Proceed with Caution When Barefoot Running

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Studies suggest that runners with lower impact-loading have reduced injury risk.
Studies suggest that runners with lower impact-loading have reduced injury risk.

With the increasing popularity of minimalist footwear and barefoot running, it is imperative that clinicians understand running mechanics and the potential implications of these footwear options. 


Approximately 19 million Americans run at least 100 days per year.1 Although running is excellent cardiovascular exercise, a published systematic review reported that the incidence of lower-extremity injuries among runners ranged from 19% to 79%.2

In recent years, there has been a trend of runners switching from traditional running shoes to barefoot running or to minimalist shoes. This switch is likely driven by the possibility of increased performance3-5 and more important, the possibility of reducing injury.6-8 Up to 22% of runners have tried running barefoot, and 30% have reported using minimalist shoes.9

Understanding foot-strike patterns


Rather than being a function of what is worn (or not worn) on the foot, the potential benefits of adopting a barefoot or alternative running style (e.g. Chi running, pose running, minimalist footwear)10 may have more to do with what part of the foot impacts the ground first. Running is often seen as a rapid series of footfalls generating high forces and impacts several hundred times per mile. Impact-loading includes the vertical impact peak (indicated in Figure 1).

Within this curve, claims of decreased injury have focused on a reduction of impact-loading, which consists of decreasing the loads and rate of loading shortly after foot strike. Impact-loading includes the vertical impact peak—which occurs shortly after foot strike before the center of mass is over the foot—and the rate of loading from foot strike to that peak. Research suggests that runners with lower impact-loading have reduced injury risk.6,7,11,12

The way the foot strikes the ground can be categorized into three distinct foot-strike patterns: 

  1. A rearfoot strike (RFS) pattern is a foot strike in which the heel, or rear third of the sole, is the first part of the foot to come in contact with the ground
  2. A midfoot strike (MFS) pattern is a foot strike in which the middle third of the sole makes contact with the ground first
  3. A forefoot strike (FFS) pattern is a foot strike in which the third of the sole makes contact with the ground first.13

Different foot-strike patterns affect the profile of the force curve generated when the foot hits the ground, and this in turn affects the transmission of energy through the musculoskeletal system.

As observed in Figure 1, the typical RFS is characterized by a pronounced vertical impact peak of the vertical ground reaction force, whereas the MFS and FFS patterns do not have a pronounced vertical impact peak. 


The vertical impact peak, which occurs within the first 50 milliseconds of stance, results from the abrupt collision of the heel with the running surface. This collision causes part of the body's mass to decelerate rapidly (i.e., the leg), while the rest of the body decelerates more gradually. Therefore, runners who land heel-first during a running stride (RFS) generate higher peak impact forces that are transmitted more rapidly throughout the musculoskeletal system compared with FFS runners.8,14,15

Because of this reduced impact-loading in MFS/FFS runners, it is hypothesized that runners who adopt a MFS or FFS pattern associated with an alternative running style will ultimately decrease impact loading.14,15

There are minimal data to describe the distributions of foot-strike patterns among recreational runners, as all of the data are from half-marathon or full-marathon races. Among marathoners, 75% to 89% ran with an RFS pattern, 3% to 24% ran with an MFS pattern, and only 1% to 2% ran with an FFS pattern.16,17

Certainly, a potential bias exists in the distribution numbers based on the study participants' ability to train for and compete in a half-marathon or full marathon: Despite the increasing popularity of recreational road racing, only 2.2 million runners (including those running multiple races and international runners) completed half-marathons and/or full marathons in the United States during 2011.18,19 Since only a small percentage of American runners (<12%) run half- or full marathons, these reported distributions may not translate to all recreational runners. 


Injury implications of foot-strike patterns


RFS with higher impact-loading appears to carry a higher risk of injury compared with RFS with lower impacts. Researchers have reported that RFS runners with retrospective tibial stress fractures had higher impact loads than did uninjured RFS runners.11 Additionally, a two-year prospective study found that RFS runners who sustained an injury of any type had higher impact-loading than did uninjured RFS runners.12

These studies suggest that even within RFS (and without changing foot-strike pattern), decreased impact-loading may reduce injury risk. As impact-loading is reduced in MFS and FFS runners, it has been theorized that running injuries can be mediated by changing one's foot-strike pattern from RFS to MFS or FFS. To date, this conclusion has not been strongly supported by a large prospective study. 


In contrast to RFS runners, experienced barefoot runners maintain an FFS pattern with a plantar-flexed ankle.15 Landing on the forefoot with a plantar-flexed ankle results in attenuation of peak impact forces when compared with running shod and utilizing an RFS pattern.15 A 2010 study found reduced impact-loading in barefoot runners compared with shod runners.14

Again, this reduction in peak impact force is not necessarily a function of running without shoes; it is more likely associated with which portion of the foot strikes the ground first. Although the authors of the 2010 study suggested that reduction in forces associated with an FFS pattern may reduce injury in runners, they acknowledged that there had only been anecdotal reports of injury reduction in barefoot runners.14

Only recently, a small retrospective analysis of 52 collegiate cross-country runners indicated that runners who utilized an RFS pattern experienced twice as many stress injuries as did those who utilized an FFS pattern.8

Altering foot-strike patterns 


There is currently no justification for changing the foot-strike pattern in an asymptomatic runner. However, emerging evidence shows that changes to foot-strike patterns may be a useful tool for mitigating the effects of injuries related to running.

In a case series of 10 individuals who suffered from chronic exertional compartment syndrome, all were able to change their running style from an RFS to an FFS pattern over a six-week period of supervised instruction.6 The changed running style resulted in decreased intracompartmental pressures as measured by an orthopedic surgeon using an intracompartmental pressure monitor. The subjects continued to run and train with a reduction in pain one year after the intervention began.6

In another case series, three runners underwent eight supervised sessions of gait-retraining over a two-week period to adopt a non-RFS pattern, which reduced their patellofemoral pain. The new patterns were maintained for at least three months with a reduction in pain.7

Researchers have utilized real-time audio and/or visual feedback to decrease impact-loading in runners.20 Some individuals changed from an RFS pattern to an FFS pattern, and others decreased loads while maintaining an RFS pattern. Before recommending altering foot-strike patterns to mitigate injury, more research in larger cohorts of runners is necessary. 


Other than the previously discussed studies, there is a paucity of literature supporting injury reduction in barefoot or alternative running styles. Other reports associating resolution of injury with alterations in foot-strike pattern have been anecdotal. Review articles have described the need for larger prospective studies to support more definitively the hypothesis that non-RFS runners are experiencing fewer injuries.21

No known large-scale studies systematically support either hypothesis. Larger-scale prospective studies are ultimately needed to determine the strength of relationship between foot-strike patterns and injury. Challengingly, these studies will need to control for running mileage, injury history, and other factors that may confound the results.


Minimalist footwear and barefoot running


Prior to the 1970s, endurance runners wore narrow, thin-soled shoes that would now be considered track flats. Since then, traditional running shoes have evolved to include a wide and thickly cushioned sole likely to reduce pain of repeated heel strikes in RFS. 

Barefoot running and minimalist shoes offer less heel-cushioning. It is postulated that when an RFS runner changes from a traditional shoe to a minimalist shoe (or no shoe), landing on the heel will ultimately be too painful to maintain due to the lack of cushioning.

One theory holds that in order to avoid heel pain and keep running, runners will naturally transition to MFS or FFS. A positive side effect of this pain and alteration of foot-strike pattern is the reduction in impact-loading with an MFS or FFS running style.

Researchers have reported that lower-extremity kinematics while wearing minimalist shoes, such as Vibram FiveFingers, were similar to running barefoot in terms of peak impact forces, with a tendency to land on the forefoot with the ankle in plantarflexion.15 However, a non-peer-reviewed study examining runners who had recently transitioned to minimalist shoes found that some runners maintained RFS patterns.22

Additionally, clinicians and researchers anecdotally report that this presumed alteration in foot-strike pattern does not always occur with a change in footwear. Therefore, transitioning to minimalist footwear or barefoot running may increase injury risk if runners increase their loads by maintaining an RFS pattern despite the reduced or eliminated heel-cushioning.


Transitioning from traditional footwear


Regardless of the science that supports or refutes the potential benefits, some patients will insist on running barefoot or with minimalist footwear. The clinician should inquire about the intentions and goals of such a patient to help him or her make a sound decision and avoid injury. When transitioning from a traditional running shoe, patients should be advised to proceed gradually and to stop running if they experience pain (Table 1).

Table 1. Tips for transitioning from traditional running shoes

Be patient. Plan to make the transition over at least six to eight weeks.
Focus on landing softly on the forefoot, not on the heel.
Try running in place to get the feel for forefoot landings.
Run no more than 10% of your typical distance for the first two to three weeks.
Gradually increase mileage by 10% to 20% every couple of weeks.
Avoid running two days in a row for the first four weeks.
Strengthen the leg and foot muscles.
Stretch the calf, foot, and hamstrings after running.
Consistent soreness after several weeks indicates a need to rest and reduce mileage.
Stop running if you experience pain.
Source: Carabajal S. "Patience key when transitioning to minimalist running shoes." Army Medicine. Available at: http://www.army.mil/article/65166, accessed Jan. 8, 2014.

The feet and lower extremities need time to adapt to the changes in loading patterns.23 Runners are advised to start by walking in the alternate shoe type and then cautiously add short periods of running.

Some shoe companies have developed protocols for a safe transition from traditional footwear to the minimalist- or barefoot-style shoe.24,25 The common theme among the different protocols is a gradual progression in wear time for the newer type of shoe. Some protocols recommend that the transition occur over a six-to-eight-week period.24,26 However, these protocols have not been scientifically studied to examine injury risk during the transition.

Patients should be warned that it may take longer for some to transition away from traditional footwear. Patients should also be alerted to the potential hazards of running barefoot in extremely hot and cold environments or on exceptionally rigorous surfaces that may increase risk of injury. 


Even when the implications of such a transition are well understood, modifying one's foot-strike pattern or making substantial changes in footwear is not without risk. There have been case reports of metatarsal stress fractures in experienced runners attempting to transition to barefoot-simulating footwear.27 However, stress fractures are a common injury in runners with traditional footwear, so it is difficult to determine if the new shoe caused the injury.

Patients transitioning to barefoot running or minimalist shoes may experience foot and calf pain, muscle strains, blisters, cuts and abrasions or plantar fasciitis.28 Even after a 10-week transition, runners using minimalist shoes had a significantly higher occurrence of bone-marrow edema identified by MRI when compared with a control group using a traditional running shoe.29

Conclusion


Some recreational runners have begun switching from traditional running shoes for a multitude of reasons, including injury prevention, rehabilitation, improved performance, and even to alter their foot-strike pattern. Because clinical research is limited, it is difficult to predict how or if minimalist shoes or alterations in biomechanics may influence the musculoskeletal health of these runners.

Limited studies show that FFS and MFS reduce peak impact forces that are transmitted through the skeletal system and may have different and possibly reduced injury profiles. Recent research indicates that runners with lower impact-loading have lower injury rates. However, no long-term research exists regarding altering foot-strike pattern (or footwear) and injury rates.

More research is needed before clinicians can routinely recommend that injured runners transition to an alternate foot-strike pattern or to minimalist or barefoot running. Individuals who insist on using minimalist footwear or on transitioning to barefoot running should be advised to make a gradual transition and to cease running in the event of pain. 


Bradley J. Warr, PhD, Rebecca E. Fellin, PhD, and Joseph F. Seay, PhD, are clinical researchers with the U.S. Army Research Institute of Environmental Medicine, Military Performance Division, in Natick, Mass. The opinions or assertions expressed in this article are the private views of the authors and are not the official views of the U.S. Army or the Department of Defense.

The authors would like to acknowledge Dr. Allison Altman for her contribution of data used in Figure 1. Research was supported in part by an appointment (Dr. Fellin) to the Postgraduate Research Participation Program funded by the U.S. Army Research Institute of Environmental Medicine and administered by the Oak Ridge Institute for Science and Engineering.

References


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  7. Cheung RT, Davis IS. Landing pattern modification to improve patellofemoral pain in runners: a case series. J Orthop Sports Phys Ther. 2011;41:914-919.

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  12. Davis I, Bowser B, Mullineaux DR. Do impacts cause running injuries? A prospective investigation. Presented at the American Society of Biomechanics 34th Annual Meeting; Providence, R.I.; August 2010. Available at www.asbweb.org/conferences/2010/abstracts/472.pdf. 

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  14. Lieberman DE, Venkadesan M, Werbel WA, et al. Foot strike patterns and collision forces in habitually barefoot versus shod runners. Nature. 2010;463:531-535.

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  16. Hasegawa H, Yamauchi T, Kraemer WJ. Foot strike patterns of runners at the 15-km point during an elite-level half marathon. J Strength Cond Res. 2007;21:888-893.

  17. Larson P, Higgins E, Kaminski J, et al. Foot strike patterns of recreational and sub-elite runners in a long-distance road race. J Sports Sci. 2011;29:1665-1673.

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  19. Running USA. Annual half-marathon report 2012. Available at 
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  20. Crowell HP, Davis IS. Gait retraining to reduce lower extremity loading in runners. Clin Biomech (Bristol, Avon). 2011;26:78-83. 

  21. Jenkins DW, Cauthon DJ. Barefoot running claims and controversies: a review of the literature. J Am Podiatr Med Assoc. 2011;101:231-246.

  22. The American Council on Exercise. Like barefoot, only better? Available at www.acefitness.org/certifiednewsarticle/1641/.

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  26. Army Medicine. Minimalist running shoes. Available at 
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  29. Ridge ST, Johnson AW, Mitchell UH, et al. Foot bone marrow edema after a 10-wk transition to minimalist running shoes. Med Sci Sports Exerc. 2013;45:1363-1368.



All electronic documents accessed October 15, 2013.


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