I’ve often heard runners say that they buy shoes that are slightly too big to allow for their feet to swell whilst running.
This idea of “sizing up” and buying a shoe that is half or maybe even a full size bigger than you would normally wear doesn’t quite make sense to me. Here’s why:
Firstly I’d question if your feet do actually swell during running. Whilst there is some evidence that over hydrating can cause feet swelling (link) and that oedema can occur during prolonged exercise such as ultra distance events, it isn’t guaranteed to happen to everyone. Secondly, even if they do swell, your feet will tend to get fatter rather than longer so to accommodate that what you actually need is a wider shoe rather than a larger one.
Lets take a hypothetical situation: A runner who normally wears a size 9 shoe decides to wear a size 10 for a long race. They hope that this will prevent painful feet by allowing their feet to swell. So, what happens during the first 4 or so hours of the race before their feet swell? They are running in a pair of shoes that is a size too big for them!
As humans we develop a complex sense called proprioception or kinesthesia which allows us to perceive movement and body position and is hugely important in controlling motor skills, such as running. Imagine if we have done all our training in a pair of size 9 shoes and our brain has sensed how if feels to run in these shoes, how to react to the myriad of stimuli and sensations of running in them. Then we go and try to race in a larger shoe. That hard wiring of the brain to know just how high to lift the foot to avoid tripping suddenly needs to be re learnt. For a while we are clumsy and have to think about how we are placing our feet rather than it being instinctive.
Have you ever noticed that you are much more likely to to trip, stumble or stub your toe towards the end of a long run when you are fatigued? It’s more likely to happen late into an ultra than it is on a 10k, even though you are running much more slowly. Fatigue, such as experienced towards the end of a long race affects both muscle function and proprioception, increasing the likelihood of tripping. Now add in running in shoes that are too big, it’s a perfect storm!
If you do experience foot swelling whilst running do you actually need a bigger shoe size or could you just loosen the laces? Maybe you just need a shoe that has a bit more room in the toe box? Or you could use a removable insole and take it out when your feet feel uncomfortable in order to give the shoe more volume.
We are individuals and it is important to find what works for you, but don’t just assume that you need to size up your shoes for your long runs. I did the Paddy Buckley Round on a very warm day. I wore the same pair of Inov-8 Roclites that I had worn both on long hill days and short, fast training runs. Once laced up I didn’t touch the laces again until I’d finished, not even to change my socks!