BUFFALO, NY — A University at Buffalo researcher has good news for athletes and fitness enthusiasts who prefer thick, heavily cushioned running shoes. Although these shoes are becoming increasingly popular because they offer comfort and a high degree of impact protection, these benefits were thought to come at the expense of increased overall leg stiffness, which impaired the normal stride of the leg. a runner and could increase muscle fatigue.
Plenty of research suggests such a result when running on a soft surface, like a synthetic rubber track, but no one had actually tested how the cushioned midsole of a running shoe affects overall leg stiffness.
“Our results show that runners don’t have to worry about the amount of cushioning,” says Nicholas Holowka, PhD, assistant professor of anthropology at UB College of Arts and Sciences and first author of the paper. “This element of the shoe’s design does not interrupt your normal running style in any significant or meaningful way.”
The results of the study conducted with Daniel Lieberman, professor of human evolutionary biology at Harvard University; Emmanuel Virot, post-doctoral fellow at Harvard; and Yale University medical student Stephen Gillinov appear in the Journal of Biomechanics.
The stiffness of the legs can be compared to the tension of a spring. If the leg alone were modeled as a single spring, this coil would have one level of stiffness. The leg, however, is made up of many muscles that control degrees of stiffness. When running on padded surfaces, leg stiffness increases, but this is not the case when running in heavily padded shoes.
“There is an optimal leg stiffness for runners, but if you increase your leg stiffness beyond that point, you’ll be using more muscle to stiffen that leg spring, which means more energy and fatigue. over long distances,” says Holowka, an expert. on the biomechanics of walking and running. “We were interested in the idea that when people run on elastic surfaces, with some flexibility, they unconsciously change the stiffness of their leg to maintain optimal stiffness. Was it the same with the padding of their shoes?
At a glance, the lack of research into midsole thickness and running style seems startling, but Holowka says the issue is more complicated than it appears.
“It’s very difficult to take all the factors into account in a way that allows you to specifically isolate the stiffness of the shoe itself,” he says. “If you try to compare different shoes, you have differences in design, like heel height or arch support, which makes it difficult, if not impossible, to examine the effects of shoe cushioning.
“Our study aimed to examine this single variable.”
And to do that, Holowka’s team created custom-made sandals for the study.
The researchers recruited 20 experienced runners and measured them in four different conditions: barefoot and sandals made of three different materials. The first sandals were a commercially available model inspired by the shoes of the Tarahumara, an indigenous people living in Mexico who developed a tradition of long-distance running. These sandals, made from the common shoe cushioning material of ethylene-vinyl acetate (EVA) foam, served as the molds for two other similar models with varying degrees of padding.
Participants ran on treadmills that measured the forces the body exerted against the ground. Their movements were also measured using a specialized camera system. The data contributed to a model of the leg as a linear spring, which allowed the researchers to calculate the stiffness of the leg under different conditions.
“We went into this with the assumption that padding might change leg stiffness, but that just wasn’t supported,” says Holowka. “The results show that your running style still feels natural even when running in these heavily cushioned shoes.
“Our results tell us something that was previously unknown about shoe design, essentially the extent to which shoe cushioning influences normal running style.”
And that’s important information for runners who prefer heavily cushioned shoes but are concerned about how these shoes affect running style, according to Holowka.
“You can have that cushioning if you like it and still run with normal natural leg stiffness,” he says.