Football boots Q&A, with Dr Katrine Okholm Kryger

What are some of the criteria that need to be considered when designing a football boot?

Designing a football boot is quite a holistic thing and you have to consider many different aspects. Obviously, you have to consider it from a performance perspective and a safety perspective – you want the player to perform optimally but you don’t want them to get injured. You also want the experience of wearing the football boot to be optimal – you want it to be comfortable, not too heavy, and it has to feel right on the foot. Those are the three key criteria that you focus on.

You then work around the interactions that the boot has. The interactions that the boot has with the player wearing it, which often comes through the comfort and the fit. It has to have optimal interactions with the surface, so there we look at traction and the stud design. It has to have an optimal interaction with the ball – that is mostly the upper that we’re thinking about there – so that is largely a question around the materials used to create the boot. And then thinking about potential interactions with other players is important as well, as there could be a safety hazard, not just in terms of the player wearing the boot but with other players as well. When there was a fashion of wearing bladed studs – long thin studs – we had quite a few nasty incidences where thighs and faces were lacerated.

Other than the effect of blades, how can the wrong footwear lead to injuries? What kinds of issues do you see when boots haven’t been designed properly?

It’s multi-factorial. You can talk about injuries from two perspectives: acute and overuse. Acute is a problem that happens on the spot, and often that is related to the traction of football boots and where studs get stuck in the ground. So that can result in ankle sprains, ACL injuries, really not nice things. Or it could be that the traction is too low and you slide and over-stretch a muscle.

At the same time, there are also overuse injuries, which are caused by the repetitive load on tissues. Where the tissues sort of give in, that might start an inflammatory response or you might see stress fractures of bones.

Specifically with football boots, if you have high pressure from studs placed under the first and fifth metatarsals or just below the toes – the small bones there – you occasionally see stress fractures in football players because the pressure is too high or the bending point is wrong. A football boot doesn’t just bend wherever you want it to bend, like a running shoe would which follows a foot’s naturally anatomy when you run; a football boot bends between the studs and if the studs are not based where the foot is meant to bend, it will bend over bone and that is not very nice. Another risk factor for stress fractures is poor fit generally, around things like the plantar fascia, the Achilles tendon and poor fitting around the heel.

I think the last area you want to think about in terms of injuries and football boot design is what I call ‘invisible injuries’: blisters and friction burns. These are all things that we don’t talk about because players still play with them, but do they play optimally when their foot aches every time they run because they have a blister? These injuries are not recorded anywhere because all of our epidemiological data is about what prevents you playing, but we need to understand that some injuries, like blisters, will probably decrease your performance ability. Again, that’s related to the fit of the boot – if it’s rubbing on your skin then you will get blisters and friction burns.

What can you do to make football boots fit better?

The foot is a complex shape. You can make boots fit better underneath by putting insoles in, but if your foot is simply too wide, there is very little you can do because it would have an overhang at the edge. You can’t simply fix a football boot to make it wider without redesigning the boot from the outset to make it fit that person’s foot.

When I was doing my PhD, I was working with a football boot manufacturer who showed me photos of an England international player at the time who was of West African descent. West African descent is often related to very wide feet compared to Caucasian male feet, which is what we traditionally shape football boots and most other shoes around. This player came in for his football boot fitting and said he was a size 12 or 13. But when we measured his feet, he was actually a size 8 – he’d needed a 12 or 13 to accommodate the width of his feet. So he’d been playing for England in a boot that was literally four or five sizes too big.

I was shown pictures where they had literally cut open the toe box of his boots and there was probably a five-centimetre gap between the end of his toes and the end of the football boot. Because he had such wide feet, he had never worn anything else. He had basically been running about in clown shoes.

Is it currently possible to make custom football boots?

Manufacturers can make custom shoes but the number of players with custom-made shoes – and by custom-made, I mean shoes that have been shaped specifically for their own foot – that’s really only happening with players you see in adverts. Even in a top Premier League men’s team, you’ll probably have only two, three or maybe four players with fully customised boots, the others will have maybe minor adjustments done to them.

Custom shoes are still very expensive – customisation might be the future where each pair will be unique to fit each player perfectly, but we’re not there yet, and especially not there for women. For women, it’s not just a question of fit; boots also have to be optimised to make optimal use of traction, optimal bending points, etc. So there is a lot more to consider before making perfect football boots for female players.

So what are the differences between men and women’s feet?

The beauty of feet is that every foot is unique but we can talk about the trends between the sexes – I’m certainly not saying every female foot is like this, or every male foot is like this, and of course the ethnicity issue is important for both men and women. But talking generally, the shape of women’s feet is different. We don’t have complete data on how it’s different, but I am working on that at the moment by doing 3D scans of elite female footballers’ feet to have a fuller understanding.

We do know things like the ratio of the toes to the foot length, to the area where the foot is meant to bend, will be different. We know the arch height is often higher in women. We know the heel is shaped differently, so irritation around the Achilles tendon is more likely to happen in women who play in men’s football boots.

Then we know that men and women move differently. We have different muscle masses, we have different power outputs, so the traction that we require to play optimally – the length of the studs, the shape of the studs, the number of studs – will vary between men and women. We don’t know what is optimal for women yet but we strongly question the idea that a soft ground football boot for men would be the optimal soft ground football boot for women. It’s still an area where we need more research, but I’m working on it.

How far along this journey are you?

We are at the stage where there is an acknowledgement that we need to know these things. We need to ensure that women are specifically considered when it comes to sports footwear and sports research. There are changes now that are slowly happening.

We actually just published a paper with the medical team from the England women’s football team, staff from three Women’s Super League teams, Leah Williamson who is captain of England, and some amazing researchers. This paper posed 10 questions about technology in women’s football and what we still need to address. It highlights where we are and what we still need to consider. At least people want to listen now and it’s not treated as a niche subject or something where there’s no money.

When I did my PhD, I worked on men’s football boots and I mentioned multiple times that maybe it would be worth considering women as well. People were very nice and said yes, it would be nice, but we’re not there yet, it’s a niche market – which is ironic because even then it was the biggest sport in the world for women. Today I’m invited to talk about this issue at conferences and people really want to listen and hear about the issue, and even change their way of thinking. That’s really amazing.

Are there any takeaway messages for podiatrists? Anything they should be thinking about or recommending when it comes to patients’ footwear?

First of all, my favourite thing to highlight is that comfort and fit are the priorities. Encourage patients to try out different boots and shoes based on comfort and fit. Football boots in particular are sold on performance marketing claims – you have speed boots, touch control boots, power boots – the marketing focuses on the type of player you are or, more likely, the type of player you want to be. My PhD research on men’s football highlighted that these claims, or the key design factors they put in boots to prove these performance claims, make no difference whatsoever.

The only study where I found a difference was around comfort. We took very lightweight footballs – speed boots – and made players run around in them for 90 minutes, and we could actually prove that they became slower in the last 20 or 30 minutes of the game because they were less comfortable. Therefore, in those boots, they couldn’t perform to the same standards over 90 minutes. So comfort is the priority always, and then fit is a little more difficult.

It’s also important to have a basic understanding of what’s out there. You need to know the main brands, the main designs that they offer, and the key differences are between them – some have a slightly wider toe box, for example.

Then it’s important to be critical about the stud designs and not just accept they may be good for soft ground for women players just because they are designed as soft ground boots for men. If players have come to a podiatrist, often they are returning from an injury, so we don’t want to overload players, especially if they have had an ankle strain or an ACL injury. If they are at a late stage of their rehab and coming back to play, maybe suggest that they use a boot with lower traction as a safer choice than going for the highest traction possible. That means, instead of a soft ground boot they might want to go for a firm ground outsole.

It’s about being a bit cautious. Soft ground boots will stop you faster but your body will then have to cope with that load going through it. If there is a little bit more give, the load will be less, meaning it will give their body more time to adapt, so it’s a safer choice I would say.

Dr Katrine Okholm Kryger is senior lecturer in sports rehabilitation at St Mary’s University and one of the world’s leading football boot experts