Exercise: two-edged sword?

Which is it? Is exercise beneficial or hazardous to your heart? It depends on who you are.

You've probably heard the reports of famous athletes dying on basketball courts, runners found dead with their running shoes on, executives discovered slumped over their treadmills, or middle-aged fathers unearthed alongside their snow shovels. Recent examples include runner/writer Jim Fixx, basketball stars Reggie Lewis, "Pistol Pete" Maravich, and Hank Gathers, and MCI chairman Bill McGowan. During the "blizzard of the century" in 1993, scores of people along the Eastern seaboard died of sudden heart attack while shoveling their driveways.

Every day millions of people vigorously swim laps, run or cycle on back roads and trails, swat racquetballs or shoot hoops at gymnasiums, and dance aerobically at health clubs. Most do so because they believe that they'll feel and look better, and perhaps live longer, because they're keeping their heart in good shape. But in light of recent media reports, how can you be sure that your next run or game will not be your last, that it will not be your heart that fails when you take up that snow shovel?

On the other side, researchers worldwide have published results showing that people who exercise on a regular basis are less likely on average to die of heart disease than those who refrain. Dr. Leiv Sandvik, of Norway, for example, has shown that physically fit men have a risk of heart disease 60 percent lower than the unfit. A group of researchers from Harvard have concluded that inactive people have a risk for heart disease that is 90 percent higher than for those who exercise regularly. The American Heart Association is now so convinced that they have listed inactivity as a major risk factor for heart disease. And the Centers for Disease Control and Prevention has determined that when all the evidence is considered, lack of exercise is just as responsible for the epidemic of heart disease as is high blood pressure, high blood cholesterol, and smoking.

So, which is it? Is exercise beneficial--or hazardous--to your heart? Well, it appears to depend on who you are.

When exercise kills. A recent study of 100 athletes who died young (average age 18), in their prime, showed that 90 of them had heart or blood-vessel birth defects. Most common was hypertrophic cardiomyopathy, a thickening of the heart's main pumping muscle. In other words, when a young athlete dies during or shortly after exercise, it is most often a result of a defect in the structure of the heart or blood vessel that was present at birth. There are renewed calls by many experts that despite the rarity of these types of deaths and the cost of testing, young athletes should be examined prior to sports participation.

For most individuals over age 30 who die during or shortly after exercise, the cause is entirely different--a narrowing of the coronary blood vessels of the heart because of cholesterol and fat deposits called atherosclerosis.

It appears that when people with these narrowed coronary blood vessels exert themselves heavily during exercise, the increase in heart rate and blood pressure may cause a disruption of the deposits, setting in motion a chain of events that causes a complete blockage and heart attack. In other words, middle-aged and older adults who die during exercise tend to be people who already have some heart disease. They are at high risk to begin with, and the vigorous exercise triggers the final heart attack event.

Dr. Murray Mittleman, of the Harvard Medical School, recently studied the heart attack episodes of 1,228 men and women and found that heavy physical exertion was especially risky for people who were habitually inactive. People who usually exercised very little, and then went out and exercised vigorously (e.g., shoveling snow) were much more likely to have suffered a heart attack than those who were accustomed to exercise. Dr. Mittleman has concluded that every year in the United States, 75,000 Americans suffer a heart attack after vigorous exercise, and that these victims tend to be sedentary and at high risk for heart attack to begin with.

In one study of 36 marathon runners who had died suddenly or suffered a heart attack, Dr. Timothy Noakes, of Cape Town, South Africa, found that in most of the cases a strong family history of heart disease, high blood cholesterol, or early warning symptoms (e.g., chest pain) were present. Most of the runners had symptoms of heart disease but denied they had them, and continued training and racing until they finally had a heart attack or died. Jim Fixx, who died at age 52 of a heart attack during a training run, also had experienced early warning symptoms but chose to ignore them.

A rare event. What does all this information mean for you? First of all, it's important to understand that the risk of a heart attack during exercise is low, despite media reports. Most researchers have found that in a given year, less than 10 out of 100,000 men will have a heart attack during exercise. These victims tend to be men who were sedentary, already had heart disease, or were at high risk for it, and then exercised too hard for their fitness level. If you are at low risk for heart disease, have not experienced any symptoms, and exercise moderately, your risk is extremely low, and you have little to worry about. You should experience a strong decrease in heart disease risk because of the regular exercise program.

If you're at high risk. People at high risk for heart disease should avoid heavy exertion until being cleared by their physicians after taking a maximal treadmill EKG test. Even after clearance, intense exercise should be avoided until fitness has been gradually improved and heart disease risk factors have been brought under control.

For most adults, moderate exercise is defined as normal walking or moderate sports play, in which the breathing is deep but controlled so that a conversation can be carried on with a partner (see chart). Regular moderate exercise is particularly recommended for high-risk individuals who need to avoid the perils associated with high-intensity exercise. The message is simple--the two-edged sword of exercise can either slash the risk of heart disease for those who use it wisely, or have the potential to cut down those at risk for this disease when used injudiciously.