The Impact (Literally!) of Athletic Shoes

Running shoes should be replaced regularly to reduce your chances of injury. Many biomechanical problems can be corrected and running injuries prevented by the right pair of shoes. In fact, physical therapists and sports medicine physicians will look to the shoe for the source of running injuries from the knee down. The shock-absorbing capability of the shoe's midsole diminishes gradually and becomes inadequate after 350–500 miles. The number of miles depends on such factors as your weight, the training terrain, environmental conditions, and how light or heavy you are on your feet. Even if the upper part of the shoe does not show much wear, the shock-absorption quality may already be gone. If you are running approximately 20 miles per week, you should be replacing your shoes every 4–6 months, depending upon your shock-absorption needs. Use your runner's diary to note the condition of your running shoes. If you decide to change brands for any reason, you can track your comments as well as compare shoe performance.

Even if you are a careful runner, stretching consistently and not overextending yourself in your runs, you can incur injury from running in poorly designed shoes. By recognizing potential problems associated with faulty shoe design, you become a more discerning shoe buyer and ensure that the shoes you are wearing meet your biomechanical needs.

Shoes and Achilles Tendonitis

Shoes with inflexible soles cause the calf muscles to work harder and can contribute to the development of Achilles tendonitis, in which the Achilles tendon becomes inflamed. The mechanical reason for this is best explained by looking at the foot as a fulcrum-and-lever system. Shoes with inflexible soles make the lever arm (the foot) function over a longer distance and make the tip of the shoe the location of the fulcrum (the pivot point). Ideally, the shoe should flex at the point where the toes join the foot (which also happens to be the widest part of the shoe), offering more support. The shoes should also have a slight heel lift, which most running shoes do.

Shoes that have too much heel cushioning, including some air-cushioned models, can also contribute to Achilles tendonitis. After the heel strikes the ground, it continues moving as the shoe's cushioning continues to absorb shock. This continued motion can stretch a susceptible Achilles tendon excessively.

Shoes and Plantar Fasciitis

Running shoes that are too flexible in the midsole or that flex before the point at which the toes join the foot can both stretch the plantar fascia (the bowstring-like tissue on the sole of your foot) and contribute to excessive pronation in the foot. The resulting lack of stability occurs not just in the shoe's transverse plane (where the shoe actually flexes) but also in its longitudinal plane, thereby reducing the effectiveness of the shoe in controlling pronation.

Make sure you lace your shoes carefully before running. Too tight a shoe can make the tendons on the top of your foot sore or squeeze your metatarsals (long bones in the feet) too tightly. This in turn can result in feelings of numbness and/or tingling in your feet, particularly on long training runs. Too loose a shoe can make your foot less stable, resulting in excessive pronation and increasing the possibility of blisters.

Tips for Buying and Wearing Shoes

A shoe's midsole degrades from use. Given the lifespan of a running shoe, if you are running about 20 miles a week, you should consider changing shoes at weeks 20–25. Although the shoes are no longer good for running, they can still serve as casual wear for walking and for working in the yard. You can extend the life of your shoes somewhat by rotating back and forth between two pairs, so one same pair of shoes is not getting all the wear every time you run.

When assessing the condition of your running shoes, realize that even a new-looking shoe might lack adequate shock absorption. Use the 350- to 500-mile guideline instead of trying to guess how worn your shoes should look. Some runners mark the date they begin wearing the shoes in permanent marker somewhere on the shoe so they at least know how old the shoes are. You may want to track the mileage on your running shoes in your running log, too.

When buying your running shoes, make sure there is about a thumb's width between your toe and the front of the shoe. This helps prevent runner's (black) toe and/or losing your toenails. The shape and depth of the front of the shoe also affects these problems. When purchasing minimalist shoes, fit the shoe to your longest toe (which may not be your big toe).

Shoes have a shelf life. They lose about 100 miles of life per year in the closet even if they are never worn. For this reason, be careful of buying discount running shoes online. They may be selling “old” shoes that come to you with a reduced lifespan. Also, be wary of “running” shoes that are sold at department stores and retailers for $29.99, $39.99, and $49.99. Even if they are made by a major running shoe company, these sneakers are not real running shoes. Your best bet is to visit your local running shoe store and be fitted with a proper pair of running shoes. Plan on spending at least $100.

Don't even dream of running a marathon in a new pair of shoes. Your shoes should have at least 70 miles logged on them (including one long training run of 20 miles or longer) to be broken in well enough to run a marathon.

Guide to Shoes and Foot-Related Problems

The following list indicates appropriate shoe designs for certain foot conditions:

  • Low arch: This condition may need support if you are an overpronator, so choose a stable shoe with good rear foot control.

  • High arch: This foot may need more shock-absorption qualities in a shoe.

  • Normal foot: This foot is ideal. You can avoid motion-control shoes and heavier shoes. This is a good foot for minimalist shoes.

  • Post-stress fracture: Plan on replacing your shoes frequently (perhaps sooner than every 350–500 miles). Buy shoes with adequate shock absorption. You may need to make changes to your running form, training, or running surface as well.

  • Achilles tendonitis: Tendonitis necessitates avoiding air soles, excessively spongy heels, and stiff-soled shoes.

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