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Placing the Risks and Benefits of Physical Activity in Perspective

In general, engaging in regular physical activity reduces an individual's risk of death due to heart disease — but in susceptible individuals, vigorous activity can increase the risk of an acute myocardial infarction (heart attack) or of sudden cardiac death (SCD). Individuals with advanced atherosclerosis — a disorder that involves a narrowing of the arteries due to a buildup of fatty deposits on their inner walls — are especially susceptible to such risks.

The incidence of both acute myocardial infarction and SCD is greatest in generally sedentary individuals, especially those who engage in unaccustomed physical activity. A paper published in the New England Journal of Medicine found that habitually sedentary men were 56 times more likely to experience cardiac death during or after vigorous exercise than when at rest; by contrast, very physically active men were only five times more likely to die during or after vigorous exercise than when at rest. Another New England Journal of Medicine paper reported that an acute myocardial infarction was 50 times more likely during or soon after vigorous physical exercise in the least active than in the most active subjects.

So while sedentary individuals are advised to change their lifestyle and take up regular physical exercise — starting with low-intensity activities and gradually increasing the intensity at which they exercise — they may require pre-activity screening. Individuals with any health limitations need both medical clearance and, preferably, a professional fitness coach. Individuals identified as being at high risk for cardiac problems should abstain from certain activities. For relevant guidelines, read "When to consult a health-care provider before engaging in physical activities."

It is important to emphasize, however, that even the most restrictive practices will never be able to completely prevent cardiovascular events associated with exercise. It is thus essential that individuals who exercise recognize and report the symptoms that often precede a cardiac event; these are known as "prodromal symptoms" and may include one or more of the following:

  • Chest pain (known as "angina")
  • Increasing fatigue
  • Indigestion, heartburn or other gastrointestinal symptoms
  • Excessive breathlessness
  • Ear or neck pain
  • A feeling of vague malaise
  • Upper respiratory tract infections
  • Dizziness, palpitations or a severe headache

Such symptoms have been shown to be present in 50 percent of joggers, 75 percent of squash players, 81 percent of distance runners and 60 percent of scuba divers who die while exercising. People who exercise must be aware of these facts, and physicians should query patients during medical exams about their exercise habits and their knowledge of prodromal symptoms. Divers who experience any of the symptoms above during exercise should obtain a medical evaluation before they resume diving.

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