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WEDNESDAY, March 31 (HealthDayNews) -- This spring's new shoe styles are a fashionista's dream: delicate straps, dainty bows, flowers that bloom at the toes and oh, yes, heels that sometimes go sky-high.

But before you shop, be aware of a new formula, courtesy of a British physics expert, that will help you figure out exactly how high you can go without risking life and limb.

The key? Your "Q" factor.

The formula was released just a little too late for Carrie Bradshaw of HBO's "Sex and the City," who galloped off screen in her teetering Manolo Blahniks in February when the popular series ended. (But hey, there's still the inevitable reunion shows and maybe that movie, so she may put it to good use yet.)

"It's not supposed to be taken too seriously," says Paul Stevenson, a physicist at the University of Surrey who normally researches the structure of atomic nuclei. But when Dianne Stilwell, the University's Institute of Physics public relations specialist and a high-heel fan, asked him to put some science behind women's stilettos, he couldn't resist. "She asked me if I could come up with some way a physicist might describe walking in high heels," he says. "This was the result."

At least part of the formula, he says, is based on real physics. It takes into account such absolutes as your shoe size and years of experience wearing high heels. It also factors in less objective information, such as how much you love the shoes, how likely they are to land you a date or other flattering attention, and how fashionable they are.

It also takes into account the probable effect of drinking while wearing the high heels.

The basic formula (if "basic" is what you can call it) is this: H = Q x [12 + (3 x S/8)]. In this, H is the maximum heel height, in centimeters. Q is the sociological factor (more later on this). S is the shoe size; it must be a good enough base of support to keep you upright.

The Q factor of the formula -- a formula unto itself, and more subjective than mathematical -- encompasses several variables and gets a bit complicated (but put the calculator away; Stevenson does the math for us). Here, Q = [P x L x (Y + 9)] / [(T + 1) x (A + 1) x (Y + 10) x (L + 20)}.

To further decode: P is the probability the shoes will land you a date or other flattering attention. L is the price of the shoes, in British pounds. T is the time elapsed since the shoe was the height of fashion (zero means it's red-hot). A is the units of alcohol consumed while wearing the shoe. Y is the years of experience wearing high heels.

Sparing you the math, here's an example from Stevenson: If you have an extremely fashionable shoe that costs 200 pounds ($363 U.S.), have 10 years of experience, and decide not to drink alcohol for the event to which you're wearing the shoes, your Q value is 0.65. If your shoe size is 6 U.K. (7.5 U.S., an average size) and you plug the Q factor into the general equation, then your maximum heel high is 9.26 centimeters, or about three and a half inches.

If you don't drink, how many more inches do you get in the trade-off? "Quite a lot," Stevenson says. In the same example, if you have just one drink, your recommended maximum heel height is cut in half -- just under a two-inch heel.

Now for Carrie. If she uses this formula, considering her a five-year-or-more wearer, she can cope with a heel height of just over five inches, Stevenson says. That's if she's sober: If she overindulges, the safe height plummets.

A woman podiatrist who occasionally wears high heels laughs at the formula but doesn't discount it. "I think the formula is great," says Kathleen Stone, a member of the board of trustees for the American Podiatric Medical Association.

"It's a fun way to look at high heels," she says, although certain parts of the formula, such as the shoe size, are more scientific than others.

Stone recommends different height of heels to her women patients, depending on the planned activity. "For daytime, I recommend an inch to an inch and a half," she says. "For anything fun, where you are not going to be standing on your feet all night, you can go higher."

But not too high, she warns. "Three-inch heels are dangerous," she says. They throw the body off balance and boost the risk for a fall. "I've seen women fall off three-inch heels and get injured," she says.

And while shoes with wrap-around-the-ankle straps are hot stuff this spring, ankles wrapped in Ace bandages are decidedly not.

More information

To find out more about footwear, visit the American Podiatric Medical Association., which also has a page on on-the-job shoe choices.

(SOURCES: Paul Stevenson, M.A., D.Phil., lecturer, University of Surrey, Britain; Kathleen Stone, D.P.M., podiatrist, Glendale, Ariz., and member, board of trustees, American Podiatric Medical Association)

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