The effect of resistance training, detraining and retraining on muscle strength and power, myofibre size, satellite cells and myonuclei in older men

Effect of Detraining on Muscle Strength, Functional Capacity, Mental Health, and Body Composition in Individuals with Spinal Cord Injury

Spinal cord injury (SCI) is a condition that significantly affects the quality of life (QoL) of individuals, causing motor, physiological, social, and psychological impairments. Physical exercise plays a crucial role in maintaining the health and functional capacity of these individuals, helping to minimize the negative impacts of SCI. The aim of this study was to evaluate the effect of detraining (DT) (reduction or cessation of physical exercise) during the pandemic on five individuals with thoracic SCI. We assessed muscle strength using strength tests, functional capacity using a functional agility test, mental health using anxiety and depression inventories, and body composition using dual-energy X-ray absorptiometry (DEXA). The results after 33 months of DT showed significant losses in functional agility and MS, as well as a worsening in symptoms of anxiety and depression. It was observed that total body mass and fat mass (FM) exhibited varied behaviors among the individuals. Similarly, the results for lean body mass were heterogeneous, with one participant showing significant deterioration. It is concluded that DT caused by the pandemic worsened the physical and mental condition of individuals with SCI, highlighting the importance of continuous exercise for this population and underscoring the need for individual assessments to fully understand the impacts of DT.

Fast and slow myofiber nuclei, satellite cells, and size distribution with lifelong endurance exercise in men and women

We previously observed lifelong endurance exercise (LLE) influenced quadriceps whole-muscle and myofiber size in a fiber-type and sex-specific manner. The current follow-up exploratory investigation examined myofiber size regulators and myofiber size distribution in vastus lateralis biopsies from these same LLE men (n = 21, 74 ± 1 years) and women (n = 7, 72 ± 2 years) as well as old, healthy nonexercisers (OH; men: n = 10, 75 ± 1 years; women: n = 10, 75 ± 1 years) and young exercisers (YE; men: n = 10, 25 ± 1 years; women: n = 10, 25 ± 1 years). LLE exercised ~5 days/week, ~7 h/week for the previous 52 ± 1 years. Slow (myosin heavy chain (MHC) I) and fast (MHC IIa) myofiber nuclei/fiber, myonuclear domain, satellite cells/fiber, and satellite cell density were not influenced (p > 0.05) by LLE in men and women. The aging groups had ~50%-60% higher proportion of large (>7000 μm2) and small (<3000 μm2) myofibers (OH; men: 44%, women: 48%, LLE; men: 42%, women: 42%, YE; men: 27%, women: 29%). LLE men had triple the proportion of large slow fibers (LLE: 21%, YE: 7%, OH: 7%), while LLE women had more small slow fibers (LLE: 15%, YE: 8%, OH: 9%). LLE reduced by ~50% the proportion of small fast (MHC II containing) fibers in the aging men (OH: 14%, LLE: 7%) and women (OH: 35%, LLE: 18%). These data, coupled with previous findings, suggest that myonuclei and satellite cell content are uninfluenced by lifelong endurance exercise in men ~60-90 years, and this now also extends to septuagenarian lifelong endurance exercise women. Additionally, lifelong endurance exercise appears to influence the relative abundance of small and large myofibers (fast and slow) differently between men and women.

Detraining among Athletes-Is Withdrawal of Adaptive Cardiovascular Changes a Hint for the Differential Diagnosis of Physically Active People?

An athlete's training aims to achieve the highest possible sports results by improving physical dispositions which lead to cardiac adaptive changes. The annual training cycle is divided into periods. The preparatory period begins with gradually increasing training intensity and volume until the competitive period occurs, when the athlete's maximum performance is expected. Finally, the athlete enters a phase of loss of fitness, which is called detraining. Detraining is a time of resting both physically and mentally from the training regime and usually lasts about 4 weeks for endurance athletes. We collected data from much research on athletes' detraining. According to these data, the earliest change after detraining seems to be a decrease in left ventricular wall thickness and left ventricular mass, followed by decreased performance parameters, diastolic diameter of the left ventricle and size of the left atrium. A reversal of adaptive changes affects the left heart chamber first, then the right atrium and, finally, the right ventricle. Training reduction is often proposed as a method of differentiating an athlete's heart from cardiomyopathies. The aim of this study is to consider the diagnostic value of detraining in differentiating athletes' hearts from cardiomyopathies. We suggest that detraining cannot be conclusive in differentiating the disease from adaptive changes. Although a withdrawal of the characteristic morphological, functional and electrocardiographic changes occurs in healthy athletes during detraining, it can also concern individuals with cardiomyopathies due to the lower expression of abnormal features after decreased training loads. Therefore, a quick diagnosis and individual assessments using imaging and genetic tests are essential to recommend a proper type of activity.

Satellite Cell-Derived Exosomes: A Novel Approach to Alleviate Skeletal Muscle Atrophy and Fibrosis

Skeletal muscle atrophy coincides with extensive fibrous tissue hyperplasia in muscle-atrophied patients, and fibrous tissue plays a vital role in skeletal muscle function and hinders muscle fiber regeneration. However, effective drugs to manage skeletal muscle atrophy and fibrosis remain elusive. This study isolated and characterized exosomes derived from skeletal muscle satellite cells (MuSC-Exo). The study investigated their effects on denervated skeletal muscle atrophy and fibrosis in Sprague Dawley (SD) rats via intramuscular injection. MuSC-Exo demonstrated the potential to alleviate skeletal muscle atrophy and fibrosis. The underlying mechanism using single-cell RNA sequencing data and functional analysis are analyzed. Mechanistic studies reveal close associations between fibroblasts and myoblasts, with the transforming growth factor β1 (TGF-β1)-Smad3-Pax7 axis governing fibroblast activation in atrophic skeletal muscle. MuSC-Exo intervention inhibited the TGF-β1/Smad3 pathway and improved muscle atrophy and fibrosis. In conclusion, MuSC-Exo-based therapy may represent a novel strategy to alleviate skeletal muscle atrophy and reduce excessive fibrotic tissue by targeting Pax7 through the TGF-β1/Smad3 pathway.

The COVID-19 lockdown as a model of detraining in division 1 college softball players

BACKGROUND

The COVID-19 pandemic interrupted the organized training of softball players, similar to the abrupt cessation of sports participation that can happen after an injury. Thus, the COVID-19 pandemic offers a unique model to study how sudden detraining influences softball players.

METHODS

We recruited a sample of convenience of National Collegiate Athletic Association Division 1 softball players. They participated in three data collections: pre-lockdown (Jan 2020, T1), post-lockdown (Sept 2020, T2), and before the 2021 season (Jan 2021, T3). Between T1 and T2, players received an at-home conditioning and throwing program, but compliance was not strictly monitored. Between T2-T3, players resumed formal fall training (team-organized workouts, on-field practice, and within-team scrimmage games). At each time point, we collected bilaterally: 1) shoulder internal rotation (IR) and external rotation (ER) range of motion (ROM); 2) shoulder IR and ER strength; 3) hip IR and ER ROM; and 4) hip abduction and extension strength. We used four independent (2 Sides × 3 Timepoints) MANOVA with repeated measures; we followed up significant MANOVA main effect of time with Sidak posthoc tests for pairwise comparisons between time points.

RESULTS

Fifteen players participated in this study. We found a significant MANOVA main effect of time for shoulder and hip ROM (p < 0.01). Between T1-T2, dominant shoulder ER ROM decreased 6.5°, dominant shoulder IR ROM increased 4.3°, and lead hip IR ROM increased 4.4°. Between T2-T3, dominant shoulder ER ROM increased 6.3° and trail hip ER ROM increased 5.9°. We found a significant MANOVA main effect of time for shoulder strength (p = 0.03) but not for hip strength (p = 0.18). Between T2-T3, non-dominant shoulder IR and ER increased 1.8 kg and 1.5 kg, respectively.

CONCLUSION

A sudden and prolonged cessation of organized training generated changes in shoulder and hip ROM but affected strength to a lesser extent. The loss of shoulder ER and increased lead hip IR ROM are maladaptive as they are associated with injury in overhead athletes. Resuming team-organized training and scrimmage reversed some (shoulder ER), but not all of these changes. Practitioners should monitor clinical variables regularly and be aware of potential changes due to unexpected and prolonged interruptions in training, such as when players suffer sports-related injuries.

Detraining and Retraining Effects from a Multicomponent Training Program on the Functional Capacity and Health Profile of Physically Active Prehypertensive Older Women

BACKGROUND

Resuming a physical exercise program after a period of cessation is common in older women. Monitoring the responses during this detraining (DT) and retraining (RT) may allow us to analyze how the body reacts to an increase and a reduction in physical inactivity. Therefore, we conducted a follow-up training, DT, and RT in prehypertensive older women to analyze the response to these periods.

METHODS

Twenty-three prehypertensive older women (EG; 68.3 ± 2.8 years; 1.61 ± 0.44 m) performed 36 weeks of the multicomponent training program (MTP) followed by twelve weeks of DT plus eight weeks of RT. Fifteen prehypertensive older women (CG; 66.3 ± 3.2 years; 1.59 ± 0.37 m) maintained their normal routine. Functional capacity (FC), lipid, and hemodynamic profile were assessed before, during 24 and 36 weeks of the MTP, after 4 and 12 weeks of DT, and after 8 weeks of RT.

RESULTS

After 24 weeks of the MTP, only SBP did not improve. Four weeks of DT did not affect lower body strength (30-CS), TC, or GL. Eight weeks of RT improved BP (SBP: -2.52%; ES: 0.36; p < 0.00; DBP: -1.45%; ES: 0.44; p < 0.02), handgrip strength (3.77%; ES: 0.51; p < 0.00), and 30-CS (3.17%; ES: 0.38; p < 0.04) compared with 36 weeks of the MTP.

CONCLUSIONS

Eight weeks of RT allowed patients to recover the benefits lost with detraining, which after only four weeks affected them negatively, and the systematic practice of exercise contributed to greater regulation of BP since 24 weeks of the MTP proved not to be enough to promote positive effects of SBP.

Resistance training maintains physical function but does not prevent changes in body composition and biochemical markers after detraining in aging adults

OBJECTIVE

The objective of the present study was to analyze the effects of 10 weeks of resistance training (RT) and subsequent 4 weeks of detraining on physical function, body composition, and biochemical markers in aging adults.

METHODS

The study sample was selected by convenience and consisted of 12 women with a mean age of 58 ± 7 years. Physical function [Latin-American Group of Development for Maturity (GDLAM) general index], body composition, total and fractional cholesterol, triglycerides, and glycemia were assessed before and after RT (10 weeks) and detraining (4 weeks).

RESULTS

After 10 weeks of RT, there were improvements in fat-free mass (39.1 ± 4.2 vs. 39.9 ± 4.4 kg; p < 0.05 and d = 0.2), fat mass (39.9 ± 6.3% vs. 38.7 ± 6.4%; p < 0.05 and d = -0.2), conicity index (1.47 ± 0.07 vs. 1.43 ± 0.06; p = 0.001 and d = -0.6), and physical function (GDLAM index [27.2 ± 5.5 vs. 25.0 ± 4.7; p = 0.001 and d = -0.4]). Significant improvements were also found in total cholesterol (271.8 ± 75.7 vs. 217.2 ± 52.2 mg/dL; p < 0.01 and d = -0.8), LDL-cholesterol (196.5 ± 61.6 vs. 159.3 ± 38.5 mg/dL; p < 0.01 and d = -0.7), HDL-cholesterol (53.1 ± 7.3 vs. 64.3 ± 23.7 mg/dL; p < 0.05 and d = 0.7), and triglycerides (165.8 ± 32.6 vs. 139.9 ± 46.6 mg/dL; p = 0.001 and d = -0.6). After the detraining period, all benefits in physical function were successfully maintained.

CONCLUSION

RT provided benefits in physical function, body composition, and biochemical markers in aging adults. However, 4-week detraining impaired body composition and biochemical markers in the investigated sample.

Exercise Promotes Tissue Regeneration: Mechanisms Involved and Therapeutic Scope

Exercise has well-recognized beneficial effects on the whole body. Previous studies suggest that exercise could promote tissue regeneration and repair in various organs. In this review, we have summarized the major effects of exercise on tissue regeneration primarily mediated by stem cells and progenitor cells in skeletal muscle, nervous system, and vascular system. The protective function of exercise-induced stem cell activation under pathological conditions and aging in different organs have also been discussed in detail. Moreover, we have described the primary molecular mechanisms involved in exercise-induced tissue regeneration, including the roles of growth factors, signaling pathways, oxidative stress, metabolic factors, and non-coding RNAs. We have also summarized therapeutic approaches that target crucial signaling pathways and molecules responsible for exercise-induced tissue regeneration, such as IGF1, PI3K, and microRNAs. Collectively, the comprehensive understanding of exercise-induced tissue regeneration will facilitate the discovery of novel drug targets and therapeutic strategies.

Mental and physical conditions associated with physical inactivity among Farhangian University students during virtual classes: A cross-sectional study

Background

The level of mobility and general health has decreased among students in virtual classes during COVID-19 pandemic. The present cross-sectional study aims to investigate the mental and physical conditions related to inactivity among the students of Farhangian University during the virtual classes.

Methods

This is a cross-sectional study. 475 students (214 females and 261 males) were selected as the statistical sample of the study based on Morgan’s Table from Farhangian University, Iran. The statistical population includes students studying at Farhangian University of Mazandaran province that using Convenience Sampling the sample size based on Morgan’s Table, 475 students consisting of 214 females and 261 males were randomly selected as the statistical sample of the study. The research instruments of this study include International Physical Activity Questionnaire, Saehan Caliper (SH5020), Coopersmith Self-Esteem Scale, Beck Depression Questionnaire, and Nordic Skeletal and Muscular Disorders Questionnaire. For data analysis, independent sample t-test was employed to compare two groups. All analyses were conducted using spss24 software.

Results

With respect to students’ skeletal-muscular disorders, findings proved that both genders suffered physical conditions during virtual classes. The research findings showed that the average weekly activity level among women is 634 Met/min with a standard deviation of ±281, and the average weekly activity level among men is 472 Met/min with a standard deviation of ±231. Fat percentage by gender, men’s average fat percentage is 47.21% (S. D ± 4.74) and women’s average fat percentage is 31.55% (S. D ± 4.37). Also, the self-esteem scores of male and female students were obtained 29.72 and 29.43, respectively, and the difference between the two was considered significant (p &lt; 0.05). On the other hand, 67% (No. 25) of female students and 32% (No. 12) of male students suffered from high depression. Also, based on students’ skeletal-muscular disorders, findings of our study showed that both genders suffered physical conditions during virtual classes.

Conclusion

This study suggests increasing the level of physical activity to reduce body fat mass, increase mental health and reduce skeletal disorders, which can be properly accomplished through university planning and prioritizing the health of male and female students.

Fiber-Type Shifting in Sarcopenia of Old Age: Proteomic Profiling of the Contractile Apparatus of Skeletal Muscles

The progressive loss of skeletal muscle mass and concomitant reduction in contractile strength plays a central role in frailty syndrome. Age-related neuronal impairments are closely associated with sarcopenia in the elderly, which is characterized by severe muscular atrophy that can considerably lessen the overall quality of life at old age. Mass-spectrometry-based proteomic surveys of senescent human skeletal muscles, as well as animal models of sarcopenia, have decisively improved our understanding of the molecular and cellular consequences of muscular atrophy and associated fiber-type shifting during aging. This review outlines the mass spectrometric identification of proteome-wide changes in atrophying skeletal muscles, with a focus on contractile proteins as potential markers of changes in fiber-type distribution patterns. The observed trend of fast-to-slow transitions in individual human skeletal muscles during the aging process is most likely linked to a preferential susceptibility of fast-twitching muscle fibers to muscular atrophy. Studies with senescent animal models, including mostly aged rodent skeletal muscles, have confirmed fiber-type shifting. The proteomic analysis of fast versus slow isoforms of key contractile proteins, such as myosin heavy chains, myosin light chains, actins, troponins and tropomyosins, suggests them as suitable bioanalytical tools of fiber-type transitions during aging.

PCM1 labeling reveals myonuclear and nuclear dynamics in skeletal muscle across species

Myonuclei transcriptionally regulate muscle fibers during homeostasis and adaptation to exercise. Their subcellular location and quantity are important when characterizing phenotypes of myopathies, the effect of treatments, and understanding the roles of satellite cells in muscle adaptation and muscle "memory." Difficulties arise in identifying myonuclei due to their proximity to the sarcolemma and closely residing interstitial cell neighbors. We aimed to determine to what extent (pericentriolar material-1) PCM1 is a specific marker of myonuclei in vitro and in vivo. Single isolated myofibers and cross sections from mice and humans were studied from several models including wild-type and Lamin A/C mutant mice after functional overload and damage and recovery in humans following forced eccentric contractions. Fibers were immunolabeled for PCM1, Pax7, and DNA. C2C12 myoblasts were also studied to investigate changes in PCM1 localization during myogenesis. PCM1 was detected at not only the nuclear envelope of myonuclei in mature myofibers and in newly formed myotubes but also centrosomes in proliferating myogenic precursors, which may or may not fuse to join the myofiber syncytium. PCM1 was also detected in nonmyogenic nuclei near the sarcolemma, especially in regenerating areas of the Lmna^+/ΔK32 mouse and damaged human muscle. Although PCM1 is not completely specific to myonuclei, the impact that PCM1+ macrophages and interstitial cells have on myonuclei counts would be small in healthy muscle. PCM1 may prove useful as a marker of satellite cell dynamics due to the distinct change in localization during differentiation, revealing satellite cells in their quiescent (PCM1-), proliferating (PCM1+ centrosome), and prefusion states (PCM1+ nuclear envelope).

Sex-based comparisons of muscle cellular adaptations after 10 weeks of progressive resistance training in middle-aged adults

Resistance training combined with adequate protein intake supports skeletal muscle strength and hypertrophy. These adaptations are supported by the action of muscle stem cells (MuSCs), which are regulated, in part, by fibro-adipogenic progenitors (FAPs) and circulating factors delivered through capillaries. It is unclear if middle-aged males and females have similar adaptations to resistance training at the cellular level. To address this gap, 27 (13 males, 14 females) middle-aged (40-64 yr) adults participated in 10 wk of whole body resistance training with dietary counseling. Muscle biopsies were collected from the vastus lateralis pre- and posttraining. Type II fiber cross-sectional area increased similarly with training in both sexes (P = 0.014). MuSC content was not altered with training; however, training increased PDGFRα⁺/CD90⁺ FAP content (P < 0.0001) and reduced PDGFRα⁺/CD90^- FAP content (P = 0.044), independent of sex. The number of CD31⁺ capillaries per fiber also increased similarly in both sexes (P < 0.05). These results suggest that muscle fiber hypertrophy, stem/progenitor cell, and capillary adaptations are similar between middle-aged males and females in response to whole body resistance training.NEW & NOTEWORTHY We demonstrate that resistance training-induced increases in fiber hypertrophy, FAP content, and capillarization are similar between middle-aged males and females.

Application of diffusion microstructure imaging in musculoskeletal radiology - translation from head to shoulders

OBJECTIVES

Quantitative MRI techniques, such as diffusion microstructure imaging (DMI), are increasingly applied for advanced tissue characterization. We determined its value in rotator cuff (RC) muscle imaging by studying the association of DMI parameters to isometric strength and fat fraction (FF).

METHODS

Healthy individuals prospectively underwent 3T-MRI of the shoulder using DMI and chemical shift encoding-based water-fat imaging. RC muscles were segmented and quantitative MRI metrics (V-ISO, free fluid; V-intra, compartment inside of muscle fibers; V-extra, compartment outside of muscle fibers, and FF) were extracted. Isometric shoulder strength was quantified using specific clinical tests. Sex-related differences were assessed with Student's t. Association of DMI-metrics, FF, and strength was tested. A factorial two-way ANOVA was performed to compare the main effects of sex and external/internal strength-ratio and their interaction effects on quantitative imaging parameters ratios of infraspinatus/subscapularis.

RESULTS

Among 22 participants (mean age: 26.7 ± 3.1 years, 50% female, mean BMI: 22.6 ± 1.9 kg/m²), FF of the individual RC muscles did not correlate with strength or DMI parameters (all p > 0.05). Subjects with higher V-intra (r = 0.57 to 0.87, p < 0.01) and lower V-ISO (r = -0.6 to -0.88, p < 0.01) had higher internal and external rotation strength. Moreover, V-intra was higher and V-ISO was lower in all RC muscles in males compared to female subjects (all p < 0.01). There was a sex-independent association of external/internal strength-ratio with the ratio of V-extra of infraspinatus/subscapularis (p = 0.02).

CONCLUSIONS

Quantitative DMI parameters may provide incremental information about muscular function and microstructure in young athletes and may serve as a potential biomarker.

KEY POINTS

• Diffusion microstructure imaging was successfully applied to non-invasively assess the microstructure of rotator cuff muscles in healthy volunteers. • Sex-related differences in the microstructural composition of the rotator cuff were observed. • Muscular microstructural metrics correlated with rotator cuff strength and may serve as an imaging biomarker of muscular integrity and function.

Branched-chain amino acid supplementation suppresses the detraining-induced reduction of mitochondrial content in mouse skeletal muscle

Exercise training enhances oxidative capacity whereas detraining reduces mitochondrial content in skeletal muscle. The strategy to suppress the detraining-induced reduction of mitochondrial content has not been fully elucidated. As previous studies reported that branched-chain amino acid (BCAA) ingestion increased mitochondrial content in skeletal muscle, we evaluated whether BCAA supplementation could suppress the detraining-induced reduction of mitochondrial content. Six-week-old male Institute of Cancer Research (ICR) mice were randomly divided into four groups as follows: control (Con), endurance training (Tr), detraining (DeTr), and detraining with BCAA supplementation (DeTr + BCAA). Mice in Tr, DeTr, and DeTr + BCAA performed treadmill running exercises [20-30 m/min, 60 min, 5 times/week, 4 weeks]. Then, mice in DeTr and DeTr + BCAA were administered with water or BCAA [0.6 mg/g of body weight, twice daily] for 2 weeks of detraining. In whole skeletal muscle, mitochondrial enzyme activities and protein content were decreased after 2 weeks of detraining, but the reduction was suppressed by BCAA supplementation. Peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α) protein content, a master regulator of mitochondrial biogenesis, was decreased by detraining irrespective of BCAA ingestion. Regarding mitochondrial degradation, BCL2/adenovirus E1B 19 kDa protein-interacting protein 3 (BNIP3), a mitophagy-related protein, was significantly higher in the Tr group than in the DeTr + BCAA group, but not different from in the DeTr group. With respect to mitochondrial quality, BCAA ingestion did not affect oxygen consumption rate (OCR) and reactive oxygen species (ROS) production in isolated mitochondria. Our findings suggest that BCAA ingestion suppresses the detraining-induced reduction of mitochondrial content partly through inhibiting mitophagy.

Going nuclear: Molecular adaptations to exercise mediated by myonuclei

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

Role of mitochondria-associated endoplasmic reticulum membranes in insulin sensitivity, energy metabolism, and contraction of skeletal muscle

Skeletal muscle has a critical role in the regulation of the energy balance of the organism, particularly as the principal tissue responsible for insulin-stimulated glucose disposal and as the major site of peripheral insulin resistance (IR), which has been related to accumulation of lipid intermediates, reduced oxidative capacity of mitochondria and endoplasmic reticulum (ER) stress. These organelles form contact sites, known as mitochondria-associated ER membranes (MAMs). This interconnection seems to be involved in various cellular processes, including Ca²⁺ transport and energy metabolism; therefore, MAMs could play an important role in maintaining cellular homeostasis. Evidence suggests that alterations in MAMs may contribute to IR. However, the evidence does not refer to a specific subcellular location, which is of interest due to the fact that skeletal muscle is constituted by oxidative and glycolytic fibers as well as different mitochondrial populations that appear to respond differently to stimuli and pathological conditions. In this review, we show the available evidence of possible differential responses in the formation of MAMs in skeletal muscle as well as its role in insulin signaling and the beneficial effect it could have in the regulation of energetic metabolism and muscular contraction.

Myonuclear permanence in skeletal muscle memory: a systematic review and meta-analysis of human and animal studies

One aspect of skeletal muscle memory is the ability of a previously trained muscle to hypertrophy more rapidly following a period of detraining. Although the molecular basis of muscle memory remains to be fully elucidated, one potential mechanism thought to mediate muscle memory is the permanent retention of myonuclei acquired during the initial phase of hypertrophic growth. However, myonuclear permanence is debated and would benefit from a meta-analysis to clarify the current state of the field for this important aspect of skeletal muscle plasticity. The objective of this study was to perform a meta-analysis to assess the permanence of myonuclei associated with changes in physical activity and ageing. When available, the abundance of satellite cells (SCs) was also considered given their potential influence on changes in myonuclear abundance. One hundred forty-seven peer-reviewed articles were identified for inclusion across five separate meta-analyses; (1-2) human and rodent studies assessed muscle response to hypertrophy; (3-4) human and rodent studies assessed muscle response to atrophy; and (5) human studies assessed muscle response with ageing. Skeletal muscle hypertrophy was associated with higher myonuclear content that was retained in rodents, but not humans, with atrophy (SMD = -0.60, 95% CI -1.71 to 0.51, P = 0.29, and MD = 83.46, 95% CI -649.41 to 816.32, P = 0.82; respectively). Myonuclear and SC content were both lower following atrophy in humans (MD = -11, 95% CI -0.19 to -0.03, P = 0.005, and SMD = -0.49, 95% CI -0.77 to -0.22, P = 0.0005; respectively), although the response in rodents was affected by the type of muscle under consideration and the mode of atrophy. Whereas rodent myonuclei were found to be more permanent regardless of the mode of atrophy, atrophy of ≥30% was associated with a reduction in myonuclear content (SMD = -1.02, 95% CI -1.53 to -0.51, P = 0.0001). In humans, sarcopenia was accompanied by a lower myonuclear and SC content (MD = 0.47, 95% CI 0.09 to 0.85, P = 0.02, and SMD = 0.78, 95% CI 0.37-1.19, P = 0.0002; respectively). The major finding from the present meta-analysis is that myonuclei are not permanent but are lost during periods of atrophy and with ageing. These findings do not support the concept of skeletal muscle memory based on the permanence of myonuclei and suggest other mechanisms, such as epigenetics, may have a more important role in mediating this aspect of skeletal muscle plasticity.

Characteristics and Expression of circ_003628 and Its Promoted Effect on Proliferation and Differentiation of Skeletal Muscle Satellite Cells in Goats

Simple Summary

Circular RNAs (circRNAs) are new regulators of the development of skeletal muscle in mammals. Herein, circ_003628 in Longissimus dorsi muscle tissue of goats, previously found by RNA-seq, was selected to construct an expression profile in different caprine tissues, and investigate the effect on proliferation and differentiation of caprine skeletal muscle satellite cells (SMSCs), using RT-qPCR, EdU, CCK-8 and immunofluorescence assays. The results showed that circ_003628 had the highest expression level both in the longissimus dorsi muscle among nine caprine tissues collected, and on day 6 after differentiation during SMSCs differentiation periods. The interfering of circ_003628 inhibited the viability, proliferation, and differentiation of goat SMSCs.

Abstract

In our previous a study, circ_003628 was one of the most highly expressed circular RNAs (circRNAs) in the Longissimus dorsi muscle of goats found by RNA-seq, suggesting that the circRNA may be important for caprine muscle growth and development. However, there have been no reports describing the molecular mechanisms by which circ_003628 regulates the activities of goat skeletal muscle satellite cells (SMSCs). In this study, reverse transcriptase-PCR (RT-PCR) and DNA sequencing were used to validate the authenticity of circ_003628, and its characteristics, expression profile and effect on goat SMSCs were also studied using real-time quantitative-PCR (RT-qPCR), EdU, CCK-8 and immunofluorescence assays. Circ_003628 is partially originated from 13 exons, 12 introns and 3′-untranslated regions (UTR) of caprine Myosin Heavy Chain 1 (MYH1), and 25 exons and 5′ UTR of Myosin Heavy Chain 4 (MYH4), as well as intergenic sequences between the two genes. A total of 77.07% of circ_003628 were located in the nuclei of goat SMSCs, while 22.93% were expressed in the cytoplasm. The circRNAs were only expressed in triceps brachii, quadriceps femoris and longissimus dorsi muscle tissues in nine caprine tissues investigated, with the highest expression level in longissimus dorsi muscle. The expression level of circ_003628 gradually increased during differentiation periods of goat SMSCs and reached the maximum on day 6 after differentiation. The small interfering RNA of circ_003628 (named si-circ_003628) inhibited the viability and proliferation of goat SMSCs, and also decreased the expression of four cell proliferation marker genes: paired box 7 (Pax7), cyclin-dependent kinase 2 (CDK2), CDK4 and CyclinD1 in goat SMSCs. Transfection of si-circ_003628 significantly decreased the area of MyHC-labeled myotubes of goat SMSCs, as well as the expression levels of three differentiation marker genes: myosin heavy chain (MyHC), myogenin (MyoG), and myocyte enhancer factor 2C (MEF2C). These results suggest that circ_003628 promotes the viability, proliferation, and differentiation of goat SMSCs, and they also provide an improved understanding of the roles of circ_003628 in skeletal muscle growth and development in goats.

Neither myonuclear accretion nor a myonuclear domain size ceiling is a feature of the attenuated hypertrophic potential of aged human skeletal muscle

Ageing limits growth capacity of skeletal muscle (e.g. in response to resistance exercise), but the role of satellite cell (SC) function in driving this phenomenon is poorly defined. Younger (Y) (~ 23 years) and older (O) men (~ 69 years) (normal-weight BMI) underwent 6 weeks of unilateral resistance exercise training (RET). Muscle biopsies were taken at baseline and after 3-/6-week training. We determined muscle size by fibre CSA (and type), SC number, myonuclei counts and DNA synthesis (via D₂O ingestion). At baseline, there were no significant differences in fibre areas between Y and O. RET increased type I fibre area in Y from baseline at both 3 weeks and 6 weeks (baseline: 4509 ± 534 µm², 3 weeks; 5497 ± 510 µm² P < 0.05, 6 weeks; 5402 ± 352 µm² P < 0.05), whilst O increased from baseline at 6 weeks only (baseline 5120 ± 403 µm², 3 weeks; 5606 ± 620 µm², 6 weeks; 6017 ± 482 µm² P < 0.05). However, type II fibre area increased from baseline in Y at both 3 weeks and 6 weeks (baseline: 4949 ± 459 µm², 3 weeks; 6145 ± 484 µm² (P < 0.01), 6 weeks; 5992 ± 491 µm² (P < 0.01), whilst O showed no change (baseline 5210 ± 410 µm², 3 weeks; 5356 ± 535 µm² (P = 0.9), 6 weeks; 5857 ± 478 µm² (P = 0.1). At baseline, there were no differences in fibre myonuclei number between Y and O. RET increased type I fibre myonuclei number from baseline in both Y and O at 3 weeks and 6 weeks with RET (younger: baseline 2.47 ± 0.16, 3 weeks; 3.19 ± 0.16 (P < 0.001), 6 weeks; 3.70 ± 0.29 (P < 0.0001); older: baseline 2.29 ± 0.09, 3 weeks; 3.01 ± 0.09 (P < 0.001), 6 weeks; 3.65 ± 0.18 (P < 0.0001)). Similarly, type II fibre myonuclei number increased from baseline in both Y and O at 3 weeks and 6 weeks (younger: baseline 2.49 ± 0.14, 3 weeks; 3.31 ± 0.21 (P < 0.001), 6 weeks; 3.86 ± 0.29 (P < 0.0001); older: baseline 2.43 ± 0.12, 3 weeks; 3.37 ± 0.12 (P < 0.001), 6 weeks; 3.81 ± 0.15 (P < 0.0001)). DNA synthesis rates %.d^-1 exhibited a main effect of training but no age discrimination. Declines in myonuclei addition do not underlie impaired muscle growth capacity in older humans, supporting ribosomal and proteostasis impairments as we have previously reported.

Three-Month vs. One-Year Detraining Effects after Multicomponent Exercise Program in Hypertensive Older Women

Background: Chronic diseases are the leading causes of death and disability in older women. Physical exercise training programs promote beneficial effects for health and quality of life. However, exercise interruption periods may be detrimental for the hemodynamic and lipidic profiles of hypertensive older women with dyslipidemia. Methods: Nineteen hypertensive older women with dyslipidemia (exercise group: 67.5 ± 5.4 years, 1.53 ± 3.42 m, 71.84 ± 7.45 kg) performed a supervised multicomponent exercise training program (METP) during nine months, followed by a one-year detraining period (DT), while fourteen hypertensive older women (control group: 66.4 ± 5.2 years, 1.56 ± 3.10 m, 69.38 ± 5.24 kg) with dyslipidemia kept their continued daily routine without exercise. For both groups, hemodynamic and lipidic profiles and functional capacities (FCs) were assessed four times: before and after the METP and after 3 and 12 months of DT (no exercise was carried out). Results: The METP improved hemodynamic and lipidic profiles (p < 0.05), while three months of DT decreased all (p < 0.05) parameters, with the exception of diastolic blood pressure (DBP). One year of DT significantly (p < 0.01) decreased systolic blood pressure (7.85%), DBP (2.29%), resting heart rate (7.95%), blood glucose (19.14%), total cholesterol (10.27%), triglycerides (6.92%) and FC—agility (4.24%), lower- (−12.75%) and upper-body strength (−12.17%), cardiorespiratory capacity (−4.81%) and lower- (−16.16%) and upper-body flexibility (−11.11%). Conclusion: Nine months of the exercise program significantly improved the hemodynamic and lipid profiles as well as the functional capacities of hypertensive older women with dyslipidemia. Although a detraining period is detrimental to these benefits, it seems that the first three months are more prominent in these alterations.

Effect of physical exercise cessation on strength, functional, metabolic and structural outcomes in older adults: a protocol for systematic review and meta-analysis

INTRODUCTION

There is not a doubt that tailored exercise is an effective non-pharmacological approach for preventing, mitigating and even reversing ageing-related alterations. However, older adults are likely to experience prolonged periods of inactivity and training cessation periods as a consequence of falls or hospitalisation. Although recent evidence supports that exercise could have a protective effect and help in recovering, there is to date a lack of consensus about what kind of physical exercise prescription and training duration would produce better outcomes after training cessation periods. The current study will determine the effects that available exercise prescriptions produced in older adults in preserving physical conditioning following inactivity periods.

METHODS AND ANALYSIS

A systematic search of the literature will be conducted in three databases, namely PubMed, Scopus and Web of Science, from inception to 1 February 2021. Only randomised controlled trials written in English or Spanish will be eligible. No year of publication restriction will be applied. Eligible studies will contain information on population (older adults over 60 years old), intervention (inactivity period, exercise programme their duration), comparator (treatment as usual or waiting list) and outcomes (strength, functional capacity, metabolic health and skeletal muscle structure). Two independent reviewers will (1) search, screen and select studies, (2) extract data about their main characteristics and (3) evaluate their methodological and reporting quality. When disagreements emerge, the reviewers will discuss to reach a consensus. We plan to conduct meta-analysis to quantitatively synthesise the effects under study.

ETHICS AND DISSEMINATION

As systematic reviews use publicly available data, no formal ethical review and approval are needed. Findings will be published in a peer-reviewed journal(s) and presented at conferences.

PROSPERO REGISTRATION NUMBER

CRD42021235092.

Skeletal muscle atrophy: From mechanisms to treatments

Skeletal muscle is a crucial tissue for movement, gestural assistance, metabolic homeostasis, and thermogenesis. It makes up approximately 40% of the total body weight and 50% of total protein. However, several pathological abnormalities (e.g., chronic diseases, cancer, long-term infection, aging) can induce an imbalance in skeletal muscle protein synthesis and degradation, which triggers muscle wasting and even leads to atrophy. Skeletal muscle atrophy is characterized by weakening, shrinking, and decreasing muscle mass and fiber cross-sectional area at the histological level. It manifests as a reduction in force production, easy fatigue and decreased exercise capability, along with a lower quality of life. Mechanistically, there are several pathophysiological processes involved in skeletal muscle atrophy, including oxidative stress and inflammation, which then activate signal transduction, such as the ubiquitin proteasome system, autophagy lysosome system, and mTOR. Considering the great economic and social burden that muscle atrophy can inflict, effective prevention and treatment strategies are essential but still limited. Exercise is widely acknowledged as the most effective therapy for skeletal muscle atrophy; unfortunately, it is not applicable for all patients. Several active substances for skeletal muscle atrophy have been discovered and evaluated in clinical trials, however, they have not been marketed to date. Knowledge is being gained on the underlying mechanisms, highlighting more promising treatment strategies in the future. In this paper, the mechanisms and treatment strategies for skeletal muscle atrophy are briefly reviewed.

Nucleus Type-Specific DNA Methylomics Reveals Epigenetic "Memory" of Prior Adaptation in Skeletal Muscle

Using a mouse model of conditional and inducible in vivo fluorescent myonuclear labeling (HSA-GFP), sorting purification of nuclei, low-input reduced representation bisulfite sequencing (RRBS), and a translatable and reversible model of exercise (progressive weighted wheel running, PoWeR), we provide the first nucleus type-specific epigenetic information on skeletal muscle adaptation and detraining. Adult (>4 mo) HSA-GFP mice performed PoWeR for 8 wk then detrained for 12 wk; age-matched untrained mice were used to control for the long duration of the study. Myonuclei and interstitial nuclei from plantaris muscles were isolated for RRBS. Relative to untrained, PoWeR caused similar myonuclear CpG hypo- and hyper-methylation of promoter regions and substantial hypomethylation in interstitial nuclear promoters. Over-representation analysis of promoters revealed a larger number of hyper- versus hypo-methylated pathways in both nuclear populations after training and evidence for reciprocal regulation of methylation between nucleus types, with hypomethylation of promoter regions in Wnt signaling-related genes in myonuclei and hypermethylation in interstitial nuclei. After 12 wk of detraining, promoter CpGs in documented muscle remodeling-associated genes and pathways that were differentially methylated immediately after PoWeR were persistently differentially methylated in myonuclei, along with long-term promoter hypomethylation in interstitial nuclei. No enduring gene expression changes in muscle tissue were observed using RNA-sequencing. Upon 4 wk of retraining, mice that trained previously grew more at the whole muscle and fiber type-specific cellular level than training naïve mice, with no difference in myonuclear number. Muscle nuclei have a methylation epi-memory of prior training that may augment muscle adaptability to retraining.

Detraining Effects on Musculoskeletal Parameters in Early Postmenopausal Osteopenic Women: 3-Month Follow-Up of the Randomized Controlled ACTLIFE Study

Periods of absence from supervised group exercise while maintaining physical activity might be a frequent pattern in adults' exercise habits. The aim of the present study was to determine detraining effects on musculoskeletal outcomes after a 3-month detraining period in early post-menopausal, osteopenic women. Due to the COVID-19 pandemic, we terminated the 18-month randomized controlled ACTLIFE exercise intervention immediately after the 13-month follow-up assessment. This put an abrupt stop to the high-intensity aerobic and resistance group exercise sessions undertaken three times per week by the exercise group (EG: n = 27) and the gentle exercise program performed once per week for the attention control group (CG: n = 27); but both groups were permitted to conduct individual outdoor activity for the 3-month lock-down period. Study endpoints were lean body mass (LBM), bone mineral density (BMD) at the lumbar spine (LS), maximum hip-/leg extension strength and power. Detraining-induced reductions of LBM, hip/leg strength and power (but not BMD-LS) were significantly greater (p < 0.001 to p = 0.044) compared with the CG. Significant exercise effects, i.e. differences between EG and CG, present after 13 months of exercise, were lost after 3 months of detraining for LBM (p = 0.157) and BMD-LS (p = 0.065), but not for strength (p < 0.001) and power (p < 0.001). Of note, self-reported individual outdoor activities and exercise increased by about 40% in both groups during the lock-down period. Three months' absence from a supervised group exercise protocol resulted in considerable detraining effects for musculoskeletal parameters. Thus, exercise programs for adults should be continuous rather than intermittent.Trial registration number: ClinicalTrials.gov: NCT04420806, 06.05.2020.

Impact of Tailored Multicomponent Exercise for Prevent Weakness and Falls on Nursing Home Residents' Functional Capacity

OBJECTIVES

We aimed to determine whether the benefits of long (24 weeks) and short (4 weeks) training programs persisted after short (6 weeks) and long (14 weeks) periods of inactivity in older adult nursing home residents with sarcopenia.

DESIGN

Multicenter randomized trial.

INTERVENTION

The Vivifrail tailored, multicomponent exercise program (http://vivifrail.com) was conducted to individually prescribe exercise for frail older adults, depending on their functional capacity. The training included 4 levels combining strength and power, balance, flexibility, and cardiovascular endurance exercises.

SETTING AND PARTICIPANTS

Twenty-four institutionalized older adults (87.1 ± 7.1 years, 58.3% women) diagnosed with sarcopenia were allocated into 2 groups: the Long Training-Short Detraining (LT-SD) group completed 24 weeks of supervised Vivifrail training followed by 6 weeks of detraining; the Short Training-Long Detraining (ST-LD) group completed 4 weeks of training and 14 weeks of detraining.

MEASURES

Changes in functional capacity and strength were evaluated at baseline, and after short and long training and detraining periods.

RESULTS

Benefits after short and long exercise interventions persisted when compared with baseline. Vivifrail training was highly effective in the short term (4 weeks) in increasing functional and strength performance (effect size = 0.32-1.44, P < .044) with the exception of handgrip strength. Continued training during 24 weeks produced 10% to 20% additional improvements (P < .036). Frailty status was reversed in 36% of participants, with 59% achieving high self-autonomy. Detraining resulted in a 10% to 25% loss of strength and functional capacity even after 24 weeks of training (effects size = 0.24-0.92, P < .039).

CONCLUSIONS AND IMPLICATIONS

Intermittent strategies such as 4 weeks of supervised exercise 3 times yearly with no more than 14 weeks of inactivity between exercise periods appears as an efficient solution to the global challenge of maintaining functional capacity and can even reverse frailty in vulnerable institutionalized older adults.

Variability in vastus lateralis fiber type distribution, fiber size, and myonuclear content along and between the legs

Human skeletal muscle characteristics such as fiber type composition, fiber size, and myonuclear content are widely studied in clinical and sports-related contexts. Being aware of the methodological and biological variability of the characteristics is a critical aspect in study design and outcome interpretation, but comprehensive data on the variability of morphological features in human skeletal muscle are currently limited. Accordingly, in the present study, m. vastus lateralis biopsies (10 per subject) from young and healthy individuals, collected in a systematic manner, were analyzed for various characteristics using immunohistochemistry (n = 7) and SDS-PAGE (n = 25). None of the analyzed parameters, fiber type % (FT%), type I and II fiber cross-sectional area (fCSA), percentage fiber type area (fCSA%), myosin heavy chain composition (MyHC%), type IIX content, myonuclear content, or myonuclear domain, varied in a systematic manner longitudinally along the muscle or between the two legs. The average within-subject coefficient of variation for FT%, fCSA, fCSA%, and MyHC% ranged between 13% and 18% but was only 5% for fiber-specific myonuclear content, which reduced the variability for myonuclear domain size to 11%-12%. Pure type IIX fibers and type IIX MyHC were randomly distributed and present in <24% of the analyzed samples, with the average content being 0.1% and 1.1%, respectively. In conclusion, leg or longitudinal orientation does not seem to be an important aspect to consider when investigating human vastus lateralis characteristics. However, single muscle biopsies should preferably not be used when studying fiber type- and fiber size-related aspects, given the notable sample-to-sample variability.NEW & NOTEWORTHY This study provides a comprehensive analysis of the variability of key human skeletal muscle fiber characteristics in multiple sites along and between the m. vastus lateralis of healthy and active individuals. We found a notable but nonsystematic variability in fiber type and size, whereas myonuclear content was distinctively less variable, and the prevalence of type IIX fibers was random and very low. These data are important to consider when designing and interpreting studies including m. vastus lateralis biopsies.

Detraining Effects on Muscle Quality in Older Men with Osteosarcopenia. Follow-Up of the Randomized Controlled Franconian Osteopenia and Sarcopenia Trial (FrOST)

The present study aimed to determine the effect of detraining on muscle quality (MQ) in older men with osteosarcopenia. Forty-three community-dwelling older men (78 ± 4 years) were randomly allocated to a consistently supervised high-intensity resistance exercise training (HIRT) group (n = 21) or a control group (CG, n = 22). The HIRT scheduled a periodized single set protocol twice weekly. After the intervention, the men were subjected to six months of detraining. Muscle quality (MQ), defined as maximum isokinetic hip/leg extensor strength per unit of mid-thigh intra-fascia volume, was determined by magnetic resonance imaging (MRI) or per unit of thigh muscle mass assessed by dual-energy X-ray absorptiometry (DXA). Intention-to-treat analysis with multiple imputations was applied. We observed significant exercise effects for MQ (p = 0.001). During detraining, the HIRT group lost about one-third of the intervention-induced gain and displayed significantly (p = 0.001) higher MQ reductions compared to the CG. Nevertheless, after training and detraining, the overall intervention effect on MQ remained significant (p ≤ 0.004). In summary, six months of absence from HIRT induce a significant deleterious effect on MQ in older osteosarcopenic men. We conclude that intermitted training programs with training breaks of six months and longer should be replaced by largely continuous exercise programs, at least when addressing MQ parameters.

Time-dependent effects of inspiratory muscle training and detraining on cardiac autonomic control in older women

Inspiratory muscle training improved maximal inspiratory pressure (MIP) and vagal-mediated heart rate variability (HRV) in older women. However, it is unknown what occurs if the training is discontinued (detraining protocol). The aim of this study was to investigate the IMT and detraining effects on resting HRV in older women. Twelve healthy older women (60-72 yrs) enrolled in home-based IMT at 50% MIP (IMT-group) or placebo at 5% MIP (Sham-group) protocol for 4 weeks using a mechanical pressure threshold loading device. The participants were not engaged in any other exercise protocol at that time. During IMT and Sham interventions, the inspiratory load was adjusted weekly by the actual MIP and resting heart rate variability (HRV) evaluated. After training cessation (4 weeks of detraining), participants returned to the lab for HRV and MIP recordings. Adherence to IMT was superior to 95%. IMT increased MIP (23 ± 8 cmH₂O) and vagal-mediated HRV (normalized HF; 37 ± 8%), following by the reduction of sympatho-vagal balance (LF/HF), from the second week to the end of the protocol compared to sham-group. After detraining, IMT-group reduced MIP (-23 ± 8 cmH₂O) and vagal-mediated HRV (normalized HF; -38 ± 14%) returning to baseline values. In conclusion, MIP and vagal-HRV improvements induced by IMT were reversed by four weeks of detraining.

Physical Activity and Redox Balance in the Elderly: Signal Transduction Mechanisms

Reactive Oxygen Species (ROS) are molecules naturally produced by cells. If their levels are too high, the cellular antioxidant machinery intervenes to bring back their quantity to physiological conditions. Since aging often induces malfunctioning in this machinery, ROS are considered an effective cause of age-associated diseases. Exercise stimulates ROS production on one side, and the antioxidant systems on the other side. The effects of exercise on oxidative stress markers have been shown in blood, vascular tissue, brain, cardiac and skeletal muscle, both in young and aged people. However, the intensity and volume of exercise and the individual subject characteristics are important to envisage future strategies to adequately personalize the balance of the oxidant/antioxidant environment. Here, we reviewed the literature that deals with the effects of physical activity on redox balance in young and aged people, with insights into the molecular mechanisms involved. Although many molecular pathways are involved, we are still far from a comprehensive view of the mechanisms that stand behind the effects of physical activity during aging. Although we believe that future precision medicine will be able to transform exercise administration from wellness to targeted prevention, as yet we admit that the topic is still in its infancy.

Incorporating Nutrition, Vests, Education, and Strength Training (INVEST) in Bone Health: Trial Design and Methods

BACKGROUND

Achievement of 5-10% weight loss (WL) among older adults living with obesity considerably improves prognosis of health-related outcomes; however, concomitant declines in bone mineral density (BMD) limit overall benefit by increasing fracture risk. Declines in mechanical loading contribute to WL-associated BMD loss, with pilot data signaling the addition of external weight replacement (via weighted vest use) during intentional WL mitigates bone loss at weight bearing sites to a similar degree as resistance exercise training (RT). Definitive data in support of weighted vest use as a potential strategy to mitigate WL-associated bone loss in this population are needed.

METHODS

In the Incorporating Nutrition, Vests, Education, and Strength Training (INVEST) in Bone Health trial (NCT04076618), 192 older adults (60-85 years) who are overweight (BMI ≥ 27 kg/m²) with at least one obesity-related risk factor or obese (BMI = 30-40 kg/m²) will be randomly assigned to participate in one of three 12-month intervention groups: WL alone, WL + weighted vest use (WL + VEST), or WL + RT. The primary aim is to determine the effects of WL + VEST compared to WL alone and WL + RT on indicators of bone health and subsequent fracture risk.

DISCUSSION

Determining effective, translatable strategies that minimize bone loss during intentional WL among older adults holds public health potential. The INVEST in Bone Health trial offers an innovative approach for increasing mechanical stress during intentional WL in the absence of RT. If successful, findings from this study will provide evidence in support of a scalable solution to minimize bone loss during intentional WL among older adults with obesity.

Detraining effects after 18 months of high intensity resistance training on osteosarcopenia in older men-Six-month follow-up of the randomized controlled Franconian Osteopenia and Sarcopenia Trial (FrOST)

PURPOSE

Detraining after dedicated exercise programs might be a frequent situation in older people's exercise patterns. The aim of the present study was thus to determine the effects of 6 months of detraining after 18 months of high intensity resistance exercise (HIT-RT) on musculoskeletal outcomes in older men with sarcopenia.

METHODS

Community-dwelling men aged 72 years and older with osteosarcopenia (n = 43) were randomly assigned to an 18-month HIT-RT (EG: n = 21) or a non-training control group (CG, n = 22). After the intervention, participants of the EG stopped HIT-RT for 6 months, but continued their habitual physical activity. Study outcomes were skeletal muscle mass index, bone mineral density (BMD) at the lumbar-spine and total-hip, maximum hip/leg-extensor strength, handgrip strength and gait velocity. We applied an intention-to-treat analysis with multiple imputation.

RESULTS

Changes in the HIT-RT were much more pronounced during the detraining period compared with the CG, although this effect was only significant for skeletal muscle mass index and hip-/leg-extensor strength (p = .002 and p = .013), but not for lumbar-spine BMD (p = .068), total-hip BMD (p = .069), handgrip strength (p = .066) or gait velocity (p = .067). Apart from total-hip BMD (p = .055), handgrip strength (p = .069) and gait velocity (p = .881) values of the HIT-RT group decreased significantly during detraining. However, after 24 months, overall effects (p < .001) were still observed for skeletal muscle mass index and hip-/leg-extensor strength.

CONCLUSION

Although unable to state from which point in time relevant detraining effects emerge, we conclude that health care providers should focus on continuous rather than intermitted exercise programs for older people. Clinical trial number: clinicalTrials.gov: NCT03453463; NCT04444661.

Muscle memory: myonuclear accretion, maintenance, morphology, and miRNA levels with training and detraining in adult mice

BACKGROUND

In the context of mass regulation, 'muscle memory' can be defined as long-lasting cellular adaptations to hypertrophic exercise training that persist during detraining-induced atrophy and may facilitate future adaptation. The cellular basis of muscle memory is not clearly defined but may be related to myonuclear number and/or epigenetic changes within muscle fibres.

METHODS

Utilizing progressive weighted wheel running (PoWeR), a novel murine exercise training model, we explored myonuclear dynamics and skeletal muscle miRNA levels with training and detraining utilizing immunohistochemistry, single fibre myonuclear analysis, and quantitative analysis of miRNAs. We also used a genetically inducible mouse model of fluorescent myonuclear labelling to study myonuclear adaptations early during exercise.

RESULTS

In the soleus, oxidative type 2a fibres were larger after 2 months of PoWeR (P = 0.02), but muscle fibre size and myonuclear number did not return to untrained levels after 6 months of detraining. Soleus type 1 fibres were not larger after PoWeR but had significantly more myonuclei, as well as central nuclei (P < 0.0001), the latter from satellite cell-derived or resident myonuclei, appearing early during training and remaining with detraining. In the gastrocnemius muscle, oxidative type 2a fibres of the deep region were larger and contained more myonuclei after PoWeR (P < 0.003), both of which returned to untrained levels after detraining. In the gastrocnemius and plantaris, two muscles where myonuclear number was comparable with untrained levels after 6 months of detraining, myonuclei were significantly elongated with detraining (P < 0.0001). In the gastrocnemius, miR-1 was lower with training and remained lower after detraining (P < 0.002).

CONCLUSIONS

This study found that (i) myonuclei gained during hypertrophy are lost with detraining across muscles, even in oxidative fibres; (ii) complete reversal of muscle adaptations, including myonuclear number, to untrained levels occurs within 6 months in the plantaris and gastrocnemius; (iii) the murine soleus is resistant to detraining; (iv) myonuclear accretion occurs early with wheel running and can be uncoupled from muscle fibre hypertrophy; (v) resident (non-satellite cell-derived) myonuclei can adopt a central location; (vi) myonuclei change shape with training and detraining; and (vii) miR-1 levels may reflect a memory of previous adaptation that facilitates future growth.

Physical Exercise and Immune System in the Elderly: Implications and Importance in COVID-19 Pandemic Period

Physical exercise is seen as the main ally for health promotion, preventing and protecting the organism from several diseases. According to WHO, there is a tendency of constant growth in the elderly population in the coming years. The regular practice of exercises by the elderly becomes relevant to minimize the deleterious effects of the aging process and to increase the fitness index. Recently, the world population started a confrontation against Corona Virus Disease (COVID-19), which is the most significant public health challenge globally. Although social isolation is a reasonable measure in an attempt to stop contamination by COVID-19, this measure has limited the ability of individuals to exercise outdoors or in gyms and health clubs, which increased the risk of developing chronic illnesses related to a sedentary lifestyle. The critical point is that the recent recommendations on exercise prescription to combat the potentially harmful effects of COVID-19 failure to adequately address resistance exercise interventions as home-based exercise strategy. Thus, in this paper, we discussed the physical exercise as medicine if the training status is enough to protect the elderly against COVID-19 infection, about the role of physical activity on immunosuppression. Possible risks for COVID-19 infection, and the old training methods, such as no-load resistance training as possible resistance exercise strategies and high-intensity interval training, as new proposals of home-based exercise interventions, could perform during the current COVID-19 pandemic.

Strength testing or strength training: considerations for future research

Maximal strength testing is often performed to assess the efficacy of training programs or as a way to prescribe exercise load. Generally, it is believed that high load exercise is superior to low load exercise at increasing absolute strength, however this is not always the case (i.e. strength increases similarly between groups). We hypothesized that some of the discrepancy in the literature may be related to performing the strength test itself. To investigate this further we reviewed the literature looking for studies comparing high load and low load exercise. The included studies were separated into 'no extra practice' and 'practice'. No extra practice means the strength test was only performed at pre and post whereas practice refers to additional strength tests performed throughout the training intervention. Our results indicated that the differences between high load and low load exercise can be reduced when the group training with a low load is allowed additional exposure to the maximal strength test. This suggests that repeated exposure to strength tests may augment low load training adaptations and influence the outcomes. We discuss potential moderators of this relationship (e.g. how low is the low load, complexity of the skill) and offer considerations for future research. Based on this it would be recommended that when investigating the effects of low load training strength tests should be limited to pre and post intervention or if a control group is utilized then the control group should receive the same number of exposures to the strength test.

Preserved Capacity for Adaptations in Strength and Muscle Regulatory Factors in Elderly in Response to Resistance Exercise Training and Deconditioning

Aging is related to an inevitable loss of muscle mass and strength. The mechanisms behind age-related loss of muscle tissue are not fully understood but may, among other things, be induced by age-related differences in myogenic regulatory factors. Resistance exercise training and deconditioning offers a model to investigate differences in myogenic regulatory factors that may be important for age-related loss of muscle mass and strength. Nine elderly (82 ± 7 years old) and nine young, healthy persons (22 ± 2 years old) participated in the study. Exercise consisted of six weeks of resistance training of the quadriceps muscle followed by eight weeks of deconditioning. Muscle biopsy samples before and after training and during the deconditioning period were analyzed for MyoD, myogenin, insulin-like growth-factor I receptor, activin receptor IIB, smad2, porin, and citrate synthase. Muscle strength improved with resistance training by 78% (95.0 ± 22.0 kg) in the elderly to a similar extent as in the young participants (83.5%; 178.2 ± 44.2 kg) and returned to baseline in both groups after eight weeks of deconditioning. No difference was seen in expression of muscle regulatory factors between elderly and young in response to exercise training and deconditioning. In conclusion, the capacity to gain muscle strength with resistance exercise training in elderly was not impaired, highlighting this as a potent tool to combat age-related loss of muscle function, possibly due to preserved regulation of myogenic factors in elderly compared with young muscle.