Effects of Aging on Type II Muscle Fibers: A Systematic Review of the Literature

Age-related breakdown in networks of inter-muscular coordination

Assessing inter-muscular coordination in older adults is crucial, as it directly impacts an individual's ability for independent functioning, injury prevention, and active engagement in daily activities. However, the precise mechanisms by which distinct muscle fiber types synchronize their activity across muscles to generate coordinated movements in older adults remain unknown. Our objective is to investigate how distinct muscle groups dynamically synchronize with each other in young and older adults during exercise. Thirty-five young adults and nine older adults performed one bodyweight squat set until exhaustion. Simultaneous surface electromyography (sEMG) recordings were taken from the left and right vastus lateralis, and left and right erector spinae. To quantify inter-muscular coordination, we first obtained ten time series of sEMG band power for each muscle, representing the dynamics of different muscle fiber types. Next, we calculated the bivariate equal-time Pearson's cross-correlation for each pair of sEMG band power time series across all leg and back muscles. The main results show (i) an overall reduction in the degree of inter-muscular coordination, and (ii) increased stratification of the inter-muscular network in older adults compared to young adults. These findings suggest that as individuals age, the global inter-muscular network becomes less flexible and adaptable, hindering its ability to reorganize effectively in response to fatigue or other stimuli. This network approach opens new avenues for developing novel network-based markers to characterize multilevel inter-muscular interactions, which can help target functional deficits and potentially reduce the risk of falls and neuro-muscular injuries in older adults.

The role of interleukin-10 in mitigating endoplasmic reticulum stress in aged mice through exercise

Although unfolded protein response (UPR) is essential for cellular protection, its prolonged activation may induce apoptosis, compromising cellular longevity. The aging process increases the endoplasmic reticulum (ER) stress in skeletal muscle. However, whether combined exercise can prevent age-induced ER stress in skeletal muscle remains unknown. Evidence suggests that ER stress may increase inflammation by counteracting the positive effects of interleukin-10 (IL-10), whereas its administration in cells inhibits ER stress and apoptosis. This study verified the effects of aging and combined exercise on physical performance, ER stress markers, and inflammation in the quadriceps of mice. Moreover, we verified the effects of IL-10 on ER stress markers. C57BL/6 mice were distributed into young (Y, 6 mo old), old sedentary (OS, sedentary, 24 mo old), and old trained group (OT, submitted to short-term combined exercise, 24 mo old). To clarify the role of IL-10 in UPR pathways, knockout mice lacking IL-10 were used. The OS mice presented worse physical performance and higher ER stress-related proteins, such as C/EBP homologous protein (CHOP) and phospho-eukaryotic translation initiation factor 2 alpha (p-eIF2α/eIF2α). The exercise protocol increased muscle strength and IL-10 protein levels in OT while inducing the downregulation of CHOP protein levels compared with OS. Furthermore, mice lacking IL-10 increased BiP, CHOP, and p-eIF2α/eIF2α protein levels, indicating this cytokine can regulate the ER stress response in skeletal muscle. Bioinformatics analysis showed that endurance and resistance training downregulated DNA damage inducible transcript 3 (DDIT3) and XBP1 gene expression in the vastus lateralis of older people, reinforcing our findings. Thus, combined exercise is a potential therapeutic intervention for promoting adjustments in ER stress markers in aged skeletal muscle.NEW & NOTEWORTHY Aging elevates endoplasmic reticulum (ER) stress in skeletal muscle, potentially heightening inflammation by opposing interleukin-10 (IL-10) effects. This study found that short-term combined exercise boosted strength and IL-10 protein levels while reducing CHOP protein levels in older mice. In addition, IL-10-deficient mice exhibited increased ER stress markers, highlighting IL-10's role in regulating ER stress in skeletal muscle. Consequently, combined exercise emerges as a therapeutic intervention to elevate IL-10 and adjust ER stress markers in aging.

Accelerated aging of skeletal muscle and the immune system in patients with chronic liver disease

Patients with chronic liver disease (CLD) often present with significant frailty, sarcopenia, and impaired immune function. However, the mechanisms driving the development of these age-related phenotypes are not fully understood. To determine whether accelerated biological aging may play a role in CLD, epigenetic, transcriptomic, and phenotypic assessments were performed on the skeletal muscle tissue and immune cells of CLD patients and age-matched healthy controls. Accelerated biological aging of the skeletal muscle tissue of CLD patients was detected, as evidenced by an increase in epigenetic age compared with chronological age (mean +2.2 ± 4.8 years compared with healthy controls at -3.0 ± 3.2 years, p = 0.0001). Considering disease etiology, age acceleration was significantly greater in both the alcohol-related (ArLD) (p = 0.01) and nonalcoholic fatty liver disease (NAFLD) (p = 0.0026) subgroups than in the healthy control subgroup, with no age acceleration observed in the immune-mediated subgroup or healthy control subgroup (p = 0.3). The skeletal muscle transcriptome was also enriched for genes associated with cellular senescence. Similarly, blood cell epigenetic age was significantly greater than that in control individuals, as calculated using the PhenoAge (p < 0.0001), DunedinPACE (p < 0.0001), or Hannum (p = 0.01) epigenetic clocks, with no difference using the Horvath clock. Analysis of the IMM-Age score indicated a prematurely aged immune phenotype in CLD patients that was 2-fold greater than that observed in age-matched healthy controls (p < 0.0001). These findings suggested that accelerated cellular aging may contribute to a phenotype associated with advanced age in CLD patients. Therefore, therapeutic interventions to reduce biological aging in CLD patients may improve health outcomes.

Resistance Training in the Heat: Mechanisms of Hypertrophy and Performance Enhancement

ABSTRACT

Pryor, JL, Sweet, D, Rosbrook, P, Qiao, J, Hess, HW, and Looney, DP. Resistance training in the heat: Mechanisms of hypertrophy and performance enhancement. J Strength Cond Res 38(7): 1350-1357, 2024-The addition of heat stress to resistance exercise or heated resistance exercise (HRE) is growing in popularity as emerging evidence indicates altered neuromuscular function and an amplification of several mechanistic targets of protein synthesis. Studies demonstrating increased protein synthesis activity have shown temperature-dependent mammalian target of rapamycin phosphorylation, supplemental calcium release, augmented heat shock protein expression, and altered immune and hormone activity. These intriguing observations have largely stemmed from myotube, isolated muscle fiber, or rodent models using passive heating alone or in combination with immobilization or injury models. A growing number of translational studies in humans show comparable results employing local tissue or whole-body heat with and without resistance exercise. While few, these translational studies are immensely valuable as they are most applicable to sport and exercise. As such, this brief narrative review aims to discuss evidence primarily from human HRE studies detailing the neuromuscular, hormonal, and molecular responses to HRE and subsequent strength and hypertrophy adaptations. Much remains unknown in this exciting new area of inquiry from both a mechanistic and functional perspective warranting continued research.

Exercise microdosing for skeletal muscle health applications to spaceflight

Findings from a recent 70-day bedrest investigation suggested intermittent exercise testing in the control group may have served as a partial countermeasure for skeletal muscle size, function, and fiber-type shifts. The purpose of the current study was to investigate the metabolic and skeletal muscle molecular responses to the testing protocols. Eight males (29 ± 2 yr) completed muscle power (6 × 4 s; peak muscle power: 1,369 ± 86 W) and V̇o2max (13 ± 1 min; 3.2 ± 0.2 L/min) tests on specially designed supine cycle ergometers during two separate trials. Blood catecholamines and lactate were measured pre-, immediately post-, and 4-h postexercise. Muscle homogenate and muscle fiber-type-specific [myosin heavy chain (MHC) I and MHC IIa] mRNA levels of exercise markers (myostatin, IκBα, myogenin, MuRF-1, ABRA, RRAD, Fn14, PDK4) and MHC I, IIa, and IIx were measured from vastus lateralis muscle biopsies obtained pre- and 4-h postexercise. The muscle power test altered (P ≤ 0.05) norepinephrine (+124%), epinephrine (+145%), lactate (+300%), and muscle homogenate mRNA (IκBα, myogenin, MuRF-1, RRAD, Fn14). The V̇o2max test altered (P ≤ 0.05) norepinephrine (+1,394%), epinephrine (+1,412%), lactate (+736%), and muscle homogenate mRNA (myostatin, IκBα, myogenin, MuRF-1, ABRA, RRAD, Fn14, PDK4). In general, both tests influenced MHC IIa muscle fibers more than MHC I with respect to the number of genes that responded and the magnitude of response. Both tests also influenced MHC mRNA expression in a muscle fiber-type-specific manner. These findings provide unique insights into the adaptive response of skeletal muscle to small doses of exercise and could help shape exercise dosing for astronauts and Earth-based individuals.NEW & NOTEWORTHY Declines in skeletal muscle health are a concern for astronauts on long-duration spaceflights. The current findings add to the growing body of exercise countermeasures data, suggesting that small doses of specific exercise can be beneficial for certain aspects of skeletal muscle health. This information can be used in conjunction with other components of existing exercise programs for astronauts and might translate to other areas focused on skeletal muscle health (e.g., sports medicine, rehabilitation, aging).

Strength in arms: empowering older adults against the risk of slipping and falling-a theoretical perspective

Background

Slips and falls are a serious health concern, particularly among older adults. Current physical therapy protocols strengthen the legs to improve balance. However, arm movements help maintain balance during a slip incident. Understanding how arm movements improve balance may help clinicians develop more comprehensive fall-prevention protocols to improve patient outcomes.

Clinical question

What limitations exist in current fall prevention protocols for reducing falls in older adults during slip incidents, and what new strategies can enhance these outcomes?

Key results

Slip incidents often result in a sideways loss of balance, leading to hip fractures in older adults. During a slip, the legs do not produce sideways motion and are less effective in regaining balance in this direction. Contrary, the arms produce 100 + degrees of abduction and this motion reduces falls by 200%+ during a slip incident. Notably, older adults exhibit 35.7% decreased arm abduction acceleration responses compared to younger adults during a slip incident. This delay may be attributed to age-related decreases in type II fibers of the deltoid. High-velocity and ballistic training have been shown to improve the proportion and size of type II fibers as well as improve fall outcomes when focused on the lower extremities.

Clinical application

Therefore, I propose incorporating arm abductor training, alongside leg exercises, as a cost-effective and low-risk intervention to enhance the slip responses in older adults. In light of its minimal risk and considerable potential benefits, starting arm abductor exercises with older adults is a sensible move.

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.

Anabolic Resistance in the Pathogenesis of Sarcopenia in the Elderly: Role of Nutrition and Exercise in Young and Old People

The development of sarcopenia in the elderly is associated with many potential factors and/or processes that impair the renovation and maintenance of skeletal muscle mass and strength as ageing progresses. Among them, a defect by skeletal muscle to respond to anabolic stimuli is to be considered. Common anabolic stimuli/signals in skeletal muscle are hormones (insulin, growth hormones, IGF-1, androgens, and β-agonists such epinephrine), substrates (amino acids such as protein precursors on top, but also glucose and fat, as source of energy), metabolites (such as β-agonists and HMB), various biochemical/intracellular mediators), physical exercise, neurogenic and immune-modulating factors, etc. Each of them may exhibit a reduced effect upon skeletal muscle in ageing. In this article, we overview the role of anabolic signals on muscle metabolism, as well as currently available evidence of resistance, at the skeletal muscle level, to anabolic factors, from both in vitro and in vivo studies. Some indications on how to augment the effects of anabolic signals on skeletal muscle are provided.

Age-related changes in mobility assessments correlate with repetitive goal-directed arm-movement performance

BACKGROUND

There is ample evidence that mobility abilities between healthy young and elderly people differ. However, we do not know whether these differences are based on different lower leg motor capacity or instead reveal a general motor condition that could be detected by monitoring upper-limb motor behavior. We therefore captured body movements during a standard mobility task, namely the Timed Up and Go test (TUG) with subjects following different instructions while performing a rapid, repetitive goal-directed arm-movement test (arm-movement test). We hypothesized that we would be able to predict gait-related parameters from arm motor behavior, even regardless of age.

METHODS

Sixty healthy individuals were assigned to three groups (young: mean 26 ± 3 years, middle-aged 48 ± 9, old 68 ± 7). They performed the arm-movement and TUG test under three conditions: preferred (at preferred movement speed), dual-task (while counting backwards), and fast (at fast movement speed). We recorded the number of contacts within 20 s and the TUG duration. We also extracted TUG walking sequences to analyze spatiotemporal gait parameters and evaluated the correlation between arm-movement and TUG results.

RESULTS

The TUG condition at preferred speed revealed differences in gait speed and step length only between young and old, while dual-task and fast execution increased performance differences significantly among all 3 groups. Our old group's gait speed decreased the most doing the dual-task, while the young group's gait speed increased the most during the fast condition. As in our TUG results, arm-movements were significant faster in young than in middle-aged and old. We observed significant correlations between arm movements and the fast TUG condition, and that the number of contacts closely predicts TUG timefast and gait speedfast. This prediction is more accurate when including age.

CONCLUSION

We found that the age-related decline in mobility performance that TUG reveals strongly depends on the test instruction: the dual-task and fast condition clearly strengthened group contrasts. Interestingly, a fast TUG performance was predictable by the performance in a fast repetitive goal-directed arm-movements test, even beyond the age effect. We assume that arm movements and the fast TUG condition reflect similarly reduced motor function.

TRIAL REGISTRATION

German Clinical Trials Register (DRKS) number: DRKS00016999, prospectively registered on March, 26, 2019.

The life and times of cellular senescence in skeletal muscle: friend or foe for homeostasis and adaptation?

A gradual decline in skeletal muscle mass and function is closely tied to increased mortality and disease risk during organismal aging. Exercise training is the most effective way to enhance muscle health, but the adaptive response to exercise as well as muscle repair potential is blunted in older individuals. Numerous mechanisms contribute to the loss of muscle mass and plasticity as aging progresses. An emerging body of recent evidence implicates an accumulation of senescent ("zombie") cells in muscle as a contributing factor to the aging phenotype. Senescent cells cannot divide but can release inflammatory factors and create an unfavorable environment for homeostasis and adaptation. On balance, some evidence indicates that cells with senescent characteristics can be beneficial for the muscle adaptive process, specifically at younger ages. Emerging evidence also suggests that multinuclear muscle fibers could become senescent. In this review, we summarize current literature on the prevalence of senescent cells in skeletal muscle and highlight the consequences of senescent cell removal on muscle mass, function, and adaptability. We examine key limitations in the field of senescence specifically in skeletal muscle and identify areas of research that require future investigation.NEW & NOTEWORTHY There is evidence to suggest that senescent "zombie" cells may or may not accrue in aging skeletal muscle. When muscle is perturbed regardless of age, senescent-like cells do appear, and the benefits of removing them could be age-dependent. More work is needed to determine the magnitude of accumulation and source of senescent cells in muscle. Regardless, pharmacological senolytic treatment of aged muscle is beneficial for adaptation.

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.

Sex-Related Differences in Functional Fitness Outcomes in Older Adults

Sex-related differences in changes in functional fitness over time were longitudinally assessed in older adults participating in a group-based multimodal exercise program. From a database, functional fitness scores were obtained for 89 older adults (71.6 ± 6.5 years old) who had completed two assessments, 5-8 years apart. Lower body strength, upper body strength, aerobic endurance, flexibility, and change of direction performances were compared over time and with normative values. Females (p = .02), but not males, had an improvement in upper body strength over time. Females were also more flexible than males at both assessments (p ≤ .02). Of those who had five consecutive assessments, females were more flexible than males (p ≤ .05) and had a faster change of direction ability (p < .001). When compared with normative values, our results indicate that typical time-related functional fitness loss can be attenuated with group exercise. Our results further support the need to tailor exercise prescription according to the individual.

Sphingolipids accumulate in aged muscle, and their reduction counteracts sarcopenia

Age-related muscle dysfunction and sarcopenia are major causes of physical incapacitation in older adults and currently lack viable treatment strategies. Here we find that sphingolipids accumulate in mouse skeletal muscle upon aging and that both genetic and pharmacological inhibition of sphingolipid synthesis prevent age-related decline in muscle mass while enhancing strength and exercise capacity. Inhibition of sphingolipid synthesis confers increased myogenic potential and promotes protein synthesis. Within the sphingolipid pathway, we show that accumulation of dihydroceramides is the culprit disturbing myofibrillar homeostasis. The relevance of sphingolipid pathways in human aging is demonstrated in two cohorts, the UK Biobank and Helsinki Birth Cohort Study in which gene expression-reducing variants of SPTLC1 and DEGS1 are associated with improved and reduced fitness of older individuals, respectively. These findings identify sphingolipid synthesis inhibition as an attractive therapeutic strategy for age-related sarcopenia and co-occurring pathologies.

Organotypic cultures as aging associated disease models

Aging remains a primary risk factor for a host of diseases, including leading causes of death. Aging and associated diseases are inherently multifactorial, with numerous contributing factors and phenotypes at the molecular, cellular, tissue, and organismal scales. Despite the complexity of aging phenomena, models currently used in aging research possess limitations. Frequently used in vivo models often have important physiological differences, age at different rates, or are genetically engineered to match late disease phenotypes rather than early causes. Conversely, routinely used in vitro models lack the complex tissue-scale and systemic cues that are disrupted in aging. To fill in gaps between in vivo and traditional in vitro models, researchers have increasingly been turning to organotypic models, which provide increased physiological relevance with the accessibility and control of in vitro context. While powerful tools, the development of these models is a field of its own, and many aging researchers may be unaware of recent progress in organotypic models, or hesitant to include these models in their own work. In this review, we describe recent progress in tissue engineering applied to organotypic models, highlighting examples explicitly linked to aging and associated disease, as well as examples of models that are relevant to aging. We specifically highlight progress made in skin, gut, and skeletal muscle, and describe how recently demonstrated models have been used for aging studies or similar phenotypes. Throughout, this review emphasizes the accessibility of these models and aims to provide a resource for researchers seeking to leverage these powerful tools.

The Effect of Resist and Assist Torque of Hip Joint Motor-based Gait Assistance Robot on Gait Function in the Elderly

OBJECTIVES The purpose of this study was to investigate the effects of assist and resistance torque on the spatiotemporal gait characteristics, and the symmetry and asymmetry of gait using a Gait Enhancing and Motivating System (GEMS) in the elderly.METHODS A cross-sectional and repeated measure design was used. A total of 18 participants (9 males, 9 females; age: 63.5 ± 5.02 years; mass: 64.26 ± 6.87 kg; height: 164.06 ± 7.15 cm) were recruited from a local community, and spatiotemporal gait data were collected with OptoGait system and GEMS. Spatiotemporal gait variables and differences between the dominant and non-dominant legs of these variables were assessed (step length, step time, stance phase, swing phase, single support, load response, pre swing phase, stride time, stride length, double support, cadence, and gait speed). The effects of three modes including normal, assist, and resist modes using GEMS were investigated twice for each participant on a 9-meter walkway. A one-way repeated measure analysis of variance followed by Bonferroni post-hoc tests was conducted.RESULTS The assist mode increased step time, swing phase, stride time and reduced stance phase, pre-swing phase, double support, cadence, and gait speed as compared to normal mode. The resist mode increased stance phase, load response, pre-swing phase, double support, cadence, and reduced step time, swing phase, and stride time. In dominant leg, assist mode showed increased step time and reduced pre-swing phase than normal mode, and greater step time than resist mode (<i>p</i> < 0.05). However, there was no effect of external torque on symmetry and asymmetry between both legs (<i>p</i> > 0.05).CONCLUSIONS The resistance and assist torque of GEMS alter spatiotemporal characteristics during the stance and swing phase of gait in the elderly. However, the resistance torque and assist torque of GEMS did not increase or decrease the gait asymmetry between the dominant and non-dominant legs.

25-Hydroxyvitamin D Serum Levels Linked to Single Nucleotide Polymorphisms (SNPs) (rs2228570, rs2282679, rs10741657) in Skeletal Muscle Aging in Institutionalized Elderly Men Not Supplemented with Vitamin D

Sarcopenia (Sp) is the loss of skeletal muscle mass associated with aging that results in an involution of muscle function and strength. Vitamin D deficiency is a common health problem worldwide, especially among the elderly, and hypovitaminosis D leads to musculoskeletal disorders. The aim of this study was to evaluate the impact and presence of a possible linkage between Single Nucleotide Polymorphisms (SNPs) CYP2R1 (rs10741657), GC (rs2282679), and VDR (rs2228570), serum 25-OH/D concentrations and the link with the degree of sarcopenia in 19 institutionalized elderly men not supplemented with vitamin D. Levels of 25-OH vitamin D were quantified with a commercial enzyme-linked immunosorbent assay kit and 3 SNPs were genotyped with KASPar assays. Significant differences in 25-OH/D concentration were determined between the bi-allelic combinations of rs228679 and rs228570. We detected statistically significant weak positive correlations between the AA (rs10741657 and rs228570) and TT (rs228679) and alleles and 25-OH/D and the probability of having higher 25-OH/D concentrations was 2- to 3-fold higher. However, the GG alleles of the 3 SNPs showed that the probability of having optimal 25-0H/D concentrations decreases by 32% for rs10741657, 38% for rs228679, and 74% for rs228570, showing a strong negative correlation between the degree of sarcopenia and 25-OH/D levels. Allelic variations in CYP2R1 (rs10741657), GC (rs2282679), and VDR (rs10741657) affect vitamin D levels and decisively influence the degree of sarcopenia in institutionalized elderly people.

Ablation of Ghrelin Receptor Mitigates the Metabolic Decline of Aging Skeletal Muscle

The orexigenic hormone ghrelin has multifaceted roles in health and disease. We have reported that ablation of the ghrelin receptor, growth hormone secretagogue receptor (GHS-R), protects against metabolic dysfunction of adipose tissues in aging. Our further observation interestingly revealed that GHS-R deficiency phenocopies the effects of myokine irisin. In this study, we aim to determine whether GHS-R affects the metabolic functions of aging skeletal muscle and whether GHS-R regulates the muscular functions via irisin. We first studied the expression of metabolic signature genes in gastrocnemius muscle of young, middle-aged and old mice. Then, old GHS-R knockout (Ghsr^−/−) mice and their wild type counterparts were used to assess the impact of GHS-R ablation on the metabolic characteristics of gastrocnemius and soleus muscle. There was an increase of GHS-R expression in skeletal muscle during aging, inversely correlated with the decline of metabolic functions. Remarkedly the muscle of old GHS-R knockout (Ghsr^−/−) mice exhibited a youthful metabolic profile and better maintenance of oxidative type 2 muscle fibers. Furthermore, old Ghsr^−/− mice showed improved treadmill performance, supporting better functionality. Also intriguing to note was the fact that old GHS-R-ablated mice showed increased expression of the irisin precursor FNDC5 in the muscle and elevated plasma irisin levels in circulation, which supports a potential interrelationship between GHS-R and irisin. Overall, our work suggests that GHS-R has deleterious effects on the metabolism of aging muscle, which may be at least partially mediated by myokine irisin.

Impact of Ageing on Female Metabolic Flexibility: A Cross-Sectional Pilot Study in over-60 Active Women

BACKGROUND

Ageing affects metabolic flexibility, although physical status could influence this relationship. This cross-sectional study aims to describe and analyse the metabolic flexibility/inflexibility in a group of active older women, together with the impact of ageing and physical status on their oxidation rates and maximal fat oxidation (MFO).

METHODS

Fifteen volunteers (69.00 ± 6.97 years)-from 24 women-completed an incremental cycling test until the second ventilatory threshold. Intensity increased 10 W each 3 min 15 s, starting at 30 W. Gas exchange, heart rate, rate of perceived effort, pain scale and muscle power were registered, together with lactate. VO2 and VCO2 were considered for fat and carbohydrate oxidation (FATox and CHOox; Frayn's equation) at intensities 60%, 80% and 100% from the peak power in the test (P100). Psychophysiological parameters were compared at MFO/FATmax and P100, together with the energy expenditure calculations around MFO (included FAT and CHO contributions), and the main correlation analyses, with and without P100 and VO2 as covariates.

RESULTS

FATox was low at MFO (0.13; 95% CI [0.09-0.17] mg/min/kgFFM; 3.50; 95% CI [2.49-4.50] mg/min/kgFFM), with short oxidation-rate curves shifting down and leftward. CHOox and FATox were both low for reduced power with age (77.14 ± 18.58 W and 39.29 ± 9.17 W at P100 and MFO, respectively), all accompanied by a fall in energy expenditure (5.44 ± 2.58 kcal/min and 3.32 ± 1.55 kcal/min at P100 and MFO, respectively). Power appears as a determinant factor, given its strong and negative significant association with age (r = - 0.85, p < 0.005; R2 = 0.72) and moderate with MFO (r = - 0.54, p = 0.04; R2 = 0.29). In turn, energy expenditure shows a positive and moderate association with muscle power (r = 52, p = 0.04).

CONCLUSIONS

Despite the drop in substrates oxidation with age, physical status (i.e. larger muscular power and energy expenditure) suggests a key role in the preservation of metabolic health with ageing in active women.

Muscle fiber type-dependence effect of exercise on genomic networks in aged mice models

Skeletal muscles are made up of various muscle fiber type including slow and fast-twitch fibers. Because each muscle fiber has its own physiological characteristics, the effects of aging and exercise vary depending on the type of muscle fiber. We used bioinformatics screening techniques such as differentially expressed gene analysis, gene ontology analysis and gene set enrichment analysis, to try to understand the genetic differences between muscle fiber types. The experiment and gene expression profiling in this study used the soleus (SOL, slow-twitch muscle) and gastrocnemius (GAS, fast-twitch muscle). According to our findings, fatty acid metabolism is significantly up-regulated in SOL compared to GAS, whereas the glucose metabolism pathway is significantly down-regulated in SOL compared to GAS.

Furthermore, apoptosis and myogenesis patterns differ between SOL and GAS. SOL did not show differences in apoptosis due to the aging effect, but apoptosis in GAS was significantly up-regulated with age. Apoptosis in GAS of old groups is significantly reduced after 4 weeks of aerobic exercise, but no such finding was found in SOL. In terms of myogenesis, exercise intervention up-regulated this process in GAS of old groups but not in SOL. Taken together, muscle fiber type significantly interacts with aging and exercise. Despite the importance of the interaction between these factors, large-scale gene expression data has rarely been studied. We hope to contribute to a better understanding of the relationship between muscle fiber type, aging and exercise at the molecular level.

Initial Muscle Quality Affects Individual Responsiveness of Interleukin-6 and Creatine Kinase following Acute Eccentric Exercise in Sedentary Obese Older Women

This study aimed to evaluate the time course and responsiveness of plasma interleukin-6 (IL-6) and creatine kinase (CK) levels following acute eccentric resistance exercise in sedentary obese older women with a different muscle quality index (MQI). Eighty-eight participants (69.4 ± 6.06 years) completed an acute eccentric resistance exercise (7 sets of 10 repetitions at 110% of 10-repetition maximum with 3 min rest interval). Participants were divided into two groups: high or low MQI according to 50th percentile cut-off. The responsiveness was based on minimal clinical important difference. There were no differences between groups and time on IL-6 and CK levels (p > 0.05). However, the high MQI group displayed a lower proportion of low responders (1 for laboratory and 2 for field-based vs. 5 and 4) and a higher proportion of high responders for IL-6 (7 for laboratory and 6 for field-based vs. 4 and 5) compared to low MQI group. In addition, the high MQI group showed a higher proportion of high responders for CK (11 for laboratory and 9 for field-based vs. 6 and 6) compared to low MQI. A prior MQI screening can provide feedback to understand the magnitude response. Individual responsiveness should be taken into consideration for maximizing eccentric exercise prescription.

Adiponectin receptor agonist AdipoRon improves skeletal muscle function in aged mice

The loss of skeletal muscle function with age, known as sarcopenia, significantly reduces independence and quality of life and can have significant metabolic consequences. Although exercise is effective in treating sarcopenia it is not always a viable option clinically, and currently, there are no pharmacological therapeutic interventions for sarcopenia. Here, we show that chronic treatment with pan-adiponectin receptor agonist AdipoRon improved muscle function in male mice by a mechanism linked to skeletal muscle metabolism and tissue remodeling. In aged mice, 6 weeks of AdipoRon treatment improved skeletal muscle functional measures in vivo and ex vivo. Improvements were linked to changes in fiber type, including an enrichment of oxidative fibers, and an increase in mitochondrial activity. In young mice, 6 weeks of AdipoRon treatment improved contractile force and activated the energy-sensing kinase AMPK and the mitochondrial regulator PGC-1a (peroxisome proliferator-activated receptor gamma coactivator one alpha). In cultured cells, the AdipoRon induced stimulation of AMPK and PGC-1a was associated with increased mitochondrial membrane potential, reorganization of mitochondrial architecture, increased respiration, and increased ATP production. Furthermore, the ability of AdipoRon to stimulate AMPK and PGC1a was conserved in nonhuman primate cultured cells. These data show that AdipoRon is an effective agent for the prevention of sarcopenia in mice and indicate that its effects translate to primates, suggesting it may also be a suitable therapeutic for sarcopenia in clinical application.

Reactive Oxygen Species (ROS) and Antioxidants as Immunomodulators in Exercise: Implications for Heme Oxygenase and Bilirubin

Exercise is commonly prescribed as a lifestyle treatment for chronic metabolic diseases as it functions as an insulin sensitizer, cardio-protectant, and essential lifestyle tool for effective weight maintenance. Exercise boosts the production of reactive oxygen species (ROS) and subsequent transient oxidative damage, which also upregulates counterbalancing endogenous antioxidants to protect from ROS-induced damage and inflammation. Exercise elevates heme oxygenase-1 (HO-1) and biliverdin reductase A (BVRA) expression as built-in protective mechanisms, which produce the most potent antioxidant, bilirubin. Together, these mitigate inflammation and adiposity. Moderately raising plasma bilirubin protects in two ways: (1) via its antioxidant capacity to reduce ROS and inflammation, and (2) its newly defined function as a hormone that activates the nuclear receptor transcription factor PPARα. It is now understood that increasing plasma bilirubin can also drive metabolic adaptions, which improve deleterious outcomes of weight gain and obesity, such as inflammation, type II diabetes, and cardiovascular diseases. The main objective of this review is to describe the function of bilirubin as an antioxidant and metabolic hormone and how the HO-1-BVRA-bilirubin-PPARα axis influences inflammation, metabolic function and interacts with exercise to improve outcomes of weight management.

Recovery From Eccentric Squat Exercise in Resistance-Trained Young and Master Athletes With Similar Maximum Strength: Combining Cold Water Immersion and Compression

The aim of this study was to investigate whether recovery from eccentric squat exercise varies depending on age and to assess whether the use of a mixed-method recovery (MMR) consisting of cold water immersion and compression tights benefits recovery. Sixteen healthy and resistance-trained young (age, 22.1±2.1years; N=8) and master male athletes (age, 52.4±3.5years; N=8), who had a similar half squat 1-repetition maximum relative to body weight, completed two identical squat exercise training sessions, separated by a 2-week washout period. Training sessions were followed by either MMR or passive recovery (PR). Internal training loads [heart rate and blood lactate concentration (BLa)] were recorded during and after squat sessions. Furthermore, maximal voluntary isometric contraction (MVIC) force, countermovement jump (CMJ) height, resting twitch force of the knee extensors, serum concentration of creatine kinase (CK), muscle soreness (MS), and perceived physical performance capability (PPC) were determined before and after training as well as after 24, 48, and 72h of recovery. A three-way mixed ANOVA revealed a significant time effect of the squat protocol on markers of fatigue and recovery (p<0.05; decreased MVIC, CMJ, twitch force, and PPC; increased CK and MS). Age-related differences were found for BLa, MS, and PPC (higher post-exercise fatigue in younger athletes). A significant two-way interaction between recovery strategy and time of measurement was found for MS and PPC (p<0.05; faster recovery after MMR). In three participants (two young and one master athlete), the individual results revealed a consistently positive response to MMR. In conclusion, master athletes neither reach higher fatigue levels nor recover more slowly than the younger athletes. Furthermore, the results indicate that MMR after resistance exercise does not contribute to a faster recovery of physical performance, neuromuscular function, or muscle damage, but promotes recovery of perceptual measures regardless of age.

Impaired Function and Altered Morphology in the Skeletal Muscles of Adult Men and Women With Type 1 Diabetes

CONTEXT

Previous investigations on skeletal muscle health in type 1 diabetes (T1D) have generally focused on later stages of disease progression where comorbidities are present and are posited as a primary mechanism of muscle dysfunction.

OBJECTIVE

To investigate skeletal muscle function and morphology across the adult lifespan in those with and without T1D.

DESIGN

Participants underwent maximal contraction (MVC) testing, resting muscle biopsy, and venous blood sampling.

SETTING

Procedures in this study were undertaken at the McMaster University Medical Centre.

PARTICIPANTS

Sixty-five healthy adult (18-78 years old) men/males and women/females (T1D = 34; control = 31) matched for age/biological sex/body mass index; self-reported physical activity levels were included.

MAIN OUTCOME MEASURES

Our primary measure in this study was MVC, with supporting histological/immunofluorescent measures.

RESULTS

After 35 years of age ("older adults"), MVC declined quicker in T1D subjects compared to controls. Loss of strength in T1D was accompanied by morphological changes associated with accelerated aging. Type 1 myofiber grouping was higher in T1D, and the groups were larger and more numerous than in controls. Older T1D females exhibited more myofibers expressing multiple myosin heavy chain isoforms (hybrid fibers) than controls, another feature of accelerated aging. Conversely, T1D males exhibited a shift toward type 2 fibers, with less evidence of myofiber grouping or hybrid fibers.

CONCLUSIONS

These data suggest impairments to skeletal muscle function and morphology exist in T1D. The decline in strength with T1D is accelerated after 35 years of age and may be responsible for the earlier onset of frailty, which characterizes those with diabetes.

β2-adrenergic receptor agonist counteracts skeletal muscle atrophy and oxidative stress in uremic mice

In patients with chronic kidney disease, skeletal muscle dysfunction is associated with mortality. Uremic sarcopenia is caused by ageing, malnutrition, and chronic inflammation, but the molecular mechanism and potential therapeutics have not been fully elucidated yet. We hypothesize that accumulated uremic toxins might exert a direct deteriorative effect on skeletal muscle and explore the pharmacological treatment in experimental animal and culture cell models. The mice intraperitoneally injected with indoxyl sulfate (IS) after unilateral nephrectomy displayed an elevation of IS concentration in skeletal muscle and a reduction of instantaneous muscle strength, along with the predominant loss of fast-twitch myofibers and intramuscular reactive oxygen species (ROS) generation. The addition of IS in the culture media decreased the size of fully differentiated mouse C2C12 myotubes as well. ROS accumulation and mitochondrial dysfunction were also noted. Next, the effect of the β2-adrenergic receptor (β2-AR) agonist, clenbuterol, was evaluated as a potential treatment for uremic sarcopenia. In mice injected with IS, clenbuterol treatment increased the muscle mass and restored the tissue ROS level but failed to improve muscle weakness. In C2C12 myotubes stimulated with IS, although β2-AR activation also attenuated myotube size reduction and ROS accumulation as did other anti-oxidant reagents, it failed to augment the mitochondrial membrane potential. In conclusion, IS provokes muscular strength loss (uremic dynapenia), ROS generation, and mitochondrial impairment. Although the β2-AR agonist can increase the muscular mass with ROS reduction, development of therapeutic interventions for restoring skeletal muscle function is still awaited.

Sprint interval training (SIT) reduces serum epidermal growth factor (EGF), but not other inflammatory cytokines in trained older men

Purpose

The present study aimed to investigate the effect of age on circulating pro- and anti-inflammatory cytokines and growth factors. A secondary aim was to investigate whether a novel sprint interval training (SIT) intervention (3 × 20 s ‘all out’ static sprints, twice a week for 8 weeks) would affect inflammatory markers in older men.

Methods

Nine older men [68 (1) years] and eleven younger men [28 (2) years] comprised the younger group. Aerobic fitness and inflammatory markers were taken at baseline for both groups and following the SIT intervention for the older group.

Results

Interleukin (IL)-8, vascular endothelial growth factor (VEGF), and monocyte chemoattractant protein-1 (MCP-1) were unchanged for the older and younger groups at baseline (IL-8, p = 0.819; MCP-1, p = 0.248; VEGF, p = 0.264). Epidermal growth factor (EGF) was greater in the older group compared to the younger group at baseline [142 (20) pg mL⁻¹ and 60 (12) pg mL⁻¹, respectively, p = 0.001, Cohen's d = 1.64]. Following SIT, older men decreased EGF to 100 (12) pg mL⁻¹ which was similar to that of young men who did not undergo training (p = 0.113, Cohen's d = 1.07).

Conclusion

Older aerobically trained men have greater serum EGF than younger aerobically trained men. A novel SIT intervention in older men can shift circulating EGF towards trained younger concentrations. As lower EGF has previously been associated with longevity in C. elegans, the manipulative effect of SIT on EGF in healthy ageing in the human may be of further interest.

Mechanical Properties of Single Muscle Fibers: Understanding Poor Muscle Quality in Older Adults with Diabetes

Background

While aging causes muscle weakness, type 2 diabetes mellitus (T2DM) is also considered a high-risk factor for the induction of skeletal muscle weakness. Previous studies have reported increased collagen content in insulin-resistant skeletal muscles. Here, we studied the mechanical properties of aged skeletal muscle in patients with T2DM to investigate whether aged skeletal muscles with T2DM induce higher passive tension due to the abundance of extracellular matrix (ECM) inside or outside of the muscle fibers.

Methods

Samples from the gluteus maximus muscles of older adults with diabetes (T2DM) and non-diabetic (non-DM) older adults who underwent elective orthopedic surgery were collected. Permeabilized single muscle fibers from these samples were used to identify their mechanical properties. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) was used to quantify titin and fiber type distributions in these samples.

Results

We confirmed a significant predominance of type I fiber ratio in both T2DM and non-DM aged muscles. While the average cross-sectional area and maximal active tension of the single fibers were smaller in the T2DM group than those in the non-DM group, the difference was not statistically significant. T2DM subjects showed significantly greater passive tension and lower titin-/ECM-based passive tension ratios than those in non-DM subjects, which indicated that more ECM but less titin contributed to the total passive tension.

Conclusion

Based on our findings, we concluded that T2DM may cause increased passive stiffness of single skeletal muscle fibers in older adults because of an excessive accumulation of ECM in and around single muscle fibers due to increased insulin resistance.

Sarcopenia during COVID-19 lockdown restrictions: long-term health effects of short-term muscle loss

The COVID-19 pandemic is an extraordinary global emergency that has led to the implementation of unprecedented measures in order to stem the spread of the infection. Internationally, governments are enforcing measures such as travel bans, quarantine, isolation, and social distancing leading to an extended period of time at home. This has resulted in reductions in physical activity and changes in dietary intakes that have the potential to accelerate sarcopenia, a deterioration of muscle mass and function (more likely in older populations), as well as increases in body fat. These changes in body composition are associated with a number of chronic, lifestyle diseases including cardiovascular disease (CVD), diabetes, osteoporosis, frailty, cognitive decline, and depression. Furthermore, CVD, diabetes, and elevated body fat are associated with greater risk of COVID-19 infection and more severe symptomology, underscoring the importance of avoiding the development of such morbidities. Here we review mechanisms of sarcopenia and their relation to the current data on the effects of COVID-19 confinement on physical activity, dietary habits, sleep, and stress as well as extended bed rest due to COVID-19 hospitalization. The potential of these factors to lead to an increased likelihood of muscle loss and chronic disease will be discussed. By offering a number of home-based strategies including resistance exercise, higher protein intakes and supplementation, we can potentially guide public health authorities to avoid a lifestyle disease and rehabilitation crisis post-COVID-19. Such strategies may also serve as useful preventative measures for reducing the likelihood of sarcopenia in general and in the event of future periods of isolation.

Pharmacological blockade of TNFα prevents sarcopenia and prolongs survival in aging mice

Sarcopenia is a hallmark of aging. Inflammation due to increased generation of cytokines such as TNFα, IL-1β and IL-6 has been implicated in the pathogenesis of sarcopenia. In skeletal muscle of C57BL/6 mice from 12 until 28 months of age, we observed a progressive reduction of myofiber cross sectional area, loss of type II fibers and infiltration by inflammatory cells. Muscle strength decreased in parallel. Pharmacological TNFα blockade by weekly subcutaneous injection of Etanercept from 16 to 28 months of age prevented atrophy and loss of type II fibers, with significant improvements in muscle function and mice lifespan. The effects on leukocyte recruitment were limited. These results provide a proof of principle that endogenous TNFα is sufficient to cause sarcopenia and to reduce animal survival, and open a novel perspective on novel potential pharmacological treatment strategies based on TNFα blockade to prevent the noxious events associated with aging.

The relationship between age and fitness profiles in elite male ice hockey players

BACKGROUND

The present study investigated relationships between age, body composition and performance in elite male ice hockey players.

METHODS

199 players performed off-ice tests (countermovement jump height (CMJ) and body composition) and on-ice tests (5-10-5 Pro Agility test, 30-m sprint test and the maximal Yo-Yo Intermittent Recovery Ice Hockey test (Yo-Yo IR1-IH<inf>MAX</inf>) for assessment of aerobic capacity.

RESULTS

No overall correlations between age and performance were present except small-moderate positive associations between age and body- and muscle mass (r=0.24-0.30, P≤0.05). The youngest age group (YOU; 18-21 years) were 4-9% lighter than all other age groups and possessed 7% less muscle mass compared to the oldest players (OLD; 30-33 years) (P≤0.05), whereas no differences were present in body fat percentage. OLD were 2-3% inferior to the second youngest (SEC; 22-25 years) and mid-age group (MID; 26-29 years) in sprint and agility performance in addition to a 6-10% lower CMJ height (P≤0.05). The younger age groups differed only by a 7 and 5% better CMJ performance in MID compared to YOU and SEC, respectively (P≤0.05). In contrast, no differences were found in distance covered on the Yo-Yo IR1-IH<inf>max</inf>.

CONCLUSIONS

Only small-moderate associations between age and body composition were present unlike for the remaining performance parameters. Nevertheless, a consistently lower high-intensity exercise performance was evident in the oldest- and a lower body weight in the youngest players, whereas aerobic capacity was similar. This suggests that capabilities related to size, strength and power are the most critical parameters differing between young and old ice hockey players.

Normalized maximal rate of torque development during voluntary and stimulated static contraction in human tibialis anterior: Influence of age

The risk of falling in older adults has been related, among other factors, to the reduction of the rate of torque development (RTD) with age. It is well known that both structural/peripheral and neural factors can influence the RTD. The purpose of this study was to compare the normalized RTD in young and older participants obtained during a) rapid voluntary tension production and b) neuromuscular electrical stimulation. The tibialis anterior of 19 young subjects (10 males and 9 females; age 21-33 years old) and 19 older participants (10 males and 9 females; age 65-80 years old) was studied. The subjects performed a series of maximal isometric explosive dorsiflexions and underwent trains of supra-maximal electrical stimulations (35 Hz) on the tibialis anterior motor point. Muscle shortening was indirectly measured using a laser (surface mechanomyogram, MMG). Both torque and MMG were normalized to their maximum value. Using a 20 ms sliding window on the normalized torque signal, the normalized maximum RTD was calculated for both voluntary and stimulated contractions. Active stiffness of the muscle- tendon unit was calculated as the area of the normalized torque with respect to the normalized MMG. Normalized maximum RTD was found significantly lower in older adults during voluntary activity (young: 751.9 ± 216.3%/s and old: 513.9 ± 173.9%/s; P < .001), and higher during stimulated contractions (young: 753.1 ± 225.9%/s and old: 890.1 ± 221.3%/s; P = .009). Interestingly, active stiffness was also higher in older adults (young: 3524.6 ± 984.6‰ and old 4144.6 ± 816.6‰; P = .041) and significantly correlated to the normalized maximum RTD during stimulated contractions. This dichotomy suggests that modifications in the structural/peripheral muscle properties are not sufficient to counteract the age-related decrease in neural drive to the muscle during voluntary isometric contractions in aged participants.

Effect of Neuromuscular Electrical Stimulation on Masseter Muscle Thickness and Maximal Bite Force Among Healthy Community-Dwelling Persons Aged 65 Years and Older: A Randomized, Double Blind, Placebo-Controlled Study

Aim: This study investigated the effect of neuromuscular electrical stimulation (NMES) on masseter muscle thickness and maximal bite force among healthy community-dwelling elderly persons older than 65 years. Materials and methods: A total of 40 participants were randomly assigned to the experimental and placebo groups. In the experimental group, NMES was applied to both masseter muscles, and electrical signals were gradually increased until the participants felt a grabbing sensation (range 6.0–7.5 mA) in the masseter muscle. The placebo group, in contrast, underwent NMES in the same manner and procedure as the experimental group with less electrical intensity (0.5 mA). All interventions were administered five times a week for six weeks, 20 min per day. The outcomes were masseter muscle thickness assessed using ultrasound and maximal bite force using a bite force meter. The level of significance was set as p < 0.05. Results: The experimental group showed a significant increase in both masseter muscle thickness and maximal bite force as compared with the placebo group (p = 0.002 and 0.019, respectively). Moreover, the degree of change in the masseter muscle thickness and maximal bite force significantly increased in the experimental and placebo groups (p < 0.001, both). Conclusions: This study demonstrated that NMES could be an effective modality for increasing masseter muscle thickness and maximal bite force in healthy older adults.

Muscle Mass and Muscle Strength Relationships to Balance: The Role of Age and Physical Activity

OBJECTIVE

To investigate the relations of balance to muscle mass (MM) and muscle strength (MS), depending on age and physical activity, which is of particular importance to functional independence in older people.

METHODS

This cross-sectional study included 802 volunteers (69.82 ± 5.60 years). The Fullerton Advanced Balance scale was used to assess balance and a composite score, including arm curl and chair stand tests for assessing MS. MM was estimated by dual-energy X-ray absorptiometry and physical activity by questionnaire.

RESULTS

Greater MM (r = .26, p < .001) and MS (r = .53, p < .001) were positively correlated to balance. The old-old adults and less active individuals attained lower balance. Notably, moderation and subsequent simple slope analyses revealed that the relations of balance, MM, and MS were larger in less active and the old-old adults.

CONCLUSIONS

The old-old and less active adults were more prone to muscle weakness and balance impairments. Tailored interventions should particularly consider these vulnerable groups.

Low survival rate and muscle fiber-dependent aging effects in the McArdle disease mouse model

McArdle disease is an autosomal recessive disorder caused by the absence of the muscle glycogen phosphorylase, which leads to impairment of glycogen breakdown. The McArdle mouse, a model heavily affected by glycogen accumulation and exercise intolerance, was used to characterize disease progression at three different ages. The molecular and histopathological consequences of the disease were analyzed in five different hind-limb muscles (soleus, extensor digitorum longus, tibialis anterior, gastrocnemius and quadriceps) of young (8-week-old), adult (35-week-old) and old (70-week-old) mice. We found that McArdle mice have a high perinatal and post-weaning mortality. We also observed a progressive muscle degeneration, fibrosis and inflammation process that was not associated with an increase in muscle glycogen content during aging. Additionally, this progressive degeneration varied among muscle and fiber types. Finally, the lack of glycogen content increase was associated with the inactivation of glycogen synthase and not with compensatory expression of the Pygl and/or Pygb genes in mature muscle.

Validation of a clinically-relevant rodent model of statin-associated muscle symptoms for use in pharmacological studies

Various rodent models of statin-associated muscle symptoms (SAMS) have been used to investigate the aetiology of statin myotoxicity. Variability between these models, however, may be contributing to the ambiguity currently surrounding the pathogenesis of SAMS. Furthermore, few studies have assessed the reproducibility of these models. The aim of this study was to compare two established rodent models of statin myotoxicity, differing in treatment duration and dose, to determine which reproducibly caused changes characteristic of SAMS. Isolated skeletal muscle organ bath experiments, biochemical analyses, real-time quantitative-PCR and biometric assessments were used to compare changes in skeletal muscle and renal integrity in statin-treated animals and time-matched control groups. The SIM80 model (80 mg kg^-1 day^-1 simvastatin for 14 days) produced fibre-selective skeletal muscle damage characteristic of SAMS. Indeed, fast-twitch gastrocnemius muscles showed increased Atrogin-1 expression, reduced peak force of contraction and decreased Myh2 expression while slow-twitch soleus muscles were unaffected. Contrastingly, the SIM50 model (50 mg kg^-1 day^-1 simvastatin for 30 days) produced little evidence of significant skeletal muscle damage. Neither statin treatment protocol caused significant pathological changes to the kidney. The results of this study indicate that the SIM80 model induces a type of SAMS in rodents that resembles the presentation of statin-induced myalgia in humans. The findings support that the SIM80 model is reproducible and can thus be reliably used as a platform to assess the aetiology and treatment of this condition.

Structural muscular adaptations in upper limb after stroke: a systematic review

BACKGROUND

Stroke is a leading cause of disability in the adult population, impairing upper limb (UL) movements affecting activities of daily living. Muscle weakness has been associated to disabilities in this population, but much attention is given to central nervous system alterations and less to skeletal muscles.

OBJECTIVE

The objective of this review is to carry out a systematic literature review to identify structural muscle alterations in the UL of poststroke individuals.

METHOD

The search was performed in December, 2017. MEDLINE, PubMed, SCOPUS, CINAHL, and Science Direct were used as electronic databases. There was no restriction regarding language and publication dates. Studies conducted on poststroke subjects and results on UL skeletal muscle alterations identified by imaging tests were included.

RESULTS

Seven studies were included. The sample size and the variables varied among the studies. All the studies compared the paretic UL with the nonparetic UL and one of the studies also compared healthy subjects. Ultrasonography was the most used measurement tool to assess muscle adaptation.

CONCLUSIONS

This review demonstrated little evidence with poor to fair quality on the structural muscle adaptations in the poststroke subjects, showing muscle atrophy, a higher stiffness, and amount of fibrous and fat tissue without alterations in lean tissue of distal muscles of the paretic UL compared to the nonparetic limb. However, the nonparetic side also presented alterations, which makes it an inappropriate comparison. Thus, well-designed studies addressing this issue are required.

Muscle Mass, Muscle Morphology and Bone Health Among Community-Dwelling Older Men: Findings from the Hertfordshire Sarcopenia Study (HSS)

Sarcopenia and osteoporosis are associated with poor health outcomes in older people. Relationships between muscle and bone have typically been reported at a functional or macroscopic level. The aims of this study were to describe the relationships between muscle morphology and bone health among participants of the Hertfordshire Sarcopenia Study (HSS). 105 older men, mean age 72.5 (SD 2.5) years, were recruited into the HSS. Whole body lean mass as well as appendicular lean mass, lumbar spine and femoral neck bone mineral content (BMC) and bone mineral density (BMD) were obtained through dual-energy X-ray absorptiometry scanning. Percutaneous biopsy of the vastus lateralis was performed successfully in 99 participants. Image analysis was used to determine the muscle morphology variables of slow-twitch (type I) and fast-twitch (type II) myofibre area, myofibre density, capillary and satellite cell (SC) density. There were strong relationships between whole and appendicular lean body mass in relation to femoral neck BMC and BMD (r ≥ 0.43, p < 0.001). Type II fibre area was associated with both femoral neck BMC (r = 0.27, p = 0.01) and BMD (r = 0.26, p = 0.01) with relationships robust to adjustment for age and height. In unadjusted analysis, SC density was associated with whole body area (r = 0.30, p = 0.011) and both BMC (r = 0.26, p = 0.031) and area (r = 0.29, p = 0.017) of the femoral neck. We have demonstrated associations between BMC and changes in muscle at a cellular level predominantly involving type II myofibres. Interventions targeted at improving muscle mass, function and quality may improve overall musculoskeletal health. Larger studies that include women are needed to explore these relationships further.

MODERATE INTENSITY IS A BETTER STIMULUS TO INDUCE QUADRIPECS FEMORIS POWER IN ELDERLY ADULTS

ABSTRACT Introduction: The best strategy for improving knee extensor power, a major functional capacity indicator in older adults, is power training. Nonetheless, the training intensity required to induce optimal gains is yet to be found. Objective: Our purpose was to compare knee extensor peak power responses between low, moderate, and high intensity load conditions (30%, 50% and 70% of 1RM). Methods: Thirteen sedentary elderly women performed six knee extensions in each load condition, calculating knee extensor mechanical work/power output and knee extension peak angular velocity. Results: No difference in peak power was found between the high (207.0 ± 68.1 W) and moderate (206.1 ± 71.6 W) load conditions (p = 0.994), and both had higher values (p ≤0.004) than the low intensity condition (135.6 ± 56.3 W). Conclusion: Moderate load at 50% of 1RM appears to be the preferred strategy for inducing knee extensor power output because in contrast with the high intensity condition, the moderate load yielded higher angular peak velocity, which is also a functional indicator. Level of Evidence ll; Therapeutic studies - Investigating treatment results.

Single Muscle Fiber Proteomics Reveals Fiber-Type-Specific Features of Human Muscle Aging

Skeletal muscle is a key tissue in human aging, which affects different muscle fiber types unequally. We developed a highly sensitive single muscle fiber proteomics workflow to study human aging and show that the senescence of slow and fast muscle fibers is characterized by diverging metabolic and protein quality control adaptations. Whereas mitochondrial content declines with aging in both fiber types, glycolysis and glycogen metabolism are upregulated in slow but downregulated in fast muscle fibers. Aging mitochondria decrease expression of the redox enzyme monoamine oxidase A. Slow fibers upregulate a subset of actin and myosin chaperones, whereas an opposite change happens in fast fibers. These changes in metabolism and sarcomere quality control may be related to the ability of slow, but not fast, muscle fibers to maintain their mass during aging. We conclude that single muscle fiber analysis by proteomics can elucidate pathophysiology in a sub-type-specific manner.

How do we define and measure sarcopenia? Protocol for a systematic review

BACKGROUND

The loss of muscle mass is a natural aging consequence. A reduction of muscle mass that surpasses the physiological rate is considered the key factor responsible for the development of a geriatric syndrome called sarcopenia. However, a new understanding of the importance of muscle quality over quantity is rising; as a result, different definitions for sarcopenia has been used. Due to the negative impact on elder's health and quality of life, the number of research investigating the causes, prevalence, and management of sarcopenia is increasing, although a consensus on sarcopenia definition is still missing. This systematic review will assess observational studies reporting the presence of sarcopenia aiming to verify how sarcopenia is defined, the diagnosis criteria, and the tools used for assessment. In addition, we will investigate the influence of the definition and diagnostic tools on the prevalence rate.

METHODS

Keywords related to the condition, population, and type of study will be combined to build a search strategy for each of the following databases MEDLINE, EMBASE, CINAHL (Cumulative Index to Nursing and Allied Health Literature), Web of Science, and Google Scholar. Two independent reviewers will analyze the retrieved papers for eligibility and the methodological quality of eligible studies. The definition of sarcopenia and diagnostic tools used in each study and the prevalence estimates will be extracted. Descriptive statistics will be used to report the definitions of sarcopenia, diagnostic tools, and whether these influence or not, the prevalence rates.

DISCUSSION

Sarcopenia is receiving greater attention in geriatrics research in recent years. Therefore, it is important to investigate how this condition is defined in the literature and whether these definitions can interfere with the reported estimates devoting more efforts on the topic. The results of this study can help to determine the most used definitions of sarcopenia reported in the literature, its strengths and limitations, and open a discussion about a need for a more valid, easy, and suitable one.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO CRD42015020832.

Spectral components in electromyograms from four regions of the human masseter, in natural dentate and edentulous subjects with removable prostheses and implants

OBJECTIVE

To compare the frequency or spectral components between different regions of the superficial masseter in young natural dentate and total edentulous older adults rehabilitated with removable prostheses and fixed-implant support. A secondary objective was to compare these components between the three groups.

DESIGN

21 young natural dentate and 28 edentulous (14 with removable prostheses and 14 with fixed-implant support) were assessed. High-density surface electromyography (sEMG) was recorded in four portions of the superficial masseter during submaximal isometric bites. Spectral components were obtained through a spectral analysis of the sEMG signals. An analysis of mixed models was used to compare the spectral components.

RESULTS

In all groups, the spectral components of the anterior portion were lower than in the posterior region (p < 0.05). Both edentulous groups showed lower spectral components and median frequency slope than the natural dentate group (p < 0.05). The removable prostheses group showed the greatest differences with natural dentate group.

CONCLUSIONS

There were significant differences in the spectral components recorded in the different regions of the superficial masseter. The lower spectral components and fatigability of older adults rehabilitated with prostheses could be a cause of a greater loss of type II fibers, especially in the removable prostheses group.

AAV1.NT-3 gene therapy increases muscle fiber diameter through activation of mTOR pathway and metabolic remodeling in a CMT mouse model

Neurotrophin 3 (NT-3) has well-recognized effects on peripheral nerve and Schwann cells, promoting axonal regeneration and associated myelination. In this study, we assessed the effects of AAV.NT-3 gene therapy on the oxidative state of the neurogenic muscle from the TremblerJ (Tr ^J ) mice at 16 weeks post-gene injection and found that the muscle fiber size increase was associated with a change in the oxidative state of muscle fibers towards normalization of the fiber type ratio seen in the wild type. NT-3-induced fiber size increase was most prominent for the fast twitch glycolytic fiber population. These changes in the Tr ^J muscle were accompanied by increased phosphorylation levels of 4E-BP1 and S6 proteins as evidence of mTORC1 activation. In parallel, the expression levels of the mitochondrial biogenesis regulator PGC1α, and the markers of glycolysis (HK1 and PK1) increased in the Tr^J muscle. In vitro studies showed that recombinant NT-3 can directly induce Akt/mTOR pathway activation in the TrkC expressing myotubes but not in myoblasts. In addition, myogenin expression levels were increased in myotubes while p75 ^NTR expression was downregulated compared to myoblasts, indicating that NT-3 induced myoblast differentiation is associated with mTORC1 activation. These studies for the first time have shown that NT-3 increases muscle fiber diameter in the neurogenic muscle through direct activation of mTOR pathway and that the fiber size increase is more prominent for fast twitch glycolytic fibers.

Loss of maximal explosive power of lower limbs after 2 weeks of disuse and incomplete recovery after retraining in older adults

KEY POINTS

Disuse in older adults can critically decrease lower limb muscle power, leading to compromised mobility and overall quality of life. We studied how muscle power and its determinants (muscle mass, single muscle fibre properties and motor control) adapted to 2 weeks of disuse and subsequent 2 weeks of physical training in young and older people. Disuse decreased lower limb muscle power in both groups; however, different adaptations in single muscle fibre properties and co-contraction of leg muscles were observed between young and older individuals. Six physical training sessions performed after disuse promoted the recovery of muscle mass and power. However, they were not sufficient to restore muscle power to pre-disuse values in older individuals, suggesting that further countermeasures are required to counteract the disuse-induced loss of muscle power in older adults.

ABSTRACT

Disuse-induced loss of muscle power can be detrimental in older individuals, seriously impairing functional capacity. In this study, we examined the changes in maximal explosive power (MEP) of lower limbs induced by a 14-day disuse (bed-rest, BR) and a subsequent 14-day retraining, to assess whether the impact of disuse was greater in older than in young men, and to analyse the causes of such adaptations. Sixteen older adults (Old: 55-65 years) and seven Young (18-30 years) individuals participated in this study. In a subgroup of eight Old subjects, countermeasures based on cognitive training and protein supplementation were applied. MEP was measured with an explosive ergometer, muscle mass was determined by magnetic resonance, motor control was studied by EMG, and single muscle fibres were analysed in vastus lateralis biopsy samples. MEP was ∼33% lower in Old than in Young individuals, and remained significantly lower (-19%) when normalized by muscle volume. BR significantly affected MEP in Old (-15%) but not in Young. Retraining tended to increase MEP; however, this intervention was not sufficient to restore pre-BR values in Old. Ankle co-contraction increased after BR in Old only, and remained elevated after retraining (+30%). Significant atrophy occurred in slow fibres in Old, and in fast fibres in Young. After retraining, the recovery of muscle fibre thickness was partial. The proposed countermeasures were not sufficient to affect muscle mass and power. The greater impact of disuse and smaller retraining-induced recovery observed in Old highlight the importance of designing suitable rehabilitation protocols for older individuals.

Differential impact of tongue exercise on intrinsic lingual muscles

OBJECTIVES/HYPOTHESIS

Aging is associated with muscle fiber hypotrophy and decreased percentages of rapidly contracting myosin heavy chain (MyHC) type IIb muscle fibers. Tongue exercise programs used to treat dysphagia target age-related decline in tongue muscle function, but the impact of exercise on the intrinsic tongue muscles is unknown. We hypothesized that exercise would induce muscle fiber hypertrophy and increase the percentage of MyHC IIa fibers in the intrinsic tongue.

STUDY DESIGN

Animal model.

METHODS

Eight old and eight young-adult rats underwent 8 weeks of tongue exercise training, and 8 animals of each age group served as controls. Longitudinal, transverse, and verticalis muscle samples from the anterior, middle, and posterior regions of the tongue were sectioned and stained to determine muscle fiber diameter and MyHC composition.

RESULTS

MyHC fiber type distribution was altered by exercise, and the effects differed by muscle and region of the tongue. In the exercise groups, as compared to the control groups, the anterior transverse and middle superior longitudinal muscles had significantly reduced percentages of MyHC IIx positive fibers and higher percentages of rapidly contracting fatigable MyHC IIb positive muscle fibers, whereas the middle transverse and posterior longitudinal muscles had increased percentages of the less rapidly contracting and more fatigue-resistant MyHC IIa fibers. The impact of exercise did not differ with age, as there was no significant interaction between age and exercise. Tongue exercise had no significant effect on muscle fiber diameter.

CONCLUSIONS

The impact of exercise varied among the tongue muscles, which may indicate different functional contributions to the tongue exercise task.

LEVEL OF EVIDENCE

NA Laryngoscope, 128:2245-2251, 2018.

Age-related effect of cell death on fiber morphology and number in tongue muscle

INTRODUCTION

Multiple pathways may exist for age-related tongue muscle degeneration. Cell death is one mechanism contributing to muscle atrophy and decreased function. We hypothesized with aging, apoptosis, and apoptotic regulators would be increased, and muscle fiber size and number would be reduced in extrinsic tongue muscles.

METHODS

Cell death indices, expression of caspase-3 and Bcl-2, and measures of muscle morphology and number were determined in extrinsic tongue muscles of young and old rats.

RESULTS

Significant increases in cell death, caspase-3, and Bcl-2 were observed in all extrinsic tongue muscles along with reductions in muscle fiber number in old rats.

DISCUSSION

We demonstrated that apoptosis indices increase with age in lingual muscles and that alterations in apoptotic regulators may be associated with age-related degeneration in muscle fiber size and number. These observed apoptotic processes may be detrimental to muscle function, and may contribute to degradation of cranial functions with age. Muscle Nerve 57: E29-E37, 2018.

An Age-Related Morphometric Profile of Skeletal Muscle in Healthy Untrained Women

There is a paucity of data on muscle biopsies in females of mixed ages in terms of age-related changes. Cross sections of autopsy material including the quadriceps femoris and biceps brachii muscles were obtained from 23 healthy women, aged 24–82 years, who had suffered sudden death. We calculated the percentage of the number, and the mean diameter, of type I and type II muscle fibers within the fascicles as well as in their peripheral parts. The number of type II fibers were shown to reduce significantly with age (p < 0.005), especially in the fascicle periphery, but the percentage of type 1 fibers did not alter significantly. It was noted that type II fibers diminished in size with age, indicating a relationship between fiber size and age. This result became more apparent in the fascicle periphery (p < 0.05). In women, type II muscle fibers were seen to reduce in size and number with advancing age. We postulate that regular physical activity can increase the size of type II muscle fibers, thus helping to both prevent and treat age-related muscle loss.

Biological aging and physical fitness in men aged 20-70 years from Kraków, Poland

OBJECTIVES

The increasing problem of population aging requires appropriate economic and health-related measures to mitigate its negative effects. The aim was to categorize the biological age of men between 20 and 70 years of age and assess its relationship to their physical activity and fitness.

METHODS

Data included morphological variables, total body water, the results of five Eurofit motor tests and the percentage of maximum heart rate (HR%), during a cardiovascular test of more than 1,400 20-70 year-old men living in Kraków. Biological age was estimated with regression equations.

RESULTS

There were significant and consistent differences in physical fitness profiles between the three established groups of relations between biological and chronological age (biologically younger, equal, and older). These three categories of biological age were generally consistent with the regression analysis of physical fitness results, although declared physical activity seemed to be an independent factor.

CONCLUSIONS

The selected morphological variables represent a set of characteristics useful for the determination of the biological age. The existing relationship between physical activity and biological age indicates that physical activity may contribute to the inhibition of involutional changes, even if it had only been performed regularly in the past. Am. J. Hum. Biol. 28:503-509, 2016. © 2015 Wiley Periodicals, Inc.