August 4, 2005
Groundbreaking Study of 5700 Women Finds Not Enough Exercise Means Serious Risk for Heart Problems, Death
CHICAGO - In a groundbreaking first of its kind study, researchers studied over 5,700 women's fitness levels relative to age and lifestyle, and found that women who score less than 85 percent of their age predicted exercise capacity on an exercise stress test have a two times greater risk for serious heart problems and death.
"The current American College of Cardiology (ACC)/American Heart Association (AHA) exercise guidelines and standards are based on exclusively male data" says Dr. Martha Gulati, study author and preventive cardiologist at Rush University Medical Center, Chicago. "Women were being measured on the same scale as men. From the study we see a woman and man of the same age, that exercise the same amount, have a different age-predicted exercise capacity. This study provides women and clinicians a simple chart that is able to predict with adjusted levels factoring in age, lifestyle and exercise capacity."Gulati says a goal of the research was to create a simple chart (nomogram) women could use to interpret their exercise capacity, based on normative values for their age.
The author explains the 5,721 asymptomatic (normal) women came from The St. James Women Take Heart Project. "The women came from a call for volunteers in 1992 from the Chicago metropolitan area which resulted in a cohort of asymptomatic women. They were 35 years or older, had no active cardiovascular disease and had to be able to walk on a treadmill. Another cohort of 4,471 symptomatic women in the study were from the Economics of Noninvasive Diagnosis (END) study group, from six medical centers, and referred for stress test for evaluation of suspected coronary disease. This cohort was used to validate the model."
All women underwent an exercise treadmill test, using the Bruce Protocol. Gulati said she and her colleagues measured the level of fitness in units of metabolic equivalents (MET) achieved on a treadmill stress test. A MET unit it equal to what you are doing when lying at rest, and any activity greater than that is an increment of one MET. The researchers then calculated the percent exercise capacity as a number.
Gulati explains to chart a woman's percent-predicated exercise capacity, one draws a line between age and fitness (measured in METs). The line will intersect a diagonal line, which is the percent-predicted exercise capacity. She gives the example that a 30-year-old woman and a 60-year-old woman who each achieved at 7 METs would achieved a different percent predicted for age. The 30-year-old would have only reached a 65 percent fitness level, while the 60-year old women would have reached 100 percent of her age predicted fitness level.
The researchers found that normal, healthy women who not able to achieve 85 percent of the predicated exercise capacity were twice as likely to die than those who achieve greater than or equal to 85 percent. The results were confirmed in the symptomatic group. Gulati says this is particularly important in younger women, because younger women are at an increased risk of cardiac death the further they are deviated from their age-predicted fitness level.
These findings contrast with what has been previously reported in males and set the standards for both males and females.
A 50-year-old male must achieve 9.2 percent METs to achieve 100 percent age-predicted exercise capacity. For a 50 year-old-woman, her 100 percent age-predicted exercise capacity would only be 8.2 METs. "This does not mean that women should exercise less than men, but rather that women and men have age-predicted fitness goals," says Gulati.
Gulati says these findings provide women specific normative values and will likely be incorporated within the ACC/AHA guidelines. "Most exercise stress testing systems automatically calculate the exercise capacity/METs achieved. Minimal additional programming would be needed to calculate the percent-predicted exercise capacity achieved for age and gender to further assist clinicians with risk assessment."
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