C L I N I C A L F O C U S : D I A B E T E S , O B E S I T Y, W E I G H T M A N A G E M E N T, A N D EXERCISE REGIMEN
Barefoot Versus Shoe Running: From the Past to the Present
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DOI: 10.3810/psm.2014.02.2045
Yonatan Kaplan, PT, MSc Physical Therapy and Sports Medicine Institute, Lerner Sports Center, Hebrew University of Jerusalem, Jerusalem, Israel
Abstract
Introduction: Barefoot running is not a new concept, but relatively few people choose to engage in barefoot running on a regular basis. Despite the technological developments in modern running footwear, as many as 79% of runners are injured every year. Although benefits of barefoot running have been proposed, there are also potential risks associated with it. Objective: To review the evidence-based literature concerning barefoot/minimal footwear running and the implications for the practicing physician. Materials and Methods: Multiple publications were reviewed using an electronic search of databases such as Medline, Cinahl, Embase, PubMed, and Cochrane Database from inception until August 30, 2013 using the search terms barefoot running, barefoot running biomechanics, and shoe vs. barefoot running. Results: Ninety-six relevant articles were found. Most were reviews of biomechanical and kinematic studies. Analysis: There are notable differences in gait and other parameters between barefoot running and shoe running. Based on these findings and much anecdotal evidence, one could conclude 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. Conclusion: Although there is no evidence that 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, as it may minimize the risks of injury. Keywords: barefoot running; shoe running; biomechanics; minimalistic shoes; running
Introduction
Correspondence:Yonatan Kaplan, PT, MSc, Jerusalem Sports Medicine Institute, Lerner Sports Center, Hebrew University of Jerusalem, Churchill St 1, Mount Scopus, 64460, Jerusalem, Israel. Tel: +9722-502-3941 Fax: +9722-581-2102 E-mail: [email protected]
30
The earliest human runners almost certainly did not use footwear. There is no known archaeological or paleontological evidence that has suggested that footwear was used by early members of the genus Homo, who first appeared in the fossil record around 2 million years ago, or by early Homo sapiens, who first appeared around 200 000 years ago.1 It has been argued that as humans evolved to run barefoot, this style of running served to minimize impact peaks and provided increased proprioception and foot strength in order to help avoid injury.2 This barefoot phenomenon is commonly found in biblical figures, legends from the Roman and Greek era, and many works of art. The end of the “barefoot era” is still considered a relatively modern trend, as footwear only became habitual as a means to protect against acute injury, such as stepping on a sharp rock or scorching hot sand. Throughout this time, running had evolved from a necessary form of locomotion to an athletic and recreational pursuit. By the late 1970s, the popularity of running surged, and footwear manufacturers developed running shoes.3 Since the advent of modern running footwear, modifications have been developed to counteract any running injuries that could result from endurance running. Footwear
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Barefoot Versus Shoe Running
companies created cushioned and waffled soles in order to decrease the physical stress caused by repetitive impact, regardless of the lack of scientific evidence demonstrating their effectiveness.3 Modern barefoot running first rose to prominence in 1960, when Abebe Bikila of Ethiopia won the Olympic marathon in Rome barefoot after discovering that Adidas, the Olympic shoe supplier, had run out of shoes in his size. He was in pain because he had received shoes that were too small, so he decided to simply run barefoot; Bikila had trained running barefoot prior to the Olympics.4 He would go on to defend his Olympic title 4 years later in Tokyo while wearing shoes and setting a new world record. Amid this environment and spurred by Christopher McDougall’s5 2009 book, Born to Run: A Hidden Tribe, Superathletes, and the Greatest Race the World Has Never Seen, the “minimalist” movement has infiltrated the endurance running community. In his groundbreaking best seller, McDougall described the unique running style of the Tarahumara Indians; members of this tribe from Mexico’s Copper Canyon routinely run hundreds of miles per week wearing sandals with tire-tread soles. Instead of running with long strides and a pronounced heel strike, these runners used a “barefoot style” characterized by a short stride, light steps, and footwear with minimal protection and maximal flexibility. Despite the technological developments in modern running footwear, as many as 79% of runners today suffer from injuries annually.3,6 The vast majority of these injuries involve the knee, leg, and foot.7 Risk factors for development of running-related injury have been characterized broadly into 4 categories: systemic (age, gender, weight, knee alignment, arch type, flexibility); running or training related (training frequency/alterations/terrain, race distance, running experience, shoe age and type, pace); health (previous injury, medical problems); and lifestyle (alcohol use, smoking, cross-training).7 Based on this injury statistic alone, barefoot running has become an alternative method to prevent certain running injuries. The revived trend of barefoot running has become a popular topic for research and further investigation in the running and medical community. The Barefoot Running Society was founded in 2009 and has quickly caught the attention of many runners; the society already has . 1500 members.8 Testimonials, blogs, and personal anecdotes have been publicized, which gained the attention of runners whose shoes put them at risk for injury. But what is lacking is scientific-based evidence demonstrating that barefoot running is the superior option for athletes. Many concerns remain about whether this
natural running style can compensate for the biomechanical injuries often caused by modern running shoes. The number of researchers investigating barefoot running and the number of publications addressing this topic have increased 3-fold since 2005. Research has demonstrated that increasing mileage increases the risk of injury,9–11 and certain anatomic variables are correlated with specific injuries. Notably, greater foot pronation correlates with shin splints,9,12 greater quadriceps angle correlates with patellofemoral pain,13,14 higher arches correlate with bone-related injuries,15 and lower arches correlate with soft tissue damage.15 In a recent study, it was found that running barefoot decreased peak patellofemoral joint stress by 12% (P = 0.001) compared with shoe running. The reduction in patellofemoral joint stress was a result of reduced patella-femoral joint reaction forces while running barefoot.16 Prospective injury studies have found associations linking both higher and lower than normal arches to all injuries, excessive or reduced hindfoot inversion to more stress fractures, greater knee valgus with all injuries, and higher tubercle sulcus angles with shin splints.11 Unfortunately, many endurance runners are unable or unwilling to decrease their mileage, and the aforementioned previous efforts focusing on correcting anatomic variables via orthotics or shoe modifications have not produced significant reductions in patient injury rates.17–19
Materials and Methods
To review the most up to date evidence-based knowledge concerning barefoot/minimal footwear running and its implications for the practicing physician, an in-depth literature review was conducted. Multiple publications were reviewed using an electronic search of databases such as Medline, Cinahl, Embase, PubMed, and Cochrane Database from their inception to August 30, 2013 using the search terms barefoot running, barefoot running biomechanics, and shoe vs. barefoot running.
Results
The results of the literature review are summarized in the flow diagram (Figure 1). The search led to 88 articles, and an additional 8 articles were identified through other sources, such as communication with content experts in the field of barefoot running. After 2 duplicates were removed, a total of 94 potential articles remained. Ten of the articles were excluded because they did not meet the criteria listed in the methods section. Upon further screening, an additional 54 articles were excluded because they were of poor research
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Yonatan Kaplan
quality. Thirty full-text articles were finally reviewed; most were reviews of biomechanical and kinematic studies.
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Discussion Biomechanical Differences
Understanding the biomechanical differences between barefoot and shoe running is essential. Foot strike patterns yield a continuum of force and kinematic data that illustrate how one runs. With the use of a force plate, the initial contact of the runner gives a measurement of the location of the center of pressure along the long axis of the foot as a percentage of the total foot length.20 This continuum can be further classified into a rear foot strike (RFS), midfoot strike (MFS), and forefoot strike (FFS), which allows the observer to identify where the runner is placing the most weight. The foot strike pattern can also be classified on a continuum, ranging from 0% to 100% (extreme rear foot to extreme forefoot) using the strike index, a measure requiring force plate data.20 Various factors influence the selection of foot strike patterns, such as running speed, training level, substrate mechanical properties, running distance, and running frequency.21,22 For instance, at endurance running speeds, runners tend to use an RFS; at faster speeds they use an MFS and FFS.1 It has been reported that about 75% of all shoe runners use an RFS (Figure 2), 24% use an MFS, and the remaining 1% use an FFS.20 Barefoot runners, on the other hand, have been shown to strike the ground with their forefoot or midfoot first, although it should be noted that not all habitual barefoot runners prefer running with an FFS.2 A Harvard study conducted on foot strike patterns of barefoot runners reported on the differences among the RFS, MFS, and FFS patterns.2 Runners who wear traditional Figure 1. Flow diagram representing the literature review.
r unning shoes tend to use an RFS, meaning that the heel hits the ground first, causing the lower limb to come to a halt during impact, while the body continues to move across the knee. The heel then absorbs about 2 to 3 times the body’s weight upon initial impact. An MFS, on the other hand, keeps the foot in line with the hip and prevents the heel from coming in contact with the ground. With a larger foot surface area that is hitting the ground, a reduction in overall force is seen, and this allows the knees to act more like a shock absorber. An FFS is similar to the MFS; however, the ball of the foot strikes just below the fourth and fifth metatarsal. The study concluded that the body experiences less stoppage at impact and there is more shock absorption distributed among the knees, hips, and back. The FFS pattern that is common in barefoot running is also associated with a reduction in impact loading and stride length, increased sensory feedback from the foot–ground contact, and a shift in lower absorption from the knee to the ankle.6,8,16,21–25 This “minimalistic” running style, which is marked by a soft FFS and shorter, quicker strides, has become increasingly popular in the running community. Biomechanical studies have suggested that these features of barefoot-style running may lead to a reduction in injury rates. A barefoot runner, therefore, is able to disperse impact forces more efficiently and generate smaller collision forces than are individuals wearing standard cushioned shoes. This ability to absorb impact more efficiently can be explained by the adaptations of somatosensory feedback of plantar mechanoreceptors that can “feel the ground,” a function that is likely diminished in shoe runners.3 Opponents of barefoot running maintain that the “minimalist” style may alter the type, but not the incidence, of running injuries. Many runners have fallen into the trap of misinterpreting, misquoting, and misusing research to support their claims that barefoot running reduces injury. Critics have repeatedly stated that there is little evidence linking running injuries to high impact, yet the barefoot running c ommunity Figure 2. Barefoot forefoot (left) and hindfoot (right) shoe landing.31
Reprinted with permission from Lieberman D. Biomechanical Differences Between Different Foot Strikes. http://barefootrunning.fas.harvard. edu/4BiomechanicsofFootStrike.html. #Accessed August 8, 2013.
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Barefoot Versus Shoe Running
claims that the evidence does show this linkage, and considers high impact to be the cause of all injuries. Several articles found both retrospective and prospective correlations among load rates, impact loading, and running injuries,26 and running shoes make a convenient scapegoat. Athletic shoes were found to disperse forces differently during running. Yan et al27 conducted a systematic review comparing impact attenuation of athletic shoes versus barefoot running. They found that athletic shoes worn during running reduced the loading rate but did not affect the vertical force. Non-athletic shoes worn during running reduced tibial acceleration but did not affect loading rate or vertical force. This review concluded that the impact attenuating effect of shoes has potentially both adverse and beneficial effects depending on the variable and activity under investigation. Based on mass alone, one might intuit that running barefoot would exact a lower metabolic cost than running in shoes. Numerous studies have shown that adding mass to shoes increases submaximal oxygen consumption (Vo2) by approximately 1% per 100 g per shoe. Submaximal oxygen consumption increased by approximately 1% for each 100 g added per foot, whether barefoot or shoe (P , 0.001). However, athletes practicing barefoot and shoe running did not significantly differ in their Vo2 or metabolic power. A consequence of these 2 findings was that for footwear conditions of equal mass, shoe running had approximately 3% to 4% lower Vo2 and metabolic power demand than did barefoot running (P , 0.05).28
Minimalistic Shoes
The running shoe has undergone various modifications in attempts to reduce the risk of running injuries. Special features such as cushioning and pronation correction have been added to the modern running shoe, but runners still report frequent injuries.5 In response to this problem, modern shoe manufacturers have tried to replicate the most natural running shoe design—the human foot itself. Minimalist running shoes (Figure 3) have therefore been developed to replicate the lower limb kinematics of barefoot running with the invention of the 5-finger shoe.29 The purpose of this shoe is to allow the runner to adjust according to the more subtle impacts and forces felt with minimal cushioning and support. Various shoe lines such as Vibram FiveFingers, Nike Free, and Saucony Kinvara have been developed to replicate a barefoot running style. This shoe type has been effective in imitating barefoot conditions while providing a small amount of protection. The guidelines for the true “minimalist” running shoe is that it should be lightweight (, 8 oz) and highly flexible, with an expanded toe box, no elevated heel (heel–toe drop , 5 mm),
Figure 3. Example of a minimalistic shoe.
reduced padding, and minimal artificial support (eg, air gel compartments). All of these features allow the runner to “run barefoot” while avoiding acute puncture wounds, severe changes in surface temperature, infection, and other problems encountered in the barefoot state. Fewer injuries were reported at the hip, knee, lower leg, ankle, and foot than with traditional running shoes.20 Researchers have further explored the biomechanics of minimalist shoes. A recent study conducted by Bonacci et al16 sought to determine whether minimalist shoes replicate the mechanics of barefoot running. Interestingly enough, the results showed that barefoot running demonstrated a 24% decrease in negative work done at the knee and a 19% increase in positive work done at the ankle compared with the minimalist shoe. The authors concluded that barefoot running was significantly different from all shoe conditions, including a minimalist and lightweight shoe. In contrast, a separate study was conducted to assess whether the Vibram FiveFingers was effective in minimizing the experience of barefoot running.29 Lower limb kinematics were found to be similar among the barefoot runners and those who ran in Vibram FiveFingers with regard to the foot position.29 Therefore, it is difficult to draw conclusions as to whether the minimalist-type shoe accurately mimics the biomechanics of barefoot running. It has been suggested that with practice, running with minimalist shoes may closely mimic the barefoot form, which may be ideal in terms of a softer impact, MFS or FFS patterns, and shorter, more frequent strides.3 Making such a change in footwear could potentially reduce injury rates; however, not a single study has shown that minimalist shoes are the best option to avoid injury.3
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Disadvantages of Shoe Running
Shoes were found to restrict the natural barefoot motion because they impose a specific foot motion pattern during the push-off phase.30 This is due to the occurrence of more eversion at a faster rate during barefoot locomotion than during shoe locomotion. The sole of the shoe was shown to constrain both the torsional (eversion/inversion) and adduction range of motion of the foot. Therefore, these findings have implications for matching footwear design characteristics to individual natural foot function. The longitudinal arch has been observed to decrease in length by an average of 4.7 mm, suggesting that barefoot runners activate foot musculature that is usually inactive when wearing shoes. These muscles allow the foot to dampen impact and may remove stress from the plantar fascia.3
Disadvantages of Barefoot Running
Running barefoot on extremely hot pavement or in extremely cold weather might damage the soles of one’s feet. Nails, broken glass, pebbles, and other objects can puncture the soles of the feet or lead to stubbed toes (Figure 4). Puncture wounds on the soles and stress fractures in the metatarsals are additional reasons why podiatrists and many critics argue that barefoot running is not better than running in shoes. Although impact reductions in barefoot running may be beneficial in isolation, the increase in power absorption at the distal segments may result in an increased risk of injury at the foot and ankle.23 Such a large increase in ankle power seen in FFS running could be potentially injurious. The American Podiatric Medical Association cautions would-be barefoot runners that there is simply not enough research on the immediate and long-terms benefits of the practice, and advises individuals to consult with a podiatrist about specific running programs. Overall, barefoot running changes the amount of work done at the knee and ankle joints, and this Figure 4. Puncture wound on the sole.
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may have therapeutic and performance implication for runners. As a consequence of the various landing strategies in both barefoot and shoe running (RFS, MFS, and FFS) and the lack of clear evidence of which running method is more beneficial in reducing the incidence and severity of injuries, this topic continues to stimulate research.
Clinical Implications
There is an important advisory role for the clinician or health care provider pertaining to the subjects of shoe versus barefoot versus minimalistic shoe running. Typical questions asked of the family physician and sports physician include which type of running style is better for the joints and which type of running style will minimize the incidence and variation of injuries. Medical personnel should discuss with their patients the previously mentioned 4 categories of risk factors for development of running-related injury. If endurance shoe runners complain of increased symptoms in or around the knee, the physician should consider advising them to change their foot strike to a more mid-forefoot pattern or even to attempt a more minimalistic-type running style. Conversely, barefoot or minimalistic shoe running tends to increase the impact load around the lower leg and ankle area, thus increasing the risk of injuries in this area. In this scenario, the physician should advise the runner to change to a more RFS pattern or even to try different running shoes. Finally, the transition to barefoot running from shoe running should proceed cautiously to prevent injury.
Summary
Despite a series of modifications to the modern running shoe, endurance runners continue to be plagued by overuse injuries. Therefore, barefoot running has become an area of interest for many runners in terms of injury prevention. Biomechanical evidence has suggested that barefoot running promotes a more FFS and MFS strike pattern as opposed to shoe running, which encourages a more RFS pattern. Research has shown that in each type of foot strike pattern, there is a significant difference between the dispersion of collision forces. Although biomechanical evidence exists to support the ability of barefoot runners to disperse impact forces, there is no conclusive research that demonstrates that running barefoot or running in minimalistic shoes leads to a reduction in injuries. Clearly, more outcome-based research is needed. High-quality randomized controlled trials need to be conducted involving multiple large prospective cohorts, to see whether in fact running barefoot or running in minimalistic shoes leads to a statistically significant reduction in
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Barefoot Versus Shoe Running
injuries. Finally, changing runners’ minds may be difficult. Despite clear evidence that shoes do not help reduce shock on the knees, runners wearing shoes win the biggest races (and are handsomely compensated by shoe companies for doing so!) with few exceptions. To runners, scientific evidence may prove ineffective in countering the countless impressions they see on television and on the race course.
Acknowledgments
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The author thanks Mrs Sari Diament and Miss Melia Rosen for their editing assistance in preparing this manuscript.
Conflict of Interest Statement
Yonatan Kaplan, PT, MSc, declares no conflicts of interest or financial disclosures.
References 1. Hatala KG, Dingwall HL, Wunderlich RE, Richmond, BG. Variation in foot strike patterns during running among habitually barefoot populations. PloS One. 2013;8(1):e52548. 2. Lieberman DE, Madhusudhan V, Werbel W, et al. Foot strike patterns and collision forces in habitually barefoot versus shoe runners. Nature. 2010;463(7280):531–535. 3. Rixe JA, Gallo RA, Silvis ML. The barefoot debate: Can minimalist shoes reduce running-related injuries? Curr Sports Med Rep. 2012;11(3):160–165. 4. Redding C. In Africa, sports is the thing. Crisis. 1998;62–63. 5. McDougall C. Born to Run: A Hidden Tribe, Superathletes, and the Greatest Race the World Has Never Seen. New York: Knopf Doubleday; 2009. 6. Altman AR, Davis IS. Barefoot running: biomechanics and implications for running injuries. Curr Sports Med Rep. 2012;11(5):244–250. 7. van Gent RN, Siem D, van Middelkoop M, Van Os AG, BiermaZeinstra SMA, Koes BW. Incidence and determinants of lower extremity running injuries in long distance runners: a systematic review. Br J Sports Med. 2007;41(8):469–480. 8. Collier R. The rise of barefoot running. Can Med Assoc J. 2011;183(1): E37–E38. 9. Harrast MA, Colonno D. Stress fractures in runners. Clin Sports Med. 2010;29(3):399–416. 10. Macera CA, Pate RR, Powell KE, Jackson KL, Kendrick JS, Craven TE. Predicting lower-extremity injuries among habitual runners. Arch Intern Med. 1989;149(11):2565. 11. Wen DY. Risk factors for overuse injuries in runners. Curr Sports Med Rep. 2007;6(5):307–313. 12. Moen MH, Tol JL, Weir A, Steunebrink M, De Winter TC. Medial tibial stress syndrome: a critical review. Sports Med. 2009;39(7):523–546.
13. Cowan DN, Jones BH, Frykman PN, et al. Lower limb morphology and risk of overuse injury among male infantry trainees. Med Sci Sports Exerc. 1996;28(8):945–952. 14. Lin F, Wilson NA, Makhsous M, et al. In vivo patellar tracking induced by individual quadriceps components in individuals with Patellofemoral pain. J Biomech. 2010;43(2):235–241. 15. Williams DS III, McClay IS, Hamill J. Arch structure and injury patterns in runners. Clin Biomech. 2001;16(4):341–347. 16. Bonacci J, Saunders PU, Hicks A, Rantalainen T, Vicenzino BGT, Spratford W. Running in a minimalist and lightweight shoe is not the same as running barefoot: a biomechanical study. Br J Sports Med. 2013;47(6):387–392. 17. Knapik JJ, Brosch LC, Venuto M, et al. Effect on injuries of assigning shoes based on foot shape in air force basic training. Am J Prev Med. 2010;38(1):S197–S211. 18. Knapik JJ, Trone D, Swedler D, et al. Injury reduction effectiveness of assigning running shoes based on plantar shape in Marine Corps basic training. Am J Sports Med. 2010;38(9):1759–1767. 19. Richards CE, Magin PJ, Callister R. Is your prescription of distance running shoes evidence based? Br J Sports Med. 2009;43(3):159–162. 20. Altman AR, Davis IS. A kinematic method for foot strike pattern detection in barefoot and shod runners. Gait Posture. 2012;35(2):298–300. 21. Perl DP, Daoud AI, Lieberman DE. Effects of footwear and strike type on running economy. Med Sci Sports Exerc. 2012;44(7):1335–1343. 22. Goss DL, Gross MT. Relationships among self-reported shoe type, foot strike pattern and injury incidence. US Army Med Dep. Oct–Dec 2012;25–30. 23. Williams Blaise III DB, Green DH, Wurzinger B. Changes in lower extremity movement and power absorption during forefoot striking and barefoot running. Int J Sports Phys Ther. 2012;7(5):525. 24. Divert C, Mornieux G, Freychat P, Baly L, Mayer F, Belli A. Barefootshod running differences: Shoe or mass effect? Int J Sports Med. 2008;29(6):512–518. 25. De Wit B, De Clercq D, Aerts P. Biomechanical analysis of the stance phase during barefoot and shod running. J Biomech. 2000;33(3):269–278. 26. Zadpoor AA, Nikooyan AA. The relationship between lower-extremity stress fractures and the ground reaction force: a systematic review [published online ahead of print September 16, 2010]. Clin Biomech (Bristol, Avon). 2011;26(1):23–28. doi:10.1016/j.clinbiomech.2010.08.005. 27. Yan FA, Sinclair PJ, Hiller C, Wegener C, Smith RM. Impact attenuation during weight bearing activities in barefoot vs. shod conditions: a systematic review. Gait Posture. 2013;38(2):75–186. 28. Franz JR, Wierzbinski CM, Kram R. Metabolic cost of running barefoot versus shod: Is lighter better? Med Sci Sports Exerc. 2012:44(8):1519–1525. 29. Squadrone R, Gallozzi C. Biomechanical and physiological comparison of barefoot and two shod conditions in experienced barefoot runners. J Sports Med Phys Fitness. 2009;49(1):6–13. 30. Morio C, Lake MJ, Gueguen N, Rao G, Baly L. The influence of footwear on footmotion during walking and running. J Biomech. 2009;42(13):2081–2088. 31. Lieberman D. Biomechanical Differences Between Different Foot Strikes. http://barefootrunning.fas.harvard.edu/4BiomechanicsofFootStrike. html. Accessed August 8, 2013.
© The Physician and Sportsmedicine, Volume 42, Issue 1, February 2014, ISSN – 0091-3847 35 ResearchSHARE®: www.research-share.com • Permissions: [email protected] • Reprints: [email protected] Warning: No duplication rights exist for this journal. Only JTE Multimedia, LLC holds rights to this publication. Please contact the publisher directly with any queries.
Barefoot Versus Shoe Running: From the Past to the Present
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DOI: 10.3810/psm.2014.02.2045
Yonatan Kaplan, PT, MSc Physical Therapy and Sports Medicine Institute, Lerner Sports Center, Hebrew University of Jerusalem, Jerusalem, Israel
Abstract
Introduction: Barefoot running is not a new concept, but relatively few people choose to engage in barefoot running on a regular basis. Despite the technological developments in modern running footwear, as many as 79% of runners are injured every year. Although benefits of barefoot running have been proposed, there are also potential risks associated with it. Objective: To review the evidence-based literature concerning barefoot/minimal footwear running and the implications for the practicing physician. Materials and Methods: Multiple publications were reviewed using an electronic search of databases such as Medline, Cinahl, Embase, PubMed, and Cochrane Database from inception until August 30, 2013 using the search terms barefoot running, barefoot running biomechanics, and shoe vs. barefoot running. Results: Ninety-six relevant articles were found. Most were reviews of biomechanical and kinematic studies. Analysis: There are notable differences in gait and other parameters between barefoot running and shoe running. Based on these findings and much anecdotal evidence, one could conclude 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. Conclusion: Although there is no evidence that 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, as it may minimize the risks of injury. Keywords: barefoot running; shoe running; biomechanics; minimalistic shoes; running
Introduction
Correspondence:Yonatan Kaplan, PT, MSc, Jerusalem Sports Medicine Institute, Lerner Sports Center, Hebrew University of Jerusalem, Churchill St 1, Mount Scopus, 64460, Jerusalem, Israel. Tel: +9722-502-3941 Fax: +9722-581-2102 E-mail: [email protected]
30
The earliest human runners almost certainly did not use footwear. There is no known archaeological or paleontological evidence that has suggested that footwear was used by early members of the genus Homo, who first appeared in the fossil record around 2 million years ago, or by early Homo sapiens, who first appeared around 200 000 years ago.1 It has been argued that as humans evolved to run barefoot, this style of running served to minimize impact peaks and provided increased proprioception and foot strength in order to help avoid injury.2 This barefoot phenomenon is commonly found in biblical figures, legends from the Roman and Greek era, and many works of art. The end of the “barefoot era” is still considered a relatively modern trend, as footwear only became habitual as a means to protect against acute injury, such as stepping on a sharp rock or scorching hot sand. Throughout this time, running had evolved from a necessary form of locomotion to an athletic and recreational pursuit. By the late 1970s, the popularity of running surged, and footwear manufacturers developed running shoes.3 Since the advent of modern running footwear, modifications have been developed to counteract any running injuries that could result from endurance running. Footwear
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Barefoot Versus Shoe Running
companies created cushioned and waffled soles in order to decrease the physical stress caused by repetitive impact, regardless of the lack of scientific evidence demonstrating their effectiveness.3 Modern barefoot running first rose to prominence in 1960, when Abebe Bikila of Ethiopia won the Olympic marathon in Rome barefoot after discovering that Adidas, the Olympic shoe supplier, had run out of shoes in his size. He was in pain because he had received shoes that were too small, so he decided to simply run barefoot; Bikila had trained running barefoot prior to the Olympics.4 He would go on to defend his Olympic title 4 years later in Tokyo while wearing shoes and setting a new world record. Amid this environment and spurred by Christopher McDougall’s5 2009 book, Born to Run: A Hidden Tribe, Superathletes, and the Greatest Race the World Has Never Seen, the “minimalist” movement has infiltrated the endurance running community. In his groundbreaking best seller, McDougall described the unique running style of the Tarahumara Indians; members of this tribe from Mexico’s Copper Canyon routinely run hundreds of miles per week wearing sandals with tire-tread soles. Instead of running with long strides and a pronounced heel strike, these runners used a “barefoot style” characterized by a short stride, light steps, and footwear with minimal protection and maximal flexibility. Despite the technological developments in modern running footwear, as many as 79% of runners today suffer from injuries annually.3,6 The vast majority of these injuries involve the knee, leg, and foot.7 Risk factors for development of running-related injury have been characterized broadly into 4 categories: systemic (age, gender, weight, knee alignment, arch type, flexibility); running or training related (training frequency/alterations/terrain, race distance, running experience, shoe age and type, pace); health (previous injury, medical problems); and lifestyle (alcohol use, smoking, cross-training).7 Based on this injury statistic alone, barefoot running has become an alternative method to prevent certain running injuries. The revived trend of barefoot running has become a popular topic for research and further investigation in the running and medical community. The Barefoot Running Society was founded in 2009 and has quickly caught the attention of many runners; the society already has . 1500 members.8 Testimonials, blogs, and personal anecdotes have been publicized, which gained the attention of runners whose shoes put them at risk for injury. But what is lacking is scientific-based evidence demonstrating that barefoot running is the superior option for athletes. Many concerns remain about whether this
natural running style can compensate for the biomechanical injuries often caused by modern running shoes. The number of researchers investigating barefoot running and the number of publications addressing this topic have increased 3-fold since 2005. Research has demonstrated that increasing mileage increases the risk of injury,9–11 and certain anatomic variables are correlated with specific injuries. Notably, greater foot pronation correlates with shin splints,9,12 greater quadriceps angle correlates with patellofemoral pain,13,14 higher arches correlate with bone-related injuries,15 and lower arches correlate with soft tissue damage.15 In a recent study, it was found that running barefoot decreased peak patellofemoral joint stress by 12% (P = 0.001) compared with shoe running. The reduction in patellofemoral joint stress was a result of reduced patella-femoral joint reaction forces while running barefoot.16 Prospective injury studies have found associations linking both higher and lower than normal arches to all injuries, excessive or reduced hindfoot inversion to more stress fractures, greater knee valgus with all injuries, and higher tubercle sulcus angles with shin splints.11 Unfortunately, many endurance runners are unable or unwilling to decrease their mileage, and the aforementioned previous efforts focusing on correcting anatomic variables via orthotics or shoe modifications have not produced significant reductions in patient injury rates.17–19
Materials and Methods
To review the most up to date evidence-based knowledge concerning barefoot/minimal footwear running and its implications for the practicing physician, an in-depth literature review was conducted. Multiple publications were reviewed using an electronic search of databases such as Medline, Cinahl, Embase, PubMed, and Cochrane Database from their inception to August 30, 2013 using the search terms barefoot running, barefoot running biomechanics, and shoe vs. barefoot running.
Results
The results of the literature review are summarized in the flow diagram (Figure 1). The search led to 88 articles, and an additional 8 articles were identified through other sources, such as communication with content experts in the field of barefoot running. After 2 duplicates were removed, a total of 94 potential articles remained. Ten of the articles were excluded because they did not meet the criteria listed in the methods section. Upon further screening, an additional 54 articles were excluded because they were of poor research
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Yonatan Kaplan
quality. Thirty full-text articles were finally reviewed; most were reviews of biomechanical and kinematic studies.
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Discussion Biomechanical Differences
Understanding the biomechanical differences between barefoot and shoe running is essential. Foot strike patterns yield a continuum of force and kinematic data that illustrate how one runs. With the use of a force plate, the initial contact of the runner gives a measurement of the location of the center of pressure along the long axis of the foot as a percentage of the total foot length.20 This continuum can be further classified into a rear foot strike (RFS), midfoot strike (MFS), and forefoot strike (FFS), which allows the observer to identify where the runner is placing the most weight. The foot strike pattern can also be classified on a continuum, ranging from 0% to 100% (extreme rear foot to extreme forefoot) using the strike index, a measure requiring force plate data.20 Various factors influence the selection of foot strike patterns, such as running speed, training level, substrate mechanical properties, running distance, and running frequency.21,22 For instance, at endurance running speeds, runners tend to use an RFS; at faster speeds they use an MFS and FFS.1 It has been reported that about 75% of all shoe runners use an RFS (Figure 2), 24% use an MFS, and the remaining 1% use an FFS.20 Barefoot runners, on the other hand, have been shown to strike the ground with their forefoot or midfoot first, although it should be noted that not all habitual barefoot runners prefer running with an FFS.2 A Harvard study conducted on foot strike patterns of barefoot runners reported on the differences among the RFS, MFS, and FFS patterns.2 Runners who wear traditional Figure 1. Flow diagram representing the literature review.
r unning shoes tend to use an RFS, meaning that the heel hits the ground first, causing the lower limb to come to a halt during impact, while the body continues to move across the knee. The heel then absorbs about 2 to 3 times the body’s weight upon initial impact. An MFS, on the other hand, keeps the foot in line with the hip and prevents the heel from coming in contact with the ground. With a larger foot surface area that is hitting the ground, a reduction in overall force is seen, and this allows the knees to act more like a shock absorber. An FFS is similar to the MFS; however, the ball of the foot strikes just below the fourth and fifth metatarsal. The study concluded that the body experiences less stoppage at impact and there is more shock absorption distributed among the knees, hips, and back. The FFS pattern that is common in barefoot running is also associated with a reduction in impact loading and stride length, increased sensory feedback from the foot–ground contact, and a shift in lower absorption from the knee to the ankle.6,8,16,21–25 This “minimalistic” running style, which is marked by a soft FFS and shorter, quicker strides, has become increasingly popular in the running community. Biomechanical studies have suggested that these features of barefoot-style running may lead to a reduction in injury rates. A barefoot runner, therefore, is able to disperse impact forces more efficiently and generate smaller collision forces than are individuals wearing standard cushioned shoes. This ability to absorb impact more efficiently can be explained by the adaptations of somatosensory feedback of plantar mechanoreceptors that can “feel the ground,” a function that is likely diminished in shoe runners.3 Opponents of barefoot running maintain that the “minimalist” style may alter the type, but not the incidence, of running injuries. Many runners have fallen into the trap of misinterpreting, misquoting, and misusing research to support their claims that barefoot running reduces injury. Critics have repeatedly stated that there is little evidence linking running injuries to high impact, yet the barefoot running c ommunity Figure 2. Barefoot forefoot (left) and hindfoot (right) shoe landing.31
Reprinted with permission from Lieberman D. Biomechanical Differences Between Different Foot Strikes. http://barefootrunning.fas.harvard. edu/4BiomechanicsofFootStrike.html. #Accessed August 8, 2013.
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Barefoot Versus Shoe Running
claims that the evidence does show this linkage, and considers high impact to be the cause of all injuries. Several articles found both retrospective and prospective correlations among load rates, impact loading, and running injuries,26 and running shoes make a convenient scapegoat. Athletic shoes were found to disperse forces differently during running. Yan et al27 conducted a systematic review comparing impact attenuation of athletic shoes versus barefoot running. They found that athletic shoes worn during running reduced the loading rate but did not affect the vertical force. Non-athletic shoes worn during running reduced tibial acceleration but did not affect loading rate or vertical force. This review concluded that the impact attenuating effect of shoes has potentially both adverse and beneficial effects depending on the variable and activity under investigation. Based on mass alone, one might intuit that running barefoot would exact a lower metabolic cost than running in shoes. Numerous studies have shown that adding mass to shoes increases submaximal oxygen consumption (Vo2) by approximately 1% per 100 g per shoe. Submaximal oxygen consumption increased by approximately 1% for each 100 g added per foot, whether barefoot or shoe (P , 0.001). However, athletes practicing barefoot and shoe running did not significantly differ in their Vo2 or metabolic power. A consequence of these 2 findings was that for footwear conditions of equal mass, shoe running had approximately 3% to 4% lower Vo2 and metabolic power demand than did barefoot running (P , 0.05).28
Minimalistic Shoes
The running shoe has undergone various modifications in attempts to reduce the risk of running injuries. Special features such as cushioning and pronation correction have been added to the modern running shoe, but runners still report frequent injuries.5 In response to this problem, modern shoe manufacturers have tried to replicate the most natural running shoe design—the human foot itself. Minimalist running shoes (Figure 3) have therefore been developed to replicate the lower limb kinematics of barefoot running with the invention of the 5-finger shoe.29 The purpose of this shoe is to allow the runner to adjust according to the more subtle impacts and forces felt with minimal cushioning and support. Various shoe lines such as Vibram FiveFingers, Nike Free, and Saucony Kinvara have been developed to replicate a barefoot running style. This shoe type has been effective in imitating barefoot conditions while providing a small amount of protection. The guidelines for the true “minimalist” running shoe is that it should be lightweight (, 8 oz) and highly flexible, with an expanded toe box, no elevated heel (heel–toe drop , 5 mm),
Figure 3. Example of a minimalistic shoe.
reduced padding, and minimal artificial support (eg, air gel compartments). All of these features allow the runner to “run barefoot” while avoiding acute puncture wounds, severe changes in surface temperature, infection, and other problems encountered in the barefoot state. Fewer injuries were reported at the hip, knee, lower leg, ankle, and foot than with traditional running shoes.20 Researchers have further explored the biomechanics of minimalist shoes. A recent study conducted by Bonacci et al16 sought to determine whether minimalist shoes replicate the mechanics of barefoot running. Interestingly enough, the results showed that barefoot running demonstrated a 24% decrease in negative work done at the knee and a 19% increase in positive work done at the ankle compared with the minimalist shoe. The authors concluded that barefoot running was significantly different from all shoe conditions, including a minimalist and lightweight shoe. In contrast, a separate study was conducted to assess whether the Vibram FiveFingers was effective in minimizing the experience of barefoot running.29 Lower limb kinematics were found to be similar among the barefoot runners and those who ran in Vibram FiveFingers with regard to the foot position.29 Therefore, it is difficult to draw conclusions as to whether the minimalist-type shoe accurately mimics the biomechanics of barefoot running. It has been suggested that with practice, running with minimalist shoes may closely mimic the barefoot form, which may be ideal in terms of a softer impact, MFS or FFS patterns, and shorter, more frequent strides.3 Making such a change in footwear could potentially reduce injury rates; however, not a single study has shown that minimalist shoes are the best option to avoid injury.3
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Disadvantages of Shoe Running
Shoes were found to restrict the natural barefoot motion because they impose a specific foot motion pattern during the push-off phase.30 This is due to the occurrence of more eversion at a faster rate during barefoot locomotion than during shoe locomotion. The sole of the shoe was shown to constrain both the torsional (eversion/inversion) and adduction range of motion of the foot. Therefore, these findings have implications for matching footwear design characteristics to individual natural foot function. The longitudinal arch has been observed to decrease in length by an average of 4.7 mm, suggesting that barefoot runners activate foot musculature that is usually inactive when wearing shoes. These muscles allow the foot to dampen impact and may remove stress from the plantar fascia.3
Disadvantages of Barefoot Running
Running barefoot on extremely hot pavement or in extremely cold weather might damage the soles of one’s feet. Nails, broken glass, pebbles, and other objects can puncture the soles of the feet or lead to stubbed toes (Figure 4). Puncture wounds on the soles and stress fractures in the metatarsals are additional reasons why podiatrists and many critics argue that barefoot running is not better than running in shoes. Although impact reductions in barefoot running may be beneficial in isolation, the increase in power absorption at the distal segments may result in an increased risk of injury at the foot and ankle.23 Such a large increase in ankle power seen in FFS running could be potentially injurious. The American Podiatric Medical Association cautions would-be barefoot runners that there is simply not enough research on the immediate and long-terms benefits of the practice, and advises individuals to consult with a podiatrist about specific running programs. Overall, barefoot running changes the amount of work done at the knee and ankle joints, and this Figure 4. Puncture wound on the sole.
34
may have therapeutic and performance implication for runners. As a consequence of the various landing strategies in both barefoot and shoe running (RFS, MFS, and FFS) and the lack of clear evidence of which running method is more beneficial in reducing the incidence and severity of injuries, this topic continues to stimulate research.
Clinical Implications
There is an important advisory role for the clinician or health care provider pertaining to the subjects of shoe versus barefoot versus minimalistic shoe running. Typical questions asked of the family physician and sports physician include which type of running style is better for the joints and which type of running style will minimize the incidence and variation of injuries. Medical personnel should discuss with their patients the previously mentioned 4 categories of risk factors for development of running-related injury. If endurance shoe runners complain of increased symptoms in or around the knee, the physician should consider advising them to change their foot strike to a more mid-forefoot pattern or even to attempt a more minimalistic-type running style. Conversely, barefoot or minimalistic shoe running tends to increase the impact load around the lower leg and ankle area, thus increasing the risk of injuries in this area. In this scenario, the physician should advise the runner to change to a more RFS pattern or even to try different running shoes. Finally, the transition to barefoot running from shoe running should proceed cautiously to prevent injury.
Summary
Despite a series of modifications to the modern running shoe, endurance runners continue to be plagued by overuse injuries. Therefore, barefoot running has become an area of interest for many runners in terms of injury prevention. Biomechanical evidence has suggested that barefoot running promotes a more FFS and MFS strike pattern as opposed to shoe running, which encourages a more RFS pattern. Research has shown that in each type of foot strike pattern, there is a significant difference between the dispersion of collision forces. Although biomechanical evidence exists to support the ability of barefoot runners to disperse impact forces, there is no conclusive research that demonstrates that running barefoot or running in minimalistic shoes leads to a reduction in injuries. Clearly, more outcome-based research is needed. High-quality randomized controlled trials need to be conducted involving multiple large prospective cohorts, to see whether in fact running barefoot or running in minimalistic shoes leads to a statistically significant reduction in
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Barefoot Versus Shoe Running
injuries. Finally, changing runners’ minds may be difficult. Despite clear evidence that shoes do not help reduce shock on the knees, runners wearing shoes win the biggest races (and are handsomely compensated by shoe companies for doing so!) with few exceptions. To runners, scientific evidence may prove ineffective in countering the countless impressions they see on television and on the race course.
Acknowledgments
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The author thanks Mrs Sari Diament and Miss Melia Rosen for their editing assistance in preparing this manuscript.
Conflict of Interest Statement
Yonatan Kaplan, PT, MSc, declares no conflicts of interest or financial disclosures.
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