Zero-drop, carbon-fibre plates, minimalist or maximalist – runners love to discuss and debate the latest shoe types and features. Far fewer long-run chats and online forums are dedicated to discussing running-shoe size. But how well a shoe matches the length, width and shape of your feet may actually matter as much, if not more than, as the cushioning that goes underneath them. ‘From a kinetic-chain standpoint, your foot is the first point of contact with the ground; your whole skeletal structure is supported by your feet,’ says exercise physiologist Allison Bowersock. Here’s how to find a shoe that fits – and what can go wrong when you wear one that doesn’t.
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How to find a running shoe that fits
Conventional wisdom holds that your running shoes should be about a size bigger than your usual size. There’s a grain of truth to that – increased blood flow and swelling during and after exercise do make your feet expand, so your running shoes tend to be larger. However, because of sizing variations in all types of shoes, there are too many variables to know exactly how the numbers will align, says Kevin Vincent, associate professor at the University of Florida, US, and director of theUF Running Medicine Clinic.
So, start with some hard data: if you haven’t had your feet measured since you were at school, go for a fitting. The length and width of your feet change because of factors such as ageing, injuries and pregnancy.
‘The size you wore when you were 18 might not be the same size you wear when you’re 42, just like you’re probably not wearing the same size trousers,’ says Geoffrey Gray, a physiotherapist, and the founder and director of research at footwear-testing company Heeluxe (heeluxe.com).
‘And that’s OK. But we need to get those measurements to know how to change it.’ In fact, he recommends getting measured once a year.
Ideally, you’d have this done at a specialist running shop. Trained salespeople have a feel for which brands run large or small and in which ways. Furthermore, trying on the shoe is the only way for you to know how comfortable it is. Go later in the day or after a run, when your feet are more swollen, says Vincent.
What happens when you wear the wrong-size running shoes?
If you wear shoes that are too short, your toes can butt up against the front. This, says Vincent, contributes to the bane of runners’ existence – black and missing toenails. This contact can also damage toe ligaments and the metatarsals, leading to deformities such as hammer toes, he says. Over time, you can also develop Freiberg’s infraction – a stress fracture of the second metatarsal – from repeated impact.
Plus, squeezing your toes together too tightly forces the muscles of your foot out of alignment, says Gray. As a result, you might feel foot fatigue and develop pain in your arches, or bunions.
At the front of your ankle, there’s a bundle of nerves, tendons and blood vessels, says Vincent. They’re secured by a tight band of tissue, but running shoes that fit too snugly can compress them, causing pain around the top of your foot or numbness and tingling throughout them.
Going too big, meanwhile, means your foot shifts around in your shoe. If a shoe doesn’t lock down over your navicular bone, your foot can move back and forth with each step. The rubbing of shifting shoes and bunching socks against skin creates blisters, says Vincent. Plus, you can end up with bruised toes and toenails this way, as your foot bangs into the front of the shoe with each slide, notes Gray.
Finally, if you’re wearing stability shoes that have a rigid medial post (a piece of EVA plastic in the midsole), getting the sizing wrong in either direction can alter where it falls on your instep. You may inadvertently put pressure on your plantar nerves, which run across the bottom of your feet, says Vincent. Constriction there can cause numbness, tingling, and pain on the bottom of your foot that can mimic conditions such as plantar fasciitis.
How often do runners wear the wrong-size shoe – and why?
About three-quarters of the people tested in Gray’s lab are wearing the wrong-size shoe, mostly too small. There’s no standard for what sizing numbers mean, says Gray, so sizing can be inconsistent between brands.
Sizes can also shift when a company releases a new version of a shoe. ‘Sometimes it doesn’t fit the same because the material changes or how they did the construction of the forefoot changes – and every time they change the forefoot, you can change the length of the shoe,’ says Vincent.
And then there’s the question of width. In general, our feet stay the same length but grow wider with time.
And women tend to have a greater differential in width between heel and forefoot, but are often squeezed into shoes that narrow near the toes for aesthetic reasons, says Vincent.
Shoes in wider widths are marked with letters, from B onward for women, or D onward for men. Meanwhile, a few brands – eg Altra – have wider toeboxes even in regular widths. That’s often better for conditions like bunions, where your forefoot needs more space.
Given all these variables, finding the right size in your ideal brand and model can take some fine-tuning. You might have to repeat the process each time you change shoes or your model gets an update. But it’s worth it for miles of comfortable and injury-free running.
How to make sure your running shoe fits right:
How to assess the size of a shoe:
- Take the insole out of the shoe and stand on it–it should match your foot. Your toes should not spill over the front or sides and the tip should come to a point roughly where your toes narrow.
- Put the insole back in and put the shoes on. Lace them tightly enough to lock the shoe over the top of your foot, but not so tightly that you constrict nerves. You should be able to slide a finger between knot and shoe.
- Stand up and check the feel and fit. You want about a thumbnail’s worth of width between your longest toe and the front of the shoe (your longest toe may be your second toe). As for width, check there’s little to no pressure on your little toe and only slight pressure on your big toe.
- Walk and, if possible, run. Check that your heel doesn’t slip and that nothing pinches or rubs against your ankle. Also, check the fabric of the upper –if it gathers, you might need a smaller size and if it bulges or stretches, you might need to go bigger.
- Don’t buy tight shoes, thinking you’ll break them in; they should fit well right from the start.
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