Cath Lab Digest

Whether it is fielding patient questions about the emerging rocker bottom shoes or addressing irritation of the forefoot due to the cosmetic material of running shoes, being able to understand, evaluate and recommend athletic footwear is essential. Accordingly, this author reviews four key shoe components, discusses principles of effective motion control and offers insights on walking shoes, cross-trainers and rocker bottom shoes.

Modern athletic shoes have evolved since the founding of the first sports shoe store in the 1890s. The store was subsequently re-named Reebok in 1958. In 1917, the first popular “sneaker” brand Keds^® and the high top boot Converse All Star^® were introduced. By 1932, the Chuck Taylor name was added and the Converse All Star Chuck Taylor^® became a household name that remains popular today. Reportedly 60 percent of Americans have owned or own these shoes.¹ These key events and developments set the stage for modern athletic shoes.

   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.