Mysteries of the Running Shoe Revealed

Trail shoes are designed primarily for extra durability, traction and stability to handle the rough, uneven terrain of trails. While many basic training shoes cut weight by eliminating the durable outsole around the midfoot, trail shoes have a hard rubber outsole along the entire length of the shoe. Their treads have deep, toothy lugs to carry you safely through the mud of the great outdoors.

Unless you do almost all of your miles on trails, however, you may be better off using regular trainers. Trail shoes are not essential to trail running, and because there are far fewer models available than for training shoes, it may be more difficult to find a shoe that fits your biomechanical needs. If, however, you find yourself logging most of your running time out in the woods, you may be well served by picking up a pair of trail shoes.

What makes these things tick?

Every model of running shoe is designed for a specific type of foot. There are engineers who likely toil through the night doing God-knows-what just to build a shoe that will neutralize the flaws and imbalances in your specific foot type. The difficulty, of course, is figuring out which shoe is the one for you. The more you understand about how running shoes are constructed, the better you will know what to look for at the store. Herewith a quick primer on the anatomy of the running shoe. We'll start from the bottom up, literally.

Outer sole. The very bottom of the shoe. This is the shoe's first defense against the pounding you put it through -- literally where the rubber meets the road. The important features here are durability and traction. While the outer sole should be durable, be aware that harder soles tend to be heavier and have less cushion than softer ones. Ultimately the exact design of the treads are not terribly important. For all the variety in sole designs, from simple to outrageously complex, most have an equally good grip.

Midsole. The midsole is where the important stuff happens: the cushioning. Stuffed between the outersole and the foot bed, it is constructed of different kinds of foam, sometimes sharing space with capsules of air or gel to increase the cushioning. Obviously, the softer the midsole material, the more cushioning and the softer your ride. You can compare midsole softness among different shoes simply by squeezing the midsole with your thumb at both the heel and forefoot -- the greater the indentation, the softer the midsole. Keep in mind, however, that a soft midsole will compress and grow flat faster than a more rigid material.

Along with good cushioning, the midsole should also provide good stability and adequate flexibility in the forefoot, around the balls of your feet. These last two features, though, tend to fight each other. A soft midsole allows flexibility at the expense of stability. The key, of course, is to find the right balance for you.

Last. The last is the inside shape of the shoe, which is designed around a three-dimensional model. There are three basic shapes that the last might take: straight, curved, or semi-curved. When looking at a shoe from the bottom, a straight last is one that is symmetrical relative to a line drawn from the middle of the heel to the middle of the toe. A curved last curves markedly inward at the insole. The semi-curved last, as you might guess, splits the difference with a slight curve at the insole.

A curved last makes for a more comfortable ride for runners with rigid, high arches who need more shock absorption and foot movement. A straight last, on the other hand, has more material at the midsole, offering added support for runners with low, flexible arches or those who tend to over-pronate. The semi-curved last is good for those with a normal arch and neutral foot motion.

The way that the rest of the shoe is attached to the last is also important. The three techniques that are used are called slip lasting, board lasting and partial or combination lasting. In slip lasting, the upper materials of the shoe (the part that fits over the top of your foot) are pulled over the last and glued or stitched directly to the midsole. In board lasting, however,the upper is attached to the bottom of a flexible board atop the midsole. Partial or combination lasting uses the board method in the heel and the slip method in the forefoot. The way to tell what construction a shoe uses is to remove the shoe liner: if you see stitching, the shoe is slip-lasted; if you see a board and no stitching, the shoe is board-lasted.

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