A woman who walks with a seductive sway of her hips is unlikely to be ovulating, a finding that sheds light on the complex sexual signals that women give to men, New Scientist reports.
A team at Queen's University in Ontario, Canada, dressed female volunteers in suits which had light reflectors placed on the joints and limbs and filmed them walking in order to analyse their gait, the British weekly says.
The women also gave a saliva sample to assess their hormone levels.
Women who were in the fertile period of their menstrual cycle walked with smaller hip movements and with their knees closer together, the scientists found.
Forty male volunteers were shown the footage of the women and were asked to rate those with the sexiest walk. The winners were those who turned out to be in the least fertile part of their cycle.
The study appears to run counter to recent research that found men respond more readily towards women at ovulation. A US paper published last month found that lap dancers earn more tips during their fertile period than during the non-fertile part of their cycle.
But, the Canadian researchers believe, there is no contradiction, because a fertile woman gives out "come-hither" signals at close range rather than at a distance.
These signals come through scent molecules called pheromones and facial expressions. The proximity means a woman can vet a potential mate for fitness before allowing him to come close to her.
In contrast, men can pick up the attractiveness of a woman's walk from a long distance -- and a "sexy" walk, visible from afar, could therefore act as an unwitting signal to less appealing males.
So, having a less sexy walk at the time of ovulation gives a woman an evolutionary advantage: she can hide her fertile period from an undesirable man who might want to take advantage of her at the time.
The research, by Meghan Provost, is to be published in the US journal Archives of Sexual Behavior, says the report. It appears in this Saturday's issue of New Scientist.