#128 – Irene Davis, Ph.D.: The evolution of the foot, running injuries, and minimalist shoes

Hey everyone. Welcome to the Drive Podcast. I'm your host Peter Attia. This podcast, my website and my weekly newsletter all focus on the goal of translating the science of longevity into something accessible for everyone. Our goal is to provide the best content in health and wellness, full stop, and we've assembled a great team of analysts to make this happen. If you enjoy this podcast, we've created a membership program that brings you far more in depth content. If you want to take your knowledge of this space to the next level, at the end of this episode, I'll explain what those benefits are. Or if you want to learn more now, head over to peterattiamd.com subscribe Now without further delay, here's today's episode. My guest this week is Dr. Irene Davis. Irene is a Professor of Physical Medicine and Rehabilitation at Harvard Medical School. She's also the founding Director of the Spalding National Running center, one of the premier centers in the United States devoted exclusively to the diagnosis, treatment and prevention of running injuries in runners of all ages and abilities. Irene holds two bachelor's degrees, one in Exercise Science from the University of Massachusetts and one in Physical Therapy from the University of Florida. She then went on to earn her Master's degree in Biomechanics from the University of Virginia before finally going on to get her PhD in biomechanics from Penn State. In this episode we talk about a lot of things and Irene is someone I've been wanting to talk with for about six months and I was hoping to do it in person so I could actually go to her lab, but alas, Covid turned this into yet another video interview. Nevertheless, the wait was worth it. In this episode we talk about a number of things. We start with the evolution of running. So when did we stand up as Homo erectus and then when did we begin to run? How did we run? What was the mechanic of that run? And then what changed about 50 years ago? Because what's really interesting when you think about this is we went from 2 million years ago till about 50 years ago sort of doing the same thing. And then 50 years ago something changed. We talk a lot about what that change was and how that change led to where we are today. We had a little nerdy in this episode, but I think the show notes are going to make this really easy to follow and I go out of my way to stop and have Irene re explain things and try to re explain things much myself so that people who aren't as familiar with the terminology can understand it. And I think we do a pretty good job of explaining the direction of the forces and just making sure people understand some of the lingo that we use. But that said, the show notes will be very valuable as we especially discuss some of the movement patterns, the gait patterns, the muscles within the foot and the legs, and even things as simple as the different types of strike patterns and what we mean by minimalist shoes. We have a very lengthy discussion about minimalist shoes versus conventional shoes, motion control shoes, cushion control shoes. We do talk a lot about running and walking, but I think a lot of what we talk about goes even beyond that. And we have also a pretty detailed discussion about orthotics, plantar fasciitis, and all of the common injuries that many of you have probably either heard about, know people who have suffered from or have suffered from yourself. So without further delay, please enjoy my conversation with Irene Davis. Irene, thanks so much for making time today. I know you're incredibly busy as evidenced by the fact that you had to change our last meeting in exchange for something that was obviously much more important, that we certainly could understand, which was making time to speak with folks at the dod. And I can imagine how they're very interested in what you do. Tell me a little bit about how you came to be doing what you are doing. For example, what did you study during your PhD?

I'm actually going to go back a little bit further. So when I started out in college, I really didn't know what I wanted to do. I honestly wanted to be an FBI agent and wrote a letter to J. Edgar Hoover, who wrote me a letter back that I still have and framed that said that women aren't allowed in the FBI. So at that point I really didn't know what I wanted to do. So I went to school and started taking classes in exercise science, which led me to wanting to understand how the body works and combine it with medicine. And most people who go into physical therapy often think about either medicine or pt. And I decided to go the PT route, got a degree in physical therapy and worked for a while. But I think I've always had an inquisitive mind and I kind of knew that I would go back to school for just for additional education and thought that I would probably end up going on for my PhD. So I went on. I did my master's in biomechanics and then went on to Penn state into my PhD in biomechanics. The person at Penn State that I went to work with was Dr. Peter Cavanaugh, who is one of the pioneers in running Mechanics. And what I thought was really cool was I was able to bring in my medical sort of physical therapy clinical perspective to biomechanics and marry them. That's really what I did. It's when I started that sort of journey of understanding the relationship between mechanics and injuries. And then I took a position at the University of Delaware to start my career.

And on a personal level, was there an injury that you had growing up? Did you know somebody? Were you close to somebody who'd been through the churn of physical therapy, either with or without successful results that kind of created this passion within you?

So the physical therapy part. Early on I had a cousin who in a diving accident became a quadriplegic. When I watched the physical therapist work with him, I was really inspired. And I actually started my career in spinal cord rehab, but then moved on to. After I started my graduate degrees, I moved into outpatient physical therapy because it was easier to do part time PT in that kind of environment. And then because of my interest in biomechanics and injuries, really orthopedics was really kind of the better match for me, but really started with that. That's how I kind of got interested. But my interest in biomechanics actually came from the fact that my cousin and other people with quadriplegia have to move 100% of their body with 25% of their muscle power. And, and it's a biomechanical feat. So you have to learn how to use your body in ways that we don't normally use it and you have to understand mechanics. And that's really what got me interested in biomechanics.

You know, I've been thinking about how I wanted to approach this subject with you. And a lot of times I come into an interview and I have a pretty clear sense of how I want to do that. And I got to be honest with you, I'm still sitting here as we're talking thinking, God, we could maybe we approach it this way, maybe approach it that way. So I'm just going to take a stab at one of the ways I wanted to talk about this with you. And if it goes in a place that's interesting, wonderful, and if not, will pivot. But does it make sense to talk about this through an evolutionary lens? Does it make sense to start from the standpoint of what did our ancestors do biomechanically? I don't know, several million years ago that today we do radically different. So in terms of our evolution having been the driving factor, even more than sort of the Environmental change, which I know we're going to talk about the environmental changes later, but just help me understand sort of what the step function changes have been, if any, in the biomechanics of our species.

So if you don't mind, I wouldn't mind stepping back one more step and talk about the evolution of my thought that leads to the evolution that you're referring to. So when I started out at the University of Delaware, I had done some work as a physical therapist doing orthotics. And I became the person who taught the orthotics, the foot orthotic component of our program. I was making orthotics, I was doing research in foot orthotics and really kind of got into the mindset that some people have feet that can't support themselves. And it was interesting. It was kind of like a perfect storm for me because I was doing research in the area of impacts and injuries. And I realized that when people land on the ball of their foot, and I'm sure we'll talk about this later, the impacts are lower. And people who are barefoot runners tend to run in the ball of their foot. So maybe that's really the way we were meant to run. And footwear can interfere with these things. And so all of these things kind of came together at the same time that the Born to Run book came out. And again made me start to think it wasn't really the Born to Run book, but again, it kind of made me re examine my thinking and it kind of brought me back to when I was a physical therapist in rehab, where we would try to take away as much support and bracing to our patients, even in wheelchairs, a lower back, less lower extremity bracing, so that they would use what they had. And yet my thinking in terms of feet was completely opposite. And then the other part of it I was thinking about is a physical therapist. We don't brace anything else permanently if you have an orthopedic problem. And yet with the feet, somehow we think someone needs. And I did thought we needed to have bracing in the foot. I needed to give them orthotics for every pair of shoes they had, and they were going to need those forever. Instead of thinking that these feet actually have these amazing muscles and that they have just as much of an ability to strengthen as my quads and my hamstrings and my biceps. And so it really started to change my thinking then. And then there were papers that came out that showed that when people are placed into shoes that match their foot type, which is really how we got to these motion control and cushion shoes. And I can give you a little history there, too, when we have a chance. But when you look at the studies that have been done, what they found is that when you match the foot to the shoe, so a motion control shoe for a very low, flat foot that's flexible, a cushioned shoe for a high arch, rigid foot and stability shoe for a normal arch. And then you compare that to a group of people who all got the same shoe, regardless of their foot type. There was no difference in the injury patterns. This was done by Joe Knappek in the military, I think something like 7,000 military individuals in different branches of the service. So that started making me think, wait a minute, because I used to prescribe footwear in that way as well. So all of this, along with really kind of meeting Dan Lieberman, who's an evolutionary biologist, who invited me onto the nature paper from 2010, and it was at a time when I was moving from the University of Delaware up to Harvard, which is where he was as well, I really started thinking about the evolution. So when we think about the evolution of our foot, when we went from walking man to running man, so that would be Australopithecus to Homo erectus, we actually started to develop not just changes in our feet, but changes in our body. And there's a great paper by Dan Lieberman and Dennis Bramble. It's Bramble and Lieberman looking at the changes, the anatomical changes that occurred as we went from walking to running. And what they found is that things like the longitudinal arch, the medial longitudinal arch developed. At that point, our joint surfaces got larger because we had higher forces going from walking to running. And so those surfaces had to be larger in order to distribute the forces. Our Achilles tendon got longer in order to store the energy. You can walk with a very short Achilles. You don't need to store energy, but for running, you do. And so we saw these changes that occurred, and that's really kind of what I have focused on, is the changes from walking to running, because my interest has been in running. But those changes occurred probably not just simply for running, but they certainly optimized us for running. And they had, I think, 23 markers of endurance running. It's a very fascinating paper. The title of it's called Born to Run, which is interesting. I think that we really evolved to have feet that are very well on their own, well equipped to be able to walk and run without any kind of support. When you think about the structure of Our feet, we've got 26 bones. We have 33 articulations, those articulations that have six degrees of freedom of motion. The foot is a very complex structure, just like the hand. It's very much like the hand, the anatomy. It also has four layers of arch muscles, four layers of 10 muscles just in the arch. So it allows this foot to have diverse function, from being a stable base of support, to being an adapter on uneven terrain, to being a shock attenuator, to being a spring to be a rigid lever for push off. All of those functions come from the fact that it has that kind of complexity and that kind of beauty.

That was really interesting. And there was a lot I'd like to unpack there. You mentioned Dan Lieberman. I saw Dan lecture for the first time in the summer of 2011. I actually remember it quite well. And I remember being blown away by a lot of things he said. One of the things he said, if I heard him correctly, and if I remember correctly, was that over 24 hours, no animal could cover a greater distance than humans. And obviously there are lots of animals that can run faster than humans for short distance, but over 24 hours, we're going to win the day. And again, this was part of the sort of born to run thesis. I want to just go back and make sure I have a couple things correct. So when did we approximately stand up? How many years ago was that?

Oh, now you're testing me. I can tell you when we started to run. We've been running for 2 million years.

Wow. Okay. That's longer than I would have thought. So 2 million years of it was essentially a transition from walk to run. Do you have a sense of how much. I mean, again, how much speed did we give up, acute speed, when we went from when we stood up? In other words, I'm guessing that when we were on all fours, we could move very quickly over a short period of time, a hundred yards or so, but probably not that quickly over miles. And so standing up gave us that transition. Right. We were able to then go slower, potentially over the first few meters, but we could, as Lieberman pointed out, go much greater distances. Is that accurate?

Yeah, it probably is accurate, but I think I would really yield to someone like Dan for that kind of information, because I wouldn't be confident that I'm giving you accurate information.

Well, Dan is definitely someone I'd like to have on this show. I'll save those questions for Dan.

Yeah, I think that would be good. I do know that when we transitioned from walking to running. It was at a time when our brains were getting bigger and we needed meat and we didn't have spears at that time, so we had to really outrun our prey. So we're not very fast runners, but we are good endurance runners. And the reason for that is because we can pant off our heat. Whereas these big animals like kudus have their guts sort of slosh up against their diaphragm and they can only do one breath for every step. And so they aren't able to pant off their heat very well. So basically what we would do is we would carve them out of the herd because we'll be able to follow one and we would just run them to an exhaustion and then club them. So that's why that endurance running was so important for us. So we are probably among the slowest of the animal kingdom when it comes to speed. Speed. But as you said, we are very good endurance runners.

The other thing you said, Irene, that impressed me was effectively the malleable nature of your thinking. I've met many people who come up in one school of thought, and I'll just use the example you gave, but it's true of doctors, it's true of anybody, which was, hey, we're going to put everybody into orthotics if they have the foot issue, and we're going to try to fit you to the fanciest motion control shoe or cushion control shoe or whatever. And it seems that somehow, in the presence of new information, you seemed to very easily be able to let go of that and actually challenge yourself and say, wait a minute. I was very impressed by the way you described it, because I'm sitting here saying, how the hell did I not see something so obvious? Which is. And I'm not an orthopedic surgeon, but I certainly am familiar enough with the field to say there's really no long term use for a brace. I mean, we always want people to strengthen themselves intrinsically rather than rely on extrinsic support. And yet I think up until probably two years ago, I took it on face value that, yeah, orthotics are a great thing if you need them. Never questioning it as you did.

I felt the same way about myself at that time. I said to myself, how have I thought this even for this length of time? And I think it really was because of what I had said to you. There was a number of things coming together with my research, with other people's research that started to make sense to me, that maybe we Aren't supposed to be in this kind of footwear. And maybe this kind of footwear changes the way that we run, and maybe we should be trying to strengthen our feet. There were just a lot of things that came together at that time that kind of pushed me into thinking differently. But I really believe that you have to evolve. We have to evolve in our relationships. Right. And we have to evolve in our spirituality. We have to involve in our scientific thinking as well. And I've always believed that.

Does it make sense first, in your opinion, to talk about what perfect intrinsic support of the foot looks like and then start to talk about how we got where we got? In other words, do you want to follow this through a time sequence of, okay, so 2 million years ago, we're out there running. Basically, we did that up until when? I mean, when were shoes even brought into the equation?

Let me talk about it in that way. So if we look at the fact that we've been running for 2 million years and we don't know exactly when the first emerged. Some of the first footwear that we found were found in the caves in Fort Rock, Oregon, and they were dated to be 10,000 years old. Not saying they're the first, but when we looked at them, they basically were made out of sagebrush bark and had a flat surface with straps that kept it on the top of the foot. When you think about that, they're kind of like huarachi sandals. The purpose of it is to protect the bottom surface of the foot from the elements. And when you think of other clothing that has developed short of being fashionistas, it's been to protect us from the cold, the rain, the heat, the snow. And that was really the prime purpose of footwear up until. I'm not exactly sure the dates of when we started to get into some of the high heeled shoes and some of those things, but in terms of athletic footwear, I'd like to talk about that.

Before we do, I just want to go back to this thing, which. Why is it that we even needed anything to protect our feet? Like there's no other animal out there that needs to protect his feet. So a polar bear has enough padding and insulation on the bottom of its feet that it can easily walk through its environment. This is true of every single animal. Why did man not evolve enough protection of the foot to be resistant to scratching, cutting, and extremes of temperature?

I think that's probably another really good question for Dan. I hate to pass that on, but we do develop calluses on our feet. That help us to protect us from the elements. I don't know what happened that made us. Maybe it's a comfort issue where it was just more comfortable. You can walk out on rocks, and you've seen people walk across really sharp rocks and be able to do it very lightly, but it's just maybe easier, maybe faster, maybe more comfortable. I mean, that's what I'm thinking is likely to be the reason why we ended up developing footwear.

So we basically short circuited natural selection on that particular element, perhaps.

Yeah.

And maybe that speaks to all of clothing, actually, aside from maybe some of the social modesty or whatever that came from it. But it might have been that, hey, we could wait another million years and we'll develop really tough feet. But what the hell, we've now got a brain that tells us how to put something on these things that will short circuit that evolutionary period. Okay.

But you know that if you end up going barefoot a lot, that you develop calluses on the bottom of the foot that are protective to the feet. So we do have the ability to develop that protective feature.

It's funny that you mention Oregon, where they discovered the first shoe, because, of course, Oregon is the epicenter of another big revolution in shoes vis a vis running shoes. So where did running shoes, per se, this idea that we're going to put something that's more cushiony on our feet? It's funny, Ike, I haven't paid much attention to what running looked like 200 years ago or 100 years. You know, if you look back at the Olympics at the turn of the last century, what were athletes wearing in the marathon? Were they wearing basically just a flat piece of leather that protected the bottom of their feet?

Exactly. And up until probably the 60s, the kind of footwear that we were wearing were really what we would call minimal footwear today. And it basically was something that protected the bottom surface of the foot. There were some developments in terms of spikes for track, and so there has been a development of footwear along that line. But when we're talking about distance running, endurance running, people are running in very flat shoes. And then what happened is we had the running boom, and people got very excited about running. And a lot of people who were not very fit, fitter than us today, but in their time, not as fit as, say, runners who were part of a high school team or collegiate track or cross country team, took this on very quickly. They developed some injuries. And some of the first injuries were Achilles problems because people were used to walking around with a little bit of a heel in their shoe. 2 inch heel. Men's shoes got a little bit of a heel and these shoes were flat to begin with. And the Achilles, it doesn't take much. You take out a lift. You know, if you just go down and walk in a flat shoe for a period of time, you can develop an Achilles 10 knives if you don't do it slowly. And so people started to develop some problems with their Achilles, so they started to add a lift in the shoe.

Just to explain that for folks who might not be familiar enough with the anatomy, the Achilles is the tendon that's basically joining the bottom of the big muscle of the calf, the gastrocnemius. Right around the heel.

Right, exactly. It's an extension of the calf muscle and it's the attachment structure to the heel.

So the more pointy your toe is relative to your heel, or the more your heel is raised, the more compressed that Achilles tendon is. In other words, the less stretched out it is.

That's right. That's exactly right.

So if you're used to walking around with 2 to 3 inches of heel elevation and, and then you start running with something that has no elevation, you've got a double whammy, which is one, you're applying a huge stretch to something that hasn't been stretched. And then going back to something you said a few minutes ago, the force of that, the force transfer in that transition from a walking to a running stride multiplies that stretch by some factor that's probably not linear and therefore quite destructive.

Exactly. You hit the nail on the head. That was one aspect. So that created this change of adding a little bit of a heel lift to athletic shoes. And this is where the heel to toe drop comes from. The next thing that happened is there were some other injuries that occurred. And I learned about this because I was writing a paper on the re emergence of the minimal shoe, and I wanted to know how we ever got to having a motion control and a cushioning shoe. How do we get these divergent types of footwear?

Can you explain what those are? I mean, cushioning to me sounds obvious, but explain it in some detail.

So a motion control running shoe is a shoe that actually has a very stiff heel counter and it has material that's stiffer on the inside of the midsole of the shoe that helps to prevent the foot from rolling in and also may have some plastic support reinforcements on the inside of the shoe and more arch support to prevent the foot from rolling in. So that would be a motion control shoe, and that's typically designed for people who roll in too much. This was what the original idea was. The other shoe is called a cushioning shoe, and it's for someone typically who has a high arch that doesn't move a lot and needs more cushioning. But what happened is we started to see many more injuries in runners after the running boon. And interestingly, if you look at PubMed and you try to determine when the first. I think the first running injury article was in 1970s. It was in the early 1970s. Right. So before then we had lots of people running. And if there was a lot of running injuries, you would have seen literature on it. I'm not saying there weren't any running injuries. Of course there probably were, but wasn't such a huge issue as it has become. So I really think that it's part of the fact that these people were not trained to cushion the landings, because when you land, you've got to cushion it and you've got to control it. So if you don't have the muscles and you don't have the motor control to be able to control as your foot comes down so that you can actually attenuate the shock that you get when you land so you're not using the muscles correctly, you're not landing softly, then you're going to have injuries related to impact and related to too much motion. Does that make sense?

It certainly does. I want to make sure I understand what we're calling a running injury, because as I've become more and more obsessed with this topic, what I've come to realize is that if the feet aren't working correctly, the injury can go all the way to the neck. In other words, what I used to assume is if your feet aren't working right, your feet can hurt. But then you realize, well, actually that translates up to the knee and, oh, that translates into the hip. Well, actually, that translates into the pelvis and the back and the L spine and the T spine and the C spine. And before you know it, you realize if a person isn't connected to the ground correctly, a lot of things go wrong. So when you talk about this wave of running injuries that showed up on PubMed in the early 70s, do you mean specifically foot injuries or what type of injuries are you referring to?

I think the very first reference might have been tibial stress fractures. But if you look at the distribution of running injuries, you're right. They can go all the way up to the neck. The majority of them are from the knee down. If you look at the distribution. The knee is the most common site for injuries. The lower leg, the ankle, the foot, from the knee down, and the knee is the primary attenuator of shock. So it takes a brunt of the load. You do most of your shock attenuation through the knee.

What is that load, by the way? I mean, I remember knowing this at one point. My undergrad is in engineering in mechanical engineering, so we did a few courses in biomechanical, but I've forgotten so much of it. But I do remember being blown away at what the load was, that it was experienced by the knee. So if you took like 175 pound man and he was running, the shock forces felt in the knee were astronomical, were much higher than what you would expect. If you were just thinking about this.

The ground reaction force when you land is typically the peak ground reaction force in running is typically about two and a half to three times your body weight. That's the force that your body feels. At the knee itself, it's even higher. So it can be seven times your body weight. So if you're 200 pounds, it could be 1400 pounds. So Nike actually called in three sports podiatrists when they saw all of these injuries that were occurring. I got this information from an individual called Jeff Johnson. And Jeff was with Nike in the early, early days of Nike, and he worked with them. And he's the person that told me that when the injury started to occur, they brought these sports podiatrists in. But he said that when he was running back in the 50s and 60s, in high school and college, he said that nobody was getting injured and that people were running in rubber soles with canvas tops on them. And he said they developed legs of steel. Those were his words, legs of steel. And they weren't having the knee pain and the stress fractures. And of course, that's very anecdotal, but I think it's interesting that speaks to that. But then when the running wound started, we started to see this very quick rise in injuries. So they brought these sports podiatrists in. And what they told them is based on what they were seeing, they felt that the injuries were related to too much impact and too much motion. And it was that they had no science behind it. And I truly believe that's what they thought clinically. But it was that information that created this divergent motion control and cushion shoe that we described. What they did is they, rather than have the runners adapt to the running, they took the shoe and adapted it to the runner. So instead of making their feet stronger and making them land softer, runners who are running in shoes that have no cushioning at all, basically like minimal shoes, they adapted it. And the problem with that is that then you start into the cycle where if you give people cushioning, they actually land harder. And that's been shown by a number of different research studies. And when you put a support, the muscles get weaker. And there are lots of studies that show that when you take the support away, take an arch support away, the muscles of the foot get stronger. When you add cushioning, you land harder. There have been a number of studies that have shown that that new Hoka shoe causes people to hit harder.

Let's unpack that for a second because the first thing makes a ton of sense. I can really see why removing an arch support will actually allow the foot to become stronger. Take away the extrinsic support, the intrinsic muscles are forced to adapt. Help me understand why the cushioning of the shoe will have the relationship you've described, which is a bit counterintuitive that it would actually increase the force. Assume you mean the force all the way from the ground to foot and then foot to knee.

That's exactly right. I'm going to give you an example. So if you are going to hit somebody with your fist, you think you're going to hit them harder if your fist is bare or if you have a padding like a glove.

In boxing, you're right. We typically do hit harder with a glove. And I think a lot of it has to do with the weight of the glove. You wear a 12 ounce glove, you have more mass that is being thrown. So are you saying it's the mass effect as well of the shoe potentially?

I don't think it's just the mass effect. I think it's the fact that you have this protection so you can hit harder and it does attenuate some of the load, but it doesn't attenuate all of the load. What I believe and what's difficult is we don't have a lot of good data pre cushioned shoes, I.e. high speed data that looks at foot strike pattern. I think that we evolved to put primarily land on the ball of her feet because when you land on your foot barefoot, it's going to hurt. And there was a study done by one of my colleagues looking at the pressure pain threshold of the heel. And what they did is they applied pressure and then they determined when somebody felt pain. And what they found is that when the pressure exceeds the pressure, that you have in walking, that's when people start to have pain, which tells us that we naturally. This heel pad was designed, was adapted for attenuating loads of walking because you figured we were born to be barefoot, we should be able to do these things barefoot. But running on your heel is very painful, can be very painful because you don't have the cushioning. And there have been other studies that have shown that really is footwear that has changed our mechanics from a forefoot strike to a rear foot strike.

Now, it seems to me that maybe somebody's already done this, but you could go back and look at lots of old film of runners going back into the 1800s and the early part of the 1900s. And if this argument is correct, you would see that everybody would be a four foot striker until the advent of cushioned shoes. In other words, this would suggest that heel striking is something that's really only been brought about in the last 50 years. Is that true?

It's mostly true. I think that as a barefoot runner, it's been shown that they do vary. So barefoot runners may land on their heel. If you're running in grass, you may have more of a tendency to land on your heel. When you land on your heel, you can stride out more. And so for a given cadence, you can go faster. So it may be advantageous if you're on a soft surface to land on your heel. But when you're on relatively firm surfaces, there's more of a tendency to land on the ball of your foot. And if you look at some of the vases, the prehistoric vases that depict man running, they're always running on the ball of their foot. And if you look at the Boston robot that runs, guess what? He runs on the ball of his foot. I honestly believe that optimally we were adapted to do that. And that's why we have a long Achilles tendon. We have a much bigger calf than we do in anterior. We have much bigger muscle in the back than we do muscle in the front. And when you think about that, one of the most common injuries that runners have when they first start running is this shin splints that they call explain.

To people what a shin splint actually is.

It's pain on the front part of the leg, and particularly in the anterior, the muscle in the front part of the leg. And if you're not used to running, landing on your heel and having to use the muscle on the front part of your leg to lower your foot down, you could have an overuse injury for a while. Until it gets used to it. And so they get sore in the front part of their leg.

Let's explain that to people, because I think a lot of people won't appreciate that. I think many people might not understand that you have these muscles in the front of your leg, the tibialis anterior, et cetera. They're in these packed, these tight little fascial compartments. And the point you're making, that of course I can see, because I'm looking at you, is an important one, which is. And so the listener. I just hope they can sort of picture this as the heel is coming to the ground. They have to eccentrically allow the rest of the foot to come down. And in doing so, you're not using the big muscle in the back of the calf muscle. You have to use that front muscle to control the toes as they come down. And you're saying, look, those muscles are not nearly as big as the muscle in the back. They're going to fatigue long before the muscle in the back. Your point here is, if you just look at the shape of the human lower leg, it's designed to carry more load in the back than in the front.

That's correct. Here's another really interesting biomechanical fact. When you land on the ball of your foot, you shift the load from the quadriceps, the muscle in the front of your thigh, and your knee, to the ankle and the calf. And when you land on your heel, as a heel striker, you shift the load from the calf to the knee. When you think about the knee being the most common site for injury, then it makes sense. And the knee was not really designed to take those kinds of loads in running repeatedly. So. But the calf is this big muscle. And what happens is, when you land on the ball of your foot, because you have this time in which you're bringing your heel down to the ground, you have that time to attenuate that force. Whereas when you land on your heel, you come in and it's almost like a. You get a very distinct impact. In fact, when you look at the force that the ground pushes back up at you, the ground reaction force of a rear foot striker versus a forefoot striker. A rear foot striker has an impact peak followed by a propulsive peak. This impact peak is a very quick rise to peak. A forfeit striker has a very nice smooth curve that's very gentle. And so this impact peak is associated with a very quick application of force to the body called the load rate.

Right. And let's explain why that matters. So if you can picture an X axis that shows time and a Y axis that shows force. The narrower the force is applied over time, the more problematic it is. And that's what you're describing, which is when you strike with the toe, that force peak is spread out. You can picture a curve over a longer part of the time axis as opposed to a spike function, which is when you're heel striking. That first transfer of force is an up and down spike before you reach the propulsive phase, which is over a broader application of time. Correct?

Absolutely. And the steeper the slope of that first impact peak, the greater the rate of loading. And studies have shown that rates of loading are related to running related injuries. So the softer you land, the less your chance of getting injured.

You've obviously explained a couple of benefits to heel striking. You can take a longer stride. I think it's worth anybody sort of playing with that in their mind. And you can see why you could take a longer stride if you could strike with your heel as opposed to your toe. And you've said that, look, there might be times when you were running on a sandy beach or you're running in the grass where the contact surface is malleable enough that you can get away with it. But so far what we've learned is for the most part we've probably had 2 million years of running on a tow strike or forefoot strike pattern. And basically what happened is once people who weren't frankly fit enough to be running due to the other sedentary changes that came with our most recent evolution, coupled with some well intentioned but probably ill informed podiatrists suggested, hey, we've got to lessen the load, we've got to put some cushion here and we've got to make it easier for the Achilles tendon which has become deconditioned. Basically, about 50 years ago, we started building shoes to fit a modern day problem, as opposed to taking a modern day problem and deconstructing it to its evolutionary origin. Is that kind of a summary of what you've said?

It's exactly right. And that's exactly our approach that we take in our clinic. So when people come to us with injuries and they come to us and many of them come with foot orthotics, habituated to foot orthotics and habituated to standard shoes. Our goal, we believe that the closer we are to the way we evolve to move, the less the risk for injury. What you and I are doing right now, we're sitting, it's very unnatural what we evolved to do was to squat. We really try to get people back into shoes that allow their feet to do what they were adapted to do and to run in a pattern that is closer to our evolutionary legacy.

Do you believe that there are some people who shouldn't be running? And I say that not from the standpoint of somebody who is so injured and they have no cartilage left. But I mean, if you took the average teenager who for all intents and purposes still has their body intact, but either they're too overweight or they've spent too much time in a high shoe, meaning a heel to toe ratio that's too great, or there's something about the length of their tibia to their femur that just doesn't seem optimal. In other words, like we say this, that we're born to run, but that's obviously a great general statement. But do you think that there's some nuance to this and that, you know, there's just some people for which running is never going to be a good idea, or do you think that. No, Peter, truly, anybody who still has cartilage left in those joints can be trained to do this thing?

Well, I don't believe in 100% of anything. There's always going to be exceptions. You know that from a medical standpoint as well. But I believe that running is an activity of daily living. People talk about running being a skill. I don't think it is. We learn to run on our own. We're not taught. If you have children, you'll see, you'll watch them go from crawling to walking to running. You don't get out there and you're not training them. Now, there are some runners that can be trained to have better technique. But you know what? You could train walkers to have better technique as well. We evolved to run, and it's something that we need for fight or flight. You know, you're going to run away from the boogeyman. You got to run after your kids. Running is something that is ingrained in us. Having said that, someone is born with a huge leg length discrepancy that is really going to abnormally load them when they run. That's probably not a good idea. If somebody has some really extreme foot deformities, maybe running isn't the best idea. But I think if we looked at the distribution, the normal distribution of structure, most people can run. And I think that the problem, it starts really, Peter, from when we are children. I would love for you to take a look at a video. There's a trailer on the Motivation Factor. The Motivation Factor is a 90 minute documentary about a program at La Sierra High School that was in Carmichael, California. Stan Laprotte, a Marine in 1955, brought a program to La Sierra where he had every single child. He recognized that only 40% of kids are involved in sports. I mean, some kids don't want to, some don't feel they can. So he wanted every single child to be fit. And he took those kids and every single one of them had PE five days a week, 55 minutes, and they went through a marine type boot camp program. But he did it in a way that was highly motivational. So the kids started out in white shorts and then you moved. You had criteria and you were on teams. The white shorts were a team. And when you got to move, everybody cheered you on. You got to the red team. So these kids progressed all the way up. They finally had to add on what they called the Navy Blue team. And only 21 of probably at least 20,000 people that went through their school because it was a 30 year program and they had 800,000 kids per class. Only 21 made that this program yielded children and teenagers that were so fit. Peter, when you look at this trailer of the documentary, you're going to be incredibly impressed. They look like they're all military. I think about that, and I think that that's not hard to do. He did it without any real fancy equipment. The kids were doing monkey bars, they were doing push ups, they were doing calisthenics, they were doing the pegboards, they were doing man carries. They did all kinds of things that were building not only strength but physical literacy. They taught them how to move. Those kids are all going to be able to run. The reason I talk about this and those kids today are now 55 to probably 79 years old. And we're actually proposing a study to follow them, to look at them now where they are now and compare them to a comparable group that was growing up at that same time.

So to see if that sort of critical window of exposure was going to like an exposure to language or something during a period of time that's critical would stay with them.

In the documentary they all talk about how much this program changed their life. They attribute their success to it. Some of them were in really troubled homes. But aside from that, the physical part of it is that when you see this documentary, you see this video of these kids, every one of them are fit. So I believe aside from being born with some kind of neurological disability or certainly those are the ones that I would say probably don't have that same potential. But if you're born with a normally intact neuromuscular system, I think everybody has the ability to look like that. Because I saw it. I saw it in this class. It's amazing. Every single kid, now their body types are a little bit different, but they were all fit, they were all strong. Every one of them ran. They had to run a mile. Each short level was a different time for their mile. They all ran. So I think running. This is coming back to your question. I think it is innateness. And I think everyone who has a pretty normally intact neuromuscular system can run. But to answer your question, should that teenager who's overweight and has been doing video games go out and run? Probably not. You need to get fit to run. These kids are growing up being fit. But if you're not fit, going out and running right away is not the best thing to do because I think you need to develop that strength and that motor control. I've had a lot of people who are obese that run and run without pain. If you run the ball of your foot, you soften the landing. Going from a rear foot to a forefoot strike. So landing on your heel versus your ball, your foot does not change the peak force. The peak force is the same. It changes that first impact. You remove that impact. And when you think about the landings, you have a thousand foot strikes per mile. You run 20 miles a week, that's 20,000 foot strikes per week. You do that for a year, that's a million foot strikes per foot per year. So that impact, you get that every single time. I think that one of the things that we feel is that by getting off your heels, we actually reduce you bring you farther away from your injury threshold, which we all have an injury threshold. Our goal is trying to make sure that we keep people as far below it as possible.

Do you have a force plate treadmill in your lab?

We do.

Can you explain to folks what you see when you put. Like if I were to come to your lab and we were to experiment and you'd put me in making this up, One day I'm going to run in a minimalist shoe. One day I'm going to run in a hoka, which would be the exact opposite of a minimalist shoe. One day I'm going to heel strike. One day I'm going to forefoot strike. What are the different things you see in that? Two by two. So minimalist versus maximalist shoe, heel versus Toe strike. What does the force plate treadmill show you in terms of a magnitude effect, especially as we start to now map that out for what you said, which is a million of those a year is not an unheard of amount for someone even running modestly.

Well, the first thing I want to ask you is, can I invite you to come and do that?

I would happily do that.

Okay. I would love it.

You're in Boston when I always have a reason to be there. So. Yeah. I've never run on a force plate treadmill, by the way, so I'd love to know what that's like.

So if you're running in a cushioned, a highly cushioned shoe, most likely you're going to be landing on your heel.

Which, by the way, I used to run in a hoka, so I can relate. I know what that feels like. I know what it's like to heel strike in a hoka.

So when you heel strike in a hoka, compared to heel striking in a conventional regular shoe, normal shoe, a Nike Air Pegasus, let's say you're likely to have, based on research, higher slopes, it's called the load rate. So a quicker application of force during that first impact peak. If you compare a forfeit strike in regular shoes to a forfeit strike in minimal shoes, you're going to see differences there. The forefoot strike in minimal shoes, your slope will be slightly less than forefoot striking in regular shoes. But that's the vertical direction and that's all we've been talking about so far. I want to introduce the concept because a force plate will give you the amount of force in the vertical direction, the amount of force you're applying in an anterior posterior, front to back direction, and the amount of force that you can apply in a medial lateral direction. So what happens is when you forefoot strike in a pair of conventional shoes, you have a tendency to land in more plantar flexion than in minimal shoes, which puts a greater load on the Achilles that we talked about in your calf. And you have a tendency to have a greater force in the anterior posterior direction.

Explain what you're doing with your hand there. For people who might not be familiar.

With that terminology, I'm pointing my toes and I'm coming into the ground, approaching the ground with a very pointed finger foot, and that tends to push forward on the ground and the ground pushes back at you. So you get this high braking force in the medial lateral direction. When you forefoot strike in a pair of regular shoes, you have a tendency to be more on the outside of your foot when you land. This is called inversion. This is you're landing on the lateral border of your foot with your medial border up.

Right. And I think of that as inversion because the bottoms of your feet now start to point inward to the midline of your body.

That's correct. When you land that way, because you're coming down on the outside of your foot, you're kind of pushing outward. You have a greater lateral force that you're applying to the ground, so you have a greater medial by the ground reaction force. So basically what's happening is you increase the force in the medial lateral direction when you are forefoot striking in a pair of regular shoes. When you forefoot strike in a pair of minimal shoes, your toes are less pointed, you tend to be less inverted, so your foot is more level when you land. And so you reduce the forces in the vertical direction, the rates of loading the slope, you reduce the slope in the anterior posterior direction, and you reduce the slope slope in the medial lateral direction. So it's the softest landing. When people try to transition to a forefoot strike pattern in a pair of regular shoes, they often come to me with problems with their Achilles, the tendon in the back, and also problems with the tendon of the muscle on the outside of the leg called the peroneal tendon. It's a tendon on the outside of the leg. They're so tipped laterally and they're stretching that out. Exactly. Our recommendation is if you're gonna forefoot strike, there's an interaction between footwear and foot strike, and it's important if you're gonna decide you want to transition to a forefoot strike pattern. It should be done in minimal shoes. But if you're gonna stay a rear foot striker, make sure you put cushioning under your heel because you're gonna need it because you're hitting hard.

Now let's get one more idea across, which is there are shoes that have cushioning that have no heel raise. I'm blanking on a brand. I have a friend who wears them and I think it starts with an A, but I could be wrong. But it's got about a 3/4 inch sole, but it's the same at the front and the back. So it has zero elevation of the heel, but it has some cushioning. And of course, we wouldn't consider that a minimalist shoe, would we?

You might be thinking of the topas it's not.

I could look it up. But I guess the point is, when you say minimalist, we're talking really about two features. No elevation of heel and no cushion or support, correct?

Yes. When I talk about minimal, I'm talking about a shoe you can roll up and put in your pocket.

Okay. How many brands are there of those shoes? I wear a brand called Xero. There are another couple of brands out there.

There are. There's many, I think. But some of the big brands that you think about are vivobarefoot.

Yep, that's the one I was thinking of. They seem to make a pretty nice looking product.

Yep. And then there's Innovate.

Okay, so is Innovate a true minimalist? I mean, I love innovates and I have them, but I've sort of migrated over to the zero because it has a wider toe box. And I'm also one of the things I've been working very hard on, which I'd also like to come back to. So I'll just mention it now and we'll park it. Is spreading my toes. So at the outset, when you were describing the anatomy of the foot, I was using my hand to pretend it was a foot. You saw me doing that and you made the comment just like the hand. And I, through a colleague, had an epiphany a year ago, which is, can you imagine how unhelpful your hands would be if they were shoved into tight gloves most of the time, as opposed to being able to spread apart? And since that time, I've been working greatly to sort of enhance the spread of my toes so that I could actually use these feet the way I can use my hands. And so for that reason, that's when I went from the Innov8 to the 0 was to be able to actually get those toes across. But you're saying the Innovate is still a minimalist shoe because it meets the criteria that it can be rolled up into a ball.

Some of these minimal companies actually have shoes that have some midsole. So as long as the shoe has no midsole. So some of them have real true minimal models and then some that add a little bit of cushioning into them. So what I'm saying is, if it's a model that has no cushioning, has no arch support, has a flexible heel counter, flexible upper, and you can roll it up, it's a minimal shoe. Now, what happened after the the Vibram lawsuit, which, by the way, was not about injury, but about false reporting of increased muscle size with the use of the shoe.

I'm not aware of the lawsuit.

There was a lawsuit that came out against Vibram. And it was basically about false advertising. Although a lot of people. Because when Vibram shoes first came out, a lot of people thought you could just put these shoes on and run. And we need to talk at some point about transitioning. But there were some reports of injuries with them. And I say it's just like if you were to go to the gym and lift 100 pounds when you never lift and gotten injured, you wouldn't say, don't ever do that again. You'd say, don't do it that way. Well, what happened with this is it really turned people against the minimal shoe. And a lot of people think that the lawsuit against Vibram was about injury, because people. There were some reported injuries in the literature. It was about the fact that the Nike Free shoe, which was the very first barefoot type shoe, wasn't really quite truly barefoot or minimal, had shown that you increase muscle size when you take away the support in the arch. And since the Vibram shoe took away the support of the arch, they were advertising this could strengthen your feet. That's what happened. So what it did is a lot of the shoe companies sort of pulled back and started adding a little bit more to their minimal shoes. I think New Balance had a new Balance minimus that had no midsole. Minimus trail, I think, had no midsole. And then they started to put a little bit of a midsole in there, because I think that they thought that that was what we needed to do to try to prevent injury. But I call those shoes partial minimal shoes because some of them have a little bit of a heel to toe drop, some of them have a little bit of arch support, some of them have some cushioning, and they have various degrees. The Nike Free, for example, was the very first shoe. There was somebody at Nike, his name was Jeff Pichata, and he was tasked with studying barefoot running and coming up with a shoe that mimicked it. That's why it has all those flex grooves on the bottom of the sole, so it can be very flexible. He took away the arch support. He took away the stiff hill counter.

I mean, that's a pretty thick shoe, isn't it, though? An inch of cushioning, right?

Yes. His plan was to have a Nike maybe 0 to 10, like no cushion.

All the way up to full cushion.

Barefoot all the way up to having cushioning. And they started out, I think, with the 5.0, and they did do a 3.0 and a 7.0. I don't know if you remember these and they were either more or less cushioned. But the problem with the minimal shoes are that the studies that have been done have demonstrated that when people run in a partial minimal shoe, they run closer to running in a regular shoe.

Than barefoot, in which case it defeats the purpose because they're still heel striking, but now they have less cushion.

Exactly. And a study that was done looking at a regular shoe, partial minimal shoe, and a minimal shoe over the course of a training cycle of 12 weeks, the partial minimal shoe had twice the injuries as the minimal shoe. And the authors suggest that it may be, and they didn't look at biomechanics, but it may be because the partial minimal shoe, they still were heel striking, but now you have less cushioning. Which is why I say, if you're going to land on your heel, put cushioning under it. I'm not going to try to convince people to run a certain way. When people come to me with injuries, then we have a conversation about why we might want to change footstrike. But if people are out there and they're happy, I'm happy for them. I just say, you need to put cushioning under there, and you need to change those shoes every three to 500 miles. I don't know if you know the shoes that you have. The Xero shoes are guaranteed for 5,000 miles.

I did not know that. And I don't know if my wife will let me keep any one pair for that long.

I know, I know.

They're growing on her. She initially called them my clown shoes. She was so unimpressed with them. But then I got her three pair. They've just evolved in terms of their fanciness now. So she likes them a little bit more.

Yeah, they're a little nicer.

You brought up something that I want to go a little deeper into. So I made this mistake before with a friend, which was they were wearing orthotics. This was after I'd sort of bought into the thesis that, hey, you don't want to be using orthotics indefinitely. You want to regain the strength that is intrinsic to your own foot. And I sort of tried to help him wean off the orthotics, but I think I did it too quickly, and it ended up kind of causing him pain. So walk us through how you handle a patient. So patient comes to you. I'll just make up an example, but feel free to come up with a different one if this isn't instructive. But this is someone who's athletic, a former athlete, even A former runner, for that matter, who goes on to. Perhaps they stop running and they come back to running. They develop very bad plantar fasciitis. They see a podiatrist who says, the diagnosis is low arches or high arches or some arches, and they need to be in a stiff orthotic. And now they're in an orthotic. And now they come to you and they say, God, I'd really love to run again, but this plantar fasciitis just won't quit. What can you do for me, Dr. Davis?

I always try to educate my patients because they need to buy into this. Our approach is 180 degrees from the approach that they've been given. And I don't want to diss someone else. I just want to say we've got a different approach. And our approach is rather than adapt to you, we want you to adapt to running. And so that requires you using your muscles and your body in a different way. And I give them the example of a neck brace. This is always really very illustrative for them. So if you put someone in a neck brace for life, what's going to happen to your neck muscles? And they say, well, they're going to get weak and I'm not going to be able to hold my head up. So if I give you a foot orthotic for life, what's going to happen to those muscles? We all think that the arch is going to fall, and the arch doesn't fall. The arch actually gets stronger. So when you use that kind of analogy, a light bulb goes on like, wow. Yeah. They don't realize they have 10 muscles in their arch. So I go through that anatomy with them, and I'll show them a picture of it. I go, you've got 10 muscles and four layers in your arch of your foot. They can get stronger. Unless you're paralyzed. I don't think you're paralyzed, right? No. So what we're going to do is we're going to slowly wean you from those orthotics. And at the same time, we're going to be giving you exercises to strengthen your feet so that it can start to take on the load that it's supposed to take off. So what we do is we slowly wean them, and we usually wean them out in the same way I used to wean people in, which is, I'll say, take them out for an hour in the morning, but keep them with you. You don't want to take them out and go cold turkey. And it depends Again, on how much they're doing. If they're walking to work and they're going three miles, you don't want that to be the hour that they take them out. Maybe walk a half a mile without them or a mile without them, and then just slowly take them out and use your body to judge. If your feet are feeling sore, put them back in. And we never take them away from them, and they always can have them. So if they decide at some point they want to go back to. Most people come to us wanting to get out of them because they're a pain, they're expensive, and they've got to replace them at times, and they stink, and they just don't like the idea of it. A lot of people don't. So that's how we wean them out. And at the same time, we are strengthening their feet. And we also. Once. Once somebody has weaned out of them and they're able to walk comfortably without their orthotics in their regular shoes, then we put them in a pair of minimal shoes like the ones you have. There are lots of different brands. We have three brands in our office where they can try them on, decide what they like. Some people's feet are narrower.

So what are the three brands you like people to try?

I want to kind of be shoe agnostic, because I love them all.

Yeah, yeah.

The three we have, just because people have given them to us really are the innovates, the Vivo brand, barefoots and zeros. Those are the ones that people have donated the shoes to us, I think, to their advantage, because those are the ones people are going to try, but there are others as well. And so we get them walking in the minimal shoes because we published a study that showed that simply walking in minimal shoes is as efficacious, as effective as a foot strengthening program. So we had three groups of people in this study. Sarah Ridge from BYU was the first author. One group walked around in their regular shoes. Another group slowly progressed their walking steps in minimal shoes. And the third group went through our footcore program over eight weeks. And the footcore group and the minimal shoe group had almost the same amount of strengthening. Footcore group had a little bit more strengthening. But it's very powerful when you think just put. Putting a pair of shoes on is going to strengthen your feet. And so we have them do that right from the get go. If someone comes to us with plantar fasciitis, it's not right from the get go. And in orthotics, we take that Slowly, because it's important that they develop. They've got to give the foot time to adapt to not having the orthotic.

So what does that look like? Let's go through that in some detail.

Yeah. So it depends on the person and how long they've been in the shoes and how weak their feet are. So what we do is we just try to slowly wean them out over the course of maybe two to three weeks of weaning them out.

And that's sort of the protocol you described earlier, which was maybe just take it off for an hour in the morning as you walk around the house.

And then an hour in the midday and an hour at night. Maybe something like that.

Yeah, got it. Okay. So the first goal of therapy for that patient is if I could get you for a day to just through your activities of daily living, not require full arch support, that's a win. That's step one.

That's step one. That'S right. And then we build their foot strength and we get them to wear the minimal shoes just walking. And our program, when we transition someone from regular shoes, even if they're not in orthotics, to a minimal shoe and forefoot strike, requires what we call our pregait program. So that program can be anywhere from one to three months, depending on the person and their age. The older you are, the more time time it takes. Typically, we're a little less plastic as we age, but it's a program in which we do foot strengthening. We're also addressing other issues. It's not just foot problems, but foot, hip, knee. We're working on functional activities, teaching them how to use those foot intrinsic muscles when they're moving. So it's not enough just to strengthen. You've actually got to teach people how to engage them during the activity. And then we do a lot of off the treadmill copy kinds of activities like hopping and lunging and plyometrics and jump roping and all kinds of things that helped get them to move dynamically but not run. These are components of running. And once they've met certain criteria, which can take anywhere from one to three months, depending on the person and what kind of pain they're in, then we put them on the treadmill and we start to do the retraining. When somebody is wanting to transition to minimal shoes, even if they're completely healthy, I can't emphasize enough that it's not just putting a new pair of shoes on, it's changing the way that you even walk. And it's Putting greater demands on your foot and your ankle. And so you need to give yourself time. And so you need to walk and make sure you can walk for maybe 30 minutes briskly, and then start to interject some running slowly, because if you don't, you're going to load the foot faster than it's ready. And you can create problems like plantar fasciitis or worse, a metatarsal stress fracture. The bones of the foot, every bone, your tibia, those are really protected by muscle. So when you have one of the long bones of your foot, the muscles on the bottom of your foot and the muscles on the top of your foot are balanced so that the strain in the metatarsal is minimized. But if you have an imbalance in that muscle strength, then you're going to get additional strain on these metatarsals, which can lead repetitively to a stress fracture. So it's really important that they strengthen.

You know, Irene, I've looked at more CT scans and MRI scans of people than I can ever possibly count. And let's just say you're looking through the trunk or the legs. The difference between a muscular person who's super fit and someone who's never exercised in their life is so apparent. At the level of every muscle, there's the obvious muscles. You look at the quadriceps. You look at the quadriceps of a muscular person, I mean, you can see those four muscles. They are huge. But even at the level of the rectus abdominis muscles, you take a look at a person who's never done a core exercise or a crunch in their life, and they barely have like, half a centimeter thick of a rectus abdominis muscle. And then you look at somebody who's incredibly fit all round, you see a rectus abdominis muscle that's easily an inch thick. I've never bothered to look at the MRI of a foot for the same thing. But hearing you talk about this makes me wonder, if you look at a person who, who runs in a minimalist shoe, who's been doing it forever, who's got these amazingly intrinsically powerful feet, and then you look at somebody who's using a highly supported shoe. If I show you those two CT scans or MRI scans just on the basis of the musculature, can you see a clear difference?

I don't look at those very often just because I'm more on the rehab side of things. I know that research shows, it's been done with ultrasound, that when people run in minimal shoes, the Volume. We've done a study looking at volume of the foot intrinsic muscles as well as the cross sectional area of each muscle gets bigger, significantly bigger. So I would say likely, yes, you would be able to notice it. I know that those numbers definitely increase. What I also know is there was a study recently done that was presented at a meeting. It hasn't quite, it's in review right now that took healthy feet and put them in pair of orthotics for 12 weeks. And then they had a control group that just were in a pair of shoes over 12 weeks. They measured that baseline and at the end of that time period, the intrinsic muscles size reduced between 10 and 17%. 10 and 17% reduction. And the other group, there was no change at all. Who wouldn't expect it? What does that tell you? We know that when you take away the support, the muscles get bigger. But it makes sense. But no one has actually shown this, that when you actually add support, those muscles get smaller. It makes perfect sense. And yet we don't think about that. We don't even think about the importance of those foot muscles. There was a recent clinical guidelines in the physical therapy journal looking at clinical guidelines for treating plantar fasciitis. And they have all kinds of recommendations. Ultrasound, orthotics, ice, stretching, everything but strengthening. And if you look at the clinical guidelines for something like ankle sprain or knee injury or shoulder injury, they all include strengthening. And that's my own profession that highlights the lack of appreciation for the muscles in the foot. And they're very, very important.

So how many podiatrists would agree with your approach versus disagree with your approach? And is there a position statement taken by the field as a whole on this? Because I've been to podiatrists myself three times in my entire life and every time I did, I walked out with a set of orthotics. Now, it could be that that's just a bad sample size, but that would lead me to believe that the entire field of orthotics is built around that. And I could be very skeptical and say that it has to do with reimbursement and they're making money on the orthotics and all sorts of things. I'll refrain from that speculation. But where does the field as a whole sit in relation to what we're discussing now?

So when I first started talking about this, I used to present at the foot orthotic meetings with a group of podiatrists. So when I started to change, I think they were very surprised and I Have debated on stage a very good friend of mine, colleague, who is very dug in about his dogma in orthotics. And I think it's because they think it's working. I have to believe that he thinks that this is the right thing to do. But we went back and forth. Now, this was probably, I don't know, eight years ago. Now. I don't know what he's thinking now. But I can tell you that more and more podiatrists are telling me, but now they think about orthotics as more of a temporary thing. So I think we're moving in that direction. There are some podiatrists. There's one that I have been in touch with recently who is very much on the barefoot running and all of that. And he doesn't prescribe orthotics at all, which is really unusual. I went down to Australia. I was invited down. And again, this was probably about six, seven, eight years ago. Again, same time period, probably they asked me to give a talk on barefoot running. I thought, gosh, do they really want to hear this? Because it was a big podiatric group. I found that a lot of them were very open to the idea of treating people with exercise and not orthotics. It could be somewhat regional. And these were also younger podiatrists. So the ones that are coming up are thinking differently. My husband tells me, because I am a very impatient person. And he said to me, irene, the way that you change things, the way that you bend bamboo, is a little at a time. You add some water and you bend it, Things are going to be slow to change, and you just have to keep at it. So my goal is to get people back into minimal shoes from day one because I think they're important for kids. I don't think we should be putting kids into really structured shoes, let their feet develop. I think they're important for adults. I also think they're very important in the aging. When you have a shoe that allows your foot to be closer to the ground, you're more stable. That allows the muscles to act. Because one of the things that happens with aging, as you start to lose muscle power, you lose it in your feet and lower extremities first. It goes from the feet up. So if you can do something to help to preserve that strength, that's a good thing. I think it's really important. We're in the process right now. A group of us are writing a paper about the minimal shoe across lifespan, because I think it's not just about athletics, it's about getting people into shoes that let their feet do what they're supposed to do.

I've really come to believe that as well. Irene. I got my little guys some zeros last year because I sort of realized we were putting them into. In an ideal world, I'd love for them to run around barefoot for the reasons you suggest. But look, you want to protect, protect the bottom of their feet. The concrete gets too hot, okay, fine. But putting the zeros on them and hopefully they'll skip some of the stuff that the rest of us did. And to your point, I think as people age, the analogy I like to think about when I talk about feet is the tires on a race car. You watch something like Formula one, right, which is the pinnacle of motorsport. And what you have to remember is all of that power, that thousand horsepower engine, that million dollar car has only four points of contact with the road, and they're called tires. Every bit of force generation in the AP direction and in the medial lateral direction is transmitted through the drivetrain, through the tires to the road, full stop. That's it. So now imagine how much you could de engineer tires to distance them from the road, how much you could create lateral instability, how much you could remove grip from them. And I think about that through the lens of our foot. If you cram your foot into a narrow little box and remove it from the surface of the road, it's sort of like making your tire have less grip, more slip angle, and less lateral stability. None of those things are desirable in a tire. I think if you just sort of think about the importance of connecting to the ground, it does start to become pretty obvious. And I actually like the way you're thinking about it, which is, let's not shoehorn everyone into this box. If somebody comes along and says, look, I'll never be able to give up heel striking, well, that's not a person. That should be going to a minimalist shoe. That's fine. Let's hope that everything else is going okay. I do want to ask you, like, what is a good reference for somebody? Let's say there's somebody listening to this now, who's wearing a maximalist shoe, who's heel striking and either does or doesn't have injury, but says, you know, I want to start thinking about this transition. What are the references to learn how to forefoot strike. Is this just something you just go out and do and start concentrating on?

To be honest with you, I know that there are. People have written books about it, there are Courses on pose and chi. Running. I guess I believe that. That it is our. If you take your shoes off, it's a natural way you want to run. Now, you might still land on your heel for a little while because you're used to it. But it's interesting. When I was in college, I was running maybe about 20 miles a week just to stay fit. And I ended up with. I think. I can't remember what the injury was, but every time I stopped, it would go away. And then when I'd start running, it came back. So I gave up running. I did a lot of inline skating, a ton of inline skating. Did some. Some marathon races and stuff in it. When Born to Run came out. And I met Chris McDougal because Chris came down to. He lived in Lancaster, lives in Lancaster now. And he came down to the University of Delaware because he was doing a story for. I think it was the Times. And he wanted me to run him on the treadmill and run him barefoot and that kind of thing. So we got talking and I said to him, you know, I haven't run in so long, and I think I'd really like to run again. Should I get those Vibram shoes? And he said, you know what? Start barefoot. Just start barefoot and your feet will teach you. And I did. That's what I did. I started running again barefoot. My feet did teach me. It's like, you don't need to be taught to walk now. If somebody has really bad posture. You have all kinds of postures in walking as well. We can improve walking. I'm not saying that you can't improve the technique of someone in running, but I feel like sometimes people overthink it. Get people in that do these really strange things, like they're kicking their butt and they're not running fast, they're running slow, but they're kicking their butt. Like, why are you kicking your feet up so well that, you know, I was told to do that.

So it seems like maybe just going to grass, going to a forgiving environment and running barefoot and doing it for very short periods of time instead of doing, like a long run, say, look, I'm going to go and run a few hundred yards, stop running, regroup. I'll give you an example. I learned to swim as an adult. I guess we could sit here and debate whether swimming is innate to our species. It seems there's probably a very early window in which if you're exposed to swimming when you're, you know, a few months old, it tends to come naturally. But Certainly anyone who's watched a five year old who's never swim, you realize it doesn't look too innate, but nevertheless, I'm 31 when I'm learning to swim. And the only way I could really do it was to understand the technique and do it in very short bursts with lots of rest, so that my technique wouldn't deteriorate, which basically amounted to doing a lot of drills and never really swimming more than 50 yards or 50 meters at a time until I slowly learned how to piece those together. And I haven't read Chi Running. My wife actually has it because Terry Laughlin, who's the guy that taught me how to swim, he's no longer alive, but Terry created a program called Total Immersion for Swimming. He was very good friends with. I forget, is it Danny? What's the guy who wrote Chi Running?

Oh, yeah, I've met him. Danny, Yeah. I can't remember Danny's last name.

I can't recall. But Terry and Danny were friends. And when Terry knew that my wife was a runner, he got her connected. And I guess I should go back and read the book. I'm very curious now about what the methods are, but it really is whether you decide you never want to run for the sake of running, or whether you decide, I actually do want to run. I want to use running as a form of my exercise. I just don't think you can make a strong enough case for why it's imperative that we learn to use our feet better. That's sort of my thinking on this subject matter is the minimalist shoe becomes a vehicle through which we learn to acquire the contact of our feet to the ground. And if you want to run, that's essential.

Yeah, I agree. I want to go back to something that you said about when you start running. This is another thing I asked Chris. First of all, I asked him, should I wear the Vibrams? He goes, no, you really need to go barefoot so you get all the sensory input. And I said, you know, I like to paint my toes. I go, chris, I don't want to get calluses. He goes, honey, the world is your pumice stone. But he told me, don't start in grass. And the reason for that is that when you start in grass, well, first of all, grass is what more dangerous? I've never cut my foot. I have burned my foot on hot pavement at times because I wasn't smart enough not to run when it was really hot. But the problem with running grass is, first of all, you can't see what's there. I'd be a little nervous running barefoot in grass, honestly. I've cut my foot in the sand, sharp shells and things like that. So if you can't see what's underneath it. But the other thing is that when you run on a soft surface, you stiffen your leg. This is amazing thing about our leg spring. You have this ability, this innate ability to modulate the stiffness of your leg. So when you land on hard surfaces, you make your leg compliant. So if you're going to step off of a three foot step and land on concrete, you're going to land as soft as you can. You're going to flex your ankles, your knees, your hips. But if you land in sand, you're going to stiffen. You don't want to collapse into it. So you stiffen on soft surfaces. And there's lots and lots of studies that have shown this, this is definitely true. This is why when you have a cushioned shoe, we'll go back to that, that you tend to land hard. If you train on grass, there's nothing wrong with starting on grass, it's fine. But when you train on hard surfaces, it teaches you to be really compliant. And that's what Chris told me to do. He said, start on the hard surfaces. If you're going to run, do most of your running on hard surfaces. Like people who compete mostly always on hard surfaces. Unless you're doing track, then you need to train your leg to be compliant. I tell people you can mix it up, it's fine, but make sure you do a good part of your training on the surface. You're going to do most of your running on. So don't do all of it on soft surfaces, really. And again, the hardest part is making your leg nice and compression compliant. And when you make it compliant, you're actually using muscles to attenuate. So it's work, it's work to make it compliant. So yeah, I would start that way.

Thanks for clarifying that. That's interesting. Now I want to go up the chain a little bit. You alluded to the knee and I want to talk about other issues of the knee. So is knee valgus an issue? Are you concerned with that? Do you see when a person's running and they have a significant valgus and I'll let you know, explain to people what that is. How much of an issue is that and is that basically always a pathologic finding? Sometimes a pathologic finding. And does it always result from the foot?

There's a lot of questions there I'm.

Known for that, Irene. That's what I do. I'm going to give you a lot of questions.

I'm known for saying there's never 100% of anything. I'll never say always and never say never. There are people who have terrible alignment that aren't injured and there are people have good alignment that are injured. And part of it is because these injuries are multifactorial. And if we just take the mechanical part of it, part of it's related to your structure, it's just how you're built and then how you move, your motor control and then your dosage, how quickly you ramp up and how much dosage you have. So you could have someone who has a problem with their alignment, but they're keeping their dosage down so they don't get injured. So you can look at them and it looks like that they should be injured, but they're not. That might just because they're keeping their dosage down. You can have someone that looks really well lined and really good mechanics, but because they did too much too quick. So it really is not a one to one. And here's the other thing that's really interesting. You can have someone who's got knee valgus and have five people. One could have a knee problem, it manifests as a knee problem. One it could manifest as a hip problem. Another person could be their medial foot, another person could be their plantar fascia. So it's not a mapping of one to one. And you can have somebody with knee problems. One of them might have excessive valgus, another might have a really stiff landing. Do you see what I'm saying? So it's what makes it so much fun to figure out. But it's not straightforward, it's not a one to one one mapping. Having said that, there are these patterns that we tend to see with injuries, so I had to kind of preface it with that. But the two features that we see most often with injuries, and we've had over 700 through the running injury clinic so far at our center, are high impacts, landing hard, and malalignment in general. But the most common malalignment is a medialization of their leg. So when I say that, I mean there's valgus. So the knees come in towards each other. So instead of the legs being straight, the knees bow in, they can bow out. That's why there's other alignments. This is most common though. The kneecap rotates inward, so the kneecaps start to look at each other a Rotation inward of the leg often and the pelvis drops to each side. Every time you land, other side drops down. Then you land on the other leg, the other side drops down. It can be just on one side. All those seem to go together and they're the most common. And I think that a lot of that relates. If we talk about evolution, it goes back to the fact that when we sit as much as we're sitting now in our lives, we don't have the core stability short of if we're really going at it and really making sure that we're addressing our core, which not a lot of people do. And that core instability, just like the instability of the foot, you don't have the core muscle. We call it the foot core for a reason. It's just like the lumbo pelvic core. If those muscles aren't doing their job, then the prime movers can't do their job and you have malfunction. So I believe that we see a lot of this instability because we are so weak in our cores and we don't have that kind of stability. And those kids I mentioned from La Sierra High School, I betcha if I looked at them run, they wouldn't have those kind of mechanics. So it is a very common kind of problem that we see in terms of mechanics is that Valgus Irene, when.

You talk about the elevation and depression of the hemipelvis, I think everybody knows what you're talking about, which is basically the hip hiking that occurs one side to the other.

It's actually not a hiking, it's the other hip dropping.

I see. So the one side is actually staying level, the other side's actually dropped. Depressing.

Okay, right. And it's the side. So if you're on your right leg, it's the right hip that keeps the left hip from falling down. So it's the opposite side that drops. So if on my right leg, it's my right hip muscles that hold my hip, my pelvis level.

I got it.

Because the left foot's not on the ground, it's not under load, it's swinging through. So this drops unless these muscles are doing their job. And then when you go to the other leg, so now I'm on my left leg, then my pelvis is going to drop to my right because the left hip muscles are not doing their job.

You mentioned the core, which is obviously a very broad term. So are you referring to the intrinsic muscles of the pelvis along with the transversalis fascia and all of these muscles, or is it also, in part, the result of the adductors and abductors being too weak. This is such a complicated part of the anatomy that it's hard to get a handle on what muscles. Let's use the example you gave. So the right foot is on the ground striking. The left foot is now sweeping. The left hip has now gone down right. So what's not firing that should be.

I think it's all of the above. I think you need that stability of the small muscles that actually stabilize the hip and its socket. I think you need the abdominals that prevent the pelvis from anteriorly tilting. So you get a tilting of the top part of the pelvis forward and the back part of the pelvis backwards. That tilting is also associated with rotation inward of the thigh. They kind of go together. And then if the abductors are not doing their job, you get the drop. It really is all of it. But you need that stability also of the core. And the core really is the sort of the transverse, the deep muscles that stabilize. And it's not always weakness. We think about it. We talk to our patients and say, you've got your hardware and your software. Your hardware is the strength of your musculoskeletal system. That's your hardware, but the software is your motor pattern. So we see people who are not that weak, but they are a mess mechanically because they just aren't using the muscles in the way that they should.

Another injury I'd like to ask you about is, which I've struggled with not in a long time. I got it under control by strengthening my abductors. But is IT band? And a lot of people get this really miserable pain on the side of their knee. And I think most people are familiar with what that is. But the IT band is this sort of tendinous thing that connects to a muscle called the tensor fasciae latae, which is basically at your hip. What are some of the things that you see exacerbating that IT BAND syndrome? And do any of them actually tie all the way down to the foot? And what we've talked about, it can.

That's a very good point. So we did a study looking at people with IT BAND syndrome compared to healthy controls. And we looked at their mechanics, and we have two studies. One of them was retrospective. That means that these people were now healed, but they had a history of IT BAND syndrome. And we compared them to their controls. Then we had another study where we had people who were healthy to start out with, and we looked to see who got injured and who did not. That is a stronger design because there you can say they didn't have the injury. Here are the mechanics, and it led to this injury. Whereas when you look retrospectively, which is easier to do from a scientific standpoint, you've got to wait for the injuries in a prospective design, but in a retrospective, you can just go and get. People have a history, but you don't know whether the injury caused it or it was there before. We've done both kinds of studies and we found the exact same results, which to me is very comprehensive. What we found in the mechanics was that people with IT band syndrome had greater inward angulation of their thigh, which can kind of contribute to valgus. And the reason that that's important is because the IT band attaches to the distal thigh. There's a very robust attachment not just to the tibia Gertie's tubercle, which is a little bump on the lateral lower leg bone, but it also attaches to the end of the thigh bone. And so when the thigh comes in too much, it stretches it. The other thing that stretches it is when the pelvis drops, because the IT band comes all the way up, and it does in certain tensor fasciae latae and the glutes. So the drop of the pelvis and the inward angulation of the thigh just puts a big strain on the IT band. And if it's already tight, as you flex and extend your knee, it goes back and forth over the bump on the lateral end of the thigh bone. So it just rubs. You get this pressure. You can have that pressure, excessive pressure to start with. And if you increase the amount that your hip comes in and your pelvis drops, it just further exacerbates it. So that's one cause of it. The other mechanic that we saw, both retrospectively and prospectively, again, very strong results, was internal rotation of the tibia. So the tibia is the lower leg bone. Now, the IT band also attaches to the tibia. So as the tibia rotates inward, it stretches the IT band. So when you ask me about the foot, the tibia is connected to the. The leg bone is connected to the foot bone. So if you're excessively pronating, it can excessively internally rotate your tibia. It can be from the foot and it can be from the hip. And when you think about the knee, in all kinds of knee injuries, it's the joint in the middle of the foot and the hip. So it often is the victim of issues with the foot or the hip.

Pronating in this context is the opposite of inversion.

Yes, pronating and supinating, it's just another term for it. But yeah, so you're rolling your foot inward too much. The analogy would be the eversion. Inversion and eversion sometimes also referred to as supination and pronation.

That's very interesting. It speaks to this idea that you've got to be able to at least try to identify the cause of this with some gait analysis. I think in my case, when my IT band hurt, I just assumed it was the first explanation you gave. And it was because once I took on a robust prediction program of strengthening the glute mead, basically, especially from an eccentric standpoint. So really did a lot of eccentric strengthening of the glute mead. All of a sudden you now have the ability to keep the femur out. You take that valgus and lengthening away of the IT band and the pain gets better. I was experiencing it on a bicycle, actually. Not running nevertheless. But the point here is, I never even thought about it through the lens of if you have enough eversion or pronation, you're going to pull on the other head of that tendon which is attaching to the tuberosity of the tibia. I mean, it's really an amazing field you're in because it is truly an engineering field. I mean, it's a structural. One of the things I'm doing with my daughter right now this summer is we're working on physics. She's in sixth grade. It's more about the fun of physics. But last week we worked on free body diagrams, drawing form forces and the direction of this force, the direction of that force, and the magnitude of this versus that. And we're basically just doing Newtonian physics and going through the three laws. This would be a great thing for me to now show her as she's sort of thinking about this muscle's pulling this way, but if this one's pulling that way, look what could happen.

And the ground reaction force is another great example because they are equal and opposite. It's Newton's third law. You push down, the ground pushes you up. So when you push down on the ground, you're a free body diagram of the world. You are pushing down on the world, but the world's so massive it doesn't move. And you get all the Chinese people on the other side, they're pushing up, remember, on the other side of the world. But the force that's coming back at you because your mass is so much smaller creates your movement. So it is all physics. And this is why I have loved being in this field, is because I get to marry physics with medicine.

Let's go back and close the loop then on that sort of forced discussion around how it is that joints can experience an amplification of that force.

So the reason that it amplifies the force is because the ground reaction force, the muscles have to respond to the ground reaction force. And so if you have a force that is directed, say let's take the knee and is directed behind the knee, it's going to create a flexion moment the knee. And so the knee has to extend in order for you to be able to prevent yourself from collapsing. So it creates these muscle forces around the joint. And when the muscle forces act around the joint, they compress the joint inward and so they create an increase. That's how they get amplified.

It's really amazing because, and this will be probably more than you would want to explain to a 12 year old, but this is where the free body diagrams become really complicated. Because it's not just I hit this thing with 200 newtons, it hit me back at 200 newtons. No, that 200 newtons gets into the joint and then the joint has its own internal moment arm that's going to add, as you said earlier, potentially 7x the that force. And then of course, depending on the length of that moment arm, I mean, we're talking about really serious forces here. Do you ever just sit back and look at this and think, how the hell did we even evolve? Like it's so remarkable at what our bodies are capable of, isn't it?

Yeah, it is. And the fact that we're so adaptable is the thing that's amazing. I mean, this is why I love mechanics, because we can adapt. We can't change our structure short of doing osteotomies, which I'm not qualified to do, meaning making changes in alignment in the bones. Mechanics, though, is something that's very modifiable. And for a long time people did not believe that. When I first started in this business, I was a young scientist and I went to a meeting and I talked about gait retraining runners. Wow. I got virtual tomatoes thrown at me. I remember it and people saying, you can't change the way somebody moves, moves. That we have these automatic generators of gait. But if you actually study it, we do have the ability, suprachortical ability to modulate our gait pattern. And so it's been really fun to be able to say Okay, I see that in your gait. I'm going to change it. It's not easy, I have to say it's not easy because in order to change somebody's gait, you have to give them a lot of practice. They've got a certain pattern that they have and they've had it for 20 years, 40 years, 60 years, depending on how old they are. And we've done gateway training across that age span. You need to be able to give them feedback to begin with so that they start to learn. Okay, this is right. This is what I see. That's right. If it's visual feedback, this is what it feels like. Now I know what's right. Then you have to start to fade the feedback. So now they have to feel what's right without having it, because they're not going to have it. And then you have to give them a lot of practice. That process of changing your gait, though, I think it's worth it. If you've been injured and we think that the mechanics are causing the injury, you have to be patient with it and even when you finish. So in our program, I started to tell you, we have a say on average a two month pregate, then they have a three time a week, four week gait retraining on the treadmill. And then they go out for 10 weeks under our supervision. They're out running on their own, but we check in with them. They come and see us at two weeks and at four weeks and they have to start really slow. They can't go really fast because even though they've maybe got the pattern now, if they want to start ramping up, they got to give the team tissues the time to adapt. It is a process that takes patience. And if someone's going to come to us and say, hey, I'm doing this New York marathon, two months, we say, we can't do this right now. We'll give you some exercises and try to help you out. But you're going to need a lot more time than that.

What percentage of those patients, Irene, are people that have no injury but have bought into this thesis, which is my gait's probably not adequate and I'm going to get injured one day. So I want to do this in a totally preventative manner versus people who are actually under the spell of some injury at the time that they show up.

So in order to be able to have the treatments paid for, you have to have an injury. They wouldn't get it covered in terms of retraining. So I Would say we have had people come in for just an eval for us to kind of take a look at their gait. Sometimes a spouse will give it to the their spouses, a Christmas gift or something like that. But in terms of people who come through the program, it's 100% people who've.

Been injured, which seems to be a bit of a failure of the system. That's sort of the same problem we have in medicine, which is, look, we'll wait till you have type 2 diabetes, at which point it's going to cost the healthcare system somewhere between seven and $12,000 a year, including insulin. But God forbid we spend, I don't know, $500 a year on pre prevention to make sure you never get type 2 diabetes. It seems to me that a great investment, at least for the people who are motivated, would be taking people who are not injured and teaching them what you are talking about.

So let me tell you about a study of one of my colleagues. He was one of my postdocs that he went on and did a study where he took 320 novice, meaning they'd been running a year or less. I think they'd all been running at least a year, but not much more than that. And then what he did is he took half of them and had them train on a treadmill. Because the same kind of retraining program we have where they had a monitor and they could see those impacts that I was telling you about. And I can give you some graphs of these. And so what they did is they were told to get rid of the impact, to land softer. And he didn't monitor what they did, but in order to do that, they probably got off their heels. And then the other group went through the same eight sessions. They did eight sessions. They slowly ramp up from 10 minutes to 30 minutes over this eight sessions. And then he followed them for a year. And these are healthy people. 62% reduction in injuries in the group that was trained to land softer. 62% reduction over the course of a year. That's huge.

What's most amazing to me in that study, if I understand you correctly, Irene, is that they weren't given an explicit instruction of how to change their form. It was basically they adapted to the visual stimulus of just make that spike smaller and they figured out what to do. And then in what sounds like a relatively short period of time, made the adjustment. The adjustment stuck. Am I replaying that correctly to you?

Yes, I think you are. The thing that we're not sure of, because he didn't. And this is one of the criticisms of the studies that he never brought them back later to see if it did stick. So not sure. And it may be that so some people did get reduce the spike where others may have eliminated it by being on the ball of their foot. I would like to know if the people on the ball of their foot had less injuries. Dan's group did a study Dan Lieberman's group did a study looking it's retrospective of the Harvard track team and found that the kids who were forefoot strikers on the track team had half of the running. He classified them into over overuse injuries and they had half of the injuries of the rear foot strikers. Because it's retrospective, it's not as strong as being prospective. But another really interesting piece of information in terms of how this might apply to running teams is that there's a group, it's a close Christian community and I won't name them because they don't want to be named, but it's a close Christian community. The dock of the closed Christian community basically went through medical school. He's a physician and he had all kinds of foot related problems and all of his residents and fellows and colleagues who were giving him advice and he got like three pairs of orthotics and nothing helped him. It was when Born to Run had come out and he kind of looked at it and put the book down and they decided to read it and then he decided that he's going to try to go barefoot and minimal and it cured his problem. Resolved his problem. Not to say it's cured it, but it resolved his problem. So now he, as a member of this community, they pay for your medical school and then you come back into the community and he's the physician in the community. The track team of this community had had some members that had season ending injuries, running injuries. But before that he started to prescribe minimal shoes for some of his patients that weren't responding to standard of care. So he used to really send all of his foot related patients to a podiatrist. And then he started deciding, hey, I'm going to try this because it worked for me. So he had this first woman who just wasn't getting better with the orthotics and the standard of care. So he said, look, I know you may think I'm crazy, but would you be willing to try this? And it worked. And they tried it again. And he tried it again. And he tried it again to the point where he was so convinced that this was working they actually decide the footwear. They have a clothing store because nobody pays for anything. It's all common money. And then a clothing store. He ordered minimal shoes. So 80% of their community now are in minimal shoes. And he showed a graph of the number of referrals to podiatrists went down as his prescription of minimal footwear went up. And with that success in the normal community with one walking, he decided to try it with the cross country team. He was the physician for the cross country team. The coaches went along with it. So they basically started in January and had the kids start transitioning in January before the September season. So they had, what, nine months of slowly working into the minimal shoes. And they ended up that year having no injuries and winning their division. And then they had a second year of, I think, winning. They got bumped up, even though we're a small school, because they were so successful. They got bumped up to the next division. I think they came in second. And they had basically no injuries like one sprained ankle, but no tibial stress fractures, no plantar fasciitis, no anterior knee pain. No it. All the things that you see. And he's had a third year. I think this is the third year. And then we had. Yeah, he had a third year because Covid. I haven't really talked to him since. Since I can't publish this because they want to stay private. And I understand that, but it's just unfortunate I can't publish it. But basically it's just an example when you have this kind of ability to control it and you look and see that it can have that kind of result. This is why I say I would love to see people all start their kids this way and have people run this way. I think our running mechanics would improve. I think we wouldn't have the same kind of problems with. I don't think we'd have the same kind of problems with knees. This is my hypothesis, and I admit it's a hypothesis. And some people think I'm a little bit crazy, but I don't. We're really coming back to your points about evolution. It's the way that we evolved to be. And so I feel like we have everything we need and that when we start to add shoes. We haven't talked about this much. You add torques to the ankle, knee, and the hip. So when you look at the torques at the ankle, knee and hip, they are the lowest with barefoot, that's like your gold standard. And the minute you start to add footwear, low heel and Higher heel and more athletic shoes with more flares to the outer sole, the torques go up. Now, does the increase in torques cause a problem? I don't know, but they certainly are increased above what we're adapted from. It's like, how do we facilitate natural movement in a modern world? And it's a challenge.

I share your view, I share your bias. I'll say that that if you took every kid when they were born and you kept them in minimalist footwear and they never sat down in chairs, so you squatted, you sat on logs, you stood, but this idea of a desk and a chair was taken away, I would put those as two of the five most important things, things you could do. Like if I could be czar of the world and I could have five things that I would do to change human health. And I was given the liberty of going and starting at the beginning. So saying you could implement these changes from the moment a person is born. Those are two of the five I'd take right there.

I couldn't agree with you more because we see so many problems with feet and hips and it's all related to that. I just couldn't agree with you more. I think that we got to start it there and I think that we would be solving a lot of the problems. We're going to get phys ed and this is going a little off topic, but I'm really wanting to see phys ed back in schools every single day. And not just dodgeball, but activities that actually calisthenics, push ups, sit ups, using your upper extremities, monkey bars, kids hanging from. I mean, we don't do that anymore. I think we need to really encourage that kind of activity. The statistics are overwhelming. It's just so unbelievable. I think by the time adolescence, you're 12 to 17 years old, on average, kids have at least one chronic disease. Not all kids. Maybe it was 40% of kids. I can't remember the exact numbers, but it was really alarming. And a fairly large percent of them had two chronic diseases as adolescents. That to me is really alarming. We shouldn't be having chronic diseases as kids. Diabetes is really high in kids now. It's grown, it's really increased.

Yeah. And I think the chronic injury issue is another problem, which is if you're a kid that if you're having knee pain and hip pain and all these sorts of issues when you're 18 or when you're in college, it's not like it's going to get better when you're out of college without a very deliberate effort.

We definitely need to get our kids so that they're not doing a single sport. It's been shown that those kids actually burn out quicker. They get injured at a higher rate, that it's important for kids to be using their bodies in a number of different ways. That multi sport athlete is much healthier than the single sport that's doing soccer all year long.

Irene, I gotta say I'm pretty glad that Hoover sent you that rejection letter.

Yeah, me too.

50 years ago. Right? Because I think the human condition is a better place for you not having become an FBI agent, though I'm sure you would have been an excellent one at that. And despite what you said about your patience, I don't detect in you someone who has an unhealthy amount of impatience. I detect in you just the right amount of impatience, which is you've kicked the hornet's nest enough, You've stirred up the pot enough. But what impresses me the most in this discussion, and I knew from reading what you'd written and sort of your credentials that this would be an interesting discussion. But what doesn't come across in all of those is how malleable you've been in your thinking and how many ways and times you've changed your view based on new evidence that's put forth. And that leads me to believe that five years from now, if we speak again, you're going to have something different to say, which I always view as a sign of good thoughtfulness. With that said, I want to thank you very much for your time. I know people are going to enjoy this, hopefully half as much as I did.

Peter, it's been really fun talking to you because I think we are like minded and like spirited. Thank you very much for the opportunity. I really have enjoyed it. They're not always as much fun as this one was.

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