NEW YORK (Reuters) - Couples wanting to improve their sex lives may want to look at how they divide household chores, because men and women who follow traditional roles have sex more often than other couples, researchers said on Wednesday.

In a study that analyzed the roles of 4,500 heterosexual married couples in the United States, researchers found that when women handled the cooking, cleaning and shopping, and men did yard work and car maintenance, they had more active sex lives.

"The results show that gender still organizes quite a bit of everyday life in marriage," Julie Brines, a University of Washington (UW) associate professor of sociology and a co-author of the study, said in a statement.

"In particular, it seems that the gender identities husbands and wives express through the chores they do also help structure sexual behavior."

The findings, which are published in the American Sociological Review journal, showed that couples with traditional roles at home had sex 1.6 times more per month than those in which the husband did all the traditionally female work.

But Brines and her colleagues said the findings should not be used by men as an excuse not to help out at home.

"Men who refuse to help around the house could increase conflict in their marriage and lower their wives' marital satisfaction," said lead author Sabino Kornrich, a former UW graduate student who is now a researcher at the Juan March Institute in Madrid.

Although the data used in the study was collected from 1992 to 1994, which is the most recent survey looking into sexual frequency among married couples, Brines said it is unlikely that sex in the marital home has changed much since then.

"Marriage today isn't what it was 30 or 40 years ago, but there are some things that remain important," she said. "Sex and housework are still key aspects of sharing a life, and both are related to marital satisfaction and how spouses express their gender identity."