The simple answer is you should replace your running shoes every 250 to 500 miles or every six months. But this is not always the case.
There are many factors that affect the life span of any shoe. Other than the obvious reasons such as worn, torn uppers and soles, one must consider other factors as well.
- Your weight, foot type and biomechanics (how your foot hits the inside of the shoe)
- How often and how long you are standing, walking and/or running and on what surface type
- The material of the shoe
- Weather conditions
Therefore, you can not completely rely on the looks of the shoe itself. It may not look worn on the outside, but the inside can be problematic. How? The part of the shoe to most likely wear down first is the midsole. The midsoles are typically made from Ethyl Vinyl Acetate (EVA) and nowadays, different types of foam. Both will eventually begin to break down after enough use. How fast it breaks down is highly dependent on the above mentioned factors.
When the midsole breaks down it can cause our bodies to automatically adjust or compensate for imbalances that can lead to pain and/or discomfort (” Overuse injury”). The midsole is the main reason most will say to replace the shoe every 250 to 500 miles. If you are heavier or a very hard foot slapping runner, you may want to stick with the lower number. Also keep in mind that extreme weather such as cold can also affect the responsiveness of the midsole.
VERY SIMPLE SHOE ANATOMY:
Where you run can also play a role in how long your running shoes will last.
If you have shoes designed for road running but run on trails, the torsions of trail running may break the shoe down faster. Therefore, it is best to use trail shoes for trails, road shoes for roads, etc.
Finally, running form can impact your running shoes. How much time you spend on the ground will vary among runners, thus affecting the surface contact. Therefore, the mileage varies among runners. If you are a forfoot striker (very bad for most foot types and yes it is proven that heel strike does not increase injuries) then the forfoot which is typically not as strong as the rearfoot will break down sooner.
If you notice unusual wear on certain parts of your shoe it may be a sign your biomechanics are off. A shoe insert or orthotic could help realign your body to prevent this uneven, excessive wear.
When you decide it is time for a new pair of shoes, remember to break into the new ones slowly. If possible wean into the new shoes for the first couple of runs to help your body readjust to the new pair. Also, it is best to not wear the same pair every day, allow a full day for the shoe to air out and dry- preferably with a shoe tree to preserve the shape. Rotating shoes will eventually lead to prolong shoe life.
In short, there are no set miles or time frame to replace your running shoes-or any shoe for that matter. Pay attention to not only the shoe, but your body. If you start feeling a discomfort it may be time to replace your running shoes.
Happy Running (and Walking)!
David J. Sables, D.P.M., C.Ped
ArchMasters-Orthotics, Shoes & Footcare, LLC