Alterations of protein turnover underlying disuse atrophy in human skeletal muscle

Various jobs of proteolytic enzymes in skeletal muscle during unloading: facts and speculations

Skeletal muscles, namely, postural muscles, as soleus, suffer from atrophy under disuse. Muscle atrophy development caused by unloading differs from that induced by denervation or other stimuli. Disuse atrophy is supposed to be the result of shift of protein synthesis/proteolysis balance towards protein degradation increase. Maintaining of the balance involves many systems of synthesis and proteolysis, whose activation leads to muscle adaptation to disuse rather than muscle degeneration. Here, we review recent data on activity of signaling systems involved in muscle atrophy development under unloading and muscle adaptation to the lack of support.

Regulation of muscle protein synthesis in humans

PURPOSE OF REVIEW

Investigations into the regulation of muscle protein synthesis (MPS) are a cornerstone of understanding the control of muscle mass. Rates of MPS are finely tuned according to levels of activity, nutrient availability and health status. For instance, rates of MPS are positively regulated by exercise and nutrition, and negatively regulated by inactivity (e.g. disuse), ageing (i.e. sarcopenia) and in muscle-wasting related diseases (e.g. cancer).

RECENT FINDINGS

Skeletal muscles display a high degree of intrinsic regulation. Increases in MPS after exercise occur independently of the systemic milieu for example growth hormone/testosterone concentrations. In the absence of exercise, increases in MPS after feeding are of finite duration despite enduring precursor availability; that is muscles can sense they are 'full'. Intriguingly, exercise delays this 'muscle-full' response to allow for building and repair. In contrast, muscle-wasting conditions exhibit a premature 'muscle-full' response to nutrition and exercise (i.e. anabolic resistance), which may cause atrophy. Observations of 'dissociations' between MPS and anabolic signalling pathways have cast doubt on how much we understand of the molecular regulation of human MPS.

SUMMARY

Anabolic and anticatabolic interventions in health and disease should be aimed at manipulating the 'muscle-full' set point to maximize muscle maintenance/hypertrophy.

Mechanistic links between oxidative stress and disuse muscle atrophy

Long periods of skeletal muscle inactivity promote a loss of muscle protein resulting in fiber atrophy. This disuse-induced muscle atrophy results from decreased protein synthesis and increased protein degradation. Recent studies have increased our insight into this complicated process, and evidence indicates that disturbed redox signaling is an important regulator of cell signaling pathways that control both protein synthesis and proteolysis in skeletal muscle. The objective of this review is to outline the role that reactive oxygen species play in the regulation of inactivity-induced skeletal muscle atrophy. Specifically, this report will provide an overview of experimental models used to investigate disuse muscle atrophy and will also highlight the intracellular sources of reactive oxygen species and reactive nitrogen species in inactive skeletal muscle. We then will provide a detailed discussion of the evidence that links oxidants to the cell signaling pathways that control both protein synthesis and degradation. Finally, by presenting unresolved issues related to oxidative stress and muscle atrophy, we hope that this review will serve as a stimulus for new research in this exciting field.

Nutrition for sports performance: issues and opportunities

Diet can significantly influence athletic performance, but recent research developments have substantially changed our understanding of sport and exercise nutrition. Athletes adopt various nutritional strategies in training and competition in the pursuit of success. The aim of training is to promote changes in the structure and function of muscle and other tissues by selective modulation of protein synthesis and breakdown in response to the training stimulus. This process is affected by the availability of essential amino acids in the post-exercise period. Athletes have been encouraged to eat diets high in carbohydrate, but low-carbohydrate diets up-regulate the capacity of muscle for fat oxidation, potentially sparing the limited carbohydrate stores. Such diets, however, do not enhance endurance performance. It is not yet known whether the increased capacity for fat oxidation that results from training in a carbohydrate-deficient state can promote loss of body fat. Preventing excessive fluid deficits will maintain exercise capacity, and ensuring adequate hydration status can also reduce subjective perception of effort. This latter effect may be important in encouraging exercise participation and promoting adherence to exercise programmes. Dietary supplement use is popular in sport, and a few supplements may improve performance in specific exercise tasks. Athletes must be cautious, however, not to contravene the doping regulations. There is an increasing recognition of the role of the brain in determining exercise performance: various nutritional strategies have been proposed, but with limited success. Nutrition strategies developed for use by athletes can also be used to achieve functional benefits in other populations.

Changes in body composition after transjugular intrahepatic portosystemic stent in cirrhosis: a critical review of literature

Change in body composition with reduced muscle mass with or without loss of fat mass occurs in 60-90% of patients with cirrhosis. This has an adverse impact on the outcome of these patients and is an understudied area. Transjugular intrahepatic portosystemic stent (TIPS) is now a standard therapy for portal hypertension but its beneficial impact on nutritional indices is not well recognized. We included all publications on TIPS that had any nutritional index as an outcome measure or end point. Given the heterogeneity of the patient population, differences in study design and outcome measures, a meta-analysis was not feasible. Data were summarized and interpreted. A total of eight studies have been published on the changes in body composition after TIPS in cirrhosis in a total of 152 patients followed for 3-12 months. Improvement in fat-free mass and fluid-free or ascites-free body weight was reported in all studies. Plasma leptin, IGF1, insulin sensitivity, rate of glucose disposal and growth hormone did not change after TIPS. One study measured muscle strength that improved. Direct measurement of skeletal muscle mass was not performed in any study. TIPS resulted in an improvement in body composition. Given the clinical significance of skeletal muscle and fat mass in cirrhosis, nutritional indices should be considered to be an important outcome measure in patients with TIPS. The mechanism of these is unclear, but its clinical implication is that this may contribute to the improved survival after TIPS.

Plasma from septic shock patients induces loss of muscle protein

Introduction

ICU-acquired muscle weakness commonly occurs in patients with septic shock and is associated with poor outcome. Although atrophy is known to be involved, it is unclear whether ligands in plasma from these patients are responsible for initiating degradation of muscle proteins. The aim of the present study was to investigate if plasma from septic shock patients induces skeletal muscle atrophy and to examine the time course of plasma-induced muscle atrophy during ICU stay.

Methods

Plasma was derived from septic shock patients within 24 hours after hospital admission (n = 21) and healthy controls (n = 12). From nine patients with septic shock plasma was additionally derived at two, five and seven days after ICU admission. These plasma samples were added to skeletal myotubes, cultured from murine myoblasts. After incubation for 24 hours, myotubes were harvested and analyzed on myosin content, mRNA expression of E3-ligase and Nuclear Factor Kappa B (NFκB) activity. Plasma samples were analyzed on cytokine concentrations.

Results

Myosin content was approximately 25% lower in myotubes exposed to plasma from septic shock patients than in myotubes exposed to plasma from controls (P < 0.01). Furthermore, patient plasma increased expression of E3-ligases Muscle RING Finger protein-1 (MuRF-1) and Muscle Atrophy F-box protein (MAFbx) (P < 0.01), enhanced NFκB activity (P < 0.05) and elevated levels of ubiquitinated myosin in myotubes. Myosin loss was significantly associated with elevated plasma levels of interleukin (IL)-6 in septic shock patients (P < 0.001). Addition of antiIL-6 to septic shock plasma diminished the loss of myosin in exposed myotubes by approximately 25% (P < 0.05). Patient plasma obtained later during ICU stay did not significantly reduce myosin content compared to controls.

Conclusions

Plasma from patients with septic shock induces loss of myosin and activates key regulators of proteolysis in skeletal myotubes. IL-6 is an important player in sepsis-induced muscle atrophy in this model. The potential to induce atrophy is strongest in plasma obtained during the early phase of human sepsis.

Daily torpor reduces mass and changes stress and power output of soleus and EDL muscles in the Djungarian hamster, Phodopus sungorus

Djungarian hamsters (Phodopus sungorus) undergo bouts of daily torpor in response to reduced photoperiod. Metabolic rate, body temperature and energy cost are reduced during torpor. The present study exposed Djungarian hamsters to two different photoperiod regimes at a room temperature of 19–21°C: long photoperiod (control, 16 h:8 h light:dark, N=8) and short photoperiod (torpor, 8 h:16 h light:dark, N=8). After 14 weeks, muscle mechanics were analyzed in each group, examining both extensor digitorum longus (EDL) muscle and soleus muscle from each individual. Control hamsters had significantly greater body mass (43%), EDL mass (24%), EDL length (9%) and soleus mass (48%) than the torpor hamsters. However, there were no significant differences between control and torpor groups in forearm length or soleus muscle length. There were no significant differences in either muscle between control and torpor hamsters in maximum twitch stress (force per unit area), tetanus force generation or relaxation times. Maximum soleus tetanic stress was 43% greater (P=0.039) and soleus work loop power output (P&lt;0.001) was higher in torpor than in control hamsters. Maximum EDL tetanic stress was 26% greater in control than in torpor hamsters (P=0.046), but there was no significant effect on EDL power output (P=0.38). Rate of fatigue was not affected by torpor in either soleus or EDL muscles (P&gt;0.43). Overall, extended use of daily torpor had no effect on the rate at which stress or work was produced in soleus and EDL muscles in Djungarian hamsters; however, torpor did increase the stress and power produced by the soleus.

Nutrition for acute exercise-induced injuries

BACKGROUND/AIMS

Injuries are an unavoidable aspect of participation in physical activity. Little information about nutritional support for injuries exists.

REVIEW

Immediately following injury, wound healing begins with an inflammatory response. Excessive anti-inflammatory measures may impair recovery. Many injuries result in limb immobilization. Immobilization results in muscle loss due to increased periods of negative muscle protein balance. Oxidative capacity of muscle is also decreased. Nutrient and energy deficiencies should be avoided. Energy expenditure may be reduced during immobilization, but inflammation, wound healing and the energy cost of ambulation limit the reduction of energy expenditure. There is little rationale for increasing protein intake during immobilization. There is a theoretical rationale for leucine and omega-3 fatty acid supplementation to help reduce muscle atrophy. During rehabilitation and recovery from immobilization, increased activity, in particular resistance exercise will increase muscle protein synthesis and restore sensitivity to anabolic stimuli. Ample, but not excessive, protein and energy must be consumed to support muscle growth. During rehabilitation and recovery, nutritional needs are very much like those for any athlete desiring muscle growth.

CONCLUSION

Nutrition is important for optimal wound healing. The most important consideration is to avoid malnutrition and to apply a risk/benefit approach.

Infantile muscular dystrophy in Canadian aboriginals is an αB-crystallinopathy

OBJECTIVE

A recessively transmitted fatal hypertonic infantile muscular dystrophy has been described in Canadian aboriginals. The affected infants present with progressive limb and axial muscle stiffness and develop severe respiratory insufficiency, and most die in the first year of life. We sought to determine the genetic basis of this disease.

METHODS

We performed histochemical, immunocytochemical, electron microscopy, and molecular genetic studies in a cohort of 12 patients affected by this disease.

RESULTS

Conventional histochemical and electron microscopy studies suggested myofibrillar myopathy (MFM). Therefore, we searched for ectopic expression of multiple proteins typical of MFM. Alpha B-crystallin (αBC) expression was absent from all fibers using a monoclonal antibody raised against the entire protein. However, a monoclonal antibody directed against the first 10 residues of αBC immunostained portions of abnormal fibers. Pursuing this clue, we searched for mutations in the gene for αBC (CRYAB) in available DNA samples of 8 patients. All harbored a homozygous deletion, c.60C, predicting a Ser to Ala change at codon 21 and a stop codon after 23 missense residues (p.Ser21AlafsX24). Clinically unaffected parents were heterozygous for this mutation.

INTERPRETATION

The homozygous c.60delC in CRYAB pinpoints the genetic basis of the fatal infantile hypertonic muscular dystrophy of Canadian aboriginals. MFMs are typically transmitted by dominant inheritance, but in this disease the parental phenotype is rescued by limited expression of the highly truncated nonfunctional mutant gene product. The severe patient phenotype is due to homozygosity for the markedly hypomorphic allele. Ann Neurol, 2011.

Mechanisms regulating muscle mass during disuse atrophy and rehabilitation in humans

Muscle mass loss accompanies periods of bedrest and limb immobilization in humans and requires rehabilitation exercise to effectively restore mass and function. Although recent evidence points to an early and transient rise in muscle protein breakdown contributing to this decline in muscle mass, the driving factor seems to be a reduction in muscle protein synthesis, not least in part due to the development of anabolic resistance to amino acid provision. Although the AKT signaling pathway has been identified in small animals as central to the regulation of muscle protein synthesis, several studies in humans have now demonstrated a disassociation between AKT signaling and muscle protein synthesis during feeding, exercise, and immobilization, suggesting that the mechanisms regulating protein synthesis in human skeletal muscle are more complex than initially thought (at least in non-inflammatory states). During rehabilitation, exercise-induced myogenesis may in part be responsible for the recovery of muscle mass. Rapid and sustained exercise-induced suppression of myostatin mRNA expression, that precedes any gain in muscle mass, points to this, along with other myogenic proteins, as being potential regulators of muscle regeneration during exercise rehabilitation in humans.

Effect of denervation-induced muscle disuse on mitochondrial protein import

This study determined whether muscle disuse affects mitochondrial protein import and whether changes in protein import are related to mitochondrial content and function. Protein import was measured using a model of unilateral peroneal nerve denervation in rats for 3 ( n = 10), 7 ( n = 12), or 14 ( n = 14) days. We compared the import of preproteins into the matrix of subsarcolemmal (SS) and intermyofibrillar (IMF) mitochondria isolated from the denervated and the contralateral control tibialis anterior muscles. Denervation led to 50% and 29% reductions in protein import after 14 days of disuse in SS and IMF mitochondria, respectively. This was accompanied by significant decreases in mitochondrial state 3 respiration, muscle mass, and whole muscle cytochrome c oxidase activity. To investigate the mechanisms involved, we assessed disuse-related changes in 1) protein import machinery components and 2) mitochondrial function, reflected by respiration and reactive oxygen species (ROS) production. Denervation significantly reduced the expression of translocases localized in the inner membrane (Tim23), outer membrane (Tom20), and mitochondrial heat shock protein 70 (mtHsp70), especially in the SS subfraction. Denervation also resulted in elevated ROS generation, and exogenous ROS was found to markedly reduce protein import. Thus our data indicate that protein import kinetics are closely related to alterations in mitochondrial respiratory capacity ( r = 0.95) and are negatively impacted by ROS. Deleterious changes in the protein import system likely facilitate the reduction in mitochondrial content and the increase in organelle dysfunction (i.e., increased ROS production and decreased respiration) during chronic disuse, which likely contribute to the activation of degradative pathways leading to muscle atrophy.

The science of muscle hypertrophy: making dietary protein count

Growing evidence supports the conclusion that consumption of protein in close temporal proximity to the performance of resistance exercise promotes greater muscular hypertrophy. We can also state with good certainty that merely consuming energy, as carbohydrate for example, is also not sufficient to maximise muscle protein synthesis leading to anabolism and net new muscle protein accretion. Recent work also indicates that certain types of proteins, particular those that are rapidly digested and high in leucine content (i.e. whey protein), appear to be more efficient at stimulating muscle protein synthesis. Continued practice of consumption of these types or proteins after exercise should lead to greater hypertrophy. Reviews of numerous training studies indicate that studies in which milk proteins and principally whey protein show an advantage of these proteins over and above isoenergetic carbohydrate and soya protein in promoting hypertrophy. Thus, the combined evidence suggests a strategic advantage of practising early post-exercise consumption of whey protein or dairy-based protein to promote muscle protein synthesis, net muscle protein accretion and ultimately hypertrophy.

Resistance exercise and appropriate nutrition to counteract muscle wasting and promote muscle hypertrophy

PURPOSE OF REVIEW

Loss of skeletal muscle mass is a common feature of a number of clinical scenarios including limb casting, bed rest, and various disorders such as HIV-AIDS, sepsis, cancer cachexia, heart failure, and uremia. Commonly, muscle disuse (hypodynamia) is the sole reason, or a large part, of why muscle mass is lost. The reduction in strength, or dynapenia, that accompanies these conditions is also a function of the degree of hypodynamia and is related to muscle loss.

RECENT FINDINGS

The major and consistent finding in a number of human-based models of muscle wasting is a decline in the synthesis of new muscle proteins both in the postabsorptive and fed states. Thus, countermeasures are best suited to those that augment muscle protein synthesis and not those that attempt to counteract proteolysis. Our main thesis is that retention of muscle mass in wasting conditions will be achieved to the greatest extent by focussing on increased muscle use with moderate-to-high resistance loads as the primary countermeasure with a secondary countermeasure being to provide adequate nutritional support. Either intervention alone will alleviate some part of hypodynamia-induced muscle mass loss and dynapenia; however, together nutrition and muscular contraction will result in greater mitigation of muscle loss.

SUMMARY

Advances in our understanding of hypodynamia-induced muscle loss, a condition common to almost all syndromes of muscle wasting, has led to a focus on reduced basal and feeding-induced elevations in protein synthesis. Countermeasures for wasting should focus on stimulating anabolism rather than alleviating catabolism.

Low-volume resistance exercise attenuates the decline in strength and muscle mass associated with immobilization

We determined the effectiveness of low-volume resistance exercise (EX) for the attenuation of loss of muscle mass and strength during leg immobilization. Men (N = 5) and women (N = 12, age 24 ± 5 years, body mass index 25.4 ± 3.6 kg/m(2)) were divided into two groups: exercise (EX; n = 12) and control (CON; n = 5). Subjects wore a knee brace on one leg that prevented weight bearing for 14 days. Resistance exercise (EX; 80% of maximal) was performed by the immobilized limb every other day. Immobilization induced a significant reduction (P < 0.05) in muscle fiber and thigh cross-sectional area (CSA), isometric knee extensor, and plantarflexor strength in the CON (P < 0.01) but not in the EX group. There were significant losses in triceps surae CSA in the CON and EX groups (P < 0.05), but the losses were greater in CON subjects (P < 0.01). A minimal volume (140 contractions in 14 days) of resistive exercise is an effective countermeasure against immobilization-induced atrophy of the quadriceps femoris but is only partially effective for the triceps surae.

Effects of 3 days unloading on molecular regulators of muscle size in humans

Changes in skeletal muscle mass are controlled by mechanisms that dictate protein synthesis or degradation. The current human study explored whether changes in activation of the phosphoinositide 3-kinase (PI3K)-Akt1, p38, myostatin, and mRNA expression of markers of protein degradation and synthesis occur soon after withdrawal of weight bearing. Biopsies of the vastus lateralis muscle (VL) and soleus muscle (Sol) were obtained from eight healthy men before and following 3 days of unilateral lower limb suspension (ULLS). Akt1, Forkhead box class O (FOXO)-1A, FOXO-3A, p38, and eukaryotic translation initiation factor 4E binding protein 1 (4E-BP1) phosphorylation and protein levels and myostatin protein level were analyzed by Western blot. Levels of mRNA of IGF1, FOXO-1A, FOXO-3A, atrogin-1, MuRF-1, caspase-3, calpain-2, calpain-3, 4E-BP1, and myostatin were measured using real-time PCR. The amounts of phosphorylated Akt1, FOXO-1A, FOXO-3A, and p38 were unaltered ( P > 0.05) after ULLS. Similarly, mRNA levels of IGF1, FOXO-1A, FOXO-3A, caspase-3, calpain-2, and calpain-3 showed no changes ( P > 0.05). The mRNA levels of atrogin-1 and MuRF-1, as well as the mRNA and protein phosphorylation of 4E-BP1, increased ( P < 0.05) in VL but not in Sol. Both muscles showed increased ( P < 0.05) myostatin mRNA and protein following ULLS. These results suggest that pathways other than PI3K-Akt stimulate atrogin-1 and MuRF-1 expression within 3 days of ULLS. Alternatively, transient changes in these pathways occurred in the early phase of ULLS. The increased myostatin mRNA and protein expression also indicate that multiple processes are involved in the early phase of muscle wasting. Further, the reported difference in gene expression pattern across muscles suggests that mechanisms regulating protein content in human skeletal muscle are influenced by phenotype and/or function.

Forty-eight hours of unloading and 24 h of reloading lead to changes in global gene expression patterns related to ubiquitination and oxidative stress in humans

Although short-term disuse does not result in measurable muscle atrophy, studies suggest that molecular changes associated with protein degradation may be initiated within days of the onset of a disuse stimulus. We examined the global gene expression patterns in sedentary men (n = 7, mean age ± SD = 22.1 ± 3.7 yr) following 48 h unloading (UL) via unilateral lower limb suspension and 24 h reloading (RL). Biopsy samples of the left vastus lateralis muscle were collected at baseline, 48 h UL, and 24 h RL. Expression changes were measured by microarray and gene clustering; identification of enriched functions and canonical pathways were performed using the Database for Annotation, Visualization and Integrated Discovery (DAVID) and Ingenuity Pathway Analysis (IPA). Four genes were validated with quantitative RT-PCR (qRT-PCR), and protein levels were measured with Western blot. Of the upregulated genes after UL, the most enriched functional group and highest ranked canonical pathway were related to protein ubiquitination. The oxidative stress response pathway was the second highest ranked canonical pathway. Of the downregulated genes, functions related to mitochondrial metabolism were the most highly enriched. In general, gene expression patterns following UL persisted following RL. qRT-PCR confirmed increases in mRNA for ubiquitin proteasome pathway-related E3 ligase Atrogin1 (but not accompanying increases in protein products) and stress response gene heme oxygenase-1 (HMOX, which showed a trend toward increases in protein products at 48 h UL) as well as extracellular matrix (ECM) component COL4A3. The gene expression patterns were not reversed on RL, suggesting that molecular responses to short-term periods of skeletal muscle inactivity may persist after activity resumes.

An overview of the therapeutic effects of leucine supplementation on skeletal muscle under atrophic conditions

The characterization of the mechanisms underlying skeletal muscle atrophy under different conditions has been a constant focus of research. Among anti-atrophic therapies, amino acid supplementation, particularly with leucine, has received a lot of attention. Supplementation has been shown to have remarkable effects on muscle remodeling through protein turnover modulation. This may then impact physiological parameters related to muscle function, and even quality of life. In light of this, leucine supplementation could be a useful therapy for mitigating the atrophic effects of catabolic conditions. The purpose of this review is to present the major results of human studies evaluating the effects of leucine supplementation on structure and function of skeletal muscle in atrophic conditions such as muscle disuse, sarcopenia, and cancer.

Muscle fiber conduction slowing and decreased levels of circulating muscle proteins after short-term dexamethasone administration in healthy subjects

CONTEXT

Glucocorticoids are known to decrease protein synthesis and impair membrane excitability of muscle fibers. However, their short-term effects on muscle structure and function of healthy subjects remain poorly understood.

OBJECTIVE

Our objective was to investigate whether steroid administration could decrease the circulating levels of muscle proteins and modify myoelectric indexes of sarcolemmal excitability and fatigability.

DESIGN

We conducted a single-blind, placebo-controlled study in 20 men randomized to receive dexamethasone (8 mg/d) or placebo for 1 wk. Blood sampling, force measurements for knee extensors and elbow flexors, and electrophysiological tests for biceps brachii, vastus lateralis and medialis, and tibialis anterior muscles were performed before and after the intervention.

RESULTS

Dexamethasone administration improved force by 6.0 +/- 6.0% (P = 0.01) for elbow flexors and by 8.5 +/- 5.5% (P < 0.01) for knee extensors, decreased levels of creatine kinase by 50.5 +/- 30.0% (P < 0.01) and myoglobin by 41.8 +/- 17.5% (P < 0.01), and impaired sarcolemmal excitability, as shown by the decline of muscle fiber conduction velocity for the four muscles (range from -6 to -10.5%, P < 0.05). Moreover, significant reductions of the myoelectric manifestations of fatigue were observed for the four muscles; the decrease in the rate of change of the mean frequency of the electromyographic power spectrum ranged from -22.6 to -43.9% (P < 0.05). In contrast, no significant changes were observed in muscle excitability and fatigability in subjects who received the placebo.

CONCLUSIONS

The demonstration that glucocorticoid-induced muscle impairments can be unraveled by means of blood sampling and noninvasive electrophysiological tests has clinical implications for the early identification of subclinical or preclinical forms of myopathy in treated patients.

Protecting muscle mass and function in older adults during bed rest

PURPOSE OF REVIEW

To highlight the losses in muscle mass, strength, power, and functional capacity incurred in older adults during bed rest-mediated inactivity and to provide practical recommendations for both the prevention and rehabilitation of these losses.

RECENT FINDINGS

In addition to sarcopenic muscle loss, older adults lose lean tissue more rapidly than the young during prolonged periods of physical inactivity. Amino acid or protein supplementation has the potential to maintain muscle protein synthesis and may reduce inactivity-induced muscle loss, but should ideally be part of an integrated countermeasure regimen consisting of nutrition, exercise, and, when appropriate, pharmacologic interventions.

SUMMARY

In accordance with recent mechanistic advances, we recommend an applied, broad-based two-phase approach to limit inactivity-mediated losses of muscle mass and function in older adults: (i) Lifestyle: consume a moderate amount (25-30 g) of high-quality protein with each meal and incorporate habitual exercise in close temporal proximity to protein-containing meals; (ii) Crises: react aggressively to combat the accelerated loss of muscle mass and function during acute catabolic crises and periods of reduced physical activity. As a base strategy, this should include nutritional support such as targeted protein or amino acid supplementation and integrated physical therapy.

Weakness in the ICU: a call to action

Muscle weakness is prevalent in critically ill patients and can have a dramatic effect on short- and long-term outcomes, yet there are currently no interventions with proven efficacy in preventing or treating this complication. In a new randomized trial, researchers found that serial electrical muscle stimulation significantly mitigated ultrasound-defined muscle atrophy, and the treatment was not linked to adverse effects. Although preliminary, these results, together with other recent studies, indicate a paradigm shift to a proactive approach in managing neuromuscular complications in the ICU.