A:There is no specific sign to tell that your shoes are no longer providing the proper amount of cushioning and support. The cushioning materials are usually ethylene vinyl acetate (EVA) or polyurethane (PU). These materials are both plastics that have a finite amount of "life" as shock absorbers.
The life span is shortened by exposure to ultraviolet light, ozone, heat, and repeated impacts. Impacts from running are further affected by your weight and the surfaces on which you run. The more weight or the harder the surface, the shorter the life of the shoe. Due to these factors, the life span is usually 300-500 miles. Remember to keep the above factors in mind when thinking about replacing shoes.
Changing your shoes before they are completely without cushioning and support will not cause any problems. Changing them after complete loss of cushioning and support can cause severe problems.
