{"id":2753,"date":"2023-10-04T18:14:20","date_gmt":"2023-10-04T07:14:20","guid":{"rendered":"https:\/\/pro.blister-prevention.com\/?p=2753"},"modified":"2023-10-04T18:58:37","modified_gmt":"2023-10-04T07:58:37","slug":"massage-and-foot-blisters","status":"publish","type":"post","link":"https:\/\/pro.blister-prevention.com\/office-hours\/massage-and-foot-blisters\/","title":{"rendered":"4 Things Massage Can Teach Us About Foot Blisters"},"content":{"rendered":"\n
Hi everyone, thanks for joining me for Blister Prevention Office Hours this month. It’s Rebecca Rushton here. Today, we’re going to talk about the four things we can learn about foot blisters from massage. We’re going to look at a few technical things, but I’m going to make this really not overly technical, because I’m not really that good at physics myself and I get lost in all of that talk. But my aim is to make this meaningful and accurate, but really easy to understand. So we’re going to have a look at things like shear, rubbing, friction, coefficient of friction. Plus four takeaways from this presentation, and the one big difference between massage and foot blisters, that is really important.<\/p>\n\n\n\n
So, first of all, where is shear in this picture? Is it in front of the thumbs, under the thumbs or behind the thumbs? If the masseuse was literally just pushing straight down, there would be no shear. All there would be is compression under the thumbs. But as soon as the thumbs start to move in one direction, let’s say they move upwards, then there will be shear deformation within the skin and the soft tissues under the thumbs and just back from the thumbs. The point I’m trying to make here is that this puckering of skin at the top, that’s not the important part, that’s not where shear is. It’s under and a little bit behind the thumbs.<\/p>\n\n\n\n
Next rubbing – a very benign term that on the surface of it doesn’t need any explanation. But in fact, it does. Because every single rub action can be divided into two separate parts. The first part where there’s no relative motion. And the second part where there is relative motion. When we think about rubbing, I dare say, most of us just think about the part where there is relative motion. And we forget about the first part. But you’re going to see in a moment that it\u2019s probably the first part that’s the most important when we’re talking about the magnitude of shear deformation. What would be really helpful is, instead of there just being the one word that describes both of these in combination, which is rubbing, is if we had a term that described the first part, and another term to describe the second part. Ideally these words would already be in most people’s vocabulary, so it would be easy to explain blisters and shear a lot more easily to our patients. The fact is, there are no such words. All we have is rubbing which is applied to the second part of the rubbing action – where there is relative motion, and nothing for the first part – where there has been deformation of the soft tissues, but no relative motion yet.<\/p>\n\n\n\n
So we’re going to have a look at this with the example of massage. Firstly, with no<\/span> oil, as the masseuse presses down and starts to move their thumbs forward, the thumbs get stuck on the skin. It’s hard to move them relative to the skin and the motion of the thumbs is confined to \u201cgive\u201d in the soft tissues. So there’s no relative motion<\/span> between the skin of the thumbs and the skin of the person’s back, but there is some sort of movement within the soft tissues under the skin. The degree of movement is determined by the “give” in the soft tissues, and that’s exactly what shear deformation is. So shear magnitudes are quite large in this situation, particularly if we are pressing down and forward hard, trying to get the thumbs to move. To get relative motion between the thumbs and the patient’s back, we have to either reduce pressure or we have to make it more slippery. That means reducing the coefficient of friction.<\/p>\n\n\n\n If we compare that to when there is oil added to the equation, obviously, the thumbs slide very easily due to the reduced coefficient of friction. We’ve made it more slippery between that interface of the thumbs and the skin of the patient\u2019s back. Even if you press really hard, you’ll get a lot of compression, but you won’t get a lot of shear. So, in this case, reducing the coefficient of friction, making it more slippery, which creates more rubbing and less shear. <\/p>\n\n\n\n Just let that sink in for a moment. So, rubbing is the answer here to less shear.<\/p>\n\n\n\n Let\u2019s quickly look at friction. Friction is basically the force that resists the movement of the thumbs over this person’s back. There’s a movement force from the thumbs moving forward. Friction is working to oppose that motion. So it is working in the opposite direction. And it’s defined by the coefficient of friction times the normal force. So the lower the coefficient of friction (the more slippery it is), the lower the friction force. And similarly, the lower the pressure (or the normal force) the less hard you press, the lower the friction force.<\/p>\n\n\n\n What we’re looking at here is this part of the Blister Prevention Mechanisms chart. Friction force: that’s the force that resists the movement of the thumbs over the person’s back. It is determined by how slippery or grippy it is, and how lightly (or firmly) you press.<\/p>\n\n\n\n Every single rub action can be divided into two separate parts. The part where there’s no relative motion and the part where there is relative motion. We often ignore the first part. And I’m going to show you in a moment, the part where there is no relative motion, determines the magnitude of shear deformation. So in fact it’s actually very important when we’re talking about shear and shear-related damage.<\/p>\n\n\n\n Shear deformation magnitudes can be reduced by either reducing pressure, or reducing the coefficient of friction. Pressing less hard, your thumbs will find it easier to move and there’ll be less shear. Similarly, make it more slippery and your thumbs will move much easier, and there will be less shear (a lower shear magnitude). Rubbing is often the solution to reducing the magnitude of shear deformation, rather than the problem. Another one just to sit on for a moment. Rubbing is often the solution. Yet, so many of us and basically all of our patients think that rubbing is the enemy – rubbing is what causes blisters. It’s not!<\/p>\n\n\n\n What else can we learn? Let’s have a quick look at coefficient of friction. There are two measurements of coefficient of friction. There’s the static and the dynamic (often referred to as kinetic or sliding coefficient of friction). So, here’s a graph. You can see the first part of the red line going up at an angle. This is the period where there is static friction. This is the first part of the rub – there’s no relative motion between the thumbs and the patient’s back.<\/p>\n\n\n\n The next bit is the part where there is relative motion. Look how the kinetic coefficient of friction is lower than the static coefficient of friction peak. So this is the motion. This is where the thumbs are still stuck on the person’s back and have not moved yet, and this is where they’ve moved. Isn’t that interesting? <\/p>\n\n\n\n So, we think about rubbing as this part (dynamic friction). But if we’re thinking about shear-related skin trauma, we should be thinking about static friction. Because peak coefficient of friction is within the static coefficient of friction range.<\/p>\n\n\n\n Every pair of surfaces has a particular coefficient of friction and you’ll see in the table at the bottom there are different pairs of materials, and you’ll see in every occasion (except for teflon on teflon), the static coefficient of friction is higher than the kinetic coefficient of friction.<\/p>\n\n\n\nMassage with oil<\/h3>\n\n\n\n
Friction<\/h2>\n\n\n\n
Takeaway 1:<\/h2>\n\n\n\n
Takeaway 2:<\/h2>\n\n\n\n
Coefficient of friction<\/h2>\n\n\n\n