By Emily Delzell
Barefoot-simulating and minimalist shoes are capturing the imagination of runners who hope to avoid injury and increase performance by adopting a forefoot or midfoot strike pattern, but recent research suggests runners don’t necessarily convert their gait simply by switching shoes.
Complicating the issue for runners is an explosion of designs marketed as minimalist, ranging from the New Balance Minimus Zero with its zero-drop heel-to-toe differential to more cushioned, “transitional” shoes, such as the Saucony Kinvara, which has a 4-mm drop.
It’s the more cushy models that concern Irene Davis, PhD, PT, director of the Spaulding National Running Center at Harvard Medical School in Boston.
“We’ve done a study of runners wearing Nike Frees 3.0 [these have a 3-mm drop] and found they still very much heel strike in these,” Davis said.
The 14 participants in Davis’s study were novice minimalist runners who donned the Nike Frees, reached a comfortable running speed on a treadmill, and then ran for 10 minutes. The volunteer runners, adult men who ran at least 10 miles a week, also completed a treadmill trial in a traditional running shoe with a 12-mm drop. The study, which is currently being prepared for submission, is a continuation of an earlier investigation presented at the 2009 annual meeting of the American College of Sports Medicine.
Davis’s co-author, Rich Willy, PT, PhD, OCS, an assistant professor in the Physical Therapy College of Health Sciences and Professions at Ohio University in Athens, said, “We thought that over 10 minutes the runners might soften their foot strike, but they all tended to land very hard on their heels with very high impacts.”
Willy noted that participants had statistically higher loading rates and vertical impact peaks in the minimalist shoes compared with the traditional shoes.
Trampas TenBroek, PhD, manager for sports research at New Balance in Lawrence, MA, thinks these findings and others like them might be influenced by research settings.
“I think it’s difficult to draw conclusions from research on minimal footwear and footstrike for several reasons, including the use of varying running surfaces that have different mechanical characteristics. Runways, for example, don’t require enough consecutive strides to always elicit a wholesale footstrike change, while treadmills may not be firm enough to elicit a change,” he said.
TenBroek also notes runners are often clued in to what’s expected of them in research settings.
“Runners have done a great job researching and discussing this topic [minimalist shoes]. This means when you bring them in for research they might know enough to have a hard time doing what might otherwise feel natural,” he said.
But TenBroek agrees with Davis that cushioning influences footstrike.
“Shock attenuation, pressure reduction, and environmental protection all play a role in which footstrike people choose to use given a particular combination of running surface and shoes,” he said.
Many shoes marketed as minimalist fall into a category Wendy Weimar, PhD, assistant professor of biomechanics at Auburn University in Auburn, AL, calls transitional shoes.
“I think these shoes can be great in helping people step down to a zero-drop shoe or even running barefoot. But, as Americans, we tend not to be very patient and a lot of people are jumping into a full minimalist shoe without transition and this can cause pain and discomfort,” she said.
A zero-drop is not the only criterion Weimar thinks minimalist shoes should fulfill.
“In my opinion a flexible sole and toe box also has to be in the mix,” she said. “Vibrams, for example, take really good advantage of the windlass mechanism—the ability to extend your toes right at heel contact.”
Weimar owns two pairs of Nike Frees and has noticed that even their small heel-to-toe differential loads the forefoot, restricting the ability to take advantage of the mechanism.
Willy R, Davis IS. A comparison of treadmill running in minimal footwear compared to standard running shoes. Presented at American College of Sports Medicine 56th Annual Meeting; Seattle, WA; May 2009.