Key Principles To Evaluating Athletic Footwear
When it comes to evaluating athletic shoes, it is important to have an understanding of the terminology and technology when communicating with colleagues and patients. Unfortunately, there is no industry standard for any of the current terminology in shoe construction. There is also a lack of standard terminology in regard to placing shoes in their appropriate biomechanical category.
The primary terms and categories of running shoes include motion control, stability and cushioning. Even though these terms are in common use, they have great variation in their application, often no consistency and even contradictory usage among manufacturers. Some companies have even discarded these terms of evaluation in favor of their own “new” terms, like guidance or support.
However, for the purpose of this article, the term motion control shoe will include at least dual density ethylene vinyl acetate (EVA) midsole, midfoot torsion and flexion stability. Stability shoes have these same components but have less torsion and flexion stability than motion control shoes. Cushion shoes have no medial high density EVA, preferably only “mild” midfoot torsion and flexion stability, and therefore are constructed to primarily provide shock absorption.
A Guide To The Four Basic Shoe Components
In addition to understanding basic terminology, one must have both a general and specific knowledge of basic shoe components. Having a strong understanding of the four components of a shoe is critical to evaluate shoes clinically and understand the research that is available. These components are the outsole, midsole, midsole cushioning device(s) and insole.
The different outsoles currently in use are primarily carbon rubber, solid rubber, blown rubber and thermoplastic polyurethane.
• Carbon rubber is used in the plantar lateral heel area to reduce breakdown due to high impact loads at lateral heel strike.
• Solid rubber, either synthetic or natural rubber, is used for a full-length outsole. Solid rubber is very durable and has more shock absorption than carbon rubber.
• Blown rubber is synthetic rubber with tiny air pockets for extra cushioning. Blown rubber is used in the forefoot.
• Thermoplastic polyurethane (TPU) is commonly used in the midfoot of the shoe for structural support.
Midsole materials include ethylene vinyl acetate, polyurethane and combination EVA.
• Ethylene vinyl acetate has good cushioning but less durability than polyurethane.
• Polyurethane, which is often used in the rearfoot with EVA in the forefoot, has high durability but less cushioning than EVA or combination EVA.
• Combination EVA is comprised of EVA and rubber, often around 60 percent EVA and 40 percent rubber. This is often used in higher end shoes to provide greater cushioning, shock absorption and durability in comparison to EVA.
Research has shown the use of stiff midsole materials reduces eversion and eversion excursion.2 The technology of integrating higher density EVA in the medial portion of the heel to midfoot remains a hallmark of modern motion control shoes by all manufacturers. This is one of the simple clinical evaluations of shoes a clinician can perform in the office, even if he or she is unfamiliar with specific shoe models. Using this evaluation, the clinician can begin to determine if patients are in the correct shoe for their biomechanics and whether the current shoe is contributing to the injury.
When it comes to midsole cushioning devices, each manufacturer has different technology (air, gel, etc.). When these devices are placed laterally in the shoe’s midsole, they decelerate pronation movements of the rearfoot.3 Clinically, this can reduce injuries, especially in those with excessive pronation, as this deceleration of pronation decreases the force acting upon the soft tissues. These lateral cushioning devices have also played a role in reducing shock-related injuries (such as an uncompensated forefoot valgus or plantarflexed first ray) in the supinated foot.
Finally, there are the inexpensive EVA insoles that are standard within the shoes. However, one can replace even this insole with a custom orthotic or simple over the counter insoles. Research has shown that simple, cushioning, high-quality insoles reduce mean vertical ground reaction force peak, ground reaction force loading rate and peak tibial acceleration.4 Therefore, even upgrading the standard insole in shoes can reduce forces on the lower extremity and significantly aid in treating and preventing athletic injuries.
Studies have determined that when these four seemingly simple components are used in motion control shoes, they can control rearfoot motion and attenuate shock in cushioned shoes.5 Williams and colleagues found that runners with low arched feet are more likely to sustain soft tissue injuries and those with high arched feet are more likely to have bone injuries such as stress fractures.6 We can properly identify these feet and make appropriate shoe recommendations that help reduce or avoid injuries.
In decades of evaluating shoes, I have found consistent features in motion control shoes that can help the clinician evaluate and recommend appropriate shoes. Checking for midfoot torsion stability, midfoot flexion stability and heel counter rigidity, in conjunction with high density EVA medial posting, can help determine the level of motion control that a shoe possesses.
Classically, my clinic divides shoes into four categories: maximum, moderate and mild motion control shoes with the fourth category being neutral/cushion shoes. Even with neutral/cushion shoes, we recommend shoes that have stable midfoot portions as reflected in the torsion and flexion tests. This simple categorization then allows us to assess a patient’s biomechanics and recommend a category of shoe most appropriate for his or her foot. This has consistently allowed us to make accurate recommendations that do in fact reduce injuries. Along the same lines, Knapp and co-workers matched appropriate high arched feet to appropriate shoes to reduce lower extremity and back injuries by 50 percent.7
What You Should Know About Lacing And Shoe Uppers
In addition, a look at the upper and lacing of shoes can help in treating and diagnosing foot problems. Running shoe uppers are typically made of mesh with synthetic leather for cosmetics and to reinforce high stress areas. The mesh provides breathability, which dissipates heat and transfers moisture, which can reduce the risk of blisters and fungal infections. The synthetic materials for cosmetics and reinforcements generally do not affect performance. However, the stitching for the reinforcements can cause ridges that irritate the fifth toe or fifth metatarsal head area.
The more common problem is that the reinforced or cosmetic material causes an irritation at the forefoot flex point in the shoe with secondary skin and sometimes joint irritation. We have been known to use a scalpel to cut out a layer of synthetic material to leave only the mesh so there is no irritation. Sometimes this is difficult to do to a $120 running shoe.
Finally, lacing irritation due to the tongue pad being too thin can cause irritation to the dorsal nerves. Changing the lacing by “skipping” this area, generally over the first metatarsocuneiform joint, or adding additional tongue padding will generally cure this nerve irritation.
Pertinent Pointers On Walking Shoes And Cross-Training Shoes
For a small sampling of shoes and brands we commonly recommend for the aforementioned categories we utilize, see “What You Can Recommend For Motion Control And Neutral/Cushion Shoes” below. Our complete list is much more comprehensive and lengthy than this article will allow. We then match the patient’s evaluated foot type to the appropriate shoe category.
Walking shoes. Typically, running shoes are the best recommendation for walking. Running shoes offer specific biomechanical categories, a complete range of shoe widths (AA to EEEE, depending on the brand), last shapes (straight, semi-straight, slightly curved and curved) and are readily available in most markets. One can utilize a more traditional walking shoe with a leather upper. However, there are no biomechanical categories to match different foot types and limited choices in last shapes to match foot shapes.
Cross-trainers. This shoe category has been weak in both its availability in various models and consistency in models from year to year. We almost exclusively recommend that patients use specific “tennis” shoe brands and models as opposed to shoes that are marketed as cross-training shoes. These shoes offer all the needed features of a cross trainer for jumping, side-to-side movement and cushioning that a traditional cross-trainer needs. However, tennis shoes also offer a great deal of consistency year-to-year, excellent durability (some with guarantees for length of wear) and up-to-date technology to meet the demands of amateur and professional tennis players.
Essential Insights On Rocker Bottom Shoes
Rocker bottom. Midfoot and/or forefoot rocker bottom shoes include negative heels or solid ankle cushion heel (SACH) heels. This new category of mass market shoes previously was only available through custom shoe modification.
The MBT® (Masai Group International) features a SACH heel concept with a midfoot and forefoot rocker bottom. This is the most well known rocker bottom shoe and is credited with starting this new wave of popular shoes.
Shape-ups® (Skechers) include a SACH heel concept that extends into the midfoot with a midfoot and forefoot rocker bottom. This provides more cushioning but is more unstable in the frontal plane. This shoe is the most heavily marketed and readily available at local stores.
Chung Shi shoes (Foot Solutions) feature a negative heel concept with a midfoot rocker bottom and less rigid forefoot rocker bottom. These are limited in their availability.
Cogent shoes (Cogent Motion) feature a negative heel concept with a midfoot rocker bottom and a less rigid forefoot rocker bottom. These are becoming more readily available but also have the greatest midfoot “flat spot,” which has offered some benefits for prolonged standing but sometimes less comfort with walking.
There are many other upcoming rocker bottom shoes with a new brand available almost monthly, making it difficult to keep up on the brands and availability at this time.
The primary medical indications for these styles of shoes are ankle arthritis, midfoot arthritis, hallux rigidus and chronic forefoot metatarsalgia. Contraindications or at least areas of significant concern are instability, diminished general proprioception (as in elderly patients), equinus or a history of Achilles tendinopathy.
When Patients Have To Stand For Prolonged Periods Of Time
Prolonged standing activities. Dansko® Professional Clogs (Dansko) have been the mainstay of shoes for prolonged standing. The unique last of this shoe redistributes load off the forefoot, into the arch and heel, with standing. As the patient walks, the stiff forefoot rocker decreases range of motion demands on the metatarsophalangeal joints. These shoes work well with hallux rigidus, midfoot arthritis, metatarsalgia, capsulitis and bunion pain. Contraindications or at least areas of significant concern are instability and diminished general proprioception (as in elderly patients). Patients would utilize these shoes primarily for prolonged standing and they can function better than any other shoe.
In Conclusion
Although podiatrists are experts in the foot and ankle, we cannot truly be experts unless we understand shoes. That understanding must include a basic knowledge of design features, specific technologies that have proven effective and at least a basic familiarity with selecting appropriate shoes to match a patient’s biomechanics and specific foot problem. Anything less than this will cause a partial and at times complete failure in the treatment of patients with foot, ankle and even knee-related problems.
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