Ever wonder why your feet hurt? Apparently, shoes are the problem. Not just stiletto heels, mind you - pretty much all shoes, including and especially shoes designed to cushion the feet, are problematic.

Last year, researchers at the University of the Witwatersrand in Johannesburg, South Africa, published a study titled "Shod Versus Unshod: The Emergence of Forefoot Pathology in Modern Humans?" in the podiatry journal The Foot. The study examined 180 modern humans from three different population groups (Sotho, Zulu, and European), comparing their feet to one another's, as well as to the feet of 2,000-year-old skeletons. The researchers concluded that, prior to the invention of shoes, people had healthier feet. Among the modern subjects, the Zulu population, which often goes barefoot, had the healthiest feet while the Europeans--i.e., the habitual shoe-wearers--had the unhealthiest. One of the lead researchers, Dr. Bernhard Zipfel, when commenting on his findings, lamented that the American Podiatric Medical Association does not "actively encourage outdoor barefoot walking for healthy individuals. This flies in the face of the increasing scientific evidence, including our study, that most of the commercially available footwear is not good for the feet."

Okay, so shoes can be less than comfortable. If you've ever suffered through a wedding in four-inch heels or patent-leather dress shoes, you've probably figured this out. But does that really mean we don't walk correctly? (Yes.) I mean, don't we instinctively know how to walk? (Yes, sort of.) Isn't walking totally natural? Yes--but shoes aren't.

"Natural gait is biomechanically impossible for any shoe-wearing person," wrote Dr. William A. Rossi in a 1999 article in Podiatry Management. "It took 4 million years to develop our unique human foot and our consequent distinctive form of gait, a remarkable feat of bioengineering. Yet, in only a few thousand years, and with one carelessly designed instrument, our shoes, we have warped the pure anatomical form of human gait, obstructing its engineering efficiency, afflicting it with strains and stresses and denying it its natural grace of form and ease of movement head to foot." In other words: Feet good. Shoes bad.

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Here's another example: If you wear high heels for a long time, your tendons shorten--and then it's only comfortable for you to wear high heels. One saleswoman I spoke to at a running-shoe store described how, each summer, the store is flooded with young women complaining of a painful tingling in the soles of their feet--what she calls "flip-flop-itis," which is the result of women's suddenly switching from heeled winter boots to summer flip-flops. This is the shoe paradox: We've come to believe that shoes, not bare feet, are natural and comfortable, when in fact wearing shoes simply creates the need for wearing shoes.

Okay, but what about a good pair of athletic shoes? After all, they swaddle your foot in padding to protect you from the unforgiving concrete. But that padding? That's no good for you either. Consider a paper titled "Athletic Footwear: Unsafe Due to Perceptual Illusions," published in a 1991 issue of Medicine and Science in Sports and Exercise. "Wearers of expensive running shoes that are promoted as having additional features that protect (e.g., more cushioning, 'pronation correction') are injured significantly more frequently than runners wearing inexpensive shoes (costing less than $40)." According to another study, people in expensive cushioned running shoes were twice as likely to suffer an injury--31.9 injuries per 1,000 kilometers, as compared with 14.3--than were people who went running in hard-soled shoes.