This American Heart Association (AHA) Scientific Statement discusses the cardiovascular and health implications of moderate to vigorous physical activity; as well as high-volume, high-intensity exercise regimens; with a goal to provide updated information to help advise patients on appropriate preparticipation screening, and the benefits and risks of physical activity in various circumstances. The following are key points to remember:

1. Epidemiological analyses and biological plausibility support a cause-and-effect relationship between increased levels of physical activity and cardiorespiratory fitness and reduced cardiovascular disease mortality, and suggest that being unfit is an independent risk factor for coronary heart disease. Cardioprotective effects of regular physical exercise include antiatherosclerotic, antiarrhythmia, anti-ischemic, antithrombotic, and psychological factors.
2. The risks of sudden cardiac death (SCD) and acute myocardial infarction (AMI) transiently increase during and shortly after exercise, but with various studies suggesting widely varying estimates of risk (with a 3-fold to 17-fold increase in SCD risk during and up to 30 minutes after vigorous exercise, and a 2-fold to 10-fold increase in AMI within 1 hour of vigorous exercise). However, the absolute risk of experiencing SCD or AMI during exercise is small.
3. AMI and SCD risks are higher in association when physical activity is strenuous, sudden, unaccustomed, or involves high levels of anaerobic metabolism.
4. Cardiac events during amateur athletic events such as marathons and half-marathons attract media attention. To address concern regarding risks associated with these events, one large study of 10.9 million participants in US marathons from 2000 to 2010 found a 0.39 per 100,000 participant risk of sudden cardiac arrest; the risk was higher for men (0.90 per 100,000) than for women (0.16 per 100,000), and for a full marathon (1.01 per 100,000) than for a half-marathon (0.27 per 100,000).
5. Recent evidence suggests that nonacute coronary disease and exercise-induced myocardial ischemia (rather than acute plaque rupture) are the cause of most exercise-related SCD in middle-aged adults, and that acute plaque rupture is the second most common cause.
6. Exercise training is accepted to have a deleterious effect on arrhythmogenic right ventricular cardiomyopathy. However, it is unknown whether high-volume, high-intensity endurance exercise training induces similar negative effects on other genetic cardiac conditions.
7. New recommendations for exercise screening are summarized in the following four points:
   • Physically active asymptomatic individuals without known cardiovascular, metabolic, or renal disease (CMRD) may continue their usual moderate or vigorous exercise and progress gradually as tolerated. Those who develop signs or symptoms of CMRD should immediately discontinue exercise and seek guidance from a medical professional before resuming exercise of any intensity.
   • Physically active asymptomatic individuals with known CMRD who have been medically evaluated within 12 months may continue a moderate-intensity exercise program unless they develop signs or symptoms, which requires immediate cessation of exercise and medical reassessment.
   • Physically inactive individuals without known CMRD may begin light- to moderate-intensity exercise without medical guidance and, provided they remain asymptomatic, progress gradually in intensity.
   • Physically inactive individuals with known CMRD or signs/symptoms that are suggestive of these diseases should seek medical guidance before starting an exercise program, regardless of the intensity.
8. There is insufficient evidence to justify routine cardiovascular screening in young athletes. Although a resting electrocardiogram (ECG) can enhance the detection of disorders associated with an increased risk of SCD, it also is associated with a high rate of false-positive results that then lead to additional testing and possible psychological harm. The AHA/American College of Cardiology scientific statement concluding that available data do not support a public health benefit from using 12-lead ECG as a universal screening tool for athletes is in contrast to a European Society of Cardiology recommendation.
9. Long-term exercise training is associated with benign alterations of cardiac structure and function, including chamber enlargement, improved cardiac function and compliance, and sinus bradycardia and sinus arrhythmia. Emerging evidence, however, suggests that habitual high-volume, high-intensity exercise training can induce cardiac maladaptations including increased risk for atrial fibrillation, coronary artery calcification, and myocardial fibrosis.
10. There is an established curvilinear relationship between exercise volume and cardiovascular health risks, suggesting that higher volumes of exercise are associated with progressively lower cardiovascular risk. A proposed U-shaped relationship between exercise volume and cardiovascular risk suggests that higher volumes and higher-intensity exercise are associated with an increased cardiac risk compared to more modest levels of exercise. This scientific statement concludes that, with a possible exception for atrial fibrillation, there is currently no evidence to reject the curvilinear relationship between exercise volume and cardiovascular risk.
11. Supervised exercise training and habitual physical activity are a Class I recommendation for patients with cardiovascular disease.
12. Patients should be counseled to include a warm-up and a cool-down period during exercise training. Previously inactive patients with or without known cardiovascular disease should be counseled to avoid unaccustomed, vigorous physical exertion and highly strenuous physical activities, to recognize potential exertional-related warning symptoms and signs, and to adapt exercise to the environment.

Clinical Topics: Acute Coronary Syndromes, Arrhythmias and Clinical EP, Cardiovascular Care Team, Diabetes and Cardiometabolic Disease, Heart Failure and Cardiomyopathies, Prevention, Sports and Exercise Cardiology, Implantable Devices, Genetic Arrhythmic Conditions, SCD/Ventricular Arrhythmias, Atrial Fibrillation/Supraventricular Arrhythmias, Exercise

Keywords: Acute Coronary Syndrome, Anaerobiosis, Arrhythmias, Cardiac, Arrhythmia, Sinus, Arrhythmogenic Right Ventricular Dysplasia, Athletes, Atrial Fibrillation, Bradycardia, Coronary Disease, Death, Sudden, Cardiac, Electrocardiography, Exercise, Exercise Therapy, Fibrinolytic Agents, Fibrosis, Myocardial Infarction, Myocardial Ischemia, Physical Exertion, Plaque, Atherosclerotic, Primary Prevention, Public Health, Risk Assessment, Risk Factors, Sedentary Behavior

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