Research suggests that when transitioning to a minimalist running shoe, foot strike pattern is key to preventing lower extremity injuries. A transitional minimalist shoe, with slightly thicker and softer soles, may help prevent certain injuries in some runners.
By Everett B. Lohman III, DSc, PT, OCS
Humans have been running barefoot or in minimal footwear (moccasins and sandals) since the beginning of time.1 It was not until the 1970s that Nike revolutionized the running world with what turned out to be the prototype of the traditional running shoe.2 The year 2012 has been hyped by shoe manufacturers as “The Year of the Minimalist Shoe,” when they predict that sales of these lightweight minimally supportive running shoes will surpass those of conventional or traditional running shoes. Minimalist shoes have been on the market for more than a decade, since Nike re-revolutionized running shoes in 2001 with introduction of the Nike Free, which helped sparked the “minimalist revolution.”
Running is associated with numerous health benefits for the mind and body, but there also are numerous risks for lower extremity injury associated with running.3,4 Despite advances in running shoe technology, as many as 60% of runners suffer lower extremity injuries annually.2 Reports of injury related to minimalist shoes have been primarily anecdotal, lacking longitudinal prevalence studies, and appearing on web blog sites and as case reports. However, those anecdotal reports suggest that, despite the apparent lack of arch support or motion control provided by these minimalist shoes, fewer impact-related or adverse motion-related (pronation) lower extremity injuries have been reported than initially predicted by many movement scientists, myself included.
The question on many runners’ minds is “Does purchasing a specific type of running shoe or altering my running style change my risk of sustaining a lower extremity running-related injury?”
Comparison of running shoes
Conventional or traditional running shoes that have dominated the market since the 1970s are typically constructed with thick rearfoot cushioning that results in an elevated heel. These shoes were thought to potentially reduce impact forces and minimize lower extremity injuries.
The differential between the heel and toe region of the running shoe is referred to as the “heel drop” or simply the “drop.” Many traditional running shoes have a drop of 12 mm to 14 mm (approximately .45 in to .6 in), meaning that the heel region is 12 mm to 14 mm higher than the toe region. An example would be a running shoe with a 24-mm heel height in the rear and a 10-mm forefoot sole thickness, resulting in a 14 mm differential and a forward-sloping drop. This forward slope design was introduced to reduce stress to the Achilles tendon.5
In addition to a pronounced drop, traditional running shoes tend to have a wide heel that is designed to help control motion and prevent inversion ankle sprains. Many of these traditional running shoes are constructed with even more supportive structural features to provide motion control specifically. The traditional running shoe design promotes a heel-to-toe running pattern2 that has landing characteristics similar to those of walking gait—a heel strike contact when the heel makes the initial ground contact. Conversely, minimalist running shoes, as the name implies, lack the supportive construction and are intended not to control motion, but rather to promote motion with the thin flexible midsole.
Many minimalist shoes have a “zero drop” meaning that there is no difference in the heel and toe elevation (0 mm). This trend has continued in the 2012 line of minimalist shoes; however, not all minimalist shoes have the same characteristics. The minimalist running shoe can be further divided into three subdivisions: the barefoot-style shoe, the “minimalist” shoe, and the transitional or neutral shoe. The barefoot-style shoe sole is extremely flexible and thin with a zero heel drop; its primary function is to offer some protection from road or trail debris but not cushioning. These shoes typically have an ultra-wide toe box to allow the toes to splay during initial ground contact to better absorb ground reaction forces (GRF). These ultra-lightweight shoes typically weigh less than 7 oz. The middle subdivision, the minimalist shoe, has characteristics that include some midfoot cushioning, a flexible sole, and a wide toe box. Although wide, these shoes typically have a slightly narrower toe box than the barefoot-style shoe. The typical heel-to-forefoot drop ranges from 0 mm to 3 mm; however, some shoes in this subdivision may have up to a 6-mm drop.
Many running experts and healthcare practitioners are recommending that runners initially purchase a transitional shoe when planning to convert from a traditional shoe to a barefoot or minimalist running shoe. A transitional minimalist shoe has many similarities to the traditional running shoe; however, it is more flexible and lightweight with a moderate heel-to-forefoot drop that typically ranges from 4 mm to 8 mm. It is the author’s opinion that transitional shoes, with their moderate drop, are more Achilles friendly than the other types of minimalist shoes. However, a few shoes marketed as transitional have a 0-mm heel drop, so practitioners should caution consumers to review the shoe specifications prior to purchasing. Transitional shoes often have a thicker stack height (height of the material placed between the foot and ground), ranging from 12 mm to 26 mm. Those with a thick stack look similar to the traditional thick-soled running shoes. The cushioning varies by brand from soft to firm.
Although it is too early for scientific evidence, anecdotally, the abrupt change from the traditional running shoes with a drop of 12 mm to 14 mm to the zero-drop minimalist running shoe could predispose some runners to excessive stress on the Achilles tendon. The assumption is that the runners will self-initiate a forefoot or midfoot strike pattern2 when wearing these minimalist-style running shoes (Figure 1). This switch to a forefoot or midfoot contact running pattern is typically what does happen in runners wearing minimalist shoes; however, those who fail to change their running gait pattern may be at higher risk of injury.
Scientific evidence does not support the theories that thick-soled elevated running shoes reduce impact-related or adverse motion induced injuries. A systematic review published in 2009 concluded that there is no evidence that the traditional running shoe prevents injuries.6 It is not that GRFs have a significantly greater peak force during traditional shod running than barefoot or minimalist running, but rather that the abrupt spike (“transient force”) that occurs in the first 0.1 second of initial contact when heel striking may have the greatest potential risk for impact-related lower extremity injuries.2 Running patterns that promote forefoot or midfoot initial contact, either barefoot or shod, produce a smoother GRF that lacks the transient spike.2,3
Two studies suggest that traditional running shoes, with their thick cushioning and elevated heels, might actually increase the risk of ankle sprain if decreased proprioception limits the delivery of somatosensory afferent information to the spinal cord and brain in time for the muscle recruitment needed to prevent an injury.7 The increased lever arm from the wide elevated heel prevents normal pronation motion and increases ankle sprains.8,9
Many runners are concerned with the lack of arch support in the minimalist shoe. Traditional running shoe selection is often based on arch type or foot shape: Low, medium, or high arch. However, a 2010 study of 2676 military recruits failed to show that matching shoe type to foot shape made a difference in injury rates compared with a control group.10 Another study suggested that wearing ultraflexible minimalist shoes during a 12-week exercise program significantly reduces plantar fasciitis pain earlier than wearing traditional running shoes.11 The authors suggested that intrinsic foot muscles are recruited and strengthened while wearing minimalist shoes with wide toe boxes.
Other authors have also suggested that traditional running shoes, with their arch support (and tight toe boxes), could potentially weaken the foot intrinsic muscles, leading to collapse of the medial longitudinal arch and resulting in increased foot pronation, which in turn stresses the plantar fascia and delays recovery from plantar fasciitis.2 Weakened intrinsic muscles have also been reported from continued semirigid orthotic use. However, there is no current evidence to support this hypothesis.12
Comparison of running gait
Traditional shod running has been studied extensively, and, depending on the running speed, investigators have identified as many as 78 subdivisions of running gait.13 Running gait patterns differ considerably between shod runners wearing traditional running shoes and those wearing the newer minimalist running shoes. The main difference is the weight acceptance period of the running gait cycle and stride length.
Shod runners wearing traditional running shoes typically make ground contact (initial contact) with the heel and then the foot becomes flat during loading response. Eccentric or elongating contractions of the pretibial muscles, including the tibialis anterior, help control the plantar flexion created by this heel-to-toe contact pattern, preventing the forefoot from slapping the ground and in turn absorbing shock and protecting the metatarsals.13,14 This, however, can result in excessive stress to the pretibial muscles and their attachment site, the lateral aspect of the tibia.13 Running gait while wearing minimalist shoes is similar to barefoot running.3 While running barefoot or in minimalist shoes, initial foot contact should occur with the forefoot or the midfoot rather than the heel (Figure 1). This results in a forefoot-to-heel or a midfoot-to-heel pattern. The gastroc-soleus complex eccentrically contracts to control the foot and ankle in forefoot strikers,2 potentially increasing stress on the Achilles tendon. For runners with a history of Achilles tendinitis switching to minimalist shoes, a midfoot strike pattern in a transitional shoe may be advisable to reduce the risk of reinjury.
In my clinical observations, most habitual heel strikers wearing traditional running shoes will instinctively switch to a forefoot strike pattern when they are faced with a situation that requires running barefoot. This also often occurs when switching to a minimalist shoe. However, it is important to acknowledge that not all runners adopt a forefoot or midfoot strike pattern by simply donning a pair of minimalist shoes. Runners who maintain a heel strike-running pattern when switching to a minimalist shoe or to barefoot running increase their risk of injuries. Many minimalist running shoe companies place disclaimers or warning labels on the shoe boxes or websites cautioning the consumer to either limit the initial duration of wearing their product (time or distance) or recommending the avoidance of initial contact with the heels. Although admirable, it seems unlikely that most consumers will access this information or fully understand the potential consequences of ignoring the advice.
There are numerous other differences in running gait between shoe types. Shod runners wearing traditional running shoes tend to achieve an almost fully extended knee (approximately 11°) during terminal swing at the end of the late float period and during initial contact.13 Barefoot and shod runners wearing minimalist shoes tend to have less knee extension during terminal swing and land with a more flexed knee, resulting in less GRF being transferred up the lower extremity. Increased knee flexion promotes flatter foot placement, which prevents the overloading of the heel.15
Heel strike initial contact, as commonly seen in traditional running, requires approximately 20° of ankle dorsiflexion, a position that locks the dome of the talus in the ankle mortise between the distal tibia and fibula. Forefoot contact runners achieve greater ankle plantar flexion and knee flexion.2,15 Forefoot strikers land in approximately 20° of ankle plantar flexion, which is the unlocked or open-packed position of the talocrural joint (ankle). Midfoot strikers make contact with the metatarsal heads and the calcaneus (heel) at approximately the same time, landing in approximately 10° of ankle plantar flexion. This plantar flexed position promotes more “shock absorption” than heel striking in the dorsiflexed position. Horizontal foot placement reduces pressures acting on the heel.15
During midfoot and forefoot contact, GRF travel vertically through the ankle axis, whereas during heel contact the GRF occur posterior to the axis, resulting in a rotary motion (Figure 2). This rotary force produced from heel-to-toe running necessitates considerable eccentric pretibial muscle contraction that could potentially lead to the increased prevalence of conditions such as shin splints.3
In addition to greater knee flexion during forefoot and midfoot contact in minimalist or barefoot running, a small amount of trunk flexion or forward leaning should also occur. Flexion of these major lower extremity and trunk joints promotes more shock attenuation, arresting the potentially harmful transient impact forces through muscle tuning.16 Due to increased knee flexion, forefoot and midfoot strikers have shorter step/stride lengths,17 which results in the foot contact occurring directly under the center of gravity (COG). Heel-strike running, commonly promoted by traditional running shoes, results in the knee and ankle joints being positioned at or near the closed-packed positions at contact with a more erect trunk (Figure 2). Traditional shod runners, with their relatively straight and rigid leg shank at initial contact, tend to have a considerably longer stride length, causing the heel contact to occur in front of the COG. This results in a deceleration impact resulting in the creation of a transient spike within the GRF,2 which may be potentially injurious to lower extremity structures. Although the maximum GRF does not vary considerably between heel strike and forefoot strike patterns, heel-strike runners typically have two peaks instead of a single peak. The first peak (impact or transient peak) occurs during weight acceptance (initial contact and loading response) while the second peak (thrust peak) occurs during single limb stance (Figure 3).2,3,18,19 As mentioned earlier, it is the first peak, the transient peak, that some authors have hypothesized is the most potentially injurious.2 It is important to reemphasize that it is the runner and not the shoe who determines the actual strike pattern; shoe selection only influences, but does not dictate, the strike selection.
Emerging research findings regarding landing pattern modifications to treat running-related pathology are being published. One study used eight running gait retraining sessions over a one-month period in runners with patellofemoral pain. The runners were instructed to switch from a heel contact to a forefoot initial contact pattern. Biofeedback was used to help reinforce the preferred landing pattern. This new forefoot landing pattern was maintained at the three-month follow up and the subjects reported a reduction in pain and an increase in function.24
In a similar study, runners with chronic exertional compartment syndrome received running gait instruction to switch to a forefoot-strike pattern to eliminate the heel-strike pattern. At the end of the six-week study the forefoot landing intervention led to decreased postrunning intracompartment pressure.14 At the one year follow up, subjects reported continued reduction in pain and increased function. For certain pathologies, these recent studies suggest that a forefoot-landing pattern reduces existing pathology and prevents injuries.
Some runners are leery of the thin-soled minimalist running shoes, fearing that the sole will not absorb ground impact forces. Several studies suggest that maximum GRF does not vary significantly across running pattern, surface hardness, or shoe selection.2,3,20 The human central nervous system (CNS) utilizes “muscle tuning,” or selective lower extremity muscle contractions, to maintain relatively constant GRF regardless of sole thickness or firmness21 and minimize soft tissue compartment vibration.16,22 While running at a constant speed runners can adjust leg stiffness just prior to impact regardless of the surface or shoe hardness.22 However, failure of the body to attenuate these forces or vibrations may result in soft tissue and bony microtrauma in the lower extremities.23
It is my opinion that runners with properly functioning muscle tuning will typically adapt rapidly to the minimalist shoe. When transitioning to the minimalist running shoe, it would appear that foot strike pattern is more important for preventing lower extremity injuries than shoe sole firmness and thickness. However, the initial selection of a transitional minimalist shoe, with slightly thicker and softer soles, may help ensure that the CNS and muscles adapt adequately before transitioning to the more “aggressive” minimalist running shoes or to running barefoot.
The take-home message is that there is not a single best shoe or a panacea on the market. Although the minimalist shoe may be the best selection for many, if the transition does not occur in a moderate and controlled manner, injuries may occur. There are three primary forces acting on the human body during running: compression, tension, and shear. Minimalist running shoes may minimize certain impact (compression) and shear injuries; however, they may predispose runners to some forms of tension-related injury such as Achilles tendinitis. Although this conclusion is based primarily on theory rather than scientific evidence, it does seem likely that individuals with recurrent or longstanding Achilles tendon issues might want to reconsider minimalist shoes, select a transition-style shoe, or lengthen the recommended transition period.
Finally, the transition from a traditional running shoe to a minimalist running shoe is much more complicated than simply “purchase and wear.” Runners making the transition must ensure that they alter their running gait to include a midfoot or forefoot contact pattern. This alteration is instinctive in many runners, but certainly not in all. As science begins to catch up with the minimalist running trend, researchers can more conclusively determine whether running in minimalist shoes that mimic barefoot running, if done correctly, is a safe alternative. After all, it appears that the “Minimalist Movement” is here to stay.
Everett B. Lohman III, DSc, PT, OCS, is assistant dean of graduate academic affairs at Loma Linda University, School of Allied Health Professions, in Loma Linda, CA.
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