Editor's note: A podiatrist and runner based in Akron, Ohio, Dr. Campitelli lectures on the topic of running injuries, shoes and running form. This past July, he gave a talk on his philosophy to the American Podiatric Medical Association, entitled, "Minimalist Shoes Versus Supportive Shoes: Focus on Form and Training Patterns, Not Footwear." His insight into transitioning into minimalistic shoes is featured in the upcoming book, Ready to Run: Unlocking Your Potential to Run Naturally.
Twenty years ago in 1994 when I was studying to become an athletic trainer the magic number for replacing a pair of running shoes was 300 to 500 miles. Four years later during medical school the information we were again being taught was that if runners were having any type of injuries or issues one of the first places we were to look were how many miles they had on their shoes. Anything in the range of 300 to 500 miles was considered old and needed replaced. Fast forward to 2014 and what we find is that nothing has changed in regards to how many miles you should accumulate on your shoes before tossing them. It has remained 300 to 500 miles. How can this be?
With all of the advancements in running shoes and technology how is it not possible that we can't find a shoe to last more than 300 to 500 miles? As crazy as this may sound, it's a territory that no one has revisited since 1985 when the paper written on how many miles a running shoe can obtain before breaking down.
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The change in shock absorption properties of running shoes was evaluated as a function of miles run. Different models of running shoes encompassing a wide range in retail price were obtained and mechanically tested to simulate the repeated heel strikes of running. The energy absorbed by the shoes was determined from the area under the load deformation curve at the equivalent of 0, 5, 10, 25, 50, 75, 100, 125, 150, 200, 250, 300, and 500 miles of running. Shoes were also tested at similar intervals after having been worn by volunteers during normal training.
An approximate 33 percent difference in the initial shock absorption was observed in the different shoe models. In general, the shoes retained approximately 75 percent of their initial shock absorption capability after 50 miles of simulated running, and approximately 67 percent after 100 to 150 miles. Between 250 and 500 miles the shoes retained less than 60 percent of their initial shock absorption capacity. No differences in shock absorption characteristics were apparent based upon either shoe price or the manufacturer model. The results of shoes tested by the volunteer runners also showed a marked reduction in shock absorption with mileage. The loss, however, was not as great as in the machine-simulated running, with approximately 70 percent of initial shock absorption retained at 500 miles.
Obviously the engineering and materials have improved over the past twenty years, so why hasn't the life span of a shoe increased ? Some say they have but the manufacturers refuse to publish the data on the absorption and breakdown process because customers would be requesting refunds claiming their shoes have "failed" too early.