#897 Difference between plantar plate stress and strain - DOC

#897 Difference between plantar plate stress and strain

What are the four forms of stress and strain that can affect runners with plantar plate injuries? Well, that is what we’re talking about today on the Doc On The Run Podcast.



I know I talk a lot about how necessary it is to reduce the stress and strain on the plantar plate ligament when you are a runner, and you are trying to get ready for a race but still heal this injury. It is really difficult to do, not impossible, but it is not easy.

There is a couple of differences between stress and strain when you look them up and if you look them up, although we think about stress being really bad and there are lots of definitions saying it’s really bad, the reality is that stress is your body’s natural response to challenges or stresses that make it grow, respond, and become stronger.

Strain is different. If you look up strain, the definition of strain is a force tending to pull or stretch something to such an extent that it causes damage. That’s not so good, right? So, basically strain is a gone too far form of stress. And if you want to make sure that you don’t go too far in applying stress to your plantar plate ligament as you are returning to running and working out, you should think about the four kinds of stress that are applied to the plantar plate from running, standing, walking, and working out. I’m going to go through those for you real quick.

Compressive stress

The first one is compressive stress. Compressive stress is where you squish something. So, if you look at the insert in your running shoe, if you take it out, you’ll see a wear pattern and the foam will be thinner underneath things like your metatarsal heads, the bones where you can feel them on the ball of the foot, right? Where the plantar plate ligaments are.

When you look at the insert and you know that you’ve squished it and you know that you’ve compressed that foam over time, you are also compressing the plantar plate ligament between the inside of the shoe and the bones because the plantar plate is in between. So, if you have a lot of pressure and it looks like you’ve really compressed that area under the metatarsal head, that might be an indication that you have too much compressive stress there and that you want to do something about it to reduce some of that so that it can stop aggravating the plantar plate ligament.

Tensile stress

The second one is tensile stress and tensile stress is the worst one. This is the one that I’m talking about the most. When I say you shouldn’t do lunges, you shouldn’t do pushups, you shouldn’t do planks, or elliptical trainers, or calf raises, things where you are banging your heel up off of the ground and you are bending the toes and you are stretching the plantar plate around the bottom of the metatarsal head, you are asking for it if you do that. That is the worst thing you can do.

Many of the runners that I see who got plantar plate injuries were doing one of those kinds of workouts to supplement their running fitness and that’s what really led to their injury. So, you don’t want to stretch the plantar plate ligament. Stretching it too much, that’s tensile stress. You don’t want to do that.

Shear stress

The next one is shear stress. Now, shear stress is not probably something you are going to find with runners talked about so much, but I’ll tell you a thing that is an example of shear stress that you will certainly understand.

I was doing a race with one of my best friends. We had committed to doing the race together. We trained and trained and trained, but he got super busy with work and guess what? He didn’t train enough. But he’s a super strong cyclist and he’s super competitive. So, I said, look, no problem. We’ll just do the race together. It’ll be fun no matter what. And we got to do the Ironman together, or at least that was the plan.

We got in the water. We did the entire swim together, got out of the water after 2.4 miles and took off on the bike together. But in the middle of the crowd getting out of there, somehow, I lost him. He disappeared. And he is a faster cyclist than me and I thought we were going to do it together, but he left me. I’m not dumb enough to try to catch him because I knew I would be cooked if I did.

So, when I got to transition after 112 miles on the bike, I found him sitting in a chair in the change tent and he looked white as a sheet, and he was beat. And he said, “Oh man, I just need to rest a minute.” I was like, you can rest on the run. We got to go. And we took off. We walked a little bit. We ran a little bit and then after six miles, something like that, he basically was like, “I can’t run anymore.”

Well, pretty much the whole way on the marathon course, there are cones dividing the road from one side to the other to keep people separated on the out and back section of that course. He came up with a great idea. He said, all right, this is what we’re going to do. We’re going to run from this cone to that cone and then we’ll walk from that cone to the next cone. We did that for the rest of the marathon.

I knew because I’m a podiatrist and all I think about is this sort of stuff. I knew that this was going to be really hard on my foot to start and stop over and over and over every hundred feet or so for 20 miles. So, I deliberately took off on my left foot and stopped with my left foot. Now that is sheer stress. Every time you stop suddenly and your foot slides in the shoe, that’s sheer stress.

What does it do? It causes a blister, right? So, at the end of the event, underneath the plantar plate ligaments on the ball of foot, I had a blister that was literally about that big. I could barely walk. I was seeing patients in the office, hardly stand on it and my buddy, he got two of them. He got them on both feet because he didn’t think about that. And frankly, we were both too tired. I didn’t even talk about it with him. I don’t know that I like thought about it so consciously. It’s just, I was just trying to just keep things together, keep moving and not really do it. So, we hadn’t talked about it. He got them on both feet. That’s sheer stress.

If you have a tendency to get blisters, if you’ve got calluses right under your plantar plate, that’s probably because you have sheer stress. You want to do something to address that because that shearing of the plantar plate under the ball of the foot, the same shearing that causes calluses in that area can cause trouble that can slow down the healing of the plantar plate.

Torsional stress

The last one is torsional stress. That is twisting motion. So, if your toe is twisting, that can strain the plantar plate ligament because it’s wringing it out like a towel. Your toe is not going to go around in a circle, but anytime that you change direction, or if you pronate and you push the toe to the side, if your toe looks like it’s crooked, if you are running barefoot on a treadmill and it seems like your toes moving to the side, that’s torsional stress that’s applied to it.

That also can really slow down healing, particularly if the ligament is torn on one side or the other side and you see that on an MRI and ultrasound, well, you definitely want to make sure that you do something to combat that torsional stress because it can slow down the healing.

Everything you have to do, regardless of which stress, which strain is being applied to the plantar plate ligament, everything you do should be focusing on stopping that stress so that the collagen can repair itself, the ligament can get stronger, and you can get back to running without this being a nagging injury. So, that’s what you really have to focus on.

If you want to learn more about the exact strategies I use with runners who call me with these injuries and the exact strategies I teach to physicians when I go lecture at medical conferences, I have all that stuff put together and it’s in the Plantar Plate Masterclass. You can get it for free at www.docontherun.com/plantarplatemasterclass. So go sign up, check it out, and I’ll see you in the training.