Shoe Gear And Heel Pain: What Does The Literature Reveal?
Shoe gear has the potential to play a significant role in the treatment and prevention of lower extremity injuries. Heel pain is a prevalent complaint resulting from several pathologies, including plantar fasciitis and Achilles tendonitis. The shoe gear industry has, in turn, developed numerous shoe modifications that intend to prevent and help treat painful foot and ankle conditions, including those disorders affecting the heel.
Running is a popular fitness and recreational activity despite a very high estimated injury rate of up to 56 percent of runners annually.1 Over 50 percent of running injuries are overuse injuries resulting from the associated high, repetitive loading.1 An extensive amount of research and design effort goes into running shoe technology in an effort to lessen the incidence of lower extremity injuries. While most shoe gear research focuses on runners, many of these shoe gear technologies may apply to non-athletes and shoe gear for other sports.
Abnormal mechanics are one of the main factors that leads to overuse injury. Both abnormal movement patterns (kinematics) and excessive musculoskeletal loading (kinetics) put an individual at an increased risk for injury.2,3 In terms of abnormal movement patterns, both the magnitude and rate of foot pronation are contributing factors implicated in overuse running injuries.4 Excessive musculoskeletal loading also links to overuse injuries in runners, including both the magnitude of the impact forces, which results from the rapid collision of the foot with the ground, and the rate of impact loading.3 In our observation, shoe gear manufacturers have developed numerous technologies that aim to optimize running mechanics, specifically, to control the rate of pronation, reduce impact forces, and reduce the rate of impact loading.
While innovation is commonly beneficial, in our observation, many of the changes in shoe gear technology may stem from commercial and financial goals and not necessarily science. Studies examining the effect of shoe gear on lower extremity injuries are very limited, owing to the need for large study populations of long duration and the difficulty of separating out numerous compounding variables associated with injury risk. With the advancement of gait analysis modalities, researchers have begun to examine the effect of shoe gear on biomechanical parameters, including foot strike position, ground reaction forces, stride length, loading rates, hindfoot position, and tibia rotation. By examining the effect of shoe gear on these biomechanical factors associated with running injury, one can infer the potential effect of shoe gear on running injuries.
A Brief History Of Shoe Gear Technology
The shoe gear industry has a rich history with design and technology changes aiming to optimize performance and lower injury risk. Early running shoes had almost no cushioning and consisted of a flat rubber outsole, a thin insole, and a lightweight upper. In the 1968 Olympics in Mexico City, one of the first shoes with a cushioned midsole made its debut. The Cortez, a shoe made by the Japanese company Onitsuka Tiger®, introduced the novel concept of midsole cushioning that aimed to reduce harsh foot strike.5
In the 1970s, many shoe gear companies began to focus on stability and motion control. In the late 1970s, Brooks® introduced the varus heel wedge that aimed to reduce overpronation in runners. With time many companies followed suit, developing shoes based around correcting the abnormal movement pattern of overpronation. Development of the diagonal roll bar, similar to the varus wedge but consisting of two layers of foam with a stiffer layer on the medial portion of the shoe, was also to prevent overpronation, as was the medial post, consisting of a firm density material on the medial arch portion of the midsole.5
In addition to shoe gear aimed at motion control, many shoe companies also developed technologies to limit impact forces and the rate of impact loading. Additional cushioning aimed to alleviate the shock produced by heel striking. Ethylene-vinyl acetate (EVA), introduced in the mid-1970s, offered more rebound and better shock absorption to midsoles. It rapidly became, and has remained, the predominant cushioning compound used in running shoes.5 In 1977, Nike® introduced the revolutionary Air sole cushioning consisting of pressurized air packets in the heel aiming to cushion heel strike.5
Considering Shoe Technologies And Resulting Biomechanics
Both foot strike and stride length receive considerable attention in the running literature since significant changes in these parameters occur with different types of shoe gear. Specifically, in our experience, running barefoot and in some minimalist-type shoes can cause individuals with a traditionally shod rearfoot strike gait pattern to adopt a reduction in stride length and a forefoot/midfoot strike gait pattern. Thus, these shoe gear modifications can serve as a trigger to achieve the modifications of reduced stride length and a forefoot/ midfoot strike gait pattern.
Minimalist Shoes. Despite the introduction of cushioning and motion control technologies, runners continued to experience high injury rates. Many athletes seeking modalities to improve performance and reduce injury risk turned toward minimalist shoes and barefoot running. Barefoot running became popular in 2010 with Christopher McDougall’s best-selling book, Born to Run: A Hidden Tribe, Superathletes and the Greatest Race the World Has Never Seen,6 and Lieberman and colleagues’ feature on the cover of Nature that examined foot strike patterns and collision forces in barefoot runners.7
Traditional running shoe biomechanics typically exhibit an increased stride length and a rearfoot strike (RFS) gait pattern, resulting in a high impact peak and a high loading rate.8 Research attributes both high impact forces and increased rates of impact loading to increasing the risk of running-related injuries of the lower extremity.9–12 When examining hindfoot position at heel strike, Daoud and team found double the injury rate in runners with a rearfoot strike gait among Harvard cross-country runners.13 In contrast to this study, Warr and colleagues found no difference in self-reported injury with a rearfoot strike versus a forefoot/midfoot strike gait pattern.14 Warr’s study, however, did rely on self-reported historical data, possibly limited by individuals’ ability to recall past injury.
Minimalist shoe design typically includes a thin midsole and no heel raise (“zero drop”) to promote running with a forefoot/midfoot strike pattern and shorter stride length. These gait changes result in a reduction of impact loading, reduction in peak vertical ground reaction forces (GRFs), and reduction in horizontal GRFs.3 Given that high impact loading and high GRFs associate with an increased incidence of injuries including tibial stress fracture,12,15–17 plantar fasciitis,10 and patellofemoral pain,18,19 it is thought that changing these biomechanical factors, through the use of minimalist shoes, will result in a reduction in the occurrence of these lower extremity injuries.
Maximalist Shoes. In contrast to minimalist shoes, maximalist shoes consist of an extremely thick, cushioned midsole, wide, stable platform, and frequently a rocker sole. The maximalist design concept is believed to significantly reduce impact, decrease leg fatigue, increase energy return, and add stability.5 One of the first companies to embrace this technology, HOKA® One One, first launched their maximalist shoe design in 2010, offering a stark contrast to the, then popular, minimalist shoes.
Maximalist shoes, however, are similar to minimalist shoes in that, in our experience, they conceptually avoid a heavy rearfoot strike gait pattern and aim to reduce impact peak and loading rate. Despite the popularity of maximalist running shoes, there is little research examining the effect of maximalist shoes on the biomechanical factors, namely impact peak and the rate of impact loading, associated with lower extremity injury. Pollard and colleagues examined the effect of running in maximalist shoes compared to neutral shoes before and after a five-kilometer run.20 This study found an increase in both impact force and loading rate when running in maximalist shoes. This study was limited by the fact that the maximalist running shoe was novel to the participants.
Hannigan and Pollard further examined the effect of maximalist shoes on impact force and loading rate after a six-week transition period.21 This study similarly found that both impact force and loading rate increased when running in maximalist shoes compared to traditional running shoes following a six-week transition period to adopt the use of maximalist shoes. Despite these studies, we find runners anecdotally report a reduction in running-related pain, faster recovery, and reduced injury rates using maximalist shoes. Further research is necessary to examine the long-term effects of the use of maximalist shoes on lower extremity injury risk in runners.
The Relationship Between Shoe Innovations And Heel Pain
Plantar fasciitis, one of the most frequent causes of heel pain in runners, other athletes, and non-athletic individuals, is reported as one of the most frequent overuse injuries and one of the top five running-related injuries.1,22 Numerous factors can contribute to the development of plantar fasciitis, in our experience, including repetitive loading of the plantar fascia, overpronation, and decreased ankle joint dorsiflexion. Specifically, Pohl and team found a greater vertical ground reaction force loading rate and low medial longitudinal arch height to be associated with a history of plantar fasciitis in runners.10 In a subsequent prospective study, Davis and colleagues found a predisposal to plantar fasciitis in runners with high vertical loading rate, high impact peaks, and peak positive acceleration of the tibia.23 While studies directly attributing the effect of shoe gear on the incidence of plantar fasciitis are limited due to many factors, including the need for large study numbers of long duration and multiple confounding factors making it difficult to isolate factors contributing to injury risk, one can infer that shoe gear modifications that can modify biomechanical risk factors associated with plantar fasciitis have the potential to lower the incidence of this pathology.
Despite the difficulty of examining the direct effect of shoe gear modifications on the incidence of plantar fasciitis, several studies attempt to examine the role of different shoe gear technologies, often in combination with other treatment modalities, in the management of plantar fasciitis. Fong and colleagues examined the effect of combining rocker sole shoes and custom-made orthoses to treat plantar fasciitis.24 The authors found that the combined effect of these modalities had a larger role in the management of plantar fasciitis compared to their individual effects.
Mizel and team found that a night splint and shoe modification consisting of a steel shank and anterior rocker bottom was an effective treatment option for plantar fasciitis.25 Ryan and coworkers compared the effect of a multielement exercise model with a conventional training shoe versus an ultraflexible training shoe in the treatment of plantar fasciitis. The study found that both treatment arms were effective modalities for treating plantar fasciitis, but the use of the ultraflexible shoe resulted in faster resolution of symptoms.26
In Summary
Numerous athletes and non-athletes provide personal reports of the effects of shoe gear on decreasing lower extremity injury, specifically injuries associated with heel pain. Currently, studies examining the specific effect of shoe gear on lower extremity injuries remain limited. While advances in biomechanical research give us a better understanding of the individual factors associated with injury risk, large studies examining the specific effect of shoe gear on lower extremity injury risk are lacking. Further research is necessary to specifically examine the effect of various shoe gear technologies on lower extremity injury incidence.
Dr. Hoffman is a Fellow of the American College of Foot and Ankle Surgeons and practices with Denver Health in Denver, Colo.
Dr. Jerabek is a Diplomate of the American Board of Podiatric Medicine and practices with Denver Health in Denver, Colo.
Dr. Gorski is a Diplomate of the American Board of Podiatric Medicine and practices with Denver Health Orthopedics in Denver, Colo.
Dr. Thompson is an Associate Professor of Health Sciences at Fort Lewis College in Durango, Colo.
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