Mayo Clinic researchers are calling for a change in the formula doctors use to determine peak exercise heart rate.
They say the formula of "220 minus age,” commonly used to diagnose heart conditions, may be flawed because it does not account for important differences between men and women.
According to research to be presented at the American College of Cardiology's 63rd Annual Scientific Session, a revised formula would better determine the maximum number of heart beats per minute.
"The standard that's currently in use is somewhat outdated," says Thomas Allison, M.D., cardiologist and director of stress testing at Mayo Clinic, and senior author of the study, Science Daily reports.
"We want to make sure that when people do the stress test, they have an accurate expectation of what a normal peak heart rate is. Every so often, you need to recalibrate what's considered normal."
The old formula was developed from a study that included few women, which is typical of many older medical studies.
Getting the formula correct is important, because knowing the maximum is an indicator of heart health.
A new formula would improve the accuracy of test results for conditions such as coronary heart disease, heart valve disease and heart failure, researchers say.
For the study, Mayo Clinic analyzed 25,000 stress-test results for men and women 40 to 89-years old with no history of cardiovascular disease.
They identified significant differences between men and women.
Researchers found that although peak heart rate declines with age for both sexes, the rate declines more gradually in women.
This difference results in an overestimated peak heart rate in younger women and underestimated peak heart rate in older women, CBS News reports.
While the study did not look at reasons for the gender differences, the researchers speculate that hormones, particularly the male hormone testosterone, are involved.
As a result of the findings, researchers have developed a new formula.
They say the maximum heart rate for women aged 40 to 89 should be 200 minus 67 percent of their age. For men, the preferred formula is 216 minus 93 percent of their age.
The researchers also found that younger men have a lower resting heart rate and higher peak heart rate than women. And they found men's heart rates rise more dramatically during exercise and return to normal more quickly after stopping.
"We want to make sure that when people do the stress test, they have an accurate expectation of what a normal peak heart rate is," Allison said in an American College of Cardiology news release.
Because of limited test results for women under 40, the researchers were unable to recommend a new formula for this group.
But heart experts welcomed the preliminary results, CBS News reports.
"This is timely and we've needed it for a while," says Dr. Suzanne Steinbaum, director of women and heart disease at Lenox Hill Hospital in New York City.
"All of these differences are very important, not only for diagnosis, but also for teaching people how best to exercise to get the most cardiovascular fitness," she said.