June 2017

Minimalist shoes: Risks and benefits for runners

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Although there may be benefits to a change in running footwear, there are also risks associated with a switch to minimalist running shoes. Alterations in anatomy, physiology, and biomechanics associated with transitioning to minimalist footwear are likely to be unique to each runner. 

By J. Todd Walker, MD; Donna Moxley Scarborough, PT, MS; Eric M. Berkson, MD; and Matthew J. Salzler, MD

Despite footwear companies engineering numerous different footwear types, many runners continue to experience injuries.1-4 The incidence of running injuries remains high, with recent research reporting moderate to severe injuries in 74% of competitive cross-country runners.5

One recent attempt to help alleviate injuries in runners has been the development of minimalist footwear, designed to promote a barefoot-like running pattern. Proponents of minimalist footwear cite its more “natural” running style compared with traditional cushioned footwear. They point to reports noting the forefoot-strike pattern typical of barefoot runners is associated with lower impact forces than traditionally shod running, and that the biomechanical changes associated with switching from traditional to minimalist footwear often include adoption of a forefoot running style.6,7 Minimalist footwear has gained popularity among runners hoping to increase endurance and performance while decreasing the risk of running-related injuries.8,9

Reports of injuries sustained while wearing minimalist footwear, however, have appeared in the literature.10-14 Of note, one minimalist footwear company recently settled a class action lawsuit in which customers challenged claims of improved foot and leg strength and range of motion while using minimalist footwear.15 Research investigating the impact forces and injuries sustained during the transition from traditional shoes to minimalist footwear soon followed.16

Many lower extremity clinicians are seeing these injured patients, and, anecdotally, the demand for therapy to manage running injuries associated with minimalist footwear appears to be increasing. Practitioners managing these patients will benefit from an understanding of the biomechanics associated with runners’ use of—and, in particular, their transition to—minimalist footwear.

Anecdotally, the demand for therapeutic strategies to manage and prevent running- related injuries associated with minimalist footwear appears to be increasing.

Biomechanics basics

Traditionally shod runners experience different biomechanics compared with minimalist and barefoot runners.17 Several studies have reported on the relationship of stride frequency and stride length to footwear conditions.18,19 One study, which compared the running biomechanics associated with six shod/barefoot conditions in nonelite runners, found greater stride frequency and shorter stride length for minimalist or barefoot conditions than for traditional shoe wear.19 However, there are variations in these biomechanical associations that are likely due to the position of the foot and ankle when the foot first hits the ground.18 One of the major contributors to running biomechanics is how the foot strikes the ground.

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Foot-strike pattern is typically classified as a rearfoot-, midfoot-, or forefoot-strike pattern, based on the plantar flexion and dorsiflexion angles of the foot/ankle complex at initial contact with the ground.18 Researchers have reported that traditionally shod runners land more commonly in a rearfoot-strike style, while barefoot running is more likely to be associated with a forefoot strike.6,18 Minimalist footwear attempts to promote this forefoot-strike pattern by offering less support and less of a material barrier between the sole of the foot and the ground, compared with traditional running shoes.6,20

Ground reaction forces and loading rates also have been examined in barefoot and minimalist literature, with some researchers reporting them as risk factors for foot and ankle injuries.16,21-23 Many have reported rearfoot striking is associated with higher impact transient forces than forefoot striking.24,25 Intuitively, it would seem that transitioning from a rearfoot-strike pattern to a forefoot pattern should be associated with a decrease in impact forces and therefore a decrease in injuries. However, research suggests that though some rearfoot strikers became forefoot strikers when transitioning to minimalist footwear, others remained rearfoot strikers;25-27 more importantly, during the transition, many runners developed injuries, and the magnitude of impact forces in those runners, surprisingly, were inversely correlated with injury severity.16

Researchers continue to examine the effect of impact forces on injuries, but impact forces alone are unlikely to explain running-related injury rates. It’s likely that individual anatomic variation, the ability to adapt to neuromuscular changes, and the ability of one’s tissues to withstand variable loads all contribute to injury rates.

Is it safe?

One could argue that the popularity of minimalist footwear also stems from recent media coverage, including the bestselling book, Born to Run.28-30 Unfortunately, there is no definitive evidence demonstrating that minimalist footwear has decreased injuries in runners. Patients are beginning to present to healthcare professionals with injuries while using minimalist footwear.

Although the incidence of injuries sustained in minimalist runners is still unknown, a 2012 study reported a range of injuries sustained while using minimalist shoe wear.10 Salzler et al analyzed 10 patients presenting to an orthopedic surgery outpatient clinic with injuries sustained while using minimalist footwear.10 Injuries included eight metatarsal stress fractures, one calcaneal stress fracture, and a plantar fascia rupture diagnosed with x-ray imaging and magnetic resonance imaging (MRI). All 10 patients were experienced runners, uninjured within the prior year, who decided to transition from traditional running shoes to minimalist footwear. It is important to note, however, that the time spent transitioning varied greatly among these patients and may have played a role in the development of their injuries.

Clinical implications

Collectively, it’s the role of physicians, physical therapists, and athletic trainers to discuss with runners the clinical implications of transitioning from traditional to minimalist footwear. Minimalist footwear provides limited plantar cushioning for impact upon foot strike compared with traditional footwear, but offers more protection against trauma than barefoot running. Even experienced runners have sustained both soft tissue and metatarsal injuries during the transition to minimalist footwear; therefore, runners should be aware that the changes in foot-strike pattern and impact forces that occur during the transition to minimalist footwear—as well as changes that may be expected but do not actually occur—may predispose them to injury.

Further, the time required to transition safely is unknown, even though the majority of injuries sustained have been reported to occur early in the transition.10 Runners should be counseled that there is still no conclusive evidence that minimalist footwear will reduce injuries. If an injury does occur while transitioning to minimalist footwear, a patient should expect a decrease in the distance he or she is normally able to run. If presenting to a clinician, a patient may need imaging (eg, x-ray, MRI) to aid in the diagnosis of specific injuries.

Injuries and impact forces

In one of the first studies to investigate injury rate and severity, as well as foot-strike patterns, impact forces, and associations among them, we prospectively studied 14 traditionally shod runners as they transitioned to minimalist footwear.16 Twelve of the 14 runners sustained injuries an average of six weeks into training. Injuries to the metatarsal head and gastrocnemius and arch pain were the most common injuries. Changes in foot-strike pattern occurred during the transition as expected. Because of their injuries, runners decreased their weekly running distance by more than five miles, compared with their pretransition mileage.

Interestingly, as mentioned earlier, we found that high baseline impact transient peaks in both traditional and minimalist shoes were associated with lower injury severity scores. This suggests impact forces are not the only risk factor for injury and that our understanding of foot and ankle injuries in runners is not yet complete—it’s also possible runners were more accustomed to higher impact forces. It’s important to note that, despite instruction, none of the study participants followed the industry-provided guidelines for making the transition; it’s useful for healthcare professionals to realize that this finding could reflect the habits of many runners seen clinically, and that there is an opportunity to reinforce the importance of a gradual transition to avoid injury.

Gait training programs

Recent research has shown some runners maintain a rearfoot-strike pattern during transition to minimalist footwear and in turn sustain higher loading rates.25-27 This could explain why some runners experience injuries during the transition, especially injuries to the hindfoot, while wearing minimalist shoes. A 2016 study by Warne et al31 assessed the combination of a gait training program advocating a forefoot-strike pattern while transitioning to minimalist footwear over six weeks. Fourteen experienced male runners received a combined intervention that included gait retraining in addition to their transition to minimalist shoes. Twelve runners completed the study and were compared with a control group who underwent gait retraining but did not use minimalist footwear.

Two participants in the combined group dropped out of the study due to injuries, seven others reported leg soreness, and three participants had to reduce their running. Only one participant in the control group decreased running distance due to muscle soreness. The loading rate was shown to be significantly lower compared with baseline in participants in the combined group, though loading rates were significantly higher in the minimalist footwear than in conventional footwear at baseline and after the intervention.

Clinically, these findings could enhance counsel to patients about options for reducing loading rates and impact forces during a transition to minimalist footwear. The number of injuries associated with the transition is important, especially in the context of reported decreased loading rates and impact forces throughout the transition period. It may be helpful to counsel patients that even with gait retraining and reduced loading rates, one might expect an injury that could decrease running distance.

An overview article of gait pattern retraining for runners described the concept of using a wearable feedback system for aiding transition from rearfoot- to forefoot-strike pattern in a successful case study of a female runner who reported reduction of knee pain within seven weeks.32 Monitored running progression and progressive lower extremity strengthening exercises were also implemented.

The authors noted key aspects to consider in designing a successful transition to minimalist shoe wear and forefoot running program, including gradual alteration of running biomechanics, consideration of anatomical traits with known vulnerability to running injury, proper guidelines for running mileage/frequency, improving lower extremity/core strength, and neuromuscular control of movement exercises. The research to date supports the need for further exploration of all components of a comprehensive transition program.

Take time for strengthening

The intrinsic and extrinsic musculature of the foot and ankle have been associated with injuries sustained in runners and patients with chronic plantar fasciitis.33,34 Clinically, it seems reasonable to assume that strengthening the musculature of the foot and ankle could help prevent injuries, as well as facilitate rehabilitation.

A 2016 study by Chen et al35 studied the effects of minimalist footwear on the intrinsic and extrinsic foot muscle volume using MRI. Runners in the study completed a six-month transition to minimalist footwear program that included an exercise program described as a high-intensity program directed at the calf musculature. MRI studies were performed at baseline and six months, and results showed a significant increase in muscle volume in the leg and forefoot. No injuries occurred during the transition, but it is unknown if any of the asymptomatic patients had findings on imaging modalities early in the transition, as the images were only taken at six-month intervals. This study suggests that a longer transition and high-intensity exercise program directed toward the gastrocsoleus complex could help reduce the risk of injuries related to minimalist footwear.

Conclusion

The incidence of foot injuries sustained while running remains high despite theoretically improved footwear. Runners and athletes will continue to try different commercially available products aimed at improving their level of function and preventing injuries; these include minimalist footwear.

Practitioners treating and advising runners should know the risks and benefits of minimalist footwear. Information provided to runners should include education about foot-strike patterns and other risk factors, and the fact that footwear alone is likely not a panacea for reducing injury risk. Although there may be benefits to a change in footwear, there are also inherent risks in the transition to minimalist running shoes. It’s likely that changes in anatomy, physiology, and biomechanics during the transition will be unique to each runner, making generalized statements about the effects of transitioning difficult.

It’s also difficult to make conclusions about minimalist footwear relative to barefoot running, or about variations of minimalist footwear, with regard to injury risk. Clinicians will likely see runners using traditional and minimalist footwear continuing to present to clinics in need of guidance and treatment. For runners interested in transitioning to minimalist footwear, it’s important to discuss the range of potential changes in foot strike and impact forces that might result, and the clinical implications these might have. While many runners will have smooth transitions, some may have injuries early in the process that negatively affect their running mileage. These injuries might include soreness, muscle strains and tears, and stress fractures.

Risk factors associated with running continues to be a topic of debate. Specifically, the role of impact forces on injuries sustained during the transition will need additional study, as it’s possible impact transient forces may not contribute to injuries to the degree that was once thought. Runners searching for ways to increase foot and ankle strength could benefit from minimalist footwear, though the risks and benefits should be discussed in detail, as even the most experienced runner could experience injuries during transition.

Currently, while the use of or transition to minimalist footwear may benefit many individuals, we recognize the risks of injury associated with such transitions and are unable to currently recommend for or against the use of minimalist footwear.

J. Todd Walker, MD, is a resident in orthopedic surgery at the University of California, San Diego, and research fellow at the Sanford Consortium for Regenerative Medicine in San Diego. Donna Moxley Scarborough, PT, MS, is a PhD candidate at Massachusetts General Hospital Institute of Health Professions and former director of sports performance and analytics at Massachusetts General Hospital in Boston. Eric M. Berkson, MD, is an orthopedic surgeon specializing in sports medicine at Massachusetts General Hospital. Matthew J. Salzler, MD, is an orthopedic surgeon specializing in sports medicine at Tufts Medical Center in Boston.

References are available at lermagazine.com.

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