Researchers look at why we slip and fall and how to prevent it

By MARTY LEVINE

One team of Pitt researchers is coming closer to understanding the science behind what makes us slip and fall, and how better to prevent it — and we need to pick ourselves up off the floor and take notice.

The science of measuring friction, lubrication and how things contact, vibrate and wear down — your shoes against the ground, for instance — is called "tribology." Kurt Beschorner, Swanson School of Engineering faculty member, studies the biomechanics of how shoes grip or slide on surfaces dry and wet, down to the nanometer level.

"It's not a really well-known sub-discipline, and I, like a lot of people who end up doing tribology, didn't set out with that specialization in mind," he says.

As an undergraduate mechanical engineering student, Beschorner discovered how the science applied to humans via biomechanics. Then, doing his Ph.D. in Pitt's Human Movement and Balance Lab, he found fellow researchers already trying to understand slip-and-fall accidents. "It became clear," he said, that this area "was really underdeveloped." The lubrication of engines and tire traction had long been studied, but more modern research hadn't been well applied to humans and their footwear.

Beschorner and Tevis Jacobs, a Swanson School faculty member in mechanical and materials science, are in the second year of a two-year grant from the National Institute for Occupational Safety & Health to measure surface roughness on the smallest scale ever. They’re also working with the Tile Council of America, which is intent on designing tiles with the best grip.

We know ice is ultra-slick. But we know that it would be useless to have shoes that stuck immediately and immovably to every surface. So where, between those two extremes, is that sweet spot for the safest strolling? What is the best surface and what are the most useful shoes?

It's all about creating the right kind and amount of friction. Friction is happening under lots of different conditions, wet and dry. Floors that seem smooth have some degree of friction, and the Beschorner/Jacobs study is focused on hysteresis friction — the vibration of materials in shoe soles when contacting various sizes and arrays of bumps on the floor, especially the unseen, tiny variety.

"Flooring, even if it looks flat, it's really rough when you zoom in on it," Beschorner notes. Sure, the rough bits are ultra-tiny, he says, "but here's the thing about things that are really, really tiny — there are lots of them."

The team of researchers is testing flooring in several ways, including examining the surface characteristics with electron microscopy and "walking" over flooring with a mechanical calf and foot to which various shoes are fitted, measuring the many forces each shoe encounters, including friction, with different flooring materials and conditions.

The study's long-term goals are to help shoe companies create grippier shoes, and flooring companies to improve floor design, as well as "to find effective ways to give consumers information so they can make better informed decisions about the traction or friction of the shoes and flooring they are purchasing."

Already, he says, "we have some compelling results that we believe justify continuing the research" and the team intends to look for further funding.

In the meantime, they will present an abstract of these early results at a fluid engineering conference in Osaka next month, showing that their testing and modeling is working to predict the risk of slipping.

When you walk, the vibrations in your shoes happen at different frequencies in different spots, the study is finding. Larger-scale features on a floor vibrate your shoe-bottom materials at lower frequencies, while smaller-scale features create higher frequency vibrations because they are closer together. "The more energy that is lost from that vibration reduces the risk of slipping," he explains. The surface grips your shoe better.

But shoe manufacturers (those that test their shoes for gripping ability) don't measure the footwear at a high-enough frequency of vibration to catch the most significant slipping point, he adds — as the study's early results are showing.

The properties of the rubber make a large difference in the outcome of these friction tests, "and consumers largely lack access to this information," Beschorner says. Falls with large consequences happen not only among the elderly but also among many types of workers indoors and out, so falls can be costly in lost business and in lives.

"It's really common that the falls can start a cascade of events," from other injurious side effects to death. In fact, he says, falls are often the top cause of injuries for emergency room visits, exceeded in some years only by vehicle accidents.

"How do we design the places we work and live in ways that hazards are more apparent or can be avoided altogether?

"There's a lot we could do from a public health perspective" to help prevent falls, including giving people better safety information before the purchase of footwear and flooring. "It's not very different from buying tires," he points out. "The more we can give people good information for their buying decisions, the more we can move the needle" toward safer ambulation.

Marty Levine is a staff writer for the University Times. Reach him at [email protected] or 412-758-4859.

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