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2012 33: 787Foot Ankle IntAndrew R. Hsu
Topical Review: Barefoot Running
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American Orthopaedic Foot & Ankle Society
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FOOT & ANKLE INTERNATIONALCopyright 2012 by the American Orthopaedic Foot & Ankle SocietyDOI: 10.3113/FAI.2012.0787
Topical Review: Barefoot Running
Andrew R. Hsu, MDChicago, IL
Key Words: Barefoot Running; Biomechanics; Gait
Barefoot running has seen a resurgence of popularity inrecent years driven by claims of enhanced running efficiencyand injury prevention as individuals continue to explore alter-native training strategies to improve performance.19,62,65 Thisrising interest has sparked a significant growth of scientificresearch investigating the physiology, biomechanics, perfor-mance effects, and injury mechanisms of barefoot running.It has been established that footwear plays a significantrole in the pathophysiology of foot and ankle disordersby creating biomechanical changes in force transmission,lower extremity position, and gait kinematics.11,44,46,65
Since the invention of modern cushioned heel footwearin the 1970s, there has been a worldwide proliferation ofshoe manufacturers with claims of improved foot safetyand injury prevention that have gone unproven. Despiteprevious discussions in the scientific community in the1980s regarding the effects of barefoot running,6,16,28,59,60
there has been renewed mainstream media interest regardingbarefoot running as recreational and professional athletesexplore new training programs to increase strength andendurance.
Foot and ankle injuries associated with running includestress fractures, plantar fasciitis, and ligamentous injuries,among many others.1,2 Specific causative factors for theseinjuries such as anatomic and kinematic variables are notwell delineated or understood. Studies investigating therole of footwear in injury patterns report conflicting data
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Corresponding Author:Andrew R. Hsu, MDDepartment of Orthopaedic SurgeryRush University Medical Center1611 West Harrison Street, Suite 200Chicago, IL 60612E-mail: email@example.com
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as to whether the cushioned heel of modern shoes isbeneficial or detrimental to gait and foot force transmis-sion during running.7,20,34,65 There is considerable ongoingdebate regarding the proposed benefits and harms of bare-foot running with little consensus other than the needfor future well-designed studies.37 Proponents of barefootrunning argue that the development of modern footwearis detrimental from an evolutionary perspective as humansadapted a successful characteristic gait as a result of barefootstimulation.4,44 One of the central arguments in favor of bare-foot running is that the hindfoot strike induced by modernfootwear increases ground impact forces and decreases adap-tive foot proprioception, thus potentially increasing rates ofinjury.
A landmark study by Lieberman et al. showed that habit-ually barefoot endurance runners landed on the forefootor midfoot with a more plantarflexed ankle, whereas shod(footwear) runners landed on the hindfoot with significantlyhigher collision forces.44 The clinical implications of theseresults have not been investigated and remain theoretical.Those who oppose barefoot running contend that it is anexercise fad that is potentially harmful to individuals whoare not properly trained.43 Despite the increased recent atten-tion given to barefoot running as a potential performance-enhancing training strategy, the scientific evidence is lacking,without any clear conclusions for or against its use. Thereare also initial reports being published of injuries, such asmetatarsal stress fractures, induced by barefoot-simulatingfootwear that strongly caution against an abrupt transitionfrom shod to barefoot running.17
With the increased demand for minimalistic shoes, foot-wear manufacturers have released multiple lines of barefoot-simulating footwear to provide the flexibility and feel ofbarefoot running while also protecting the plantar foot fromenvironmental hazards. Currently, there are no clinical guide-lines that exist to help patients with and without estab-lished foot pathology transition to barefoot running in asafe and effective manner. Despite the lack of scientificevidence, the popularity of barefoot running among thepublic continues to steadily rise, and the growing numberof barefoot runners has significant potential implications for
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the incidence rates of foot and ankle injuries in the generalpopulation. The purpose of this review is to present thephysiologic and biomechanical evidence in the literaturebehind barefoot running to help inform physicians caringfor patients interested or involved in this alternative formof training. A literature review of English-language arti-cles in medical publications that investigated barefoot and/orshod running was conducted in PubMed MEDLINE and theCochrane Database of Systemic Reviews from 1969 through2012. Primary studies, review articles, meta-analyses, andcase reports were included from the foot and ankle surgery,orthopaedic surgery, sports medicine, biomechanical, exer-cise physiology, and internal medicine literature.
The characteristic striding bipedal locomotion of man hasbeen one of the defining characteristics of humans and ourancestors for more than 2 million years.4 The specializedanatomy of the human foot represents the end product ofbarefoot bipedalism evolution with gait adaptations that haveremained largely unchanged until modern times.4 Devel-opmental adaptations, such as a robust and pliable mediallongitudinal arch, improved the mechanics of running in earlyman by storing and releasing elastic energy with increasedefficiency through mass-spring mechanics.30 Early permu-tations of footwear consisted of simple, thin coverings ofleather with string that had no arch or heel support andmainly served to protect against environmental hazards tothe skin of the sole.46,60 The advent of modern shoes withelevated and cushioned heels did not occur until the 1970s,when the prevailing thought was that human feet were fragileand unable to withstand the large impact stresses of runningwithout adequate support, elastic cushioning, and motioncontrol.
The counterargument supporting barefoot running is thatincreasingly padded and restrictive shoes cause disuseatrophy and stiffness of the intrinsic foot musculature, thusplacing larger demands on the surrounding joints and plantarfascia.60 In essence, if humans have evolved to run bare-foot over millions of years, it logically follows that naturalselection and evolution did not adapt the foot to runningin shoes. One of the main pieces of evidence in support ofbarefoot running is the unchanging prevalence and epidemi-ology of foot and ankle injuries in modern times. Despite thetechnological and research-driven design advances made infootwear over the past 30 years,50 the rates of running-relatedinjuries in the general population has remained relativelyconstant, with an incidence ranging from 35% to 79% instudies published between 1982 and 2010.25,35,45,51,68,69,71
In these studies, the most common site of injury reportedis the knee (7% to 50%) followed by the lower extremity(9% to 32%) and the foot (3% to 38%). However, injuryrates of the foot and ankle in competitive sports may becurrently increasing,23 and this has led many researchers to
the conclusion that footwear does not have adequate protec-tive effects or adaptive changes and may in fact exacerbaterunning injuries.
Despite persistently elevated injury rates, the use ofincreasingly cushioned and restrictive footwear has grownto become nearly ubiquitous in modern society, althoughthere is no supporting evidence of its clinical benefits. Someresearchers believe that among different types of footwear,cushioned heel running shoes have little to no benefit overless supportive footwear and may prove harmful in thelong term.9,49,50,52,55,56,58 One of the early supporters ofbarefoot running in the scientific literature was Robbins andHanna, who found significantly higher rates of foot injuryin individuals wearing shoes in Haiti compared with thosewho were habitually barefoot.60 Although injury rates werelikely multifactorial in this study, these findings provideda key springboard for subsequent research exploring thepotential benefits and risks of barefoot running. An analysisof the physiologic and biomechanical studies of barefootrunning in the literature reveals that its effects can be brokendown into five main categories: (1) anatomic adaptations,(2) metabolic demands, (3) proprioception, (4) impact forces,and (5) coordinative strategy.
Anatomic adaptationsAnthropometric studies have provided valuable insight
into the effects of footwear on anatomic adaptations of thefoot, including intrinsic flexibility, muscular strength, andarch development.27,49 A guiding principle to foot adaptationis that the musculoskeletal system is responsive to loadingand requires stress in order to remodel and become stronger.Therefore, shoes with stiff soles and movement controlprevent bones and muscles from properly adapting to loadsincurred during impact activities such as running. Wolf etal. investigated foot pathology in children and cautioned thatyoung children should not wear restrictive footwear becauseof potential foot deformity and stiffness.73 Using foot modelanalyses, the authors demonstrated that footwear constrainsthe natural movements of the foot, particularly in regardsto forefoot to hindfoot motion. There was a 4% decreasein medial arch length when going from barefoot to shodconditions along with a 5 loss of range of motion in foottorsion along the longitudinal foot axis.73
The idea of avoiding restrictive footwear in childrenis supported by the American Academy of Pediatrics,which has stated that children should not wear shoes untilnecessitated by the surrounding environment because ofimpaired intrinsic musculature development caused by rigidfootwear.67 Sachithanandam and Joseph have shown that theearlier a child begins wearing footwear, the higher is thelikelihood of developing flatfoot deformity.63 Correlation ofthe static footprints of skeletally mature individuals with theage at which they began to use footwear showed a 1.8-fold
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Foot & Ankle International/Vol. 33, No. 9/September 2012 BAREFOOT RUNNING 789
increase in the incidence of flatfoot between subjects whofirst wore shoes before 6 years of age compared with thosewho started at the age of 16.63 Kadambande et al. comparedhabitually shod and barefoot individuals and found that footpliability was significantly decreased with similar intrinsicfoot musculature in the shod group.27 Rao and Joseph inves-tigated the effects of footwear on medial arch development inchildren and found that footwear had a 3-fold increase (9%versus 3%) in the incidence of flatfoot and was detrimental tothe development of the longitudinal arch and strength of theplantar intrinsic muscles.49 Further analysis showed that chil-dren wearing closed-toe shoes had a 2-fold higher incidence(13% versus 6%) of flatfoot compared with those wearingsandals without arch or heel support. Significant differencesin the development of foot musculature between barefoot andshod individuals have also been seen in adult populations.
Bruggemann and Potthast showed that running with bare-foot simulation footwear significantly increased the cross-sectional size and strength of intrinsic foot muscles in adultswith a 20% increase in metatarsophalangeal flexor strength inbarefoot simulation subjects compared with shod conditions.5
A proposed conclusion from these results was that strongerintrinsic musculature can elevate the arch of the foot to createa more effective shock absorber by deflecting the medial archof the foot on loading. Divert et al. have further shown thatbarefoot running causes elevated electromyographic activityin the preactivation of plantarflexion muscles, including thegastrocnemius and soleus, thus decreasing stress to the lowerextremity.13
Metabolic demands and proprioception
Studies have shown reduced oxygen consumption andlowered rate of perceived exertion in barefoot versus shodrunning groups with an overall decrease in energy expen-diture of roughly 5.7%.6,8,19 Divert et al. studied thesemetabolic differences and stated that the increased energyuse with shod running was likely attributable to effects offootwear mass along with shoe-related shock attenuationand a decreased net running efficiency.14 However, Perlet al. recently investigated differences in running economybetween minimal shoes and standard running shoes andfound a 3% improvement in oxygen transport in minimallyshod runners after controlling for shoe mass and stridefrequency.48 Webb et al. noted that the repetitive deformationof the shoe with each foot strike multiplied many times overduring a run removes elastic energy that could otherwise besaved and transferred if barefoot.72
Plantar proprioception during running activates reflexesand variable kinematic gait patterns to help maintain stability,avoid painful impacts, and modulate leg stiffness to avoidtraumatic and repetitive injuries.43 Robbins et al. inves-tigated proprioception while barefoot under static condi-tions to detect changes in ground slope and found that...