July 2014

The rise and fall of minimalist footwear

7cover-iStock17908024MDv2Once thought by some to be the next big thing in running, minimalist footwear has been scrutinized in recent years by researchers and class-action plaintiffs who claim the shoes do not provide the same benefits as barefoot running and may in fact increase the risk of injury in some runners.

By Cary Groner

The recent settlement of the class-action lawsuit against Vibram USA, maker of the FiveFingers running shoe, brought public attention back to the issue of minimalist footwear and its purported benefits.1 The suit alleged false advertising in the company’s claims that the shoes could reduce injuries and strengthen foot muscles. Vibram avoided the potentially disastrous public relations of a court battle while continuing to deny wrongdoing, even as it arranged refunds for those who had allegedly been unduly influenced by its ads.

All such legal jockeying aside, however, questions remain about the effects of minimalist footwear on factors such as biomechanics and injury rates. One result of the many new studies has been to distinguish the biomechanical effects associated with minimalist shoes from those encountered by people who run barefoot; it turns out that the body often responds very differently to these apparently similar conditions. This has what politicians might call “broad policy implications,” because it affects not only the research community and the shoe business, but also the clinicians who help athletes train—and heal them when their training goes awry.

“You have to fortify a system; you can’t just suddenly load it,” said Irene Davis, PhD, PT, a professor in the Department of Physical Medicine and Rehabilitation at Harvard Medical School and director of the Spaulding National Running Center in Boston. Davis is working with colleagues to develop strengthening programs that may reduce the risk of injury in those transitioning to minimalist running.

“If you do it slowly enough, your body will adapt,” she said. “We just don’t know yet how slow is slow enough.”

Got hurt?

Not surprisingly, injury prevention is the primary concern. In a 2007 review from the Netherlands, researchers reported that the annual incidence of lower extremity running injuries ranged from roughly 19% to 79%, most of them in the knee.2 Statistically that’s a broad band, of course, and it reflects the heterogeneity of runners and their approaches to training.

It’s one thing to quantify injuries and another to identify what caused them, however. In recent years, Harvard evolutionary biologist Daniel Lieberman, PhD, has popularized the notion that running injuries may be associated with a high “impact transient” related to the rear- foot strike pattern that typically occurs when people run in modern thick-heeled shoes.3 Lieberman’s research has been seized upon by the minimalist running community, which strives to make the case that the nonrearfoot (midfoot or forefoot) strike pattern more often associated with barefoot and minimalist footwear is how the human foot evolved to function, hence is more natural.

This conclusion seems intuitive, but it has its limitations. First, there’s little evidence linking impact transient to injury rates.4 Second, when you start talking about the ancestral envi­ron­ment of homo sapiens, you’d do well to remember that until about 200 years ago most of us were dead by age 40, so it’s problematic to extrapolate such conjectures to modern people who often run well into their 60s or 70s and must deal with the debilities of age. Third, natural doesn’t always equal desirable: plague and typhoid and cholera are all perfectly natural, but nobody’s eager to contract them.

On the other hand, any physical activity with an annual injury rate averaging 50% is worthy of biomechanical scrutiny, and at least some research does suggest that rearfoot strikers are more likely to be injured than forefoot strikers.5 The question is whether studies will support the conclusion that the solution lies in running either barefoot or in minimalist shoes.

Distinctions

As noted, new research is, in fact, discerning important differences between barefoot and minimalist running, and the focus here is on the latter. Even this becomes complicated, however, because there are “true” minimalist shoes (eg, the Vibram FiveFingers), then there are “transition” shoes that offer some midsole padding (eg, the Nike Free), though less than in the traditional running shoes, with their increased heel cushioning, that date back to the 1970s. Current research can lead to a variety of conclusions.

For example, in a 2011 study by Joseph Hamill, PhD, professor and associate dean of research for the School of Public Health and Health Sciences, and colleagues from the University of Massachusetts Amherst, habitual rearfoot-strikers ran with a heel-toe strike pattern when shod regardless of the thickness of the midsole; in contrast, when barefoot, they all immediately switched to a midfoot strike.6

A 2013 study from Australia reached similar conclusions.7 In 22 highly trained runners who ran barefoot and in three shod conditions—minimalist shoe (Nike Free 3.0), racing flat, and the runner’s usual training shoes—barefoot running mechanics were significantly different from all shod conditions, including the minimalist shoes. However, there were small differences in stride length and frequency between minimalist and traditional shoes.

In another paper, peak impact forces for minimalist shoes were significantly lower than for traditional shoes and similar to those in barefoot running.8 Lower limb kinematics were similar to those achieved barefoot, as well. In spatiotemporal variables, however, the minimalist shoes were closer to the traditional shoes, with the exception of contact time.

A 2014 paper in Gait & Posture compared acute impact forces and running patterns in individuals who were barefoot and in shoes with five different sole thicknesses (0, 2, 4, 8, and 16 mm).9 The authors, Chambon et al, reported that midsole thickness had no effect on ground reaction force or tibial acceleration, and that the presence of even very thin footwear significantly influenced running patterns versus barefoot.

According to Christopher MacLean, PhD, the director of the Fortius Lab & Applied Biomechanics at the Fortius Institute in Burnaby, British Columbia, Canada, such research reinforces the notion that the reduction of sensory feedback by even the thinnest layer of cushioning has biomechanical repercussions.

“In terms of impact peak and loading rates, which are the key vertical ground reaction forces we look at, it appears that as soon as you put on an enclosed shoe—regardless of characteristics such as stack height [ie, sole thickness], impact forces and loading rates are similar,” he said. “It’s only when runners perform tasks completely barefoot that we see changes in the habitual rearfoot strike.”

Another study published this year compared several variables—stride length and frequency, contact and flight time, and foot-strike patterns—in 14 competitive runners in traditional shoes, minimalist shoes, or barefoot.10 Though there were some acute differences in flight and contact times, the researchers found no significant deviations in foot-strike patterns, including between minimalist and traditional footwear; everyone landed more or less in a midfoot strike. This finding is at variance with other research, including much of that just cited, and the authors speculated that the common midfoot strike could have been due to learned patterns or to running on the treadmill.

Finally, a study presented at the annual conference of the American College of Sports Medicine this May studied running patterns in 1003 soldiers from five military bases, 53 of whom ran in minimalist shoes.11 Of those, fully 60% were heel strikers, versus 84% of those who wore traditional shoes. Compelling, too, was that only about half of runners accurately identified their foot-strike patterns.

Heel and toe

7cover-shutterstock_190813763v2According to Irene Davis, runners tend to strike with their heels in the presence of even minimal padding, which explains some of these results. Davis told LER that true minimal shoes should ultimately lead to a midfoot or forefoot strike, though that isn’t always the case. Part of the issue has to do with sensory feedback, and as noted above, research has shown that many runners can’t accurately identify their own foot-strike patterns.

“When you put someone on the treadmill bare-foot, they have all this sensory input, which is why we do all of our training and physical therapy barefoot,” Davis said. “A truly minimal shoe has just a rubber sole, and even that filters out important information; that’s the clear difference between barefoot and minimalist running.”

Research has delineated the rough parameters of strike patterns. In one study from Japan, 75% of distance runners were heel strikers, versus 24% midfoot and 1% forefoot strikers.12 In another, of nonelite runners in a distance event, 88.9% were rearfoot, 3.4% were midfoot, and 1.8% were forefoot strikers.13 By contrast, a study of runners in a barefoot/minimalist event in New York City by the same author found that, of barefoot runners, 59.2% were forefoot strikers, 20.1% were midfoot strikers, and 20.7% were rearfoot strikers. Of those in minimalist footwear at the same event, however, just 33.3% were forefoot strikers, 19.1% were midfoot strikers, and 47.6% were rearfoot strikers. There were, in other words, significantly different strike patterns depending on whether the runners went barefoot or wore minimalist shoes.14 The author, Peter Larson, PhD, wrote that “running in a minimally cushioned shoe may encourage kinematic patterns that are different than running in a traditionally cushioned shoe, but may not always encourage kinematic patterns similar to that in barefoot running.”

Larson, a gait analyst at Performance Health Spine and Sport Therapy in Concord, NH, told LER he was surprised by the different strike patterns in barefoot and minimalist runners, but that new research may partly explain it.15

“There’s variation in heel strikes that can be distinguished kinetically,” he said. “If you go minimal and continue to heel strike, that doesn’t necessarily mean that your form hasn’t changed; it may have in subtle ways, in terms of gait, stride length, and cadence. Some people make initial contact with the heel, but the maximum vertical loading actually occurs when the foot goes to flat.”

Biomechanics and loading

Researchers get obsessive about foot-strike patterns partly because they both affect and reflect the upstream kinetic chain. In a 2012 paper coauthored with Allison Altman, PhD, a postdoctoral research scientist in the McKay Orthopaedic Research Laboratory at the University of Delaware, Irene Davis provided a succinct summary of research related to the biomechanical effects of foot-strike patterns.16 For example, a rearfoot strike results in the impact transient described earlier, leading to high loading rates in early stance. Forefoot striking eliminates this impact transient by eccentrically loading the posterior calf muscles, and midfoot striking falls somewhere in between. Forefoot striking is also associated with a shorter stride length, in which the foot lands closer to the body’s center of mass. And a 10% reduction in stride length, even if rearfoot striking, significantly reduces the load absorbed by the knees and hips.17

Of course, when forces are offloaded from one area they have to go somewhere else, and forefoot striking increases the strain on the calf, Achilles tendon, and meta­tarsals.16

“Your mass is the same whether you’re wearing shoes or not, whether you have a forefoot or a rearfoot strike,” said Reed Ferber, PhD, ATC, an associate professor of kinesiology at the University of Calgary in Canada. “Your maximal loading is the same; all you’re doing is taking that load and redistributing it throughout your body.”

In a study comparing running in standard and partially (slightly cushioned) minimalist shoes, Irene Davis reported that running in minimalist shoes did not acutely lead to a forefoot or midfoot strike; moreover, it increased loading of the lower extremities versus traditional shoes.18

Another paper in the British Journal of Sports Medicine reported similar findings last year. In that case, researchers randomly assigned 103 recreational runners to either a traditional shoe, a partially minimalist shoe, or a fully minimalist shoe, then started them on a 12-week training program.19 Of the 99 runners included in the final analysis, 23 reported injuries (resulting in time away from running). Those wearing the traditional shoe had the fewest injuries (four), those in the partially minimalist shoe had the most (12), and those in fully minimalist shoes had seven injuries but reported the most shin and calf pain.

That study’s lead author, Michael Ryan, PhD, a research fellow at the Center for Musculoskeletal Research at Griffith University in Queensland, Australia, told LER that although he likes minimalist footwear, anyone adopting it should proceed with caution.

“True minimalist shoes provide feedback that can help you listen to your body and adopt a stride that reduces load in the hip and lower back, but they pose a potentially higher risk of injury,” he said. “Partially minimalist shoes, on the other hand, don’t have that sensory side, because there’s some cushion. They don’t change mechanics much versus a conventional shoe, but they place more stress on your body.”

Injuries

As noted earlier, despite the attention placed on foot-strike patterns, it’s difficult to connect the dots with injuries.

“Injuries are multifactorial, and there’s no evidence to support or refute the injury-causative or injury-preventive nature of minimalist running or forefoot strike,” said Reed Ferber. “There is simply research to say that you run differently. There is less loading on your knee and hip joints, but significantly greater loading and strain within the Achilles tendon; in fact, forty-eight extra body weights are absorbed by the Achilles tendon every mile,20 which could be injury-causative.”

In a 2012 paper in Foot & Ankle International, researchers reported that in 10 experienced runners who had injuries within a year of transitioning to minimalist footwear, those injuries included eight metatarsal stress fractures, a calcaneal stress fracture, and a rupture of the plantar fascia.21

Metatarsal stress fractures have gained increasing attention because they receive much of the relocated load when runners transition from a rearfoot strike to a nonrearfoot strike pattern. Another paper reported these injuries in two experienced male runners who had adopted minimalist footwear.22

Sarah Ridge, PhD, an assistant professor of exercise science at Brigham Young University in Provo, UT, has studied the effects of minimalist running on bone marrow edema. In a 2013 article, she and her colleagues performed magnetic resonance imaging exams on the feet of experienced recreational runners before and after a 10-week transition from traditional to minimalist running in Vibram Five­Fingers and compared them with controls who continued to run in traditional shoes.23 Edema was rated on a scale from 0 to 4; 0 or 1 represented normal remodeling, 2 to 3 indicated abnormally high edema, and 4 was a fracture. Scores were similar between groups prior to training, but after 10 weeks more runners in the minimalist group (10 of 19) had edema scores of 2 or higher than in the control group (1 of 17). Moreover, in the minimalist group, one runner had a calcaneal fracture and one had a second metatarsal fracture.

“Some level of edema is good—it’s part of the normal remodeling process—but if you go past that, it’s an indicator of injury potential,” Ridge told LER.

She and her colleagues followed the Vibram website transition recommendations at the time, which suggested a 10% increase per week in distance run in FiveFingers (the recommendations have since changed; the site now notes that the transition may take weeks to more than a year, and urges runners to listen to their feet and stop if they experience pain). Nevertheless, most of the study participants couldn’t manage that transition.

“There were only one or two subjects running about ninety percent in their Vibrams by the end of the study,” Ridge said. “For most of them, it was not the majority of their mileage. It seems that what we thought was a slow transition wasn’t slow enough. You need to take more time to get used to the added stress of running in noncushioned shoes.”

Transitioning

As a result of such findings, clinicians are looking more deeply into the types of training that may be necessary for runners who decide to transition to minimalist approaches.

Irene Davis’s transition to barefoot running was managed carefully over many months. Reed Ferber, too, considers a proper transition vital.

“You have to have a flexible gastroc-soleus complex, a flexible Achilles tendon, and really strong plantar flexors, which are going to absorb force when you land on your forefoot,” he said. “Transitioning isn’t just a matter of practicing to run barefoot, or practicing a forefoot strike; it’s also getting very flexible and strong in your ankle musculature.”

Regarding the suggestion that running patterns practiced in the ancestral environment by strong young people can be adopted by modern athletes in their 50s and 60s, Ferber further defined the problem.

“We know that one of the primary variables that distinguishes older from younger runners is flexibility in the big toe and ankle,” he said. “If older runners decide to make that transition—say, to reduce the loading on the knee joint—they may want to take years, and ideally do it under the supervision of a coach and a sport physiotherapist.”

As part of a comprehensive approach, Christopher MacLean reports good results from increasing stride frequency, in that swifter cadence typically brings with it shorter stride, and has been shown to decrease knee load.24

“I have individuals who are symptomatic when running at their selected stride frequency, but when we increase it they are able to run comfortably,” he said.

MacLean also noted that population-based study results may not apply to all individuals.

“People want to grab onto something and apply it to everyone,” MacLean continued. “In research, we force conclusions based on group data, but in doing so we often lose the vital information about how each subject responded. You have to consider how an individual athlete needs to be managed.”

Craig Payne, DipPod, MPH, a retired lecturer in podiatry at La Trobe University in Melbourne, Australia, and occasional online provocateur on the “Running Research Junkie” blog, agreed.

“It comes down to this: Different running techniques load different tissues differently,” he said. “It’s not a matter of one being better than another; individuals need to work out which suits them best. I suspect that those with a history of knee injury may do better in minimalist shoes than those with a history of ankle or Achilles injuries.”

Joseph Hamill, of the University of Massachusetts, shares this view, with a further caveat.

“Changing to a different type of shoe may ease patellofemoral pain, but it may cause a different injury,” he said. “Nothing in life is free; when you change your footfall pattern, you’re just changing one type of injury for another.”

Cary Groner is a freelance writer in the San Francisco Bay Area.

REFERENCES

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14. Larson P. Comparison of foot strike patterns of barefoot and minimally shod runners in a recreational road race. J Sport Health Sci In press.

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18. Willy R, Davis I. Kinematic and kinetic comparison of running in standard and minimalist shoes. Med Sci Sports Exerc 2014;46(2):318-323.

19. Ryan M, Elashi M, Newsham-West R, Taunton J. Examining injury risk and pain perception in runners using minimalist footwear. Br J Sports Med 2013 Dec 19. [Epub ahead of print]

20. Almonroeder T, Willson JD, Kernozek TW. The effect of foot strike pattern on Achilles tendon loading during running. Ann Biomed Eng 2013;41(8):1758-1766.

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24. Lenhart RL, Thelen DG, Wille CM, et al. Increasing running step rate reduces patellofemoral joint forces. Med Sci Sports Exerc 2014;46(3):557-564.

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