Moisture on Your Feet – Moist, Very Wet or Very Dry

September 22, 2013 by · 1 Comment
Filed under: blister care, Foot Care, Health, Sports, Travel 

Back in May I posted an article about Training With Wet Feet. My being invited to work on the medical team at the Jungle Marathons in Vietnam and the Amazon prompted the article. While the Vietnam race had to be cancelled, the Amazon race is happening – in a bit over two weeks.

As I wrote in that article, it was long felt the best way to manage your feet was to keep them as dry as possible. This was more and more evident as Denise Jones and I worked the Badwater Ultramarathon in the heat of Death Valley each July. Runners who kept their feet dry typically finished better than those who had wet feet. This was also based on our experiences at Western States and other events.

Then came the invite to help at the Jungle Marathons.

The Jungle Marathons are run by Race Director Shirley Thompson and the Medical Team Manager is Vicky Kypta. They found their runners had a better race when they trained with wet feet. As part of their instructions to their race participants, they stress the importance of training with wet feet.

The reason for this is the Jungle Marathons are wet. Very wet is typical in the jungle. Whether through rivers or streams, the Amazon is full of water.

When I am helping runners at the race in early October, I will be closely monitoring the condition of their feet. I expect runners will use lubricants and other products to control the moisture, or powder, socks, well-draining shoes, and maybe a few home-grown tricks.

Over the past few months, I have shared some of the findings by Rebecca Rushton, a podiatrist from Australia. In her Blister Prevention Report, she talks about managing moisture control. She supports her report with studies from medical and other professional journals. What she found through the studies is that you could reduce the incidence of blisters by keeping the skin either very dry or very wet.

Rebecca writes that, “… the very high or very low skin moisture strategies aim to reduce the coefficient of friction value between the sock and the skin to below blister-causing levels.”

The Coefficient of Friction

The coefficient of friction (COF) is the number that represents the slipperiness or stickiness between two surfaces. According to studies, this number is generally below 1.0. Inside the shoe, the COF between the foot’s skin, and the sock and insole can range from 0.5 and 0.9. Compare this to the COF between a sock and a polished floor – about 0.2.

In Rushton’s report, she illustrates this with an example of a runner whose feet sweat a lot. His socks become damp, creating a moist condition. The COF in this case might be 0.7. By moving away from a moist condition to either very dry or very wet, the runner might reduce the COF to 0.5. If the runner’s blister-causing threshold is 0.6, getting to 0.5 will reduce his chances of blistering. Reducing the COF between your skin and socks/insole combination is important to having healthy feet.

Moist Skin

Moist skin produces higher friction than very dry or very wet skin. Whether skin is dry and becomes moist through sweat or through a water moisture source, or is very wet and becomes moist through heat or simply drying out, when it hits this middle stage, it becomes more susceptible to blistering.

Very Dry Skin

Drying the skin can be done with powders, antiperspirants or other drying agents, used by themselves or in conjunction with moisture control socks. Keeping the skin very dry is tough because our feet sweat naturally. Humid or hot conditions can also make it hard to keep the skin dry. Dumping water over your head to cool yourself can result in water running down your legs into your shoes – defeating your efforts to keep your feet dry. Airing your feet with shoes and socks off can help. If you use powders, make sure it is high quality and does not cake, which can be an irritant. When counting on any of these methods to keep your skin dry, you mush also have shoes that allow moisture to escape. That may include shoes with mesh uppers and drain holes in the arches and heels.

Very Wet Skin

Increasing skin moisture leads to very wet, lubricated skin that reduces the skin’s coefficient of friction. This can be through the use of a lubricant and or by simply having wet feet. The thing to remember is that over time, 1-3 hours, friction will increase as the lubricant is absorbed into the socks – so ongoing application is required.

Amazon Wet Foot

Amazon Wet Foot

Remember too what happens to your skin when you spend too much time in the water. It becomes weaker and less able to resist trauma on wrinkly skin. In extreme cases, the skin can fold over on itself and split. Severe maceration can be painful and athletes say it feel like a giant blister on the bottom of their feet.

In the Amazon Jungle Marathon, the trick will be to dry the feet at the end of each day’s stage. Because the feet will be wet during much of each day’s stage, the runners will have to find the balance between very dry and very wet, avoiding moist as much as possible.

Here’s some advice from my previous post about training with wet feet.

As said earlier, stop and deal with any hot spots as soon as you feel them. Check for folds in your socks, friction from dirt or sand, pressure inside your shoes – and get rid of these irritants. Lube the area or apply a piece of tape or blister prevention patch to help. This may seem like common sense, but many people ignore this simple step.

At the end of each day’s stage, remove your wet shoes and socks, dry your feet and air them as much as possible. If your feet have tape on them, remove the tape to dry the skin underneath. Wear sandals or Crocs around camp to keep your feet away from the wet ground and dirt and sand. Walking around barefoot will often aggravate wet, cold, and soft macerated skin. Later in the day or the next morning, re-tape your feet and patch any blisters.

Rest assured that I will write about how everyone’s feet held up in the wet Amazon jungle.

Credit is due to Rebecca Rushton for her Blister Prevention Report. Her website is Blister Prevention. Check out her website and sign up for her newsletter and free reports.

Here is the link to the Jungle Marathon Amazon.

If you want to read more, check out this article I did in November 2012 about Stuart Crispin who completed the race in Vibram FiveFingers.

More on Shear and Blister Treatments

August 26, 2013 by · Leave a Comment
Filed under: blister care, Foot Care, Footwear 

Back on June 17 I introduced the concept of shear with a post by podiatrist Rebecca Rushton from Australia who has studied blisters and identified shear as a major factor in blisters.

It’s best to start by refreshing our memories about what was shared on the previous article. Here’s the link in case you want to see the full post: An Introduction to Shear and Blister Formation. Otherwise, here’s a short piece from that post:

Poor blister prevention outcomes are due in no small part to the misunderstanding of the cause of this obstinate injury. The force that causes ‘friction’ blisters is not friction. And it’s not rubbing. It’s shear. But if you ask 100 people the question “what causes blisters”, nobody would answer “shear”. Shear is the sliding of layers across one another – internal layers that are structurally connected. Those connections can break and when fluid fills that cavity, you have a blister! What Does Shear Look Like?  Try this … Step 1: Place the tip of your right index finger on the back of your left hand. Step 2: 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. 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 your hand skin 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.

That’s shear.

Managing shear is key to managing blisters. Let’s look at several ways to reduce shear.

The first way is to make sure your footwear fits. Many people buy shoes that seem comfortable in the store but don’t make sure they feel ok by wearing them around the house for a few days. Make sure they have enough room in the toe box both in height and length. Make sure there is not undue pressure on soft tissues over any bony spots (sides of the forefoot, ball of the foot, sides and back of the heel, over the instep, etc.). Make sure they are not too loose, allowing too much movement leading to skin abrasions, hot spots, and then blisters.

Using a cushioning product is a second way to reduce shear. This might be a gel pad under the ball of the foot or under the heel bone, or a replacement insole meant to pad and cushion.

Applying power during an adventure race

Applying power during an adventure race

A third method is to manage skin moisture. This can include skin-drying strategies and skin lubrication. Studies have shown that you can reduce the incidence of blisters by keeping the skin either very dry or very wet. Drying the skin can be done with powder, benzoin, alcohol wipes, and antiperspirants. Lubricants can include SportSlick, BodyGlide, BlisterShield, and other popular products. Zinc oxide is also effective at controlling moisture. The method of having runners train with wet feet has been successfully used by Shirley Thompson and Vicky Kypta of the Jungle Marathon Amazon. They have found that the feet of their race participants have been better with this suggestion given to runners before the race.

The fourth method of controlling shear is with socks. This may include double layer socks or wearing two pairs of socks – a thin liner and usually, a thicker second sock. This allows movement between the two sock layers. Injinji toe socks are great for those with toe blister problems.

Next time, we’ll talk about  a fifth way to reduce shear – Engo Blister Prevention Patches.

In the mean time, check out ZombieRunner for many products that can help with cushioning, skin-drying and lubricants, and socks.

An Introduction to Shear and Blister Formation

June 17, 2013 by · 2 Comments
Filed under: blister care, Foot Care, Health, Sports 

This is a guest post by podiatrist Rebecca Rushton from Australia. She has looked at blisters, how they are formed, what causes them, and how to prevent them. For years, the common thinking about blister causes has been friction, heat, and moisture. Rebecca’s research has led her to identify shear as a leading cause of blisters. Read the article and then check out her website. Over the next months, Rebecca and I will take an in-depth look into blisters, their formation, and treatments. Her website Blister Prevention has a lot of valuable information on blisters (more on that at the end of this post). Here’s Rebecca’s article.

An Introduction to Shear and Blister Formation

Foot blisters continue to wreak havoc with endurance athletes’ feet in spite of their best preventative efforts.

Poor blister prevention outcomes are due in no small part to the misunderstanding of the cause of this obstinate injury.

The force that causes ‘friction’ blisters is not friction. And it’s not rubbing. It’s shear. But if you ask 100 people the question “what causes blisters”, nobody would answer “shear”.

Shear is the sliding of layers across one another – internal layers that are structurally connected. Those connections can break and when fluid fills that cavity, you have a blister!

What Does Shear Look Like?  Try this …

Step 1: Place the tip of your right index finger on the back of your left hand.

Step 2: 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.

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 your hand skin 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.

Rubbing Causes Abrasions

Most of us use the term rubbing to mean two surfaces moving across one another – like when you rub your hands together.  The type of skin injury that rubbing causes is abrasions. An abrasion is where the top layers of skin are rubbed off – you end up with a red raw sore. Blisters (from shear) and abrasions (from rubbing) are completely different entities – they have different mechanisms of injury and affect different layers of the skin. Here’s a video on blisters versus abrasions on the feet.

Is the distinction important? Yes it is. The lack of understanding of blister causation is at the heart of why foot blisters continue to plague athletes.

Achieving True Blister Prevention Success

There are 3 factors that influence shear. Impacting on these is how we can minimise shear and prevent blisters.

1) Type of skin

Thinner and more mobile skin (like we saw earlier on the back of the hand) will abrade before it blisters.  In contrast, thicker and less mobile skin (like on the palm of your hand) is the type of skin more likely to form and maintain a blister.  Do the same experiment we did before but with your index finger on your palm – the skin is noticeably thicker and less mobile in comparison. (This is why blisters are most common on the soles and palms)!

Apart from the thickness and mobility characteristics which determine the ability to blister (and which you can’t do an awful lot about), shear is influenced by two other factors: friction and bone movement. You need both, not just one, to create skin shear. The good news is that these things we really can change! Change one or more of these, in one of many ways, and you can successfully prevent foot blisters.

The cause and influencing factors of foot blisters

The cause and influencing factors of foot blisters

2) Friction

Friction is the force that resists the movement of one surface against another. It’s the degree of slip or grip between surfaces. Low friction (slippery) is when two surfaces glide easily against each other. High friction (sticky) is when the two surfaces tend to grip together.

The moist in-shoe environment during exercise causes high friction levels between the shoe, sock and skin. This causes these materials 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.

3) Bone Movement

Meanwhile, as we run the bones move back and forth. With the skin remaining stationary (for longer) and the bones moving back and forth as far as they can go, the soft tissue in between stretches – that’s what shear is.

This concept of friction and bone movement leading to shear is depicted in the diagram below and in this video demonstrating shear.

Orange = shoe | White = sock | Brown = skin | Purple = section of soft tissue undergoing shear
Orange = shoe | White = sock | Brown = skin | Purple = section of soft tissue undergoing shear

The purple area is a section soft tissue between the skin surface and its underlying bone. Although the heel itself has not lifted within the shoe due to high friction levels, the bone has moved up relative to the skin surface causing shear to the soft tissues in between.

About Rebecca

Rebecca’s website Blister Prevention has a lot of valuable tips and techniques, and information on blisters. Take some time and explore the site, subscribe to updates and receive a copy of her ebook, Blister Prevention for Active People. Rebecca is a podiatrist in Australia.

Next Up? More on Shear and Blister Treatments

Over the next month or two, we will talk more about shear and common blister treatments – including what works and doesn’t work. Make sure you are a subscriber to this blog to receive each post. You can do that at the box at the upper right side of this page.

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