Because of limited test results for women under 40, the researchers were unable to recommend a new formula for this group.
Allison's team also found that younger men have a lower resting heart rate and higher peak heart rate than women. In addition, men's heart rates rise more dramatically during exercise and return to normal more quickly after stopping, the researchers said.
Heart experts welcomed the preliminary results.
"This is timely and we've needed it for a while," said 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.
However, Steinbaum thinks it will take more research before a new formula that takes sex differences into account could become standard practice. Still, women might want to try the proposed formula on their own, she said. "It's worth considering implementing these new guidelines in their exercise routine," she said.
While the study did not look at the reasons for the gender differences, the researchers speculate that hormones, particularly the male hormone testosterone, are involved.
Also, when the current formula was developed, medical studies recruited few women, Allison said.
"It's logical that an equation developed 40 years ago based on a group that was predominantly men might not be accurate when applied to women today," he said.
Dr. Kevin Marzo, chief of cardiology at Winthrop-University Hospital in Mineola, N.Y., said the original formula stems from research in the early 1970s.
"Once again we learn that men and women are very different and our medical research and treatments need to be gender- specific," he said.
Research presented at meetings is typically considered preliminary until published in a peer-reviewed medical journal.