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.
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.
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.