WASHINGTON (AP) - Many shoe manufacturers don't know what a woman's foot is really like, and those that do know aren't telling, a researcher says.

Sports shoes are the most likely to be designed to conform to the anatomy of a woman's foot, said researcher Peter J. Cavanagh of Penn State University. Even here, however, there's no way to be sure that companies which studied women's feet incorporate everything they have learned, he said.

"Few manufacturers have looked at this in great detail," Cavanagh said.

Most shoemakers base women's shoes on a last, the form on which the shoe is made, that is a scaled-down version of a men's last, he said.

Women are not men with smaller feet, Cavanagh said. Some major makers of sports shoes have measured differences in men's and women's feet. But the companies don't publish their data, so there's no way to tell how much they know, he said.

Cavanagh and graduate student Roshna E. Wunderlich examined data on the anatomy of men's and women's feet. Their findings are reported in the April issue of the American College of Sports Medicine journal, Medicine and Science in Sports and Exercise. It's the first journal article to publicly list sex differences in feet, Cavanagh said.

The data came from an Army examination of the feet of 293 men and 491 women. While the data on each sex were examined separately, and used to help design Army boots, differences between the sexes were not analyzed before, the report said.

Women have smaller feet than men - a fact that's long been known. But even holding foot length constant, statistically giving men and women the same shoe size, there were anatomical differences, the researchers found.

Women have thicker ankles and calves, higher arches and narrower heels, Cavanagh said. "A woman with the standard foot size common to men and women would have about three quarters of an inch greater calf circumference, and that would be about a quarter of an inch higher," he said. "That is pretty much, if you have a narrow-fitting ski boot."

Also, women's ankles are about one-quarter inch closer to the ground, and men's big toes are a little thicker, Cavanagh said.

Such differences in anatomy could throw off the fit even in a shoe that is the right size based on length, but a woman might not realize what the problem was, Cavanagh said.

The anatomical differences could be one factor in the epidemic of cramped, pinched feet that stalks women, Cavanagh said. "In our society, women generally choose shoes that are not good for their feet to walk around in on a daily basis," he said.

One study found almost 90 percent of women were wearing shoes that were smaller than their feet, by an average of one half inch, he said.

Other factors account for most of the bad fit problem, however. One is style - women's shoes tend to be narrow in the forefoot, cramping the toes and causing bunions, Cavanagh said. Women commonly complain that their shoes are too loose in the heel, he said. So a shoe that fits in the back of the foot might be too tight in the front, he said.

Foot doctors know this because they see the results. "It's a sore point because, as a practitioner, such a large proportion of problems we see are clearly related to improper shoe wear," said Dr. Gail P. Dalton of Atlanta, who chairs the shoe wear committee of the American Orthopaedic Foot and Ankle Society. Matching the shape of the shoe to the shape of the foot would cut the number of injuries, she said.

It would be a public service if the bigger sports shoe companies would make their anatomical data public so other manufacturers could use it, Cavanagh said.

Companies are loathe to do that. They figure they paid for what they know, they get a competitive advantage from it, and they will keep it.

"We do believe it is part of our intellectual property," said Mario Lafortune, director of the Nike sport research lab in Beaverton, Ore.

"We don't release it all publicly, but all the research and findings are put into our shoes and the evolution of our footwear," said Sharan Barbano, group director for women's products at Reebok in Canton, Mass.

As a former world-competitive runner, she knows what a difference the right shoe makes, Barbano said. When she started running, in the late '70s, women had to run in men's shoes because women's sports shoes were not available, Barbano said.

The companies say they base continual improvements on their research. Cavanagh and Dalton counter that they could prove it by revealing their data.

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