Belinda Goldsmith, New York: Women who wiggle when they walk, or men who walk with a shoulder swagger, were perceived as more attractive than those without a sway in a series of five studies conducted by researchers from New York University and Texas A&M University.

The findings give scientific backing to Marilyn Monroe's decision to adjust the stiletto heels of her shoes, making one heel shorter than the other so she swayed as she walked.

The studies, involving about 700 participants and collated in a report published in the Proceedings of the National Academy of Sciences, found it was not just body shape that was the secret of attraction but also movement.

"People have always tried to identify the magical formula for beauty and we knew body shape was important but we found movement was also key," researcher Kerri Johnson, from New York University's Department of Psychology, told Reuters.

She said three of the five studies used animated silhouettes of people, with volunteer participants asked to rate their attractiveness without telling them the gender. She said the attractiveness ratings of women were over 50 percent higher when they walked with feminine hip sway.

Attractiveness ratings of men more than doubled when they walked with masculine shoulder swagger.

The other two studies involved training people to walk in different ways, recording those walks while blacking out other factors such as hair and clothes, and asking participants to judge their attractiveness.

These studies came up with the same conclusions.

Johnson said a body of evidence had built up suggesting that a simple measurement, such as the waist-to-hip ratio, can predict the attractiveness of a woman with those with hourglass figures coming out tops. But she said this was the first time that movement had been proven to also play a role.

Johnson said the researchers now planned to study whether the perception of attractiveness was influenced by the extent of the hip wiggle or shoulder swagger.

"If I watch the undergraduate women walk around campus, they are more likely to walk in a feminine way with a hip sway if there are men around rather than if they are just off down the corridor to the water fountain," said Johnson.

"But we don't know how much difference the extent of the movement can make."