Interactions between insulin and exercise

The paradox of fatty-acid β-oxidation in muscle insulin resistance: Metabolic control and muscle heterogeneity

The skeletal muscle is a metabolically heterogeneous tissue that plays a key role in maintaining whole-body glucose homeostasis. It is well known that muscle insulin resistance (IR) precedes the development of type 2 diabetes. There is a consensus that the accumulation of specific lipid species in the tissue can drive IR. However, the role of the mitochondrial fatty-acid β-oxidation in IR and, consequently, in the control of glucose uptake remains paradoxical: interventions that either inhibit or activate fatty-acid β-oxidation have been shown to prevent IR. We here discuss the current theories and evidence for the interplay between β-oxidation and glucose uptake in IR. To address the underlying intricacies, we (1) dive into the control of glucose uptake fluxes into muscle tissues using the framework of Metabolic Control Analysis, and (2) disentangle concepts of flux and catalytic capacities taking into account skeletal muscle heterogeneity. Finally, we speculate about hitherto unexplored mechanisms that could bring contrasting evidence together. Elucidating how β-oxidation is connected to muscle IR and the underlying role of muscle heterogeneity enhances disease understanding and paves the way for new treatments for type 2 diabetes.

IGF1 promotes human myotube differentiation toward a mature metabolic and contractile phenotype

Skeletal muscle mediates the beneficial effects of exercise, thereby improving insulin sensitivity and reducing the risk for type 2 diabetes. Current human skeletal muscle models in vitro are incapable of fully recapitulating its physiological functions especially muscle contractility. By supplementation of insulin-like growth factor 1 (IGF1), a growth factor secreted by myofibers in vivo, we aimed to overcome these limitations. We monitored the differentiation process starting from primary human CD56-positive myoblasts in the presence/absence of IGF1 in serum-free medium in daily collected samples for 10 days. IGF1-supported differentiation formed thicker multinucleated myotubes showing physiological contraction upon electrical pulse stimulation (EPS) following day 6. Myotubes without IGF1 were almost incapable of contraction. IGF1 treatment shifted the proteome toward skeletal muscle-specific proteins that contribute to myofibril and sarcomere assembly, striated muscle contraction, and ATP production. Elevated PPARGC1A, MYH7, and reduced MYH1/2 suggest a more oxidative phenotype further demonstrated by higher abundance of proteins of the respiratory chain and elevated mitochondrial respiration. IGF1-treatment also upregulated glucose transporter (GLUT)4 and increased insulin-dependent glucose uptake compared with myotubes differentiated without IGF1. To conclude, addition of IGF1 to serum-free medium significantly improves the differentiation of human myotubes that showed enhanced myofibril formation, response to electrical pulse stimulation, oxidative respiratory capacity, and glucose metabolism overcoming limitations of previous standards. This novel protocol enables investigation of muscular exercise on a molecular level.NEW & NOTEWORTHY Human skeletal muscle models are highly valuable to study how exercise prevents type 2 diabetes without invasive biopsies. Current models did not fully recapitulate the function of skeletal muscle especially during exercise. By supplementing insulin-like growth factor 1 (IGF1), the authors developed a functional human skeletal muscle model characterized by inducible contractility and increased oxidative and insulin-sensitive metabolism. The novel protocol overcomes the limitations of previous standards and enables investigation of exercise on a molecular level.

Unraveling athletic performance: Transcriptomics and external load monitoring in handball competition

OBJECTIVE

This study aims to comprehend the impact of handball practice on sub-elite athletes by investigating transcriptomic changes that occur during a match. The primary focus encompasses a dual objective: firstly, to identify and characterize these transcriptomic alterations, and secondly, to establish correlations between internal factors (gene expression), and external loads measured through Electronic Performance and Tracking Systems (EPTS variables). Ultimately, this comprehensive analysis seeks to evaluate both acute and chronic responses to exercise within the context of handball training.

METHODS

The study included sixteen elite male athletes from the FC Barcelona handball second team. Blood samples were extracted at three different time points: before the match at baseline levels (T1), immediately upon completion (T2), and 24 hours after completion (T3). Differential gene expression, Gene Ontology Term and Kyoto Encyclopedia of Genes and Genomes pathway enrichment analyses were conducted in two comparisons: Comparison 1 (T1 vs T2) and Comparison 2 (T1 vs T3). Further, the correlation between gene expression levels and training variables (external load) was conducted.

RESULTS

In T1 vs T2, 3717 of the 14632 genes detected were differentially expressed (adjusted p-value < 0.05), and enrichment of terms related to the immune system, mitochondria, and metabolic processes was found. Further, significant linear correlations were obtained between High-Speed running (HSR) and high-intensity variables such as acceleration ACC and deceleration DEC values with amino acids, and inflammatory and oxidative environment-related pathways, both in chronic and acute response.

CONCLUSIONS

This research highlights the effects of external workload on elite athletes during a handball match and throughout the season. The study identifies deregulation in the immune system, mitochondrial functions, and various metabolic pathways during the match. Additionally, it establishes correlations between the external load and pathways associated with amino acids, inflammation, oxidative environment, and regulation. These findings offer insights into the immediate and chronic responses of athletes to physical effort.

Exercising Safely with the MiniMed™ 780G Automated Insulin Delivery System

The physical and psychological benefits of exercise are particularly pertinent to people with type 1 diabetes (T1D). The variability in subcutaneous insulin absorption and the delay in offset and onset in glucose lowering action impose limitations, given the rapidly varying insulin requirements with exercise. Simultaneously, there are challenges to glucose monitoring. Consequently, those with T1D are less likely to exercise because of concerns regarding glucose instability. While glucose control with exercise can be enhanced using automated insulin delivery (AID), all commercially available AID systems remain limited by the pharmacokinetics of subcutaneous insulin delivery. Although glycemic responses may vary with exercises of differing intensities and durations, the principles providing the foundation for guidelines include minimization of insulin on board before exercise commencement, judicious and timely carbohydrate supplementation, and when possible, a reduction in insulin delivered in anticipation of planned exercise. There is an increasing body of evidence in support of superior glucose control with AID over manual insulin dosing in people in T1D who wish to exercise. The MiniMed™ 780G AID system varies basal insulin delivery with superimposed automated correction boluses. It incorporates a temporary (elevated glucose) target of 8.3 mmol/L (150 mg/dL) and when it is functioning, the autocorrection boluses are stopped. As the device has recently become commercially available, there are limited data assessing glucose control with the MiniMed™ 780G under exercise conditions. Importantly, when exercise was planned and implemented within consensus guidelines, %time in range and %time below range targets were met. A practical approach to exercising with the device is provided with illustrative case studies. While there are limitations to spontaneity imposed on any AID device due to the pharmacokinetics associated with the subcutaneous delivery of current insulin formulations, the MiniMed™ 780G system provides people with T1D an excellent option for exercising safely if the appropriate strategies are implemented.

Case report: catamenial hyperglycemia: the trigger of recurrent DKA in a female patient with three-year follow-up

Background

Catamenial hyperglycemia is a rare type of spontaneous, recurring Diabetic Ketoacidosis(DKA) in females during the luteal phase, most commonly observed in type 1 diabetes mellitus. Even with controlled serum glucose levels, adherence to a diabetic diet, medications, and in the absence of other common influencing factors such as infection, glucose levels tend to increase during the premenstrual period. This uncommon issue related to the menstrual cycle phase has not been extensively researched. Therefore, this study aims to diagnose catamenial hyperglycemia promptly and initiate early treatment to prevent complications.

Case report

We presented a case of a 19-year-old girl who experienced recurrent DKA during the premenstrual period, without an apparent cause. She was admitted multiple times to various hospitals and sought consultations, undergoing numerous laboratory and imaging examinations, yet the etiology remained elusive. Ultimately, she received a diagnosis of catamenial diabetic hyperglycemia. To prevent recurrence of complications associated with catamenial hyperglycemia, we initiated a comprehensive approach which included continuous glucose monitoring, adherence to a strict diabetic diet, diabetic health education, regular exercise, timely medication administration, and increase in insulin dosage during the premenstrual period based on glucose levels.

Conclusions

Although catamenial hyperglycemia is rare, it should be considered a cause of recurrent hyperglycemia in any postpubertal female to prevent complications. The specific underlying mechanisms responsible for catamenial hyperglycemia or DKA remain unidentified.

Transcellular Barriers to Glucose Delivery in the Body

Glucose is the universal fuel of most mammalian cells, and it is largely replenished through dietary intake. Glucose availability to tissues is paramount for the maintenance of homeostatic energetics and, hence, supply should match demand by the consuming organs. In its journey through the body, glucose encounters cellular barriers for transit at the levels of the absorbing intestinal epithelial wall, the renal epithelium mediating glucose reabsorption, and the tight capillary endothelia (especially in the brain). Glucose transiting through these cellular barriers must escape degradation to ensure optimal glucose delivery to the bloodstream or tissues. The liver, which stores glycogen and generates glucose de novo, must similarly be able to release it intact to the circulation. We present the most up-to-date knowledge on glucose handling by the gut, liver, brain endothelium, and kidney, and discuss underlying molecular mechanisms and open questions. Diseases associated with defects in glucose delivery and homeostasis are also briefly addressed. We propose that the universal problem of sparing glucose from catabolism in favor of translocation across the barriers posed by epithelia and endothelia is resolved through common mechanisms involving glucose transfer to the endoplasmic reticulum, from where glucose exits the cells via unconventional cellular mechanisms.

Athletes' nutritional demands: a narrative review of nutritional requirements

Nutrition serves as the cornerstone of an athlete's life, exerting a profound impact on their performance and overall well-being. To unlock their full potential, athletes must adhere to a well-balanced diet tailored to their specific nutritional needs. This approach not only enables them to achieve optimal performance levels but also facilitates efficient recovery and reduces the risk of injuries. In addition to maintaining a balanced diet, many athletes also embrace the use of nutritional supplements to complement their dietary intake and support their training goals. These supplements cover a wide range of options, addressing nutrient deficiencies, enhancing recovery, promoting muscle synthesis, boosting energy levels, and optimizing performance in their respective sports or activities. The primary objective of this narrative review is to comprehensively explore the diverse nutritional requirements that athletes face to optimize their performance, recovery, and overall well-being. Through a thorough literature search across databases such as PubMed, Google Scholar, and Scopus, we aim to provide evidence-based recommendations and shed light on the optimal daily intakes of carbohydrates, protein, fats, micronutrients, hydration strategies, ergogenic aids, nutritional supplements, and nutrient timing. Furthermore, our aim is to dispel common misconceptions regarding sports nutrition, providing athletes with accurate information and empowering them in their nutritional choices.

Acute effects of exercise intensity on butyrylcholinesterase and ghrelin in young men: A randomized controlled study

Background/objectives

Butyrylcholinesterase (BChE), a liver-derived enzyme that hydrolyzes acylated ghrelin to des-acylated ghrelin, may trigger a potential mechanism responsible for the acute exercise-induced suppression of acylated ghrelin. However, studies examining the effects of an acute bout of high-intensity exercise on BChE and acylated ghrelin have yielded inconsistent findings. This study aimed to examine the acute effects of exercise intensity on BChE, acylated ghrelin and des-acylated ghrelin concentrations in humans.

Methods

Fifteen young men (aged 22.7 ± 1.8 years, mean ± standard deviation) completed three, half-day laboratory-based trials (i.e., high-intensity exercise, low-intensity exercise and control), in a random order. In the exercise trials, the participants ran for 60 min (from 09:30 to 10:30) at a speed eliciting 70 % (high-intensity) or 40 % (low-intensity) of their maximum oxygen uptake and then rested for 90 min. In the control trial, participants sat on a chair for the entire trial (from 09:30 to 12:00). Venous blood samples were collected at 09:30, 10:00, 10:30, 11:00, 11:30 and 12:00.

Results

The BChE concentration was not altered over time among the three trials. Total acylated and des-acylated ghrelin area under the curve during the first 60 min (i.e., from 0 min to 60 min) of the main trial were lower in the high-intensity exercise trial than in the control (acylated ghrelin, mean difference: 62.6 pg/mL, p < 0.001; des-acylated ghrelin, mean difference: 31.4 pg/mL, p = 0.035) and the low-intensity exercise trial (acylated ghrelin, mean difference: 87.7 pg/mL, p < 0.001; des-acylated ghrelin, mean difference: 43.0 pg/mL, p = 0.042).

Conclusion

The findings suggest that BChE may not be involved in the modulation of ghrelin even though lowered acylated ghrelin concentration was observed after high-intensity exercise.

Association between pre-exercise food ingestion timing and reactive hypoglycemia: Insights from a large database of continuous glucose monitoring data

Using a large database of continuous glucose monitoring (CGM) data, this study aimed to gain insights into the association between pre-exercise food ingestion timing and reactive hypoglycemia. A group of 6,761 users self-reported 48,799 pre-exercise food ingestion events and logged minute-by-minute CGM, which was used to detect reactive hypoglycemia (<70 mg/dL) in the first 30 min of exercise. A linear and a non-linear binomial logistic regression model was used to investigate the association between food ingestion timing and the probability of experiencing reactive hypoglycemia. An analysis of variance was conducted to compare the predictive ability of the models. On average, reactive hypoglycemia was detected in 8.34 ± 3.04% of the total events, with <15% of individuals experiencing hypoglycemia in >20% of their events. The majority of the reactive hypoglycemia events were found with pre-exercise food timing between ∼30 and ∼90 min, with a peak at ∼60 min. The superior accuracy (62.05 vs 45.1%) and F-score (0.75 vs 0.59) of the non-linear vs the linear model were statistically superior (P < 0.0001). These results support the notion of an unfavourable 30-to-90 min pre-exercise food ingestion time window which can significantly impact the likelihood of reactive hypoglycemia in some individuals.

Repeated oral sucrose dosing after the second wind is unnecessary in patients with McArdle disease: Results from a randomized, placebo-controlled, double-blind, cross-over study

It is well-established that oral sucrose ingested shortly before exercise improves early exercise tolerance in individuals with McArdle disease. This is by supplying blood-borne glucose for muscle metabolism to compensate for the blocked glycogenolysis. The present study investigated if individuals with McArdle disease could benefit further from repeated sucrose ingestion during prolonged exercise. In this double-blind, placebo-controlled, cross-over study, the participants were randomized to ingest either sucrose or placebo first and subsequently the opposite on two separate days. The participants ingested the drink 10 min before and thrice (after 10, 25, and 40 min) during a 60-min submaximal exercise test on a cycle ergometer. The primary outcome was exercise capacity as indicated by heart rate (HR) and perceived exertion (PE) responses to exercise. Secondary outcomes included changes in blood metabolites, insulin and carbohydrate, and fatty acid oxidation rates during exercise. Nine participants with McArdle disease were included in the study. We confirmed improvement of exercise capacity with oral sucrose vs. placebo during early exercise (pre-second wind) indicated by lower peak HR and PE (p < 0.02). We found no further beneficial effect with repeated sucrose versus placebo ingestion during prolonged exercise, as indicated by no difference in HR or PE post-second wind (p > 0.05). Glucose, lactate, insulin, and carbohydrate oxidation rates increased, and fatty acid oxidation decreased with sucrose versus placebo (p ≤ 0.0002). We can conclude that repeated sucrose ingestion is not recommended during prolonged exercise. This finding can prevent excessive caloric intake and reduce the risk of obesity and insulin resistance.

AMPK and the Endocrine Control of Metabolism

Complex multicellular organisms require a coordinated response from multiple tissues to maintain whole-body homeostasis in the face of energetic stressors such as fasting, cold, and exercise. It is also essential that energy is stored efficiently with feeding and the chronic nutrient surplus that occurs with obesity. Mammals have adapted several endocrine signals that regulate metabolism in response to changes in nutrient availability and energy demand. These include hormones altered by fasting and refeeding including insulin, glucagon, glucagon-like peptide-1, catecholamines, ghrelin, and fibroblast growth factor 21; adipokines such as leptin and adiponectin; cell stress-induced cytokines like tumor necrosis factor alpha and growth differentiating factor 15, and lastly exerkines such as interleukin-6 and irisin. Over the last 2 decades, it has become apparent that many of these endocrine factors control metabolism by regulating the activity of the AMPK (adenosine monophosphate-activated protein kinase). AMPK is a master regulator of nutrient homeostasis, phosphorylating over 100 distinct substrates that are critical for controlling autophagy, carbohydrate, fatty acid, cholesterol, and protein metabolism. In this review, we discuss how AMPK integrates endocrine signals to maintain energy balance in response to diverse homeostatic challenges. We also present some considerations with respect to experimental design which should enhance reproducibility and the fidelity of the conclusions.

NOX2 deficiency exacerbates diet-induced obesity and impairs molecular training adaptations in skeletal muscle

The production of reactive oxygen species (ROS) by NADPH oxidase (NOX) 2 has been linked to both insulin resistance and exercise training adaptations in skeletal muscle. This study explores the previously unexamined role of NOX2 in the interplay between diet-induced insulin resistance and exercise training (ET). Using a mouse model that harbors a point mutation in the essential NOX2 regulatory subunit, p47phox (Ncf1*), we investigated the impact of this mutation on various metabolic adaptations. Wild-type (WT) and Ncf1* mice were assigned to three groups: chow diet, 60% energy fat diet (HFD), and HFD with access to running wheels (HFD + E). After a 16-week intervention, a comprehensive phenotypic assessment was performed, including body composition, glucose tolerance, energy intake, muscle insulin signaling, redox-related proteins, and mitochondrial adaptations. The results revealed that NOX2 deficiency exacerbated the impact of HFD on body weight, body composition, and glucose intolerance. Moreover, in Ncf1* mice, ET did not improve glucose tolerance or increase muscle cross-sectional area. ET normalized body fat independently of genotype. The lack of NOX2 activity during ET reduced several metabolic adaptations in skeletal muscle, including insulin signaling and expression of Hexokinase II and oxidative phosphorylation complexes. In conclusion, these findings suggest that NOX2 mediates key beneficial effects of exercise training in the context of diet-induced obesity.

GDF15 increases insulin action in the liver and adipose tissue via a β-adrenergic receptor-mediated mechanism

Growth differentiation factor 15 (GDF15) induces weight loss and increases insulin action in obese rodents. Whether and how GDF15 improves insulin action without weight loss is unknown. Obese rats were treated with GDF15 and displayed increased insulin tolerance 5 h later. Lean and obese female and male mice were treated with GDF15 on days 1, 3, and 5 without weight loss and displayed increased insulin sensitivity during a euglycemic hyperinsulinemic clamp on day 6 due to enhanced suppression of endogenous glucose production and increased glucose uptake in WAT and BAT. GDF15 also reduced glucagon levels during clamp independently of the GFRAL receptor. The insulin-sensitizing effect of GDF15 was completely abrogated in GFRAL KO mice and also by treatment with the β-adrenergic antagonist propranolol and in β1,β2-adrenergic receptor KO mice. GDF15 activation of the GFRAL receptor increases β-adrenergic signaling, in turn, improving insulin action in the liver and white and brown adipose tissue.

Multitissue responses to exercise: a MoTrPAC feasibility study

We assessed the feasibility of the Molecular Transducers of Physical Activity Consortium (MoTrPAC) human adult clinical exercise protocols, while also documenting select cardiovascular, metabolic, and molecular responses to these protocols. After phenotyping and familiarization sessions, 20 subjects (25 ± 2 yr, 12 M, 8 W) completed an endurance exercise bout (n = 8, 40 min cycling at 70% V̇o2max), a resistance exercise bout (n = 6, ∼45 min, 3 sets of ∼10 repetition maximum, 8 exercises), or a resting control period (n = 6, 40 min rest). Blood samples were taken before, during, and after (10 min, 2 h, and 3.5 h) exercise or rest for levels of catecholamines, cortisol, glucagon, insulin, glucose, free fatty acids, and lactate. Heart rate was recorded throughout exercise (or rest). Skeletal muscle (vastus lateralis) and adipose (periumbilical) biopsies were taken before and ∼4 h following exercise or rest for mRNA levels of genes related to energy metabolism, growth, angiogenesis, and circadian processes. Coordination of the timing of procedural components (e.g., local anesthetic delivery, biopsy incisions, tumescent delivery, intravenous line flushes, sample collection and processing, exercise transitions, and team dynamics) was reasonable to orchestrate while considering subject burden and scientific objectives. The cardiovascular and metabolic alterations reflected a dynamic and unique response to endurance and resistance exercise, whereas skeletal muscle was transcriptionally more responsive than adipose 4 h postexercise. In summary, the current report provides the first evidence of protocol execution and feasibility of key components of the MoTrPAC human adult clinical exercise protocols. Scientists should consider designing exercise studies in various populations to interface with the MoTrPAC protocols and DataHub.NEW & NOTEWORTHY This study highlights the feasibility of key aspects of the MoTrPAC adult human clinical protocols. This initial preview of what can be expected from acute exercise trial data from MoTrPAC provides an impetus for scientists to design exercise studies to interlace with the rich phenotypic and -omics data that will populate the MoTrPAC DataHub at the completion of the parent protocol.

Associations between spirometric measures and exercise capacity in type 2 diabetes

BACKGROUND

Physical exercise aids glycemic control and the prevention of diabetes-related complications. However, exercise beyond an individual's pulmonary functional capacity may be detrimental. To date, little is known about the relationship between pulmonary function and exercise capacity in people with type 2 diabetes (T2D). We investigated the relationship between pulmonary function and exercise capacity in T2D.

METHODS

Spirometry and 6-min walk test (6MWT) were conducted for 263 systematically sampled adults with T2D without primary heart/lung disease. The primary measure of exercise capacity was the 6-min walk distance (6MWD); impaired exercise capacity was defined as 6MWD<400 m. Logistic regression analyses were used to assess the associations between spirometric measures and exercise capacity with adjustments for age, sex, height, body mass index, diabetes duration, glycated hemoglobin concentration, smoking, suboptimum blood pressure control, and total cholesterol concentration.

RESULTS

Compared with individuals with normal spirometry, those with pulmonary restriction/obstruction had significantly lower 6MWD (404.67 m vs. 451.70),p < 0.001). The proportion of individuals with impaired exercise capacity was higher in individuals with impaired pulmonary function compared with those with normal pulmonary function (39.8% vs. 20.7%,p = 0.001). In the unadjusted models, decreasing Z-score FEV1 [odds ratio 1.40, 95% confidence interval (1.07-1.83),p = 0.013] and Z-score FVC [1.37 (1.06-1.76),0.016], but not Z-score FEV1/FVC ratio [1.00 (0.78-1.27),0.972] were significantly associated with impaired exercise capacity. In the fully adjusted model, the strength of association remained statistically significant for Z-score FEV1 [1.60 (1.06-2.41),0.025] but not Z-score FVC [1.48 (0.98-2.23),0.065].

CONCLUSIONS

Our study shows inverse associations between FEV1 and impaired exercise capacity in T2D, Future research could characterize optimal exercise levels based on a patient's FEV1.

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.

Effect of exercise training on insulin-stimulated glucose disposal: a systematic review and meta-analysis of randomized controlled trials

BACKGROUND AND OBJECTIVE

The effect of exercise training on whole-body insulin sensitivity has not been systematically summarized. We aimed to summarize the data from randomized controlled trials evaluating the effect of exercise training on insulin action, in adults.

SUBJECTS

MEDLINE, EMBASE, and CENTRAL databases were searched until January 2021. Randomized controlled trials lasting ≥4 weeks, including adults, and evaluating the effect of exercise on insulin-stimulated glucose disposal measured using the hyperinsulinemic euglycemic clamp, were included.

METHODS

Three reviewers extracted summary data from published trials. The primary outcome was insulin-stimulated glucose disposal. Standardized weighted mean differences (SMD) in glucose disposal between intervention and control were compared. The PEDro scale was used to assess risk of bias.

RESULTS

We included 25 trials (36 interventions, N = 851). Exercise increased insulin-stimulated glucose disposal relative to control, SMD = 0.52 (95% confidence interval [CI]: 0.39, 0.65; p < 0.001; I2 = 47%) without significantly suppressing hepatic glucose production. In trials without isotopic tracers, exercise increased glucose disposal (SMD = 0.63; 95% CI: 0.48, 0.77; p < 0.001, I2 = 55%). In trials with isotopic tracers, exercise increased glucose disposal only when tracers were added to the exogenous glucose used for clamping (SMD = 0.34; 95% CI: 0.03, 0.66, p = 0.034. I2 = 0%). In a meta-regression model including aerobic exercise, weight change, and tracer technique, only percent weight change explained between trial heterogeneity (β = 0.069; 95% CI: 0.005, 0.013). The PEDro rating indicated relatively low risk of bias (5.8 ± 0.22).

CONCLUSIONS

Exercise training for at least four weeks significantly increases insulin-stimulated glucose disposal. Weight loss maximizes the effect and may be needed to improve hepatic insulin sensitivity. Differences in tracer methodology contribute to divergent outcomes and should be considered when assessing conclusions from research examining the effect of exercise on insulin action.

REGISTRATION

PROSPERO (CRD42019124381).

Is There an Optimal Time of Day for Exercise? A Commentary on When to Exercise for People Living With Type 1 or Type 2 Diabetes

Exercise is a cornerstone of diabetes self-care because of its association with many health benefits. Several studies that have explored the best time of day to exercise to inform clinical recommendations have yielded mixed results. For example, for people with prediabetes or type 2 diabetes, there may be benefits to timing exercise to occur after meals, whereas people with type 1 diabetes may benefit from performing exercise earlier in the day. One common thread is the health benefits of consistent exercise, suggesting that the issue of exercise timing may be secondary to the goal of helping people with diabetes establish an exercise routine that best fits their life.

Effects of short-term endurance and strength exercise in the molecular regulation of skeletal muscle in hyperinsulinemic and hyperglycemic Slc2a4+/- mice

OBJECTIVE

Intriguingly, hyperinsulinemia, and hyperglycemia can predispose insulin resistance, obesity, and type 2 diabetes, leading to metabolic disturbances. Conversely, physical exercise stimulates skeletal muscle glucose uptake, improving whole-body glucose homeostasis. Therefore, we investigated the impact of short-term physical activity in a mouse model (Slc2a4+/-) that spontaneously develops hyperinsulinemia and hyperglycemia even when fed on a chow diet.

METHODS

Slc2a4+/- mice were used, that performed 5 days of endurance or strength exercise training. Further analysis included physiological tests (GTT and ITT), skeletal muscle glucose uptake, skeletal muscle RNA-sequencing, mitochondrial function, and experiments with C2C12 cell line.

RESULTS

When Slc2a4+/- mice were submitted to the endurance or strength training protocol, improvements were observed in the skeletal muscle glucose uptake and glucose metabolism, associated with broad transcriptomic modulation, that was, in part, related to mitochondrial adaptations. The endurance training, but not the strength protocol, was effective in improving skeletal muscle mitochondrial activity and unfolded protein response markers (UPRmt). Moreover, experiments with C2C12 cells indicated that insulin or glucose levels could contribute to these mitochondrial adaptations in skeletal muscle.

CONCLUSIONS

Both short-term exercise protocols were efficient in whole-body glucose homeostasis and insulin resistance. While endurance exercise plays an important role in transcriptome and mitochondrial activity, strength exercise mostly affects post-translational mechanisms and protein synthesis in skeletal muscle. Thus, the performance of both types of physical exercise proved to be a very effective way to mitigate the impacts of hyperglycemia and hyperinsulinemia in the Slc2a4+/- mouse model.

Acute and long-term exercise adaptation of adipose tissue and skeletal muscle in humans: a matched transcriptomics approach after 8-week training-intervention

BACKGROUND

Exercise exerts many health benefits by directly inducing molecular alterations in physically utilized skeletal muscle. Molecular adaptations of subcutaneous adipose tissue (SCAT) might also contribute to the prevention of metabolic diseases.

AIM

To characterize the response of human SCAT based on changes in transcripts and mitochondrial respiration to acute and repeated bouts of exercise in comparison to skeletal muscle.

METHODS

Sedentary participants (27 ± 4 yrs) with overweight or obesity underwent 8-week supervised endurance exercise 3×1h/week at 80% VO2peak. Before, 60 min after the first and last exercise bout and 5 days post intervention, biopsies were taken for transcriptomic analyses and high-resolution respirometry (n = 14, 8 female/6 male).

RESULTS

In SCAT, we found 37 acutely regulated transcripts (FC > 1.2, FDR < 10%) after the first exercise bout compared to 394, respectively, in skeletal muscle. Regulation of only 5 transcripts overlapped between tissues highlighting their differential response. Upstream and enrichment analyses revealed reduced transcripts of lipid uptake, storage and lipogenesis directly after exercise in SCAT and point to β-adrenergic regulation as potential major driver. The data also suggest an exercise-induced modulation of the circadian clock in SCAT. Neither term was associated with transcriptomic changes in skeletal muscle. No evidence for beigeing/browning was found in SCAT along with unchanged respiration.

CONCLUSIONS

Adipose tissue responds completely distinct from adaptations of skeletal muscle to exercise. The acute and repeated reduction in transcripts of lipid storage and lipogenesis, interconnected with a modulated circadian rhythm, can counteract metabolic syndrome progression toward diabetes.

Behavioral state-dependent modulation of insulin-producing cells in Drosophila

Insulin signaling plays a pivotal role in metabolic control and aging, and insulin accordingly is a key factor in several human diseases. Despite this importance, the in vivo activity dynamics of insulin-producing cells (IPCs) are poorly understood. Here, we characterized the effects of locomotion on the activity of IPCs in Drosophila. Using in vivo electrophysiology and calcium imaging, we found that IPCs were strongly inhibited during walking and flight and that their activity rebounded and overshot after cessation of locomotion. Moreover, IPC activity changed rapidly during behavioral transitions, revealing that IPCs are modulated on fast timescales in behaving animals. Optogenetic activation of locomotor networks ex vivo, in the absence of actual locomotion or changes in hemolymph sugar levels, was sufficient to inhibit IPCs. This demonstrates that the behavioral state-dependent inhibition of IPCs is actively controlled by neuronal pathways and is independent of changes in glucose concentration. By contrast, the overshoot in IPC activity after locomotion was absent ex vivo and after starvation, indicating that it was not purely driven by feedforward signals but additionally required feedback derived from changes in hemolymph sugar concentration. We hypothesize that IPC inhibition during locomotion supports mobilization of fuel stores during metabolically demanding behaviors, while the rebound in IPC activity after locomotion contributes to replenishing muscle glycogen stores. In addition, the rapid dynamics of IPC modulation support a potential role of insulin in the state-dependent modulation of sensorimotor processing.

Exercise in adults with type 1 diabetes mellitus

Regular physical activity improves cardiometabolic and musculoskeletal health, helps with weight management, improves cognitive and psychosocial functioning, and is associated with reduced mortality related to cancer and diabetes mellitus. However, turnover rates of glucose in the blood increase dramatically during exercise, which often results in either hypoglycaemia or hyperglycaemia as well as increased glycaemic variability in individuals with type 1 diabetes mellitus (T1DM). A complex neuroendocrine response to an acute exercise session helps to maintain circulating levels of glucose in a fairly tight range in healthy individuals, while several abnormal physiological processes and limitations of insulin therapy limit the capacity of people with T1DM to exercise in a normoglycaemic state. Knowledge of the acute and chronic effects of exercise and regular physical activity is critical for the formulation of clinical strategies for the management of insulin and nutrition for active patients with T1DM. Emerging diabetes-related technologies, such as continuous glucose monitors, automated insulin delivery systems and the administration of solubilized glucagon, are demonstrating efficacy for preserving glucose homeostasis during and after exercise in this population of patients. This Review highlights the beneficial effects of regular exercise and details the complex endocrine and metabolic responses to different types of exercise for adults with T1DM. An overview of basic clinical strategies for the preservation of glucose homeostasis using emerging technologies is also provided.

Sclerostin Influences Exercise-Induced Adaptations in Body Composition and White Adipose Tissue Morphology in Male Mice

Sclerostin is an inhibitor of the osteogenic Wnt/β-catenin signaling pathway that also has an endocrine role in regulating adipocyte differentiation and metabolism. Additionally, subcutaneous white adipose tissue (scWAT) sclerostin content decreases following exercise training (EXT). Therefore, we hypothesized that EXT-induced reductions in adipose tissue sclerostin may play a role in regulating adaptations in body composition and whole-body metabolism. To test this hypothesis, 10-week-old male C57BL/6J mice were either sedentary (SED) or performing 1 hour of treadmill running at ~65% to 70% maximum oxygen consumption (VO_2max ) 5 day/week (EXT) for 4 weeks and had subcutaneous injections of either saline (C) or recombinant sclerostin (S) (0.1 mg/kg body mass) 5 day/week; thus, making four groups (SED-C, EXT-C, SED-S, and EXT-S; n = 12/group). No differences in body mass were observed between experimental groups, whereas food intake was higher in EXT (p = 0.03) and S (p = 0.08) groups. There was a higher resting energy expenditure in all groups compared to SED-C. EXT-C had increased lean mass and decreased fat mass percentage compared to SED-C and SED-S. No differences in body composition were observed in either the SED-S or EXT-S groups. Lower scWAT (inguinal), epididymal white adipose tissue (eWAT) (visceral epididymal) mass, and scWAT adipocyte cell size and increased percentage of multilocular cells in scWAT were observed in the EXT-C group compared to SED-C, whereas lower eWAT was only observed in the EXT-S group. EXT mice had increased scWAT low-density lipoprotein receptor-related protein 4 (Lrp4) and mitochondrial content and sclerostin treatment only inhibited increased Lrp4 content with EXT. Together, these results provide evidence that reductions in resting sclerostin with exercise training may influence associated alterations in energy metabolism and body composition, particularly in scWAT. © 2023 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).

Evolution of the diagnostic value of "the sugar of the blood": hitting the sweet spot to identify alterations in glucose dynamics

In this paper, we provide an overview of the evolution of the definition of hyperglycemia during the past century and the alterations in glucose dynamics that cause fasting and postprandial hyperglycemia. We discuss how extensive mechanistic, physiological research into the factors and pathways that regulate the appearance of glucose in the circulation and its uptake and metabolism by tissues and organs has contributed knowledge that has advanced our understanding of different types of hyperglycemia, namely prediabetes and diabetes and their subtypes (impaired fasting plasma glucose, impaired glucose tolerance, combined impaired fasting plasma glucose, impaired glucose tolerance, type 1 diabetes, type 2 diabetes, gestational diabetes mellitus), their relationships with medical complications, and how to prevent and treat hyperglycemia.

Skeletal muscle mechanisms contributing to improved glycemic control following intense interval exercise and training

High-intensity and sprint interval training (HIIT and SIT, respectively) enhance insulin sensitivity and glycemic control in both healthy adults and those with cardiometabolic diseases. The beneficial effects of intense interval training on glycemic control include both improvements seen in the hours to days following a single session of HIIT/SIT and those which accrue with chronic training. Skeletal muscle is the largest site of insulin-stimulated glucose uptake and plays an integral role in the beneficial effects of exercise on glycemic control. Here we summarize the skeletal muscle responses that contribute to improved glycemic control during and following a single session of interval exercise and evaluate the relationship between skeletal muscle remodelling and improved insulin sensitivity following HIIT/SIT training interventions. Recent evidence suggests that targeting skeletal muscle mechanisms via nutritional interventions around exercise, particularly with carbohydrate manipulation, can enhance the acute glycemic benefits of HIIT. There is also some evidence of sex-based differences in the glycemic benefits of intense interval exercise, with blunted responses observed after training in females relative to males. Differences in skeletal muscle metabolism between males and females may contribute to sex differences in insulin sensitivity following HIIT/SIT, but well-controlled studies evaluating purported muscle mechanisms alongside measurement of insulin sensitivity are needed. Given the greater representation of males in muscle physiology literature, there is also a need for more research involving female-only cohorts to enhance our basic understanding of how intense interval training influences muscle insulin sensitivity in females across the lifespan.

Effect of sera from elite athletes on cytokine secretion and insulin signaling in preadipocytes and skeletal muscle cells

Introduction: The immunomodulatory effect of physical activity can impact insulin signaling differentially in adipose tissues and skeletal muscle cells, depending on sport intensity. In this study, the effect of serum from elite athletes with varying endurance levels and playing different power sports on cytokine secretion and insulin signaling in preadipocyte and skeletal muscle cell lines was investigated. Methods: Preadipocytes (3T3-L1) and skeletal muscle cells (C2C12) were cultured in media containing pooled sera from elite athletes who play high-endurance (HE), high-power (HP), or low-endurance/low-power (LE/LP) sports for 72 h. Secreted cytokines (IL-6 and TNF-alpha) were assessed in the supernatant, and insulin signaling phosphoproteins levels were measured in lysates following treatment using cells multiplex immunoassays. Results: Sera from LE/LP and HP induced TNF-α secretion in C2C12, while serum from HE reduced IL-6 secretion compared to non-athlete serum control. All elite athlete sera groups caused decreased insulin sensitivity in 3T3-L1 cells, whereas in C2C12 cells, only HE athlete serum reduced insulin signaling, while LE/LP and HP caused increased insulin sensitivity. Conclusion: Sera from elite athletes of different sport disciplines can affect the inflammatory status and insulin signaling of preadipocytes and myoblasts differently, with risk of developing insulin resistance. Furthermore, investigation of the functional relevance of these effects on exercise physiology and pathophysiology is warranted.

The Influence of Family History of Type 2 Diabetes on Metabolism during Submaximal Aerobic Exercise and in the Recovery Period in Postmenopausal Women

Aging and family history of type 2 diabetes (T2D) are known risk factors of T2D. Younger first-degree relatives (FDR) of T2D patients have shown early metabolic alterations, which could limit exercise's ability to prevent T2D. Thus, the objective was to determine whether exercise metabolism was altered during submaximal exercise in FDR postmenopausal women. Nineteen inactive postmenopausal women (control: 10, FDR: 9) aged 60 to 75 years old underwent an incremental test on a cycle ergometer with intensity ranging from 40 to 70% of peak power output. Participants consumed 50 mg of 13C-palmitate 2 h before the test. At the end of each stage, glucose, lactate, glycerol, non-esterified fatty acids and 13C-palmitate were measured in plasma, and 13CO2 was measured in breath samples. Gas exchanges and heart rate were both monitored continuously. There were no between-group differences in substrate oxidation, plasma substrate concentrations or 13C recovered in plasma or breath. Interestingly, despite exercising at a similar relative intensity to control, FDR were consistently at a lower percentage of heart rate reserve. Overall, substrate plasma concentration and oxidation are not affected by family history of T2D in postmenopausal women and therefore not a participating mechanism in the altered response to exercise previously reported. More studies are required to better understand the mechanisms involved in this response.

Involvement of the extracellular matrix and integrin signalling proteins in skeletal muscle glucose uptake

Whole-body euglycaemia is partly maintained by two cellular processes that encourage glucose uptake in skeletal muscle, the insulin- and contraction-stimulated pathways, with research suggesting convergence between these two processes. The normal structural integrity of the skeletal muscle requires an intact actin cytoskeleton as well as integrin-associated proteins, and thus those structures are likely fundamental for effective glucose uptake in skeletal muscle. In contrast, excessive extracellular matrix (ECM) remodelling and integrin expression in skeletal muscle may contribute to insulin resistance owing to an increased physical barrier causing reduced nutrient and hormonal flux. This review explores the role of the ECM and the actin cytoskeleton in insulin- and contraction-mediated glucose uptake in skeletal muscle. This is a clinically important area of research given that defects in the structural integrity of the ECM and integrin-associated proteins may contribute to loss of muscle function and decreased glucose uptake in type 2 diabetes.

The Effects of 24 Weeks of Non-Face-to-Face Home Exercise on Body Composition, Physical Fitness, Cardiovascular Function, and Blood Profiles in Pre-Metabolic Syndrome Korean Adults: A Pilot Study

Background: This study assessed Korean residents’ health improvements by reducing chronic disease morbidity through customized health management. After identifying each participant’s strength and health through physical examinations and blood pressure tests, the effects of 24 weeks of online, non-face-to-face home workouts on body composition, physical fitness, cardiovascular function, and blood profiles in Korean adults with pre-metabolic syndrome were determined. Methods: Adults living in Chungcheongbuk-do, aged 19−65, and at the pre-metabolic syndrome stage were recruited at the Jeungpyeong-gun Public Health Center, Chungcheongbuk-do, Korea. For 24 weeks, from February 2022 to July 2022, they exercised for 60−70 min, three times a week, on average, at a maximum heart rate of 60−70%. The “Mobile Healthcare” application was used to record exercise time, number of exercises, number of sets, and Rating of Perceived Exertion at the end of each exercise. Body composition, physical fitness, cardiovascular function, and blood profiles were measured before and after participation. Results: There were no significant differences in weight, body mass index, body fat, waist-to-hip ratio, waist circumference, systolic blood pressure, diastolic blood pressure, resting heart rate levels, or glucose levels after participation in the workout (p > 0.05). However, muscle strength/handgrip strength, sitting-rising test results, single-leg balance, triglycerides, high-density lipoprotein, low-density lipoprotein, and total cholesterol showed a statistically significant difference (p < 0.05). Conclusions: Although the 24 weeks of non-face-to-face home workouts did not positively affect body composition or cardiovascular function, it improved physical fitness and dyslipidemia.

Phosphoproteomics of three exercise modalities identifies canonical signaling and C18ORF25 as an AMPK substrate regulating skeletal muscle function

Exercise induces signaling networks to improve muscle function and confer health benefits. To identify divergent and common signaling networks during and after different exercise modalities, we performed a phosphoproteomic analysis of human skeletal muscle from a cross-over intervention of endurance, sprint, and resistance exercise. This identified 5,486 phosphosites regulated during or after at least one type of exercise modality and only 420 core phosphosites common to all exercise. One of these core phosphosites was S67 on the uncharacterized protein C18ORF25, which we validated as an AMPK substrate. Mice lacking C18ORF25 have reduced skeletal muscle fiber size, exercise capacity, and muscle contractile function, and this was associated with reduced phosphorylation of contractile and Ca2+ handling proteins. Expression of C18ORF25 S66/67D phospho-mimetic reversed the decreased muscle force production. This work defines the divergent and canonical exercise phosphoproteome across different modalities and identifies C18ORF25 as a regulator of exercise signaling and muscle function.

Effects of endurance training on metabolic enzyme activity and transporter protein levels in the skeletal muscles of orchiectomized mice

This study investigated whether endurance training attenuates orchiectomy (ORX)-induced metabolic alterations. At 7 days of recovery after sham operation or ORX surgery, the mice were randomized to remain sedentary or undergo 5 weeks of treadmill running training (15-20 m/min, 60 min, 5 days/week). ORX decreased glycogen concentration in the gastrocnemius muscle, enhanced phosphofructokinase activity in the plantaris muscle, and decreased lactate dehydrogenase activity in the plantaris and soleus muscles. Mitochondrial enzyme activities and protein content in the plantaris and soleus muscles were also decreased after ORX, but preserved, in part, by endurance training. In the treadmill running test (15 m/min, 60 min) after 4 weeks of training, orchiectomized sedentary mice showed impaired exercise performance, which was restored by endurance training. Thus, endurance training could be a potential therapeutic strategy to prevent the hypoandrogenism-induced decline in muscle mitochondrial content and physical performance.