The Right Time To Change Your Running Shoe

We’ve all heard of the recommendations by shoe companies and running stores about running shoes; when to replace and after 400-500 miles miles we should buy a new pair of running shoes to avoid injury. While most of the visible wear to a shoe occurs on the upper fabric and the “outsole,” the hard rubber bottom of a running shoe, the wear that most affects biomechanics occurs inside the midsole. The midsole is the thick layer of EVA foam that cushions impact and, in some cases, is designed to modulate your foot mechanics.

Many shoes have a “dual density midsole,” denoted by a gray block of denser foam under the arch. This medial wedge, as it is called in the shoe industry, is designed to resist pronation. While EVA foam is quite resilient, research shows that it still breaks down over the course of thousands of footstrikes.

Numbers wise, a good running shoe should last you between 400 and 600 miles, but your build, running style, surface and training load all factor in to what end of that range your shoes will fall. Smaller runners, or more efficient runners who are light on their feet, often won’t do as much damage to their shoe and a lot of times will be able to squeeze a little more mileage out of them. Bigger runners, or runners who pound the pavement with unforgiving force, will likely be at the lower end of the mileage range. Everyone’s different.

The Study and Research

In a fairly old study, Cook, Kester, and Brunet at Tulane University examined the degradation in mechanical shock absorption in a variety of different shoes. First, using a “running machine” which simulated the impact associated with running hundreds of miles in a pair of shoes, the researchers tested in a controlled way how the shock absorption changed over time. Then, they compared these artificially worn shoes to shoes worn by actual runners over an equivalent volume of running. 

In the machine-simulated running, shoes had decreased to 75% of their initial cushion after only 50 miles; this cushioning dropped to 67% after 150 miles and ultimately to 60% after 500 miles. The shoes worn by the real runners also declined in cushioning, following the same pattern of rapid decrease in cushion initially, tapering off and nearly leveling out at 500 miles of running. But when worn by real runners, the shoes only dropped to 80% of their initial cushioning.

In one of the few good studies on the subject, Kong, Candelaria, and Smith at the University of Texas at El Paso examined the changes in running mechanics after a group of 24 runners covered 200 miles over the course of their regular training.

The runners were split into three groups, each of which wore a different shoe—an air-cushioned shoe (Nike), a gel-cushioned shoe (ASICS), and a spring-cushioned shoe (Spira). The results highlight a few important findings. At the initial evaluation of running mechanics (before the 200 miles of training), there were no differences between the groups. There were only minor changes in running mechanics after the 200 miles of wear on the shoes and no changes in actual forces measured.


Warning Sign

Like any product used regularly, they will wear out eventually. How quickly this happens is determined by your mileage, body weight and foot type. Apart from keeping a mileage log, there are a few tell-tale signs to help you decide when to buy your next shoes: 

1. The outer sole has worn through to the white midsole

2. The midsole feels too soft and collapses easily under pressure. 
Press a thumb into the center of the shoe, where the midsole is. If the midsole feels tough and unyielding (rather than cushy with some "give"), then it may be time for a new pair.

3. The heel counter becomes mobile and less supportive

4. Your toes wear through the toe-box, and the shoe upper tears

5. One shoe sole becomes asymmetrically worn compared with the other

6. One or both shoes no longer stand up straight when placed on a flat surface

Otherwise, listen to your body. When the midsole of a shoe starts to break down it’s not supporting and protecting your foot, or the rest of your body, as well as it was when you first started running in it. How do you know when breakdown is occurring in a shoe? Easy. Your body will tell you. If you notice any mysterious new discomfort in your feet, legs, knees, hips or back, you probably need new shoes. Other indicators that your shoes are worn out are hot spots or blisters in unexpected places. That can mean your shoes have stretched and your feet are moving around too much.

Source:

https://runnersconnect.net
http://www.asics.com
http://running.competitor.com
http://greatist.com
https://www.rei.com

Run On!