Physical activity, cardiorespiratory fitness, and cardiovascular health: A clinical practice statement of the ASPC Part I: Bioenergetics, contemporary physical activity recommendations, benefits, risks, extreme exercise regimens, potential maladaptations

Regular moderate-to-vigorous physical activity (PA) and increased levels of cardiorespiratory fitness (CRF) or aerobic capacity are widely promoted as cardioprotective measures in the primary and secondary prevention of atherosclerotic cardiovascular (CV) disease (CVD). Nevertheless, physical inactivity and sedentary behaviors remain a worldwide concern. The continuing coronavirus (COVID-19) pandemic has been especially devastating to patients with known or occult CVD since sitting time and recreational PA have been reported to increase and decrease by 28% and 33%, respectively. Herein, in this first of a 2-part series, we discuss foundational factors in exercise programming, with specific reference to energy metabolism, contemporary PA recommendations, the dose-response relationship of exercise as medicine, the benefits of regular exercise training, including the exercise preconditioning cardioprotective phenotype, as well as the CV risks of PA. Finally, we discuss the 'extreme exercise hypothesis,' specifically the potential maladaptations resulting from high-volume, high-intensity training programs, including accelerated coronary artery calcification and incident atrial fibrillation. The latter is commonly depicted by a reverse J-shaped or U-shaped curve. On the other hand, longevity data argue against this relationship, as elite endurance athletes live 3-6 years longer than the general population.

Exercise Preconditioning as a Cardioprotective Phenotype

Cardiovascular disease (CVD) is potentiated by risk factors including physical inactivity and remains a leading cause of morbidity and mortality. Although regular physical activity does not reverse atherosclerotic coronary disease, precursory exercise improves clinical outcomes in those experiencing life-threatening CVD events. Exercise preconditioning describes the cardioprotective phenotype whereby even a few exercise bouts confer short-term multifaceted protection against acute myocardial infarction. First described decades ago in animal investigations, cardioprotective mechanisms responsible for exercise preconditioning have been identified through reductionist preclinical studies, including the upregulation of endogenous antioxidant enzymes, improved calcium handling, and enhanced bioenergetic regulation during a supply-demand mismatch. Until recently, translation of this research was only inferred from clinically-directed animal models of exercise involving ischemia-reperfusion injury, and reinforced by the gene products of exercise preconditioning that are common to mammalian species. However, recent clinical investigations confirm that exercise preconditions the human heart. This discovery means that simply the initiation of a remedial exercise regimen in those with abnormal CVD risk factor profiles will provide immediate cardioprotective benefits and improved clinical outcomes following acute cardiac events. In conclusion, the prophylactic biochemical adaptations to aerobic exercise are complemented by the long-term adaptive benefits of vascular and architectural remodeling in those who adopt a physically active lifestyle.

Mechanisms Involved in Cardioprotection Induced by Physical Exercise

Significance: Regular exercise training can reduce myocardial damage caused by acute ischemia/reperfusion (I/R). Exercise can reproduce the phenomenon of ischemic preconditioning, due to the capacity of brief periods of ischemia to reduce myocardial damage caused by acute I/R. In addition, exercise may also activate the multiple kinase cascade responsible for cardioprotection even in the absence of ischemia. Recent Advances: Animal and human studies highlighted the fact that, besides to reduce risk factors related to cardiovascular disease, the beneficial effects of exercise are also due to its ability to induce conditioning of the heart. Exercise behaves as a physiological stress that triggers beneficial adaptive cellular responses, inducing a protective phenotype in the heart. The factors contributing to the exercise-induced heart preconditioning include stimulation of the anti-radical defense system and nitric oxide production, opioids, myokines, and adenosine-5'-triphosphate (ATP) dependent potassium channels. They appear to be also involved in the protective effect exerted by exercise against cardiotoxicity related to chemotherapy. Critical Issues and Future Directions: Although several experimental evidences on the protective effect of exercise have been obtained, the mechanisms underlying this phenomenon have not yet been fully clarified. Further studies are warranted to define precise exercise prescriptions in patients at risk of myocardial infarction or undergoing chemotherapy.

Cardioprotection in right heart failure

Ischaemic and pharmacological conditioning of the left ventricle is mediated by the activation of signalling cascades, which finally converge at the mitochondria and reduce ischaemia/reperfusion (I/R) injury. Whereas the molecular mechanisms of conditioning in the left ventricle are well characterized, cardioprotection of the right ventricle is principally feasible but less established. Similar to what is known for the left ventricle, a dysregulation in signalling pathways seems to play a role in I/R injury of the healthy and failing right ventricle and in the ability/inability of the right ventricle to respond to a conditioning stimulus. The maintenance of mitochondrial function seems to be crucial in both ventricles to reduce I/R injury. As far as currently known, similar molecular mechanisms mediate ischaemic and pharmacological preconditioning in the left and right ventricles. However, the two ventricles seem to respond differently towards exercise‐induced preconditioning.

LINKED ARTICLES

This article is part of a themed issue on Risk factors, comorbidities, and comedications in cardioprotection. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v177.23/issuetoc

Exercise benefits in cardiovascular disease: beyond attenuation of traditional risk factors

Despite strong scientific evidence supporting the benefits of regular exercise for the prevention and management of cardiovascular disease (CVD), physical inactivity is highly prevalent worldwide. In addition to merely changing well-known risk factors for systemic CVD, regular exercise can also improve cardiovascular health through non-traditional mechanisms. Understanding the pathways through which exercise influences different physiological systems is important and might yield new therapeutic strategies to target pathophysiological mechanisms in CVD. This Review includes a critical discussion of how regular exercise can have antiatherogenic effects in the vasculature, improve autonomic balance (thereby reducing the risk of malignant arrhythmias), and induce cardioprotection against ischaemia-reperfusion injury, independent of effects on traditional CVD risk factors. This Review also describes how exercise promotes a healthy anti-inflammatory milieu (largely through the release of muscle-derived myokines), stimulates myocardial regeneration, and ameliorates age-related loss of muscle mass and strength, a frequently overlooked non-traditional CVD risk factor. Finally, we discuss how the benefits of exercise might also occur via promotion of a healthy gut microbiota. We argue, therefore, that a holistic view of all body systems is necessary and useful when analysing the role of exercise in cardiovascular health.

Exercise-induced cardiac opioid system activation attenuates apoptosis pathway in obese rats

AIM

To compare the effect of 150 min vs. 300 min of weekly moderate intensity exercise training on the activation of the opioid system and apoptosis in the hearts of a diet-induced obesity model.

METHODS

Male Wistar rats were fed with either control (CON) or high fat (HF) diet for 32 weeks. At the 20th week, HF group was subdivided into sedentary, low (LEV, 150 min·week^-1) or high (HEV, 300 min·week^-1) exercise volume. After 12 weeks of exercise, body mass gain, adiposity index, systolic blood pressure, cardiac morphometry, apoptosis biomarkers and opioid system expression were evaluated.

RESULTS

Sedentary animals fed with HF presented pathological cardiac hypertrophy and higher body mass gain, systolic blood pressure and adiposity index than control group. Both exercise volumes induced physiological cardiac hypertrophy, restored systolic blood pressure and improved adiposity index, but only 300 min·week^-1 reduced body mass gain. HF group exhibited lower proenkephalin, PI3K, ERK and GSK-3β expression, and greater activated caspase-3 expression than control group. Compared to HF, no changes in the cardiac opioid system were observed in the 150 min·week^-1 of exercise training, while 300 min·week^-1 showed greater proenkephalin, DOR, KOR, MOR, Akt, ERK and GSK-3β expression, and lower activated caspase-3 expression.

CONCLUSION

300 min·week^-1 of exercise training triggered opioid system activation and provided greater cardioprotection against obesity than 150 min·week^-1. Our findings provide translational aspect with clinical relevance about the critical dose of exercise training necessary to reduce cardiovascular risk factors caused by obesity.

Preprodynorphin gene mutation causes progressive cardiac conduction disease: A whole-exome analysis of a pedigree

AIMS

Progressive cardiac conduction disease (PCCD) is a rare heart disease that usually shows familial inheritance. Potential genetic risk factors for PCCD have been mostly limited to genes that encode ion channels, cardiac transcription factors, T-box transcription factors, gap junction proteins, energy metabolism regulators and structural proteins.

MAIN METHODS

Subjects in the present study came from a family who exhibited the autosomal dominant inheritance of PCCD. The primary proband had syncope and an electrocardiogram typical for PCCD, which started in the left bundle branch block, and passed to the atrioventricular block. The patient received a permanent pacemaker in 2013. Pathogenic mutations in the proband's family were identified using whole-exome sequencing and Sanger sequencing.

KEY FINDINGS

The results for the family members were verified using Sanger sequencing, while the results for healthy unrelated individuals were verified using SNaPShot. All patients in the family shared two adjacent missense mutations in the preprodynorphin (PDYN) gene (c.581A > T, c.580G > C; p.D194L).

SIGNIFICANCE

The PDYN double mutation c.581A > T and c.580G > C (p.D194L) may be linked to the onset of familial PCCD. The effects of these mutations on electrophysiology require further investigation.

The cTnT response to acute exercise at the onset of an endurance training program: evidence of exercise preconditioning?

PURPOSE

Exercise induces a cardioprotective effect referred to as "preconditioning". Whether the preconditioning impacts upon the cardiac troponin T (cTnT) response to subsequent exercise bouts is unclear. This study investigated the effects of an initial exercise bout, a second exercise bout 48 h later, as well as subsequent exercise every 48 h for 4 days or a single identical exercise bout after 8 days of inactivity gap on cTnT response to acute exercise.

METHODS

Twenty-eight sedentary overweight young women were randomly assigned to either six bouts of exercise each separated by 48 h or three bouts of exercise with 48 h between the first two bouts and 8 days between the second and third bouts. All exercise bouts were identical (60% [Formula: see text], 200 kJ) and the total testing period (10 days) was the same for both groups. cTnT was assessed before and after the 1st, 2nd, and final exercise bouts.

RESULTS

cTnT increased (129%, P < 0.05) after the first bout of exercise in both groups (peak post-exercise cTnT, median [range], ng l^-1: 3.43[< 3.00-27.26]) with no between-group differences in the response. The second exercise bout had no significant (P > 0.05) effect on post-exercise cTnT (< 3.00[< 3.00-21.96]). The final exercise bout resulted in an increase (190%, P < 0.05) in cTnT (4.35[< 3.00-13.05]) in both groups.

CONCLUSIONS

A single bout exercise resulted in a temporary blunting of cTnT response to acute exercise 48 h later. The effect of exercise preconditioning was not preserved, regardless of whether followed by repeated exercise every 48 h or a cessation of exercise for 8 days.

Cardioprotection by intermittent hypoxia conditioning: evidence, mechanisms, and therapeutic potential

The calibrated application of limited-duration, cyclic, moderately intense hypoxia-reoxygenation increases cardiac resistance to ischemia-reperfusion stress. These intermittent hypoxic conditioning (IHC) programs consistently produce striking reductions in myocardial infarction and ventricular tachyarrhythmias after coronary artery occlusion and reperfusion and, in many cases, improve contractile function and coronary blood flow. These IHC protocols are fundamentally different from those used to simulate sleep apnea, a recognized cardiovascular risk factor. In clinical studies, IHC improved exercise capacity and decreased arrhythmias in patients with coronary artery or pulmonary disease and produced robust, persistent, antihypertensive effects in patients with essential hypertension. The protection afforded by IHC develops gradually and depends on β-adrenergic, δ-opioidergic, and reactive oxygen-nitrogen signaling pathways that use protein kinases and adaptive transcription factors. In summary, adaptation to intermittent hypoxia offers a practical, largely unrecognized means of protecting myocardium from impending ischemia. The myocardial and perhaps broader systemic protection provided by IHC clearly merits further evaluation as a discrete intervention and as a potential complement to conventional pharmaceutical and surgical interventions.

Cardioprotective Exercise and Pharmacologic Interventions as Complementary Antidotes to Cardiovascular Disease

Exercise and pharmacologic therapies to prevent and treat cardiovascular disease have advanced largely through independent efforts. Understanding of first-line drug therapies, findings from preclinical animal studies, and the need for research initiatives related to complementary cardioprotective exercise-pharma interventions are reviewed from the premise that contemporary cardioprotective therapies must include adjunctive exercise and lifestyle interventions in addition to pharmacologic agents.

Delta Opioid Receptors and Cardioprotection

The opioid receptor family, with associated endogenous ligands, has numerous roles throughout the body. Moreover, the delta opioid receptor (DORs) has various integrated roles within the physiological systems, including the cardiovascular system. While DORs are important modulators of cardiovascular autonomic balance, they are well-established contributors to cardioprotective mechanisms. Both endogenous and exogenous opioids acting upon DORs have roles in myocardial hibernation and protection against ischaemia-reperfusion (I-R) injury. Downstream signalling mechanisms governing protective responses alternate, depending on the timing and duration of DOR activation. The following review describes models and mechanisms of DOR-mediated cardioprotection, the impact of co-morbidities and challenges for clinical translation.

Exercise-Induced Cardioprotection and the Therapeutic Potential of RIPC

In the search for innovative solutions to treat ischemic heart disease, recent basic science and clinical approaches have focused on remote ischemic preconditioning (RIPC). Remote ischemic preconditioning involves short intervals of limb blood flow occlusion by the application of a blood pressure cuff inflated to a suprasystolic pressure. The promise of RIPC in the development of new cardioprotective therapies is founded on the premise that it is cost-effective, technically simple, and overcomes many logistical and biochemical hurdles associated with other ischemic preconditioning approaches. However, RIPC as a research subarea is still in its infancy and clinical applications for individuals at high risk of cardiovascular disease remain elusive. The thesis of the current review is that observational and mechanistic similarities between exercise-induced preconditioning and RIPC may reveal novel therapeutic links to cardioprotection. While reductionist understanding of the exercised heart is still in the formative stages, available mechanistic knowledge of exercise-induced cardioprotection is juxtaposed to RIPC and potential implications discussed. In total, additional research is needed in order to fully appreciate the mechanistic and translative connections between exercise and RIPC. Nonetheless, existing rationale are strong and suggest that RIPC approaches may be helpful in the development and application to pharmacologic interventions in those with ischemic heart disease.

κ-opioid receptor is involved in the cardioprotection induced by exercise training

The present study was designed to test the hypothesis that exercise training elicited a cardioprotective effect against ischemia and reperfusion (I/R) via the κ-opioid receptor (κ-OR)-mediated signaling pathway. Rats were randomly divided into four groups: the control group, the moderate intensity exercise (ME) group, the high intensity exercise (HE) group, and the acute exercise (AE) group. For the exercise training protocols, the rats were subjected to one week of adaptive treadmill training, while from the second week, the ME and HE groups were subjected to eight weeks of exercise training, and the AE group was subjected to three days of adaptive treadmill training and one day of vigorous exercise. After these protocols, the three exercise training groups were divided into different treatment groups, and the rats were subjected to 30 min of ischemia and 120 min of reperfusion. Changes in infarct size and serum cTnT (cardiac troponin T) caused by I/R were reduced by exercise training. Moreover, cardiac dysfunction caused by I/R was also alleviated by exercise training. These effects of exercise training were reversed by nor-BNI (a selective κ-OR antagonist), Compound C (a selective AMPK inhibitor), Akt inhibitor and L-NAME (a non-selective eNOS inhibitor). Expression of κ-OR and phosphorylation of AMPK, Akt and eNOS were significantly increased in the ME, HE and AE groups. These findings demonstrated that the cardioprotective effect of exercise training is possibly mediated by the κ-OR-AMPK-Akt-eNOS signaling pathway.

Endogenous Opiates and Behavior: 2015

This paper is the thirty-eighth consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2015 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior, and the roles of these opioid peptides and receptors in pain and analgesia, stress and social status, tolerance and dependence, learning and memory, eating and drinking, drug abuse and alcohol, sexual activity and hormones, pregnancy, development and endocrinology, mental illness and mood, seizures and neurologic disorders, electrical-related activity and neurophysiology, general activity and locomotion, gastrointestinal, renal and hepatic functions, cardiovascular responses, respiration and thermoregulation, and immunological responses.

Cardiac Ischemia/Reperfusion Injury: The Beneficial Effects of Exercise

Cardiac ischemia reperfusion injury (IRI) occurs when the myocardium is revascularized after an episode of limited or absent blood supply. Many changes, including free radical production, calcium overload, protease activation, altered membrane lipids and leukocyte activation, contribute to IRI-induced myocardium damage. Aerobic exercise is the only countermeasure against IRI that can be sustained on a regular basis in clinical practice. Interestingly, both short-term (3-5 days) and long-term (several weeks) exercise increase myocardial tolerance, reduce infarct size area and arrhythmias induced by IRI. Exercise protects the heart against IRI in a biphasic manner. The early phase of cardioprotection occurs between 30 min and 3 h following an acute exercise bout, whilst the late phase is achieved within 24 h after the exercise bout and persists for several days. As for the exercise intensity, although controversial data exists, it is feasible that the amount of cardioprotection is proportional to exercise intensity and only achieved above a critical threshold. It is known that aerobic exercise produces a cardioprotective phenotype, however the mechanisms responsible for this phenomenon remain unclear. Apparently, aerobic exercise-induced preconditioning is dependent on several factors that work together to protect the heart. Altered nitric oxide (NO) signaling, increased levels of heat shock proteins (HSPs), enhanced function of ATP-sensitive potassium channels, increased activation of opioids system, and enhanced antioxidant capacity may contribute to exercise-induced cardioprotection. Much has been discovered from animal models involving exercise-induced cardioprotection against cardiac IRI, however translating these findings to clinical practice still represents the major challenge in this field.

Coupling of myocardial stress resistance and signalling to voluntary activity and inactivity

AIMS

We examined coupling of myocardial ischaemic tolerance to physical activity and inactivity, and whether this involves modulation of survival (AKT, AMPK, ERK1/2, HSP27, EGFR) and injury (GSK3β) proteins implicated in ischaemic preconditioning and calorie restriction.

METHODS

Proteomic modifications were assessed in ventricular myocardium, and tolerance to 25-min ischaemia in ex vivo perfused hearts from C57Bl/6 mice subjected to 14-day voluntary activity in running-naïve animals (Active); 7 days of subsequent inactivity (Inactive); brief (day 3) restoration of running (Re-Active); or time-matched inactivity.

RESULTS

Active mice increased running speed and distance by 75-150% over 14 days (to ~40 m min(-1) and 10 km day(-1) ), with Active hearts resistant to post-ischaemic dysfunction (40-50% improvements in ventricular pressure development, diastolic pressure and dP/dt). Cardioprotection was accompanied by ~twofold elevations in AKT, AMPK, HSP27 and GSK3β phosphorylation and EGFR expression. Ischaemic tolerance was reversed in Inactive hearts, paralleling reduced EGFR expression and GSK3β and ERK1/2 phosphorylation (AKT, AMPK, HSP27 phosphorylation unaltered). Running characteristics, ischaemic tolerance, EGFR expression and GSK3β phosphorylation returned to Active levels within 1-3 days of restored activity (without changes in AKT, AMPK or HSP27 phosphorylation). Transcriptional responses included activity-dependent Anp induction vs. Hmox1 and Sirt3 suppression, and inactivity-dependent Adora2b induction.

CONCLUSIONS

Data confirm the sensitive coupling of ischaemic tolerance to activity: voluntary running induces cardioprotection that dissipates within 1 week of inactivity yet recovers rapidly upon subsequent activity. While exercise in naïve animals induces a molecular profile characteristic of preconditioning/calorie restriction, only GSK3β and EGFR modulation consistently parallel activity- and inactivity-dependent ischaemic tolerance.

Mitochondria in the middle: exercise preconditioning protection of striated muscle

Cellular and physiological adaptations to an atmosphere which became enriched in molecular oxygen spurred the development of a layered system of stress protection, including antioxidant and stress response proteins. At physiological levels reactive oxygen and nitrogen species regulate cell signalling as well as intracellular and intercellular communication. Exercise and physical activity confer a variety of stressors on skeletal muscle and the cardiovascular system: mechanical, metabolic, oxidative. Transient increases of stressors during acute bouts of exercise or exercise training stimulate enhancement of cellular stress protection against future insults of oxidative, metabolic and mechanical stressors that could induce injury or disease. This phenomenon has been termed both hormesis and exercise preconditioning (EPC). EPC stimulates transcription factors such as Nrf-1 and heat shock factor-1 and up-regulates gene expression of a cadre of cytosolic (e.g. glutathione peroxidase and heat shock proteins) and mitochondrial adaptive or stress proteins (e.g. manganese superoxide dismutase, mitochondrial KATP channels and peroxisome proliferator activated receptor γ coactivator-1 (PGC-1)). Stress response and antioxidant enzyme inducibility with exercise lead to protection against striated muscle damage, oxidative stress and injury. EPC may indeed provide significant clinical protection against ischaemia-reperfusion injury, Type II diabetes and ageing. New molecular mechanisms of protection, such as δ-opioid receptor regulation and mitophagy, reinforce the notion that mitochondrial adaptations (e.g. heat shock proteins, antioxidant enzymes and sirtuin-1/PGC-1 signalling) are central to the protective effects of exercise preconditioning.

δ-Opioid receptor (DOR) signaling and reactive oxygen species (ROS) mediate intermittent hypoxia induced protection of canine myocardium

Intermittent, normobaric hypoxia confers robust cardioprotection against ischemia-induced myocardial infarction and lethal ventricular arrhythmias. δ-Opioid receptor (DOR) signaling and reactive oxygen species (ROS) have been implicated in cardioprotective phenomena, but their roles in intermittent hypoxia are unknown. This study examined the contributions of DOR and ROS in mediating intermittent hypoxia-induced cardioprotection. Mongrel dogs completed a 20 day program consisting of 5-8 daily, 5-10 min cycles of moderate, normobaric hypoxia (FIO2 0.095-0.10), with intervening 4 min room air exposures. Subsets of dogs received the DOR antagonist naltrindole (200 μg/kg, sc) or antioxidant N-acetylcysteine (250 mg/kg, po) before each hypoxia session. Twenty-four hours after the last session, the left anterior descending coronary artery was occluded for 60 min and then reperfused for 5 h. Arrhythmias detected by electrocardiography were scored according to the Lambeth II conventions. Left ventricles were sectioned and stained with 2,3,5-triphenyl-tetrazolium-chloride, and infarct sizes were expressed as percentages of the area at risk (IS/AAR). Intermittent hypoxia sharply decreased IS/AAR from 41 ± 5 % (n = 12) to 1.8 ± 0.9 % (n = 9; P < 0.001) and arrhythmia score from 4.1 ± 0.3 to 0.7 ± 0.2 (P < 0.001) vs. non-hypoxic controls. Naltrindole (n = 6) abrogated the cardioprotection with IS/AAR 35 ± 5 % and arrhythmia score 3.7 ± 0.7 (P < 0.001 vs. untreated intermittent hypoxia). N-acetylcysteine (n = 6) interfered to a similar degree, with IS/AAR 42 ± 3 % and arrhythmia score 4.7 ± 0.3 (P < 0.001 vs. untreated intermittent hypoxia). Without the intervening reoxygenations, hypoxia (n = 4) was not cardioprotective (IS/AAR 50 ± 8 %; arrhythmia score 4.5 ± 0.5; P < 0.001 vs. intermittent hypoxia). Thus DOR, ROS and cyclic reoxygenation were obligatory participants in the gradually evolving cardioprotection produced by intermittent hypoxia.