E-14S Free Communication/Poster Shoes/Orthotics
In 1985 Cook demonstrated that running shoes lose significant shock-absorbing characteristics after 200 to 500 miles. Based on this study runners have typically changed shoes between 400–500 miles.
To determine the pattern of shock absorption attenuation of current running shoes.
Six of the most popular, highest ranked shock absorption (cushioning) running shoes were selected from recent reviews in Runner's World magazine and Consumer Reports. A continuous impactor (CI), a motorized machine with two impacting heads that rotate in a reciprocal manner, was utilized to simulate sequential impact forces upon the footwear over a running distance of 600 miles. Intensity of impact was adjusted to simulate the impact delivered by a 70 kg person at heel strike. The frequency of impact (i.e. cadence) was set to simulate the typical cadence of a runner running at an average running speed of 7 miles/hour. An impact tester (IT), conforming to American Society for Testing and Materials standard F1614–99, was utilized to quantify the shock absorption and energy return for the shoes. Each shoe was tested at baseline and pre-determined interval distances.
The material properties of shock absorption and energy return changed in a linear manner over the test period. All shoes showed a decrease in shock absorption with increasing mileage, but each shoe performed differently (p = 0.02). In general, most shoes did not demonstrate any significant change in energy return with increasing mileage with two exceptions in which the energy return decreased significantly with increasing mileage (p = 0.03).
This was a mechanical test that allowed us to make equal comparisons across all shoes. However, there may be differences in field trials. Nonetheless, this study demonstrated that the shock absorption capacity for today's most popular cushioned running shoes does not change as is commonly believed. These findings will help provide appropriate counsel to athletes regarding the duration of footwear use.