Women who calculate their peak heart rates for exercise using the old formula of "220 minus your age" will have to do some new math, new research suggests.
A new formula based on a large study of middle-aged women provides a more accurate estimate of the peak heart rate a healthy woman should attain during exercise.
The new formula for women is "206 minus 88 per cent of age."
Doctors say having an accurate formula is critical especially for doctors giving stress tests to patients since it will more accurately predict the risk of heart-related death among those patients.
The "220 minus your age" formula used for decades was calculated based on studies of men. But women are not just small men, say researchers at Northwestern University's Feinberg School of Medicine in Chicago, who came up with the new formula.
"There is a physiologic response in women that is different from men," said study author Dr. Martha Gulati, an assistant professor of medicine and preventive medicine at Northwestern.
The differences in the new formulas are subtle but could be significant for those at risk of heart trouble. For example, the original formula would have held that a 50-year-old woman should have a peak heart rate of 170 beats per minute. The new formula would put the maximum heart rate at 162 beats.
The new formula is based on an analysis of 5,437 healthy women aged 35 and older (average age 52) who took part in the St. James Women Take Heart Project, launched in the Chicago area in 1992.
"Using the [original] formula, we are more likely to tell women they have a worse prognosis than they do," Gulati said in an American Heart Association news release.
"With this gender-specific formula, our risk predictions in women will be more accurate."
The research is published in the latest issue of Circulation.
The new formula is trickier to calculate, the researchers acknowledged, but it can be done easily with a calculator. Gulati is currently working on an iPhone application for a quick calculation.
