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When Should I Replace My Running Shoes?

September 28, 2017

 

This is one of the most common questions I hear from runners so it's fitting that it's also my first post.  Unfortunately, many runners don’t get around to asking me this question until it’s too late and they become injured, but hopefully you're here before that happens.

 

Let’s start with a basic recommendation before getting slightly more personalized.  The standard recommendation is to change your shoes every 400 to 600 miles.  This is due to the fact that over time, the foam which is used for cushioning and support starts to break down and lose its ability to absorb shock.  This may result in anywhere from a 30-50% loss in shock absorption ability over the course of 500 miles.  Consequently, this can potentially result in injuries from increased impact forces or compensations from the uneven loss of padding. For example, a loss of padding may result in increased forces on the heel or metatarsal bones of the ball of the foot depending on your foot structure, causing anything from stress fractures, plantar fasciitis, or even shin splints.

 

Another factor to consider is shoes may lose some of their shock absorption without even being worn.  Think of it as the foam getting stale and losing the ability to bounce back into its natural state as easily. This can happen over as little as a two to three year period of just sitting on the shelf.  It may be something you never noticed, and some people debate whether it actually happens at all, but it’s worth mentioning and I personally believe it's true.

 

I used to run in the exact same pair of New Balance running shoes.  I found two models of them I loved and so I’d buy them every time they were on sale.  I had amassed about 10 pairs in total, so by the time I got around to using them some were four years out of production. At first I didn’t notice any difference in quality or cushioning.  Every time I started wearing a new shoe It felt, well, new. They all felt springy and my legs and feet thanked me every time I switched to a new pair, regardless of the age.  One thing I did notice, however, was that they just didn’t seem to last as long as they did in the past, capping out at about 350 miles before they just felt flat to me.  When I finally bit the bullet and bought a newer model, things went back to normal for me and the shoes once again lasted about 450 miles.  In a way it’s sad, because I really do like finding a specific model of shoe I love and stockpiling them when they go on sale.  After all, running shoes are expensive, and finding that perfect fit can be almost impossible.  I still stockpile shoes, but I do so with the knowledge that they just aren’t going to last me quite as long as they do in their first one to two years of production.

 

Two of the exact same model of shoes.  One worn and the other brand new.  Note the thinning rubber and wrinkles in the foam from hundreds of miles of compression.

 

All of this information about shoe cushioning degrading and the number of miles a shoe can take needs to be taken with a grain of salt, as actually measuring these properties can be difficult. This is because there are a number of personal factors and shoe related factors that actually go into a shoe degrading.  For instance, How much force are you subjecting the shoe to?  Heavy runners or people who primarily run on hard concrete may notice that their shoes wear out more quickly than light runners who mix it up on trails and roads. For this reason, I recommend that runners who are heavier or run on hard surfaces should consider changing their shoes between 300 and 400 miles.  Conversely, trail runners may be able to extend the life of their shoes 500-700 miles.  It's always a good idea to avoid concrete as much as possible, as concrete is the hardest road surface and may degrade the shoe faster.

 

Taken further, it's also important to consider the type of shoe you’re wearing.  It has been my experience that mild stability shoes, or the more “maximalist shoes,” will last longer than a more traditional neutral or minimal shoe will. This is likely due to the shear volume of foam in the maximalist shoe, and the dense midfoot foam in the stability shoe. The rubber tread may also be a factor, as the density or thickness of the rubber can dictate how long a shoe might last.  At the very least, it gives information about where you are placing the most friction or pressure on the shoe, and which areas you should check in every shoe you wear.  Once that rubber is worn down to the foam it is absolutely time to change up shoes or risk injury.

Notice the complete loss of rubber in these two shoes. They are both long since dead. The distribution of loss is different here, as the left shoe is mine and the right my dad's.   He used to use hot glue on the areas of worn rubber to add some more mileage back into the shoe.  

 

The most important factor in shoe gear change has nothing to do with mileage, shoe type, or even weight.  The most important factor is how you feel.  One of the many benefits of running is how it puts you in tune with your body.  My experience has been that the more you run, and the more experience you have with switching out shoes, the more in tune you’ll be.  Shoes should make you feel faster and should add fluidity to your movement.  Noticing them is usually a sign that something is off. For me, when my shoe is “flat” and needs changing, I first start to feel as if the surface I’m running on is getting harder.  I notice every impact more, and my feet just don’t seem to recharge as quickly before my next run.  If I still continue to run on those shoes I’ll start feeling weaker, primarily in my feet and lower legs to the point that I feel slow on consecutive days despite running at the same effort and often even pace as I’ve been running at. Finally, If I still continue running on those shoes, I’ll start to get symptoms of shin splints or some mild tendonitis, the early signs of an overuse injury.

 

This is going to feel different for everyone, but the point is your body can feel the difference in a “flat” sneaker.  You just need to learn how to listen.  If you want to verify this, simply take a new pair of sneakers and run a mile in them.  Then grab an old pair with at least 400 miles on it and run a mile in those.  It shouldn’t be hard to tell the difference.  The trick is to be able to tell the difference over a gradual use of the same shoe, but this ability can absolutely be developed with time and a little guess and check.

 

With all of that information in mind, a couple of tips I have are to keep a running log, or use a running watch to log the number of miles you’ve run in a particular shoe. 400-600 miles can come up much quicker than you expect so you should keep track of roughly how many months a shoe will probably last you.  For instance, if you run 40 miles per week, then a shoe will likely last you between 2.5 and 4 months.  I often recommend runners to buy 2 pairs of whatever running shoes they really like using.  Alternating them daily or weekly can help extend the life of each shoe by giving the cushion adequate time to spring back after a run.  Finally, do not walk in your dedicated pair of running shoes.  I see patients who do this all the time and it drives me crazy.  Your dedicated running shoe should only be used for running, otherwise it can shorten its life.  With the cost of shoes these days, none of us want to lose potential weeks from a shoe.

 

Do you have any questions when to replace your running shoes? Are there other tips you'd like to add? Please feel free to comment.

 

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