It might make women think twice before putting on high heels for a date.
Men find the shoes attractive not because they are glamorous or give the illusion of longer legs but because they make a woman arch her back – which is a signal that she is ready for sex, a study suggests.
It seems to be not the stilettos or kitten heels which are important, but the angle of a woman's back to her bottom.
The theory was tested by showing men photographs of women wearing heels or flats, but with the picture cropped at their ankles.
The closer their back arched to an optimum angle of 45 degrees, the more likely men were to find them attractive.
The authors, led by Dr David Lewis at Murdoch University in Australia, state that this arched back in high heels may communicate information about a woman's 'openness to mating advances'.
In many animals, arching of the lower back is a signal of sexual proceptivity – the tendency to engage in behaviour which instigates or 'promotes' sex.
The study states: 'Because no high-heeled shoes were present in any of the Study 2 stimuli, the current findings cannot be explained by an association between high-heeled footwear and perceptions of women's sexuality, a media-constructed preference for high-heeled shoes, or any other reason that men might have a preference for the shoes themselves.
For the same reason, hypotheses suggesting that high heels influence men's judgments of women because of the appearance or colour of the shoes cannot account for the current findings.'
The researchers recruited 56 women in tight clothing to be photographed in flat shoes, before providing five-inch heels for them to wear.
The photographs, cropping out the women's faces as well as their shoes, were shown to 82 men to be rated for attractiveness.
Two years ago the theory was first proposed that men were most attracted to women with a back curving exactly 45 degrees above the top of her bottom.
The findings provided an explanation for the sex symbol status of celebrities like Kim Kardashian and Jennifer Lopez, as 'buttock mass' was found to increase the angle.
The latest study supports this theory, with men finding women in heels most attractive when they were closest to the 45-degree angle.
The researchers also found men were more attracted to female celebrities when they were wearing heels, and that the shoes changed the arch of women's backs by approximately two degrees.
Explaining why this 'lumbar curvature' angle of 45 degrees is so important, the study states: 'Lumbar curvature may also communicate information about a woman's openness to matign advances – in other mammalian species, lordosis behaviour (i.e. arching of the lower back) is a sign of sexual proceptivity.'
The authors say celebrities, dressed up to enhance their appearance, may arch their back even more to look more beautiful in heels.
An arched back may also be attractive to men, as an evolutionary signal that women are fit for bearing their children, the researchers suggest.
During pregnancy, too much curvature of the spine would have been associated with risks like herniated discs, and not enough curvature would have been associated with muscle fatigue and injury.
The study is published in the journal Frontiers in Psychology.
Men fancy women in heels even when they cannot see the shoes, researchers found.
