Bed-rest-induced insulin resistance occurs primarily in muscle

DYNamic Assessment of Multi-Organ level dysfunction in patients recovering from COVID-19: DYNAMO COVID-19

We evaluated the impacts of COVID-19 on multi-organ and metabolic function in patients following severe hospitalised infection compared to controls. Patients (n = 21) without previous diabetes, cardiovascular or cerebrovascular disease were recruited 5-7 months post-discharge alongside controls (n = 10) with similar age, sex and body mass. Perceived fatigue was estimated (Fatigue Severity Scale) and the following were conducted: oral glucose tolerance (OGTT) alongside whole-body fuel oxidation, validated magnetic resonance imaging and spectroscopy during resting and supine controlled exercise, dual-energy X-ray absorptiometry, short physical performance battery (SPPB), intra-muscular electromyography, quadriceps strength and fatigability, and daily step-count. There was a greater insulin response (incremental area under the curve, median (inter-quartile range)) during the OGTT in patients [18,289 (12,497-27,448) mIU/min/L] versus controls [8655 (7948-11,040) mIU/min/L], P < 0.001. Blood glucose response and fasting and post-prandial fuel oxidation rates were not different. This greater insulin resistance was not explained by differences in systemic inflammation or whole-body/regional adiposity, but step-count (P = 0.07) and SPPB scores (P = 0.004) were lower in patients. Liver volume was 28% greater in patients than controls, and fat fraction adjusted liver T1, a measure of inflammation, was raised in patients. Patients displayed greater perceived fatigue scores, though leg muscle volume, strength, force-loss, motor unit properties and post-exercise muscle phosphocreatine resynthesis were comparable. Further, cardiac and cerebral architecture and function (at rest and on exercise) were not different. In this cross-sectional study, individuals without known previous morbidity who survived severe COVID-19 exhibited greater insulin resistance, pointing to a need for physical function intervention in recovery.

Five days of bed rest in young and old adults: Retainment of skeletal muscle mass with neuromuscular electrical stimulation

The consequences of short-term disuse are well known, but effective countermeasures remain elusive. This study investigated the effects of neuromuscular electrical stimulation (NMES) during 5 days of bed rest on retaining lower limb muscle mass and muscle function in healthy young and old participants. One leg received NMES of the quadriceps muscle (3 × 30min/day) (NMES), and the other served as a control (CON). Isometric quadriceps strength (MVC), rate of force development (RFD), lower limb lean mass, and muscle thickness were assessed pre-and post-intervention. Muscle thickness remained unaltered with NMES in young and increased in old following bed rest, while it decreased in CON legs. In old participants, mid-thigh lean mass (MTLM) was preserved with NMES while decreased in CON legs. In the young, only a tendency to change with bed rest was detected for MTLM. MVC and early-phase RFD decreased in young and old, irrespective of NMES. In contrast, late-phase RFD was retained in young participants with NMES, while it decreased in young CON legs, and in the old, irrespective of NMES. NMES during short-term bed rest preserved muscle thickness but not maximal muscle strength. While young and old adults demonstrated similar adaptive responses in preventing the loss of skeletal muscle thickness, RFD was retained in the young only.

The impact of forearm immobilization and acipimox administration on muscle amino acid metabolism and insulin sensitivity in healthy, young volunteers

Although the mechanisms underpinning short-term muscle disuse atrophy and associated insulin resistance remain to be elucidated, perturbed lipid metabolism might be involved. Our aim was to determine the impact of acipimox administration [i.e., pharmacologically lowering circulating nonesterified fatty acid (NEFA) availability] on muscle amino acid metabolism and insulin sensitivity during short-term disuse. Eighteen healthy individuals (age: 22 ± 1 years; body mass index: 24.0 ± 0.6 kg·m-2) underwent 2 days forearm immobilization with placebo (PLA; n = 9) or acipimox (ACI; 250 mg Olbetam; n = 9) ingestion four times daily. Before and after immobilization, whole body glucose disposal rate (GDR), forearm glucose uptake (FGU; i.e., muscle insulin sensitivity), and amino acid kinetics were measured under fasting and hyperinsulinemic-hyperaminoacidemic-euglycemic clamp conditions using forearm balance and l-[ring-2H5]-phenylalanine infusions. Immobilization did not affect GDR but decreased insulin-stimulated FGU in both groups, more so in ACI (from 53 ± 8 to 12 ± 5 µmol·min-1) than PLA (from 52 ± 8 to 38 ± 13 µmol·min-1; P < 0.05). In ACI only, and in contrast to our hypothesis, fasting arterialized NEFA concentrations were elevated to 1.3 ± 0.1 mmol·L-1 postimmobilization (P < 0.05), and fasting forearm NEFA balance increased approximately fourfold (P = 0.10). Forearm phenylalanine net balance decreased following immobilization (P < 0.10), driven by an increased rate of appearance [from 32 ± 5 (fasting) and 21 ± 4 (clamp) preimmobilization to 53 ± 8 and 31 ± 4 postimmobilization; P < 0.05] while the rate of disappearance was unaffected by disuse or acipimox. Disuse-induced insulin resistance is accompanied by early signs of negative net muscle amino acid balance, which is driven by accelerated muscle amino acid efflux. Acutely elevated NEFA availability worsened muscle insulin resistance without affecting amino acid kinetics, suggesting increased muscle NEFA uptake may contribute to inactivity-induced insulin resistance but does not cause anabolic resistance.NEW & NOTEWORTHY We demonstrate that 2 days of forearm cast immobilization in healthy young volunteers leads to the rapid development of insulin resistance, which is accompanied by accelerated muscle amino acid efflux in the absence of impaired muscle amino acid uptake. Acutely elevated fasting nonesterified fatty acid (NEFA) availability as a result of acipimox supplementation worsened muscle insulin resistance without affecting amino acid kinetics, suggesting increased muscle NEFA uptake may contribute to inactivity-induced insulin resistance but does not cause anabolic resistance.

Daily blood flow restriction does not preserve muscle mass and strength during 2 weeks of bed rest

We measured the impact of blood flow restriction on muscle protein synthesis rates, muscle mass and strength during 2 weeks of strict bed rest. Twelve healthy, male adults (age: 24 ± 3 years, body mass index: 23.7 ± 3.1 kg/m2 ) were subjected to 14 days of strict bed rest with unilateral blood flow restriction performed three times daily in three 5 min cycles (200 mmHg). Participants consumed deuterium oxide and we collected blood and saliva samples throughout 2 weeks of bed rest. Before and immediately after bed rest, lean body mass (dual-energy X-ray absorptiometry scan) and thigh muscle volume (magnetic resonance imaging scan) were assessed in both the blood flow restricted (BFR) and control (CON) leg. Muscle biopsies were collected and unilateral muscle strength (one-repetition maximum; 1RM) was assessed for both legs before and after the bed rest period. Bed rest resulted in 1.8 ± 1.0 kg lean body mass loss (P < 0.001). Thigh muscle volume declined from 7.1 ± 1.1 to 6.7 ± 1.0 L in CON and from 7.0 ± 1.1 to 6.7 ± 1.0 L in BFR (P < 0.001), with no differences between treatments (P = 0.497). In addition, 1RM leg extension strength decreased from 60.2 ± 10.6 to 54.8 ± 10.9 kg in CON and from 59.2 ± 12.1 to 52.9 ± 12.0 kg in BFR (P = 0.014), with no differences between treatments (P = 0.594). Muscle protein synthesis rates during bed rest did not differ between the BFR and CON leg (1.11 ± 0.12 vs. 1.08 ± 0.13%/day, respectively; P = 0.302). Two weeks of bed rest substantially reduces skeletal muscle mass and strength. Blood flow restriction during bed rest does not modulate daily muscle protein synthesis rates and does not preserve muscle mass or strength. KEY POINTS: Bed rest, often necessary for recovery from illness or injury, leads to the loss of muscle mass and strength. It has been postulated that blood flow restriction may attenuate the loss of muscle mass and strength during bed rest. We investigated the effect of blood flow restriction on muscle protein synthesis rates, muscle mass and strength during 2 weeks of strict bed rest. Blood flow restriction applied during bed rest does not modulate daily muscle protein synthesis rates and does not preserve muscle mass or strength. Blood flow restriction is not effective in preventing muscle atrophy during a prolonged period of bed rest.

Preliminary investigation of the effect of non-cardiac surgery on intraoperative islet and renal function: a single-center prospective cohort study

Background

The effect of different non-cardiac surgical methods on islet and renal function remains unclear. We conducted a preliminary investigation to determine whether different surgical methods affect islet function or cause further damage to renal function.

Methods

In this prospective cohort study, the clinical data of 63 adult patients who underwent non-cardiac surgery under general anesthesia were evaluated from February 2019 to January 2020. Patients were divided into the abdominal surgery group, the laparoscopic surgery group, and the breast cancer surgery group. The primary outcome was the difference between the effects of different surgical methods on renal function.

Results

Islet and renal function were not significantly different between the groups. The correlation analysis showed that hematocrit (HCT) and hemoglobin (HB) were negatively correlated with fasting plasma glucose (FPG) (p < 0.05), MAP was positively correlated with C-peptide (p < 0.05), and HCT and Hb were positively correlated with serum creatinine (SCr) (p < 0.05). Fasting insulin (FINS) and C-peptide were negatively correlated with SCr (p < 0.05), and the homeostatic model assessment of insulin resistance (HOMA-IR) was positively correlated with SCr (p < 0.05). FINS, C-peptide, HOMA-IR, and the homeostatic model assessment of β-cell function (HOMA-β) were positively correlated with cystatin C (Cys C) (p < 0.05).

Conclusion

FINS, C-peptide, and HOMA-IR had positive effects on beta-2-microglobulin (β2-MG). FINS, C-peptide, and HOMA-IR were positively correlated with Cys C and β2-Mg. While FINS and C-peptide were negatively correlated with SCr, HOMA-IR was positively correlated with SCr.

High-protein diet with excess leucine prevents inactivity-induced insulin resistance in women

BACKGROUND AND AIMS

Muscle inactivity leads to muscle atrophy and insulin resistance. The branched-chain amino acid (BCAA) leucine interacts with the insulin signaling pathway to modulate glucose metabolism. We have tested the ability of a high-protein BCAA-enriched diet to prevent insulin resistance during long-term bed rest (BR).

METHODS

Stable isotopes were infused to determine glucose and protein kinetics in the postabsorptive state and during a hyperinsulinemic-euglycemic clamp in combination with amino acid infusion (Clamp + AA) before and at the end of 60 days of BR in two groups of healthy, young women receiving eucaloric diets containing 1 g of protein/kg per day (n = 8) or 1.45 g of protein/kg per day enriched with 0.15 g/kg per day of BCAAs (leucine/valine/isoleucine = 2/1/1) (n = 8). Body composition was determined by Dual X-ray Absorptiometry.

RESULTS

BR decreased lean body mass by 7.6 ± 0.3 % and 7.2 ± 0.8 % in the groups receiving conventional or high protein-BCAA diets, respectively. Fat mass was unchanged in both groups. At the end of BR, percent changes of insulin-mediated glucose uptake significantly (p = 0.01) decreased in the conventional diet group from 155 ± 23 % to 84 ± 10 % while did not change significantly in the high protein-BCAA diet group from 126 ± 20 % to 141 ± 27 % (BR effect, p = 0.32; BR/diet interaction, p = 0.01; Repeated Measures ANCOVA). In contrast, there were no BR/diet interactions on proteolysis and protein synthesis Clamp + AA changes in the conventional diet and the high protein-BCAA diet groups.

CONCLUSION

A high protein-BCAA enriched diet prevented inactivity-induced insulin resistance in healthy women.

The impact of short-term forearm immobilization and acipimox administration on muscle amino acid metabolism and insulin sensitivity in healthy, young volunteers

The mechanisms underpinning short-term muscle disuse atrophy remain to be elucidated, but perturbations in lipid metabolism may be involved. Specifically, positive muscle non-esterified fatty acid (NEFA) balance has been implicated in the development of disuse-induced insulin and anabolic resistance. Our aim was to determine the impact of acipimox administration (i.e. pharmacologically lowering circulating NEFA availability) on muscle amino acid metabolism and insulin sensitivity during short-term disuse. Eighteen healthy individuals (age 22±1 years, BMI 24.0±0.6 kg·m-2) underwent 2 days of forearm cast immobilization with placebo (PLA; n=9, 5M/4F) or acipimox (ACI; 250 mg Olbetam; n=9, 4M/5F) ingestion four times daily. Before and after immobilization, whole-body glucose disposal rate (GDR), forearm glucose uptake (FGU, i.e. muscle insulin sensitivity), and amino acid kinetics were measured under fasting and hyperinsulinaemic-hyperaminoacidaemic-euglycaemic clamp conditions using arteriovenous forearm balance and intravenous L-[ring-2H5]phenylalanine infusions. Immobilization did not affect GDR but decreased insulin-stimulated FGU in both groups, but to a greater degree in ACI (from 53±8 to 12±5 μmol·min-1) than in PLA (from 52±8 to 38±13 μmol·min-1; P<0.05). In ACI only, fasting arterialised NEFA concentrations were elevated to 1.3±0.1 mmol·L-1 post-immobilization (P<0.05), and fasting forearm NEFA balance increased ~4-fold (P=0.10). Forearm phenylalanine net balance tended to decrease following immobilization (P<0.10), driven by increases in phenylalanine rates of appearance (from 32±5 (fasting) and 21±4 (clamp) pre-immobilization to 53±8 and 31±4 post-immobilization; P<0.05) while rates of disappearance were unaffected and no effects of acipimox observed. Altogether, we show disuse-induced insulin resistance is accompanied by early signs of negative net muscle amino acid balance, which is driven by accelerated muscle amino acid efflux. Acutely elevated NEFA availability worsened muscle insulin resistance without affecting muscle amino acid kinetics, suggesting that disuse-associated increased muscle NEFA uptake may contribute to inactivity-induced insulin resistance but does not represent an early mechanism causing anabolic resistance.

Effect of Moderate-Intense Training and Detraining on Glucose Metabolism, Lipid Profile, and Liver Enzymes in Male Wistar Rats: A Preclinical Randomized Study

Exercise training positively regulates glucose metabolism. This study investigated the impact of training and detraining on glucose metabolism, lipid profiles, and liver enzymes. Twenty-six rats completed an initial 4-week moderate-intense training (T0-T4). Then, the animals were randomly assigned to two groups at the end of week 4: AT4: detraining for 8 weeks; AT8: training for 8 weeks and 4-week detraining. Six animals were sacrificed at T0 and T4, four animals/group at T8, and three/group at T12. The study continued for 12 weeks, and all parameters were assessed at T0, T4, T8, and T12. IPGTT significantly improved after 4 weeks of training (p < 0.01) and was further reduced in AT8 at T8. In AT8, 8-week training significantly reduced total cholesterol at T4 and T12 vs. T0 (p < 0.05), LDL at T4, T8, and T12 vs. T0 (p < 0.01), ALP at T8, T12 vs. T0 (p < 0.01), and increased HDL at T8 and ALT at T8 and T12 vs. T0 (p < 0.05). Triglycerides and hexokinase activity increased significantly at T4 and T8 (p < 0.05) and then decreased at T12 in AT8. Pyruvate and glycogen increased at T12 in AT8 vs. AT4. Eight-week training improved LPL and ATGL expressions. Training positively modulated insulin, glucose metabolism, and lipid profiles, but detraining reduced the benefits associated with the initial training.

Body and Fat mass are not Regulated, Controlled, or Defended: An introduction to the Invisible Hand' and 'Competition' Models of Metabolism

This paper presents two inter-dependent frameworks for understanding the etiology of obesity and the regain of body and fat mass after weight loss. The 'Invisible Hand of Metabolism' illustrates how physiologic states such as body and fat mass and blood glucose levels arise from the unregulated, uncontrolled, yet competitive behavior of trillions of semi-autonomous cells. The 'Competition Model of Metabolism' is an explanatory (mechanistic) framework that details how organismal and cell-specific behaviors generate the apparent stability of physiologic states despite metabolic perturbations (e.g., weight-loss and exercise). Together, these frameworks show that body and fat mass and blood glucose levels are not regulated, controlled, or defended but emerge from the complexity and functional plasticity of competitive cellular relations. Therefore, we argue that the use of abstract constructs such as 'regulation', 'control', 'glucostats', 'adipostats', and 'set-/settling-points' hinders the understanding of obesity and cardiometabolic diseases in human and nonhuman mammals.

Do dietary supplements prevent loss of muscle mass and strength during muscle disuse? A systematic review and meta-analysis of randomized controlled trials

Objective

We performed a systematic review and meta-analysis of existing randomized controlled trials (RCTs) to assess whether dietary supplements can prevent loss of muscle mass and strength during muscle disuse.

Methods

We searched the following databases: PubMed, Embase, Cochrane, Scopus, Web of Science, and CINAHL for RCTs assessing the effect of dietary supplements on disuse muscular atrophy without language and time restrictions. Muscle strength and leg lean mass were used as the primary outcome indicators. Muscle cross-sectional area (CSA), muscle fiber type distribution, peak aerobic capacity and muscle volume were used as secondary outcome indicators. The risk of bias was assessed using the Cochrane Collaboration's Risk of Bias tool. Heterogeneity was tested using the I² statistic index. Mean and standard deviation of outcome indicators were extracted from the intervention and control groups to calculate effect sizes and 95% confidence intervals, with the significance level set at P < 0.05.

Results

Twenty RCTs were included with a total of 339 subjects. The results showed that dietary supplements had no effect on muscle strength, CSA, muscle fiber type distribution, peak aerobic capacity or muscle volume. But dietary supplements have a protective effect on the lean mass of the legs.

Conclusion

Dietary supplements can improve lean leg mass, but did not show a tendency to have an effect on muscle strength, CSA, muscle fiber type distribution, peak aerobic capacity or muscle volume during muscle disuse.

Systematic review registration

https://www.crd.york.ac.uk/PROSPERO/#recordDetails, identifier: CRD42022370230.

The impact of physical inactivity on glucose homeostasis when diet is adjusted to maintain energy balance in healthy, young males

BACKGROUND & AIMS

It is unclear if dietary adjustments to maintain energy balance during reduced physical activity can offset inactivity-induced reductions in insulin sensitivity and glucose disposal to produce normal daily glucose concentrations and meal responses. Therefore, the aim of the present study was to examine the impact of long-term physical inactivity (60 days of bed rest) on daily glycemia when in energy balance.

METHODS

Interstitial glucose concentrations were measured using Continuous Glucose Monitoring Systems (CGMS) for 5 days before and towards the end of bed rest in 20 healthy, young males (Age: 34 ± 8 years; BMI: 23.5 ± 1.8 kg/m2). Energy intake was reduced during bed rest to match energy expenditure, but the types of foods and timing of meals was maintained. Fasting venous glucose and insulin concentrations were determined, as well as the change in whole-body glucose disposal using a hyperinsulinemic-euglycemic clamp (HIEC).

RESULTS

Following long-term bed rest, fasting plasma insulin concentration increased 40% (p = 0.004) and glucose disposal during the HIEC decreased 24% (p < 0.001). Interstitial daily glucose total area under the curve (tAUC) from pre-to post-bed rest increased on average by 6% (p = 0.041), despite a 20 and 25% reduction in total caloric and carbohydrate intake, respectively. The nocturnal period (00:00-06:00) showed the greatest change to glycemia with glucose tAUC for this period increasing by 9% (p = 0.005). CGMS measures of daily glycemic variability (SD, J-Index, M-value and MAG) were not changed during bed rest.

CONCLUSIONS

Reduced physical activity (bed rest) increases glycemia even when daily energy intake is reduced to maintain energy balance. However, the disturbance to daily glucose homeostasis was much more modest than the reduced capacity to dispose of glucose, and glycemic variability was not negatively affected by bed rest, likely due to positive mitigating effects from the contemporaneous reduction in dietary energy and carbohydrate intake.

CLINICAL TRIALS RECORD

NCT03594799 (registered July 20, 2018) (https://clinicaltrials.gov/ct2/show/NCT03594799).

The Key Role of Mitochondrial Function in Health and Disease

The role of mitochondrial function in health and disease has become increasingly recognized, particularly in the last two decades. Mitochondrial dysfunction as well as disruptions of cellular bioenergetics have been shown to be ubiquitous in some of the most prevalent diseases in our society, such as type 2 diabetes, cardiovascular disease, metabolic syndrome, cancer, and Alzheimer's disease. However, the etiology and pathogenesis of mitochondrial dysfunction in multiple diseases have yet to be elucidated, making it one of the most significant medical challenges in our history. However, the rapid advances in our knowledge of cellular metabolism coupled with the novel understanding at the molecular and genetic levels show tremendous promise to one day elucidate the mysteries of this ancient organelle in order to treat it therapeutically when needed. Mitochondrial DNA mutations, infections, aging, and a lack of physical activity have been identified to be major players in mitochondrial dysfunction in multiple diseases. This review examines the complexities of mitochondrial function, whose ancient incorporation into eukaryotic cells for energy purposes was key for the survival and creation of new species. Among these complexities, the tightly intertwined bioenergetics derived from the combustion of alimentary substrates and oxygen are necessary for cellular homeostasis, including the production of reactive oxygen species. This review discusses different etiological mechanisms by which mitochondria could become dysregulated, determining the fate of multiple tissues and organs and being a protagonist in the pathogenesis of many non-communicable diseases. Finally, physical activity is a canonical evolutionary characteristic of humans that remains embedded in our genes. The normalization of a lack of physical activity in our modern society has led to the perception that exercise is an "intervention". However, physical activity remains the modus vivendi engrained in our genes and being sedentary has been the real intervention and collateral effect of modern societies. It is well known that a lack of physical activity leads to mitochondrial dysfunction and, hence, it probably becomes a major etiological factor of many non-communicable diseases affecting modern societies. Since physical activity remains the only stimulus we know that can improve and maintain mitochondrial function, a significant emphasis on exercise promotion should be imperative in order to prevent multiple diseases. Finally, in populations with chronic diseases where mitochondrial dysfunction is involved, an individualized exercise prescription should be crucial for the "metabolic rehabilitation" of many patients. From lessons learned from elite athletes (the perfect human machines), it is possible to translate and apply multiple concepts to the betterment of populations with chronic diseases.

Effects of High Glucose on Human Endothelial Cells Exposed to Simulated Microgravity

A diabetogenic state induced by spaceflight provokes stress and health problems in astronauts. Microgravity (µg) is one of the main stressors in space causing hyperglycaemia. However, the underlying molecular pathways and synergistic effects of µg and hyperglycaemia are not fully understood. In this study, we investigated the effects of high glucose on EA.hy926 endothelial cells in simulated µg (s-µg) using a 3D clinostat and static normogravity (1g) conditions. After 14 days of cell culture under s-µg and 1g conditions, we compared the expression of extracellular matrix (ECM), inflammation, glucose metabolism, and apoptosis-related genes and proteins through qPCR, immunofluorescence, and Western blot analyses, respectively. Apoptosis was evaluated via TUNEL staining. Gene interactions were examined via STRING analysis. Our results show that glucose concentrations had a weaker effect than altered gravity. µg downregulated the ECM gene and protein expression and had a stronger influence on glucose metabolism than hyperglycaemia. Moreover, hyperglycaemia caused more pronounced changes in 3D cultures than in 2D cultures, including bigger and a greater number of spheroids, upregulation of NOX4 and the apoptotic proteins NF-κB and CASP3, and downregulation of fibronectin and transglutaminase-2. Our findings bring new insights into the possible molecular pathways involved in the diabetogenic vascular effects in µg.

Human adaptation to immobilization: Novel insights of impacts on glucose disposal and fuel utilization

BACKGROUND

Bed rest (BR) reduces whole-body insulin-stimulated glucose disposal (GD) and alters muscle fuel metabolism, but little is known about metabolic adaptation from acute to chronic BR nor the mechanisms involved, particularly when volunteers are maintained in energy balance.

METHODS

Healthy males (n = 10, 24.0 ± 1.3 years), maintained in energy balance, underwent 3-day BR (acute BR). A second cohort matched for sex and body mass index (n = 20, 34.2 ± 1.8 years) underwent 56-day BR (chronic BR). A hyperinsulinaemic euglycaemic clamp (60 mU/m² /min) was performed to determine rates of whole-body insulin-stimulated GD before and after BR (normalized to lean body mass). Indirect calorimetry was performed before and during steady state of each clamp to calculate rates of whole-body fuel oxidation. Muscle biopsies were taken to determine muscle glycogen, metabolite and intramyocellular lipid (IMCL) contents, and the expression of 191 mRNA targets before and after BR. Two-way repeated measures analysis of variance was used to detect differences in endpoint measures.

RESULTS

Acute BR reduced insulin-mediated GD (Pre 11.5 ± 0.7 vs. Post 9.3 ± 0.6 mg/kg/min, P < 0.001), which was unchanged in magnitude following chronic BR (Pre 10.2 ± 0.4 vs. Post 7.9 ± 0.3 mg/kg/min, P < 0.05). This reduction in GD was paralleled by the elimination of the 35% increase in insulin-stimulated muscle glycogen storage following both acute and chronic BR. Acute BR had no impact on insulin-stimulated carbohydrate (CHO; Pre 3.69 ± 0.39 vs. Post 4.34 ± 0.22 mg/kg/min) and lipid (Pre 1.13 ± 0.14 vs. Post 0.59 ± 0.11 mg/kg/min) oxidation, but chronic BR reduced CHO oxidation (Pre 3.34 ± 0.18 vs. Post 2.72 ± 0.13 mg/kg/min, P < 0.05) and blunted the magnitude of insulin-mediated inhibition of lipid oxidation (Pre 0.60 ± 0.07 vs. Post 0.85 ± 0.06 mg/kg/min, P < 0.05). Neither acute nor chronic BR increased muscle IMCL content. Plentiful mRNA abundance changes were detected following acute BR, which waned following chronic BR and reflected changes in fuel oxidation and muscle glycogen storage at this time point.

CONCLUSIONS

Acute BR suppressed insulin-stimulated GD and storage, but the extent of this suppression increased no further in chronic BR. However, insulin-mediated inhibition of fat oxidation after chronic BR was less than acute BR and was accompanied by blunted CHO oxidation. The juxtaposition of these responses shows that the regulation of GD and storage can be dissociated from substrate oxidation. Additionally, the shift in substrate oxidation after chronic BR was not explained by IMCL accumulation but reflected by muscle mRNA and pyruvate dehydrogenase kinase 4 protein abundance changes, pointing to lack of muscle contraction per se as the primary signal for muscle adaptation.

Effects of long-term simulated microgravity on liver metabolism in rhesus macaques

The liver is an essential multifunctional organ and constantly communicates with nearly all the tissues in the body. Spaceflight or simulated microgravity has a significant impact on the livers of rodent models, including lipid accumulation and inflammatory cell infiltration. Whether similar liver lipotoxicity could occur in humans is not known, even though altered circulating cholesterol profile has been reported in astronauts. Using a 42-day head-down bed rest (HDBR) model in rhesus macaques, the present study investigated whether simulated microgravity alters the liver of non-human primates at the transcriptome and metabolome levels. Its association with stress and intestinal changes was also explored. Compared to the controls, the HDBR monkeys showed mild liver injury, elevated ANGPTL3 level in the plasma, and accumulation of fat vacuoles and inflammatory cells in the liver. Altered transcriptome signatures with up-regulation of genes in lipid metabolisms and down-regulation of genes in innate immune defense were also found in HDBR group-derived liver samples. The metabolic profiling of the liver revealed mildly disturbed fatty acid metabolism in the liver of HDBR monkeys. The intestinal dysbiosis, its associated endotoxemia and changes in the composition of bile acids, and elevated stress hormone in HDBR monkeys may contribute to the altered lipid metabolisms in the liver. These data indicate that liver metabolic functions and gut-liver axis should be closely monitored in prolonged spaceflight to facilitate strategy design to improve and maintain metabolic homeostasis.

Detrimental effects of physical inactivity on peripheral and brain vasculature in humans: Insights into mechanisms, long-term health consequences and protective strategies

The growing prevalence of physical inactivity in the population highlights the urgent need for a more comprehensive understanding of how sedentary behaviour affects health, the mechanisms involved and what strategies are effective in counteracting its negative effects. Physical inactivity is an independent risk factor for different pathologies including atherosclerosis, hypertension and cardiovascular disease. It is known to progressively lead to reduced life expectancy and quality of life, and it is the fourth leading risk factor for mortality worldwide. Recent evidence indicates that uninterrupted prolonged sitting and short-term inactivity periods impair endothelial function (measured by flow-mediated dilation) and induce arterial structural alterations, predominantly in the lower body vasculature. Similar effects may occur in the cerebral vasculature, with recent evidence showing impairments in cerebral blood flow following prolonged sitting. The precise molecular and physiological mechanisms underlying inactivity-induced vascular dysfunction in humans are yet to be fully established, although evidence to date indicates that it may involve modulation of shear stress, inflammatory and vascular biomarkers. Despite the steady increase in sedentarism in our societies, only a few intervention strategies have been investigated for their efficacy in counteracting the associated vascular impairments. The current review provides a comprehensive overview of the evidence linking acute and short-term physical inactivity to detrimental effects on peripheral, central and cerebral vascular health in humans. We further examine the underlying molecular and physiological mechanisms and attempt to link these to long-term consequences for cardiovascular health. Finally, we summarize and discuss the efficacy of lifestyle interventions in offsetting the negative consequences of physical inactivity.

Cardiovasomobility: an integrative understanding of how disuse impacts cardiovascular and skeletal muscle health

Cardiovasomobility is a novel concept that encompasses the integration of cardiovascular and skeletal muscle function in health and disease with critical modification by physical activity, or lack thereof. Compelling evidence indicates that physical activity improves health while a sedentary, or inactive, lifestyle accelerates cardiovascular and skeletal muscle dysfunction and hastens disease progression. Identifying causative factors for vascular and skeletal muscle dysfunction, especially in humans, has proven difficult due to the limitations associated with cross-sectional investigations. Therefore, experimental models of physical inactivity and disuse, which mimic hospitalization, injury, and illness, provide important insight into the mechanisms and consequences of vascular and skeletal muscle dysfunction. This review provides an overview of the experimental models of disuse and inactivity and focuses on the integrated responses of the vasculature and skeletal muscle in response to disuse/inactivity. The time course and magnitude of dysfunction evoked by various models of disuse/inactivity are discussed in detail, and evidence in support of the critical roles of mitochondrial function and oxidative stress are presented. Lastly, strategies aimed at preserving vascular and skeletal muscle dysfunction during disuse/inactivity are reviewed. Within the context of cardiovasomobility, experimental manipulation of physical activity provides valuable insight into the mechanisms responsible for vascular and skeletal muscle dysfunction that limit mobility, degrade quality of life, and hasten the onset of disease.

Effects of Various Muscle Disuse States and Countermeasures on Muscle Molecular Signaling

Skeletal muscle is capable of changing its structural parameters, metabolic rate and functional characteristics within a wide range when adapting to various loading regimens and states of the organism. Prolonged muscle inactivation leads to serious negative consequences that affect the quality of life and work capacity of people. This review examines various conditions that lead to decreased levels of muscle loading and activity and describes the key molecular mechanisms of muscle responses to these conditions. It also details the theoretical foundations of various methods preventing adverse muscle changes caused by decreased motor activity and describes these methods. A number of recent studies presented in this review make it possible to determine the molecular basis of the countermeasure methods used in rehabilitation and space medicine for many years, as well as to identify promising new approaches to rehabilitation and to form a holistic understanding of the mechanisms of gravity force control over the muscular system.

Influence of an L-type SALMFamide neuropeptide on locomotory performance and muscle physiology in the sea cucumber Apostichopus japonicus

Neuropeptides in the SALMFamide family serve as muscle relaxants in echinoderms and may affect locomotion, as the motor behavior in sea cucumbers involves alternating contraction and extension of the body wall, which is under the control of longitudinal muscle. We evaluated the effect of an L-type SALMFamide neuropeptide (LSA) on locomotory performance of Apostichopus japonicus. We also investigated the metabolites of longitudinal muscle tissue using ultra performance liquid chromatography and quadrupole time-of-flight mass spectrometry (UPLC-Q-TOF-MS) to assess the potential physiological mechanisms underlying the effect of LSA. The hourly distance, cumulative duration and number of steps moved significantly increased in sea cucumbers in the fourth hour after injection with LSA. Also, the treatment enhanced the mean and maximum velocity by 9.8% and 17.8%, respectively, and increased the average stride by 12.4%. Levels of 27 metabolites in longitudinal muscle changed after LSA administration, and the increased concentration of pantothenic acid, arachidonic acid and lysophosphatidylethanolamine, and the altered phosphatidylethanolamine/phosphatidylcholine ratio are potential physiological mechanisms that could explain the observed effect of LSA on locomotor behavior in A. japonicus.

Electrical muscle stimulation: Application and potential role in aging society

Neurodegenerative diseases and sarcopenia become more prevalent as individuals age and, therefore, represent a serious issue for the healthcare system. Several studies have reported the relationship between physical activity and reduced incidence of dementia or cognitive deterioration. Thus, exercise and strength training are most recommended treatments, but it is proving difficult to engage individuals to initiate exercise and strength training. Electrical muscle stimulation (EMS) may provide an alternative and more efficient solution. Although EMS has undergone a decline in use, mainly because of stimulation discomfort, new technologies allow painless application of strong contractions. Such activation can be applied in higher exercise dosages and more efficiently than people are likely to achieve with exercise. Unlike orderly recruitment of motor units (MUs) during low intensity voluntary exercise, EMS activates large fast-twitch MUs with glycolytic fibers preferentially and this could have benefit for prevention and treatment of diabetes and chronic diseases associated with muscle atrophy that ultimately lead to bed-ridden conditions. Recent evidence highlights the potential for EMS to make a major impact on these and other lifestyle related diseases and its role as a useful modality for orthopedic and cardiac rehabilitation. This paper will discuss the potential for EMS to break new ground in effective interventions in these frontiers of medical science.

Survival assessment of the extended-wear insulin infusion set featuring lantern technology in adults with type 1 diabetes by the glucose clamp technique

Maintaining good glycaemic control with the same infusion set for longer than 3 days may improve the quality of life of insulin pump users. The aim of the current study was to assess the efficacy and safety of the novel, extended-wear infusion set over 7 days of wear in adults with type 1 diabetes. Sixteen participants completed three identical 8-hour euglycaemic clamp experiments on Days 1, 4 and 7 of infusion set wear. Between the experiments, the participants were discharged home for routine diabetes management while wearing the same extended-wear infusion set throughout the study. Time to reach the maximum glucose infusion rate (T_GIRmax ) on Day 7 was reduced by 67% compared with Day 1 (p < .001). The corresponding area under the glucose infusion rate curve (AUC_GIR ) was comparable for the first 2 h of the clamp (p = .891) but decreased by 28% over time (p < .008). While the extent of insulin absorption decreased with prolonged wear, it was accompanied by an increase in insulin absorption rate. The infusion set survival rate was 100% without leakages, occlusion alarms, severe hypoglycaemia or ketoacidosis. The extended-wear infusion set proved safe and effective during prolonged wear in real-life conditions.

Importance of hyperglycemia in COVID-19 intensive-care patients: Mechanism and treatment strategy

This review reported that coronavirus disease 2019 (COVID-19) infected patients with short time bed rest or quarantine and airway inflammation are at more risk of developing hyperglycemia and insulin resistance. This condition can induce oxidative stress, decrease immune system function, impair endothelial function, induce apoptosis, and reduce antioxidant in the lungs. We provide a possible mechanism in severe COVID-19 patients and recommend treatment strategy to reduce mortality rate and prevent adverse outcomes after intensive care unit (ICU).

The Application of Creatine Supplementation in Medical Rehabilitation

Numerous health conditions affecting the musculoskeletal, cardiopulmonary, and nervous systems can result in physical dysfunction, impaired performance, muscle weakness, and disuse-induced atrophy. Due to its well-documented anabolic potential, creatine monohydrate has been investigated as a supplemental agent to mitigate the loss of muscle mass and function in a variety of acute and chronic conditions. A review of the literature was conducted to assess the current state of knowledge regarding the effects of creatine supplementation on rehabilitation from immobilization and injury, neurodegenerative diseases, cardiopulmonary disease, and other muscular disorders. Several of the findings are encouraging, showcasing creatine's potential efficacy as a supplemental agent via preservation of muscle mass, strength, and physical function; however, the results are not consistent. For multiple diseases, only a few creatine studies with small sample sizes have been published, making it difficult to draw definitive conclusions. Rationale for discordant findings is further complicated by differences in disease pathologies, intervention protocols, creatine dosing and duration, and patient population. While creatine supplementation demonstrates promise as a therapeutic aid, more research is needed to fill gaps in knowledge within medical rehabilitation.

Blood Flow Restriction Combined with Electrical Stimulation Attenuates Thigh Muscle Disuse Atrophy

PURPOSE

This study aimed to investigate the effects of blood flow restriction (BFR) combined with electrical muscle stimulation (EMS) on skeletal muscle mass and strength during a period of limb disuse.

METHODS

Thirty healthy participants (22 ± 3 yr; 23 ± 3 kg·m-2) were randomly assigned to control (CON; n = 10), BFR alone (BFR; n = 10), or BFR combined with EMS (BFR + EMS; n = 10). All participants completed unloading of a single leg for 14 d, with no treatment (CON), or while treated with either BFR or BFR + EMS (twice daily, 5 d·wk-1). BFR treatment involved arterial three cycles of 5-min occlusion using suprasystolic pressure, each separated by 5 min of reperfusion. EMS (6 s on, 15 s off; 200 μs; 60 Hz; 15% maximal voluntary contraction [MVC]) was applied continuously throughout the three BFR cycles. Quadriceps muscle mass (whole-thigh lean mass via dual-energy x-ray absorptiometry and vastus lateralis [VL] muscle thickness via ultrasound) and strength (via knee extension MVC) were assessed before and after the 14-d unloading period.

RESULTS

After limb unloading, whole-thigh lean mass decreased in the control group (-4% ± 1%, P < 0.001) and BFR group (-3% ± 2%, P = 0.001), but not in the BFR + EMS group (-0.3% ± 3%, P = 0.8). VL muscle thickness decreased in the control group (-4% ± 4%, P = 0.005) and was trending toward a decrease in the BFR group (-8% ± 11%, P = 0.07) and increase in the BFR + EMS group (+5% ± 10%, P = 0.07). Knee extension MVC decreased over time (P < 0.005) in the control group (-18% ± 15%), BFR group (-10% ± 13%), and BFR + EMS group (-18% ± 15%), with no difference between groups (P > 0.5).

CONCLUSION

Unlike BFR performed in isolation, BFR + EMS represents an effective interventional strategy to attenuate the loss of muscle mass during limb disuse, but it does not demonstrate preservation of strength.

Aging-like metabolic and adrenal changes in microgravity: State of the art in preparation for Mars

Endocrine and metabolic changes that typically accompany aging on Earth have been consistently observed in space. Support for the role of gravity in aging has mostly come from ground simulation studies in head down bed rest. However, uncertainties remain and have to be resolved in planning for the ambitious enterprise of sending humans to Mars and back. Stress-related corticosteroid changes and metabolic adaptation to microgravity and their relationship with aging are the object of the present review mostly, albeit of course non exclusively, coming from the personal experience of the authors. The picture coming out of it is that of some, not easily proven, stress-induced cortisol increase accompanied by insulin resistance, both of which represent typical aging-like phenomena mediated by chronic low-grade inflammation. This suggests the need for humans to consider the long journey to safely land, live and work on Mars by taking advantage of integrative medicine solutions including synthetic torpor and/or continuous self-monitoring of eating, sleeping, moving to enable remotely supervised self-treatment.

Quantification of immobilization-induced changes in human calf muscle using speed-of-sound ultrasound: An observational pilot study

Short-term immobilization leads to fatty muscular degeneration, which is associated with various negative health effects. Based on literature showing very high correlations between MRI Dixon fat fraction and Speed-of-Sound (SoS), we hypothesized that we can detect short-term-immobilization-induced differences in SoS.Both calves of 10 patients with a calf cast on one side for a mean duration of 41 ± 26 days were examined in relaxed position using a standard ultrasound machine. Calf perimeters were measured for both sides. A flat Plexiglas-reflector, placed vertically on the opposite side of the probe with the calf in-between, was used as a timing reference for SoS. SoS was both manually annotated by two readers and assessed by an automatic annotation algorithm. The thickness values of the subcutaneous fat and muscle layers were manually read from the B-mode images. Differences between the cast and non-cast calves were calculated with a paired t test. Correlation analysis of SoS and calf perimeter was performed using Pearson's correlation coefficient.Paired t test showed significant differences between the cast and non-cast side for both SoS (P < .01) and leg perimeter (P < .001). SoS was reduced with the number of days after cast installment (r = -0.553, P = .097). No significant differences were found for muscle layer thickness, subcutaneous fat layer thickness, mean fat echo intensity, or mean muscle echo intensity.Short-term-immobilization led to a significant reduction in SoS in the cast calf compared to the healthy calf, indicating a potential role of SoS as a biomarker in detecting immobilization-induced fatty muscular degeneration not visible on B-mode ultrasound.

Immobilisation induces sizeable and sustained reductions in forearm glucose uptake in just 24 h but does not change lipid uptake in healthy men

KEY POINTS

The trajectory, magnitude and localisation of metabolic perturbations caused by immobilisation (IMM) are unresolved. Forearm glucose uptake (FGU) in response to glucose feeding was determined in healthy men before and during 72 h of forearm IMM, and the same measurements were made in the non-IMM contralateral limb at baseline and 72 h. In a similar study design, FGU and forearm lipid uptake were determined after a high fat mixed-meal (HFMM) in IMM and non-IMM limbs. FGU was reduced by 38%, 57% and 46% following 24, 48 and 72 h IMM, respectively, but was unchanged in the non-IMM limb. A similar FGU response to IMM was observed after a HFMM, and forearm lipid uptake was unchanged. A sizeable reduction in FGU occurs in just 24 h of IMM, which is sustained thereafter and specific to the IMM limb, making unloading per se the likely rapid driver of dysregulation.

ABSTRACT

The trajectory and magnitude of metabolic perturbations caused by muscle disuse are unknown yet central to understanding the mechanistic basis of immobilisation-associated metabolic dysregulation. To address this gap, forearm glucose uptake (FGU) was determined in 10 healthy men (age 24.9 ± 0.6 years, weight 71.9 ± 2.6 kg, BMI 22.6 ± 0.6 kg/m² ) during a 180 min oral glucose challenge before (0) and after 24, 48 and 72 h of arm immobilisation, and before and after 72 h in the contralateral non-immobilised arm (Study A). FGU was decreased from baseline at 24 h (38%, P = 0.04), 48 h (57%, P = 0.01) and 72 h (46%, P = 0.06) of immobilisation, and was also 63% less than the non-immobilised limb at 72 h (P = 0.002). In a second study, FGU and forearm lipid uptake were determined in nine healthy men (age 22.4 ± 1.3 years, weight 71.4 ± 2.8 kg, BMI 22.6 ± 0.8 kg/m² ) during a 420 min mixed-meal challenge before (0) and after 24 and 48 h of arm immobilisation and before and after 72 h in the contralateral non-immobilised arm (Study B). FGU responses were similar to Study A, and forearm lipid uptake was unchanged from pre-immobilisation in both arms over the study. A sizeable decrement in FGU in response to glucose feeding occurred within 24 h of immobilisation that was sustained and specific to the immobilised limb. Increasing lipid availability had no additional impact on the rate or magnitude of these responses or on lipid uptake. These findings highlight a lack of muscle contraction per se as a fast-acting physiological insult to FGU.

Preclinical rodent models of physical inactivity-induced muscle insulin resistance: challenges and solutions

Physical inactivity influences the development of muscle insulin resistance yet is far less understood than diet-induced muscle insulin resistance. Progress in understanding the mechanisms of physical inactivity-induced insulin resistance is limited by a lack of an appropriate preclinical model of muscle insulin resistance. Here, we discuss differences between diet and physical inactivity-induced insulin resistance, the advantages and disadvantages of the available rodent inactivity models to study insulin resistance, and our current understanding of the mechanisms of muscle insulin resistance derived from such preclinical inactivity designs. The burgeoning rise of health complications emanating from metabolic disease presents an alarming issue with mounting costs for health care and a reduced quality of life. There exists a pressing need for more complete understanding of mechanisms behind the development and progression of metabolic dysfunction. Since lifestyle modifications such as poor diet and lack of physical activity are primary catalysts of metabolic dysfunction, rodent models have been formed to explore mechanisms behind these issues. Particularly, the use of a high-fat diet has been pervasive and has been an instrumental model to gain insight into mechanisms underlying diet-induced insulin resistance (IR). However, physical inactivity (and to some extent muscle disuse) is an often overlooked and much less frequently studied lifestyle modification, which some have contended is the primary contributor in the initial development of muscle IR. In this mini-review we highlight some of the key differences between diet- and physical inactivity-induced development of muscle IR and propose reasons for the sparse volume of academic research into physical inactivity-induced IR including infrequent use of clearly translatable rodent physical inactivity models.

The Effect of Pedal Peptide-Type Neuropeptide on Locomotor Behavior and Muscle Physiology in the Sea Cucumber Apostichopus japonicus

Neuropeptides are endogenous active substances that are present in nervous tissues and participate in behavioral and physiological processes of the animal system. Locomotor behavior is basic to predation, escape, reproduction in animals, and neuropeptides play an important role in locomotion. In this study, the function of pedal peptide-type neuropeptide (PDP) in the process of locomotor behavior of the sea cucumber Apostichopus japonicus was evaluated. The locomotor behavior of A. japonicus was recorded by infrared camera before and after PDP administration, and muscle physiology was studied by ultra performance liquid chromatography and quadrupole time-off-light mass spectrometry (UPLC-Q-TOF-MS) to clarify the potential physiological mechanisms. The results showed that PDP enhanced the cumulative duration of moving significantly at the 7th h after injection, and reduced the mean and maximum velocity by 16.90 and 14.22% in A. japonicus. The data of muscle metabolomics suggested that some significantly changed metabolites were related to locomotor behavior of sea cucumbers. The decreases of phosphatidylethanolamine (PE) and phosphatidylcholine (PC) might result in the increases of lysophosphatidylcholines (lysoPC) and lysophosphatidylethanolamine (lysoPE), and suggested the change of fluidity and permeability in the muscle cell membrane, which would affect the physiology and function of muscle cells, and finally alter the locomotor behavior. In addition, the increased level of arachidonic acid (ARA) might activate K⁺ ion channels and then affect the signaling of muscle cells, or promote the sensitivity of muscle cells to Ca²⁺ and then result in the contractility of longitudinal muscles in sea cucumbers. ARA was also involved in the linoleic acid metabolism which was the only pathway that disturbed significantly after PDP administration. In conclusion, PDP participated in the regulation of locomotor behavior in the sea cucumber, and the decreased PE and PC, increased lysoPC, lysoPE and ARA might be the potential physiological mechanisms that responsible for behavioral effects of PDP in A. japonicus.

The acute muscular response to passive movement and blood flow restriction

PURPOSE

To compare the acute effects of passive movement combined with blood flow restriction (PM + BFR) to passive movement (PM) or blood flow restriction alone (BFR).

METHODS

A total of 20 healthy participants completed: time control (TC), PM, BFR and PM + BFR (one per leg, over 2 days; randomized). For PM, a dynamometer moved the leg through 3 sets of 15 knee extensions/flexions (90° at 45°/second). For BFR, a cuff was inflated to 80% arterial occlusion pressure on the upper leg. Measurements consisted of anterior muscle thickness at 60% and 70% of the upper leg before and after (-0, -5 and -10 min) conditions, ratings of perceived effort and discomfort before conditions and after each set, and of the vastus lateralis during conditions. Data, presented as mean (SD), were compared using Bayesian RMANOVA, except for perceived effort and discomfort, which were compared using a Friedman's test (non-parametric).

RESULTS

60% (Δcm before-after-0: TC = 0.04 [0.09], PM = -0.01 [0.15], BFR = 0.00 [0.11], PM + BFR = 0.01 [0.22]) and 70% (Δcm before-after-0: TC = 0.01 [0.09], PM = -0.01 [0.15], BFR = 0.02 [0.11], PM + BFR = -0.03 [0.22]) muscle thickness did not change. Perceived effort was greater than TC following PM (p = .05) and PM + BFR (p = .001). Perceived discomfort was greater following BFR and PM + BFR compared to TC (all p ≤ .002) and PM (all p ≤ .010). Changes in deoxygenation (e.g. channel 1; ΔμM start set 1-end set 3: TC = 0.9 [1.2], PM = -1.2 [1.9], BFR = 10.3 [2.7], PM + BFR = 10.3 [3.0]) were generally greater with BFR and PM + BFR (BF_inclusion  = 1.210e + 13).

CONCLUSION

Acute muscular responses to PM + BFR are not augmented over the effect of BFR alone.

Impact of sedentarism due to the COVID-19 home confinement on neuromuscular, cardiovascular and metabolic health: Physiological and pathophysiological implications and recommendations for physical and nutritional countermeasures

The COVID-19 pandemic is an unprecedented health crisis as entire populations have been asked to self-isolate and live in home-confinement for several weeks to months, which in itself represents a physiological challenge with significant health risks. This paper describes the impact of sedentarism on the human body at the level of the muscular, cardiovascular, metabolic, endocrine and nervous systems and is based on evidence from several models of inactivity, including bed rest, unilateral limb suspension, and step-reduction. Data form these studies show that muscle wasting occurs rapidly, being detectable within two days of inactivity. This loss of muscle mass is associated with fibre denervation, neuromuscular junction damage and upregulation of protein breakdown, but is mostly explained by the suppression of muscle protein synthesis. Inactivity also affects glucose homeostasis as just few days of step reduction or bed rest, reduce insulin sensitivity, principally in muscle. Additionally, aerobic capacity is impaired at all levels of the O₂ cascade, from the cardiovascular system, including peripheral circulation, to skeletal muscle oxidative function. Positive energy balance during physical inactivity is associated with fat deposition, associated with systemic inflammation and activation of antioxidant defences, exacerbating muscle loss. Importantly, these deleterious effects of inactivity can be diminished by routine exercise practice, but the exercise dose-response relationship is currently unknown. Nevertheless, low to medium-intensity high volume resistive exercise, easily implementable in home-settings, will have positive effects, particularly if combined with a 15-25% reduction in daily energy intake. This combined regimen seems ideal for preserving neuromuscular, metabolic and cardiovascular health.

Absence of MyD88 from Skeletal Muscle Protects Female Mice from Inactivity-Induced Adiposity and Insulin Resistance

OBJECTIVE

Inactivity and inflammation are linked to obesity and insulin resistance. It was hypothesized that MyD88 (mediates inflammation) knockout from muscle (MusMyD88-/- ) would prevent, whereas miR146a-/- (MyD88 inhibitor) would exacerbate, inactivity-induced metabolic disturbances.

METHODS

Cre-control, MusMyD88-/- , and miR146a-/- mice were given running wheels for 5 weeks to model an active phenotype. Afterward, half were placed into a small mouse cage (SMC) to restrict movement for 8 days. Body composition, muscle (3 H)2-deoxyglucose uptake, visceral fat histology, and tissue weight (hind limb muscles, visceral fat, and liver) were assessed. In skeletal muscle and visceral fat, RNA sequencing and mitochondrial function were performed on female MusMyD88-/- and Cre-control SMC mice.

RESULTS

The SMC induced adiposity, hyperinsulinemia, and muscle insulin-stimulated glucose uptake, which was worsened in miR146a-/- mice. In females, MusMyD88-/- mice were protected. Female MusMyD88-/- mice during the SMC period (vs. Cre-control) exhibited higher Igf1 and decreased Ip6k3 and Trim63 muscle expression. Visceral fat transcript changes corresponded to improved lipid metabolism, decreased adipose expansion (Gulp1↑, Anxa2↓, Ehd1↓) and meta-inflammation (Hmox1↓), and increased beiging (Fgf10↑). Ralgapa2, negative regulator of GLUT4 translocation, and inflammation-related gene 993011J21Rik2 were decreased in both muscle and fat.

CONCLUSIONS

Whole-body miR146a-/- exacerbated inactivity-induced fat gain and muscle insulin resistance, whereas MusMyD88-/- prevented insulin resistance in female mice.

High-fat Overfeeding Does Not Exacerbate Rapid Changes in Forearm Glucose and Fatty Acid Balance During Immobilization

CONTEXT

Physical inactivity and high-fat overfeeding have been shown to independently induce insulin resistance.

OBJECTIVE

Establish the contribution of muscle disuse and lipid availability to the development of inactivity-induced insulin resistance.

DESIGN, SETTING, PARTICIPANTS, AND INTERVENTIONS

20 healthy males underwent 7 days of forearm cast immobilization combined with a fully controlled eucaloric diet (n = 10, age 23 ± 2 yr, body mass index [BMI] 23.8 ± 1.0 kg·m-2) or a high-fat diet (HFD) providing 50% excess energy from fat (high-fat diet, n = 10, age 23 ± 2 yr, BMI 22.4 ± 0.8 kg·m-2).

MAIN OUTCOME MEASURES

Prior to casting and following 2 and 7 days of immobilization, forearm glucose uptake (FGU) and nonesterified fatty acid (NEFA) balance were assessed using the arterialized venous-deep venous (AV-V) forearm balance method following ingestion of a mixed macronutrient drink.

RESULTS

7 days of HFD increased body weight by 0.9 ± 0.2 kg (P = 0.002), but did not alter fasting, arterialized whole-blood glucose and serum insulin concentrations or the associated homeostatic model assessment of insulin resistance or Matsuda indices. Two and 7 days of forearm immobilization led to a 40 ± 7% and 52 ± 7% decrease in FGU, respectively (P < 0.001), with no difference between day 2 and 7 and no effect of HFD. Forearm NEFA balance tended to increase following 2 and 7 days of immobilization (P = 0.095).

CONCLUSIONS

Forearm immobilization leads to a rapid and substantial decrease in FGU, which is accompanied by an increase in forearm NEFA balance but is not exacerbated by excess dietary fat intake. Altogether, our data suggest that disuse-induced insulin resistance of glucose metabolism occurs as a physiological adaptation in response to the removal of muscle contraction.

Exercise Countermeasures to Neuromuscular Deconditioning in Spaceflight

The mechanical unloading of spaceflight elicits a host of physiological adaptations including reductions in muscle mass, muscle strength, and muscle function and alterations in central interpretation of visual, vestibular, and proprioceptive information. Upon return to a terrestrial, gravitational environment, these result in reduced function and performance, the potential consequences of which will be exacerbated during exploration missions to austere and distant destinations such as the moon and Mars. Exercise is a potent countermeasure to unloading-induced physiological maladaptations and has been employed since the early days of spaceflight. In-flight exercise hardware has evolved from rudimentary and largely ineffective devices to the current suite onboard the International Space Station (ISS) comprised of a cycle ergometer, treadmill, and resistance exercise device; these contemporary devices have either fully protected or significantly attenuated neuromuscular degradation in spaceflight. However, unlike current microgravity operations on the ISS, future exploration missions will include surface operations in partial gravity environments, which will require greater physiological capacity and work output of their crews. For these flights, it is critical to identify physiological thresholds below which task performance will be impaired and to develop exercise countermeasures-both pre- and in-flight-to ensure that crewmembers are able to safely and effectively complete physically demanding mission objectives. © 2020 American Physiological Society. Compr Physiol 10:171-196, 2020.

The difference in sleep, sedentary behaviour, and physical activity between older adults with 'healthy' and 'unhealthy' cardiometabolic profiles: a cross-sectional compositional data analysis approach

Background

Studies have seldom used Compositional Data Analysis (CoDA) to map the effects of sleep, sedentary behaviour, and physical activity on older adults' cardio-metabolic profiles. This study therefore aimed to illustrate how sleep, sedentary behaviour, and physical activity profiles differ between older adult groups (60-89 years), with 'low' compared to those with 'high' concentrations of endocrine cardio-metabolic disease risk markers, using CoDA.

Method

Ninety-three participants (55% female) wore a thigh-mounted triaxial accelerometer for seven consecutive free-living days. Accelerometer estimates of daily average hours of engagement in sedentary behaviour (SB), standing, light-intensity physical activity (LIPA), sporadic moderate-vigorous physical activity (sMVPA, accumulated with bouts between 1 and 10 min), 10-min moderate-vigorous physical activity (₁₀MVPA, accumulated with bouts ≥10 min), in addition to self-reported sleeping hours were reported. Fasted whole blood concentrations of total cholesterol, triglyceride, glucose, and glycated haemoglobin, and serum lipoprotein lipase (LPL), interleukin-6 (IL-6), and procollagen III N-terminal propeptide were determined.

Results

Triglyceride concentration appeared to be highly dependent on ₁₀MVPA engagement as the 'low' and 'high' concentration groups engaged in 48% more and 32% less ₁₀MVPA, respectively, relative to the geometric mean of the entire study sample. Time-use composition of the 'low' LPL group's engagement in ₁₀MVPA was 26% less, while the 'high' LPL group was 7.9% more, than the entire study sample. Time-use composition of the 'high' glucose and glycated haemoglobin groups appeared to be similar as both engaged in more Sleep and SB, and less ₁₀MVPA compared to the study sample. Participants with a 'low' IL-6 concentration engaged in 4.8% more Sleep and 2.7% less ₁₀MVPA than the entire study sample. Time-use composition of the Total Cholesterol groups was mixed with the 'low' concentration group engaging in more Standing and ₁₀MVPA but less Sleep, SB, LIPA, and sMVPA than the entire study sample.

Conclusion

Older adults should aim to increase 10MVPA engagement to improve lipid profile and decrease SB engagement to improve glucose profile.

Role of myokines in the development of skeletal muscle insulin resistance and related metabolic defects in type 2 diabetes

Due to its mass, skeletal muscle is the major site of glucose uptake and an important tissue in the development of type 2 diabetes (T2D). Muscles of patients with T2D are affected with insulin resistance and mitochondrial dysfunction, which result in impaired glucose and fatty acid metabolism. A well-established method of managing the muscle metabolic defects occurring in T2D is physical exercise. During exercise, muscles contract and secrete factors called myokines which can act in an autocrine/paracrine fashion to improve muscle energy metabolism. In patients with T2D, plasma levels as well as muscle levels (mRNA and protein) of some myokines are upregulated, while others are downregulated. The signalling pathways of certain myokines are also altered in skeletal muscle of patients with T2D. Taken together, these findings suggest that myokine secretion is an important factor contributing to the development of muscle metabolic defects during T2D. It is also of interest considering that lack of physical activity is closely linked to the occurrence of this disease. The causal relationships between sedentary behavior, factors secreted by skeletal muscle at rest and during contraction and the development of T2D remain to be elucidated. Many myokines shown to influence muscle energy metabolism still have not been characterized in the context of T2D in skeletal muscle specifically. The purpose of this review is to highlight what is known and what remains to be determined regarding myokine secretion in patients with T2D to uncover potential therapeutic targets for the management of this disease.

Dietary feeding pattern does not modulate the loss of muscle mass or the decline in metabolic health during short-term bed rest

Short periods of bed rest lead to the loss of muscle mass and quality. It has been speculated that dietary feeding pattern may have an impact upon muscle protein synthesis rates and, therefore, modulate the loss of muscle mass and quality. We subjected 20 healthy men (age: 25 ± 1 yr, body mass index: 23.8 ± 0.8 kg/m²) to 1 wk of strict bed rest with intermittent (4 meals/day) or continuous (24 h/day) enteral tube feeding. Participants consumed deuterium oxide for 7 days before bed rest and throughout the 7-day bed rest period. Prior to and immediately after bed rest, lean body mass (dual energy X-ray absorptiometry), quadriceps cross-sectional area (CSA; CT), maximal oxygen uptake capacity (V̇o_2peak), and whole body insulin sensitivity (hyperinsulinemic-euglycemic clamp) were assessed. Muscle biopsies were collected 7 days before, 1 day before, and immediately after bed rest to assess muscle tracer incorporation. Bed rest resulted in 0.3 ± 0.3 vs. 0.7 ± 0.4 kg lean tissue loss and a 1.1 ± 0.6 vs. 0.8 ± 0.5% decline in quadriceps CSA in the intermittent vs. continuous feeding group, respectively (both P < 0.05), with no differences between groups (both P > 0.05). Moreover, feeding pattern did not modulate the bed rest-induced decline in insulin sensitivity (-46 ± 3% vs. 39 ± 3%; P < 0.001) or V̇o_2peak (-2.5 ± 2.2 vs. -8.6 ± 2.2%; P < 0.010) (both P > 0.05). Myofibrillar protein synthesis rates during bed rest did not differ between the intermittent and continuous feeding group (1.33 ± 0.07 vs. 1.50 ± 0.13%/day, respectively; P > 0.05). In conclusion, dietary feeding pattern does not modulate the loss of muscle mass or the decline in metabolic health during 1 wk of bed rest in healthy men.

Disuse-induced insulin resistance susceptibility coincides with a dysregulated skeletal muscle metabolic transcriptome

Short-term muscle disuse is characterized by skeletal muscle insulin resistance, although this response is divergent across subjects. The mechanisms regulating inactivity-induced insulin resistance between populations that are more or less susceptible to disuse-induced insulin resistance are not known. RNA sequencing was conducted on vastus lateralis muscle biopsies from subjects before and after bed rest (n = 26) to describe the transcriptome of inactivity-induced insulin resistance. Subjects were separated into Low (n = 14) or High (n = 12) Susceptibility Groups based on the magnitude of change in insulin sensitivity after 5 days of bed rest. Both groups became insulin-resistant after bed rest, and there were no differences between groups in nonmetabolic characteristics (body mass, body mass index, fat mass, and lean mass). The High Susceptibility Group had more genes altered >1.5-fold (426 high versus 391 low) and more than twofold (73 high versus 55 low). Twenty-four genes were altered more than twofold in the High Susceptibility Group that did not change in the Low Susceptibility Group. 95 gene changes correlated with the changes in insulin sensitivity; 6 of these genes changed more than twofold in the High Susceptibility Group. Participants in the High Susceptibility Group were uniquely characterized with muscle gene responses described by a decrease in pathways responsible for lipid uptake and oxidation, decreased capacity for triglyceride export (APOB), increased lipogenesis (i.e., PFKFB3, FASN), and increased amino acid export (SLC43A1). These transcriptomic data provide a comprehensive examination of pathways and genes that may be useful biomarkers, or novel targets to offset muscle disuse-induced insulin resistance. NEW & NOTEWORTHY Short-term muscle disuse results in skeletal muscle insulin resistance through mechanisms that are not fully understood. Following a 5-day bed rest intervention, subjects were divided into High and Low Susceptibility Groups to inactivity-induced insulin resistance. This was followed by a genome-wide transcriptional analysis on muscle biopsy samples to gain insight on divergent insulin sensitivity responses. Our primary finding was that the skeletal muscle of subjects who experienced the most inactivity-induced insulin resistance (high susceptibility) was characterized by a decreased preference for lipid oxidation, increased lipogenesis, and increased amino acid export.

Nandrolone decanoate administration does not attenuate muscle atrophy during a short period of disuse

BACKGROUND

A few days of bed rest or immobilization following injury, disease, or surgery can lead to considerable loss of skeletal muscle mass and strength. It has been speculated that such short, successive periods of muscle disuse may be largely responsible for the age-related loss of muscle mass throughout the lifespan.

OBJECTIVE

To assess whether a single intramuscular injection of nandrolone decanoate prior to immobilization can attenuate the loss of muscle mass and strength in vivo in humans.

DESIGN, SETTING AND PARTICIPANTS

Thirty healthy (22 ± 1 years) men were subjected to 7 days of one-legged knee immobilization by means of a full leg cast with (NAD, n = 15) or without (CON, n = 15) prior intramuscular nandrolone decanoate injection (200 mg).

MEASURES

Before and immediately after immobilization, quadriceps muscle cross-sectional area (CSA) (by means of single-slice computed tomography (CT) scans of the upper leg) and one-legged knee extension strength (one-repetition maximum [1-RM]) were assessed for both legs. Furthermore, muscle biopsies from the immobilized leg were taken before and after immobilization to assess type I and type II muscle fiber cross-sectional area.

RESULTS

Quadriceps muscle CSA decreased during immobilization in both CON and NAD (-6 ± 1% and -6 ± 1%, respectively; main effect of time P<0.01), with no differences between the groups (time × treatment interaction, P = 0.59). Leg muscle strength declined following immobilization (-6 ± 2% in CON and -7 ± 3% in NAD; main effect of time, P<0.05), with no differences between groups (time × treatment interaction, P = 0.55).

CONCLUSIONS

This is the first study to report that nandrolone decanoate administration does not preserve skeletal muscle mass and strength during a short period of leg immobilization in vivo in humans.

Reduced physical activity in young and older adults: metabolic and musculoskeletal implications

BACKGROUND

Although the health benefits of regular physical activity and exercise are well established and have been incorporated into national public health recommendations, there is a relative lack of understanding pertaining to the harmful effects of physical inactivity. Experimental paradigms including complete immobilization and bed rest are not physiologically representative of sedentary living. A useful 'real-world' approach to contextualize the physiology of societal downward shifts in physical activity patterns is that of short-term daily step reduction.

RESULTS

Step-reduction studies have largely focused on musculoskeletal and metabolic health parameters, providing relevant disease models for metabolic syndrome, type 2 diabetes (T2D), nonalcoholic fatty liver disease (NAFLD), sarcopenia and osteopenia/osteoporosis. In untrained individuals, even a short-term reduction in physical activity has a significant impact on skeletal muscle protein and carbohydrate metabolism, causing anabolic resistance and peripheral insulin resistance, respectively. From a metabolic perspective, short-term inactivity-induced peripheral insulin resistance in skeletal muscle and adipose tissue, with consequent liver triglyceride accumulation, leads to hepatic insulin resistance and a characteristic dyslipidaemia. Concomitantly, various inactivity-related factors contribute to a decline in function; a reduction in cardiorespiratory fitness, muscle mass and muscle strength.

CONCLUSIONS

Physical inactivity maybe particularly deleterious in certain patient populations, such as those at high risk of T2D or in the elderly, considering concomitant sarcopenia or osteoporosis. The effects of short-term physical inactivity (with step reduction) are reversible on resumption of habitual physical activity in younger people, but less so in older adults. Nutritional interventions and resistance training offer potential strategies to prevent these deleterious metabolic and musculoskeletal effects.

IMPACT

Individuals at high risk of/with cardiometabolic disease and older adults may be more prone to these acute periods of inactivity due to acute illness or hospitalization. Understanding the risks is paramount to implementing countermeasures.

Plasma Sulphur-Containing Amino Acids, Physical Exercise and Insulin Sensitivity in Overweight Dysglycemic and Normal Weight Normoglycemic Men

Plasma sulphur-containing amino acids and related metabolites are associated with insulin sensitivity, although the mechanisms are unclear. We examined the effect of exercise on this relationship. Dysglycemic (n = 13) and normoglycemic (n = 13) men underwent 45 min cycling before and after 12 weeks exercise intervention. We performed hyperinsulinemic euglycemic clamp, mRNA-sequencing of skeletal muscle and adipose tissue biopsies, and targeted profiling of plasma metabolites by LC-MS/MS. Insulin sensitivity increased similarly in dysglycemic and normoglycemic men after 12 weeks of exercise, in parallel to similar increases in concentration of plasma glutamine, and decreased concentrations of plasma glutamate, cysteine, taurine, and glutathione. Change in plasma concentrations of cysteine and glutathione exhibited the strongest correlations to exercise-improved insulin sensitivity, and expression of a cluster of genes essential for oxidative phosphorylation and fatty acid metabolism in both skeletal muscle and adipose tissue, as well as mitochondria-related genes such as mitofilin. Forty-five min of cycling decreased plasma concentrations of glutamine and methionine, and increased plasma concentrations of glutamate, homocysteine, cystathionine, cysteine, glutathione, and taurine. Similar acute responses were seen in both groups before and after the 12 weeks training period. Both acute and long-term exercise may influence transsulphuration and glutathione biosynthesis, linking exercise-improved insulin sensitivity to oxidative stress and mitochondrial function.

Increased capillary density in skeletal muscle is not associated with impaired insulin sensitivity induced by bed rest in healthy young men

Physical inactivity alters glucose homeostasis in skeletal muscle, potentially developing into overt metabolic disease. The present study sought to investigate the role of skeletal muscle capillarization in glucose tolerance and insulin sensitivity (IS) using a classic human model of physical inactivity. Thirteen healthy males (age = 23 ± 2 years) underwent 4 days of full-time supervised and diet-controlled bed rest. Oral glucose tolerance test, indices of IS (quantitative insulin sensitivity check index (QUICKI), Matsuda index), as well as skeletal muscle biopsies with measurement of fiber type distribution, fiber cross-sectional area (FCSA), capillary-to-fiber ratio (C/F ratio), and capillary density (CD) were assessed prior to and after bed rest. Body weight and composition were unaltered by bed rest. Fasting glucose/insulin ratio (G0/I0 ratio) (−25%, P = 0.016), QUICKI (−7%, P = 0.023), and Matsuda index (−24%, P = 0.003) diminished with bed rest. Skeletal muscle FCSA decreased (−737.4 ± 763.2 μm−2 (−12%), P = 0.005) while C/F ratio was preserved, resulting in augmented CD (+93.9 ± 91.5 capillaries·mm−2 (+37%), P = 0.003) with bed rest. No association was detected between changes in skeletal muscle variables and metabolic outcomes. Independently of bed rest-induced effects, a positive linear relationship was detected between C/F ratio and G0/I0 ratio (β = 17.09, P = 0.021). In conclusion, impaired glucose homeostasis with bed rest is not prevented nor associated with enhanced skeletal muscle capillarization in healthy individuals.

Recent Progress in Space Physiology and Aging

Astronauts coming back from long-term space missions present with different health problems potentially affecting mission performance, involving all functional systems and organs and closely resembling those found in the elderly. This review points out the most recent advances in the literature in areas of expertise in which specific research groups were particularly creative, and as they relate to aging and to possible benefits on Earth for disabled people. The update of new findings and approaches in space research refers especially to neuro-immuno-endocrine-metabolic interactions, optic nerve edema, motion sickness and muscle-tendon-bone interplay and aims at providing the curious - and even possibly naïve young researchers – with a source of inspiration and of creative ideas for translational research.

Pancreatic-islet microvascular vasomotion dysfunction in mice with spinal cord injury

Patients with spinal cord injury (SCI) have an increased risk for developing type 2 diabetes. It is unknown whether the pancreatic-islet microvascular vasomotion is involved. We used female C57BL/6 mice and a 100-kilodyne T10 Infinite Horizons contusion SCI (or T10 laminectomy) to detect blood glucose and pancreatic-islet microvascular vasomotion. Blood glucose obtained from tail vein was detected using one Touch UltraEasy glucometer. Glucose tolerance test was performed by d-glucose administration intraperitoneally. Functional status of pancreatic-islet microvascular vasomotion was determined by laser Doppler monitoring. Expressions of insulin and glucagon were determined by immunohistochemistry. Expression of VEGF-A was determined by immunohistochemistry and Western blotting. Our result demonstrated that blood glucose was significantly increased at 4 h postinjury compared to that in sham group, with continuous higher blood glucose until 4 days postinjury (p < 0.05). SCI mice at day 7 and day 14 had significantly impaired glucose tolerance following glucose administration (p < 0.01). Average blood perfusion, amplitude, frequency, and relative velocity of vasomotion were significantly lower at 6 h postinjury than those in the sham group (p < 0.05), which were gradually upregulated over time. The expression of insulin was decreased, while the expression of glucagon was increased at 6 h postinjury. Similarly, the expression of VEGF-A was significantly decreased at 6 h postinjury, compared to that in sham group (p < 0.05), with slight increases by 14 days postinjury. Our study suggests that the functional status of pancreatic-islet microvascular vasomotion is impaired after injury, which may have implications for developing effective therapeutic interventions for SCI.

The impact of immobilisation and inflammation on the regulation of muscle mass and insulin resistance: different routes to similar end-points

Loss of muscle mass and insulin sensitivity are common phenotypic traits of immobilisation and increased inflammatory burden. The suppression of muscle protein synthesis is the primary driver of muscle mass loss in human immobilisation, and includes blunting of post‐prandial increases in muscle protein synthesis. However, the mechanistic drivers of this suppression are unresolved. Immobilisation also induces limb insulin resistance in humans, which appears to be attributable to the reduction in muscle contraction per se. Again mechanistic insight is missing such that we do not know how muscle senses its “inactivity status” or whether the proposed drivers of muscle insulin resistance are simply arising as a consequence of immobilisation. A heightened inflammatory state is associated with major and rapid changes in muscle protein turnover and mass, and dampened insulin‐stimulated glucose disposal and oxidation in both rodents and humans. A limited amount of research has attempted to elucidate molecular regulators of muscle mass loss and insulin resistance during increased inflammatory burden, but rarely concurrently. Nevertheless, there is evidence that Akt (protein kinase B) signalling and FOXO transcription factors form part of a common signalling pathway in this scenario, such that molecular cross‐talk between atrophy and insulin signalling during heightened inflammation is believed to be possible. To conclude, whilst muscle mass loss and insulin resistance are common end‐points of immobilisation and increased inflammatory burden, a lack of understanding of the mechanisms responsible for these traits exists such that a substantial gap in understanding of the pathophysiology in humans endures.

Physiopathological relationship between chronic obstructive pulmonary disease and insulin resistance

PURPOSE

Chronic obstructive pulmonary disease (COPD) is characterized by persistent and progressive airflow obstruction that is associated with an abnormal chronic inflammatory response in the airways and lungs to noxious particles. COPD often leads to physical inactivity and deconditioning that added to inappropriate/excessive inflammatory responses leads to systemic consequences. Studies have shown that metabolic syndrome and manifested diabetes are more frequent in COPD than in healthy subjects; a possible explanation is that different pathophysiological aspects of COPD can lead to insulin resistance. Thus, this mini-review aims to present the main studies suggesting a pathophysiological relationship between COPD and insulin resistance.

METHODS

A review of literature was conducted using PubMed and Web of Science databases with the aim of searching for studies supporting a relationship between COPD and insulin resistance.

RESULTS

A physiopathological relationship between COPD and insulin resistance was found, supported in part due to common risk factors presented by these two conditions, such as smoking and physical inactivity. Also, systemic effects (worsening of physical inactivity and sedentary behavior, inflammation and oxidative stress, body composition abnormalities) and the corticosteroid treatment of patients with COPD may play a role.

CONCLUSION

Patients with COPD should be screened for abnormalities in insulin sensitivity in order to reduce morbidity and improve health status in this population.