ENHANce) is an ongoing 5-armed triple blinded randomized controlled trial, in sarcopenic older adults (> 65y) aiming to assess the effect of combined anabolic interventions (protein, omega-3 supplement and exercise) on physical performance in these adults, compared to single/placebo interventions. Baseline data were used for a secondary, exploratory, cross-sectional analysis. Dietary PUFAs intake was assessed with 4-day food records, status with RBC membrane fatty acids profiles. Spearman's rho(ρ) correlation coefficients were calculated to explore associations of PUFAs intake and status with sarcopenia-defining parameters (muscle strength, mass and physical performance), physical activity (step count) and quality of life (SF-36, SarQoL).

RESULTS

In total, 29 subjects (9♂/20♀, mean age 76.3 ± 5.4y) were included. Total omega-3 intake of participants (1.99 ± 0.99 g/d) was below the recommended intake (♂:2.8-5.6 g/d; ♀:2.2-4.4 g/d). Intake and status of PUFAs were not correlated. Regarding correlations with outcomes, α-linolenic acid status was inversely associated with appendicular lean mass (aLM) (ρ:-0.439; p = 0.017), whereas docosahexaenoic acid status was positively associated with aLM (ρ:0.388; p = 0.038). Some omega-3 PUFAs intake and status markers were positively associated with step count, SF-36 and SarQoL scores, whereas gamma-linolenic acid status was inversely associated with SF-36 physical component summary score (ρ = -0.426; p = 0.024).

CONCLUSIONS

Although intake of omega-3 and omega-6 was low, the present exploratory study generated new hypotheses for potential correlations of PUFAs intake and status with sarcopenia outcomes in older adults with sarcopenia.

Musculoskeletal Fitness for Identifying Low Physical Function in Older Women

AIMS

This cross-sectional study aimed to analyze the relevance of musculoskeletal fitness for identifying low physical functioning in community-dwelling older women.

METHODS

Sixty-six older women (73.62 ± 8.23 yrs old) performed a musculoskeletal fitness assessment of the upper and lower limbs. A handheld dynamometer was used to evaluate upper-limb muscle strength through a handgrip (HG) test. Lower-limb power and force were assessed from a two-leg countermovement vertical jump (VJ) on a ground reaction force platform. Physical functioning was assessed subjectively using the Composite Physical Function (CPF) questionnaire and objectively by daily step count measured by accelerometry and gait speed/agility assessed by the 8-Foot Up-and-Go (TUG) test. Logistic regressions and ROC curves were carried out to define odds ratios and ideal cutoff values for discriminatory variables.

RESULTS

VJ power showed the ability to identify low physical functioning when evaluated through the CPF (14 W/kg, 1011 W), gait speed/agility (15 W/kg, 800 W), or daily accumulated steps (17 W/kg). Considering that VJ power was normalized for body mass, the increase of 1 W/kg corresponds to a decrease of 21%, 19%, or 16% in the chance of low physical functioning when expressed by these variables, respectively. HG strength and VJ force did not show a capacity to identify low physical functioning.

CONCLUSIONS

The results suggest that VJ power is the only marker of low physical functioning when considering the three benchmarks: perception of physical ability, capacity for mobility, and daily mobility.

Influence of lower limb ischemia on skeletal muscle mass depletion in patients with peripheral artery disease

OBJECTIVES

The aim of the study was to determine the change in skeletal muscle mass over time by bioelectrical impedance analysis (BIA) in patients with peripheral artery disease (PAD).

METHODS

Patients with symptomatic PAD visiting Tokyo Medical University Hospital between January 2018 and October 2020 were retrospectively analyzed. PAD was diagnosed based on ankle brachial pressure index (ABI) < 0.9 with either leg, and confirmed by duplex scan and/or computed tomography angiography as needed. Patients undergoing endovascular treatment, surgery, or supervised exercise therapy were excluded before and during the study period. Skeletal muscle mass of the extremities was measured using bioelectrical impedance analysis. The sum of skeletal muscle masses in the arms and legs was calculated as skeletal muscle mass index (SMI). Patients were scheduled to undergo BIA at an interval of 1 year.

RESULTS

Of 119 patients, 72 patients were included in the study. All patients were ambulatory and had symptoms of intermittent claudication (Fontaine's satge II). SMI significantly decreased from 6.98 ± 1.30 at baseline to 6.83 ± 1.29 at one-year follow-up. Individual skeletal muscle mass of the ischemic leg was significantly reduced after 1 year, but not in the non-ischemic leg. A decrease in SMI (defined as SMI ≥ 0.1 kg/m² per year) was independently associated with low ABI. The optimal cut-off value of ABI for the decrease in SMI was 0.72.

CONCLUSION

These results suggest that lower limb ischemia due to PAD, especially if ABI is <0.72 or less, may result in a decrease in skeletal muscle mass that affects health and physical function.

Decreased insulin-like growth factor-1 expression in response to mechanical loading is associated with skeletal muscle anabolic resistance in cancer cachexia

OBJECTIVE

Cachexia is a systemic metabolic syndrome characterized by loss of body weight and skeletal muscle mass during chronic wasting diseases, such as cancer. Skeletal muscle in cancer cachexia is less responsive to anabolic factors including mechanical loading; however, the precise molecular mechanism is largely unknown. In this study, we examined the underlying mechanism of anabolic resistance in skeletal muscle in a cancer cachexia model.

METHODS

CD2F1 mice (male, 8 weeks old) were subcutaneously transplanted (1 × 10⁶ cells per mouse) with a mouse colon cancer-derived cell line (C26) as a model of cancer cachexia. Mechanical overload of the plantaris muscle by synergist tenotomy was performed during the 2nd week and the plantaris muscle was sampled at the 4th week following C26 transplantation.

RESULTS

The hypertrophic response of skeletal muscle (increased skeletal muscle weight/protein synthesis efficiency and activation of mechanistic target of rapamycin complex 1 signaling) associated with mechanical overload was significantly suppressed during cancer cachexia. Screening of gene expression profile and pathway analysis using microarray revealed that blunted muscle protein synthesis was associated with cancer cachexia and was likely induced by downregulation of insulin-like growth factor-1 (IGF-1) and impaired activation of IGF-1-dependent signaling.

CONCLUSIONS

These observations indicate that cancer cachexia induces resistance to muscle protein synthesis, which may be a factor for inhibiting the anabolic adaptation of skeletal muscle to physical exercise in cancer patients.

Skill-Specific Differences in Equipment-Related Risk Factors for ACL Injury in Male and Female Recreational Skiers

Background

In recreational alpine skiing, the anterior cruciate ligament (ACL) is affected in approximately 50% of serious knee injuries. There are established sex-based and skill-based differences in ACL injury risk, but the potential impact of equipment used (eg, skis, bindings, and boots) has not been evaluated.

Purpose

To evaluate individual and equipment-related risk factors for an ACL injury depending on sex and skill level.

Study Design

Case-control study; Level of evidence, 3.

Methods

This was a retrospective questionnaire-based, case-control study of female and male skiers with and without ACL injuries during 6 winter seasons (from 2014-2015 to 2019-2020). Demographic data, skill level, equipment specifications, risk-taking behavior, and ownership of ski equipment were recorded. Ski geometry (ski length; sidecut radius; and widths of the tip, waist, and tail) was taken from each participant's ski. The standing heights of the front and back part of the ski binding were measured using a digital sliding caliper, and the standing height ratio was calculated. Abrasion of the ski boot sole was also measured at the toe and heel. Participants were divided by sex into less and more skilled skiers.

Results

A total of 1817 recreational skiers participated in this study, of whom 392 (21.6%) sustained an ACL injury. A greater standing height ratio and more abrasion at the toe of the boot sole were associated with increased ACL injury risk in both sexes, independent of the skill level. Riskier behavior increased the injury risk only in male skiers, independent of the skill level, and longer skis increased the injury risk only in less skilled female skiers. Older age, the use of rented/borrowed skis, and more abrasion at the heel of the boot sole were independent risk factors for ACL injury in the more skilled skiers of both sexes.

Conclusion

Individual and equipment-related risk factors for an ACL injury partly differed according to skill level and sex. Consideration of the demonstrated equipment-related factors should be implemented in order to reduce ACL injuries in recreational skiers.

Serum concentration impacts myosin heavy chain expression but not cellular respiration in human LHCN-M2 myoblasts undergoing differentiation

NEW FINDINGS

What is the central question of this study? Does the concentration of human serum affect skeletal muscle differentiation and cellular respiration of LHCN-M2 myoblasts? What is the main finding and its importance? The concentration of serum used to differentiate LHCN-M2 skeletal muscle cells impacts the coverage of myosin heavy chain, a marker of terminally differentiated myotubes. Normalisation of mitochondrial function data to total protein negates the differences observed in absolute values, which differ as a result of increased protein content when differentiation occurs with increasing concentration of serum.

ABSTRACT

The human LHCN-M2 myoblast cell line has the potential to be used to investigate skeletal muscle development and metabolism. Experiments were performed to determine how different concentrations of human serum affect myogenic differentiation and mitochondrial function of LHCN-M2 cells. LHCN-M2 myoblasts were differentiated in serum-free medium, 0.5% or 2% human serum for 5 and 10 days. Myotube formation was assessed by immunofluorescence staining of myosin heavy chain (MHC) and molecularly by mRNA expression of Myogenic differentiation 1 (MYOD1) and Myoregulatory factor 5 (MYF5). Following differentiation, mitochondrial function was assessed to establish the impact of serum concentration on mitochondrial function. Time in differentiation increased mRNA expression of MYOD1 (day 5, 6.58 ± 1.33-fold; and day 10, 4.28 ± 1.71-fold) (P = 0.012), while suppressing the expression of MYF5 (day 5, 0.21 ± 0.11-fold; and day 10, 0.06 ± 0.03-fold) (P = 0.001), regardless of the serum concentration. Higher serum concentrations increased MHC area (serum free, 11.92 ± 0.85%; 0.5%, 23.10 ± 5.82%; 2%, 43.94 ± 8.92%) (P = 0.001). Absolute basal respiration approached significance (P = 0.06) with significant differences in baseline oxygen consumption rate (P = 0.025) and proton leak (P = 0.006) when differentiated in 2% human serum, but these were not different between conditions when normalised to total protein. Our findings show that increasing concentrations of serum of LHCN-M2 skeletal muscle cells into multinucleated myotubes, but this does not affect relative mitochondrial function.

Estimation of One-Repetition Maximum, Type, and Repetition of Resistance Band Exercise Using RGB Camera and Inertial Measurement Unit Sensors

Resistance bands are widely used nowadays to enhance muscle strength due to their high portability, but the relationship between resistance band workouts and conventional dumbbell weight training is still unclear. Thus, this study suggests a convolutional neural network model that identifies the type of band workout and counts the number of repetitions and a regression model that deduces the band force that corresponds to the one-repetition maximum. Thirty subjects performed five different exercises using resistance bands and dumbbells. Joint movements during each exercise were collected using a camera and an inertial measurement unit. By using different types of input data, several models were created and compared. As a result, the accuracy of the convolutional neural network model using inertial measurement units and joint position is 98.83%. The mean absolute error of the repetition counting algorithm ranges from 0.88 (seated row) to 3.21 (overhead triceps extension). Lastly, the values of adjusted r-square for the 5 exercises are 0.8415 (chest press), 0.9202 (shoulder press), 0.8429 (seated row), 0.8778 (biceps curl), and 0.9232 (overhead triceps extension). In conclusion, the model using 10-channel inertial measurement unit data and joint position data has the best accuracy. However, the model needs to improve the inaccuracies resulting from non-linear movements and one-time performance.

Running economy in long-distance runners is positively affected by running experience and negatively by aging

INTRODUCTION

The maximum oxygen uptake (V˙O₂max), the maximum rate of oxygen that can be sustained before the onset of blood lactate accumulation, and the metabolic cost of locomotion are the main physiological factors associated with long-distance running performance. The latter is known as the running economy. Generally, runners reach peak performance in long races between 25 and 30 years of age, with a progressive decline occurring thereafter. However, it is not known whether the running economy is affected or how it is affected by aging.

AIM

To investigate the effect of age and years of running experience on the running economy of amateur long-distance runners aged 20-80 years.

METHODS

Sixty-nine recreational long-distance runners, divided into five age groups according to decade of life, participated in this study: Group 1 (n= 9) 27.2 ± 1.3 years, Group 2 (n= 18) 35.9 ± 2.2 years, Group 3 (n= 17) 43.4 ± 2.8 years, Group 4 (n= 17) 53.0 ± 2.3 years, and Group 5 (n= 8) 65.5 ± 2.9 years. For running economy assessment, oxygen cost (OC) and energy cost (EC) were measured. Furthermore, the participants were interviewed on their running experience.

RESULTS

For EC, the two independent variables composing the regression model were age (ß = 0.703, t= 5.443, p < 0.001) and running experience (ß = -0.230, t = -1.785, p= 0.07), and 34% of the energy cost variation can be explained by these two factors. EC and OC were compared among the groups. There were no significant differences between Groups 1 and 2 (p= 0.999), Groups 1 and 3 (p= 1.000), and Groups 1 and 4 (p= 0.528). However, Group 5 had a significantly higher energy cost than Group 1 (p < 0.001), Group 2 (p < 0.001), Group 3 (p < 0.001) and Group 4 (p < 0.001).

CONCLUSION

The number of years of running experience has a positive effect on running economy, but it is insufficient to overcome the negative effect of the aging process. Furthermore, running economy was significantly worse in participants aged ≥60 years compared with that in younger athletes.

The influence of a single transcranial direct current stimulation session on physical fitness in healthy subjects: a systematic review

Physical fitness is of indisputable importance for both health, and sports. Currently, the brain is being increasingly recognized as a contributor to physical fitness. Hereby, transcranial direct current stimulation (tDCS), as an ergogenic aid, has gained scientific interest. The current PRISMA-adherent review aimed to examine the effect of tDCS on the three core components of physical fitness: muscle strength, -endurance and cardiopulmonary endurance. Randomized controlled- or cross-over trials evaluating the effect of a single tDCS session (vs. sham) in healthy individuals were included. Hereby, a wide array of tDCS-related factors (e.g., tDCS montage and dose) was taken into account. Thirty-five studies (540 participants) were included. Between-study heterogeneity in factors such as age, activity level, tDCS protocol, and outcome measures was large. The capacity of tDCS to improve physical fitness varied substantially across studies. Nevertheless, muscle endurance was most susceptible to improvements following anodal tDCS (AtDCS), with 69% of studies (n = 11) investigating this core component of physical fitness reporting positive effects. The primary motor cortex and dorsolateral prefrontal cortex were targeted the most, with positive results being reported on muscle and cardiopulmonary endurance. Finally, online tDCS seemed most beneficial, and no clear relationship between tDCS and dose-related parameters seemed present. These findings can contribute to optimizing tDCS interventions during the rehabilitation of patients with a variety of (chronic) diseases such as cardiovascular disease. Therefore, future studies should focus on further unraveling the potential of AtDCS on physical fitness and, more specifically, muscle endurance in both healthy subjects and patients suffering from (chronic) diseases. This study was registered in Prospero with the registration number CRD42021258529. "To enable PROSPERO to focus on COVID-19 registrations during the 2020 pandemic, this registration record was automatically published exactly as submitted. The PROSPERO team has not checked eligibility".

Dietary Inflammatory Index and Associations with Sarcopenia Symptomology in Community-Dwelling Older Adults

Low-grade systemic inflammation is a key driver of muscle degeneration in older adults, and diets with pro-inflammatory properties may further contribute to loss of muscle mass, strength and function. Therefore, this research aimed to explore the associations between the inflammatory potential of the diet and measures of sarcopenia symptomology in community-dwelling older adults. Upper (handgrip strength, HGS) and lower extremity (sit-to-stand) muscle strength, physical performance (timed-up-and-go, TUG) and appendicular skeletal muscle mass (ASM) was assessed according to the European Working Group on Sarcopenia in Older People version 2 (EWGSOP2) criteria. Multiple 24-hr dietary recalls were used to calculate the Dietary Inflammatory Index (DII), which was then used to group participants into anti- and pro-inflammatory dietary groups. Multiple linear regression investigated associations between DII, muscle strength, physical performance, and muscle quantity adjusted for age, gender, comorbidities, waist circumference and physical activity. Adults 65-85 years (n = 110, 72.1 ± 4.7 years, 76.4% female) were recruited. One participant was identified with sarcopenia, 35.2% were pre-frail, or frail. More participants with a pro-inflammatory DII score had low muscle quantity than those with anti-inflammatory DII (3.4% vs. 6.4%, x² = 4.537, p = 0.043) and DII was negatively associated with HGS (β = -0.157, p = 0.016) and ASM (β = -0.176, p = 0.002) which remained significant after adjusting for covariates. In this population, DII was associated with less favorable muscle strength, physical performance, and muscle quantity.

Going nuclear: Molecular adaptations to exercise mediated by myonuclei

Muscle fibers are multinucleated, and muscle fiber nuclei (myonuclei) are believed to be post-mitotic and are typically situated near the periphery of the myofiber. Due to the unique organization of muscle fibers and their nuclei, the cellular and molecular mechanisms regulating myofiber homeostasis in unstressed and stressed conditions (e.g., exercise) are unique. A key role myonuclei play in regulating muscle during exercise is gene transcription. Only recently have investigators had the capability to identify molecular changes at high resolution exclusively in myonuclei in response to perturbations in vivo. The purpose of this review is to describe how myonuclei modulate their transcriptome, epigenetic status, mobility and shape, and microRNA expression in response to exercise in vivo. Given the relative paucity of high-fidelity information on myonucleus-specific contributions to exercise adaptation, we identify specific gaps in knowledge and provide perspectives on future directions of research.

Transcriptome-Wide Study of mRNAs and lncRNAs Modified by m6A RNA Methylation in the Longissimus Dorsi Muscle Development of Cattle-Yak

Cattle-yak is a hybrid F₁ generation of cattle and yak, which has a history of more than 3000 years and has shown better production performance and higher economic benefits than those of yaks. However, up to now, there has been no study on the transcriptome-wide m⁶A methylation profile of bovine skeletal muscle and its potential biological function during muscle development. Here, we observed significant changes in the expression levels of muscle-related marker genes and methylation-related enzymes during the development of cattle-yak, and the overall m⁶A content in the Longissimus dorsi muscle of 18-month-old cattle-yak decreased significantly. A total of 36,602 peaks, 11,223 genes and 8388 lncRNAs were identified in the two groups, including 2989 differential peaks (427 up-regulated peaks and 2562 down-regulated peaks), 1457 differentially expressed genes (833 up-regulated genes and 624 down-regulated genes) and 857 differentially expressed lncRNAs (293 up-regulated lncRNAs and 564 down-regulated lncRNAs). GO and KEGG analysis revealed that they were significantly enriched in some muscle-related pathways (Wnt signaling pathway and MAPK signaling pathway) and high-altitude adaptation-related pathway (HIF-1 signaling pathway). Moreover, m⁶A abundance was positively correlated with gene expression levels, while it was negatively correlated with lncRNA expression levels. This indicates that m⁶A modification played an important role in the Longissimus dorsi muscle development of cattle-yak; however, the regulation mechanism of m⁶A-modified mRNA and lncRNA may be different. This study was the first report of transcriptome-wide m⁶A-modified mRNAs and lncRNAs atlas in the Longissimus dorsi muscle development of cattle-yak, one which will provide new perspectives for genetic improvement in bovines.

Resistance training-induced improvement in physical function is not associated to changes in endocrine somatotropic activity in prefrail older adults

CONTEXT

Resistance training improves muscle function in prefrail and frail elderly. The role of the somatotropic axis in this physiologic process remains unclear. Insulin-like growth factor I (IGF-I) and its associated proteins Insulin-like growth factor binding protein 3 (IGFBP3) and acid labile subunit (ALS) build a circulating ternary complex that mediates growth hormone (GH) effects on peripheral organs and can serve as a measure of endocrine somatotropic activity.

OBJECTIVE

The aim of this study was to assess the association between resistance training-induced changes in physical performance and basal levels of IGF-I, IGFBP-3 and ALS in prefrail older adults.

METHODS

69 prefrail community-dwelling older adults, aged 65 to 94 years, were randomly assigned to a 12-week period of strength or power training or to a control group. The study was registered at clinicaltrials.gov as NCT00783159. Serum concentrations of IGF-I, IGFBP-3 and ALS were measured at rest before and after the intervention. Hormonal differences were examined in relation to changes in physical performance assessed by the Short Physical Performance Battery (SPPB).

RESULTS

While resistance training led to significant improvements in SPPB score it did not induce significant differences in somatotropic hormone concentrations. Pre- and post-intervention changes in IGF-I, IGFBP-3, ALS or IGF/IGFBP-3 molar ratio were not related to the intervention mode, even after adjustment for age, sex, nutritional status, as well as SPPB and hormone concentrations at baseline.

CONCLUSION

Training-induced improvements in physical performance in prefrail older adults were not associated with significant changes in endocrine somatotropic activity.

Fetal muscle extract improves muscle function and performance in aged mice

Background: Loss of skeletal muscle mass and function is one of the major musculoskeletal health problems in the aging population. Recent studies have demonstrated differential proteomic profiles at different fetal stages, which might be associated with muscle growth and development. We hypothesized that extract derived from fetal muscle tissues at the stage of hypertrophy could ameliorate the loss of muscle mass and strength in aged mice.

Methods: To allow sufficient raw materials for investigation, skeletal muscle extract from fetal sheep at week 16 of gestation and maternal tissue were used in the present study. iTRAQ (isobaric tags for relative and absolute quantitation) and KEGG pathway analyses identified differentially expressed proteins in fetal sheep muscle extract vs. adult sheep muscle extract. Effects of FSME and ASME on human myoblast proliferation were studied. To examine the effect of FSME in vivo, C57BL/6 male mice at 20 months of age were subjected to intramuscular administration of FSME or vehicle control for 8 weeks. A grip strength test and ex vivo muscle force frequency test were conducted. Finally, serum samples were collected for multiplex analysis to determine potential changes in immunological cytokines upon FSME injection.

Results: Compared with ASME, 697 and 412 peptides were upregulated and downregulated, respectively, in FSME, as indicated by iTRAQ analysis. These peptides were highly related to muscle development, function, and differentiation from GO enrichment analysis. FSME promoted cell proliferation of myoblast cells (+300%, p < 0.01) without causing significant cytotoxicity at the tested concentration range compared with ASME. After 8 weeks of FSME treatment, the percentage of lean mass (+10%, p < 0.05), grip strength (+50%, p < 0.01), and ability in fatigue resistance were significantly higher than those of the control group. Isometric forces stimulated by different frequencies were higher in the control group. Histologically, the control group showed a larger cross-sectional area (+20%, p < 0.01) than the FSME group. The multiplex assay indicated that FSME treatment did not lead to an elevated circulatory level of inflammatory cytokines. Of note, after FSME treatment, we observed a significant drop in the circulating level of IL-12 (p40) from 90.8 ± 48.3 pg/ml to 82.65 ± 4.4 pg/ml, G-CSF from 23476 ± 8341.9 pg/ml to 28.35 ± 24.2 pg/ml, KC from 97.09 ± 21.2 pg/ml to 29.2 ± 7.2 pg/ml, and RANTES from 325.4 ± 17.3 pg/ml to 49.96 ± 32.1 pg/ml.

Conclusion: This is the first study demonstrating the beneficial effect of fetal muscle extract on muscle health in aged mice. Further analysis of the active ingredients of the extract will shed light on the development of a novel treatment for sarcopenia.