High intensity interval training alters substrate utilization and reduces oxygen consumption in the heart

Effect of combined oral contraceptive on cardiorespiratory function and immune activation in premenopausal women involved in exercise: A systematic review protocol

BACKGROUND

The use of combined oral contraceptive (COC) is common among women of reproductive age despite the potential risk of them developing thrombotic events. There is a need to understand how COC affects cardiorespiratory function and markers of immune activation in premenopausal women involved in exercise. This highlights a need for a systematic review to enhance our understanding of how the use of COC affects cardiovascular health in premenopausal women subjected to exercise.

METHOD

This systematic review protocol was prepared following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses Protocols (PRISMA-P) 2015 statement. An extensive search of relevant literature by two independent reviewers will be conducted through the EBSCOhost interface to access databases such as MEDLINE, EMBASE, and CINAHL. Other health sources, including Cochrane CENTRAL, unpublished studies and grey literature, will also be searched. The search will include all studies that report the effect of COC on essential parameters of cardiorespiratory function and markers of immune activation in premenopausal women involved in exercise. All included studies will be appraised using appraisal tools, while appropriate extraction tools will be used for data extraction. Where possible, eligible studies will be pooled for meta-analysis. If statistical pooling is not feasible, our findings will be presented in a narrative format. The certainty of evidence will be assessed using the Grading of Recommendations, Assessment, Development and Evaluation Assessment (GRADE) tool.

TRIAL REGISTRATION

PROSPERO registration number: CRD42021265257.

Shuyu decoction exhibits anti-fatigue properties via alleviating exercise-induced immune dysfunction

ETHNOPHARMACOLOGICAL RELEVANCE

Shuyu decoction (SYD), an effective traditional Chinese medicine (TCM), has been widely used for treating deficiency-related diseases for thousands of years. Meanwhile, exercise-induced fatigue (EF), a common physiological phenomenon observed in physical training, has been treated as a deficient condition in TCM for decades. Currently, not many studies have been conducted on the effect of SYD on EF and little is known about its underlying pharmacological mechanism.

AIM OF THE STUDY

This current study was designed to assess the anti-fatigue roles of SYD and explore its effect on exercise-induced immune dysfunction.

MATERIALS AND METHODS

Eighteen rats were randomly divided into three groups: normal control (NC) group, model (M) group, and SYD group (27.8 g/kg). The M and SYD group were given treadmill training for 6 weeks. From the fourth week, the SYD group was administered SYD intragastrically for 3 consecutive weeks. After three weeks of treatment, the rats were anesthetized, and the blood and spleen tissue samples were dissected. The blood sample was devoted to the blood biochemical-related indicators, which were used to evaluate the anti-fatigue of SYD. The expression of Interleukin (IL)-6, IL-1β, tumor necrosis factor-α (TNF-α), IL-17, CD3+, and CD4+ were detected by ELISA and the level of CD8+ of blood was measured through Flow Cytometry (FC). The histopathological changes of spleen tissue samples were determined by Hematoxylin and eosin (H&E) staining and an estimation of CD3+, CD4+, and CD8+ expression of spleen tissues were calculated through FC.

RESULTS

Compared with the M group, the SYD group observed an increase in tensile force and the ratio of cortisol to testosterone (TTE/COR), whereas a reduction in the levels of lactic acid (LAC), blood urea nitrogen (BUN), creatine kinase (CK), (P < 0.01 or P < 0.05). ELISA experiments showed that SYD reduced the expressions of IL-6, IL-1β, and TNF-α, IL-17 and increased the expression of IL-10 (P < 0.01 or P < 0.05). In the HE test, SYD treatment transformed the structure of the spleen. FC experiments further showed that SYD increased the expressions of CD3+, CD4+, and CD8+ in blood and spleen tissues (P < 0.01 or P < 0.05).

CONCLUSION

Our findings indicate that SYD can alleviate EF by improving inflammation and immunity. However, the relationship between inflammatory factors and the related immune response remains to be further investigated.

Exercise, exerkines, and cardiometabolic health: from individual players to a team sport

Exercise confers numerous salutary effects that extend beyond individual organ systems to provide systemic health benefits. Here, we discuss the role of exercise in cardiovascular health. We summarize major findings from human exercise studies in cardiometabolic disease. We next describe our current understanding of cardiac-specific substrate metabolism that occurs with acute exercise and in response to exercise training. We subsequently focus on exercise-stimulated circulating biochemicals ("exerkines") as a paradigm for understanding the global health circuitry of exercise, and discuss important concepts in this emerging field before highlighting exerkines relevant in cardiovascular health and disease. Finally, this Review identifies gaps that remain in the field of exercise science and opportunities that exist to translate biologic insights into human health improvement.

Overexpression of NOX2 Exacerbates AngII-Mediated Cardiac Dysfunction and Metabolic Remodelling

The present study aimed to examine the effects of low doses of angiotensin II (AngII) on cardiac function, myocardial substrate utilization, energetics, and mitochondrial function in C57Bl/6J mice and in a transgenic mouse model with cardiomyocyte specific upregulation of NOX2 (csNOX2 TG). Mice were treated with saline (sham), 50 or 400 ng/kg/min of AngII (AngII₅₀ and AngII₄₀₀) for two weeks. In vivo blood pressure and cardiac function were measured using plethysmography and echocardiography, respectively. Ex vivo cardiac function, mechanical efficiency, and myocardial substrate utilization were assessed in isolated perfused working hearts, and mitochondrial function was measured in left ventricular homogenates. AngII₅₀ caused reduced mechanical efficiency despite having no effect on cardiac hypertrophy, function, or substrate utilization. AngII₄₀₀ slightly increased systemic blood pressure and induced cardiac hypertrophy with no effect on cardiac function, efficiency, or substrate utilization. In csNOX2 TG mice, AngII₄₀₀ induced cardiac hypertrophy and in vivo cardiac dysfunction. This was associated with a switch towards increased myocardial glucose oxidation and impaired mitochondrial oxygen consumption rates. Low doses of AngII may transiently impair cardiac efficiency, preceding the development of hypertrophy induced at higher doses. NOX2 overexpression exacerbates the AngII -induced pathology, with cardiac dysfunction and myocardial metabolic remodelling.

Multiple Applications of Different Exercise Modalities with Rodents

A large proportion of chronic diseases can be derived from a sedentary lifestyle. Raising physical activity awareness is indispensable, as lack of exercise is the fourth most common cause of death worldwide. Animal models in different research fields serve as important tools in the study of acute or chronic noncommunicable disorders. With the help of animal-based exercise research, exercise-mediated complex antioxidant and inflammatory pathways can be explored, which knowledge can be transferred to human studies. Whereas sustained physical activity has an enormous number of beneficial effects on many organ systems, these animal models are easily applicable in several research areas. This review is aimed at providing an overall picture of scientific research studies using animal models with a focus on different training modalities. Without wishing to be exhaustive, the most commonly used forms of exercise are presented.

AMPK activator O304 improves metabolic and cardiac function, and exercise capacity in aged mice

Age is associated with progressively impaired, metabolic, cardiac and vascular function, as well as reduced work/exercise capacity, mobility, and hence quality of life. Exercise exhibit positive effects on age-related dysfunctions and diseases. However, for a variety of reasons many aged individuals are unable to engage in regular physical activity, making the development of pharmacological treatments that mimics the beneficial effects of exercise highly desirable. Here we show that the pan-AMPK activator O304, which is well tolerated in humans, prevented and reverted age-associated hyperinsulinemia and insulin resistance, and improved cardiac function and exercise capacity in aged mice. These results provide preclinical evidence that O304 mimics the beneficial effects of exercise. Thus, as an exercise mimetic in clinical development, AMPK activator O304 holds great potential to mitigate metabolic dysfunction, and to improve cardiac function and exercise capacity, and hence quality of life in aged individuals.

The Regulatory Role of Oxygen Metabolism in Exercise-Induced Cardiomyocyte Regeneration

During heart failure, the heart is unable to regenerate lost or damaged cardiomyocytes and is therefore unable to generate adequate cardiac output. Previous research has demonstrated that cardiac regeneration can be promoted by a hypoxia-related oxygen metabolic mechanism. Numerous studies have indicated that exercise plays a regulatory role in the activation of regeneration capacity in both healthy and injured adult cardiomyocytes. However, the role of oxygen metabolism in regulating exercise-induced cardiomyocyte regeneration is unclear. This review focuses on the alteration of the oxygen environment and metabolism in the myocardium induced by exercise, including the effects of mild hypoxia, changes in energy metabolism, enhanced elimination of reactive oxygen species, augmentation of antioxidative capacity, and regulation of the oxygen-related metabolic and molecular pathway in the heart. Deciphering the regulatory role of oxygen metabolism and related factors during and after exercise in cardiomyocyte regeneration will provide biological insight into endogenous cardiac repair mechanisms. Furthermore, this work provides strong evidence for exercise as a cost-effective intervention to improve cardiomyocyte regeneration and restore cardiac function in this patient population.

Effects of hyperbaric environment on endurance and metabolism are exposure time-dependent in well-trained mice

Hyperbaric exposure (1.3 atmospheres absolute with 20.9% O2 ) for 1 h a day was shown to improve exercise capacity. The present study was designed to reveal whether the daily exposure time affects exercise performance and metabolism in skeletal and cardiac muscles. Male mice in the training group were housed in a cage with a wheel activity device for 7 weeks from 5 weeks old. Trained mice were then subjected to hybrid training (HT, endurance exercise for 30 min followed by sprint interval exercise for 30 min). Hyperbaric exposure was applied following daily HT for 15 min (15HT), 30 min (30HT), or 60 min (60HT) for 4 weeks. In the endurance capacity test, maximal work values were significantly increased by 30HT and 60HT. In the left ventricle (LV), activity levels of 3-hydroxyacyl-CoA-dehydrogenase, citrate synthase, and carnitine palmitoyl transferase (CPT) 2 were significantly increased by 60HT. CPT2 activity levels were markedly increased by hyperbaric exposure in red gastrocnemius (Gr) and plantaris muscle (PL). Pyruvate dehydrogenase complex activity values in PL were enhanced more by 30HT and 60HT than by HT. Protein levels of N-terminal isoform of PGC1α (NT-PGC1α) protein were significantly enhanced in three hyperbaric exposed groups in Gr, but not in LV. These results indicate that hyperbaric exposure for 30 min or longer has beneficial effects on endurance, and 60-min exposure has the potential to further increase performance by facilitating fatty acid metabolism in skeletal and cardiac muscles in highly trained mice. NT-PGC1α may have important roles for these adaptations in skeletal muscle.

Effects of voluntary exercise duration on myocardial ischaemic tolerance, kinase signaling and gene expression

AIM

Exercise is cardioprotective, though optimal interventions are unclear. We assessed duration dependent effects of exercise on myocardial ischemia-reperfusion (I-R) injury, kinase signaling and gene expression.

METHODS

Responses to brief (2 day; 2EX), intermediate (7 and 14 day; 7EX and 14EX) and extended (28 day; 28EX) voluntary wheel running (VWR) were studied in male C57Bl/6 mice. Cardiac function, I-R tolerance and survival kinase signaling were assessed in perfused hearts.

KEY FINDINGS

Mice progressively increased running distances and intensity, from 2.4 ± 0.2 km/day (0.55 ± 0.04 m/s) at 2-days to 10.6 ± 0.4 km/day (0.72 ± 0.06 m/s) after 28-days. Myocardial mass and contractility were modified at 14-28 days VWR. Cardioprotection was not 'dose-dependent', with I-R tolerance enhanced within 7 days and not further improved with greater VWR duration, volume or intensity. Protection was associated with AKT, ERK1/2 and GSK3β phosphorylation, with phospho-AMPK selectively enhanced with brief VWR. Gene expression was duration-dependent: 7 day VWR up-regulated glycolytic (Pfkm) and down-regulated maladaptive remodeling (Mmp2) genes; 28 day VWR up-regulated caveolar (Cav3), mitochondrial biogenesis (Ppargc1a, Sirt3) and titin (Ttn) genes. Interestingly, I-R tolerance in 2EX/2SED groups improved vs. groups subjected to longer sedentariness, suggesting transient protection on transition to housing with running wheels.

SIGNIFICANCE

Cardioprotection is induced with as little as 7 days VWR, yet not enhanced with further or faster running. This protection is linked to survival kinase phospho-regulation (particularly AKT and ERK1/2), with glycolytic, mitochondrial, caveolar and myofibrillar gene changes potentially contributing. Intriguingly, environmental enrichment may also protect via similar kinase regulation.

The Molecular Mechanisms Associated with Aerobic Exercise-Induced Cardiac Regeneration

The leading cause of heart failure is cardiomyopathy and damage to the cardiomyocytes. Adult mammalian cardiomyocytes have the ability to regenerate, but this cannot wholly compensate for myocardial cell loss after myocardial injury. Studies have shown that exercise has a regulatory role in the activation and promotion of regeneration of healthy and injured adult cardiomyocytes. However, current research on the effects of aerobic exercise in myocardial regeneration is not comprehensive. This review discusses the relationships between aerobic exercise and the regeneration of cardiomyocytes with respect to complex molecular and cellular mechanisms, paracrine factors, transcriptional factors, signaling pathways, and microRNAs that induce cardiac regeneration. The topics discussed herein provide a knowledge base for physical activity-induced cardiomyocyte regeneration, in which exercise enhances overall heart function and improves the efficacy of cardiac rehabilitation.

Cardiac tissue citric acid cycle intermediates in exercised very long-chain acyl-CoA dehydrogenase-deficient mice fed triheptanoin or medium-chain triglyceride

Anaplerotic odd-chain fatty acid supplementation has been suggested as an approach to replenish citric acid cycle intermediate (CACi) pools and facilitate adenosine triphosphate (ATP) production in subjects with long-chain fatty acid oxidation disorders, but the evidence that cellular CACi depletion exists and that repletion occurs following anaplerotic substrate supplementation is limited. We exercised very long-chain acyl-CoA dehydrogenase-deficient (VLCAD-/-) and wild-type (WT) mice to exhaustion and collected cardiac tissue for measurement of CACi by targeted metabolomics. In a second experimental group, VLCAD-/- and WT mice that had been fed chow prepared with either medium-chain triglyceride (MCT) oil or triheptanoin for 4 weeks were exercised for 60 minutes. VLCAD-/- mice exhibited lower succinate in cardiac muscle at exhaustion than WT mice suggesting lower CACi in VLCAD-/- with prolonged exercise. In mice fed either MCT or triheptanoin, succinate and malate were greater in VLCAD-/- mice fed triheptanoin compared to VLCAD-/- animals fed MCT but lower than WT mice fed triheptanoin. Long-chain odd acylcarnitines such as C19 were elevated in VLCAD-/- and WT mice fed triheptanoin suggesting some elongation of the heptanoate, but it is unknown what proportion of heptanoate was oxidized vs elongated. Prolonged exercise was associated with decreased cardiac muscle succinate in VLCAD-/- mice in comparison to WT mice. VLCAD-/- fed triheptanoin had increased succinate compared to VLCAD-/- mice fed MCT but lower than WT mice fed triheptanoin. Cardiac CACi were higher following dietary ingestion of an anaplerotic substrate, triheptanoin, in comparison to MCT.

Exercise Regulates MicroRNAs to Preserve Coronary and Cardiac Function in the Diabetic Heart

RATIONALE

Diabetic heart disease (DHD) is a debilitating manifestation of type 2 diabetes mellitus. Exercise has been proposed as a potential therapy for DHD, although the effectiveness of exercise in preventing or reversing the progression of DHD remains controversial. Cardiac function is critically dependent on the preservation of coronary vascular function.

OBJECTIVE

We aimed to elucidate the effectiveness and mechanisms by which exercise facilitates coronary and cardiac-protection during the onset and progression of DHD.

METHODS AND RESULTS

Diabetic db/db and nondiabetic mice, with or without underlying cardiac dysfunction (16 and 8 weeks old, respectively) were subjected to either moderate-intensity exercise or high-intensity exercise for 8 weeks. Subsequently, synchrotron microangiography, immunohistochemistry, Western blot, and real-time polymerase chain reaction were used to assess time-dependent changes in cardiac and coronary structure and function associated with diabetes mellitus and exercise and determine whether these changes reflect the observed changes in cardiac-enriched and vascular-enriched microRNAs (miRNAs). We show that, if exercise is initiated from 8 weeks of age, both moderate-intensity exercise and high-intensity exercise prevented the onset of coronary and cardiac dysfunction, apoptosis, fibrosis, microvascular rarefaction, and disruption of miRNA signaling, as seen in the nonexercised diabetic mice. Conversely, the cardiovascular benefits of moderate-intensity exercise were absent if the exercise was initiated after the diabetic mice had already established cardiac dysfunction (ie, from 16 weeks of age). The experimental silencing or upregulation of miRNA-126 activity suggests the mechanism underpinning the cardiovascular benefits of exercise were mediated, at least in part, through tissue-specific miRNAs.

CONCLUSIONS

Our findings provide the first experimental evidence for the critical importance of early exercise intervention in ameliorating the onset and progression of DHD. Our results also suggest that the beneficial effects of exercise are mediated through the normalization of cardiovascular-enriched miRNAs, which are dysregulated in DHD.

Micro-dystrophin Gene Therapy Partially Enhances Exercise Capacity in Older Adult mdx Mice

Micro-dystrophin (μDys) gene therapeutics can improve striated muscle structure and function in different animal models of Duchenne muscular dystrophy. Most studies, however, used young mdx mice that lack a pronounced dystrophic phenotype, short treatment periods, and limited muscle function tests. We, therefore, determined the relative efficacy of two previously described μDys gene therapeutics (rAAV6:μDysH3 and rAAV6:μDys5) in 6-month-old mdx mice using a 6-month treatment regimen and forced exercise. Forelimb and hindlimb grip strength, metabolic rate (VO2 max), running efficiency (energy expenditure), and serum creatine kinase levels similarly improved in mdx mice treated with either vector. Both vectors produced nearly identical dose-responses in all assays. They also partially prevented the degenerative effects of repeated high-intensity exercise on muscle histology, although none of the metrics examined was restored to normal wild-type levels. Moreover, neither vector had any consistent effect on respiration while exercising. These data together suggest that, although μDys gene therapy can improve isolated and systemic muscle function, it may be only partially effective when dystrophinopathies are advanced or when muscle structure is significantly challenged, as with high-intensity exercise. This further suggests that restoring muscle function to near-normal levels will likely require ancillary or combinatorial treatments capable of enhancing muscle strength.

The Acute Physiological Responses of Eccentric Cycling During the Recovery Periods of a High Intensity Concentric Cycling Interval Session

Eccentric and concentric exercise is associated with disparate acute and chronic responses. We uniquely interspersed workload equivalent eccentric cycling during each recovery period of a high intensity interval training (HIIT) cycling trial to determine acute cardiopulmonary, thermal and psycho-physiological responses. Twelve males [age 28 years (SD 6), peak oxygen consumption 48 mL ⋅ kg^–1 ⋅ min^–1 (SD 6)] completed two high intensity interval cycling trials [4 × 5 min, 60% peak power output (PPO)] separated by 7–10 days. The CON_R trial required participants to cycle concentrically during each recovery period (5 min, 30% PPO). The ECC_R trial modified the recovery to be eccentric cycling (5 min, 60% PPO). High intensity workload (CON_R: 187 ± 17; ECC_R: 187 ± 21 W), oxygen consumption (CON_R: 2.55 ± 0.17; ECC_R: 2.68 ± 0.20 L ⋅ min^–1), heart rate (CON_R: 165 ± 7; ECC_R: 171 ± 10 beats ⋅ min^–1) and RPE legs (CON_R: 15 ± 3; ECC_R: 15 ± 3) were equivalent between trials. Eccentric cycling recovery significantly increased external workload (CON_R: 93 ± 18; ECC_R: 196 ± 24 W, P < 0.01) yet lowered oxygen consumption (CON_R: 1.51 ± 0.18; ECC_R: 1.20 ± 0.20 L ⋅ min^–1, P < 0.05) while heart rate (CON_R: 132 ± 13; ECC_R: 137 ± 12 beats ⋅ min^–1) and RPE of the legs (CON_R: 11 ± 7; ECC_R: 12 ± 7) remained equivalent. There was no significant difference in the aural temperature between the trials (ECC_R: 37.3 ± 0.1°C; CON_R: 37.4 ± 0.1°C, P > 0.05), yet during recovery periods mean skin temperature was significantly elevated in the ECC_R (ECC_R: 33.9 ± 0.2°C; CON_R: 33.3 ± 0.2°C, P < 0.05). Participants preferred ECC_R (10/12) and rated the ECC_R as more achievable (82.8 ± 11.4 mm) than CON_R (79.4 ± 15.9 mm, P < 0.01). In conclusion, eccentric cycling during the recovery period of a HIIT training session, offers a novel approach to concurrent training methodology. The unique cardiopulmonary and skeletal muscle responses facilitate the achievement of both training stimuli within a single exercise bout.

The Impact of Moderate-Intensity Continuous or High-Intensity Interval Training on Adipogenesis and Browning of Subcutaneous Adipose Tissue in Obese Male Rats

This study compares the effect of two types of exercise training, i.e., moderate-intensity continuous training (MICT) or high-intensity interval training (HIIT) on the browning of subcutaneous white adipose tissue (scWAT) in obese male rats. Effects on fat composition, metabolites, and molecular markers of differentiation and energy expenditure were examined. Forty male Wistar rats were assigned to lean (n = 8) or obese (n = 32) groups and fed either a standard chow or high-fat obesogenic diet for 10 weeks. Eight lean and obese rats were then blood and tissue sampled, and the remaining obese animals were randomly allocated into sedentary, MICT, or HIIT (running on a treadmill 5 days/week) groups that were maintained for 12 weeks. Obesity increased plasma glucose and insulin and decreased irisin and FGF-21. In scWAT, this was accompanied with raised protein abundance of markers of adipocyte differentiation, i.e., C/EBP-α, C/EBP-β, and PPAR-γ, whereas brown fat-related genes, i.e., PRDM-16, AMPK/SIRT1/PGC-1α, were reduced as was UCP1 and markers of fatty acid transport, i.e., CD36 and CPT1. Exercise training increased protein expression of brown fat-related markers, i.e., PRDM-16, AMPK/SIRT1/PGC-1α, and UCP1, together with gene expression of fatty acid transport, i.e., CD36 and CPT1, but decreased markers of adipocyte differentiation, i.e., C/EBP-α, C/EBP-β, and plasma glucose. The majority of these adaptations were greater with HIIT compared to MICT. Our findings indicate that prolonged exercise training promotes the browning of white adipocytes, possibly through suppression of adipogenesis together with white to beige trans-differentiation and is dependent on the intensity of exercise.

Altered mitochondrial metabolism in the insulin-resistant heart

Obesity-induced insulin resistance and type 2 diabetes mellitus can ultimately result in various complications, including diabetic cardiomyopathy. In this case, cardiac dysfunction is characterized by metabolic disturbances such as impaired glucose oxidation and an increased reliance on fatty acid (FA) oxidation. Mitochondrial dysfunction has often been associated with the altered metabolic function in the diabetic heart, and may result from FA-induced lipotoxicity and uncoupling of oxidative phosphorylation. In this review, we address the metabolic changes in the diabetic heart, focusing on the loss of metabolic flexibility and cardiac mitochondrial function. We consider the alterations observed in mitochondrial substrate utilization, bioenergetics and dynamics, and highlight new areas of research which may improve our understanding of the cause and effect of cardiac mitochondrial dysfunction in diabetes. Finally, we explore how lifestyle (nutrition and exercise) and pharmacological interventions can prevent and treat metabolic and mitochondrial dysfunction in diabetes.

3-Weeks of Exercise Training Increases Ischemic-Tolerance in Hearts From High-Fat Diet Fed Mice

Physical activity is an efficient strategy to delay development of obesity and insulin resistance, and thus the progression of obesity/diabetes-related cardiomyopathy. In support of this, experimental studies using animal models of obesity show that chronic exercise prevents the development of obesity-induced cardiac dysfunction (cardiomyopathy). Whether exercise also improves the tolerance to ischemia-reperfusion in these models is less clear, and may depend on the type of exercise procedure as well as time of initiation. We have previously shown a reduction in ischemic-injury in diet-induced obese mice, when the exercise was started prior to the development of cardiac dysfunction in this model. In the present study, we aimed to explore the effect of exercise on ischemic-tolerance when exercise was initiated after the development obesity-mediated. Male C57BL/6J mice were fed a high-fat diet (HFD) for 20–22 weeks, where they were subjected to high-intensity interval training (HIT) during the last 3 weeks of the feeding period. Sedentary HFD fed and chow fed mice served as controls. Left-ventricular (LV) post-ischemic functional recovery and infarct size were measured in isolated perfused hearts. We also assessed the effect of 3-week HIT on mitochondrial function and myocardial oxygen consumption (MVO₂). Sedentary HFD fed mice developed marked obesity and insulin resistance, and demonstrated reduced post-ischemic cardiac functional recovery and increased infarct size. Three weeks of HIT did not induce cardiac hypertrophy and only had a mild effect on obesity and insulin resistance. Despite this, HIT improved post-ischemic LV functional recovery and reduced infarct size. This increase in ischemic-tolerance was accompanied by an improved mitochondrial function as well as reduced MVO₂. The present study highlights the beneficial effects of exercise training with regard to improving the ischemic-tolerance in hearts with cardiomyopathy following obesity and insulin resistance. This study also emphasizes the exercise-induced improvement of cardiac energetics and mitochondrial function in obesity/diabetes.

Metabolic Coordination of Physiological and Pathological Cardiac Remodeling

Metabolic pathways integrate to support tissue homeostasis and to prompt changes in cell phenotype. In particular, the heart consumes relatively large amounts of substrate not only to regenerate ATP for contraction but also to sustain biosynthetic reactions for replacement of cellular building blocks. Metabolic pathways also control intracellular redox state, and metabolic intermediates and end products provide signals that prompt changes in enzymatic activity and gene expression. Mounting evidence suggests that the changes in cardiac metabolism that occur during development, exercise, and pregnancy as well as with pathological stress (eg, myocardial infarction, pressure overload) are causative in cardiac remodeling. Metabolism-mediated changes in gene expression, metabolite signaling, and the channeling of glucose-derived carbon toward anabolic pathways seem critical for physiological growth of the heart, and metabolic inefficiency and loss of coordinated anabolic activity are emerging as proximal causes of pathological remodeling. This review integrates knowledge of different forms of cardiac remodeling to develop general models of how relationships between catabolic and anabolic glucose metabolism may fortify cardiac health or promote (mal)adaptive myocardial remodeling. Adoption of conceptual frameworks based in relational biology may enable further understanding of how metabolism regulates cardiac structure and function.

High intensity interval training decreases the expressions of KIF5B and Dynein in Hippocampus of Wistar male rats

Although exercise training (ET) with low to moderate intensity improves several physiological aspects of brain, the effects of high intensity interval training (HIIT) are less clear on brain plasticity and cytoplasmic transport. The present study examined the effects of HIIT on the gene and protein expressions of kinesin family member 5B (KIF5B) and Dynein in the Wistar male rat hippocampal tissue. Fourteen male Wistar rats were separated into 2 groups: (1) the training group (TG: n = 7) and (2) the control group (CG: n = 7). The exercise protocol was carried out on a rodent treadmill (5 days a week for 6 weeks). The protein contents of KIF5B and Dynein were determined by the immunohistochemical analysis. Moreover, the Real-Time polymerase chain reaction (Real-Time PCR) procedure was done to measure the KIF5B mRNA and Dynein mRNA expressions. It was observed that HIIT resulted in a significant decrease in the gene expressions of KIF5B and Dynein (P = 0.001), and also the results showed that HIIT leads to a significant decrease in KIF5B (P = 0.001) and Dynein (P = 0.02) protein content of the hippocampal tissue in comparison with sedentary rats. Our findings demonstrated that HIIT is associated with the down-regulation of gene and protein levels of KIF5B and Dynein in the rat hippocampal tissue, although the underlying mechanisms have remained unknown. These changes suggest that HIIT may have negative effects on both the anterograde and retrograde cytoplasmic transports because the cytoplasmic transport is mediated by KIF5B and Dynein.

An attempt to reverse cardiac lipotoxicity by aerobic interval training in a high-fat diet- and streptozotocin-induced type 2 diabetes rat model

BACKGROUND

Diabetes mellitus (DM) is an important risk factor for cardiovascular disease. Aerobic interval training (AIT) has been recommended to patients as a non-pharmacological strategy to manage DM. However, little is known about whether AIT intervention at the onset of DM will reverse the process of diabetic cardiomyopathy (DCM). In this study, we sought to evaluate whether AIT can reverse the process of DCM and explore the underlying mechanisms.

METHODS

Fifty Wistar rats were randomly divided into a control group (CON), DCM group (DCM) and AIT intervention group (AIT). A high-fat diet and streptozotocin (STZ) were used to induce diabetes in rats in the DCM group and AIT group. Rats in the AIT group were subjected to an 8-week AIT intervention. Fasting blood glucose (FBG), lipid profiles and insulin levels were measured. Haematoxylin and eosin (HE) staining and oil red O staining were used to identify cardiac morphology and lipid accumulation, respectively. Serum BNP levels and cardiac BNP mRNA expression were measured to ensure the safety of the AIT intervention. Free fatty acid (FFA) and diacylglycerol (DAG) concentrations were analysed by enzymatic methods. AMPK, p-AMPK, FOXO1, CD36 and PPARα gene and protein expression were detected by RT-PCR and Western blotting.

RESULTS

AIT intervention significantly reduced rat serum cardiovascular disease risk factors in DCM rats (P < 0.05). The safety of AIT intervention was illustrated by reduced serum BNP levels and cardiac BNP mRNA expression (P < 0.05) after AIT intervention in DCM rats histological analysis and FFA and DAG concentrations revealed that AIT intervention reduced the accumulation of lipid droplets within cardiomyocytes and alleviated cardiac lipotoxicity (P < 0.05). CD36 and PPARα gene and protein expression were elevated in the DCM group, and these increases were reduced by AIT intervention (P < 0.01). The normalized myocardial lipotoxicity was due to increased expression of phosphorylated AMPK and reduced FOXO1 expression after AIT intervention.

CONCLUSION

AIT intervention may alleviate cardiac lipotoxicity and reverse the process of DCM through activation of the AMPK-FOXO1 pathway.

Myocardial NADPH oxidase-4 regulates the physiological response to acute exercise

Regular exercise has widespread health benefits. Fundamental to these beneficial effects is the ability of the heart to intermittently and substantially increase its performance without incurring damage, but the underlying homeostatic mechanisms are unclear. We identify the ROS-generating NADPH oxidase-4 (Nox4) as an essential regulator of exercise performance in mice. Myocardial Nox4 levels increase during acute exercise and trigger activation of the transcription factor Nrf2, with the induction of multiple endogenous antioxidants. Cardiomyocyte-specific Nox4-deficient (csNox4KO) mice display a loss of exercise-induced Nrf2 activation, cardiac oxidative stress and reduced exercise performance. Cardiomyocyte-specific Nrf2-deficient (csNrf2KO) mice exhibit similar compromised exercise capacity, with mitochondrial and cardiac dysfunction. Supplementation with an Nrf2 activator or a mitochondria-targeted antioxidant effectively restores cardiac performance and exercise capacity in csNox4KO and csNrf2KO mice respectively. The Nox4/Nrf2 axis therefore drives a hormetic response that is required for optimal cardiac mitochondrial and contractile function during physiological exercise.

Cardiac basal autophagic activity and increased exercise capacity

To investigate whether high-intensity interval training (HIIT) and continuous moderate-intensity training (CMT) have different impacts on exercise performance and cardiac function and to determine the influence of these exercise protocols on modulating basal autophagy in the cardiac muscle of rats. Rats were assigned to three groups: sedentary control (SC), CMT, and HIIT. Total exercise volume and mean intensity were matched between the two protocols. After a 10-week training program, rats were evaluated for exercise performance, including exercise tolerance and grip strength. Blood lactate levels were measured after an incremental exercise test. Cardiac function and morphology were assessed by echocardiography. Western blotting was used to evaluate the expression of autophagy and mitochondrial markers. Transmission electron microscopy was used to evaluate mitochondrial content. The results showed that time to exhaustion and grip strength increased significantly in the HIIT group compared with the SC and CMT groups. Both training interventions significantly increased time to exhaustion, reduced blood lactate level (after an incremental exercise test) and induced adaptive changes in cardiac morphology, but without altering cardiac systolic function. The greater improvements in exercise performance with the HIIT than with the CMT protocol were related to improvement in basal autophagic adaptation and mitochondria function in cardiac muscle. Mitochondria markers were positively correlated with autophagy makers. This study shows that HIIT is more effective for improving exercise performance than CMT and this improvement is related to mitochondrial function and basal autophagic adaptation in cardiac muscle.

Improvements in cognition and associations with measures of aerobic fitness and muscular power following structured exercise

OBJECTIVES

Cognition, along with aerobic and muscular fitness, declines with age. Although research has shown that resistance and aerobic exercise may improve cognition, no consensus exists supporting the use of one approach over the other. The purpose of this study was to compare the effects of steady-state, moderate-intensity treadmill training (TM) and high-velocity circuit resistance training (HVCRT) on cognition, and to examine its relationships to aerobic fitness and neuromuscular power.

METHODS

Thirty older adults were randomly assigned to one of three groups: HVCRT, TM, or control. Exercise groups attended training 3 days/wk for 12 weeks, following a 2 week adaptation period. The NIH Cognitive Toolbox was used to assess specific components of cognition and provided an overall fluid composite score (FCS). The walking response and inhibition test (WRIT) was specifically used to assess executive function (EF) and provided an accuracy (ACC), reaction time (RT) and global score (GS). Aerobic power (AP) and maximal neuromuscular power (MP) were measured pre- and post-intervention. Relationships between variables using baseline and mean change scores were assessed.

RESULTS

Significant increases were seen from baseline in ACC (MD = 14.0, SE = 4.3, p = .01, d = 1.49), GS (MD = 25.6, SE = 8.0, p = .01, d = 1.16), and AP (MD = 1.4, SE = 0.6, p = .046, d = 0.31) for HVCRT. RT showed a trend toward a significant decrease (MD = -0.03, SE = 0.016, p = .068, d = 0.32) for HVCRT. No significant within-group differences were detected for TM or CONT. Significant correlations were seen at baseline between AP and FCS, as well as other cognitive domains; but none were detected among change scores. Although no significant correlation was evident between MP and FCS or GS, there was a trend toward higher MP values being associated with higher FCS and GS scores.

CONCLUSIONS

Our results support the use of HVCRT over TM for improving cognition in older persons, although the precise mechanisms that underlie this association remain unclear.

Systemic Oxygen Transport with Rest, Exercise, and Hypoxia: A Comparison of Humans, Rats, and Mice

The objective of this article is to compare and contrast the known characteristics of the systemic O₂ transport of humans, rats, and mice at rest and during exercise in normoxia and hypoxia. This analysis should help understand when rodent O₂ transport findings can-and cannot-be applied to human responses to similar conditions. The O₂ -transport system was analyzed as composed of four linked conductances: ventilation, alveolo-capillary diffusion, circulatory convection, and tissue capillary-cell diffusion. While the mechanisms of O₂ transport are similar in the three species, the quantitative differences are naturally large. There are abundant data on total O₂ consumption and on ventilatory and pulmonary diffusive conductances under resting conditions in the three species; however, there is much less available information on pulmonary gas exchange, circulatory O₂ convection, and tissue O₂ diffusion in mice. The scarcity of data largely derives from the difficulty of obtaining blood samples in these small animals and highlights the need for additional research in this area. In spite of the large quantitative differences in absolute and mass-specific O₂ flux, available evidence indicates that resting alveolar and arterial and venous blood PO₂ values under normoxia are similar in the three species. Additionally, at least in rats, alveolar and arterial blood PO₂ under hypoxia and exercise remain closer to the resting values than those observed in humans. This is achieved by a greater ventilatory response, coupled with a closer value of arterial to alveolar PO₂ , suggesting a greater efficacy of gas exchange in the rats. © 2018 American Physiological Society. Compr Physiol 8:1537-1573, 2018.

Metabolic Mechanisms of Exercise-Induced Cardiac Remodeling

Exercise has a myriad of physiological benefits that derive in part from its ability to improve cardiometabolic health. The periodic metabolic stress imposed by regular exercise appears fundamental in driving cardiovascular tissue adaptation. However, different types, intensities, or durations of exercise elicit different levels of metabolic stress and may promote distinct types of tissue remodeling. In this review, we discuss how exercise affects cardiac structure and function and how exercise-induced changes in metabolism regulate cardiac adaptation. Current evidence suggests that exercise typically elicits an adaptive, beneficial form of cardiac remodeling that involves cardiomyocyte growth and proliferation; however, chronic levels of extreme exercise may increase the risk for pathological cardiac remodeling or sudden cardiac death. An emerging theme underpinning acute as well as chronic cardiac adaptations to exercise is metabolic periodicity, which appears important for regulating mitochondrial quality and function, for stimulating metabolism-mediated exercise gene programs and hypertrophic kinase activity, and for coordinating biosynthetic pathway activity. In addition, circulating metabolites liberated during exercise trigger physiological cardiac growth. Further understanding of how exercise-mediated changes in metabolism orchestrate cell signaling and gene expression could facilitate therapeutic strategies to maximize the benefits of exercise and improve cardiac health.

An "Exercise" in Cardiac Metabolism

Research has demonstrated that the high capacity requirements of the heart are satisfied by a preference for oxidation of fatty acids. However, it is well known that a stressed heart, as in pathological hypertrophy, deviates from its inherent profile and relies heavily on glucose metabolism, primarily achieved by an acceleration in glycolysis. Moreover, it has been suggested that the chronically lipid overloaded heart augments fatty acid oxidation and triglyceride synthesis to an even greater degree and, thus, develops a lipotoxic phenotype. In comparison, classic studies in exercise physiology have provided a basis for the acute metabolic changes that occur during physical activity. During an acute bout of exercise, whole body glucose metabolism increases proportionately to intensity while fatty acid metabolism gradually increases throughout the duration of activity, particularly during moderate intensity. However, the studies in chronic exercise training are primarily limited to metabolic adaptations in skeletal muscle or to the mechanisms that govern physiological signaling pathways in the heart. Therefore, the purpose of this review is to discuss the precise changes that chronic exercise training elicits on cardiac metabolism, particularly on substrate utilization. Although conflicting data exists, a pattern of enhanced fatty oxidation and normalization of glycolysis emerges, which may be a therapeutic strategy to prevent or regress the metabolic phenotype of the hypertrophied heart. This review also expands on the metabolic adaptations that chronic exercise training elicits in amino acid and ketone body metabolism, which have become of increased interest recently. Lastly, challenges with exercise training studies, which could relate to several variables including model, training modality, and metabolic parameter assessed, are examined.

Beneficial Autophagic Activities, Mitochondrial Function, and Metabolic Phenotype Adaptations Promoted by High-Intensity Interval Training in a Rat Model

The effects of high-intensity interval (HIIT) and moderate-intensity continuous training (MICT) on basal autophagy and mitochondrial function in cardiac and skeletal muscle and plasma metabolic phenotypes have not been clearly characterized. Here, we investigated how 10-weeks HIIT and MICT differentially modify basal autophagy and mitochondrial markers in cardiac and skeletal muscle and conducted an untargeted metabolomics study with proton nuclear magnetic resonance (¹H NMR) spectroscopy and multivariate statistical analysis of plasma metabolic phenotypes. Male Sprague–Dawley rats were separated into three groups: sedentary control (SED), MICT, and HIIT. Rats underwent evaluation of exercise performance, including exercise tolerance and grip strength, and blood lactate levels were measured immediately after an incremental exercise test. Plasma samples were analyzed by ¹H NMR. The expression of autophagy and mitochondrial markers and autophagic flux (LC3II/LC3-I ratio) in cardiac, rectus femoris, and soleus muscle were analyzed by western blotting. Time to exhaustion and grip strength increased significantly following HIIT compared with that in both SED and MICT groups. Compared with those in the SED group, blood lactate level, and the expression of SDH, COX-IV, and SIRT3 significantly increased in rectus femoris and soleus muscle of both HIIT and MICT groups. Meanwhile, SDH and COX-IV content of cardiac muscle and COX-IV and SIRT3 content of rectus femoris and soleus muscle increased significantly following HIIT compared with that following MICT. The expression of LC3-II, ATG-3, and Beclin-1 and LC3II/LC3-I ratio were significantly increased only in soleus and cardiac muscle following HIIT. These data indicate that HIIT was more effective for improving physical performance and facilitating cardiac and skeletal muscle adaptations that increase mitochondrial function and basal autophagic activities. Moreover, ¹H NMR spectroscopy and multivariate statistical analysis identified 11 metabolites in plasma, among which fine significantly and similarly changed after both HIIT and MICT, while BCAAs isoleucine, leucine, and valine and glutamine were changed only after HIIT. Together, these data indicate distinct differences in specific metabolites and autophagy and mitochondrial markers following HIIT vs. MICT and highlight the value of metabolomic analysis in providing more detailed insight into the metabolic adaptations to exercise training.

SWEAT RATE MEASUREMENTS AFTER HIGH INTENSITY INTERVAL TRAINING USING BODY WEIGHT

ABSTRACT Introduction: Physical activity raises body temperature, increases the sweat rate and accelerates fluid loss during exercise, thereby impairing exercise performance. However, studies using the high intensity interval training (HIIT) approach and its effects on rates of perspiration and hydration are still inconclusive. Objectives: The objective of this study was to assess sweating and water loss during an HIIT workout session, using body weight, with healthy college students. Methods: Twenty male individuals (31 ± 07 years) were split into two groups: Active group (AG) and Inactive group (IG). The HIIT workout protocol, using body weight, consisted of a single bout with 1:1 stimuli, being: 30” “all out” intensity, involving jumping jack, mountain climber, burpee and squat jump exercises; and 30” of passive recovery, totaling 20 minutes of exercises. For comparison purposes, after 48 hours all the individuals underwent the continuous running protocol with intensity corresponding to 75% of maximum heart rate for 40 minutes. The intensity of the session was monitored continuously, at each 30”, using the perceived exertion scale for both protocols. To ensure euhydration status, all individuals ingested 500 ml of water 120 minutes before the training session. Results: Significant differences (p= 0.01) were found in body mass after HIIT compared to the Moderate session in both Active (HIIT: -0.60 ± 0.29 kg, Moderate: -0.26 ± 0.12 kg) and Inactive (HIIT: -0.92 ± 0.30 kg, Moderate: -0.26 ± 0.26 kg) groups, however, no differences were found between groups. Absolute sweating rate values comparing moderate and HIIT single bout in Inactive (Moderate: 10.55 ± 10.59 ml/min; HIIT: 28.90 ± 13.88 ml/min) and Active (Moderate: 9.60 ± 4.52 ml/min; HIIT: 26.00 ± 15.06 ml/min) groups were different between types of exercise, but not between groups. Conclusions: The sweating rate is influenced by the intensity of the exercise, being higher after HIIT than after a moderate exercise session. However, the sweating rate variation is not affected by the subjects’ physical activity level. Level of Evidence II; Diagnostic studies-Investigating a diagnostic test.

High Intensity Interval Training Improves Physical Performance and Frailty in Aged Mice

Sarcopenia and frailty are highly prevalent in older individuals, increasing the risk of disability and loss of independence. High intensity interval training (HIIT) may provide a robust intervention for both sarcopenia and frailty by achieving both strength and endurance benefits with lower time commitments than other exercise regimens. To better understand the impacts of HIIT during aging, we compared 24-month-old C57BL/6J sedentary mice with those that were administered 10-minute uphill treadmill HIIT sessions three times per week over 16 weeks. Baseline and end point assessments included body composition, physical performance, and frailty based on criteria from the Fried physical frailty scale. HIIT-trained mice demonstrated dramatic improvement in grip strength (HIIT 10.9% vs -3.9% in sedentary mice), treadmill endurance (32.6% vs -2.0%), and gait speed (107.0% vs 39.0%). Muscles from HIIT mice also exhibited greater mass, larger fiber size, and an increase in mitochondrial biomass. Furthermore, HIIT exercise led to a dramatic reduction in frailty scores in five of six mice that were frail or prefrail at baseline, with four ultimately becoming nonfrail. The uphill treadmill HIIT exercise sessions were well tolerated by aged mice and led to performance gains, improvement in underlying muscle physiology, and reduction in frailty.

Physical Exercise and Its Protective Effects on Diabetic Cardiomyopathy: What Is the Evidence?

As one of the most serious complications of diabetes, diabetic cardiomyopathy (DCM) imposes a huge burden on individuals and society, and represents a major public health problem. It has long been recognized that physical exercise has important health benefits for patients with type 2 diabetes, and regular physical exercise can delay or prevent the complications of diabetes. Current studies show that physical exercise has been regarded as an importantly non-pharmacological treatment for diabetes and DCM, with high efficacy and low adverse events. It can inhibit the pathological processes of myocardial apoptosis, myocardial fibrosis, and myocardial microvascular diseases through improving myocardial metabolism, enhancing the regulation of Ca²⁺, and protecting the function of mitochondria. Eventually, it can alleviate the occurrence and development of diabetic complications. Describing the mechanisms of physical exercise on DCM may provide a new theory for alleviating, or even reversing the development of DCM, and prevent it from developing to heart failure.

Beneficial effects of exercise training in heart failure are lost in male diabetic rats

Exercise training has been demonstrated to have beneficial effects in patients with heart failure (HF) or diabetes. However, it is unknown whether diabetic patients with HF will benefit from exercise training. Male Wistar rats were fed either a standard (Sham, n = 53) or high-fat, high-sucrose diet ( n = 66) for 6 mo. After 2 mo of diet, the rats were already diabetic. Rats were then randomly subjected to either myocardial infarction by coronary artery ligation (MI) or sham operation. Two months later, heart failure was documented by echocardiography and animals were randomly subjected to exercise training with treadmill for an additional 8 wk or remained sedentary. At the end, rats were euthanized and tissues were assayed by RT-PCR, immunoblotting, spectrophotometry, and immunohistology. MI induced a similar decrease in ejection fraction in diabetic and lean animals but a higher premature mortality in the diabetic group. Exercise for 8 wk resulted in a higher working power developed by MI animals with diabetes and improved glycaemia but not ejection fraction or pathological phenotype. In contrast, exercise improved the ejection fraction and increased adaptive hypertrophy after MI in the lean group. Trained diabetic rats with MI were nevertheless able to develop cardiomyocyte hypertrophy but without angiogenic responses. Exercise improved stress markers and cardiac energy metabolism in lean but not diabetic-MI rats. Hence, following HF, the benefits of exercise training on cardiac function are blunted in diabetic animals. In conclusion, exercise training only improved the myocardial profile of infarcted lean rats fed the standard diet. NEW & NOTEWORTHY Exercise training is beneficial in patients with heart failure (HF) or diabetes. However, less is known of the possible benefit of exercise training for HF patients with diabetes. Using a rat model where both diabetes and MI had been induced, we showed that 2 mo after MI, 8 wk of exercise training failed to improve cardiac function and metabolism in diabetic animals in contrast to lean animals.

Exercise of obese mice induces cardioprotection and oxygen sparing in hearts exposed to high-fat load

Exercise training is a potent therapeutic approach in obesity and diabetes that exerts protective effects against the development of diabetic cardiomyopathy and ischemic injury. Acute increases in circulating fatty acids (FAs) during an ischemic insult can challenge the heart, since high FA load is considered to have adverse cardiac effects. In the present study, we tested the hypothesis that exercise-induced cardiac effects in diet-induced obese mice are abrogated by an acute high FA load. Diet-induced obese mice were fed a high-fat diet (HFD) for 20 wk. They were exercised using moderate- and/or high-intensity exercise training (MIT and HIT, respectively) for 10 or 3 wk, and isolated perfused hearts from these mice were exposed to a high FA load. Sedentary HFD mice served as controls. Ventricular function and myocardial O2 consumption were assessed after 10 wk of HIT and MIT, and postischemic functional recovery and infarct size were examined after 3 wk of HIT. In addition to improving aerobic capacity and reducing obesity and insulin resistance, long-term exercise ameliorated the development of diet-induced cardiac dysfunction. This was associated with improved mechanical efficiency because of reduced myocardial oxygen consumption. Although to a lesser extent, 3-wk HIT also increased aerobic capacity and decreased obesity and insulin resistance. HIT also improved postischemic functional recovery and reduced infarct size. Event upon the exposure to a high FA load, short-term exercise induced an oxygen-sparing effect. This study therefore shows that exercise-induced cardioprotective effects are present under hyperlipidemic conditions and highlights the important role of myocardial energetics during ischemic stress.

NEW & NOTEWORTHY The exercise-induced cardioprotective effects in obese hearts are present under hyperlipidemic conditions, comparable to circulating levels of FA occurring with an ischemic insult. Myocardial oxygen sparing is associated with this effect, despite the general notion that high fat can decrease cardiac efficiency. This highlights the role of myocardial energetics during ischemic stress.

Complete Reversion of Cardiac Functional Adaptation Induced by Exercise Training

PURPOSE

Long-term exercise training is associated with characteristic cardiac adaptation, termed athlete's heart. Our research group previously characterized in vivo left ventricular (LV) function of exercise-induced cardiac hypertrophy in detail in a rat model; however, the effect of detraining on LV function is still unclear. We aimed at evaluating the reversibility of functional alterations of athlete's heart after detraining.

METHODS

Rats (n = 16) were divided into detrained exercised (DEx) and detrained control (DCo) groups. Trained rats swam 200 min·d for 12 wk, and control rats were taken into water for 5 min·d. After the training period, both groups remained sedentary for 8 wk. We performed echocardiography at weeks 12 and 20 to investigate the development and regression of exercise-induced structural changes. LV pressure-volume analysis was performed to calculate cardiac functional parameters. LV samples were harvested for histological examination.

RESULTS

Echocardiography showed robust LV hypertrophy after completing the training protocol (LV mass index = 2.61 ± 0.08 DEx vs 2.04 ± 0.04 g·kg DCo, P < 0.05). This adaptation regressed after detraining (LV mass index = 2.01 ± 0.03 vs 1.97 ± 0.05 g·kg, n.s.), which was confirmed by postmortem measured heart weight and histological morphometry. After the 8-wk-long detraining period, a regression of the previously described exercise-induced cardiac functional alterations was observed (DEx vs DCo): stroke volume (SV; 144.8 ± 9.0 vs 143.9 ± 9.6 μL, P = 0.949), active relaxation (τ = 11.5 ± 0.3 vs 11.3 ± 0.4 ms, P = 0.760), contractility (preload recruitable stroke work = 69.5 ± 2.7 vs 70.9 ± 2.4 mm Hg, P = 0.709), and mechanoenergetic (mechanical efficiency = 68.7 ± 1.2 vs 69.4 ± 1.8, P = 0.742) enhancement reverted completely to control values. Myocardial stiffness remained unchanged; moreover, no fibrosis was observed after the detraining period.

CONCLUSION

Functional consequences of exercise-induced physiological LV hypertrophy completely regressed after 8 wk of deconditioning.

Exercise mediated protection of diabetic heart through modulation of microRNA mediated molecular pathways

Hyperglycaemia, hypertension, dyslipidemia and insulin resistance collectively impact on the myocardium of people with diabetes, triggering molecular, structural and myocardial abnormalities. These have been suggested to aggravate oxidative stress, systemic inflammation, myocardial lipotoxicity and impaired myocardial substrate utilization. As a consequence, this leads to the development of a spectrum of cardiovascular diseases, which may include but not limited to coronary endothelial dysfunction, and left ventricular remodelling and dysfunction. Diabetic heart disease (DHD) is the term used to describe the presence of heart disease specifically in diabetic patients. Despite significant advances in medical research and long clinical history of anti-diabetic medications, the risk of heart failure in people with diabetes never declines. Interestingly, sustainable and long-term exercise regimen has emerged as an effective synergistic therapy to combat the cardiovascular complications in people with diabetes, although the precise molecular mechanism(s) underlying this protection remain unclear. This review provides an overview of the underlying mechanisms of hyperglycaemia- and insulin resistance-mediated DHD with a detailed discussion on the role of different intensities of exercise in mitigating these molecular alterations in diabetic heart. In particular, we provide the possible role of exercise on microRNAs, the key molecular regulators of several pathophysiological processes.

Acute and Chronic Exercise in Animal Models

Numerous animal cardiac exercise models using animal subjects have been established to uncover the cardiovascular physiological mechanism of exercise or to determine the effects of exercise on cardiovascular health and disease. In most cases, animal-based cardiovascular exercise modalities include treadmill running, swimming, and voluntary wheel running with a series of intensities, times, and durations. Those used animals include small rodents (e.g., mice and rats) and large animals (e.g., rabbits, dogs, goats, sheep, pigs, and horses). Depending on the research goal, each experimental protocol should also describe whether its respective exercise treatment can produce the anticipated acute or chronic cardiovascular adaptive response. In this chapter, we will briefly describe the most common kinds of animal models of acute and chronic cardiovascular exercises that are currently being conducted and are likely to be chosen in the near future. Strengths and weakness of animal-based cardiac exercise modalities are also discussed.

Disruption of mitochondrial quality control in peripheral artery disease: New therapeutic opportunities

Peripheral artery disease (PAD) is a multifactorial disease initially triggered by reduced blood supply to the lower extremities due to atherosclerotic obstructions. It is considered a major public health problem worldwide, affecting over 200 million people. Management of PAD includes smoking cessation, exercise, statin therapy, antiplatelet therapy, antihypertensive therapy and surgical intervention. Although these pharmacological and non-pharmacological interventions usually increases blood flow to the ischemic limb, morbidity and mortality associated with PAD continue to increase. This scenario raises new fundamental questions regarding the contribution of intrinsic metabolic changes in the distal affected skeletal muscle to the progression of PAD. Recent evidence suggests that disruption of skeletal muscle mitochondrial quality control triggered by intermittent ischemia-reperfusion injury is associated with increased morbidity in individuals with PAD. The mitochondrial quality control machinery relies on surveillance systems that help maintaining mitochondrial homeostasis upon stress. In this review, we describe some of the most critical mechanisms responsible for the impaired skeletal muscle mitochondrial quality control in PAD. We also discuss recent findings on the central role of mitochondrial bioenergetics and quality control mechanisms including mitochondrial fusion-fission balance, turnover, oxidative stress and aldehyde metabolism in the pathophysiology of PAD, and highlight their potential as therapeutic targets.

A new model of short acceleration-based training improves exercise performance in old mice

In order to identify a more appealing exercise strategy for the elderly, we studied a mouse model to determine whether a less time-consuming training program would improve exercise performance, enzyme activities, mitochondrial respiration, and metabolomic parameters. We compared the effects of short-session (acceleration-based) training with those of long-session endurance training in 23-month-old mice. The short-session training consisted of five acceleration-based treadmill running sessions over 2 weeks (the acceleration group), whereas the endurance training consisted of five-one-hour treadmill sessions per week for 4 weeks (the endurance group). A control group of mice was also studied. In the acceleration group, the post-training maximum running speed and time to exhaustion were significantly improved, relative to pretraining values (+8% for speed, P<.05; +10% for time to exhaustion, P<.01). The post-training maximum running speed was higher in the acceleration group than in the endurance group (by 23%; P<.001) and in the control group (by 15%; P<.05). In skeletal muscle samples, the enzymatic activities of citrate synthase, lactate dehydrogenase, and creatine kinase were significantly higher in the acceleration group than in the endurance group. Furthermore, mitochondrial respiratory activity in the gastrocnemius was higher in the acceleration group than in the control group. A metabolomic urine analysis revealed a higher mean taurine concentration and a lower mean branched amino acid concentration in the acceleration group. In old mice, acceleration-based training appears to be an efficient way of increasing performance by improving both aerobic and anaerobic metabolism, and possibly by enhancing antioxidant defenses and maintaining muscle protein balance.

High-intensity interval training, but not continuous training, reverses right ventricular hypertrophy and dysfunction in a rat model of pulmonary hypertension

Exercise is beneficial in pulmonary arterial hypertension (PAH), although studies to date indicate little effect on the elevated pulmonary pressures or maladaptive right ventricle (RV) hypertrophy associated with the disease. For chronic left ventricle failure, high-intensity interval training (HIIT) promotes greater endothelial stimulation and superior benefit than customary continuous exercise training (CExT); however, HIIT has not been tested for PAH. Therefore, here we investigated acute and chronic responses to HIIT vs. CExT in a rat model of monocrotaline (MCT)-induced mild PAH. Six weeks of treadmill training (5 times/wk) were performed, as either 30 min HIIT or 60 min low-intensity CExT. To characterize acute hemodynamic responses to the two approaches, novel recordings of simultaneous pulmonary and systemic pressures during running were obtained at pre- and 2, 4, 6, and 8 wk post-MCT using long-term implantable telemetry. MCT-induced decrement in maximal aerobic capacity was ameliorated by both HIIT and CExT, with less pronounced pulmonary vascular remodeling and no increase in RV inflammation or apoptosis observed. Most importantly, only HIIT lowered RV systolic pressure, RV hypertrophy, and total pulmonary resistance, and prompted higher cardiac index that was complemented by a RV increase in the positive inotrope apelin and reduced fibrosis. HIIT prompted a markedly pulsatile pulmonary pressure during running and was associated with greater lung endothelial nitric oxide synthase after 6 wk. We conclude that HIIT may be superior to CExT for improving hemodynamics and maladaptive RV hypertrophy in PAH. HIIT's superior outcomes may be explained by more favorable pulmonary vascular endothelial adaptation to the pulsatile HIIT stimulus.

Left ventricular vascular and metabolic adaptations to high-intensity interval and moderate intensity continuous training: a randomized trial in healthy middle-aged men

KEY POINTS

High-intensity interval training (HIIT) has become popular, time-sparing alternative to moderate intensity continuous training (MICT), although the cardiac vascular and metabolic effects of HIIT are incompletely known. We compared the effects of 2-week interventions with HIIT and MICT on myocardial perfusion and free fatty acid and glucose uptake. Insulin-stimulated myocardial glucose uptake was decreased by training without any significantly different response between the groups, whereas free fatty acid uptake remained unchanged. Adenosine-stimulated myocardial perfusion responded differently to the training modes (change in mean HIIT: -19%; MICT: +9%; P = 0.03 for interaction) and was correlated with myocardial glucose uptake for the entire dataset and especially after HIIT training. HIIT and MICT induce similar metabolic and functional changes in the heart, although myocardial vascular hyperaemic reactivity is impaired after HIIT, and this should be considered when prescribing very intense HIIT for previously untrained subjects.

ABSTRACT

High-intensity interval training (HIIT) is a time-efficient way of obtaining the health benefits of exercise, although the cardiac effects of this training mode are incompletely known. We compared the effects of short-term HIIT and moderate intensity continuous training (MICT) interventions on myocardial perfusion and metabolism and cardiac function in healthy, sedentary, middle-aged men. Twenty-eight healthy, middle-aged men were randomized to either HIIT or MICT groups (n = 14 in both) and underwent six cycle ergometer training sessions within 2 weeks (HIIT session: 4-6 × 30 s all-out cycling/4 min recovery, MICT session 40-60 min at 60% V̇O2 peak ). Cardiac magnetic resonance imaging (CMRI) was performed to measure cardiac structure and function and positron emission tomography was used to measure myocardial perfusion at baseline and during adenosine stimulation, insulin-stimulated glucose uptake (MGU) and fasting free fatty acid uptake (MFFAU). End-diastolic and end-systolic volumes increased and ejection fraction slightly decreased with both training modes, although no other changes in CMRI were observed. MFFAU and basal myocardial perfusion remained unchanged. MGU was decreased by training (HIIT from 46.5 to 35.9; MICT from 47.4 to 44.4 mmol 100 g^-1  min^-1 , P = 0.007 for time, P = 0.11 for group × time). Adenosine-stimulated myocardial perfusion responded differently to the training modes (change in mean HIIT: -19%; MICT: +9%; P = 0.03 for group × time interaction). HIIT and MICT induce similar metabolic and functional changes in the heart, although myocardial vascular hyperaemic reactivity is impaired after HIIT. This should be taken into account when prescribing very intense HIIT for previously untrained subjects.

Relationship between cardiac deformation parameters measured by cardiovascular magnetic resonance and aerobic fitness in endurance athletes

BACKGROUND

Athletic training leads to remodelling of both left and right ventricles with increased myocardial mass and cavity dilatation. Whether changes in cardiac strain parameters occur in response to training is less well established. In this study we investigated the relationship in trained athletes between cardiovascular magnetic resonance (CMR) derived strain parameters of cardiac function and fitness.

METHODS

Thirty five endurance athletes and 35 age and sex matched controls underwent CMR at 3.0 T including cine imaging in multiple planes and tissue tagging by spatial modulation of magnetization (SPAMM). CMR data were analysed quantitatively reporting circumferential strain and torsion from tagged images and left and right ventricular longitudinal strain from feature tracking of cine images. Athletes performed a maximal ramp-incremental exercise test to determine the lactate threshold (LT) and maximal oxygen uptake (V̇O2max).

RESULTS

LV circumferential strain at all levels, LV twist and torsion, LV late diastolic longitudinal strain rate, RV peak longitudinal strain and RV early and late diastolic longitudinal strain rate were all lower in athletes than controls. On multivariable linear regression only LV torsion (beta = -0.37, P = 0.03) had a significant association with LT. Only RV longitudinal late diastolic strain rate (beta = -0.35, P = 0.03) had a significant association with V̇O2max.

CONCLUSIONS

This cohort of endurance athletes had lower LV circumferential strain, LV torsion and biventricular diastolic strain rates than controls. Increased LT, which is a major determinant of performance in endurance athletes, was associated with decreased LV torsion. Further work is needed to understand the mechanisms by which this occurs.

Oxygen uptake, respiratory exchange ratio, or total distance: a comparison of methods to equalize exercise volume in Wistar rats

This study compared strategies to equalize the volume of aerobic exercise performed with different intensities by Wistar rats, based on the distance covered during exercise bouts and energy expenditure (EE, isocaloric sessions) obtained from oxygen uptake (V̇O₂) or respiratory exchange ratio (RER). Thirty-three male rats (270.5±12.8 g) underwent maximal exercise tests to determine V̇O₂ reserve (V̇O₂R), being randomly assigned to three groups: moderate-intensity continuous exercise at speed corresponding to 50% V̇O₂R (MIC; n=11); high-intensity continuous exercise at 80% V̇O₂R (HIC; n=11); and high-intensity intermittent exercise (HII; n=11) at 60% V̇O₂R (3 min) and 80% V̇O₂R (4 min). Exercise duration was calculated individually to elicit EE of 5 kcal in each session. No difference between groups was found for total running distance (MIC: 801±46, HIC: 734±42, HII: 885±64 m; P=0.13). Total EE measured by RER was systematically underestimated compared to values obtained from V̇O₂ (HII: 4.5% and MIC: 6.2%, P<0.05). Total EE (calculated from V̇O₂), and duration of HIC bouts (2.8 kcal and 30.8±2.2 min) were lower (P<0.0001) than in MIC (4.9 kcal and 64.7±1.8 min) and HII (4.7 kcal and 46.9±2.2 min). Predicted and actual values of total V̇O₂, total EE, and duration of isocaloric sessions were similar in MIC and HII (P>0.05), which were both higher than in HIC (P<0.0001). In conclusion, the time to achieve a given EE in exercise bouts with different intensities did not correspond to the total distance. Therefore, the volume of aerobic exercise in protocols involving Wistar rats should be equalized using EE rather than total covered distance.

Similar Responses of Circulating MicroRNAs to Acute High-Intensity Interval Exercise and Vigorous-Intensity Continuous Exercise

High-intensity interval exercise (HIIE) has been reported to be more beneficial for physical adaptation than low-to-moderate exercise intensity. Recently, it is becoming increasingly evident that circulating miRNAs (c-miRNAs) may distinguish between specific stress signals imposed by variations in the duration, modality, and type of exercise. The aim of this study is to investigate whether or not HIIE is superior to vigorous-intensity continuous exercise (VICE), which is contributing to develop effective fitness assessment. Twenty-six young males were enrolled, and plasma samples were collected prior to exercise and immediately after HIIE or distance-matched VICE. The miRNA level profiles in HIIE were initially determined using TaqMan Low Density Array (TLDA). And the differentially miRNAs levels were validated by stem-loop quantitative reverse-transcription PCR (RT-qPCR). Furthermore, these selective c-miRNAs were measured for VICE. Our results showed that some muscle-related miRNAs levels in the plasma, such as miR-1, miR-133a, miR-133b, and miR-206 significantly increased following HIIE or VICE compared to those at rest (P < 0.05), and there was only a significant reduction in miR-1 level for HIIE compared to VICE (P < 0.05), while no significant differences were observed for other muscle-related miRNAs between both exercises (P > 0.05). In addition, some tissue-related or unknown original miRNA levels, such as miR-485-5p, miR-509-5p, miR-517a, miR-518f, miR-520f, miR-522, miR-553, and miR-888, also significantly increased (P < 0.05) in both exercises compared to rest. However, no significant differences were found between both exercises (P > 0.05). Overall, endurance exercise assessed in this study both led to significant increases in selective c-miRNAs of comparable magnitude, suggesting that both types of endurance exercise have general stress processes. Accordingly, the similar responses to both acute exercises likely indicate both exercises can be used interchangeably. Further work is needed to reveal the functional significance and signaling mechanisms behind changes in c-miRNA turnover during exercise.

Effects of High Intensity Interval Training on Pregnant Rats, and the Placenta, Heart and Liver of Their Fetuses

OBJECTIVE

To investigate the effects of high intensity interval training (HIIT) on the maternal heart, fetuses and placentas of pregnant rats.

METHODS

Female Sprague-Dawley rats were randomly assigned to HIIT or sedentary control groups. The HIIT group was trained for 6 weeks with 10 bouts of high intensity uphill running on a treadmill for four minutes (at 85-90% of maximal oxygen consumption) for five days/week. After three weeks of HIIT, rats were mated. After six weeks (gestational day 20 in pregnant rats), echocardiography was performed to evaluate maternal cardiac function. Real-time PCR was performed for the quantification of gene expression, and oxidative stress and total antioxidant capacity was assessed in the tissue samples.

RESULTS

Maternal heart weight and systolic function were not affected by HIIT or pregnancy. In the maternal heart, expression of 11 of 22 genes related to cardiac remodeling was influenced by pregnancy but none by HIIT. Litter size, fetal weight and placental weight were not affected by HIIT. Total antioxidant capacity, malondialdehyde content, peroxidase and superoxide dismutase activity measured in the placenta, fetal heart and liver were not influenced by HIIT. HIIT reduced the expression of eNOS (p = 0.03), hypoxia-inducible factor 1α (p = 0.04) and glutathione peroxidase 4.2 (p = 0.02) in the fetal liver and increased the expression of vascular endothelial growth factor-β (p = 0.014), superoxide dismutase 1 (p = 0.001) and tissue inhibitor of metallopeptidase 3 (p = 0.049) in the fetal heart.

CONCLUSIONS

Maternal cardiac function and gene expression was not affected by HIIT. Although HIIT did not affect fetal growth, level of oxidative stress and total antioxidant capacity in the fetal tissues, some genes related to oxidative stress were altered in the fetal heart and liver indicating that protective mechanisms may be activated.

How exercise may amend metabolic disturbances in diabetic cardiomyopathy

SIGNIFICANCE

Over-nutrition and sedentary lifestyle has led to a worldwide increase in obesity, insulin resistance, and type 2 diabetes (T2D) associated with an increased risk of development of cardiovascular disorders. Diabetic cardiomyopathy, independent of hypertension or coronary disease, is induced by a range of systemic changes and may through multiple processes result in functional and structural cardiac derangements. The pathogenesis of this cardiomyopathy is complex and multifactorial, and it will eventually lead to reduced cardiac working capacity and increased susceptibility to ischemic injury.

RECENT ADVANCES

Metabolic disturbances such as altered lipid handling and substrate utilization, decreased mechanical efficiency, mitochondrial dysfunction, disturbances in nonoxidative glucose pathways, and increased oxidative stress are hallmarks of diabetic cardiomyopathy. Interestingly, several of these disturbances are found to precede the development of cardiac dysfunction.

CRITICAL ISSUES

Exercise training is effective in the prevention and treatment of obesity and T2D. In addition to its beneficial influence on diabetes/obesity-related systemic changes, it may also amend many of the metabolic disturbances characterizing the diabetic myocardium. These changes are due to both indirect effects, exercise-mediated systemic changes, and direct effects originating from the high contractile activity of the heart during physical training.

FUTURE DIRECTIONS

Revealing the molecular mechanisms behind the beneficial effects of exercise training is of considerable scientific value to generate evidence-based therapy and in the development of new treatment strategies.