May 3, 2007 -- A scientific statement released by the American Heart Association (AHA) aims to put the risks and benefits of exercise "in perspective." According to first author and Co-Chair Paul D. Thompson, MD, FAHA, many clinicians may be familiar with information summarized in the statement, but having that information compiled in a single document should help them make decisions and answer questions in their day-to-day practices.

In particular, the statement addresses the potential adverse cardiovascular events that can be triggered by exercise, how these events arise, and how often they occur and in whom, and provides strategies for reducing complications. Although the statement does not provide step-by-step guidance for dealing with different groups or scenarios, it does synthesize a lot of information from a range of exercise-related documents, and directs clinicians to those documents, where appropriate.

The statement is published online in the April 27 Published Ahead of Print issue and in the May print issue of Circulation.

Exercise Beneficial in Most, but Not All

A key point, said Dr. Thompson, is that doctors and allied healthcare professionals, while advocating regular physical activity, must keep in mind that some patients may not benefit from exercise. "We always talk about the fact that exercise and physical activity has benefits, and that in adults, even if they have mild underlying heart disease or coronary atherosclerosis, the benefits of exercise outweigh the risks, and that's where most of the evidence lies," he explained. "But as we mention in this statement, some situations aren't improved by vigorous exercise, things like hypertrophic cardiomyopathy and anomalous coronary arteries. That's pretty obvious when you think about it, but it's an addition that hasn't been made before. The simple point that some doctors and cardiologists should take from this is that there are some groups who simply don't benefit from being engaged in vigorous exercise."

A Compilation of Helpful Information

The statement reviews the well-established pathological causes of cardiac events in younger vs older adults: in people younger than 40 years, hereditary or congenital abnormalities are typically the cause of exercise-related events, whereas in people older than 40 years, coronary disease is the most common underlying cause. But, as the authors point out, habitual physical exercise has been shown to reduce the risk for events in most people, even those with occult disease, and cardiac rehabilitation appears to reduce the risk for coronary heart disease (CHD) death in people with diagnosed disease. This holds true even though vigorous exercise increases the risk for an event during exercise or soon after. "No evidence suggests that the risks of physical activity outweigh the benefits for healthy subjects. Indeed, the converse appears to be true," Thompson and colleagues write.

To heartwire , Dr. Thompson highlighted other parts of the statement that he believes will be particularly helpful to clinicians.

"This statement is a good compilation of things people ask about frequently, such as morning versus afternoon exercise. So it's a useful document for doctors who talk to patients. When patients say, 'I heard it's more dangerous to exercise in the morning,' this goes through the fact that there is a theoretical consideration of that, but very little data to support it. We come down on the side that it's more important for individuals to exercise regularly than it is that they worry about morning versus evening."

Another example, he said, is whether different types of exercise are more harmful than others -- another topic covered in the statement. "We talk about the fact that snow-shoveling has been repeatedly associated with increased cardiovascular events and probably elicits a higher cardiovascular stress than other activities," Dr. Thompson said.

Other topics covered in the statement include identification of prodromal symptoms, preparing fitness personnel and exercise facilities for cardiovascular emergencies, and preparticipation screening.

Dr. Thompson has disclosed research grants from Merck, Pfizer, AstraZeneca, and Kos Pharma. Complete disclosure information for Dr. Thompson and the other authors is available in the original article.

Circulation. Published online April 27, 2007.

2007;115:2358-2368.

The complete contents of Heartwire , a professional news service of WebMD, can be found at www.theheart.org, a Web site for cardiovascular healthcare professionals.

Clinical Context

Study Highlights

• Vigorous exercise is defined as an absolute exercise work rate of at least 6 metabolic equivalents, which approximates the energy equivalent of activities such as jogging.
• In individuals younger than 30 or 40 years, the most frequent underlying factors for sudden cardiac death are pathologic congenital cardiovascular abnormalities and myocarditis.
• Ventricular arrhythmias are most often the immediate cause of death except for Marfan syndrome, in which aortic rupture is often the proximate cause.
• In young adults with predisposing conditions such as hypertrophic cardiomyopathy or anomalous coronary arteries, the risk from vigorous physical activity is likely to exceed the benefits.
• The incidence of sudden cardiac death in young adults has been estimated at 0.9 and 2.3 per 100,000 for nonathletes and athletes, respectively.
• In older adults, studies in 2 US states estimated hourly death rate has been shown to be 7.6 to 25 times higher during exertion than during leisurely activities.
• The relative risk was greatest among the least vs the most active men.
• In older individuals who die during vigorous exercise, CHD is the most frequent underlying cause.
• Vigorous physical activity may cause coronary thrombosis by worsening mild plaque fissure.
• For patients with CHD, the relative risk for cardiac arrest during vigorous exercise has been documented at 6 to 164 times greater vs without exertion.
• Vigorous exertion transiently increases the risk for acute myocardial infarction and sudden cardiac death, especially among habitually sedentary persons.
• Soon after vigorous exercise, the risk for acute myocardial infarction may be 50 times higher for habitually inactive persons vs the most active individuals.
• Over time, regular physical activity reduces CHD events.
• Acute myocardial infarction and sudden cardiac death among adults and sudden death among nonathletes with hypertrophic cardiomyopathy are more frequent during early morning hours.
• Sudden death and cardiac arrest among young athletes occur primarily in the afternoon and early evening, associated with training and competition.
• The incidence of both acute myocardial infarction and sudden death is greatest in those habitually least physically active; no strategies have been adequately studied to evaluate their ability to reduce exercise-related acute cardiovascular events.
• Observational studies suggest that regular exercise to maintain fitness confers protection against CHD death.
• The AHA recommends preparticipation screening of high school and college athletes and screening at 2- to 4-year intervals.
• Preparticipation screening of athletes aged 12 to 35 years, including electrocardiograms, has been associated with a 90% decrease in sudden death from 3.6 to 0.4 deaths per 100,000 athletes.
• Those with risk factors for CHD should receive preparticipation screening before beginning an exercise program.
• The US Preventive Services Task Force states that insufficient evidence is available to evaluate the value of exercise testing before exercise programs, but the AHA and American College of Sports Medicine recommend exercise testing before vigorous exercise in persons with known cardiovascular disease.
• Prodromal symptoms are more common among those who experience sudden cardiac death, and attention should be paid to athletes with cardiac complaints.
• The AHA recommends that coaches and trainers be trained in cardiopulmonary resuscitation and participants in fitness facilities should be screened for heart disease.
• Active individuals should modify their exercise programs in response to variations in capacity, habitual activity, and the environment.

Pearls for Practice

• Vigorous exercise confers a risk for sudden death among nonathletes, young adults with structural heart disease, and older adults with cardiovascular risk factors.
• Preexercise screening is recommended for young athletes and those with cardiovascular risk, and athletes with prodromal cardiac symptoms should be assessed for sudden cardiac death risk.

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