Blister prevention 101

Blisters are a common problem for many marathon and ultramarathon runners. There are many ideas for how to prevent them, some of them old wives tales and some of them have a bit more credibility. But despite the use of every remedy known to mankind some of us still suffer blisters. Maybe our understanding of what causes them is incorrect and we need to try something different.

A new product caught my eye a few months ago and I contacted the distributor for more information. Rebecca from ENGO patches was kind enough to send me a sample for me to try. My feet callous on the outside of the big toe and during 100 mile races I sometimes end up with blisters underneath the callous. Its never got that bad to affect a race but can be quite painful at times.

When I received the patches I conducted a semi scientific experiment and placed one of the patches in my right shoe (you attach these to the shoe not your foot) and none in my left. After about 600ks the patch fell off so I took a look at my feet to see if there was any difference.

The result was a right foot that was significantly smoother where the callous used to be compared to the left foot. Not only did the patch prevent the callous from further developing it actually reduced the callous and therefore the risk of blistering.

Since it worked for me I thought I would share it with you. I would add that I receive no financial benefit from recommending these to you (apart from a free set of patches) and the only reason I am recommending them is I believe they are a great product that go beyond the usual tape it, lube it and hope for the best solutions.

I asked a few questions of Rebecca to get a better understanding of both the problem and the solution.

Q: In marathons and even more so in Ultramarathons blisters are common place and can have a big impact on an athlete’s race. What are the common causes of blisters?

A: You’re right Andy. The feet are susceptible to blisters because of the type of skin on the feet, the high friction conditions in the shoe and the function of the foot bones. It’s a combination of these 3 things. The more intense and the longer your run, the more the potential for these forces have a cumulative effect on the skin and the more likely it is you’ll suffer with foot blisters.

Q: Why do some runners suffer blisters and others don’t? Are there biomechanical issues that need to be addressed? Does it mean the shoes we are wearing are wrong?

A: Poor shoe selection and biomechanical issues can be relevant, but not always. Even in the absence of these factors, there’s actually a large individual variation in blister proneness. One study that comes to mind was done back in 1966 on American army personnel and it found that some participants got a blister after 3 minutes of a rubbing force, while others didn’t get a blister even after 50 minutes of that same force! Something similar was found in a research published from the UK earlier this year.

Q: It’s commonly thought that they are caused by friction between the foot and shoe and often made worse in hot or wet conditions. Is this true?

A: Partly. Heat and moisture are relevant as they increase friction levels. And as I mentioned, friction one part of blister causation.

It’s a fact that friction levels are lower in very dry or very wet conditions. But we have an in-between ‘moist’ situation when our feet are wrapped up in shoes and socks, especially marathon and ultramarathon situation. That’s why products like moisture-wicking socks, powders and antiperspirants attempt to keep the in-shoe environment dry, and lubricants aim to keep the in-shoe environment wet and lubricated. Each are attempting to avoid that in-between ‘moist’ environment.

By the way, a foot blister is not a thermal burn – that’s a common misconception. Research shows that skin temperature only increases to between 41-50 degrees Celsius with rubbing, and that’s not sufficient enough to cause a thermal burn.

Q: So if friction between shoe and foot isn’t the main cause then what is?

A: Foot blisters are caused by something called shear. Let me show you what shear looks like:
1) Place the tip of one finger on the back of your other hand.
2) Now wobble it back and forth but keep it stuck to the same bit of skin. Notice how your skin stretches? This is shear and this is what causes blisters.

Keep your finger moving back and forth. Shear might look like rubbing but it’s not. Notice how your finger tip has not moved relative to the skin of the back of your hand? But the skin on the back of your hand has moved relative to the underlying bone. This is shear. Your skin doesn’t need anything to rub over it for blisters to form. It just needs shear (this stretching of the internal tissue layers) to be excessive and repetitive enough to break the structural connections that join these tissue layers. When these connections break, fluid fills the cavity and you have a blister! So really, ‘friction’ blisters should be called ‘shear’ blisters!

Q: If ‘friction’ blisters are caused by shear how can we reduce shear enough to stop blisters?

A: Actually there are a lot of things you can do and they all centre around the 3 factors that contribute to shear: skin characteristics, friction and bone movement. Let me explain that further.

Blister Shear
The cause and influencing factors of foot blisters

Firstly, there is a small protective effect in conditioning the skin to the rigors of your running gear, the terrain and your running duration. It won’t be enough for many people but it can help.

Next is friction. Most people don’t quite understand how friction contributes to blisters and its one reason why blister remain a common injury. Friction is the force that resists the movement of one surface against another. High in-shoe friction levels cause surfaces to stick together … yes the shoe sticks to the sock, and the sock sticks to the skin, for longer. They all stick together for longer because of high friction.

Meanwhile, as we run, the bones move back and forth. With the skin remaining stationary (for longer because of high friction) the bones move back and forth as far as they can go making the skin in between stretch a lot. That’s what shear is.

I have a video that shows this for how blisters form at the back of the heel. It’s the exact same concept that we did with the finger on the back of the hand. It shows that although the heel itself does not lift within the shoe, the bone moves up and down. The soft tissues in between are made to stretch a lot … or should I say, shear a lot.

So getting back to what we can do to stop blisters: In regard to bone movement, you can either make biomechanical alterations (stretches, orthotics, shoe selection, altering running form). Or you can change the activity itself (the intensity, duration or frequency) to reduce shear. And when it comes to the friction side of the equation, there are many ways to have an impact. From lubricants to tapes, powders, antiperspirants, double socks, cushioning and pressure deflection. They all work at bit differently, some better than others and each has its pros and cons.

(For a great summary of blisters and the effective way to manage them see this interactive infographic)

Q: How do ENGO products differ to conventional approaches?

A: The biggest difference is ENGO Patches apply to the shoe rather than the skin. This negates the effect of sweat acting to loosen the patch. The other big difference is just how much it reduces friction levels and for how long. ENGO patches have a coefficient of friction (COF – the measure of friction) of 0.16. In-shoe materials have a COF of around 0.40-0.90. This low COF remains even in the presence of moisture. That’s a big thing. They’re thin enough that they make no difference to shoe-fit and they allow the targeted management of friction, which as a podiatrist, is just so important. Because not all friction is bad! Friction is needed to provide traction in the shoe and so needs to be managed discretely.

Q: Are they durable enough to survive the rigours of a long ultra or multiday stage race?

A: ENGO Patches are definitely long-lasting. You can expect around 500kms blister protection from each patch – there’s not many blister products that give you that level of protection in one application, but these do. The adhesive is strong enough to last that long and they don’t wear through even with multiday races. That’s thanks to the blue ENGO surface which is a high-tech material called polytetrafluoroethylene (PTFE).

But more than that, they’re just so convenient. Once they’re on, they’re on. There’s nothing extra you have to do on a daily basis before you head out, just get your shoes on and go. For me personally as an everyday ENGO user, this is the best thing about ENGO Patches. And endurance athletes feel the same. They’re the biggest users of ENGO because there’s no other activity where effective and long-lasting blister protection is more important.

Thanks Rebecca. If you are keen to try some ENGO patches go to the website
(I dont receive any commission or any other financial incentive if you do buy any)