Shoe friction: the enemy within

by William A. Rossi

Abstract: Shoe friction causes more discomfort to the feet than shoe pressure or other, more commonly cited, factors. The problem is exacerbated by the lack of general or medical knowledge about the dynamics of foot movement inside the shoe, and the tendency of the footwear industry to ignore the causes of foot discomfort when creating innovations such as traction-type soles. Shoes continue to be designed and manufactured with little regard for the variety of movements made and shapes assumed by feet inside footwear.

COPYRIGHT 1996 Fairchild Publications

Shoe friction is unquestionably the single most common cause of foot discomfort.

Yet, ironically, with industry people it's the least understood and least mentioned of the various factors involved in shoe comfort.

Footwear people talk a lot about "shoe pressure" and how to avoid it, such as by finding the proper size and fit. But pressure isn't the main culprit. It's shoe friction. And for the average person, there's enough foot/shoe friction daily to start a small bonfire.

Pressure and friction are two different things. Pressure is a force imposed on an object. Friction is the repeated abrasion of pressure on an object. If you press down on a hard surface with the heel of your palm, that's pressure. If you repeatedly twist your hand on that hard surface and the skin gets red and sore, that's friction.

For example, 150 million painful corns appear on American feet each year. These corns are not the result of shoe pressure, but of friction caused by movement inside the shoe. Other common friction-induced ailments include calluses, ingrown nails, blisters and bursitis.

Few people (and even doctors) understand the dynamics of the foot inside the shoe. Hence, the various efforts to create a friendly inside-shoe environment are usually more talk than action, more theory than practical solution. So the objective of shoe comfort continues to remain elusive.

The first thing to recognize is that the foot is not a static object inside a shoe. It is always mobile, always changing size and shape, even when you're sitting down.

With each step, every part of the foot—bottom, sides, top, front and rear—changes position and shape. The foot stretches lengthwise and expands in volume, due to a combination of weightbearing, torsion, resilience, stress and thermal conditions.

Now, surprise. Every foot has four sizes and shapes. One with the foot at rest, another on weightbearing, still another in motion (walking, running, etc.), and the last under thermal conditions such as heat, cold and humidity. Same foot, four different conditions.

Yet, this multiple-size foot must fit and function in a shoe of only one size and shape. You now automatically have a friction problem because the foot is fitted to only one of those four pairs of feet.

To further complicate matters, one foot of the pair will be longer, wider and of different proportions than the other. Yet, the two shoes of the pair will be exactly the same size.

Shoe people and doctors continue to prattle naively about "proper" shoe fit and comfort, as though they were simple processes of the right size, fit and shoe.

What happens with the shoe friction common to all shoe wearers?

Friction creates heat. Normal foot-surface temperature is 94 degrees, but inside the shoe it ranges from 100 to 120 or more degrees. Presto, the hotfoot condition and the habit of kicking off the shoes for relief.

Heat in turn causes perspiration buildup and the uncomfortable hot-clammy feeling. Almost all excessive foot perspiration is caused by shoe friction.

Bacteria thrive under the conditions of heat, moisture and darkness. They erode and prematurely "age" the shoe, causing it to lose shape and fit.

When heat and perspiration mix with the shoe's hundreds of chemical compounds, offensive shoe odors result (most foot odors are shoe odors).

Shoe friction is at work everywhere on the foot, not just on the upper. With each step, the foot slides forward about a half to three-fourths of an inch. That means friction not only against the upper foot, but also the sole. With each step pushoff, the foot's ball shears in an intense twisting motion against the insole. Between the sliding and the shearing, a burning sensation develops.

This condition is worsened by traction-type soles (used in about 50 percent of footwear), which abruptly "brake" with each step, causing the toes to slam against the end of the shoe. So today, we have the common "turf toe" (a.k.a. tennis toe, runner's toe, walker's toe)—a malady unknown 25 years ago prior to the traction era.

Then there's the flexibility problem. Most shoes, including sneakers and athletic footwear, fall 25 percent to 80 percent short of flexibility to match that of the foot (55 degrees). So the foot must work harder, press harder to flex with each step, thus creating more friction.

Significantly, the estimated 1 billion shoeless people of the world stand, walk, run and work on hard ground surfaces, and usually for much longer hours than shoe-wearers. Yet, they never experience any of the discomfort and foot problems of shoe-wearers. No shoe friction, no problems. Surely there's a message trying to get through here.

All of this has nothing to do with wearing "proper" shoes of the "right" size. People who don such shoes have the same shoe-friction problems.

So why haven't we, after some 6,000 years of shoemaking and with our hyped "modern technology," resolved this age-old friction and discomfort problem? Because it's been an industry tradition to circle the wagons with pipes and hypes without making a direct attack on the center. We tend to focus on the symptoms, instead of seeking and removing the causes.

For an industry filled with creative talent, we are somewhat impoverished in the fundamentals of foot-friendly shoemaking.

The consumer mantra goes on generation after generation: Why can't we have both comfortable and attractive shoes. The industry adamantly postures with its usual state of self-denial, and refuses to admit that a serious problem exists. The shoes, they insist, are fine. The problem is with the customers' feet, or with their vanity.

And so, as always, the love/hate relationship continues between consumers and their shoes. Friction between the foot and shoe then evolves into friction between the public and the trade. This has become a thorn in the side of an industry so sensitive about its public image.

When shoemakers finally eradicate the abusive frictions between foot and shoe, they just might reverse the long history of friction between consumers and the industry.