Running Shoe Components

With all the different features in running shoes today, reading a shoe's spec list can be extremely overwhelming. We hope that this article will help take some of the confusion out of those techy shoe descriptions and help you find the right shoe for your needs.

As the name suggests, the upper is the combination of materials that wrap around the top of the foot. It holds the foot in place and prevents excessive movement from side to side or up and down.

• Overlays – Synthetic materials that criss-cross the upper to provide support and reinforcement.
• Heel Counter – A rigid or semi-rigid device in the heel that keeps the foot in place.
• Collar – Foam padding surrounding the sides and rear of the shoe which helps hold the foot in place.
• Toe Box – The front portion of the upper that creates the space above and around the toes. This should be roomy enough to allow the foot to expand.

Typically made of rubber, the outsole is the bottom of the shoe. It provides traction and contributes to how soft or firm the shoe "rides" as well as its torsional rigidity and flexibility.

• Carbon Rubber – This durable rubber compound makes up the majority of running shoe outsoles.
• Blown Rubber – Air-injected rubber that is lighter, softer, and more flexible than traditional rubber. This is most commonly found in the forefoot. It provides a great feel but is less durable than carbon rubber.
• Outsole-Grade EVA – EVA foam that is designed for ground contact. It is lighter and more flexible than rubber, but it may be less durable over time.
• Shape – Outsoles range in shape from curved to straight. Curved shoes tend to be less stable, and are best for neutral runners and supinators, while more rigid, straight shoes are suited to overpronators.

Sitting between the upper and the outsole, the midsole is the part of the shoe that contains the cushioning and pronation control technologies. A shoe's midsole is typically made of plastic materials that feel and behave like foam or rubber. Midsole composition dictates the durability or longevity of the shoe, as well as the quality of the ride.

• Compression-Molded EVA – The most common insole material. EVA stands for "ethylene vinyl acetate," a combination of two types of plastics.
• Polyurethane – Another type of material that behaves like plastic or rubber and is used in midsoles. Polyurethane is not as commonly used as EVA because it tends to be heavier and firmer.
• Thermal Plastic Unit (TPU) – Thermal plastic is used in the bottom of the midsole at mid-foot to replace or support the midsole material. Thermal plastic units can also be used in the midsole to reduce overpronation.
• Durometer – Midsole resistance to indentation is indicated in durometers. The higher the durometer, the stiffer and more resilient the midsole.
• Cushioning Devices – Cushioning devices are placed in the heel and forefoot to absorb shock and resist compression. Each shoe manufacturer produces its own unique types of cushioning devices, but the function of these devices is similar across brands.
• Dual-Density or Multi-Density Midsole – A midsole that features two different densities of material is dual-density, and a midsole with more than two densities is multi-density. Shoes that are designed to prevent overpronation usually have dual- or multi-density midsoles.
• Medial Post – This is a device located on the medial, or inside, part of the shoe. A medial post is placed in a shoe to reduce overpronation. Medial posts are usually made out of plastic.

The last is how the upper is attached to the midsole. It is moulded to fit the volume and width of each particular size. There are three different types of lasts: slip, Strobel, and combination.

• Slip – The upper is wrapped around the bottom of the last, and the materials are stitched together down the middle.
• Strobel – The upper is attached to a thin material that is patterned on the shape or silhouette of the midsole. Traditional Strobel lasts use a thin cloth material, while newer variations use a sheet of EVA for a more cushioned feel.
• Combination – A traditional combination last attaches the upper to fiberboard in the rear of the shoe, while the front is either slip or Strobel lasted. Newer variations use an EVA sheet in the rear.