The Right
Level of Exercise to Keep a Healthy Heart
By Nicholas Bakalar - The New York
Times
Exercise capacity is a well-established
predictor of cardiac mortality in women, but now a new study indicates how much
exercise is enough.
In a report that compares the capacities of
thousands of women with cardiovascular symptoms and without them, researchers
have determined the degree of exercise required to assure cardiac health.
The paper appears in the Aug. 4, 2005 issue
of The New England Journal of Medicine.
The 5,271 women without symptoms were
recruited in the Chicago metropolitan area to participate in a study of heart
disease in women.
The 4,471 women with symptoms had been
referred from 1990 to 1995 for exercise stress tests for the evaluation of
suspected coronary disease.
By following these women over more than a
decade, the researchers were able to predict what effect the right amount of
exercise would have. Age-predicted exercise capacity was established by
averaging the results of the stress tests in asymptomatic women.
The study found that women who scored less
than 85 percent of their age-predicted exercise capacity had double the risk of
dying of any cause, and more than two and a half times the risk of dying of
cardiac disease.
"Previous studies never told us the
prognostic implications of not achieving your age-predicted exercise level,"
said Dr. Martha Gulati, the lead author. "This study is based on women we've
followed since 1992. We know who's dead and who's alive, and we've found that
if you achieve under 85 percent of your age-predicted exercise level, you're
considerably more likely to die from cardiac disease."
Exercise capacity is measured in
MET's (pronounced mets), or metabolic
equivalents that indicate how much oxygen the body is consuming.
(One MET is 3.5 millileters of oxygen per kilogram of body weight per
minute.)
As the activity becomes more physically
demanding, the number increases: just sitting still and breathing uses one MET;
carrying golf clubs while walking around the course uses five. For the study,
participants were tested on sophisticated hospital machines, but a hospital
stress test is neither necessary nor recommended for people who are
asymptomatic, even though it might provide useful information.
In any case, Dr. Gulati said, there is no
need to get a stress test to determine the ideal level of exercise. "It's easy
for people to see how hard they are working out," she said.
"On almost all modern gym machines," she
added, "there is a MET's indicator, even though most people probably don't use
the information it provides."
This is the first time exercise guidelines
have been established for women taking their age into account, Dr. Gulati said,
adding: "That's important because we've never known about women. Everything has
been done with men, and the guidelines are very different."
The study has enabled researchers to create
a chart, called a nomogram, that indicates the predicted exercise capacity in
MET's for any age. Such nomograms are routinely used in clinical practice for
men, but this is the first ever established for women.
"It's easy to use, and women should be using
it to guide how hard they are working out," Dr. Gulati said. For a woman of 60,
seven MET's is 100 percent of the predicted exercise capacity. But for a woman
of 30, it is only 62 percent of capacity - not enough to lower her risk for
cardiac illness.
The authors concede that their nomogram was
created from data on asymptomatic, mostly white women, and that the comparison
group was significantly more racially diverse, with a stronger representation
of black women. A nomogram derived from a more racially diverse group might
produce different recommendations.
The amount of time spent exercising is
important, of course. But Dr. Gulati said, "If you achieve the maximum, even
for a short duration, knowing that your heart can sustain it is very good
news." |
