The Running Shoe Mileage Myth

How many miles have these running shoes covered? 100 miles? 200? Would it surprise you to discover that they have just hit the 500 mile mark?  According to Runners World, I have reached the end of the road with these shoes and need to be replacing them in order to optimise performance and avoid running injury. 500 miles  as a maximum is an oft quoted figure that gets pulled out of the air regularly to suggest that the time is right to change trainers.  Some people even suggest that 300 miles is the point at which you should change. But, is there any science behind this figure? And, more importantly, am I putting my health at risk by continuing to run in these shoes?

The shoes in question are adidas Ultraboost Light. part of the Ultraboost family of trainers. I’ve been running in these shoes for almost a year (my first impressions can be read here) and they have become my “go to” shoe for long runs and triathlons (Mid-term review here). In particular, I like the knitted upper which, though quite a heavy knit, gives a firm yet comfortable fit that does not allow your foot to move about. This does mean that the shoes can feel a little snug out of the box and the knit takes a little while to relax to your foot. My recommended half-size above your normal shoe size is based on my preference for quite thin running socks. If you prefer a thick running sock then you may well want to go up a full shoe size. I also like the 10mm heel drop (the heel is 10mm higher than the toe). This helps protect the achilles tendon – an area where I’ve been prone to injury in the past. In short, these shoes, with their neutral support and light midsole, seem to be built for a runner like me. So, the question is, should these be confined to dog walking, and should I be shelling out £170 on a new pair?

An inspection of the shoe tells me that the upper is still in excellent condition. While it may have relaxed a little to accommodate my foot shape, the knit still holds my foot firmly and I notice no movement when running. Now looking at the Continental rubber shod sole, I can see a little evidence of wear on the outer rear heel of each shoe. This would confirm that, like most runners, I have a natural mild pronation from outside of heel to inside of toe when I run. It’s not marked, and as a result, I don’t feel the need for a more supportive shoe to control excessive pronation. I imagine that anyone who pronates to a larger degree would experience much higher wear on the outside of the heel than I do.

With age and high mileage, it is said that the midsole no longer provides the cushioning that you need to prevent injury. This is cited as the main reason that shoes need replacing on a regular basis. Again, looking at the Lightboost midsole on these shoes, I see no evidence of crushing or squashing and I certainly don’t think I can feel any difference  to the foot strike than when they were new. Obviously, any change in perceived cushioning is likely to be imperceptibly gradual and I could only really confirm that the cushioning was no longer up to snuff by comparing them directly with a new pair. These shoes are at a premium price (£170) and as such, I would expect them to be made of premium materials and built to last. My visual inspection of them suggests that they are still in excellent condition.

Almost all of the miles that I have run in these shoes has been on tarmac. Whenever I venture on to gravel or hillside I’ll swap to my trail shoes. I’m also very good at keeping my shoes clean. These have been through the washing machine twice on a low temperature sports shoe wash (this is usually contrary to manufacturers recommendations, but I’ve never yet found an instance when putting a running shoe through the wash (low temp, slow spin, non-bio liquid) has damaged a shoe). I think keeping shoes clean looks after the uppers in particular and prevents the kind of abrasion damage that grit can do to uppers over time. Obviously, handwash if you prefer.

On the face of it, I see no obvious reason why I should retire these Ultraboost Lights any time soon. However, that seems to go against  industry recommendations. What if invisible midsole damage has been so gradual that I haven’t noticed it? Now that I’ve reached 500 miles, am I likely to injure myself through continued usage? As a triathlete, I know from years of bitter experience that I am far more likely to injure myself on a run than I am cycling or swimming. So, anything I can do to improve my chances of not getting injured would be a powerful incentive to act. Thus, if it could be proven scientifically that buying a new pair of trainers every 300 – 500 miles would lessen my chances of injury, then I would take that evidence very seriously indeed.

At this point, I would recommend anyone who wants to find out about running shoe mileage to read Damian Hall’s excellent book, “We Can’t Run Away From This“. Damian is a professional ultra-runner who has won the Montane Spine Race. He has also come tantalisingly close to finishing the notorious Barkley Marathons. In fact, he was there to witness Jasmin Paris’ epic and history making finish last week. In short, he runs an awful lot and needs to stay injury free in order to successfully make a living. Whatever his green credentials, it would not be in his interest to counter a running industry shoe mileage narrative if it exposed him to increased risk of injury.

In the section in the book entitled “The 300-mile myth” (pp 26-31), Damian tackles the issue head on. He reviews the scientific evidence. and concludes that there is no evidence that footwear causes injury. Indeed, there is some evidence to suggest that maximally cushioned shoes actually increase the impact load on the body and that by running in very old, less cushioned shoes, you may actually build resilience to injury. A 2020 review of the available published science by L Malisoux and D Theisen in the Journal of Athletic Training concluded starkly, “Footwear does not cause injury.”

It turns out that the prime causes for running injuries are things like sudden upping of mileage; being out of condition; having a high body mass index (bmi); sudden increases in intensity of training; hills; recurring previous injuries; and uneven or loose running surfaces. Shoes don’t figure. The idea that after 300 or 500 miles your running shoes are suddenly going to cause you injury is, thus, a myth.  It is a myth that is repeated often across the industry and it is obvious why this should be the case.

In a previous blog post I discussed the carbon footprint of a pair of running shoes (usually between 8kg and 16kg of CO2 per pair). In the great scheme of things, this is not a huge figure (until you scale up to the billions pairs of trainers sold each year and the realisation that virtually all of these are destined for landfill at end of life). My Ultraboosts have a significant content made from ocean plastic and recycled plastic which reduces their carbon footprint by 10% compared to the previous model made with non-recycled materials. 10% is better than nothing, and the use of some ocean plastic is much better than taking plastic bottles out of the recycling loop and spinning them into polyester.  But, I can do a lot better than 10% by not swapping my shoes for a new pair until they are properly worn out. Simply by deciding to double the mileage and aiming for at least 1000 miles out of these shoes (hopefully more) I can at least halve the carbon footprint of my running shoe consumption.

I’ll post again when these shoes hit the 1000 mile mark.

The author is a member of the adidas blogger community and is an accredited Carbon Literacy Trainer for the Speak Carbon Collective. Please get in touch if you are interested in Carbon Literacy training in your organisation: john@creativeblogs.net

Click here for adidas men’s running shoes

For more on sustainability at adidas visit: https://www.adidas.co.uk/sustainability

There are no affiliate links in this post. The trainers were provided as part of the adidas Blogger Community Program.