One of the most frequently asked questions from fitness instructors and participants is…how long should my shoes last? Obviously this will vary from one person to the next, but there are some general rules of thumb that do apply.
The midsole or material between the upper and the outersole is generally composed of pre-compressed foam called Compression Molded E.V.A. It is a very lightweight material that has excellent resilience (or the ability to absorb shock and return it to its original shape before the impact). Constant pounding compromises the resilience of the foam and its ability to attenuate shock.
The midsole also acts as a housing for such high tech materials as AIR, GEL, etc. Yet, often with so little of these celebrated impact absorbers in the shoe, they have a negligible effect on the life of the midsole.
Therefore, the long term cushioning responsibility falls on the foam. This compression set E.V.A. has a well documented lifeline of about 500 running/walking miles. After this amount of pounding, the foam “tires” and the resilience is significantly compromised to the point where the shoes feel like it “blew a tire”. Often, this “flat” is not obvious until you try on a new pair of shoes and realize immediately why your knees or arches have been acting up.
But “running miles” are a poor measuring cup for aerobic activity. So to try and create a gauge that was meaningful to fitness enthusiasts, I tracked a group of instructors who did a consistent number of high impact classes per week and who also felt their shoes were “finished” when various body parts began to cry out for help .
With this group of thirty or so instructors, we observed a consistent pattern of wear. Here are a few examples:
a) A person doing 8 classes per week felt their shoes were “dead” in 3 months.
b) A person doing 4 classes per week felt their shoes were “dead” within 6 months.
c) A person doing 2 classes per week felt their shoes were “dead” in 12 months.
So based on 500 miles worth of running wear, the reverse math meant that each class is equivalent to about 5 running miles worth of wear and tear.
Runners / Walkers can simply add up their mileage…ex. I run for 40 min. 3 times / week... That means 3 to 4 miles / 3 times a week x 4 weeks is approximately 45 miles / month…which allows you about 12 months to do 500 miles…give or take a few steps!!!!!
THOSE DOING “AEROBICS” NOTE THIS CHART
When comparing aerobic wear and tear with running miles, we need to keep in mind two important points:
1. With fitness and aerobic exercise, there is a great deal of lateral movement, which stretches the upper more than the linear activity of running. The upper therefore may get sloppy and lose support, further limiting the life of the shoe.
2. The impact in aerobics is concentrated on the forefoot area of the shoe. Running, on the other hand tends to spread the impact more evenly across the midsole.
Do not change your shoes based totally on this chart! Use the chart as a gauge, listen to your body and compare it with a new pair of the same shoes before you decide.