Runners have a greater choice of footwear than ever before, but conflicting study results make evidence-based shoe selection a challenge. And new research suggests that even what is known isn’t consistently being put into practice.
by Ryan C. Enke, MD
Long-distance running continues to be a popular recreational pursuit in the U.S. The running boom of the 1970s opened the door for mass participation in road races and marathons, and today there are an estimated 36 million runners in the U.S.1 Increased participation, however, has led to an increased number of injuries as well. The yearly incidence of running injuries is estimated to be between 37% and 56%.2
Most running injuries are due to cumulative microtrauma or overuse.3,4 Several risk factors have been identified as predisposing athletes to these injuries.5,6 Intrinsic as well as extrinsic factors have been reported in the literature.3,5,7,8 The running shoe provides a unique interface between intrinsic and extrinsic factors.9-12 Although randomized controlled trials are lacking, several sources suggest an increased risk of injury associated with improper footwear.3-5,7
To understand the potential link between running shoe selection and injury risk, it is essential to review the normal gait pattern and biomechanical principles. Compared to walking, the running gait cycle has an increased step rate, with increased joint range of motion, a shorter stance phase, and the addition of a float phase.6 The body must absorb a tremendous amount of force, with nearly three times the athlete’s body weight experienced at each foot strike.6
Typically, the gait cycle begins with a lateral heel strike in a supinated foot position and then progresses to rapid pronation through 70% of the support phase.13 After maximal pronation, supination occurs from about 70% of support phase through toe-off.13 Pronation, which includes ankle dorsiflexion, subtalar eversion, and forefoot abduction, makes the foot more flexible to aid in shock absorption during the support phase. The effects further up the kinetic chain include tibial internal rotation, knee flexion, and hip flexion.14 Supination, which includes ankle plantar flexion, subtalar inversion, and forefoot adduction, makes the foot more rigid for propulsion. Tibial external rotation, knee extension, and hip extension occur as a result of foot supination.14 Excessive pronation or supination, therefore, can affect the entire kinetic chain.
Arch type and injury patterns
Arch type has been shown to be associated with specific patterns in ground force and muscle activation.15-17 High-arched runners tend to supinate more, with increased leg stiffness and a higher vertical loading rate, whereas low-arched runners tend to have increased pronation and eversion excursion.16,17 A rigid pes planus foot has been associated with overpronation and can lead to medial lower extremity soft-tissue and bone overload injuries.7,18-20 Pronation and low arch index have been also shown to be good predictors of anterior knee pain.19 A pes cavus foot has been associated with increased ground force and can be associated with lateral lower extremity injuries and stress fractures.4,16 The modern running shoe has, therefore, been designed to take these factors into account.
Running shoe design
The beginnings of the modern running shoe can be traced back to the 1920s, and by 1967 there were approximately 16 types of running shoes.6 Today, the running shoe industry produces hundreds of different shoe types that vary with regard to cost, style, color, and brand. The most common classification system of running shoes today includes the cushioned shoe, stability shoe, or motion control shoe. This system attempts to match arch type and its effect on pronation and supination with shoe design.4,6,7,12,21,22 The cushioned shoe has the most shock absorption capacity and is typically recommended for a pes cavus arch type with excessive supination.12,21,22 The motion control shoe offers the greatest amount of support and controls for excessive pronation commonly seen with a pes planus arch type.12,21,22 The stability shoe includes elements of both support and cushioning and is commonly prescribed for a neutral arch type or mild overpronator.12,21,22
A recent review of the literature by Richards et al concluded that there are no evidence-based studies to support running shoe recommendations based on arch type.23 Although randomized controlled trials are lacking, several sources show trends toward increased risk of injury associated with footwear worn beyond recommended mileage accumulation or lacking either cushioning or motion control elements.3,5-7 The heel wedge and increased rearfoot stability added to the running shoe between 1970 and 1984 have been credited by some with a decrease in Achilles tendon injury rates.6 Additionally, several studies do support the biomechanical principles behind modern shoe design. For example, a soft midsole has been associated with increased pronation, while an increased heel flare can reduce pronation.24 Cushioned shoes attenuate shock better for all arch types, and motion control shoes control rearfoot motion better, with a lower instantaneous loading rate in both high-arched and low-arched runners.9 Another study demonstrated that peak tibial internal rotation decreased with a motion control shoe in low-arched runners, while tibial shock was reduced with a cushioned shoe in high-arched runners.25 Altered electromyography muscle activation patterns have been observed based on running shoe design.10,15 For example, midsole hardness can affect the degree to which the leg muscles contract in helping to absorb impact forces.10,15
Conversely, others have proposed that tibiocalcaneal kinematics may be individually unique and may not be changed by shoe sole modifications.26 Individual responses to footwear modifications also may alter expected outcomes.27 According to one large meta-analysis, shock-absorbing insoles in footwear may prevent tibial stress fractures, but evidence on any other modifications is inconclusive.28 A recent prospective study found no reduction in injury rates when matching recommended running shoe design to arch type.29 Limitations of this study include the fact that runners in the control group were assigned stability shoes. Based on the most common arch types in the population, stability shoes would be recommended for a majority of runners. It would, therefore, be difficult to detect a significant difference in injury rates based on this study design
Although many experts propose matching arch type with correlative shoe design,4,6,7,12,21,22 others have suggested that running shoe comfort is a more important factor to consider, as this may be related to pressure distribution under the foot.30 Another paradigm, proposed by Nigg, suggests that impact forces serve to tune muscles to minimize vibration and that previous suggestions to realign the skeletal system with footwear may need to be reconsidered.31 Newer running shoe models are now available that include minimal support and cushioning.
Interestingly, a recent study has called into question whether shoes are necessary for running at all.32 Habitually barefoot runners tend to land on the forefoot or midfoot, while the habitually shod runner is more likely to land on the rearfoot due to the elevated heel and cushioning of the running shoe.32 Some authors claim that barefoot running may prevent the impact-related lower limb injuries experienced by many runners today.32 They cite evidence from gait studies showing that barefoot runners who land on the forefoot produce smaller peak impact forces than rearfoot strikers wearing running shoes.32 Barefoot running has also been shown to decrease joint torques at the hip, knee, and ankle compared to shod running.33 However, running shoe compliance may offset the increased torque when calculating actual joint forces.33 Torsion is the phenomenon of calcaneal and metatarsal uncoupling. One study found that modern shoes with torsional stiffness actually increase pronation, while the least amount of pronation occurs in barefoot running.34 More research is certain to come, but the practical issues of barefoot running—including tolerance of varying running surfaces and temperatures, among other factors—remain formidable barriers to its popularization.
Running shoe replacement and care
Independent of running shoe selection, proper running shoe replacement and care can be important factors in injury prevention. Running shoe mileage in excess of 400 to 500 miles has been shown to reduce shock absorption capacity, which may lead to increased injury rates.3,19,35,36 Increased running shoe mileage has been associated with a greater risk of anterior knee pain.19 One study found that after 250 to 500 miles of running, less than 60% of shock absorption remains in a pair of running shoes, and at 500 miles, only 45% to 60% of shock absorption remains.35 Another study found that peak plantar pressure increases 100% after 300 miles of running due to the loss of shock absorption capacity.37 Structural damage to the midsole material is evident on scanning electron microscopy after 450 miles.37 Wet running shoes absorb less shock than dry shoes,35 while cold ambient temperatures also significantly reduce the shock attenuation of commonly used running shoes.38
What factors do athletes consider important in shoe selection? Although a variety of recommendations exist with regard to running shoe selection and care, few authors have investigated which factors athletes feel are important in this process. A recent study quantified the factors important to adolescent cross-country runners in choosing their running footwear.39 In this study, nearly three out of every four athletes indicated that arch type compatibility with shoe design was the most important factor in choosing a running shoe.39 Interestingly, though, only slightly more than half of participants reported knowing their arch type.39 In addition, most runners did not know how many miles they ran in a single pair of running shoes before replacement.39
Nonpublished data from this study showed that when asked to match a specific arch type with common available recommendations with respect to correlative running shoe design, only 17.5%, 16.1%, and 31.4% correctly matched footwear recommended for a flatfoot, high arch, or neutral foot, respectively. About 60% of respondents answered incorrectly for all three arch types. Increased running experience was associated with a greater likelihood of a correct response.
In summary, although runners in this study claimed running shoe selection based on arch type was important, they lacked the knowledge to make decisions according to these criteria.39 To this author’s knowledge, no published studies have investigated factors considered important for shoe selection by recreational or competitive adult runners. This may be considered an important area of future research as more running shoe choices become available.
The selection and care of running shoes represents a potentially modifiable injury risk factor among runners. In spite of differing opinions on how running shoes may affect biomechanics, there is evidence that running biomechanics are altered based on shoe design.9,10,15,24,25 There is also debate as to how specific arch types may interact with running shoe design. Nonetheless, recommendations on selecting shoes based on specific arch types are common.4,6,7,12,21,22 Newer research has led to the introduction of minimally supportive shoes to simulate running barefoot, and barefoot running itself has become a topic of interest.
Today, a multitude of running shoe styles are available. When considering running shoe selection and injury prevention, it is important to remember that much of the research on running injuries is in the form of expert opinion and comparison trials, as opposed to randomized controlled trials.5 Establishing footwear’s effects on the etiology of sports injuries can be a difficult task.40 In the future, more research will be needed to validate the current recommendations in the literature regarding running shoe selection and replacement decisions.
Ryan C. Enke, MD, is a physical medicine and rehabilitation physician who staffs a running medicine clinic at Rockford Orthopedic Associates in Rockford, IL. He is the medical director of the Rockford Marathon.
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Barefoot running and minimal support shoes: Additional resources
- De Wit B, De Clercq D, Aerts P. Biomechanical analysis of the stance phase during barefoot and shod running. J Biomech 2000;33:269-278.
- Divert C, Mornieux G, Baur H, et al. Mechanical comparison of barefoot and shod running. Int J Sports Med 2005;26:593-598.
- Divert C, Mornieux G, Freychat P, et al. Barefoot-shod running differences: shoe or mass effect. Int J Sports Med 2008;29:512-518.
- Eslami M, Begon M, Farahpour N, Allard P. Forefoot-rearfoot coupling patterns and tibial internal rotation during stance phase of barefoot versus shod running. Clin Biomech 2007;22:74-80.
- Griffin JR, Mercer JA, Dufek JS. Kinematic comparison of running barefoot and in the Nike Free. Med Sci Sports Exerc 2007;39(5):S73.
- Potthast W, Niehoff A, Braunstein B, et al. Changes in morphology and function of the toe flexor muscles are related to training footwear. Presented at 20th International Society of Biomechanics Congress, Cleveland, August 2005.
- Ryan M, Fraser S, McDonald K, Taunton J. Examining the degree of pain reduction using a multielement exercise model with a conventional training shoe versus an ultraflexible training shoe for treating plantar fasciitis. Phys Sportsmed 2009;37(4):68-74.
- 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.
- Willy RW, Davis IS. Kinematic and kinetic comparison of running in a neutral cushioned shoe and a minimal shoe. Med Sci Sports Exerc 2009;41(5):390-391.