Advice

Running Shoe Components / Glossary

Running shoes are the most important piece of equipment that a runners has. They help prevent injury and they may help the running gait be more efficient. The running shoe market is huge and most of the running shoe companies make significant investment into the technology and science of running shoes. Therefore we thought we would provide you with some bed-time reading regarding the components that make up running shoes.

Running shoes are made from a combination of materials. The sole has three layers: insole, midsole, and outsole. The insole is a thin layer of man-made ethylene vinyl acetate (EVA). The components of the midsole, which provides the bulk of the cushioning, will vary among manufacturers. Generally it consists of polyurethane surrounding another material such as gel or liquid silicone, or polyurethane foam given a special brand name by the manufacturer. In some cases the polyurethane may surround capsules of compressed air. Outsoles are usually made of carbon rubber, which is hard, or blown rubber, a softer type, although manufacturers use an assortment of materials to produce different textures on the outsole.

The rest of the covering (the Upper) is usually a synthetic material such as artificial suede or a nylon weave with plastic slabs or boards supporting the shape. There may be a leather overlay or nylon overlay with leather attachments. Cloth is usually limited to the laces fitted through plastic eyelets, and nails have given way to an adhesive known as cement lasting that bonds the various components together.

As its name suggests, the upper is the combination of materials that wrap around the top of the foot. The upper consists of:

• Overlays-Synthetic materials that criss-cross the upper, and provide support and/or reinforcement.
• Heel Counter-Rigid or semi-rigid device in the heel that holds the foot in place.
• Collar-Foam padding that surrounds the sides and rear of the shoe, and helps hold the foot in place.
• Toe-box-Front portion of the upper that creates the space above and around the toes. Running shoe toe boxes should be roomy to allow the foot to expand.
• Last-The last is how the upper is attached to the midsole. The last is molded to fit the volume and width of each particular size. There are three different types of lasts: slip, strobel and combination.

The 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. Cushioning and pronation control technologies are located in the midsole.

• 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.
• Durometer-Midsole resistance to indentation is indicated in durometers. The higher the durometer, the stiffer and more resiliant the midsole.
• Cushioning devices-Cushioning devices are placed in the heel and forefoot to absorb shock and resist compression. Each shoe manufacturer produces their own unique types of cushioning devices, but the function of these devices is similar across brands.
• Dual-or multi-density midsole-A midsole that has two different densities of material is dual-density and a midsole with more thann two densities is multi-density. Shoes that are designed to prevent over-pronation usually have dual-or multi-density midsoles.
• Medial Post-A device located on the medial, or inside, part of the shoe. A medial post is placed in a shoe to reduce over-pronation. Medial posts are usually made out of plastic.
• Thermal Plastic Unit-Used to replace or support the midsole material. Most often, thermal plastic is used in the bottom of the midsole at the mid-foot. Thermal plastic units can also be used in the midsole to reduce over-pronation.

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

• Carbon Rubber-Durable rubber compound that makes up the majority of running shoe outsoles.
• Blown Rubber-Air-injected rubber that is lighter, softer and more flexible than traditional rubber. Blown rubber is most often found in the forefoot. It provides a great feel but is less durable than carbon rubber.

Blown rubber is a type of outsole common to many running shoes. Blown rubber is a rubber compound which is either expanded or mixed with air in the production process to produce a relatively light, cushier outsole-although it's less durable than carbon rubber. Many outsoles use a combination of blown rubber in the midfoot and forefoot (for a cushy ride) with carbon rubber in the rearfoot for added durability.

Carbon rubber is the other most common outsole. It is a solid rubber with carbon added to increase the durability of the outsole. A carbon rubber outsole is firmer and heavier than blown rubber but more durable.

EVA is the acronym for ethylene vinyl acetate which is the most common commercially manufactured midsole foam used in running shoes. It is sometimes referred to as CMEVA or compression-molded EVA. Every manufacturer uses EVA in at least some of its running shoes although some proprietary types of EVA are also used under different names such as Nike's Phylon and Brooks' Substance 257.

Flex grooves are an important feature. They are notches (or grooves) sliced into the outsole in the forefoot for better flexibility at toeoff. Almost all high quality running shoes use flex grooves that allow the foot to roll more naturally at toe off.

Heel counter is a plastic cup built within the upper which cups the heel to reduce excessive rearfoot motion. The heel should fit snugly without being too tight. If it's too wide, the heel will slip in and out of the shoe and cause blisters. Women, in particular, often have narrower heels than men and require a narrow heel counter, common in some brands such as Saucony.

Heel heights are the height at which the foot sits on top of the midsole and outsole. Heel heights vary from shoe to shoe and brand to brand but generally, a bigger, slower runner (especially a heel striker) wants more midsole foam for better cushioning which means a greater (or higher) heel height. Faster, efficient runners tend to strike more in the midfoot or even forefoot and usually prefer a lower heel height. A lower heel height promotes stability, but a higher heel height adds cushioning and takes some of the strain off the Achilles and calf muscles. Training shoes have the highest heel heights; racing shoes the lowest.

Last is a term you might hear in the shoe store and it is very confusing because it can refer to two entirely different things. The most important reference is to the shape of the shoe. A last is a shaped piece of wood or metal on which the shoe is actually built. Different shoes use different lasts (especially different brands) which is why shoes fit differently. Basically, there are three shapes: straight, semi-curved and curved. Semi-curved is-by far-the most popular and most runners do well in a semi-curved lasted shoe. A straight-lasted shoe offers the most medial support but there are only a handful of shoes built on a straight last. A curved lasted shoe is rare for a training shoe, but most racing shoes are built on a curved last which is indicative of a highly responsive, fast shoe.

Last can also refer to how a shoe is lasted or how the upper is attached (sewn actually) to the midsole. There are three ways: combination-lasted, slip-lasted or board-lasted. A slip-lasted shoe is entirely stitched; combination lasted shoe is stitched in the forefoot and glued in the rearfoot with a fiberboard and a board-lasted shoe has a fiberboard glued on top of the midsole. Slip-lasting is the most common although some brands-notably Asics-combination last many of its shoes. Some runners believe a combination-lasted shoe is the most stable and most supportive for orthotics but it is really personal preference. (Board-lasted shoes have gone the way of the dinosaur.) To determine which type of lasting the shoe has, remove the insole. If there's stitching in the rearfoot, it's slip-lasted. If there's a fiberboard (a cardboard-like material) on top of the midsole and stitching in the forefoot, it's combination-lasted. When in doubt, ask.

Lateral is in reference to the outer edge of a shoe orr the side of the shoe opposite the arch.

Medial side is the opposite of the lateral side. It's the arch side (or inner) of the shoe. The medial side is the side of the shoe where most of the motion-control or stability devices are located.