Barefoot Running claims & controversies

ORIGINAL ARTICLES

Barefoot Running Claims and Controversies A Review of the Literature David W. Jenkins, DPM* David J. Cauthon, RPh*

Background: Barefoot running is slowly gaining a dedicated following. Proponents of barefoot running claim many benefits, such as improved performance and reduced injuries, whereas detractors warn of the imminent risks involved.

Methods: Multiple publications were reviewed using key words.

Results: A review of the literature uncovered many studies that have looked at the barefoot condition and found notable differences in gait and other parameters. These findings, along with much anecdotal information, can lead one to extrapolate that barefoot runners should have fewer injuries, better performance, or both. Several athletic shoe companies have designed running shoes that attempt to mimic the barefoot condition and, thus, garner the purported benefits of barefoot running.

Conclusions: Although there is no evidence that either confirms or refutes improved performance and reduced injuries in barefoot runners, many of the claimed disadvantages to barefoot running are not supported by the literature. Nonetheless, it seems that barefoot running may be an acceptable training method for athletes and coaches who understand and can minimize the risks. (J Am Podiatr Med Assoc 101(3): 231-246, 2011)

Barefoot running is slowly gaining a dedicated following in developed countries around the world.

Evidence of this is seen in the popularity of barefoot running Web sites and in the explosion of articles written for the popular media. In the past several years, articles have appeared in Runner’s World, Men’s Health, Popular Mechanics, and The Wall Street Journal, as well as on several Web sites.1-5 These articles provide vast quantities of information, some based on clinical research, some based on personal experiences, and some based on wellintentioned but faulty logic. With the excitement and promise of many benefits in performance and reduced injuries, the hype is understandable.

Although barefoot running is, by definition, the opposite of a ‘‘new’’ activity, the so-called barefoot running movement is relatively new. Given the significant role that many health providers play in treating athletes, it is imperative that clinicians be attuned to athletic trends (whether they be fads or *Arizona School of Podiatric Medicine, College of Health Sciences, Midwestern University, Glendale, AZ. Corresponding author: David W. Jenkins, DPM, Arizona School of Podiatric Medicine, College of Health Sciences, Midwestern University, 19555 N 59th Ave, Glendale, AZ 85308. (E-mail: djenki@midwestern.edu)

long-lasting movements) as our patient-athletes will come to us for opinions and recommendations. This review article examines the evolving barefoot running movement and the professed benefits of enhanced performance and injury reduction from the perspective of a thorough review of the literature and the best available evidence. Nonetheless, the clinician should be better equipped to answer the many questions about barefoot running that are sure to come from their running patients.

History of Barefoot Running The Genesis Our ancestors walked with either no footwear at all or the simplest covering made of leather held on by rawhide strings (moccasins). What has changed is the creation of modern surfaces that, according to some, necessitate protective footwear. But did manmade surfaces drive this change? Was it the surfaces that led to more modern shoes or was it style, vanity, and status that drove these changes, as some investigators believe?6 Nonetheless, early dogma claimed that feet were evolutionarily unsuccessful,7 and it seemed that health-care providers

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and shoe companies considered feet inherently fragile and, thus, unable to hold up to the rigors of running without protective cushioning, support, and motion control. Now consider the barefoot running proponents who claim that generations of more confining, motion-restricting, and increasingly supportive shoes has created an atrophy of the feet through disuse, especially of those components that would be more greatly used if unshod, eg, the plantar intrinsic musculature.8 For decades, there have been strong advocates for going barefoot or pointing out the liabilities of wearing shoes.9, 10 A major reason for the fresh interest in barefoot running is the lack of improvement in runningrelated injuries despite advances in cushioning and motion control in running shoes. In 1982, in one of the earliest studies on the incidence of injuries in runners performed by Koplan et al,11 an incidence of 35% was found. In a study by Jacobs and Berson12 in 1986, 47% of survey respondents claimed that they had sustained an injury during the previous 2 years.

Two large studies13, 14 in 1989 found a similar incidence of approximately 50%. An excellent review of the epidemiologic literature by Van Mechelen15 in 1992 found an injury rate of 37% to 56%. A 2004 prospective study16 found that 79% of runners sustained a lower-extremity injury during the 6-month study, including injuries that caused a reduction in mileage and a stoppage in running. In 2006, McKean et al17 noted an injury rate of 46%.

Two of the most recent studies18, 19 found incidences of 54.8% and 59%.

Despite the steady injury rates, clinicians continue to prescribe more cushioned and controlling shoes even though there is no evidence to support the effectiveness of high-quality running shoes in preventing injury. Indeed, these recommendations may have the potential to cause harm.20 In fact, Clinghan et al21 concluded that expensive running shoes were no better at reducing impact forces than were low-cost shoes.

Although they do not ascribe an overall incidence of runners who become injured, James et al22 and Brubaker and James23 thoroughly reviewed the prevalence of specific running-related injuries, their etiology, and treatment. Interestingly, and quite possibly paradoxically, James et al22 noted in 1978, ‘‘It is our contention that if an adequately designed shoe were available, many of the problems attendant to long distance running, short of training errors, could be prevented.’’22(p46) Robbins,8 in his first of many publications on the barefoot condition, notes significantly higher injury rates in those wearing shoes in Haiti compared with

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those not wearing shoes. Although there may be other reasons for this difference, such as access to medical care, poor shoe quality, training habits, etc, this finding provided a springboard for Robbins and Hanna8 and others to scientifically explore whether barefoot running was less injurious or more beneficial.

Although not a scientific investigator, a prominent and vocal proponent of the barefoot running movement is Christopher McDougall. His past writings and recent book, Born to Run: A Hidden Tribe, Superathletes, and the Greatest Race the World Has Never Seen, discuss the Tarahumara Indians of Mexico, who routinely run ultramarathon distances without shoes or with simple coverings and reportedly have none of the modern ‘‘running injuries’’ so commonplace in modern society. He associates the ills that runners experience to shoes, and he claims that despite all of the technological advances in the past 40 years, running-related injuries have not been reduced and, indeed, are on the rise.24 The thinking of Robbins and McDougall was contrary to the idea that feet are fragile and need protection. They believed that man is designed to walk barefoot and that biomechanical function is most efficient when unshod. Coupling this with the reported paucity of running-related injuries in these legendary unshod runners, a variety of investigators have begun exploring the reasons for the lower incidence of injuries and suspected benefits. It is these claims of improved performance and reduced injuries that, in part, motivate the modern barefoot running movement. On the other hand, the numerous runners who decided to give barefoot running a try limping into the offices of foot specialists has given rise to skepticism from many health-care providers.

Time Frame and Participants For a perspective on the age of the current movement, Ken Bob Saxton, the unofficial ‘‘godfather’’ of barefoot running, ran his first official barefoot race in 1997.25 The Web site therunningbarefoot. com, which was founded by Saxton, has been accessible since 1997.26 Although there is no reliable estimate of the number of barefoot runners, proponents of the movement claim that thousands of people are running at least some of their weekly miles barefoot. The Society for Barefoot Living (http:// www.barefooters.org), which is not exclusive to runners, has more than 1,200 members.27

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Although the current attention and excitement by recreational runners is recent, barefoot running is not new to elite runners, who many years earlier saw significant world-class performances by barefoot runners. Although historically, barefoot runners have had some success at the elite level, no runner has won an Olympic medal or set a world record barefoot in more than 2 decades. Some examples of elite runners and performances include the following: 1) Abebe Bikila became the first black African to win an Olympic medal when he won gold in the 1960 Olympic Games Marathon. He ran the entire race barefoot (the same way that he had trained), but by the time he won Olympic gold in 1964 (Tokyo), he was running in Tiger shoes after getting a sponsorship from Onitsuka, the precursor to Asics.28 2) An 18-year-old Zola Budd set the world record for 5,000 m on a track in 1984 while running barefoot, but she finished seventh in the 1984 Los Angeles Olympic Games in the 3,000 m after a highly publicized collision with American Mary Decker Slaney. Now 43 years old, Zola Budd Pieterse has donned shoes while training on the master’s circuit in the United States, and she finished the 2008 New York Marathon in 2 hours 59 minutes.29 3) Herb Elliott is often mentioned as a barefoot runner because twice he graced the cover of Sports Illustrated running barefoot.30, 31 However, he clearly is wearing shoes in the 1960 videotape of his world record–setting Olympic 1,500-m race. Elliott also served as president of Puma America from 1995 to 1997 after serving as CEO of Puma Australia from 1985 to 1995.32 4) Bruce Tulloh set United Kingdom records for 3 miles in 1960 and 1961 and for 2 miles in 1962 as well as winning the 5,000 m at the European Championships in 1962. Although most of his races were run barefoot, he did resort to wearing shoes if the surface required it.33 Before recreational running became mainstream, it was not uncommon for coaches at various competitive levels to incorporate some degree of barefoot training in their workouts. Indeed, one of us (D.W.J.) regularly participated in structured barefoot workouts in high school track and crosscountry in the late 1960s. To gain an appreciation for the modern barefoot running movement regarding claims and philosophy, it is recommended that Web sites such as runningbarefoot.org and Bare-

footTed’s Adventures (http://www.barefootted.com) be perused.

Despite the numerous players on the barefoot running scene, it was a 1987 study,8 10 years before Ken Bob Saxton’s therunningbarefoot.com, that concluded, ‘‘The solution to the problem of running-related injuries could be as simple as promoting barefoot activity.’’8(p155) It was this assertion that many proponents believe was the catalyst for the scientific exploration that this article investigates.

Methods The purpose of this review was to take an allencompassing look at all aspects of this topic.

Because most studies and reviews to date have focused on one dimension of barefoot running, such as biomechanical considerations, we have chosen to investigate even the most obscure claims or concerns. We searched PubMed (MEDLINE), UpToDate, and Web publications using the key words barefoot and running. Because results from studies that did not specifically look at barefoot running may be applicable, the words barefoot and walking and finally just the word barefoot were also used.

The reference sections of applicable research articles were also considered.

Results of the Review Advantages of Barefoot Running Numerous benefits of barefoot running are touted.

Many of these will make sense logically, but an attempt to support or refute the claims is made by looking at the current best evidence. As the purported benefits are discussed, logic will also play a supportive role and, in some cases, may be the only source of ‘‘evidence.’’ Significant Alterations to Runner’s Gait. Although not necessarily an advantage, there are significant changes that are indisputable in a comparative observation of a barefoot runner versus a shod runner. These modifications will, in part, be responsible for many of the claimed advantages described herein.

Several investigators have found consistent changes when the runner is barefoot, including decreased stride length; increased stride rate; decreased range of motion at the ankle, knee, and hip; and a more plantarflexed ankle at contact. The plantarflexed position at foot strike is the most readily observable distinction. The quicker and

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shorter stride length leads to a lower contact and flight time.34-37 Another unique finding observed in the barefoot runner was higher electromyographic activity in preactivation of plantarflexory muscles (gastrocnemius lateralis, gastrocnemius medialis, and soleus).34 The significance of this finding is addressed in the ‘‘Reduction of Impact Forces’’ subsection.

Reduction of Impact Forces. Some investigators believe that impact forces associated with running are high and, along with overtraining, are responsible for many of the running-related injuries seen by clinicians.38, 39 This notion, however, is disputed by Nigg40 not by study references but by the lack of studies confirming it. Studies by Lieberman et al,37 Divert et al,34, 41 and Squadrone and Gallozzi35 determined that impact forces were reduced in those running barefoot.

Robbins found that through training, improved sensory feedback resulted in gait alterations that allowed for foot strike to be at the metatarsal heads instead of the heel. In addition, there is adaptation of the intrinsic musculature with resulting increased strength and, therefore, a medial longitudinal arch that is higher and better able to deform with impact and provide improved shock attenuation.8 Nigg40 disputes this conclusion, noting a discrepancy between peak impact force at 30 to 50 msec and maximal arch deformation at 400 msec for this to be valid.

Shakoor and Block42 hypothesized that the gait changes noted previously herein were responsible, in part, for their finding that walking barefoot resulted in decreased peak joint loads at the hips and knees in 75 patients with osteoarthritis.

Kurz and Stergiou43 looked at how shoe hardness and footwear in general affect ankle coordinative strategies during the stance portion of running. An ankle coordinative strategy is an unconscious modification of the subtalar joint to maximize gait efficiency. Although they found no real differences in the shoes evaluated, they found significant differences between shod and unshod feet. Similar to the investigators discussed in the previous sections, they noted the more plantarflexed ankle position and forefoot contact at foot strike in the barefoot runner but also observed that the ankle (really the subtalar joint) is held in a more inverted attitude as well.43 In another study by Kurz et al,44 the variability of gait was increased in barefoot versus shod runners.

They concluded that the increased variations in the lower-extremity joints may be related to the ability of the mechanoreceptors to adjust the joint pattern

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and may be a mechanism for overcoming repetitive impact forces and, therefore, running injuries.

Nonetheless, how these improved coordination strategies come about when barefoot may be due to improved overall proprioception seen in the barefoot condition (see the ‘‘Increased Proprioceptive Ability’’ subsection).

Divert et al,34 besides noting many of the typical gait alterations seen in the barefoot runner, also found higher braking and pushing impulses and higher preactivation of the triceps surae. In essence, the triceps will ready itself for the expected impact at contact. They concluded that these changes in gait were largely designed to reduce the forces of foot strike.34 Indeed, Divert et al34 speculate that some of the earlier studies that demonstrated increased impact load in barefoot running were the result of the test participants running barefoot heel-toe because they had so little time to acclimate to the process.45 Robbins and others46-48 claim that modern running shoes and manufacturers do such a good job convincing wearers of the protection they give, through marketing and by perceived comfort, that runners tended to be unaware of the forces they were subjected to while running. Shod runners would, therefore, be unlikely to institute the necessary shock-reducing behaviors and would be more susceptible to injury.46-48 Increased Economy of Running. Early investigators49, 50 found that barefoot runners have reduced oxygen consumption and, thus, reduced energy expenditure when running. One study found 4.7% higher oxygen consumption in those wearing shoes weighing 700 g versus the barefoot condition.51 By adding weight to individuals’ feet without adding a cushioned sole, Divert et al52 attributed the increased energy utilization to shoe mass and not gait changes. However, they also hypothesized that shoe-related shock attenuation may concurrently remove stored energy and add to the shod foot inefficiency.52 Webb et al53 noted that a further inefficiency in the use of energy while shod may occur when the actual repetitive deformation of the shoe with each stride requires energy that could be saved in the barefoot state. A nonsignificant difference (P . .05) in improved economy was noted by Squadrone and Gallozzi,35 but they hypothesized that barefoot running–experienced participants in their study changed their running style, making even their shod condition more economical because they ran with a barefoot running style even when in shoes.

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Increased Proprioceptive Ability. Although there are no studies, to our knowledge, that evaluate barefoot runners’ proprioceptive ability, several investigations have looked at proprioception in the barefoot condition under static circumstances. Robbins et al54 investigated the hypothesized loss of plantar tactile sensibility in males by measuring the perception of the slope of variously sloped platforms. They discovered that not only was there a demonstrated loss of proprioception with aging but also with the wearing of shoes. It was surmised that any barrier between the plantar mechanoreceptors and the supporting surface would inhibit foot position awareness.54 In earlier studies, Robbins et al found that thicker or softer shoes decreased balance in the elderly55 and in younger men.56 Reduction in Running-Related Injuries. No evidence was found that demonstrates a reduced prevalence of running injuries in barefoot runners; however, studies exist that demonstrate reduced injury factors in laboratory situations.

Ankle injuries are the most common sportsrelated injury.57, 58 Ankle injuries account for 15% to 30% of all injuries in sports with a high percentage of sideward cutting movements such as basketball, European handball, volleyball, soccer, and tennis.59 Similar values are seen with high school athletics in the United States, with studies citing that ankle injuries make up 12.3% of severe injuries and 28.3% of recurrent injuries.60, 61 A variety of investigators claim that the improved proprioceptive ability noted in the previous section directly leads to a reduction in foot position errors and, thus, fewer lateral ankle sprains. Robbins et al62 found that taping the ankle improved proprioceptive ability and, thus, foot position awareness, but compared with being barefoot, the taping group had 58% less awareness. As a follow-up, Robbins and Waked63 reiterate these findings, noting that individuals in countries where shoes are not worn have significantly fewer ankle sprains, although no reference for this observation is given. It is postulated by Robbins and Waked that ‘‘ankle sprains are caused by impaired proprioception that results in the inadequate use of anticipatory muscular movements under dynamic conditions when there is insufficient time to respond to the actual loading event.’’63(p65) Foot position, because it is affected by plantar tactile receptors, is the means for avoiding ankle sprains in the barefoot condition.63 A study by Stacoff et al59 evaluated the ability of sideward cutting movements in 12 individuals in five different shoes and barefoot and

found that those who were barefoot had significantly better lateral stability. Changes to shoes to improve lateral stability, such as in hardness, reduced midsole thickness, torsional stiffness of the sole, and using a high-cut upper, allowed some stability measurements to become more similar to being barefoot, but none of the five shoes tested were similar to being barefoot in all of the parameters tested and it, thus, was concluded that ‘‘the best lateral stability can be found in the barefoot condition.’’59(p357) Waddington and Adams64 reported similar findings when they found that elite barefoot soccer players were much better able to discriminate ankle inversion movement than were shod individuals. The proprioceptive deficiency resulting from being shod was, in part, reduced by replacing smooth insoles with textured insoles that enhance direct plantar sensory stimulation.64 Unrelated to reduced proprioception but equally contributory to ankle instability is the simple fact that a foot elevated by a shoe results in an increased lever arm between the ground reaction force and the axis of the subtalar joint, which may then impart greater supinatory forces than a foot unshod.59, 65, 66 An interesting application of the reduced lever arm seen in barefoot individuals was noted when Kerr et al67 reported a significantly greater muscle contraction of the peroneus longus in response to an unanticipated and sudden inversion force when shod versus unshod and, thus, concluded that it is a compensatory mechanism to oppose the increased moment created by the inverted foot/shoe condition.

Increased Strength of the Musculature. An anthropometric study by Kadambande et al 68 compared a group of 100 randomly selected individuals from the United Kingdom who routinely wore shoes with 100 individuals from India who never wore closed shoes. They found that the pliability of shod feet was significantly less than that of bare feet, but they did not find a significant difference in intrinsic foot muscle function. Rao and Joseph69 evaluated 2,300 children for any effect of footwear on arch development and concluded that wearing shoes (especially in early childhood) is detrimental to the development of a normal medial longitudinal arch and attributed this to stronger and more developed plantar intrinsic musculature. As discussed earlier, Robbins and Hanna8 claimed that barefoot runners develop, through training, increased muscular strength adaptation of the intrinsic musculature.

Nike claims a significant increase in intrinsic foot muscle size and strength when their minimalist shoe

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is used, which is elaborated on later herein. The most discussed research regarding this claim was a project funded by Nike whereby Bruggemann et al70 analyzed runners who wore the Nike Free minimalist shoe (Nike, Beaverton, Oregon) during their warm-up regimen for 5 months, thus simulating ‘‘barefoot’’ running. He claimed an increase in the cross-sectional size and strength of selected intrinsic muscles. Specifics of how strength was measured and what warm-ups entailed were not noted in the study. More details from this study70 are in the ‘‘Shoes that Mimic Barefoot Running (Minimalist Shoes)’’ section later herein.

Decreased Cost. If a runner changes shoes every 500 miles and runs 40 miles a week, this equates to four pairs of shoes a year. The average price of athletic footwear in 2008 was $43.71 according to the National Sporting Goods Association. Running barefoot could lead to an annual savings of $175.00.71 Decreased Risk of Foot Deformities. Regarding children, Wolf et al72 states that ‘‘optimum foot development can only occur in barefoot conditions.’’(p51) Likewise, Staheli73 claims that constrictive footwear can lead to deformity and stiffness.

The American Academy of Pediatrics states that children should not wear shoes until necessitated by environment. The Academy74 claims that rigid shoes prevent motion and development of the intrinsic musculature. Besides better arch development (see previously herein), Rao and Joseph69 found that the incidence of flatfoot in children was three times as high in those who wore shoes (8.6%) versus those who did not (2.8%). This held true even after other factors, such as age, obesity, and ligamentous laxity, were accounted for. In addition, children who wore closed-toe shoes had even higher rates (13.2%), whereas those who wore slippers and sandals were in between (8.2% and 6.0%, respectively). They, thus, concluded that when children begin to wear shoes at an early age, they have increased rates of flatfoot.69 In a follow-up study of adults, Sachithanandam and Joseph75 found that the earlier a child began wearing shoes, the higher the prevalence of flat feet. They also noted that wearing shoes longer than 8 hours per day was associated with a higher rate of flat feet.

In multisegment foot model studies by Wolf et al72 and Morio et al,76 it was determined that wearing shoes constrained the natural motions of the foot, especially regarding forefoot to rearfoot motion. Last, Zipfel and Berger77 reviewed pathologic changes to the metatarsals of rural and urban populations compared with unshod prehistoric

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populations. They found significantly more lesions in the shod groups and concluded that shoes or modern substrates may be responsible.

Disadvantages of Barefoot Running Injury from Running Surface Debris and General Hazards. Rocks, glass, and thorns are just a few of the possible hazards that barefoot runners may encounter, but no study, to our knowledge, has evaluated this risk. Nonetheless, the advocates of barefoot running claim that the solution to this problem is as simple as watching where you place your feet.26 Although an unshod foot is at greater risk for sharp object trauma, the plantar skin surface of the foot is uniquely designed to resist penetration and likewise requires 600% greater abrading loads to reach the pain threshold than do other skin surfaces.78, 79 A bizarre example of a running surface hazard that is probably unlikely in developed countries but is noted for completeness and curious interest is podoconiosis (noninfectious, nonfilarial geochemical elephantiasis). It is an unusual manifestation due to exposure of a barefoot individual to irritant alkalic clay soils in Africa, Central America, and India. The silicate particles are absorbed and cause inflammation and blockage of lymphatic channels, which results in elephantiasis.80 Although concerns such as stinging insects, blunt trauma, and even a spike injury in a competitive scenario may arise, no studies regarding these risks to a barefoot runner are found.

Thermal Injury from Extremes of Temperature on the Running Surface. No studies or surveys demonstrate risk or document successful running while barefoot on either hot or cold surfaces; however, claims on barefoot running Web sites have shown that at least some runners can adapt to these temperature extremes and not only run in them but complete full marathons.26 Although not a running surface risk, the American College of Foot and Ankle Surgeons warns of the risk of sunburn and skin cancer from going barefoot.81 Availabilty of Adequate Surfaces. Robbins and Gouw47 claimed that the human foot does not need any external cushioning to deal with the impact of running. No studies have yet determined the optimal surface for barefoot running.

Exposure to Microorganisms/Infectious Agents. Many health-care providers fear that an unprotected foot, especially one that may experience minor (or major) nicks and cuts, will be at risk

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for inoculation by microorganisms. Preventive health experts warn of the hazards of being barefoot in public showers and pools with respect to tinea pedis and plantar verrucae.82 Similarly, plantar verrucae may develop secondary to inoculation from a minor cut.83, 84 Several studies85-87 have demonstrated that being barefoot is not a risk factor for plantar verrucae or tinea pedis and may, in fact, be therapeutic for treating tinea pedis. More seriously, some individuals, many who are thought to be in excellent health, such as athletes and military personnel, are at risk for community-associated MRSA that can begin from the most minor cutaneous injury.88, 89 Although the unshod foot would be at greater risk for a puncture wound and possible tetanus, the risk of an associated infection with pseudomonas is actually reduced.90, 91 One study92 found that walking barefoot around pools is a predisposing factor for onychomycosis in immunocompromised individuals.

Although barefoot runners may be exposed to infectious agents, such as leptospirosis, tungiasis, mycetoma, strongyloidiasis, and Mycobacterium gordonae, most are found only in tropical countries with poor sanitation or are quite rare.93-96 However, the Centers for Disease Control and Prevention warns that infection by hookworm larvae with resultant cutaneous larva migrans is a real possibility for anyone performing a barefoot activity in a tropical area, including the southeastern United States.97 Runners who Require Mechanical Control for Existing Conditions. Although several studies98-104 cite the success of orthotic devices in the treatment of lower-extremity overuse–related injuries, scientific literature investigating the comparative treatment of conditions with barefoot running and orthotic devices is nonexistent.

Loss of Protective Sensation. In comparing groups of adults with puncture wounds, diabetic individuals were more likely to be barefoot when the injury occurred.105 In a study106 from rural Sri Lanka, walking barefoot was shown to be a risk factor for diabetic foot disease. Individuals going barefoot had a higher rate of foot ulcers versus those wearing some type of footwear. In addition, in diabetic individuals who wore footwear, foot ulcers and web space and nail infections were increased in those who wore footwear less than 10 hours per day versus those who wore footwear longer than 10 hours per day.106 Another study 107 compared plantar pressures seen in shod and unshod individuals while walking on a variety of surfaces and

found that shoes increased the contact area and, thus, reduced the peak pressures. Carl and Barrett108 similarly concluded that shoes and even flipflops were superior to the barefoot condition in more evenly distributing forces and reducing peak plantar pressure.

Increased Shock at Impact. Komi et al45 found increased passive peak vertical forces in barefoot (2.65 body weight) versus shod (1.95 body weight) conditions. This study used only four participants, measured forces on ten nonconsecutive impacts, and found no significant difference in stride rate and stride length, which is contrary to multiple other studies. 34-36 In a close look at methodology, however, the participants, while running barefoot, landed heel first, which is not only going to increase impact forces but is an unnatural barefoot gait.45 The results of this study have been refuted multiple times.34, 37, 39 A study by De Clercq et al109 demonstrated that barefoot runners will, at heel strike, undergo a 61% deformation of their heel pad versus a 36% deformation when the foot is shod. They concluded that the heel pad was maximally deformed during barefoot running to the point that the heel pad was no longer a shock absorber but a protective structure with a much greater risk of potential injury. However, this study,109 similar to that by Komi et al,45 required the runner to strike with the heel, which is contrary to the barefoot running gait pattern.

Increased Shock Transmission to Back Muscles. A study by Ogon et al110 found an increased rate of shock transmission to erector spinae back muscles in barefoot conditions versus shod conditions and a delayed muscle response to the acceleration of the L3 vertebrae in the barefoot group. However, this study forced the test participants to standardize their gait to strike with their heel during all of the running conditions. Gait adaptations (which include a shift away from a heel landing) have been proved multiple times to be one of the characteristics of running barefoot.8, 34-37 Implementing Barefoot Running Although significant and detailed information regarding implementation can be found on barefoot running Web sites,26, 111 no studies, to our knowledge, demonstrate the safest or most efficacious method for instituting a barefoot running program.

Robbins and Gouw47 estimated that shod individuals would require 6 weeks of adaptation for plantar skin and musculature and daily barefoot running to

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maintain adaptation. In a later article, Robbins et al78 noted unsubstantiated and anecdotal reports that claim that 3 to 4 weeks of barefoot running at 30 minutes daily is sufficient for plantar surface adaptation.

Shoes that Mimic Barefoot Running (Minimalist Shoes) Vibram FiveFingers (Vibram, Concord, Massachusetts) were introduced in 2006 and were quickly named one of Time Magazine’s Inventions of the Year in 2007. Vibram FiveFingers have been shown to be similar to barefoot running in reducing the amplitude of the impact peak vertical force and encouraging a more forwardly placed point of foot strike in a study involving eight experienced barefoot runners. Also, foot angle and ankle angle 15 msec before touchdown were similar to the barefoot condition and significantly decreased the foot angle and increased the ankle angle versus the shod condition.35 Nike introduced the Nike Free 5.0 in 2004 to provide 50% of the support and stability of a normal running shoe. They followed this up with introduction of the Nike Free 7.0 and the Nike Free 3.0 to be more stable and less stable than the 5.0, respectively. In addition to their design research, Nike funded research at the University of Cologne that was presented at the International Society of Biomechanics’ Symposium in July 2005. In that study, 50 participants were divided into two groups. Group 1 performed a warm-up routine in Nike Frees, then a workout routine in traditional training shoes three to four times a week for 5 months. Group 2 performed both routines in traditional training shoes. The researchers found significant increases in the anatomical cross-sectional area of the flexor hallucis brevis, flexor digitorum brevis, abductor hallucis, and quadrates plantae muscles in the Nike Free group but no change in the anatomical crosssectional area of the leg muscles above the ankle.

The control group showed no significant increases in the anatomical cross-sectional area of any muscles. Likewise, the strength of the flexor hallucis longus and flexor digitorum longus muscles increased in the Nike Free group but not in the control group.70 Nigg40 evaluated multiple minimalist shoes and concluded that the term barefoot shoes is a misnomer. Although different shoes may incorporate specific aspects of the barefoot condition into their shoe, a ‘‘shoe condition is not a barefoot condition.’’40(p78)

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Discussion Despite numerous upgrades and research-driven changes in running shoes, the number of runningrelated injuries has not improved, and some would say it is higher than ever. This has led many clinicians and researchers as well as coaches and runners to conclude that shoes themselves not only do not reduce injuries but may cause or aggravate running-related abnormalities. Barefoot running advocates claim numerous benefits, including stronger muscles of the foot, better proprioception, reduced ankle sprains, less impact at foot strike, increased economy of running, and the prevention of running-related injuries.

Advantages Significant Alterations to Runner’s Gait.

There is little argument that running barefoot profoundly changes many aspects of gait compared with wearing shoes. A clinical observer could make logical assumptions of how these changes might create advantages over shod running. Two such advantages, well supported by the evidence but with qualification, would be reduced impact at contact and improved proprioception.

Reduction of Impact Forces. The barefoot runner’s quicker, shorter strides and forefoot landings are quite different from those of the shod runner, who strikes at the heel. These changes are said to reduce the shock at impact and, therefore, reduce the incidence of numerous ailments associated with the shock of running impact.

Barefoot running kinematics results in a forefoot/ midfoot landing. The reduced ground reaction force at foot strike is due to ankle joint plantarflexor musculature impact attenuation (the reduced impact could also be due to a shortened stride length).

This does not necessarily mean that loading to the lower extremity at large is reduced. More recently, some investigators have questioned the concept of reduced impact in the barefoot runner. In fact, incorporating the ankle plantarflexors (gastrocnemius and soleus) during the impact phase of running, as forefoot striking encourages, will reduce impact ground reaction forces, but the additional muscle forces may increase joint and skeletal loading forces. In other words, a more active musculature will pull osseous segments together, increasing the load on the bones themselves and on the interposed joints (ankle, knee, and possibly even hip). Although the barefoot running gait has shorter strides and this would result in reduced

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impact, the frequency of strides is increased, so the overall total impact over a training run may not be altered (Tim Derrick, PhD, written communication, November 2009). Indeed, a study by Edwards et al112 suggested that shorter strides probably reduce the potential for stress fracture injuries, and runners wishing to reduce their likelihood of stress fractures should shorten their stride by 10%.

How these kinematic changes come about may be through increased sensory feedback, creating gait changes in the barefoot runner known as ankle coordinative strategies. These result in the more plantarflexed ankle position with forefoot contact at foot strike and the subtalar joint held in a more inverted attitude. The rationale for this is that the runner will modify ankle position (the so-called coordination strategy) during running to maximize performance or because impact feedback to the limb is unacceptable and must be altered. The positional modification of the subtalar joint during barefoot running is said to come about from the body’s reduced need for shock attenuation via subtalar pronation because it can obtain it from the musculature (largely the gastrocnemius). Indeed, reduced subtalar motion takes place in barefoot runners. In other words, the shod runner receives feedback from the ankle ‘‘requesting’’ more shock absorption because of how the foot lands and, thus, will land more pronated.

An increased variability of gait found in barefoot versus shod runners and higher braking and pushing impulses and higher preactivation of the triceps surae are findings that suggest that improved sensory feedback in barefoot runners is, at least in part, responsible for the reduced impact forces.

Conversely, sensory feedback is believed to be diminished by wearing running shoes.

Last, stronger intrinsic musculature that raises the long arch, resulting in a more efficient shock absorber, is another proposed mechanism for reduced impact in the barefoot condition; however, maximal arch deformation and peak impact do not correlate chronologically.

Increased Economy of Running. Another supposed benefit to running barefoot is increased economy of running, and although it is clear that elimination of the weight of the shoe will reduce energy utilization, there is evidence that after correcting for the weight of shoes, barefoot running may still be more efficient.

The initial assumption was that the reduced energy expenditure was the result of the shoe’s added mass and the expended effort in accelerating and decelerating that mass multiple times during a

run. However, could the previously noted gait changes also be playing a role in reduced energy expenditure? In other words, gait alterations seen in barefoot runners may be more efficient. Divert et al52 concluded that early studies correctly attributed the increased energy utilization to shoe mass and not gait changes. Some of the same gait alterations that reduced impact forces, such as shortened contact time, forefoot landing, and triceps surae preactivation, may also enhance the storage and restitution of elastic energy.52 Studies35, 53 also suggested that the loss of stored energy during shoe-related shock attenuation and the energy required for repetitive shoe deformation add to the shod foot inefficiency.

Increased Proprioceptive Ability. With the foot unshod, there is an intimate relationship with the supporting surface. Given that numerous studies113-119 have noted the significant role that plantar mechanoreceptors play in postural control during locomotion, it is easy to see why barefoot running advocates believe that the significant increase in sensory input will substantially increase the proprioceptive function of the foot while running. This more direct coupling of the runner to the ground would result in a finer kinesthetic tuning (position sense) to the running surface and, theoretically, fewer injuries through adjustments to impact. In addition, besides disconnecting the supporting surface from plantar sensory input, shoes, by elevating the foot from the ground, increase the distance of the foot from the supporting surface and, thus, lessen the runner’s ‘‘feel’’ for the ground.

When one is barefoot, there is improved awareness of foot position and, therefore, decreased foot position error. It was this greatly enhanced proprioception seen in the barefoot condition that Robbins and others8, 47 believed led to such better sensory feedback that it would then create gait alterations that would ultimately lead to reduced impact and, thus, reduced injury to striking structures, as was outlined in the previous subsection.

Note that the previously mentioned studies were performed on individuals who were static and not walking let alone running. In addition, many studies120-122 assessed the plantar mechanoreceptors that respond to pressure and vibration, and some investigators have concluded that lower-limb motor activity and postural control was more affected by muscle spindle proprioceptive afferents and Golgi tendon organs than by plantar cutaneous afferents and, thus, may play a much greater role in balance and proprioception. Nonetheless, most investigators116, 117, 122 claim that they are just not

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certain as to the hierarchy of importance when considering plantar mechanoreceptors, Golgi tendon organs, muscle spindle afferents, and visual clues. There is even the consideration that in an unshod condition, proprioceptive elements (plantar mechanoreceptors) may be dampened through chronic impact loading.123 Last, Robbins and Gouw46 claimed that shoes gave the runner a false sense of security and that those runners, therefore, would not incorporate the necessary gait changes to reduce impact. Their study claimed that this could be much improved by introducing simple surface irregularities to the insoles, which would impart improved sensory feedback that could assist in reducing impact.46 Reduction in Running-Related Injuries. Most of the claims regarding the reduction of runningrelated injuries in barefoot runners are made on the basis of logical assumptions, such as running barefoot results in stronger plantar intrinsic musculature; therefore, this may be responsible for the low incidence of plantar fasciitis seen in barefoot runners.8 Or, barefoot runners have less impact and because many running injuries are due to repetitive high impact, barefoot runners may have fewer injuries.39 However, no studies or even surveys have substantiated these claims.40, 124 Although there are numerous studies that demonstrate the reduced lateral ankle instability in the barefoot condition, they do not look at barefoot runners.

In their overview of ankle injuries, Robbins and Waked63 make the point that although reduced position sense while shod is a major factor in ankle sprains, unanticipated foot placement (eg, on another player’s foot) is frequently a factor as well.

Many runners have sprained an ankle on a trail when a foot was placed on an unanticipated sloped surface. It would stand to reason that an unexpected benefit of barefoot running is that in an effort to avoid surface hazards through increased visual surveillance, the barefoot runner would be much less likely to have a misstep as the cause of an ankle sprain.

Increased Strength of the Musculature. Barefoot running enthusiasts tout that by eliminating confining and restrictive shoes, the foot will more fully use the intrinsic musculature and, therefore, develop greater strength and function. Improvement in performance and reduction in injuries would then result. Evidence is conflicting on the actual strengthening potential of the barefoot condition, and even if the barefoot condition led to increased muscular strength, the claim that this results in

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reduced injuries or improved performance has not been proved scientifically.

Decreased Risk of Foot Deformities. Statements from professional organizations and studies referencing the impact of shoes on foot development in children support the notion that shoes worn by children may inhibit normal development and, hence, may increase the likelihood of deformities later in life. Although not directly related to barefoot running, these findings were included because so many barefoot running advocates extrapolate the findings to the barefoot runner as a means to explain some of the benefits.

Note that those studies on children do not suggest that those running barefoot would necessarily develop fewer deformities but that an unshod foot may be less confined and, thus, function more naturally. The foot would, therefore, be less subject to deformities and would more fully develop the intrinsic musculature. The study by Morio et al76 looked at adults and came to a similar conclusion that shoes inhibit the natural motions of the feet and that this ‘‘could play a role in possible injury mechanisms.’’ Disadvantages Although most layperson perspectives on barefoot running revolve around the advantages, there are also several possible drawbacks. Likewise, although most scientific studies on barefoot running were designed to evaluate the advantages, there are also a variety of possible shortcomings. Many of the downsides are readily obvious to those considering barefoot running and to the professionals who care for feet. Following is a summary of some of these concerns.

Injury from Running Surface. There are no published accounts of the risk of surface debris or temperature extremes to the barefoot runner. Harsh climates can significantly impact those wanting to run barefoot. Burns and frostbite are very real dangers in these types of conditions. Solutions for reducing this risk range from wearing minimalist shoes that offer some protection to watching where you place your feet. This may be easier said than done on surfaces such as grass, which would otherwise be one of the better surfaces for barefoot running. Surveys of barefoot runners regarding their experiences could verify its significance.

Availability of Adequate Surfaces. Although it may seem logical that a more cushioned surface, such as grass or a rubber track, would be preferential for barefoot running, this need for

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cushioning seems negated by the improved shock absorption while running barefoot. One of us (D.J.C.), who runs barefoot 50% of a 40-mile-perweek training program, has found that concrete or a desert surface is a much kinder surface than is asphalt or grass (Fig. 1). A hard surface, such as concrete, gives stability and instant feedback. He reports that light-colored concrete also allows foreign objects, such as rocks and glass, to be visualized well. Concerns regarding climate-related surface temperature extremes may be overcome with indoor tracks or treadmills. The complete lack of evidence on the best surface for barefoot running would bode well for the development of a survey tool that asks barefoot runners what surface they prefer and why.

Exposure to Microorganisms/Infectious Agents. Although inoculation with microorganisms is a definite risk and in some instances is documented in the literature, it seems that the fears of most people, including health-care practitioners, are exaggerated. The risk of exposure becomes critical when a person is immunosuppressed or has peripheral neuropathy. In these individuals, a minor abrasion may lead to a debilitating infection.

Runners Who Require Mechanical Control for Existing Conditions. Conceivably, foot specialists would worry that barefoot runners genuinely in need of customized support or motion control shoes to alleviate existing conditions may become injured if running barefoot. Proponents of barefoot running claim that many of these runners would adjust and ultimately have fewer injuries if they would go unshod. Runners who have been successfully treated with orthotic devices for a runningrelated injury may be reluctant to discontinue orthosis use and risk a return of their injury. Welldesigned controlled clinical trials need to be performed to determine who needs specific shoes or orthotic devices and who would be better off adding some barefoot activity. Surveys that query barefoot runners on the outcomes of giving up their orthoses would be beneficial.

Loss of Protective Sensation. Those with a lack of protective sensation are advised to never walk without shoes, even in their own home, owing to the increased risk of ulcers and even amputation.105, 106, 125, 126 Given this potential, it would seem quite inappropriate for this individual to be running barefoot.

Increased Shock at Impact. This reported finding, in conflict with multiple other studies, seems to be attributable to individuals running heel first, contrary to barefoot running kinematics. Also

Figure 1. Running barefoot on desert terrain.

in conflict with the barefoot runner’s advantage of reduced impact is a study110 that found an increased rate of shock transmission to erector spinae back muscles in barefoot conditions versus shod conditions. This study required participants to begin the contact phase with a heel strike. When given no direction regarding gait changes, barefoot individuals naturally begin running with a midfoot strike.

We believe that any study of the barefoot condition that requires its participants to adopt an unnatural gait (encouraging a heel strike) will not achieve valid results because it is not truly evaluating barefoot function.

General Hazards. Blunt trauma, such as stubbing a toe, and encounters with insects, such as scorpions, spiders, bees, and wasps, are a real concern. Less likely would be a spike injury to the barefoot runner in a competitive situation. On the other hand, if the runner is barefoot, he or she is unlikely to spike himself or herself.

Implementing Barefoot Running Many barefoot runners do not recommend a rigid schedule for implementing barefoot running. Most barefoot runners who write about their experience emphasize listening to your body and paying attention to your interactions with your surroundings. If a barefoot runner chooses to use a minimalist shoe as part of the adaptation process, they may experience additional problems (see the following subsection).

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It is recommended that those considering barefoot running very gradually increase their barefoot running activity because successful barefoot running seems highly dependent on proper implementation. There seems to be a consensus that with any new activity, a gradual buildup be taken to allow for musculoskeletal and cutaneous adaptation.

Shoes that Mimic Barefoot Running (Minimalist Shoes). Thus far, limited studies on two minimalist shoes (Vibram FiveFingers and Nike Free) indicate that kinematic changes similar to barefoot running, as well as plantar intrinsic strengthening potential, are occurring. Many coaches reported that several years ago when the Nike Free became available, large numbers of high school and college-level runners enthused with the touted claims and benefits of barefoot running and jumped into training at such a rate that many became injured (Bill Strachan, MS, verbal communication, July 2009). Part of the reason may be that the minimalist shoe gives a false sense of security and the runner will train on a surface, at a pace, or at a distance that the natural feedback, if totally barefoot, would not allow. Put another way, a foot with no covering will naturally disallow the ‘‘too much, too soon, too fast’’ pitfalls when barefoot running is initially undertaken. Nigg,40 in his review of minimalist shoes, concluded that all of the shoes, with their unique characteristics, may be beneficial to the runner but that the label ‘‘barefoot shoe’’ is more marketing than substance.

Research Needed and Unanswered Questions Many of the questions that arise from reviewing the topic of barefoot running may be answered with future research efforts. We believe that the following are just a few of the investigations that could better inform runners, coaches, and health-care providers on the merits and hazards of barefoot running: 1) Survey of why people do or do not run barefoot.

2) Effects of barefoot running on competitive performance.

3) Running-related injuries improved or eliminated by barefoot running?

4) Barefoot running mechanics and the effect on specific running-related conditions, such as plantar fasciosis, medial tibial stress syndrome, Achilles tendon disorders, and iliotibial band friction syndrome.

5) Can using barefoot running mechanics while

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running in shoes (eg, ChiRunning [http://www. chirunning.com/]) reduce injuries?

6) Could the suggested greater requirement for pronation when shod be the cause of so many running-related injuries?

7) Can miles of unshod running dampen plantar mechanoreceptors, making them less able to function proprioceptively?

8) Could a forefoot/midfoot strike produce or aggravate Achilles tendon abnormalities?

Conclusions Multiple studies demonstrate profound gait differences in those running barefoot compared with shod individuals.

Although numerous studies support the claimed advantages of the barefoot condition, such as reduced ground reaction force at impact and improved sensory feedback and proprioception, there is no evidence that these changes result in reduced injuries or improved performance in barefoot runners. It seems that these claims are extrapolated or speculative.

Some other touted benefits of the barefoot condition, such as increased strength of the plantar intrinsic musculature and a more efficient utilization of energy, have some supporting evidence, but, again, there is no evidence to show that these changes result in fewer injuries or improved performance.

Evidence is strong that walking barefoot with a lack of protective sensation is very risky and should be avoided.

Many runners may benefit from the incorporation of barefoot running into their regimen, and utilization of highly controlling shoes or orthotic devices may be detrimental for some.

Anyone implementing a barefoot training regimen should begin with a minimal amount of activity and should progress gradually to allow the plantar surface of the feet, the intrinsic musculature, and the osseous structures to adapt and avoid injury.

Those with conditions necessitating biomechanical intervention, such as motion control shoes or orthotic devices, should proceed with caution and only if professionally supervised.

Evidence that barefoot running directly prevents or improves running-related injuries is nonexistent.

More specifically, there are no studies to confirm that barefoot runners have fewer lateral ankle sprains, as the proponents claim. There is strong

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laboratory evidence that those who are barefoot have such an improved position sense that they have much less lateral ankle instability or risk of sprains.

Regarding the disadvantages involving hygiene, surface risk, and general hazards, the evidence supports the notion that many of the purported risks are overblown.

We contend that many of the purported claims may have merit, but much more research on barefoot running is needed, especially regarding comparative biomechanics and injury rates as well as surveys of runners’ opinions about barefoot running.

In closing, professional organizations and many clinicians with a keen interest in foot health and podiatric sports medicine are becoming more aware of the purported claims and risks but are going to be reluctant to support or oppose barefoot running until more definitive research and evidence are available.127 We believe that well-conducted studies will demonstrate that barefoot running will, indeed, provide many of the touted advantages and at the very least be a valuable adjunct to conventional training methods.

Nonetheless, our opinion is that in addition to a sports medicine foot specialist, those who are in the best position to judge the appropriateness and usefulness of barefoot running are the coaches and runners themselves. Indeed, many coaches at most competitive levels incorporate barefoot running as part of the overall training regimen but not exclusively (Bill Strachan, MS, verbal communication, July 2009).

Acknowledgment: Julie Jenkins for her assistance in providing photographs and proofing the manuscript and Bill Strachan for his invaluable input from the coach’s perspective.

Financial Disclosure: None reported.

Conflict of Interest: None reported.

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