Review on aging, unloading and reloading: Changes in skeletal muscle quantity and quality

The Use of Free Weight Squats in Sports: A Narrative Review-Squatting Movements, Adaptation, and Sports Performance: Physiological

ABSTRACT

Stone, MH, Hornsby, G, Mizuguchi, S, Sato, K, Gahreman, D, Duca, M, Carroll, K, Ramsey, MW, Stone, ME, and Haff, GG. The use of free weight squats in sports: a narrative review-squatting movements, adaptation, and sports performance: physiological. J Strength Cond Res 38(8): 1494-1508, 2024-The squat and its variants can provide numerous benefits including positively affecting sports performance and injury prevention, injury severity reduction, and rehabilitation. The positive benefits of squat are likely the result of training-induced neural alterations and mechanical and morphological adaptations in tendons, skeletal muscles, and bones, resulting in increased tissue stiffness and cross-sectional area (CSA). Although direct evidence is lacking, structural adaptations can also be expected to occur in ligaments. These adaptations are thought to beneficially increase force transmission and mechanical resistance (e.g., resistance to mechanical strain) and reduce the likelihood and severity of injuries. Adaptations such as these, also likely play an important role in rehabilitation, particularly for injuries that require restricted use or immobilization of body parts and thus lead to a consequential reduction in the CSA and alterations in the mechanical properties of tendons, skeletal muscles, and ligaments. Both volume and particularly intensity (e.g., levels of loading used) of training seem to be important for the mechanical and morphological adaptations for at least skeletal muscles, tendons, and bones. Therefore, the training intensity and volume used for the squat and its variations should progressively become greater while adhering to the concept of periodization and recognized training principles.

Assessing the Clinical Effectiveness of an Exergame-Based Exercise Training Program Using Ring Fit Adventure to Prevent and Postpone Frailty and Sarcopenia Among Older Adults in Rural Long-Term Care Facilities: Randomized Controlled Trial

BACKGROUND

Frailty and sarcopenia are geriatric syndromes of increasing concern and are associated with adverse health outcomes. They are more prevalent among long-term care facility (LTCF) users than among community dwellers. Exercise, especially multicomponent and progressive resistance training, is essential for managing these conditions. However, LTCFs, particularly in rural areas, face challenges in implementing structured exercise programs due to health care professional shortages. Moreover, older adults often become bored with repetitive exercise training and may lose interest over time. The Nintendo Switch Ring Fit Adventure (RFA) exergame is a novel exergame that combines resistance, aerobic, and balance exercises and offers a potential solution by boosting motivation in an immersive manner and reducing staff intervention needs.

OBJECTIVE

We aimed to evaluate the clinical effectiveness of an exergame-based exercise training program delivered via RFA (exergame-RFA) in improving muscle mass and functional performance among older adult LTCF users.

METHODS

This was a randomized controlled trial conducted from August 2022 to September 2023 and involved older adult LTCF users (aged ≥60 y) in rural southern Taiwan. Participants were randomized into an intervention group (exergame-RFA plus standard care) or a control group (standard care alone). The intervention, conducted seated with arm fit skills and trunk control exercises using the RFA, lasted 30 minutes twice weekly over 12 weeks. The primary outcomes measured were the Study of Osteoporotic Fractures index (serving as an indicator of frailty status) and the diagnostic criteria for sarcopenia (appendicular skeletal muscle mass index, handgrip strength, and gait speed). The secondary outcomes included functional performance (box and block test as well as maximum voluntary isometric contraction of the dominant upper extremity), muscle condition (muscle thickness measured using ultrasonography), activities of daily living (Kihon checklist), health-related quality of life (Short Form Health Survey-36), and cognitive function (brain health test). We used an intention-to-treat analysis, incorporating a simple imputation technique in statistical analysis. A mixed ANOVA, with time as a within-participant factor and intervention as a between-participant factor, was used to compare the training effects on outcomes.

RESULTS

We recruited 96 individuals, of whom 60 (62%) underwent randomization. Of these 60 participants, 55 (92%) completed the study. Significant group×time interactions were observed in the intervention group in all primary outcomes (all P<.001, except P=.01 for handgrip strength) and most secondary outcomes, including maximum voluntary isometric contraction of the biceps (P=.004) and triceps brachii (P<.001) muscles, biceps muscle thickness measured using ultrasonography (P<.001), box and block test (P<.001), Kihon checklist (physical function: P=.01, mood status: P=.003, and total: P=.003), and brain health test (P<.001).

CONCLUSIONS

The exergame-RFA intervention significantly improved muscle mass, strength, and functional performance among older adult users of rural LTCFs, offering a novel approach to addressing frailty and sarcopenia.

TRIAL REGISTRATION

ClinicalTrials.gov NCT05360667; https://clinicaltrials.gov/study/NCT05360667.

INTERNATIONAL REGISTERED REPORT IDENTIFIER (IRRID)

RR2-10.3389/fmed.2022.1071409.

Development of Connective Tissue Area Increases by Initial Impact With High-Intensity Exercise After Reloading in Rat Soleus Muscle

OBJECTIVE

The aim of the study is to clarify whether high-intensity exercise in atrophied skeletal muscle after reloading (1) increases the injury and promotes the development of the muscle connective tissue area in the soleus muscle and (2) delays muscle strength recovery.

DESIGN

Rats had their hindlimbs suspended for 14 days followed by hindlimb reloading and squat exercise of 30% or 70%-one-repetition maximum exercise until 14 days of reloading. The influences of reloading and exercise in muscles were examined by histological and immunofluorescence analyses based on the exercise load.

RESULTS

Seventy percent-one-repetition maximum exercise increased the extramyofiber area more than the control group and the central nuclear fiber number than the other groups after 7 days of reloading. Seventy percent-one-repetition maximum exercise resulted in a larger muscle connective tissue area than the control and reload groups after 14 days of reloading. Myogenin and M2-type macrophages after 7 days of reloading increased by reloading but were not increased by the exercise load.

CONCLUSIONS

Seventy percent-one-repetition maximum exercise to atrophied muscle increased injury early in postreloading and increased the muscle connective tissue area after 14 days of reloading, but evidence that it delays muscle strength recovery was lacking. Therefore, muscle connective tissue area induced by high-intensity exercise after reloading seems to be associated with initial exercise damage but not with repetition over 14 days.

Sex Differences and Positive Dose-Response Relationships between Serum Osteocalcin Levels and Low Muscle Strength

INTRODUCTION

Impaired handgrip strength is an indication for sarcopenia and frailty screening, and is associated with increased osteoporotic risks and all-cause mortality. Osteocalcin, secreted by osteoblasts, is a versatile factor that participates in bone turnover and muscle adaptation. The role of osteocalcin in muscle strength has mainly been discussed in animal models and requires more human data. The study aimed to investigate the association between the serum osteocalcin level and handgrip strength in middle-aged individuals and older adults with diabetes.

METHODS

Adult participants (aged 40 and above, N = 237) with diabetes were enrolled in a medical center in northern Taiwan. Subjects were divided into normal, low muscle mass without dynapenia, dynapenia without low muscle mass, and groups of low muscle mass with dynapenia according to their handgrip strength and muscle mass measurements. Physical performance, including handgrip strength, repeated sit-to-stand tests, walking speed, and short physical performance batteries, was documented. Body composition was measured by bioelectrical impedance analysis.

RESULTS

The median serum osteocalcin level was highest in the dynapenic group without low muscle mass (median [Q1, Q3], 14.1 [11.2, 16.3] ng/mL). Multivariate logistic regression showed that a higher serum osteocalcin level was associated with worse handgrip strength (OR: 3.89, 95% CI: 1.66-9.10) after adjusting for body mass index (adiposity), skeletal muscle mass index (muscle), and medication with dipeptidyl peptidase-4 inhibitor. Further sex stratification revealed a more significant association between serum osteocalcin level and impaired handgrip strength in women but not in men. The female groups showed increases in the risk of impaired handgrip strength: 4.84-fold in the osteocalcin T2 group (11.4 ≤ osteocalcin <15.0 ng/mL) and 4.54-fold in the osteocalcin T3 group (osteocalcin ≥15.0 ng/mL). Moreover, after adjusting for various confounders, 8.41-fold and 8.03-fold increases in the risk of impaired handgrip strength were observed in the osteocalcin T2 group (11.4≤ osteocalcin <15.0 ng/mL) and osteocalcin T3 group (osteocalcin ≥14.5 ng/mL), respectively.

CONCLUSION

Higher serum osteocalcin is associated with increased risks of impaired handgrip strength and impaired physical performance. Dose-dependent associations were found especially in postmenopausal women but not in men.

Medical Telemonitoring for the Management of Hypertension in Older Patients in Japan

Hypertension is the most frequent modifiable risk factor associated with cardiovascular disease (CVD) morbidity and mortality. Even in older people, strict blood pressure (BP) control has been recommended to reduce CVD event risks. However, caution should be exercised since older hypertensive patients have increased physical vulnerability due to frailty and multimorbidity, and older patients eligible for clinical trials may not represent the general population. Medical telemonitoring systems, which enable us to monitor a patient's medical condition remotely through digital communication, have become much more prevalent since the coronavirus pandemic. Among various physiological parameters, BP monitoring is well-suited to the use of such systems, which enable healthcare providers to deliver accurate and safe BP management, even in the presence of frailty and/or living in geographically remote areas. Furthermore, medical telemonitoring systems could help reduce nonadherence to antihypertensive medications and clinical inertia, and also enable multi-professional team-based management of hypertension. However, the implementation of medical telemonitoring systems in clinical practice is not easy, and substantial barriers, including the development of user-friendly devices, integration with existing clinical systems, data security, and cost of implementation and maintenance, need to be overcome. In this review, we focus on the potential of medical telemonitoring for the management of hypertension in older people in Japan.

Using exergame-based exercise to prevent and postpone the loss of muscle mass, muscle strength, cognition, and functional performance among elders in rural long-term care facilities: A protocol for a randomized controlled trial

Objective

Elderly individuals in long-term care facilities (LTCFs) have a higher prevalence of sarcopenia than those in the community. Exercise is the gold standard for preventing and treating sarcopenia. Regarding exercise, multicomponent exercises, including progressive resistance training (PRT), are beneficial. However, developing routine, structured exercise programs for the elderly in LTCFs is difficult because of a shortage of healthcare providers, particularly in rural regions. Exergame-based exercises can increase a player's motivation and reduce staff time for an intervention. Nintendo Switch RingFit Adventure (RFA) is a novel exergame that combines resistance, aerobic, and balance exercises. In this study, we aim to investigate the clinical effectiveness of RFA on muscle and functional performance parameters among the elderly in LTCFs.

Methods

The EXPPLORE (using EXergame to Prevent and Postpone the LOss of muscle mass, muscle strength, and functional performance in Rural Elders) trial is a single-center randomized controlled trial involving elderly individuals (≥60 years) living in LTCFs in rural southern Taiwan. The participants will be equally randomized to the intervention group (exergame-based exercise plus standard care) or the control group (standard care alone). Both groups will receive standard care except that the intervention group will receive exergame-based exercises at the time previously scheduled for sedentary activities in the LTCFs. The exergame-based exercise will be performed using RFA in the sitting position with a specialized design, including arm fit skills and knee assist mode. Each session of the exercise lasts 30 mins and will be performed two times per week for 12 weeks. The primary outcomes will be the osteoporotic fracture index, appendicular skeletal muscle mass index, dominant handgrip strength, and gait speed. Meanwhile, the secondary outcomes will be the dexterity and agility, muscle strength and thickness, range of motion of the joints of the dominant upper extremity, Kihon checklist, Medical Outcomes Study 36-Item Short-Form Health Survey, and Brain Health Test.

Discussion

This trial will provide valuable knowledge on whether exergames using RFA can counteract physical decline and improve quality of life and cognition among the elderly in LTCFs.

Clinical trial registration

[www.ClinicalTrials.gov], identifier [NCT05360667].

Elastic resistance training is more effective than vitamin D3 supplementation in reducing oxidative stress and strengthen antioxidant enzymes in healthy men

OBJECTIVE

Today, reducing oxidative stress and improving the antioxidant system with antioxidant supplements along with exercise training has received a lot of attention. Vitamin D plays a very important role in general health and reducing oxidative stress. The aim of this study was to examine the effect of vitamin D3 supplements during elastic-band resistance training (EBT) on oxidative stress and antioxidant indices in healthy men.

METHODS

Forty healthy men (Serum: 20 ≤ 25 (OH) D ≤ 25 ng/mL) voluntarily participated in the current study and randomly were assigned to EBT-vitamin D3 (ED, n = 10), EBT-placebo (EP, n = 10), vitamin D3 (VD, n = 10), and control (Con, n = 10). EBT was performed three times per week on non-consecutive days for eight weeks, in seven exercises. The subjects in the ED, VD, and EP consumed 50,000 IU vitamin D3 or placebo once every 2 weeks. Ten ccs blood samples were collected before and after exercise training and the total antioxidant capacity (TAC), superoxide dismutase (SOD), glutathione peroxidase (GPX), and creatine kinase (CK) activities were measured in the plasma. Malondialdehyde (MDA), as the lipid peroxidation index, and 25(OH) D were measured in the plasma.

RESULTS

We found that there was a significant difference between ED with VD (p = 0.011) and Con (p = 0.022) for MDA. A significant difference was also seen for SOD in ED with VD (p = 0.024) and Con (p = 0.038) and TAC in ED with VD (p = 0.020) and Con (p = 0.030), and GPX in ED with VD (p = 0.040) and Con (p = 0.010). While there were no significant differences between ED and EP in all mentioned variables (p > 0.05).

CONCLUSION

Finally, it can be said that elastic resistance training improved antioxidant defence. However, vitamin D3 supplementation during resistance elastic training has no synergistic effect on attenuating oxidative stress indices.

Shared and distinct mechanisms of skeletal muscle atrophy: A narrative review

Maintenance of skeletal muscle mass and function is an incredibly nuanced balance of anabolism and catabolism that can become distorted within different pathological conditions. In this paper we intend to discuss the distinct intracellular signaling events that regulate muscle protein atrophy for a given clinical occurrence. Aside from the common outcome of muscle deterioration, several conditions have at least one or more distinct mechanisms that creates unique intracellular environments that facilitate muscle loss. The subtle individuality to each of these given pathologies can provide both researchers and clinicians with specific targets of interest to further identify and increase the efficacy of medical treatments and interventions.

Effects of Neuromuscular Electrical Stimulation on Quadriceps Muscle Strength and Mass in Healthy Young and Older Adults: A Scoping Review

OBJECTIVE

Although neuromuscular electrical stimulation (NMES) has been used as a safe and relevant complement to voluntary resistance training, its effectiveness in increasing quadriceps femoris muscle strength and mass in healthy young and older adults has not been determined. The aim of this scoping review was to assess the effects of NMES on quadriceps muscle strength and mass in healthy young and older adults.

METHODS

CENTRAL, Pedro, MEDLINE, and PubMed were searched from inception to September 2019. Randomized controlled trials (RCTs) that compared NMES with control group or voluntary resistance training for healthy young and older adults were included. Study characteristics, primary and secondary outcome parameters, and details of the NMES intervention were extracted by 2 reviewers. Only studies for which full text was available in English were included.

RESULTS

Thirty-two RCTs including 796 healthy participants were identified as being eligible for young adults, and 5 RCTs including 123 healthy participants were identified as being eligible for older adults. The available evidence strongly suggests that NMES improves quadriceps muscle strength compared with a control group in young adults, but its efficacy seems lower than that of voluntary resistance training. The available limited evidence regarding the effects of NMES on quadriceps muscle mass compared with control in young adults is inconclusive, with 3 RCTs showing positive effects and 3 RCTs not showing positive effects. The very limited available evidence from 5 RCTs in older adults suggests that NMES might be beneficial for increasing quadriceps muscle strength and mass.

CONCLUSION

Overall, the evidence indicates that NMES is an efficacious method for increasing quadriceps muscle strength in young adults, whereas its impact on muscle mass requires further investigations. In addition, the effectiveness of NMES needs to be confirmed in older adults on the basis of more high-quality RCTs with larger sample sizes.

IMPACT

This scoping review of 37 RCTs including 919 people is the first study, to the authors' knowledge, to show that the use of NMES increases quadriceps muscle strength in young adults and might improve quadriceps muscle strength compared with control interventions in older adults. In both young and older adults, the effects of NMES on quadriceps muscle mass are still unclear.

Metabolic Remodeling in Skeletal Muscle Atrophy as a Therapeutic Target

Skeletal muscle is a highly responsive tissue, able to remodel its size and metabolism in response to external demand. Muscle fibers can vary from fast glycolytic to slow oxidative, and their frequency in a specific muscle is tightly regulated by fiber maturation, innervation, or external causes. Atrophic conditions, including aging, amyotrophic lateral sclerosis, and cancer-induced cachexia, differ in the causative factors and molecular signaling leading to muscle wasting; nevertheless, all of these conditions are characterized by metabolic remodeling, which contributes to the pathological progression of muscle atrophy. Here, we discuss how changes in muscle metabolism can be used as a therapeutic target and review the evidence in support of nutritional interventions and/or physical exercise as tools for counteracting muscle wasting in atrophic conditions.

Nucleoprotein-enriched diet enhances protein synthesis pathway and satellite cell activation via ERK1/2 phosphorylation in unloaded rat muscles

NEW FINDINGS

What is the central question of this study? The purpose of this study was to determine whether the nucleotides in a nucleoprotein-enriched diet could ameliorate the unloading-associated decrease in soleus muscle mass and fibre size. What is the main finding and its importance? The results indicate that the nucleotides in the nucleoprotein-enriched diet could ameliorate the unloading-associated decrease in type I fibre size and muscle mass, most probably owing to the activation of protein synthesis pathways and satellite cell proliferation and differentiation via ERK1/2 phosphorylation. Thus, nucleotide supplementation appears to be an effective countermeasure for muscle atrophy.

ABSTRACT

Hindlimb unloading decreases both the protein synthesis pathway and satellite cell activation and results in muscle atrophy. Nucleotides are included in nucleoprotein and provide the benefits of increasing extracellular signal-regulated kinase (ERK) 1/2 phosphorylation. ERK1/2 phosphorylation is also important in the activation of satellite cells, especially for myoblast proliferation and stimulating protein synthesis pathways. Therefore, we hypothesized that nucleotides in the nucleoproteins would ameliorate muscle atrophy by increasing the protein synthesis pathways and satellite cell activation during hindlimb unloading in rat soleus muscle. Twenty-four female Wistar rats were divided into four groups: control rats fed a basal diet without nucleoprotein (CON), control rats fed a nucleoprotein-enriched diet (CON+NP), hindlimb-unloaded rats fed a basal diet (HU) or hindlimb-unloaded rats fed a nucleoprotein-enriched diet (HU+NP). HU for 2 weeks resulted in reductions in phosphorylation of p70S6K and rpS6, the numbers of myoblast determination protein (MyoD)- and myogenin- positive nuclei, type I muscle fibre size and muscle mass. Both CON+NP and HU+NP rats showed an increase in ERK1/2, phosphorylation of p70S6K and rpS6, and the numbers of MyoD- and myogenin-positive nuclei compared with their basal diet groups. The NP diet also ameliorated the unloading-associated decrease in type I muscle fibre size and muscle mass. The results indicate that the nucleotides in the nucleoprotein-enriched diet could ameliorate the unloading-associated decrease in type I fibre size and muscle mass, most probably owing to the activation of protein synthesis pathways and satellite cell proliferation and differentiation via ERK1/2 phosphorylation. Thus, nucleotide supplementation appears to be an effective countermeasure for muscle atrophy.

Effects of a mixed exercise program on cancer related-fatigue and health-related quality of life in oncogeriatric patients: A feasibility study

OBJECTIVES

Cancer-related fatigue (CRF) is the most debilitating side effect occurring with cancer treatment accumulation. Although combining aerobic and resistance exercise is an effective strategy to counteract this side effect, there is a paucity of studies performed with older patients even if this is the most affected population. Hence, the objective was to assess the feasibility and the impact of a twelve-week exercise program performed during cancer treatment on CRF, quality of life, and physical capacity in older adults diagnosed with early-stage cancer.

MATERIAL AND METHODS

Twenty patients with cancer (70 ± 4 years) beginning systemic cancer treatments were recruited and randomized into two groups: 1) aerobic and resistance training (MIX) and 2) stretching (CON). Both groups were supervised three times/week for a total of twelve weeks. The primary outcome was feasibility and secondary outcomes were CRF (FACIT-Fatigue questionnaire), health-related quality of life (HRQoL) (EORTC QLQ-C30 questionnaire) and physical capacity (6MWT and grip strength).

RESULTS

In Mix, both exercise adherence (88.2%) and completion rate (86.6%) were high, which suggests that exercise is feasible in an oncologic context. In the MIX group, HRQoL improved (p = 0.05) and CRF was clinically, ableit non-significantly (p = 0.09), decreased. Concerning physical capacity, MIX showed a clinical improvement in the 6MWT during the intervention (p = 0.002) compared to CON.

CONCLUSION

This study suggests that, in older patients with cancer undergoing adjuvant or neoadjuvant systemic treatments, a mixed exercise program is feasible, well tolerated and might help mitigate CRF and HRQoL decrements.

Neuromuscular electrical stimulation and protein during bed rest increases CD11b+ skeletal muscle macrophages but does not correspond to muscle size or insulin sensitivity

With this cohort, we previously demonstrated preservation of thigh lean tissue with neuromuscular electrical stimulation combined with protein supplementation (NMES+PRO) treatment during bed rest in healthy older adults. Because macrophage polarization plays a significant role in the repair and maintenance of muscle size and insulin sensitivity, we hypothesized that muscle macrophages would be induced by NMES+PRO and would correspond to an increase in lean mass and an attenuated insulin resistance response altered by bed rest. Older adults (60-80 years old; body mass index < 30 kg/m2) underwent 5 days of bed rest and were randomized to either thrice daily treatment of NMES+PRO (n = 8) or CON (n = 8). Lean mass, insulin sensitivity, and markers of muscle macrophages, inflammation, and connective tissue were determined before and after bed rest. Glucose intolerance and insulin resistance occurred after bed rest but there was not a treatment effect (p > 0.10). Proinflammatory-like macrophages (CD11b+, CD206-) increased (p < 0.05) with NMES+PRO treatment and was different than CON. Minor changes in noncontractile tissue were observed. However, changes in muscle macrophages or extracellular matrix were not related to the preservation of thigh lean mass or insulin resistance. Daily NMES+PRO treatment during bed rest induced a muscle proinflammatory-like macrophage response and was unrelated to muscle size or metabolic function. This study is listed as clinical trial NCT02566590. Novelty Neuromuscular electrical stimulation combined with protein supplementation (NMES+PRO) increased proinflammatory-like macrophages and extracellular matrix content in older adults after bed rest. NMES+PRO changes in macrophages and noncontractile tissue macrophages were not related to muscle size preservation or insulin sensitivity.

Changes in Northern Elephant Seal Skeletal Muscle Following Thirty Days of Fasting and Reduced Activity

Northern elephant seals (NES, Mirounga angustirostris) undergo an annual molt during which they spend ∼40 days fasting on land with reduced activity and lose approximately one-quarter of their body mass. Reduced activity and muscle load in stereotypic terrestrial mammalian models results in decreased muscle mass and capacity for force production and aerobic metabolism. However, the majority of lost mass in fasting female NES is from fat while muscle mass is largely preserved. Although muscle mass is preserved, potential changes to the metabolic and contractile capacity are unknown. To assess potential changes in NES skeletal muscle during molt, we collected muscle biopsies from 6 adult female NES before the molt and after ∼30 days at the end of the molt. Skeletal muscle was assessed for respiratory capacity using high resolution respirometry, and RNA was extracted to assess changes in gene expression. Despite a month of reduced activity, fasting, and weight loss, skeletal muscle respiratory capacity was preserved with no change in OXPHOS respiratory capacity. Molt was associated with 162 upregulated genes including those favoring lipid metabolism. We identified 172 downregulated genes including those coding for ribosomal proteins and genes associated with skeletal muscle force transduction and glucose metabolism. Following ∼30 days of molt, NES skeletal muscle metabolic capacity is preserved although mechanotransduction may be compromised. In the absence of exercise stimulus, fasting-induced shifts in muscle metabolism may stimulate pathways associated with preserving the mass and metabolic capacity of slow oxidative muscle.

Changes in Body Composition of Old Rats at Different Time Points After Dexamethasone Administration

Background: Aging leads to changes in skeletal muscle quantity and quality and is accompanied with increase in body mass and fat mass, whereas fat-free mass either decreases or remains unchanged. The body composition of rodents has been an important factor for clinical trials in the laboratory. Glucocorticoids such as dexamethasone are widely used in clinical medicine, but may induce myopathy, characterized by muscle weakness, atrophy, and fatigue. In animals treated with glucocorticoids, a dose-dependent reduction of body weight has been observed. This weight loss is usually followed by muscle atrophy and a reduction of several muscle proteins, contributing to impaired muscle function. This study was designed to describe changes in body composition and BMC of 22-month-old rats during 10- and 20-day recovery period after 10-day dexamethasone administration.

Method: Data on body mass, lean body mass, fat mass and bone mineral content of the rats were obtained with dual energy X-ray absorptiometry scan.

Result: Significant reduction in body mass, lean body mass, fat mass and fast-twitch muscle mass was observed after dexamethasone treatment. Body mass, fat mass and fast-twitch muscle mass stayed decreased during 20 days after terminating the hormone administration; lean body mass reached the preadministration level after 20-day recovery period. There were no significant changes in bone mineral density during the recovery period. Dexamethasone treatment gradually reduced hindlimb grip strength that also stayed decreased during the 20-day recovery period.

Conclusion: This study demonstrated that a 10-day period of overexprosure to glycocorticoids induced longlasting changes in old rats’ body composition and these values did not attain the baseline level even after 20-day recovery period.

Muscle unloading: A comparison between spaceflight and ground-based models

Prolonged unloading of skeletal muscle, a common outcome of events such as spaceflight, bed rest and hindlimb unloading, can result in extensive metabolic, structural and functional changes in muscle fibres. With advancement in investigations of cellular and molecular mechanisms, understanding of disuse muscle atrophy has significantly increased. However, substantial gaps exist in our understanding of the processes dictating muscle plasticity during unloading, which prevent us from developing effective interventions to combat muscle loss. This review aims to update the status of knowledge and underlying mechanisms leading to cellular and molecular changes in skeletal muscle during unloading. We have also discussed advances in the understanding of contractile dysfunction during spaceflights and in ground-based models of muscle unloading. Additionally, we have elaborated on potential therapeutic interventions that show promising results in boosting muscle mass and strength during mechanical unloading. Finally, we have identified key gaps in our knowledge as well as possible research direction for the future.

Expression Levels of Long Non-Coding RNAs Change in Models of Altered Muscle Activity and Muscle Mass

Skeletal muscle is a highly plastic organ that is necessary for homeostasis and health of the human body. The size of skeletal muscle changes in response to intrinsic and extrinsic stimuli. Although protein-coding RNAs including myostatin, NF-κβ, and insulin-like growth factor-1 (IGF-1), have pivotal roles in determining the skeletal muscle mass, the role of long non-coding RNAs (lncRNAs) in the regulation of skeletal muscle mass remains to be elucidated. Here, we performed expression profiling of nine skeletal muscle differentiation-related lncRNAs (DRR, DUM1, linc-MD1, linc-YY1, LncMyod, Neat1, Myoparr, Malat1, and SRA) and three genomic imprinting-related lncRNAs (Gtl2, H19, and IG-DMR) in mouse skeletal muscle. The expression levels of these lncRNAs were examined by quantitative RT-PCR in six skeletal muscle atrophy models (denervation, casting, tail suspension, dexamethasone-administration, cancer cachexia, and fasting) and two skeletal muscle hypertrophy models (mechanical overload and deficiency of the myostatin gene). Cluster analyses of these lncRNA expression levels were successfully used to categorize the muscle atrophy models into two sub-groups. In addition, the expression of Gtl2, IG-DMR, and DUM1 was altered along with changes in the skeletal muscle size. The overview of the expression levels of lncRNAs in multiple muscle atrophy and hypertrophy models provides a novel insight into the role of lncRNAs in determining the skeletal muscle mass.

Inactivity and Skeletal Muscle Metabolism: A Vicious Cycle in Old Age

Aging is an inevitable and gradually progressive process affecting all organs and systems. The musculoskeletal system makes no exception, elderly exhibit an increased risk of sarcopenia (low muscle mass),dynapenia (declining muscle strength), and subsequent disability. Whereas in recent years the subject of skeletal muscle metabolic decline in the elderly has been gathering interest amongst researchers, as well as medical professionals, there are many challenges yet to be solved in order to counteract the effects of aging on muscle function efficiently. Noteworthy, it has been shown that aging individuals exhibit a decline in skeletal muscle metabolism, a phenomenon which may be linked to a number of predisposing (risk) factors such as telomere attrition, epigenetic changes, mitochondrial dysfunction, sedentary behavior (leading to body composition alterations), age-related low-grade systemic inflammation (inflammaging), hormonal imbalance, as well as a hypoproteic diet (unable to counterbalance the repercussions of the age-related increase in skeletal muscle catabolism). The present review aims to discuss the relationship between old age and muscle wasting in an effort to highlight the modifications in skeletal muscle metabolism associated with aging and physical activity.

Vertical Ground Reaction Force During a Water-Based Exercise Performed by Elderly Women: Equipment Use Effects

Purpose: The present study aimed to compare the vertical ground reaction force responses during the performance of the stationary running water-based exercise with and without equipment at different cadences by elderly women. Method: Nineteen elderly women (age: 68.6 ± 5.0 years; body mass: 69.0 ± 9.5 kg; height: 154.9 ± 5.6 cm) completed one session consisting of the performance of the water-based stationary running with elbow flexion and extension immersed to the xiphoid process depth. The exercise was performed in three conditions, without equipment, with water-floating and with water-resistance equipment, at three cadences (80 b·min^-1, 100 b·min^-1 and maximal) in a randomized order. Peak and impulse of vertical ground reaction force were collected during the exercise using an underwater force plate. Repeated measures two-way ANOVA was used (α = 0.05). Results: Peak vertical ground reaction force (p < .001) and impulse (p ≤ 0.002) resulted in lower values for the water-floating use (0.42-0.48 BW and 0.07-0.13 N.s/BW) in comparison to the water-resistance equipment use (0.46-0.60 BW and 0.09-0.16 N.s/BW) and to the non-use of equipment (0.45-0.60 BW and 0.07-0.17 N.s/BW), except for the impulse at the maximal cadence. In addition, peak vertical ground reaction force at 80 b·min^-1 (p = .002) and impulse at the maximal cadence (p < .001) showed lower values compared to the other cadences. Conclusion: The use of water-floating equipment minimizes the vertical ground reaction force during the stationary running water-based exercise performed by elderly women regardless of the cadence.

Glucocorticoid-Induced Changes in Rat Skeletal Muscle Biomechanical and Viscoelastic Properties: Aspects of Aging

OBJECTIVES

The purpose of this study was to estimate the state of tension (tone) and the biomechanical and viscoelastic properties of skeletal muscle in aging rats during the administration of different doses of dexamethasone and to find the relationships among the state of muscle atrophy, muscle strength, and the abovementioned muscle properties.

METHODS

Muscle state of tension, biomechanical (elasticity, dynamic stiffness) and viscoelastic (mechanical stress relaxation time, Deborah number) properties (using MyotonPRO, Myoton Ltd, Tallinn, Estonia), lean body mass (BM), and hind limb grip strength were measured before and after the administration of a 10-day treatment with dexamethasone 100 μg/100 g BM (young and old group) and 50 μg/100 g BM (old group).

RESULTS

Muscle elasticity (logarithmic decrement) was lower in old animals (1.86 ± 0.03) in comparison with young adult rats (1.38 ± 0.04) (P < .01). After the 10-day treatment with dexamethasone 100 μg/100 g BM, young adult rats had 10% lower muscle elasticity (P < .01). The same dose of dexamethasone in old rats increased tone (frequency of natural oscillation) from 29.13 ± 0.51 Hz to 38.50 ± 0.95 Hz (P < .001). There were dose-dependent differences in dynamic stiffness and tone of muscle; changes in elasticity were independent of the dose in old animals. In old rats, the muscle's viscoelastic properties decreased after dexamethasone administration. Significant correlation was found between changes in muscle logarithmic decrement and stiffness (r_s = 0.90; P < .05) in old animals.

CONCLUSIONS

Biomechanical and viscoelastic properties of skeletal muscle indicate changes in the main function of muscle during glucocorticoid-induced muscle atrophy and are in agreement with changes in hind limb strength. The myometric measurements indicate the direction and magnitude of change in muscle tissue after different doses of dexamethasone administration easily and quickly.

IS MUSCULAR AND FUNCTIONAL PERFORMANCE RELATED TO GAIT SYMMETRY IN OLDER ADULTS? A SYSTEMATIC REVIEW

BACKGROUND

Gait asymmetries are a matter of discussion concerning gait adaptation in older adults. While most studies perform unilateral gait assessments, the hypothesis that asymmetry in gait biomechanics is influenced by muscular and functional performance in older people needs to be confirmed.

PURPOSE

Here we performed a systematic review (CRD42018093189) to discuss the relationship between muscular and functional performance and gait asymmetries in older adults.

MATERIALS AND METHODS

Searches were performed using Medline via Pubmed, Scopus, PEDro, Cochrane Central, and Lilacs databases. Studies investigating leg asymmetries during overground locomotion and recording kinetics, kinematics or muscular activation parameters to determine at least one muscular or functional parameter were included.

RESULTS

Findings show that gait asymmetries, especially in step temporal parameters, are mainly related to functional outcomes, but the relationship with muscular performance was not possible to determine.

CONCLUSIONS

The relationship of gait asymmetry with muscular performance is still unknown, and there is a lack of investigations. Improvements in performance of functional tasks lead to a more symmetric gait.

Dexamethasone-induced impairment of post-injury skeletal muscle regeneration

Background

Due to the routine use of dexamethasone (DEX) in veterinary and human medicine and its negative impact on the rate of wound healing and skeletal muscle condition, we decided to investigate the effect of DEX on the inflammatory and repair phases of skeletal muscle regeneration. In this study, a porcine skeletal muscle injury model was used. The animals were divided into non-treated and DEX-treated (0.2 mg/kg/day) groups. On the 15th day of DEX administration, bupivacaine hydrochloride-induced muscle injury was performed, and the animals were sacrificed in subsequent days. Regeneration was assessed by histopathology and immunohistochemistry. In the inflammatory phase, the presence and degree of extravasation, necrosis and inflammation were evaluated, while in the repair phase, the numbers of muscle precursor cells (MPCs), myotubes and young myofibres were estimated.

Results

In the inflammatory phase, DEX increased the severity and prolonged extravasation, prolonged necrosis and inflammation at the site of the muscle injury. In the repair phase, DEX delayed and prolonged MPC presence, impaired and prolonged myotube formation, and delayed young myofibre formation. Furthermore, DEX markedly affected the kinetics of the parameters of the inflammatory phase of the skeletal muscle regeneration more than that of the repair phase.

Conclusions

DEX impairment of the inflammatory and repair phases of the skeletal muscle regeneration was proven for the first time. The drug appears to affect the inflammatory phase more than the repair phase of regeneration. In light of our results, the possibility of reduction of the regenerative capacity of skeletal muscles should be considered during DEX therapy, and its use should be based on risk–benefit assessment.

Quadriceps muscle characteristics and subcutaneous fat assessed by ultrasound and relationship with function in patients with knee osteoarthritis awaiting knee arthroplasty

BACKGROUND

Patients with severe knee osteoarthritis are evaluated for total knee replacement (TKR), whose main indications are persistent pain and severe functional limitations substantially affecting mobility. However, evaluation of pain intensity and functional disability is difficult to standardize.

OBJECTIVE

To evaluate the relationship between quadriceps muscle thickness (QMT) and quality; the QMT and subcutaneous fat thickness (SFT) and QMT and function in patients with knee OA on a waiting list for TKR.

METHODS

Cross-sectional study in consecutively-enrolled patients. Variables: SFT, QMT and rectus femoris muscle quality, assessed by echointensity (EI). Function by the Timed Up & Go Test (TUG); sociodemographic and clinical variables and physical activity were determined. Karl Pearson correlations and multiple linear regression were used.

RESULTS

61 patients (45 female, mean age 69.7 years [SD 7.2], mean BMI 33.0 [SD 5.7], mean comorbidities 3.3 [SD 2.0], 52.5% regular physical activity) were studied. Mean TUG was 15.1 (SD 6.1). Variables retained in the regression model explained 36% of variability in the TUG. Greater muscle content (percentage) (r = -0,291) was associated with better TUG scores (p = 0.001). Greater muscle EI was negatively (r = -0,364) associated with function (p = 0.006). Older age was associated with worse TUG scores while regular physical activity was associated with better TUG scores (p = 0.001 and p = 0.008, respectively).

CONCLUSIONS

A higher percentage of quadriceps muscle and better muscle quality (lower EI) was associated with better function. Age and exercise levels influenced function. Ultrasound may provide.

Coordinated regulation of skeletal muscle mass and metabolic plasticity during recovery from disuse

Skeletal muscle regeneration after disuse is essential for muscle maintenance and involves the regulation of both mass- and metabolic plasticity-related processes. However, the relation between these processes during recovery from disuse remains unclear. In this study, we explored the potential interrelationship between the molecular regulation of muscle mass and oxidative metabolism during recovery from disuse. Molecular profiles were measured in biopsies from the vastus lateralis of healthy men after 1-leg cast immobilization and after 1 wk reloading, and in mouse gastrocnemius obtained before and after hindlimb suspension and during reloading (RL-1, -2, -3, -5, and -8 d). Cluster analysis of the human recovery response revealed correlations between myogenesis and autophagy markers in 2 clusters, which were distinguished by the presence of markers of early myogenesis, autophagosome formation, and mitochondrial turnover vs. markers of late myogenesis, autophagy initiation, and mitochondrial mass. In line with these findings, an early transient increase in B-cell lymphoma-2 interacting protein-3 and sequestosome-1 protein, and GABA type A receptor-associated protein like-1 protein and mRNA and a late increase in myomaker and myosin heavy chain-8 mRNA, microtubule-associated protein 1 light chain 3-II:I ratio, and FUN14 domain-containing-1 mRNA and protein were observed in mice. In summary, the regulatory profiles of protein, mitochondrial, and myonuclear turnover are correlated and temporally associated, suggesting a coordinated regulation of muscle mass- and oxidative metabolism-related processes during recovery from disuse.-Kneppers, A., Leermakers, P., Pansters, N., Backx, E., Gosker, H., van Loon, L., Schols, A., Langen, R., Verdijk, L. Coordinated regulation of skeletal muscle mass and metabolic plasticity during recovery from disuse.

The role of quadriceps muscle strength in the development of falls in the elderly people, a cross-sectional study

Background

Falls are a major health issue in the elderly people and an important cause of bone fracture. The aim of this study was to determine the association between quadriceps muscle strength (QMS) and falls in the elderly subjects.

Methods

All eligible participants of the Amirkola Cohort Study entered the study. Data regarding demographic characteristics, clinical and laboratory examinations were provided between 2011 to 2014. Occurrence of falls during previous year was determined by interview and review of the medical records. The study patients were divided into low, moderate and high muscle strength groups according to QMS values ≥ 30, 15-30, and < 15 kg respectively). Association between muscle strength and falls was determined by using multiple logistic regression analysis with calculation of odds ratio (OR).

Results

A total 1028 participants (females, 44.3%) were analyzed and 178(17.3%) subjects experienced a fall. Individuals with falls had higher age (p = 0.001) and lower QMS value (p = 0.001). After adjustment for all clinical and demographic variables, occurrence of falls was negatively associated with QMS and positively associated with age > 70 years old. Compared to group with QMS ≥ 30 kg, the prevalence of falls in low and moderate QMS groups increased by OR = 3(95% CI, 1.78-5.05) and 2.18 (95% CI, 1.22-3.42) respectively.

Conclusion

These findings indicate that older subjects with lower QMS are at greater risk of falls. These findings provide a rational for muscle strengthening exercise in older people.

Changes in oxidative stress severity and antioxidant potential during muscle atrophy and reloading in mice

[Purpose] Changes in oxidative stress severity and antioxidant potential are routinely used as oxidative stress markers. While several studies have reported the relationship between these markers and exercise, little is known about the dynamic nature of these markers during muscle atrophy and reloading. Therefore, we examined changes in oxidative stress severity and antioxidant potential during muscle atrophy and reloading. [Subjects and Methods] Muscle atrophy was induced in mice by casting the limb for 2 weeks. Mice were then subjected to reloading for 2 weeks. The severity of oxidative stress (hydroperoxide) and antioxidant potential (degree of reduction) were quantified. [Results] Muscle atrophy was induced by cast immobilization. The muscle mass of mice recovered to similar levels as the control group following 2 weeks of reloading. The degree of oxidative stress was within the normal range throughout the experimental period. The antioxidant potential decreased to the clinical borderline level 2 weeks after immobilization, further decreased after 1 day of reloading, and then recovered to within the normal range. [Conclusion] Performing d-ROMs and BAP tests may contribute to the understanding to atrophic process of skeletal muscle in clinical practice of physical therapy.

Age-dependent increase in angiopoietin-like protein 2 accelerates skeletal muscle loss in mice

Skeletal muscle atrophy, or sarcopenia, is commonly observed in older individuals and in those with chronic disease and is associated with decreased quality of life. There is recent medical and broad concern that sarcopenia is rapidly increasing worldwide as populations age. At present, strength training is the only effective intervention for preventing sarcopenia development, but it is not known how this exercise regimen counteracts this condition. Here, we report that expression of the inflammatory mediator angiopoietin-like protein 2 (ANGPTL2) increases in skeletal muscle of aging mice. Moreover, in addition to exhibiting increased inflammation and accumulation of reactive oxygen species (ROS), denervated atrophic skeletal muscles in a mouse model of denervation-induced muscle atrophy had increased ANGPTL2 expression. Interestingly, mice with a skeletal myocyte-specific Angptl2 knockout had attenuated inflammation and ROS accumulation in denervated skeletal muscle, accompanied by increased satellite cell activity and inhibition of muscular atrophy compared with mice harboring wildtype Angptl2 Moreover, consistent with these phenotypes, wildtype mice undergoing exercise training displayed decreased ANGPTL2 expression in skeletal muscle. In conclusion, ANGPTL2 up-regulation in skeletal myocytes accelerates muscle atrophy, and exercise-induced attenuation of ANGPTL2 expression in those tissues may partially explain how exercise training prevents sarcopenia.

Relationship between strength and muscle mass in middle-aged and elderly women: a cross-sectional study

Abstract Objective: to analyze the relationship between handgrip strength and lower limb strength and the amount of segmental skeletal muscle mass in middle-aged and elderly women. Methods: an observational, cross-sectional, observational study of 540 women aged between 40 and 80 years in the cities of Parnamirim and Santa Cruz, Rio Grande do Norte, was performed. Sociodemographic data, anthropometric measurements, handgrip dynamometry, knee flexors and extensors of the dominant limbs, as well as the segmental muscle mass of the limbs were evaluated. Data were analyzed using Student's t-Test, Chi-square test, Effect Size and Pearson's Correlation (CI 95%). Results: there were statistically significant weak and moderate correlations between handgrip strength and upper limb muscle mass, knee flexion strength and lower limb muscle mass, and between knee extension strength and lower limb muscle mass for the age groups 40-59 years and 60 years or more (p<0.05). Conclusions: muscle strength correlates with skeletal muscle mass. It could therefore be an indicator of the decrease in strength. It is not the only such indicator, however, as correlations were weak and moderate, which suggests the need for more studies on this theme to elucidate which components may also influence the loss of strength with aging.

Neuromuscular Electrical Stimulation Combined with Protein Ingestion Preserves Thigh Muscle Mass But Not Muscle Function in Healthy Older Adults During 5 Days of Bed Rest

Short-term bed rest in older adults is characterized by significant loss in leg lean mass and strength posing significant health consequences. The purpose of this study was to determine in healthy older adults if the daily combination of neuromuscular electrical stimulation and protein supplementation (NMES+PRO) would protect muscle mass and function after 5 days of bed rest. Twenty healthy older adults (∼70 years) were subjected to 5 days of continuous bed rest and were randomized into one of two groups: NMES+PRO (n = 10) or control (CON) (n = 10). The NMES+PRO group received bilateral NMES to quadriceps (40 minutes/session, 3 × /day; morning, afternoon, and evening) followed by an interventional protein supplement (17 g). The CON group received an isocaloric equivalent beverage. Before and after bed rest, vastus lateralis biopsies occurred before and after acute essential amino acid (EAA) ingestion for purposes of acutely stimulating mechanistic target of rapamycin (mTORC1) signaling, a major regulator of muscle protein synthesis, in response to bed rest and NMES+PRO. Baseline (pre and post bed rest) muscle samples were also used to assess myofiber characteristics and gene expression of muscle atrophy markers. Thigh lean mass and muscle function were measured before and after bed rest. Five days of bed rest reduced thigh lean mass, muscle function, myofiber cross-sectional area, satellite cell content, blunted EAA-induced mTORC1 signaling, and increased myostatin and MAFbx mRNA expression. Interestingly, NMES+PRO during bed rest maintained thigh lean mass, but not muscle function. Thigh muscle preservation during bed rest with NMES+PRO may partly be explained by attenuation of myostatin and MAFbx mRNA expression rather than restoration of nutrient-induced mTORC1 signaling. We conclude that the combination of NMES and protein supplementation thrice a day may be an effective therapeutic tool to use to preserve thigh muscle mass during periods of short-term hospitalization in older adults. However this combined intervention was not effective to prevent the loss in muscle function.

Nucleoprotein supplementation enhances the recovery of rat soleus mass with reloading after hindlimb unloading-induced atrophy via myonuclei accretion and increased protein synthesis

Hindlimb unloading results in muscle atrophy and a period of reloading has been shown to partially recover the lost muscle mass. Two of the mechanisms involved in this recovery of muscle mass are the activation of protein synthesis pathways and an increase in myonuclei number. The additional myonuclei are provided by satellite cells that are activated by the mechanical stress associated with the reloading of the muscles and eventually incorporated into the muscle fibers. Amino acid supplementation with exercise also can increase skeletal muscle mass through enhancement of protein synthesis and nucleotide supplements can promote cell cycle activity. Therefore, we hypothesized that nucleoprotein supplementation, a combination of amino acids and nucleotides, would enhance the recovery of muscle mass to a greater extent than reloading alone after a period of unloading. Adult rats were assigned to 4 groups: control, hindlimb unloaded (HU; 14 days), reloaded (5 days) after hindlimb unloading (HUR), and reloaded after hindlimb unloading with nucleoprotein supplementation (HUR + NP). Compared with the HUR group, the HUR + NP group had larger soleus muscles and fiber cross-sectional areas, higher levels of phosphorylated rpS6, and higher numbers of myonuclei and myogenin-positive cells. These results suggest that nucleoprotein supplementation has a synergistic effect with reloading in recovering skeletal muscle properties after a period of unloading via rpS6 activation and satellite cell differentiation and incorporation into the muscle fibers. Therefore, this supplement may be an effective therapeutic regimen to include in rehabilitative strategies for a variety of muscle wasting conditions such as aging, cancer cachexia, muscular dystrophy, bed rest, and cast immobilization.

Role of Myofibrillar Protein Catabolism in Development of Glucocorticoid Myopathy: Aging and Functional Activity Aspects

Muscle weakness in corticosteroid myopathy is mainly the result of the destruction and atrophy of the myofibrillar compartment of fast-twitch muscle fibers. Decrease of titin and myosin, and the ratio of nebulin and MyHC in myopathic muscle, shows that these changes of contractile and elastic proteins are the result of increased catabolism of the abovementioned proteins in skeletal muscle. Slow regeneration of skeletal muscle is in good correlation with a decreased number of satellite cells under the basal lamina of muscle fibers. Aging causes a reduction of AMP-activated protein kinase (AMPK) activity as the result of the reduced function of the mitochondrial compartment. AMPK activity increases as a result of increased functional activity. Resistance exercise causes anabolic and anticatabolic effects in skeletal muscle: muscle fibers experience hypertrophy while higher myofibrillar proteins turn over. These changes are leading to the qualitative remodeling of muscle fibers. As a result of these changes, possible maximal muscle strength is increasing. Endurance exercise improves capillary blood supply, increases mitochondrial biogenesis and muscle oxidative capacity, and causes a faster turnover rate of sarcoplasmic proteins as well as qualitative remodeling of type I and IIA muscle fibers. The combination of resistance and endurance exercise may be the fastest way to prevent or decelerate muscle atrophy due to the anabolic and anticatabolic effects of exercise combined with an increase in oxidative capacity. The aim of the present short review is to assess the role of myofibrillar protein catabolism in the development of glucocorticoid-caused myopathy from aging and physical activity aspects.

Acute effects of stretching exercise on the soleus muscle of female aged rats

It has been shown that stretching exercises can improve the flexibility and independence of the elderly. However, although these exercises commonly constitute training programs, the morphological adaptations induced by stretching exercises in aged skeletal muscle are still unclear.

OBJECTIVE

To assess the acute effects of passive mechanical static stretching on the morphology, sarcomerogenesis and modulation of important components of the extracellular matrix of the soleus muscle of aged female rats.

METHODS

Fifteen old female rats with 26 months were divided into two groups: stretching (n=8, SG) and control (n=7, CG): The stretching protocol consisted of 4 repetitions each of 1 min with 30s interval between sets. Stretching was performed on the left soleus muscle, 3 times a week for 1 week. After three sessions, the rats were anesthetized to remove the left soleus muscle, and then euthanized. The following analyses were carried out: muscle fiber cross-sectional area and serial sarcomere number; immunohistochemistry for the quantification of collagen I, III and TGFβ-1.

RESULTS

a decrease in muscle fiber cross-sectional area of the SG was observed when compared to the CG (p=0.0001, Kruskal-Wallis); the percentage of type I collagen was significantly lower in the SG when compared to the CG (p=0.01, Kruskal-Wallis), as well as the percentage of TGFβ-1 (p=0.04, Kruskal-Wallis); collagen III was significantly higher in the SG than in the CG (7.06±6.88% vs 4.92±5.30%, p=0.01, Kruskal-Wallis).

CONCLUSION

Although the acute stretching induced muscle hypotrophy, an antifibrotic action was detected.

The impact of six months strength training, nutritional supplementation or cognitive training on DNA damage in institutionalised elderly

Aging and its aligned loss of muscle mass are associated with higher levels of DNA damage and deteriorated antioxidant defence. To improve the body's overall resistance against DNA damage, maintaining a healthy and active lifestyle is desirable, especially in the elderly. As people age, many have to change their residence from home living to an institution, which is often accompanied by malnutrition, depression and inactivity. The current study aimed at investigating the effect of a 6-month progressive resistance training (RT), with or without protein and vitamin supplementation (RTS), or cognitive training (CT), on DNA strand breaks in 105 Austrian institutionalised women and men (65-98 years). DNA damage was detected by performing the single cell gel electrophoresis (comet) assay. Physical fitness was assessed using the chair rise, the 6-min-walking and the handgrip strength test. In addition, antioxidant enzyme activities of superoxide dismutase (SOD), glutathione peroxidase (GSH-Px) and catalase (CAT) were analysed. Basal DNA damage (lysis) increased significantly after 3 months of intervention in the RT group (T1 - T2 + 20%, P = 0.001) and the RTS group (T1 - T2 + 17%, P = 0.002) and showed a similar tendency in the CT group (T1 - T2 + 21%, P = 0.059). %DNA in tail decreased in cells exposed to H2O2 significantly in the RT (T1 - T2 - 24%, P = 0.030; T1 - T3 - 18%, P = 0.019) and CT (T1 - T2 - 21%, P = 0.004; T1 - T3 - 13%, P = 0.038) groups. Only RT and RTS groups showed significant differences overtime in enzyme activity (RT + 22% CAT-activity T1 - T3, P = 0.013; RTS + 6% SOD-activity T2 - T3, P = 0.005). Contrary to the time effects, no difference between groups was detected for any parameter at any time point. Our results suggest that both CT and RT improve resistance against H2O2 induced DNA damage and that a nutritional supplement has no further protective effect in institutionalised elderly.

Skeletal muscle tissue engineering: methods to form skeletal myotubes and their applications

Skeletal muscle tissue engineering (SMTE) aims to repair or regenerate defective skeletal muscle tissue lost by traumatic injury, tumor ablation, or muscular disease. However, two decades after the introduction of SMTE, the engineering of functional skeletal muscle in the laboratory still remains a great challenge, and numerous techniques for growing functional muscle tissues are constantly being developed. This article reviews the recent findings regarding the methodology and various technical aspects of SMTE, including cell alignment and differentiation. We describe the structure and organization of muscle and discuss the methods for myoblast alignment cultured in vitro. To better understand muscle formation and to enhance the engineering of skeletal muscle, we also address the molecular basics of myogenesis and discuss different methods to induce myoblast differentiation into myotubes. We then provide an overview of different coculture systems involving skeletal muscle cells, and highlight major applications of engineered skeletal muscle tissues. Finally, potential challenges and future research directions for SMTE are outlined.

Exercise myopathy: changes in myofibrils of fast-twitch muscle fibres

The purpose of the present study was to determine the relationships between the changes of myofibrils in fast-twitch oxidative-glycolytic (type IIA) fibres and fast-twitch glycolytic (type IIB) muscle fibres, protein synthesis and degradation rate in exercise-induced myopathic skeletal muscle. Exhaustive exercise was used to induce myopathy in Wistar rats. Intensity of glycogenolysis in muscle fibres during exercise, protein synthesis rate, degradation rate and structural changes of myofibrils were measured using morphological and biochemical methods. Myofibril cross sectional area (CSA) in type IIA fibres decreased 33% and type IIB fibres 44%. Protein degradation rate increased in both type IIA and IIB fibres, 63% and 69% respectively in comparison with the control group. According to the intensity of glycogenolysis, fast oxidative-glycolytic fibres are recruited more frequently during overtraining. Myofibrils in both types of fast-twitch myopathic muscle fibres are significantly thinner as the result of more intensive protein degradation. Regeneration capacity according to the presence of satellite cells is higher in type IIA fibres than in type IIB fibres in myopathic muscle.

3D hydrogel environment rejuvenates aged pericytes for skeletal muscle tissue engineering

Skeletal muscle tissue engineering is a promising approach for the treatment of muscular disorders. However, the complex organization of muscle, combined with the difficulty in finding an appropriate source of regenerative cells and in providing an adequate blood supply to the engineered tissue, makes this a hard task to face. In the present work, we describe an innovative approach to rejuvenate adult skeletal muscle-derived pericytes (MP) based on the use of a PEG-based hydrogel scaffold. MP were isolated from young (piglet) and adult (boar) pigs to assess whether aging affects tissue regeneration efficiency. In vitro, MP from boars had similar morphology and colony forming capacity to piglet MP, but an impaired ability to form myotubes and capillary-like structures. However, the use of a PEG-based hydrogel to support adult MP significantly improved their myogenic differentiation and angiogenic potentials in vitro and in vivo. Thus, PEG-based hydrogel scaffolds may provide a progenitor cell “niche” that promotes skeletal muscle regeneration and blood vessel growth, and together with pericytes may be developed for use in regenerative applications.

Activation of alternative NF-κB signaling during recovery of disuse-induced loss of muscle oxidative phenotype

Physical inactivity-induced loss of skeletal muscle oxidative phenotype (OXPHEN), often observed in chronic disease, adversely affects physical functioning and quality of life. Potential therapeutic targets remain to be identified, since the molecular mechanisms involved in reloading-induced recovery of muscle OXPHEN remain incompletely understood. We hypothesized a role for alternative NF-κB, as a recently identified positive regulator of muscle OXPHEN, in reloading-induced alterations in muscle OXPHEN. Markers and regulators (including alternative NF-κB signaling) of muscle OXPHEN were investigated in gastrocnemius muscle of mice subjected to a hindlimb suspension/reloading (HLS/RL) protocol. Expression levels of oxidative phosphorylation subunits and slow myosin heavy chain isoforms I and IIA increased rapidly upon RL. After an initial decrease upon HLS, mRNA levels of peroxisome proliferator-activated receptor (PPAR)-γ coactivator (PGC) molecules PGC-1α and PGC-1β and mRNA levels of mitochondrial transcription factor A (Tfam) and estrogen-related receptor α increased upon RL. PPAR-δ, nuclear respiratory factor 1 (NRF-1), NRF-2α, and sirtuin 1 mRNA levels increased during RL although expression levels were unaltered upon HLS. In addition, both Tfam and NRF-1 protein levels increased significantly during the RL period. Moreover, upon RL, IKK-α mRNA and protein levels increased, and phosphorylation of P100 and subsequent processing to P52 were elevated, reflecting alternative NF-κB activation. We conclude that RL-induced recovery of muscle OXPHEN is associated with activation of alternative NF-κB signaling.

Uneven distribution of NG2 cells in the rat cerebellar vermis and changes in aging

We describe by NG2 (neuron-glia chondroitin sulphate proteoglycan 2) immunocytochemistry an uneven distribution of NG2 glial cells in the rat cerebellum, being them more represented in the central lobules of the cerebellar vermis, belonging to the cerebrocerebellum. The cerebellar distribution of NG2 cells changes in aging rats, in which the area where the cells appear to be densely scattered throughout all cerebellar layers involves also more rostral and caudal lobules. In addition, in aging rats, in the most rostral and caudal lobules belonging to the spinocerebellum, punctate reaction product is present at the apical pole of Purkinje cells, i.e. in the area where the majority of synapses between olivary climbing fibers and Purkinje cells occur. Data suggest that the different distribution of NG2 cells is correlated to differences in physiology among cerebellar areas and reflects changes during aging.

Role of exercise therapy in prevention of decline in aging muscle function: glucocorticoid myopathy and unloading

Changes in skeletal muscle quantity and quality lead to disability in the aging population. Physiological changes in aging skeletal muscle are associated with a decline in mass, strength, and inability to maintain balance. Glucocorticoids, which are in wide exploitation in various clinical scenarios, lead to the loss of the myofibrillar apparatus, changes in the extracellular matrix, and a decrease in muscle strength and motor activity, particularly in the elderly. Exercise therapy has shown to be a useful tool for the prevention of different diseases, including glucocorticoid myopathy and muscle unloading in the elderly. The purpose of the paper is to discuss the possibilities of using exercise therapy in the prevention of glucocorticoid caused myopathy and unloading in the elderly and to describe relationships between the muscle contractile apparatus and the extracellular matrix in different types of aging muscles.

Muscle weakness in the elderly: role of sarcopenia, dynapenia, and possibilities for rehabilitation

Aging is a multifactorial process leading to changes in skeletal muscle quantity and quality, which cause muscle weakness and disability in the aging population. This paper discusses the reasons for muscle weakness—and its biological and physiological mechanisms—in the elderly and describes the role of sarcopenia and dynapenia, and the possibilities to modify the age-associated decline in muscle function and decelerate the development of muscle weakness and disability. Resistance and endurance training are effective measures of exercise therapy in the elderly, which improve muscle metabolism and thereby muscle function and life quality.

Differential effects of mild therapeutic exercise during a period of inactivity on power generation in soleus type I single fibers with age

The purpose of this study was to investigate the effects of mild therapeutic exercise (treadmill) in preventing the inactivity-induced alterations in contractile properties (e.g., power, force, and velocity) of type I soleus single fibers in three different age groups. Young adult (5- to 12-mo-old), middle-aged (24- to 31-mo-old), and old (32- to 40-mo-old) F344BNF1 rats were randomly assigned to three experimental groups: weight-bearing control (CON), non-weight bearing (NWB), and NWB with exercise (NWBX). NWB rats were hindlimb suspended for 2 wk, representing inactivity. The NWBX rats were hindlimb suspended for 2 wk and received therapeutic exercise on a treadmill four times a day for 15 min each. Peak power and isometric maximal force were reduced following hindlimb suspension (HS) in all three age groups. HS decreased fiber diameter in young adult and old rats (-21 and -12%, respectively). Specific tension (isometric maximal force/cross-sectional area) was significantly reduced in both the middle-aged (-36%) and old (-23%) rats. The effects of the mild therapeutic exercise program on fiber diameter and contractile properties were age specific. Mild treadmill therapeutic exercise attenuated the HS-induced reduction in fiber diameter (+17%, 93% level of CON group) and peak power (μN·fiber length·s(-1)) (+46%, 63% level of CON group) in young adult rats. In the middle-aged animals, this exercise protocol improved peak power (+60%, 100% level of CON group) and normalized power (kN·m(-2)·fiber length·s(-1)) (+45%, 108% level of CON group). Interestingly, treadmill exercise resulted in a further reduction in shortening velocity (-42%, 67% level of CON group) and specific tension (-29%, 55% level of CON group) in the old animals. These results suggest that mild treadmill exercise is beneficial in attenuating and preventing inactivity-induced decline in peak power of type I soleus single fibers in young adult and middle-aged animals, respectively. However, this exercise program does not prevent the HS-induced decline in muscle function in the old animals.