In a continuing collaboration with Scott over at Straight to the Bar, we will be writing about the technology of fitness equipment throughout the month of July. This week I would like to discuss the most important technology that a runner will deal with: running shoes.

• Why do runners buy shoes specifically for running?

  Running shoes and shoes that are made specifically for different sports such as basketball or cycling tend to have different shapes that cater to the specific activity that they are made for. Different types of motion put different stresses on your foot and ankles, and these are accounted for in the design of specific shoes.

  For example, cycling shoes tend to have a rigid bottom that is not particularly comfortable to walk around in but provide for a much more efficient transfer of energy from the foot to the pedal. Basketball shoes provide support for the ankle to account for making hard cuts and frequent jumping.

  While not always 100% necessary, getting a shoe for a specific sport can provide performance and/or safety benefits. Even amongst just running shoes, there are 8 categories of running shoes depending upon the type of running that you plan on doing.

• Why don’t runners walk around in their running shoes all day?

  Just like tennis is different from basketball, running and walking are very different activities from a physiological standpoint. Shoes that are designed for each activity try to minimize the stress of each activity and provide the most comfort at the same time.

  Wearing your running shoes while you walk or your walking shoes while you run can lead to discomfort and can drastically shorten the lifespan of your shoes.

• What is the difference between walking and running?

  When humans walk, they tend to push off to the side with their feet and sway back and forth. Walking is a way of controlled falling, as you shift your center of gravity over the leg that is going to support your body. The motion of your foot as you walk is a slow roll onto your toes.

  Running tends to keep your center of gravity more or less central to your torso as you swing your legs along beneath you. This is more energy efficient than walking, but increases the impact when your feet hit the ground. Running causes pronation, which results from your foot striking on the outside of your heel and then rolling towards the inside of your foot.

• What is most important when choosing a running shoe?

  Running shoes were originally made of leather. They did not begin to incorporate rubber until after sneakers started to become popular because the rubber was too soft and would wear away too fast for a serious athlete.

  Adi Dassler (the founder of Adidas) created the first lightweight running shoes in the 1930s, but it was not until the 1960’s that New Balance began putting a rubber wedge between the sole of the shoe and the upper portion to raise the heel and minimize the stress on the Achilles tendon. Bill Bowerman began making shoes for his runners by using a nylon upper and a sole created by pouring polyurethane into his wife’s waffle iron.

  The secret to the success of Bowerman’s shoes were the midsole that he put into the shoes to provide extra cushioning. The midsole provides protection from being able to feel sharp or hard objects that the runner steps on, and absorbs the majority of the impact that is the trade-off for a more energy efficient form of movement than walking. The midsole also provides rebound for the foot to make the next step a little easier. By fiddling with the density of the midsole in different areas of the shoe, and by contouring the foot bed, manufacturers design shoes that fit runners of different sizes and gaits.

• What are midsoles made of?

  Most midsoles are made of EVA, polyurethane, or a combination of the two.

  EVA makes a great cushioning material and is very light and very flexible, but it tends to lose some of its rebound and resilience and becomes “compression set.” That is one of the major reasons that you should always rotate your running shoes between runs.

  Polyurethane is very strong and lasts a lot longer, but it is heavy and has less rebound than EVA. Shoes with an all polyurethane midsole are almost guaranteed to last a long time, both because of their resilience and because they will probably not be worn as often as they are likely to be too heavy for most runners.

  Most companies combine the two materials by putting the polyurethane in areas of the midsole that are put under the most stress and using EVA elsewhere. Different mixtures are the biggest separating feature between one brand of shoes and the next. What is comfortable and works for one person is also quite likely to be uncomfortable for their neighbor, so each brand of shoes can potentially have plenty of market share.

• How do I best choose or take care of my running shoes?

  If you don’t know more about running shoes than you thought that you needed to by now, then you can look through my list of shoe care tips that was published on this site about a year ago.

• What is the shelf life for running shoes?

  Shoes don’t last forever, but unless the shoes weren’t stored well (extreme heat/cold) then last year’s models will be fine. You should generally try not to purchase shoes that are more than a year old, because the mid-soles will harden and break down over time even when the shoes are not being used.

  If you do have shoes that are 3 or even 5 years old, you can probably still use them. Just be aware that you probably will not be able to run as many miles in them as you would on a pair of brand new shoes that just arrived at your local shoe store.

  It can be a delicate balance of cost-effectiveness if you want to purchase a model of shoe that you like while it is on sale and before the company tweaks it to the point that you don’t like it anymore. (Thanks to Tom in Maryland for the question.)

What have I missed? These are a few questions that I have seen floating around in various forums or that have been emailed to me or asked in person over the past few months. Is there anything else that you would like to know that was not covered by this article or by the list of tips that were previously published?

Feel free to email me or leave a comment with any thoughts or questions that you may still have.