 Hello and welcome to lecture five of the Sports Biomechanics lecture series supported by the International Society of Biomechanics in Sports and sponsored by Vicon. I'm Stuart McCurlay-Nailer from the University of Suffolk and today I'm joined by a very special guest. I have with me, Vowta Huckammer from the University of Massachusetts Amherst and Vowta is going to be delivering a talk that I know a lot of people have been looking forward to since this series was first announced. Vowta will be talking on the influence of running footwear on marathon performance with a specific kind of hint towards the sub two hour marathon. Vowta has a really interesting research portfolio on this topic and covering areas such as running shoes, drafting and even course design. So I think he's going to touch on a few of those topics today, but like me, I'm sure you're looking forward to that. I'll hand over to Vowta and just one last thing. Sorry, if anybody has any questions, if you can either use the comment or chat section on YouTube, or use the hashtag at the bottom of the screen now on Twitter. I'll keep an eye on both of those. And then once the talk is finished, I'll direct your questions to Vowta. So over to you. Thank you. Great. Thanks Stuart for that kind introduction. So yeah, my, there we go. Yep. There we go. Yeah, so I'm assistant professor at the University of Massachusetts. Sorry about that. So I'm on Twitter and my lab has a website that you can find there and I will be talking about running footwear and the two hour marathon. So this all kind of started for me about five years ago when I was a post doctoral researcher at the local motion lab run by Dr. Crum at the University of Colorado and Nike reached out to us with a very specific question about whether we can use lab measured improvements in running economy to predict improvements in distance running performance. And that I was going to do that research and do similar research over the next five years. If you would have told me that six six years earlier. I would have laughed at you because six years before I was back in the Netherlands, studying human movement sciences spending a lot of my time on the track running, dreaming about studying the biomechanics of running footwear, but not necessarily taking any steps that will get me to where I was happily in my comfort zone. And I was luckily enough that at some point this opportunity arose where I could spend some time abroad for my master's thesis research. And I had to be pushed a lot by people in my clothes around me that said like this is great for you and I was like no I just want to run on the track and stay where I am. So luckily kept pushing and I made the decision to go to the US to do my master's thesis and that sort of started everything for me and it was probably the best decision I've ever made. So eventually that got me here and that also got me in Colorado in 2015 specifically trying to answer this question. So there we go we got our first take home question for today or the stay home message. Dream big but be ready to leave your comfort zone when an opportunity arises. Otherwise you don't get anywhere. So going back to that question. I don't have the time to go into the details of the research we did. Let's tell you the conclusion that yeah at that time we learned that if we do a lab test where we see that people use less energy to run. We can use that to predict how much faster they will run. And at that time we even thought that was a one to one relationship. So that finding allowed us then to go back to the literature and looked into all the different studies done in the lab where people try to improve running economy by your different scenarios and then we could see if we could apply those to breaking the two hour marathon all with our goal within the rules for record eligibility. So we looked at aerodynamics like drafting until wind we looked at a course design and also about shoe technology obviously. But like I said important for us for this study was that we kind of wanted to acknowledge the rules and try to do this within the existing rules and basically our conclusion was that it was possible. So one of the big conclusions we had from this paper was that was possible. And one of the scenarios you see on the screen right now is we have for example on the top corner we talk about for runner drafting which is a cooperative drafting strategy so different from what happened at Monza in Vienna where Kipchoge was running behind a fresh team of pacers every lap. We sort of suggested that if we bring best together the best runners in the world and they sort of work together as a team and all of them are going the full distance, but they could still alternate who's leading and who's drafting. They could still gain a lot of time and after this review we actually followed up with more detailed simulations of these scenarios and two papers on that are actually below in the link. But I won't have time to go into details about them right now. Another thing is what specifically to those rules so the IWF rules at the time said to do the maximum allowable downhill you can have during a marathon should be about 0.1% of the overall course distance so in this case we're talking about a marathon of 42 kilometers so you can drop about 42 meters so we then said okay let's try to find a course or design a course that exactly drops 42 meters and then we quantified how much time we could gain with that, which was about 30 seconds. And then that later became relevant again when the INEOS team actually reached out to us to get some advice about the course design so we then ended up writing up our analysis over the Vienna course, including the uphill and the downhills and the turns and that's also a preprint that is freely available in the link downstairs. And then finally, we suggested that other than Dennis Kimmetto's Adidas shoes which weigh about 250 grams it should probably be possible to make a shoe that is as good but only weighs 150 grams and I would save him about 30 seconds during the first 30 seconds during the second half of the marathon. And even though in the lab we were already testing this new Nike prototype shoe that eventually became the 4% shoe, we couldn't really talk about it in the review because we hadn't published this data yet so sort of like two stories that we had to tell the one that we could tell and the one that we already know was going to be probably way more important than all of the other ones combined. But that's just how the timeline was at that time. So I'm going to be talking about running footwear and the two hour marathon. So there might be a lot of you that hope I will be talking a lot about the Nike Alpha Fly next percent shoes. There's not a lot of scientific data out there that is freely available so I can't really talk about that. Then I can't also not talk about the specific vapor fly elites that were made for the Monza breaking to attempt again because there's no data. So I don't necessarily be talking about the next percent shoe that keep chogi was wearing when he said the official world record in a marathon in Berlin, but we're going to go all the way back to 2016 to when he won the Rio Olympic marathon. And at that time, people didn't really know but he was actually wearing one of the first iterations of what became the vapor fly 4% shoe so that's actually also the shoe that we were testing in the lab. It looked very similar and this eventually became sort of the vapor fly line starting with the 4% the leads the next to the Alpha Fly. So we in Colorado studied issues like I said, and we set out to compare the Nike prototype shoe against sort of like the state of the art top of the line running shoes at that time. So we went with the Nike streak shoe and the adidas boost adios boost to shoe that basically if you looked at the world all time list in marathon times at the time we started the study. The top 10 of times set were all running either the Nike shoe or the adidas shoe so we were really starting at top of the line and use that as a baseline to compare the prototype shoe against. And obviously, since we're in a sports biomechanic lecture series we want to talk about the biomechanics. But before I can start talking about the biomechanics of the Nike shoe I want to talk a little bit more just about the mechanics of the shoe. So we were able to determine the mechanical properties of the footwear so the way we did that is, in two ways, one of them was just looking into sort of like the foam cushioning and energy return properties and we do that by vertically loading the shoe in compression, the midsole, using this instrument machine and we in this case made sure that we not just loaded it, we also made sure that we applied about a similar peak load as what a runner would experience during mid stands while running at a very fast marathon pace. We also made sure that the loading cycle was short, kind of also similar to simulate the time that the shoe typically spends on the ground during a step. And when we loaded the shoe with that loading rate that you see in the top graph, we can then measure the deformation. So we get this force deformation curve, which shows how much shoe deforms when loaded on their specific form. And here you see what would happen if you would load the shoe in this case. It's a foam so it's not necessarily a linear coil spring so you can see it's not a perfectly straight line, but for this foam, it's pretty close. And then what we can do from that the slope of this line is actually what we call the stiffness, which is force over the displacement. And we can rewrite that to show that the displacement is equal to force over the stiffness. Now the interesting part about this force deformation curve is that the area under this curve, that is actually the energy mechanical energy that is stored in the shoe when you load it. And you can see that, because we know that if this would be a perfectly straight line this would be a triangle and the area of this triangle would be equal to have times force times displacement. And you can rewrite that in different ways. One of the ways would be that the energy stored is equal to have times the spring stiffness times the displacement squared something that you all know of. Another way to rewrite it which I personally prefer is sort of substituting the displacement by the force over the stiffness, because what we see there is actually that energy storage goes up with the inverse of stiffness. So if you want to store more energy in a midsole, which you know the force of, you want to take a less stiff midsole, not a stiffer. So same for spring. If you want to store more energy, you want to have a more compliance spring because stiffness is actually in the denominator of the equation. Now this is when we load the shoe. If you then, like you saw in the diagram, we first increase the force, then we decrease the force, then we can also measure how quickly the shoe sort of bounces back. So here you can see that when you unload it, it's not following the same line. It's actually coming down slightly lower, which means that this is what we call hysteresis, and it's the energy, the area between those lines is the energy that is lost during the loading cycle. This also means that the area under the bottom line is actually the energy that is returned every loading cycle by the shoe. So we quantified all these properties, so both the stiffness or the total amount of deformation and the relative amount of energy return. So looking at the three shoes we tested, here we have this graph, which I basically just showed you for the streak shoe, which deformed about six millimeters and returns about 65% of the energy during the loading cycle. And then we can quantify that in joules, it comes out to about 3.3 joules. Then we did the same thing for the data shoe. It's about the same compliance or stiffness, it deforms about six millimeters when we load it with these two kilonewtons. But what you can see in this graph clearly is that the area between the lines is smaller, which means that there is less energy dissipated in the data shoe than in the streak shoe. If we quantify that less energy dissipated, more returned, in this case it's almost 76% that is returned. Again, we can calculate that in joules and we get about 3.6 joule energy return. Now what about the prototype? The prototype sort of used that concept that I just showed you, if you want to store more energy under the same force, you want to make less stiff or more compliance with sole. And when loaded with two kilonewtons, this shoe deforms about 12 millimeters, so it's less stiff. It means that the area under the top curve is a lot bigger, that means a lot more energy gets stored. At the same time, this new mid-sole material is also more resilient, so it's wasting less energy or dissipating less energy and there's less hysteresis. The area between the lines is also relatively smaller. In this case, this more resilient bounce here mid-sole foam returns about 87% of the energy that is stored. So combining those numbers, we'll see that the total energy return every step is about twice as high in the prototype shoe than in the other two shoes. Obviously, that's not the only feature about the shoe. We also looked into the bending stiffness of the shoe because obviously we all know that it's enforced by a carbon fiber plate, which has a purpose to provide stiffness in bending. So to determine that, you can generally use a similar setup where rather than compressing the full shoe, now you put the shoe on two supports and then compress it right in between those supports and see how much it bends. From that test, we can calculate how much torque we apply and how much it's resisting flexion, and that gives us the bending stiffness. Typically expressed in either new to mediums per radian or sometimes based on this three-point bending stiffness test in the amount of displacement in millimeters divided by the force applied. So we applied a similar test to these shoes and found that adding the carbon fiber plate to a shoe based on the properties of this specific plate makes about twice as stiff as the other two shoes. So we got a shoe that when loaded vertically returns about twice as much energy and when flex is about twice as stiff. So how does that affect running performance or running economy? So before we go into detail about the biomechanics based on the mechanics I just explained you, first going to look into what is the overall response of the human runner with the shoe. So we measure that by looking at their metabolic rate or we call it running economy. So running economy is defined as a specific metabolic rate that we measure at a specified sub-maximal running velocity. We do that in the lab. We measure oxygen uptake and we make sure that the runners are sub-maximally because we are only measuring aerobic contribution to the metabolism. So we want to make sure that when they're sub-maximal they're not relying on any anaerobic sources. And that also helps us to test multiple shoes in a series without having the runners building up fatigue from the start to the end of the protocol. And we measure that for the three different shoes and this would be the place where I would go into a lot of details about how much care we took to all of the details of the study. But I don't really have a lot of time to do that here today. I just want to give you that take home that in sports science you need to be paying attention to the details of everything you measure because that's how you get your results and that's how you get reliable results. So now to take home if you want to build a career in this field pay attention to the details and be careful with all your measurements and be careful with all your analyses. So what did we find after what I think was a very careful study? We saw that when we looked at energy cost of metabolic rate or running economy that between the Adidas shoe and the Nike Streak shoe the energy consumption was basically the same. Metabolic rate was on average the same. You can look at the gray lines. Each gray line represents one individual. Some people end up, some people went down. But then when we started adding in the third number for the prototype shoe, you can see that all of the gray lines are going down, which means that each of our 18 individuals in the study is using less metabolic energy while running in a prototype shoe. On average, the group average was 4% less. And then we didn't just test it at this velocity of 14 kilometers per hour. We also tested it at 16 and 18 kilometers per hour. And we saw that those savings were consistent at all speeds. All runners use less energy in a prototype shoe and at all the speeds, the difference for the group was about 4%. And that is then what eventually inspired Nike to name the shoe that they, the next version of the shoe that the Nike Vapify 4%. Well, that's so great, but we are biomechanists. So we are mainly interested in how does that work? We know the mechanical properties. We know that it works. People use 4% less energy, but how does that come about? And so that's why we need biomechanics. Here you see a picture of the lab setup when we did a second follow up study where we specifically focus on the running biomechanics. So our subject is running on force measuring TREP mill, which has allowed us to measure the forces, ground reaction forces, the forces exerted by the runner underground or the TREP mill. And also in the corner of the pictures, hopefully not hidden behind my face is a Vicon camera. So we had markers on the different joints of the legs and of the segments of the leg. And we were able to measure kinematics. So we have ground reaction forces from the TREP mill and kinematics from the cameras. And that allows us to do a lot of joint mechanics. So one of the joints that was a lot of interest to us was the metatarsal phalangeal joint. So this is where I'm actually quickly going to try to step out of my shared screen and go live where I'm going to show you the metatarsal phalangeal joint. So this is a foot model and these bones here are the metatarsal. So this is the mid foot. And then here there's a series of joints with the toes, the toes of the phalangeal bones. So this is the metatarsal phalangeal joint or in short the MTP joint. And it's important in walking and running because it allows us to do a nice roll off with the foot. And since this model is actually pretty stiff, I'm going to just show it with a shoe to make my point. So when we have a runner coming in landing on the ground, during the roll off, there's a specific point in time where the mid foot is moving against the toe segment. And it's applying a fourth in the other direction. And this part is actually where at this joint a negative work is performed or energy is dissipated, dissipated or stored. We actually don't know that it could be dissipated. It could be stored in the elastic structures of the foot, like the plantar fessia, things like that. Either way, you can imagine that that is negative work, and it might be dissipated, and there might be active muscle contractions going on to restrict that movement. So what if we add a carbon fiber plate to a shoe to prevent that. So this is my analog for carbon fiber plate. And we put it under the foot, you can see that in this case. There's no way that the toes aren't going to flex because they're supported by this very stiff plate. And so this is kind of what happens when you have a shoe like this. Like the normal shoe, you have to flex the stiff shoe, you don't have to flex or you have a lot of less flex. So that is the theory for the specific MTP joint. So let's see if that actually holds up in the data. Alright, and back on the data screen. So what did we see when we measured at the MTP joint? Well, first you measured the joint angle. And you can see here in green, we got in this case the Nike streak, which flexes a lot up to 30 degrees near the end phase of the stance phase just before takeoff. And then you see that the prototype shoe in orange is flexing almost half as much so a lot less. So yes, the theory works if you apply a stiff structure to the food, you get a lot less door deflection at the MTP joint. Now we can also because we measure the ground reaction forces and know where the MTP joint is relative to the ground reaction force factor, calculate the moment. And we see here that the difference in moments is small. Well, the next step what we can do is then use the joint angular velocity, the derivative of joint angle, multiply that by the moment during every instant during the stance phase, and we can get a measure of joint power. And what is interesting about joint power is that the area under the joint power curve is actually energy that is either dissipated or stored when it's negative or when it's the area is positive that is energy that is either returned or generated. So in this case, you can see that there's less energy dissipation at the MTP joint because the area, the negative area under the orange curve is a lot smaller than the negative area under the green curve. So yes, it works. But since we knew the actual mechanical properties of the shoes, we can also calculate how much the shoe by itself is contributing to this. So this is measured at the MTP joint from a runner with his food in a shoe. This is the overall combination of the food and the shoe. But we know how much the shoe is resisting flexion and we know how much it is flexion. So we can measure that. So using the angular changes at the MTP joint, combining that with our stiffness measures, we can calculate how much the shoe is resisting flex and generating a moment. When we do that, you get these curves where you can see that is fairly similar, which is interesting. It's sort of the result that we know that the orange prototype shoe is twice as stiff, but is only flexing half as much. So it's about the same when you talk about the resistance as the other shoe. Then obviously next step is we can then again combine the angular velocity with the moment to get the power that is specifically happening at the midsole of the shoe. So we can quantify the energy that is stored and returned. So again, the area between zero and the line, the negative area is the energy that is stored in bending, and then the positive area is the energy that's returned from bending. And in this case, there's no muscles in the shoe, so this is all passive elastic storage and return. So looking at this diagram, we can confirm the carbon fiber plate does function as a spring. It stores energy and it returns energy. We also know that the other shoe seems to do a little bit of it as well, and you can see that too when I flex it. The question then is, is this substantial? Is this whole 4% of metabolic energy savings that we see from running these shoes because there is some energy stored, inflection and returned by the carbon fiber plate? Well, we can quantify it and we quantified it and it comes down to about 0.16 joules per step. And then we still don't really know, is that a lot? But let me go back to what I showed you earlier when we had the numbers when we vertically loaded the shoes. From this test, we saw that every loading cycle, the shoe returns about 7.5 joules, just from vertical compression, basically from the midsole foam. Interesting was because we loaded the shoe in a way that represents the forces that it actually experiences when somebody is running every step, we know that this 7.5 joules that is returned is returned every loading cycle or if you want every step. So here you can see that the carbon fiber plate does return, store and return energy, but it's almost about 50 times smaller than the total amount of energy that is returned in the shoe in vertical compression. So, we know carbon fiber plate sort of is a good thing around the MTP joint, but it's not a big contribution as compared to the vertical compression. So what about the ankle joint? So let me step out this again briefly to show you another concept. So I just showed you that we can stiffen up the MTP joint so that there's less flexion there. I also showed you like we have an MTP joint and we can flex there. And that's usually a good thing and during normal running that helps us a lot. So when we're running and we're flexing, what happens? We keep the moment arm between the ground reaction force and the achilles tendon short. So let me show you that again. So in this case, when we have our foot and we're flexing, we means that we can apply the ground reaction force under the full toe segment. So the pivot point right now is kind of why the MTP joint is. You can imagine that my Achilles tendons that having to lift the whole body over this pivot point have a lot easier job doing this than when they have to lift it all the way over this longer moment arm, right? And if you don't believe that, what you can do at home is start stepping on a step, standing on a step. And when you're standing like this at the edge of the step, it's probably really easy on your calves. But then you just go backwards and when you're standing like this, you start feeling something in your calf muscles. You can imagine that if you're all the way forward, your calf muscles are going to work a lot harder. And even at the point of your toes, that moment is even bigger and your calf muscles need to work even harder. So that is kind of what happens with the plate and the moment arms around the ankle. So let's see if that is something that hold up held up during our tests as well. There we go. So what do we see? Well, we saw small changes. We saw that the joint angle was slightly smaller, was a little bit less door deflection at the ankle in the prototype shoes. But we saw that even though I just explained you when this is stiffer, we would expect a larger ankle moment. It wasn't really there. And that might be because what I just showed you was everything with a very straight plate. And we had this pivot point under the ball of the foot. The way Nike went around that is by giving the shoe a quite substantial toe spring, which is basically how much it comes up to the front. So you can imagine if this was a plate that was fully flat, and we have to go around this pivot point. That's a lot harder, which I just showed you. But because of this toe spring, the roll off doesn't get as much boost forward, even though it's stiffer around the MTP joint, it doesn't necessarily make it harder for the ankle. So that was a sort of a surprising finding, but we can explain it by the curvature of the shoe. We also sort of quantified how much energy is negative energy is negative work happens at the ankle joint so this is energy that is either dissipated or stored and then the positive side is the energy that is returned or generated. And we can quantify that. Again, remember for the plate. We had about point two jewels for the full shoe and compression we have seven and a half. If we just compare that to the full ankle push-off, that's 55 jewels. So that's a lot. So this spring function of the plate is so much smaller than what the ankle is doing. Well, the thing is, let me go back to that one. We have a bigger push-off, but is that necessarily or we have a smaller push-off actually in the MTP joint in the prototype shoe than in the other shoe and is that necessarily a good thing or a bad thing? We don't necessarily know that because we do know at the ankle a lot of the energy fluctuations are not necessarily energy dissipations and generations that are actively generated by muscle forces. But a lot of that is energy that is stored in Achilles tendon and then later on returned. So there is this stretch and release of a tendon. So even though we can quantify these joint mechanics, it doesn't necessarily tell us everything about how much muscle fibers are active to sort of generate these forces because we don't quantify or able to quantify the storage and return of the elastic tissues and we also are not capable to quantify or when you look at individual joints, you don't take into account any energy that is negative that might be then transferred negative from the one joint to be positive at the other joint. So that's another thing to keep in mind when looking at joint mechanics. And there's a third phenomenon that I want to explain to you to about the plate, which we didn't quantify, but it's interesting because it might be an important contributor to the function of the shoe. And that's related to the muscle shortening velocity. So I just said, when we're looking at joint mechanics, we don't know how much is happening at the level of the tendon and how much is happening at the level of the muscle fibers. So there's different approaches to that. And first I want to show you the concept how we can look at shortening velocity. So here we have a foot and it's traveling at two hour marathon pace or 21 kilometers per hour. And we can transpose the treadmill velocity into the ankle angular velocity by using the external moment arm. In this case between ankle joint and perpendicular to the velocity it's moving. Then when we know the angular velocity at the ankle joint, we know the internal moment arm between the ankle joint and Achilles tendon, and we can calculate how much the total muscle tendon unit is shortening. And this was the scenario without a plate. If we add in a carbon fiber plate, the concept still holds, but things are slightly different. So if we can start comparing the two sides, the treadmill velocities are the same. So we're still running to our marathon pace. But in this case, with this plate, people get higher up on their feet and the external moment arm is slightly higher, which means that the ankle angular velocity is actually slightly slower. So for the same running velocity, the plate sort of allows the ankle to move at a slower velocity. Which then, because the internal moment arm is similar between the two sides, results in a shorter and slower shortening velocity of the muscle tendon complex. So we talk about the calf muscles, which involves Achilles tendon. Then that is at the level of the muscle tendon. The next thing we can then look at is how much the actual muscle fascicles in the calf muscles are shortening. And people have done that, not necessarily for the Nike shoe and not necessarily for running. So Kota Takahashi did a nice study in 2016 where he looked at this for walking. And what we see on the horizontal axis is increases in bending stiffness of shoe conditions. And you can see that at peak force, the muscle fascicle shortening velocity actually decreases with increasing shoe bending stiffness. And that obviously can be expected to reduce the energy that is associated with generating those forces. Then recently, and currently not published, but it's out there in a preprint, Owen Beck did a study using similar footwear where he actually measured shortening velocity of the muscle fascicles. And by the way, you do that by applying ultrasound probes on top of the muscles and looking at the actual fascicle shortening length from the ultrasound imaging. And he saw that overall, maybe you could see that for the the stiffness condition, the shortening velocity was slightly slower, but this wasn't significant. And it's also important to note that the vapor fly shoes are expected to sit somewhere around that 45 kilo Newton per meter bending stiffness that they assess. So there it might even be higher, even though none of these things were actually significant. So what's going on there, we really don't know yet. And there's a lot of things happening. And this is a study done for a study with shoes and flat carbon fiber insoles. We know that in this shoe, there's a different geometry. There's a curved plate. All those things might have different effects on all of these things. So before I wrap up quickly want to touch on what's next. So we just saw that things are complex and we can measure things, but they don't necessarily explain us how they directly affect energy costs. And now the next challenge is how to look into findings from the one study that use the one shoe versus the other study that use the other shoe with an insole or another way of stiffening it versus other companies putting out different shoes. In this case, you see five shoes that are either just came out or are about to come out where different companies like New Balance and Sokone, Hoka and Asics. Brooks all have their own sort of next version of the vapor fly by they have a carbon fiber plate with some sort of geometry or curvature or not. And specific location in the midsole combined with a high real resilient foam, but all of these have slightly different properties. So what we're going to see in the next few years is maybe more studies into this but it's always important to keep in mind that the slight differences in geometry might have different effects on the ankle and the NTP joint. And it's hard to predict the overall outcomes. What we're going to see is a lot more marketing on the one side and a lot more fake news on the other side. So this is an example where right after Kipchoge ran his sub to our marathon. People were speculating about the shoes he was wearing. Somebody dug up and patent from Nike and pulled up one figure and then started claiming that Kipchoge was running in a shoe that had three carbon fiber plates and two layers of airpods. Then somebody went ahead and used Photoshop to actually add those second layer of airpods, which were not even in the picture of the shoes. And guess what, eventually came out that there's actually about 60 different figures in the patent application and some of them have multiple layers and multiple plates, some of them haven't got any plates. And then when it was released, we know that the Alpha Fly right now has only one plate and only one layer of airpods. So again, fake news. Other fake news people speculating about the costs, they're going to be $400 when the Alpha Fly shoes came out. And then somebody saw that video or image and just made their own version and made them $450. So there's a lot of things going out there that you have to be critical and careful about. Other things is like, this is going to be next. We already have a sub to our marathon now, but if we allow carbon fiber springs, next thing we'll have it is people bow going around and running a one hour marathon. Well, if you think about it, this guy is not running a one hour marathon and if he could he probably would be doing it. These things are really heavy, so they're not going to save him any energy but make it even harder. So just as another advice in the take home message to think critically about what you see out there on the web and think if it makes sense and see if you can find the original sources. And while I'm at it, I also give you another exciting advice that think critically about your own opinions. It's always an opportunity when there's new data or new insights to update your own opinions about things. All right, I think I'm going to wrap it up quickly want to acknowledge the people in the lab in Colorado we did the study with and the people at Nike you see here. Also want to acknowledge that being a white male gives me privileges, which gave me a step up to get where I am now. And finally want to acknowledge my current lab at UMass people in the lab we have our website up there, and our funding sources, Buma, VF and Nike. Thank you. Brilliant. Thanks for that was genuinely really, really interesting. Even from before we went on air just chatting to about I could talk for hours about this there are so many kind of interrelated components and it's really difficult trying to tease them all apart. So just as kind of one, well, maybe quick question as long to throw in just one more component. How does foot strike pattern kind of interrelate with all of this. That's a great question and that that might be something coming back to my last point too about the thing critically and the fake news so for some reason there's a lot of journalists that reach out to me talk about the shoe and they always bring up that the shoe is made for four foot strikers and that they only work when you're a four foot striker. To be honest, we don't really know that we in our first study we looked at this we had these 18 runners and about half of them by random chance were heel strikers and the other half were midfoot strikers. And when we looked at the data, there was a small indication that it was actually the heel strikers that saved about four and half percent and the four foot strikers midfoot strikers, only three and a half percent. So it was just in our sample then other people have studied the same shoes and it's similar analysis and they didn't really see that to be holding but so it seems that across the board independent of foot strike they seem to work. I mean, I must acknowledge we tested very fit runners at very fast spaces. We don't necessarily know that what happens when we're talking about a five hour marathoner or for our marathoner. Like I said, in a biomechanical so all the results I showed you were from the biomechanical study where we tested only heel strikers because those are the most common type of runners. But like I said, throughout all the different studies performed with these shoes that there is not a clear trend that it works better for either four foot strikers or rear foot strikers. And I think it definitely there is this feel that when you put the shoes on your sort of push more forward and things like that. Again, something to think about things critically taking to account physics when people start making claims about shoes that are breaking less and propelling more because overall when you're running at a consistent velocity and there's hardly any resistance. You're going to be breaking as much as you're going to be pushing off because otherwise you just keep accelerating and that's not what you do at constant speed so things like that. Be critical when people start making claims and think about it and sometimes you just need to acknowledge that we don't have the data to answer the question. Okay, yeah, brilliant. Thank you. And yeah, just one, hopefully last question I think. If it holds across kind of different running speeds different foot strike patterns. Everyone's around about 4% saving in running economy. Why are we not seeing kind of a 4% improvement in elite marathon times. That's a great question and that is some of the articles that are also in the links below that we discussed that I didn't have really time to go into detail there today but to be true, what they claim to be holding. If we want to have a 4% saving translating to a 4% faster time that needs that can only happen when the relationship between energy cost and speed is perfectly linear and goes through the origin it's a directly proportional relationship because we're talking about relative changes on the one side and they're only translating to relative changes of similar magnitude on the other side, if we have a directly proportional relationship, which we don't have some for a long time we always thought that we can estimate the relationship between running speed and running economy to be linear but now we got more data and we look at this carefully. We see that even on the treadmill, this relationship is not linear, we see that at higher speeds to go a slightly bit faster you need a lot more energy that you need at lower speeds. And then that is on the treadmill when you then translate it to an overground racing situation we also have air resistance which generally is not as important in running but if we talk about Elliott Kipchoge at two hour marathon pace it becomes a thing. So, to combine the effect of those two mechanisms the one increasing air resistance which becomes more and more important at higher speeds, and the fact that at higher speeds you need more energy to make a small improvement in speed results in the fact that the improvement that people can get in times with a 4% savings if we would assume that it was there for everybody for every runner with any food strike. Then still the people that run slower would see a bigger improvement in time than the people that run really fast. I think we did the math in the paper that is first author is Silea Kip and there we sort of show that for two hour marathon a 4% savings would only make you about two and a half percent faster. If you're slower than a four hour marathon that same 4% metabolic savings could even allow you to run more than 4% faster just because of that relationship being not directly proportional. So, while you're answering that we now have a couple more questions on YouTube. So, do you have time for a couple more questions? I have time for sure, yeah. Okay, brilliant. So, Mason Copy has asked, says, you touched briefly on weight of the shoes in the first Nike prototype study, did you normalize for weight? Yeah, that's a great question and that is something that we did. So, we know that shoe mass is really important for metabolic rate. So, we know that every 100 grams that you add to a shoe makes you about 1% slower or increases your metabolic rate by about 1%. So, making shoe 100 grams less heavy would improve running going to be about 1%. Just when we started this study, we weren't sure about the differences that we were going to see between the shoes. We didn't want to find 1.5% and then have a mass difference between the shoes that would have explained half of that. So, to be sure, we made sure that all the shoes weighed about the 250 grams that these shoes are. So, we added about 50 grams or 60 grams to the streak shoes and about 50 grams, I think, to the Nike prototypes. So, in that case, the comparisons, the 4% was purely based on the geometry of the midsole, the foam and the plate and the mass was out of the equation. On this side, we could have also not normalized the mass because the difference was so big that people wouldn't claim that it was just because of mass. And that would be a more fair comparison or ecological where you can actually compare the two shoes as they are out there in the field. So, that's sort of these decisions that you can sort of weigh on which one do you take. Do you really have an applied question. Do you want to go with the most ecological validity and take shoes that are out there as is? Or do you also have an interest in sort of like the fundamental underlying principles and then do you need to start controlling some of these parameters as much as you can. And obviously, everything I showed you about the carbon fiber plate and comparing it to those shoes. Obviously, what we would have done is have this exact same shoe with this exact same geometry and have a shoe that is the same foam but doesn't have the plate and have another version of the shoe that is exactly the same and does have the plate but doesn't have the fancy foam. And that would give us more detailed fundamental insights. And that also is less of an applied because in reality we don't use don't exist. So, yeah, it's always the trade off between those kind of decisions do we go really applied or do we go fundamental. Brilliant. And I think that ties in with your second stay home message as well of meticulousness and tickle the boxes there. And the last question at the moment at least is from Fabio Lanffadini, who says thanks for how to, can you comment a little about the effects of drafting for the two hour break in the marathon, please. Yes. So, so, like I said, in this talk, we explored this concept where we would have a team of runners drafting together so what happened during Monza in Vienna was like you do different approach which obviously didn't meet. We didn't meet the regulations for record eligibility, but they made it a separate event. And then both events actually had a different approach where we saw in Monza, this sort of arrow formation where there was the paces were an arrow formation and Elliot Kipchoge was behind them. And then in Monza, it was sort of this inverse arrow, and all of those sort of scenarios were done by by guys who know a lot more about computational fluid dynamics so in our simulations or in calculations. We typically need to go back to some data by Griffith Pew that was he collected in the late 60s published in the 70s, which is an exercise specialist just from the UK. And he had a wind tunnel and he had a runner in the wind tunnel and actually measured running economy of the runner running at a set speed in the wind tunnel on the treadmill, and then had the same runner run in a wind tunnel behind another runner. And in that study they saw that running economy was about 6% better when drafting behind somebody else so that is kind of the number that we generally use to simulate the effect. Because right now we have the technology to use a lot of computational fluid dynamic simulations and we can theoretically simulate any scenario of air resistance but the outcome of those simulations is always a drag force. So if we have a specific configuration of runners and drafters and paces. If we simulate that we, the outcome is the drag force experienced by the runner. We can see changes in drag force but how does that translate to differences in running economy and how does that translate to difference in running performance. Those are two additional steps that we always need to make so we typically shortcut that and just go with drag force towards metabolic rate. But actually in Colorado we have been doing a study that we're currently writing up where we did measure the relationship between drag force and running economy. We saw that varies a lot. Interestingly enough the one guy that was tested back in the 70s that was a study on one runner back then. And that guy is right in the middle of the 12 people that we tested in Colorado so that sort of works out. So this 5 to 6% savings is still what we can expect. We didn't have a wind tunnel we were using elastic band and hanging weights over pulleys to pull people backwards with very tiny forces. Great study to do but we hope to follow up on that and try to recreate that scenario in a wind tunnel and then validate our findings and validate our simulations. Okay brilliant I think we'll, I could keep talking for hours but I think we'll leave it there for now and then if anyone does think of any other questions we'll kind of, they can take to Twitter or kind of ask and we'll see if we can try and get a response. Sounds good. Okay, thank you. And yes just hopefully everyone enjoyed that as much as I did and got as much out of that and kind of, if you did then please share with friends, students, colleagues, anyone that you think will find that talk useful. Don't forget that's now five so we're halfway through the 10 talks that we initially announced. We've since got more lined up that will hopefully be announcing over the coming weeks but if you haven't already go back and look at those first four and keep an eye out for the five coming up which are all scheduled on YouTube as well. So I think last thing for me is just a huge thank you to Valter which I know everyone else on YouTube and Twitter is agreeing with me that was excellent and yeah hopefully I'll see you all again soon. Thanks Valter. Thank you.