Appearances can be deceptive, the researchers say

A Queen's University, Ontario, team examined volunteers' walks and the levels of sex hormones in their saliva.

They found those with alluring walks were the furthest away from ovulation.

A British expert said the research, featured by New Scientist magazine, supported the idea women disguise their fertility to deter unsuitable partners.

'Surprising results'

Women give a wide variety of subtle signals to men to advertise the fact that they are ready to conceive and Meghan Provost, the lead researcher, had expected a "sexy", hip-swinging walk to be one of those.

If women are trying to protect themselves from sexual assault at times of peak fertility, it would make sense for them to advertise attractiveness... when they are not fertile

Meghan Provost, lead researcher

She analysed the gait of female volunteers, showed video clips to 40 men, asking them to rate the attractiveness of the way the women walked, and then matched the results to the hormone tests.

She said the results, published in the journal Archives of Sexual Behavior, were so surprising that she had repeated the experiment again with another group of male viewers.

The women who were most fertile at the time of the experiment walked with fewer hip movements and with their knees closer together.

She now thinks the findings tally with other research suggesting that women want to conceal their ovulation from males other than their chosen partner.

Monogamy

A sexy walk would be too obvious, so women are thought to use changes in smell and facial expressions that can be experienced only at close range.

Ms Provost said: "If women are trying to protect themselves from sexual assault at times of peak fertility, it would make sense for them to advertise attractiveness on a broad scale when they are not fertile."

Dr John Manning, from the University of Central Lancashire, agreed with this theory.

He said it was in a woman's best interests to form a closer attachment to one man to help raise children, rather than to advertise her fertile time and be approached by a larger number of competing males.

He said: "I think that the subtle signs of ovulation are used, in a sense, to promote monogamy.

"If you want to pick up on these, you have to be already living with, or close to, the woman, so this constrains the man into daily attendance on a woman."