Is there such a thing as a pressure blister? Well, friction blisters are in part caused by pressure, in so far as pressure contributes to friction force.
- STEP 1: Press the tip of your right index finger firmly 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 the “give” in the soft tissues – how your skin stretches back and forth? This is shear deformation.
Here’s The Relevance Of Pressure (N)
- STEP 3: Wobble back and forth again but this time press softly with your finger tip. Notice how there is less shear deformation. Low pressure allows your fingertip to slide across the skin before the shear distortion becomes excessive.
- STEP 4: Now press really hard and wobble back and forth. A high compression force sees your fingertip remain stuck to your hand for longer which causes larger shear distortions.
The Coefficient of Friction (μ)
The more slippery it is, the sooner there is slippage between your fingertip and back of your hand, resulting in smaller shear distortions. The opposite is also true – the more sticky it is, the longer the stationary contact between fingertip and hand, resulting in larger shear distortions.
Take Home Message
You can implement pressure reduction with donut pads made from moleskin or thicker felt, cushioned insoles and toe protectors, or with specific orthotic prescriptions and footwear feature. However, blister prevention is not just about reducing pressure. Don’t forget about the coefficient of friction – how slippery the two materials are. We often concentrate exclusively on pressure reduction. We shouldn’t. Ask yourself how you can make things more slippery by reducing the coefficient of friction.