With all of the shoe models available on the market today, it may seem a mission:impossible to find the right shoe for your needs so here are a few things to keep in mind the next time you find yourself confronted with an overwhelming shoe wall(hopefully ours!).
The outsole is the bottom of the shoe and and is made of various types and densities of rubber providing a range of durability and traction. If you find yourself consistently wearing through the outsole before the shoe's compressive(shock-absorbing) qualities are done look for a shoe with a higher density rubber in the outsole. Softer rubber provides greater traction(think climbing shoes as an extreme example of this) but is less durable whereas more dense(firmer) rubber is much more durable but stiffer.
The midsole is where the cushioning and stability properties of a shoe originate. Generally speaking, more cushioning equals less stability and vice-versa but there are shoes (the Asics GT-2150) for example that are constructed with a compromise between the two in mind. Midsoles are constructed using various densities of foam (polyurethane and EVA are examples), spongier for more cushioning and firmer for greater stability. Additionally, running shoe companies often have their own patented cushioning materials to complement the foam in high impact area such as the heel and forefoot. For example, Asics uses gel pods.
Running shoes are constructed using 3 different shapes(straight, curved, or semi-curved) and 3 different methods of attaching the top of the shoe(upper) to the bottom(slip, board, or combination). The shape and attachment method are collectively referred to as "lasts." You can determine the shape of the shoe by looking at its bottom. A straight last is symmetrical from heel to toe, a curved last curves inward toward the toes and a semi-curved last curves inward as well but in a less pronounced fashion. If you pronate excessively (this refers to the foot's arch collapsing and rolling inward) look for a shoe with a straight or semi-curved last. If you are looking for maximum cushioning a curved last is often the best.
Slip lasting shoe construction is where the upper is pulled over the last(shoe bottom/platform) and glued or stitched directly to the midsole. Board lasting refers to the upper being attached to the bottom of a flexible board that is then attached to the midsole. Combination lasting uses both techniques: slip lasting in the forefoot and board lasting in the rearfoot/heel. You can tell how a shoe is constructed by removing the inner liner/footbed: stiching down the middle represents slip lasting and stitching along the edges or no stitching at all represents board lasting. Generally speaking, neutral(biomechanically efficient) runners should seek a combination or slip lasted shoe, over-pronators should seek a board lasted shoe(board lasting makes the shoe stiffer and thus more stable) and supinators(foot rolls outward between footstrike and toe-off) should seek a slip-lasted shoe because any medial posting/support on the inside of the shoe or other stability features such as board lasts will tend to cause the foot to supinate even more.
The heel counter is the upper heel part of the shoe. A stiff heel counter will provide greater stability to the ankle and rearfoot and thus is ideal for over-pronators. A heel counter would be considered stiff if you can squeeze the material without the sides easily collapsing in and touching each other.
Finally, the upper(top of the shoe) is usually made with stretchy nylon or nylon mesh reinforced with stiffer overlays. A more open mesh will be highly breathable but may allow the finer grit/dirt to get in. A more closed mesh will do a better job of keeping grit out but will not be as breathable. An important thing to consider is where the overlays are located on the upper, especially if you have bunions, hammer toes or any spot prone to irritation. Choose a shoe where the overlays are not directly over the sensitive area(if you have one) to minimize irritation.
For those of you that do a mix of paved road and off-road running an important decision to make is whether to go with a road or trail shoe(ideally, you'll own a pair of each!). The main differences are the following(this is highly generalized as there are a variety of hybrid shoes on the market now that offer a decent compromise between road and trail use):
Road shoes are more cushioned as pavement tends to be way less forgiving than dirt in terms of impact forces translated through the body. Trail shoes tend to be a bit stiffer as this provides greater stability on uneven surfaces. The outsole on trail shoes is more agressively lugged for traction. The upper on a trail shoe is usually more reinforced for abrasion resistance and many trail shoes have a reinforced toe bumper guard to protect the feet from rocks, etc. And of least importance(at least it should be!), from a cosmetic standpoint trail shoes usually have darker-colored uppers.
If most of your off-road running is done on mellow dirt roads(both in terms of steepness and roughness of surface) a road shoe is probably the better choice. You will sacrifice some traction but will gain a smoother ride. If you're on steep and/or technical terrain a trail shoe's greater traction and stiffness will give you confidence in your ability to stay upright.
For comparison purposes, both Asics (GT-2150 & GT-2150 Trail) and Brooks (Adrenaline GTS 10 & Adrenaline ASR 6) make road and trail versions of the same shoe in which you can readily see and feel the differences between the 2 types.
So do you feel empowered to choose the right shoe for you? Hopefully this has helped. One key thing to remember is that these are merely guidelines, as we are all an "experiment of one." Everyone is different and just because the "science" of shoe-fitting says you need to wear Shoe X doesn't necessarily mean it will be the right shoe for you. However, educating yourself on what is available is a step in the right direction; and finding a shoe store staffed with people knowledgeable about the subject and willing to take the time to find the best shoe for your needs is yet another step...that's where we come in!
Happy Running(and Walking):)