Physical Exercise for Muscle Atrophy

Finite element analysis of a three-dimensional cervical spine model with muscles based on CT scan data

BACKGROUND

The incidence of cervical spondylosis is increasing, gradually affecting people's normal lives. Establishing a finite element model of the cervical spine is one of the methods for studying cervical spondylosis. MRI (Magnetic Resonance Imaging) still has certain difficulties in transitioning from human imaging to establishing muscle models suitable for finite element analysis. Medical software provides specific morphologies and can generate muscle finite element models. Additionally, there is little research on the static analysis of cervical spine finite element models with solid muscle.

PURPOSE

A new method is proposed for establishing a finite element model of the cervical spine based on CT (Computed Tomography) data and medical software, and the model's effectiveness is validated. Human movement characteristics based on the force distribution in various parts are analyzed and predicted.

METHODS

The muscle model is reconstructed in medical software and a three-dimensional finite element model of the entire cervical spine (C0-C7) is established by combining muscle models with CT vertebral data models. 1.5 Nm of load is applied to the finite element model to simulate the cervical spine movement.

RESULTS

The finite element model was successfully established, and effectiveness was verified. Stress variations in various parts under six movements were obtained. The effectiveness of the model was basically verified.

CONCLUSION

The finite element model of the cervical spine for mechanical analysis can be successfully established by using medical software and CT data. In daily life, the C2-3, C3-4, C4-C5 intervertebral discs, rectus capitis posterior major, longus colli, and obliquus capitis inferior are more prone to injury.

The effects of exercise and mitochondrial transplantation alone or in combination against Doxorubicin-induced skeletal muscle atrophy

Doxorubicin (DOX) is a chemotherapy drug used to treat various types of cancer, but it is associated with significant side effects such as skeletal muscle atrophy. Exercise has been found to prevent skeletal muscle atrophy through the modulation of mitochondrial pathways. Mitochondrial transplantation (MT) may mitigate toxicity, neurological disorders, kidney and liver injury, and skeletal muscle atrophy. The objective of this study was to evaluate the effects of MT, exercise, and MT with exercise on DOX-induced skeletal muscle atrophy. Male Sprague Dawley rats were randomly assigned to the following groups: control, DOX, MT with DOX, exercise with DOX, and exercise with MT and DOX. A 10-day treadmill running exercise and MT (6.5 µg/100 µL) to tibialis anterior (TA) muscle were administered prior to a single injection of DOX (20 mg/kg). Our data showed that exercise and MT with exercise led to an increase in cross-sectional area of the TA muscle. Exercise, MT and MT with exercise reduced inflammation and maintained mitochondrial enzyme activity. Additionally, exercise and MT have been shown to regulate mitochondrial fusion/fission. Our findings revealed that exercise and MT with exercise prevented oxidative damage. Furthermore, MT and MT with exercise decreased apoptosis and MT with exercise triggered mitochondrial biogenesis. These findings demonstrate the importance of exercise in the prevention of skeletal muscle atrophy and emphasize the significant benefits of MT with exercise. To the best of our knowledge, this is the first study to demonstrate the therapeutic effects of MT with exercise in DOX-induced skeletal muscle atrophy.

Heme oxygenase-1: A potential therapeutic target for improving skeletal muscle atrophy

Skeletal muscle atrophy is a common muscle disease that is directly caused by an imbalance in protein synthesis and degradation. At the histological level, it is mainly characterized by a reduction in muscle mass and fiber cross-sectional area (CSA). Patients with skeletal muscle atrophy present with reduced motor ability, easy fatigue, and poor life quality. Heme oxygenase-1 (HO-1) is an inducible enzyme that catalyzes the degradation of heme and has attracted much attention for its anti-oxidation effects. In addition, there is growing evidence that HO-1 plays an important role in anti-inflammatory, anti-apoptosis, pro-angiogenesis, and maintaining skeletal muscle homeostasis, making it a potential therapeutic target for improving skeletal muscle atrophy. Here, we review the pathogenesis of skeletal muscle atrophy, the biology of HO-1 and its regulation, and the biological function of HO-1 in skeletal muscle homeostasis, with a specific focus on the role of HO-1 in skeletal muscle atrophy, aiming to observe the therapeutic potential of HO-1 for skeletal muscle atrophy.

Mitochondrial dysfunction and skeletal muscle atrophy: Causes, mechanisms, and treatment strategies

Skeletal muscle, which accounts for approximately 40% of total body weight, is one of the most dynamic and plastic tissues in the human body and plays a vital role in movement, posture and force production. More than just a component of the locomotor system, skeletal muscle functions as an endocrine organ capable of producing and secreting hundreds of bioactive molecules. Therefore, maintaining healthy skeletal muscles is crucial for supporting overall body health. Various pathological conditions, such as prolonged immobilization, cachexia, aging, drug-induced toxicity, and cardiovascular diseases (CVDs), can disrupt the balance between muscle protein synthesis and degradation, leading to skeletal muscle atrophy. Mitochondrial dysfunction is a major contributing mechanism to skeletal muscle atrophy, as it plays crucial roles in various biological processes, including energy production, metabolic flexibility, maintenance of redox homeostasis, and regulation of apoptosis. In this review, we critically examine recent knowledge regarding the causes of muscle atrophy (disuse, cachexia, aging, etc.) and its contribution to CVDs. Additionally, we highlight the mitochondrial signaling pathways involvement to skeletal muscle atrophy, such as the ubiquitin-proteasome system, autophagy and mitophagy, mitochondrial fission-fusion, and mitochondrial biogenesis. Furthermore, we discuss current strategies, including exercise, mitochondria-targeted antioxidants, in vivo transfection of PGC-1α, and the potential use of mitochondrial transplantation as a possible therapeutic approach.

Melatonin Improves Skeletal Muscle Structure and Oxidative Phenotype by Regulating Mitochondrial Dynamics and Autophagy in Zücker Diabetic Fatty Rat

Obesity-induced skeletal muscle (SKM) inflexibility is closely linked to mitochondrial dysfunction. The present study aimed to evaluate the effects of melatonin on the red vastus lateralis (RVL) muscle in obese rat models at the molecular and morphological levels. Five-week-old male Zücker diabetic fatty (ZDF) rats and their age-matched lean littermates (ZL) were orally treated either with melatonin (10 mg/kg body weight (BW)/24 h) (M-ZDF and M-ZL) or non-treated (control) (C-ZDF and C-ZL) for 12 weeks. Western blot analysis showed that mitochondrial fission, fusion, and autophagy were altered in the C-ZDF group, accompanied by reduced SIRT1 levels. Furthermore, C-ZDF rats exhibited depleted ATP production and nitro-oxidative stress, as indicated by increased nitrites levels and reduced SOD activity. Western blotting of MyH isoforms demonstrated a significant decrease in both slow and fast oxidative fiber-specific markers expression in the C-ZDF group, concomitant with an increase in the fast glycolytic fiber markers. At the tissue level, marked fiber atrophy, less oxidative fibers, and excessive lipid deposition were noted in the C-ZDF group. Interestingly, melatonin treatment partially restored mitochondrial fission/fusion imbalance in the RVL muscle by enhancing the expression of fission (Fis1 and DRP1) markers and decreasing that of fusion (OPA1 and Mfn2) markers. It was also found to restore autophagy, as indicated by increased p62 protein level and LC3BII/I ratio. In addition, melatonin treatment increased SIRT1 protein level, mitochondrial ATP production, and SOD activity and decreased nitrites production. These effects were associated with enhanced oxidative phenotype, as evidenced by amplified oxidative fiber-specific markers expression, histochemical reaction for NADH enzyme, and muscular lipid content. In this study, we showed that melatonin might have potential therapeutic implications for obesity-induced SKM metabolic inflexibility among patients with obesity and T2DM.

Mitochondrial dysfunction: roles in skeletal muscle atrophy

Mitochondria play important roles in maintaining cellular homeostasis and skeletal muscle health, and damage to mitochondria can lead to a series of pathophysiological changes. Mitochondrial dysfunction can lead to skeletal muscle atrophy, and its molecular mechanism leading to skeletal muscle atrophy is complex. Understanding the pathogenesis of mitochondrial dysfunction is useful for the prevention and treatment of skeletal muscle atrophy, and finding drugs and methods to target and modulate mitochondrial function are urgent tasks in the prevention and treatment of skeletal muscle atrophy. In this review, we first discussed the roles of normal mitochondria in skeletal muscle. Importantly, we described the effect of mitochondrial dysfunction on skeletal muscle atrophy and the molecular mechanisms involved. Furthermore, the regulatory roles of different signaling pathways (AMPK-SIRT1-PGC-1α, IGF-1-PI3K-Akt-mTOR, FoxOs, JAK-STAT3, TGF-β-Smad2/3 and NF-κB pathways, etc.) and the roles of mitochondrial factors were investigated in mitochondrial dysfunction. Next, we analyzed the manifestations of mitochondrial dysfunction in muscle atrophy caused by different diseases. Finally, we summarized the preventive and therapeutic effects of targeted regulation of mitochondrial function on skeletal muscle atrophy, including drug therapy, exercise and diet, gene therapy, stem cell therapy and physical therapy. This review is of great significance for the holistic understanding of the important role of mitochondria in skeletal muscle, which is helpful for researchers to further understanding the molecular regulatory mechanism of skeletal muscle atrophy, and has an important inspiring role for the development of therapeutic strategies for muscle atrophy targeting mitochondria in the future.

Effects of "accurate measurement" comprehensive sports activities on balance ability, body composition and bone density of female college students

Background: A sedentary lifestyle with little movement has affected modern youth, and regular exercise has real benefits for people; such studies are mostly for older adults, and more evidence is needed for adolescents. Objective: To compare differences in balance, body composition, and bone mineral density among female college students before and after an exercise intervention to provide precise evidence that exercise promotes college student health. Methods: A whole group of female students in a university was sampled and included in the statistical analysis 50 people, divided into two cohorts, 21 people in the test group and 29 people in the control group; the test group had 4 comprehensive sports activities per week and the control group had 1 comprehensive sports activities per week, and the differences in each index of balance ability, body composition and bone density before and after the intervention were compared after 3 months. Results: After exercise intervention, when maintaining balance, the area of the center of gravity movement trajectory increased by 32.36% in the test group compared with the pre-intervention period and increased by 42.80% compared with the control group, and the differences were all statistically significant (p < 0.01); body mass index (BMI), body fat rate (BFR), visceral fat area (VFA), skeletal muscle content, and Inbody score increased over time more reasonable, and the difference in the effect of time factor (effect) was statistically significant (p < 0.01); bone mineral density (BMD) and BMD Z value increased with time, and the difference in the effect of time factor was statistically significant (p < 0.05). Conclusion: Female college students' body balance ability improved substantially after exercise intervention; at the university level, female college students had a more rational body composition and continued natural increase in BMD, which were not related to exercise intervention.

Increasing Muscle Mass in Elders through Diet and Exercise: A Literature Review of Recent RCTs

This study aimed to review the current evidence on the independent and combined effects of diet and exercise and their impact on skeletal muscle mass in the elderly population. Skeletal muscle makes up approximately 40% of total body weight and is essential for performing daily activities. The combination of exercise and diet is known to be a potent anabolic stimulus through stimulation of muscle protein synthesis from amino acids. Aging is strongly associated with a generalized deterioration of physiological function, including a progressive reduction in skeletal muscle mass and strength, which in turn leads to a gradual functional impairment and an increased rate of disability resulting in falls, frailty, or even death. The term sarcopenia, which is an age-related syndrome, is primarily used to describe the gradual and generalized loss of skeletal muscle mass (mainly in type II muscle fibers) and function. Multimodal training is emerging as a popular training method that combines a wide range of physical dimensions. On the other hand, nutrition and especially protein intake provide amino acids, which are essential for muscle protein synthesis. According to ESPEN, protein intake in older people should be at least 1 g/kgbw/day. Essential amino acids, such as leucine, arginine, cysteine, and glutamine, are of particular importance for the regulation of muscle protein synthesis. For instance, a leucine intake of 3 g administered alongside each main meal has been suggested to prevent muscle loss in the elderly. In addition, studies have shown that vitamin D and other micronutrients can have a protective role and may modulate muscle growth; nevertheless, further research is needed to validate these claims. Resistance-based exercise combined with a higher intake of dietary protein, amino acids, and/or vitamin D are currently recognized as the most effective interventions to promote skeletal muscle growth. However, the results are quite controversial and contradictory, which could be explained by the high heterogeneity among studies. It is therefore necessary to further assess the impact of each individual exercise and nutritional approach, particularly protein and amino acids, on human muscle turnover so that more efficient strategies can be implemented for the augmentation of muscle mass in the elderly.

Pathophysiological Aspects of Muscle Atrophy and Osteopenia Induced by Chronic Constriction Injury (CCI) of the Sciatic Nerve in Rats

Skeletal muscle atrophy is a condition characterized by a loss of muscle mass and muscle strength caused by an imbalance between protein synthesis and protein degradation. Muscle atrophy is often associated with a loss of bone mass manifesting as osteoporosis. The aim of this study was to evaluate if chronic constriction injury (CCI) of the sciatic nerve in rats can be a valid model to study muscle atrophy and consequent osteoporosis. Body weight and body composition were assessed weekly. Magnetic resonance imaging (MRI) was performed on day zero before ligation and day 28 before sacrifice. Catabolic markers were assessed via Western blot and Quantitative Real-time PCR. After the sacrifice, a morphological analysis of the gastrocnemius muscle and Micro-Computed Tomography (Micro-CT) on the tibia bone were performed. Rats that underwent CCI had a lower body weight increase on day 28 compared to the naive group of rats (p < 0.001). Increases in lean body mass and fat mass were also significantly lower in the CCI group (p < 0.001). The weight of skeletal muscles was found to be significantly lower in the ipsilateral hindlimb compared to that of contralateral muscles; furthermore, the cross-sectional area of muscle fibers decreased significantly in the ipsilateral gastrocnemius. The CCI of the sciatic nerve induced a statistically significant increase in autophagic and UPS (Ubiquitin Proteasome System) markers and a statistically significant increase in Pax-7 (Paired Box-7) expression. Micro-CT showed a statistically significant decrease in the bone parameters of the ipsilateral tibial bone. Chronic nerve constriction appeared to be a valid model for inducing the condition of muscle atrophy, also causing changes in bone microstructure and leading to osteoporosis. Therefore, sciatic nerve constriction could be a valid approach to study muscle-bone crosstalk and to identify new strategies to prevent osteosarcopenia.

ROLE OF WHEY PROTEIN IN POST-WORKOUT RECOVERY

ABSTRACT Introduction: Evidence indicates that whey protein supplementation may accelerate tissue repair and be useful for exercise-induced muscle injury (EIMD) by accelerating recovery and elevating protein synthesis and blood amino acids. However, the potential role of whey protein after EIMD in humans is inconsistent. Objective: Find the effective role of whey protein in post-exercise recovery from EIMD. Methods: Scopus, Medline, and Google scholar, were systematically searched until March 2022. To assess the risk of bias, the Cochrane collaboration tool was applied. Weighted mean differences (WMD), 95% confidence intervals (CI), and random effect models to calculate the total effect. Results: The result of the review indicated that the decreasing impact of whey protein intake is significant on creatine kinase (CK) [WMD = −19.11 IU.L-1, CI: −36.200, −2.036; P = 0.028]. The effect of whey protein supplementation on lactate dehydrogenase (LDH) concentration indicated that the impact of whey protein on changing LDH levels is significant. In addition, subgroup analysis showed significant decreases in CK and LDH based on post-exercise follow-up times, whey protein dosage, test duration, supplementation time, exercise types, and training status. Conclusion: The results showed the efficacy of whey protein in decreasing CK and LDH levels among adults in general and in subgroup analysis. Therefore, whey protein could have an effective role in the post-exercise recovery of EIMD. Level of evidence II; Therapeutic studies – review of results.

Correlation of Delayed Onset Muscle Soreness and Inflammation Post-exercise Induced Muscle Damage

BACKGROUND: Delayed Onset Muscle Soreness (DOMS) is a common injury resulting from abnormal intensive training in athletes, mainly the result of training involving eccentric contractions. AIM: The aim of this study was to determine the correlation between the incidence of DOMS and HMGB1 as a marker of the occurrence of inflammation post Exercise Induces Muscle Damaged. METHOD: 28 male recreational students of Sports Science Department, Universitas Negeri Surabaya who met all inclusion and exclusion criteria participated in this study. Participants completed a muscle damaging exercise which consists of a 10x10 drop jump (DRP) and a bout of 40×15 m sprints with a 5 m deceleration zone (SPR) to obtain a muscle damage effect. In this study, the stretching in the exercise session was not given, this was done to get the DOMS effect after exercise. DOMS and HMGB1 was carry out 1 hour before the exercise, 12 hours after the exercise, 24 hours after the exercise and 48 hours after the exercise. RESULT: The result showed that there was a significant correlation (r=0.935, p<0.05) between DOMS and HMGB1 as a predictor of inflammation. The participants that were given EIMD eccentric exercise (DRP and SPR) showed the occurrence of DOMS and increasing of HMGB1. The result also showed that there was a correlation between DOMS and HMGB1. CONCLUSION: This study concluded that there was a correlation between DOMS and HMGB1 as a marker of inflammation as the result of the eccentric exercise of the exercise Induced Muscle Damage (EIMD).

CUL3 and COPS5 Related to the Ubiquitin-Proteasome Pathway Are Potential Genes for Muscle Atrophy in Mice

Sarcopenia is a condition that reduces muscle mass and exercise capacity. Muscle atrophy is a common manifestation of sarcopenia and can increase morbidity and mortality in specific patient populations. The aim of this study was to identify novel prognostic biomarkers for muscle atrophy and associated pathway analysis using bioinformatics methods. The samples were first divided into different age groups and different muscle type groups, respectively, and each of these samples was analyzed for differences to obtain two groups of differentially expressed genes (DEGs). The two groups of DEGs were intersected using Venn diagrams to obtain 1,630 overlapping genes, and enrichment analysis was performed to observe the Gene Ontology (GO) functional terms of overlapping genes and the enrichment of the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway. Subsequently, WGCNA (weighted gene coexpression network analysis) was used to find gene modules associated with both the age and muscle type to obtain the lightgreen module. The genes in the key modules were analyzed using PPI, and the top five genes were obtained using the MCC (maximum correntropy criterion) algorithm. Finally, CUL3 and COPS5 were obtained by comparing gene expression levels and analyzing the respective KEGG pathways using gene set enrichment analysis (GSEA). In conclusion, we identified that CUL3 and COPS5 may be novel prognostic biomarkers in muscle atrophy based on bioinformatics analysis. CUL3 and COPS5 are associated with the ubiquitin-proteasome pathway.

Impact of physical exercise and caloric restriction in patients with type 2 diabetes: Skeletal muscle insulin resistance and mitochondrial dysfunction as ideal therapeutic targets

Skeletal muscle insulin resistance and mitochondrial dysfunction are some of the major pathological defects implicated in the development of type 2 diabetes (T2D). Therefore, it has become necessary to understand how common interventions such as physical exercise and caloric restriction affect metabolic function, including physiological processes that implicate skeletal muscle dysfunction within a state of T2D. This review critically discusses evidence on the impact of physical exercise and caloric restriction on markers of insulin resistance and mitochondrial dysfunction within the skeletal muscle of patients with T2D or related metabolic complications. Importantly, relevant information from clinical studies was acquired through a systematic approach targeting major electronic databases and search engines such as PubMed, Google Scholar, and Cochrane library. The reported evidence suggests that interventions like physical exercise and caloric restriction, within a duration of approximately 2 to 4 months, can improve insulin sensitivity, in part by targeting the phosphoinositide 3-kinases/protein kinase B pathway in patients with T2D. Furthermore, both physical exercise and caloric restriction can effectively modulate markers related to improved mitochondrial function and dynamics. This was consistent with an improved modulation of mitochondrial oxidative capacity and reduced production of reactive oxygen species in patients with T2D or related metabolic complications. However, such conclusions are based on limited evidence, additional clinical trials are required to better understand these interventions on pathological mechanisms of T2D and related abnormalities.

Effect of omega-3 fatty acids supplementation on indirect blood markers of exercise-induced muscle damage: Systematic review and meta-analysis of randomized controlled trials

BACKGROUND

Omega 3 fatty acids supplementation may have an attenuative effect on exercise-induced muscle damage (EIMD) through the cell membrane stabilization. The purpose of the present meta-analysis was to evaluate the effects of omega 3 fatty acids supplementation, on indirect blood markers of muscle damage following EIMD in trained and untrained individuals.

METHODS

Scopus, Medline, and Google scholar systematically searched up to January 2021. The Cochrane Collaboration tool was used for the quality of studies. Random-effects model, weighted mean difference (WMD), and 95% confidence interval (CI) were applied for the overall effect estimating. The heterogeneity between studies was evaluated applying the chi-squared and I2 statistic.

RESULTS

The outcomes showed a significant effect of omega 3 supplementation on reducing creatine kinase (CK), lactate dehydrogenase (LDH), and myoglobin (Mb) concentrations. In addition, a subgroup analysis indicated a significant reduction in CK, LDH, and Mb concentrations, based on follow-ups after exercise, studies duration, time of supplementation, and training status.

CONCLUSION

The current meta-analysis indicated an efficacy of omega 3 in reducing CK, LDH, and Mb serum concentration among healthy individuals, overall and in subgroups analysis. Thus, omega 3 should be considered as a priority EIMD recovery agent in interventions.

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.

Body Protein Sparing in Hibernators: A Source for Biomedical Innovation

Proteins are not only the major structural components of living cells but also ensure essential physiological functions within the organism. Any change in protein abundance and/or structure is at risk for the proper body functioning and/or survival of organisms. Death following starvation is attributed to a loss of about half of total body proteins, and body protein loss induced by muscle disuse is responsible for major metabolic disorders in immobilized patients, and sedentary or elderly people. Basic knowledge of the molecular and cellular mechanisms that control proteostasis is continuously growing. Yet, finding and developing efficient treatments to limit body/muscle protein loss in humans remain a medical challenge, physical exercise and nutritional programs managing to only partially compensate for it. This is notably a major challenge for the treatment of obesity, where therapies should promote fat loss while preserving body proteins. In this context, hibernating species preserve their lean body mass, including muscles, despite total physical inactivity and low energy consumption during torpor, a state of drastic reduction in metabolic rate associated with a more or less pronounced hypothermia. The present review introduces metabolic, physiological, and behavioral adaptations, e.g., energetics, body temperature, and nutrition, of the torpor or hibernation phenotype from small to large mammals. Hibernating strategies could be linked to allometry aspects, the need for periodic rewarming from torpor, and/or the ability of animals to fast for more or less time, thus determining the capacity of individuals to save proteins. Both fat- and food-storing hibernators rely mostly on their body fat reserves during the torpid state, while minimizing body protein utilization. A number of them may also replenish lost proteins during arousals by consuming food. The review takes stock of the physiological, molecular, and cellular mechanisms that promote body protein and muscle sparing during the inactive state of hibernation. Finally, the review outlines how the detailed understanding of these mechanisms at play in various hibernators is expected to provide innovative solutions to fight human muscle atrophy, to better help the management of obese patients, or to improve the ex vivo preservation of organs.

Skeletal Muscle Anti-Atrophic Effects of Leucine Involve Myostatin Inhibition

Lack of mechanical load leads to skeletal muscle atrophy, and one major underlying mechanism involves the myostatin pathway that negatively regulates protein synthesis and also activates Atrogin-1/MAFbx and MuRF1 genes. In hindlimb immobilization, leucine was observed to attenuate the upregulation of the referred atrogenes, thereby shortening the impact on fiber cross-sectional area, nonetheless, the possible connection with myostatin is still elusive. This study sought to verify the impact of leucine supplementation on myostatin expression. Male Wistar rats were supplemented with leucine and hindlimb immobilized for 3 and 7 days, after which soleus muscles were removed for morphometric measurements and analyzed for gene and protein expression by real-time PCR and Western blotting, respectively. Muscle wasting was prominent 7 days after immobilization, as expected, leucine feeding mitigated this effect. Atrogin-1/MAFbx gene expression was upregulated only after 3 days of immobilization, and this effect was attenuated by leucine supplementation. Atrogin-1/MAFbx protein levels were elevated after 7 days of immobilization, which leucine supplementation was not able to lessen. On the other hand, myostatin gene expression was upregulated in immobilization for 3 and 7 days, which returned to normal levels after leucine supplementation. Myostatin protein levels followed gene expression at a 3-day time point only. Follistatin gene expression was upregulated during immobilization and accentuated by leucine after 3 days of supplementation. Concerning protein expression, follistatin was not altered neither by immobilization nor in immobilized animals treated with leucine. In conclusion, leucine protects against skeletal muscle mass loss during disuse, and the underlying molecular mechanisms appear to involve myostatin inhibition and Atrogin-1 normalization independently of follistatin signaling.