Q: I have been running for about two years and am happy to say I have so far avoided any serious issues. But I have noticed recently a bit of pain in my ankles and have been told it could be because my trainers need changing. The trainers look ok but the advice I was given was if you have run over 250 miles you should change your shoes. Other websites say 500 miles, so I am a little reluctant to buy another pair yet. Is there a guide for knowing when it’s time to change trainers?
A: This is a very common question I hear in clinic. Although the figure thrown around tends to rest in the 250-500 mile area, there are other factors to take into consideration that could extend/reduce the life of your favourite trainers. This helps explain how one runner may get many more miles out of the same pair of shoes than another runner. Let’s take a look at three of these factors: how much you weigh, where you run and how you run.
Despite the temptation to judge a shoe’s age by the state of its ‘upper’ (the fabric part that secures the shoe to your foot) or by wearing on the outsole (bottom of the shoe), the part of the running shoe most likely to start letting you down once you have reached a certain number of miles is the ‘midsole’, i.e. the area between the upper and the outsole. In most running shoes, the midsoles are made of a foam called Ethyl Vinyl Acetate (EVA), and it is within this foam that you find the cushioning and/or stability elements of the shoe. Some manufacturers add extra elements to the foam like air or gel, but research has yet to show whether this makes much difference.
Although EVA foam is resilient, it does start to break down after a certain amount of footstrikes, and the heavier the footstrike the quicker the break down. Studies show that for runners tested, 500 miles of running reduced the original level of cushioning by 20%. Whether this drop in cushioning is enough to cause pain and/or injury seems to depend on the individual, as research also shows us that the body uses a system of constant sensory feedback with every step we take, and when faced with changes in landing forces makes natural adjustments in the way we run in order to keep the impact forces consistent. The question is, can your body handle these adjustments? If the tissues in your legs can handle the changes in tension and load then you may well be able to last for longer with the less cushioned midsole. If you can’t then chances are you will find out about it by starting to experience some out of the ordinary niggles. Extra body weight is likely to make the task trickier, as well as potentially lead to a quicker compression of the midsole and loss of cushioning. So, if making your shoes last longer is a priority, it makes sense to get that body weight down to a sensible level, even if that means a few sessions of non-impact cross training (cycling, swimming, rowing, etc).
And so we come to where you run; the type of surface you run on can play a big part in how long a shoe will last. This is where choosing the right shoe for the right job can go a long way. Trail shoes will last well on off road tracks and mud but not so well on hard tarmac; road shoes are designed to endure the repetitive nature of road running but will soon start collapsing if forced to endure the multi terrain demands of off-road running. Extreme temperatures can also affect the integrity of the midsole. Very cold weather (running in snow/ice) can make the midsole become brittle; very hot weather can make the midsole become soft and less responsive.
The last thing we will consider is running form. Running is all about the distance you manage to cover when both feet are off the ground, known as ‘flight time’. It makes sense that whilst you are in the air, you are not wearing down your shoes. Increasing flight time is what helps you cover more ground quicker and is achieved by developing good running form. Whereas coaching sessions used to be regarded as something only for faster runners, having a professional take a look at your running form is a good idea for any level of runner, and may even help your shoes last a little longer!
As always check the niggles you are experiencing are not linked to any sudden change in your running frequency, intensity or duration. If there has been no such change and your shoes have completed 300+ miles, it could be time to buy a new pair, even if the exterior of the shoe seems fine. One piece of advice I will leave you with is make sure you break in the new pair gently, even if they are exactly the same brand and model. There may be slight factory differences that your body could want to get used to gradually. Rotate your old and new shoes for a few runs and listen to your body to see if things start feeling better.
Matt Phillips is a Running Injury Specialist & Video Gait Analyst at StrideUK & Studio57clinic in Sussex. Follow Matt on Twitter: @sportinjurymatt