Photograph of back half of a running shoe showing midsole

John Sutton knows more about this area than I do. Not only his he an ultramarathon runner but he works in the area of ‘carbon literacy’ and sustainability. I’m also sure that he’s correct that the claims that you need to replace your running shoes after a certain number of miles is driven by marketing departments.

Still, I’ve definitely experienced creeping lower-back pain when getting to around 650 miles in a pair of running shoes. Of course, now I’m wondering whether it’s all psychosomatic…

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.

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.


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.

Source: Irontwit