Influence of Footwear Longitudinal Bending Stiffness on Metatarsal Strains during Running

[00:00:04]Thank you for joining us for the HPL seminar. For a second, I was worried that the room wasn't filling up enough and then everyone just came in in the last 30 seconds. So, thanks for being here. It is my pleasure today to introduce our speaker, Dr. Colin Feringer, a post-doal fellow working with Dr. Michael Asson and Dr. Brent Edwards. Colin completed his bachelor of science in mechanical engineering from 2007 to 2012 from here at UFC before transitioning into biomedical applications through an MSE in biomedical engineering which he started in 2014 and finished in 2016 also from the University of Calgary. During his masters he investigated metatarsal overdose injuries in minimalist footwear.

[00:00:51]He then continued advancing his work at the tissue level during his PhD in biomedical engineering from 2016 to 2021.

[00:01:00]Also here at the University of Calgary in which he focused on mechanical fatigue on the patellar tendon.

[00:01:08]Outside the lab, Colin is perfecting his atome latte art skills, an effort supported by an admittedly much too elaborate espresso setup. This hobby pairs well with his life alongside his two uh two and fouryear-old sons who ensure he gets no sleep at all. So, he's busy making those espressos. And I told Colin, I also recently got into latte art and my latte looks nothing like art.

[00:01:34]Um the foam either just sinks down or sits right on top like a blob. So, if he learns that, he has to teach me.

[00:01:42]Today he will be presenting his work from his post-doal research in a talk titled effect of footwear longitudinal bending stiffness on metattorsal strains during running. Thank you for >> all right thanks Asha.

[00:01:58]So running injury uh is pretty common amongst runners. It has an annual incidence between 24 and 76% and this diagram here kind of shows some of the the most common locations in the lower limb. So starting proximally we have IT band friction syndrome moving down we get patellophmoral pain we have shin splints we can have achillesopathy and then moving into the the foot we have plant fascitis and what I'm interested in stress fractures with an incidence between 2 and 6%.

[00:02:29]So of stress fractures, metatarsal stress fractures and cramp for about 19% of those. Um the metatarscils are the bones highlighted here in red. Um you can see that they kind of bridge the gap between the hind foot and the flanges.

[00:02:41]They're these long skinny bones. Um and because of that they're they're highly aggressive. So of the five metatarsils here, most of the met stress fractures occur in the second and third metals.

[00:02:52]These guys here, those two, um 89% occur back in those two bones. And that's because of the five, these are even skinnier and they still experience quite a bit of the load that we put on them during running. So just highly susceptible to these stress fractures in these two locations.

[00:03:10]Stress fractures have a bunch of characteristics that make them pretty annoying to deal with. So they have this insidious pain during activities. You don't really know how it started. Just kind of starts out of nowhere during an activity. And over time, this can start from like a slight pain to something that becomes debilitating. you're no longer able to participate in that activity that's causing the stress fracture.

[00:03:29]Uh on top of that, they're pretty difficult to diagnose. So here's some images of a stress fracture of the second metatarsal. So this bone here, the first image on the left is an X-ray at the initial consult. So I'm not an X-ray tech, but I have no I cannot see any kind of fracture there. And then the second image is four weeks later, and the only evidence of stress fracture is this slight callous formation. So the bone's actually healing, and that's what we're seeing. We don't actually see the crack itself. So the sensitivity of um diagnosing a stress fracture with medical imaging is about 15 to 25%. So not too great. So they're they're hard to kind of pinpoint when they happen.

[00:04:02]They're hard to diagnose and they have a long recovery time to about 13 weeks. So once you get one, it's kind of difficult to to get rid of it. It's also cool to see that or not cool to see. It's interesting that females have a high risk of stress fracture by foot. So, one study showed that females um the in the risk of stress fracture is 5.7 injuries per 10,000 person years versus males with a a risk of 2.8. So, more than double.

[00:04:29]All right. So, how do stress fractures happen? Pull an example from Microsoft Office. You guys are probably a lot of you are too young to remember Clippy, but he was an annoying little assistant back in Microsoft Word. So, one day we're we're pissed off with Clippy. We want to break him. So what we're going to do is we're gonna flex the paper bub open and flex it back close. Now that's one loading cycle and it's not enough to break them right away. So try again. We do second loading cycle. If we keep repeating this over time any number of times eventually it'll be come to a time where there's failure. So what's interesting about this is that failure wasn't one loading cycle that outright overloaded that paperclip and caused it to break. It's many cycles frequently over and over again that are causing damage to a group in that material and over time that'll cause to fail.

[00:05:18]That's kind of similar to what's happening in a stress fracture. So in stress fracture pathophysiology we have this repetitive submaximal loading that's occurring on the tissue. So in our um case for running we're putting load on our foot every time we take a step and that leads to the accumulation of micro damage within the bone. So here is an example of some micro damage. which is just a small little crack there that happens in the bone matrix and over time that micro damage accumulates.

[00:05:44]So in response to this micro damage bone has this targeted repair response. So what it can do is it can try and find and repair that damage and in the ideal situation that bone will the specialized cells that come and repair it will do their job. That micro damage will get repaired. However, there's some other cases that can arise in response to that targeted repair.

[00:06:04]there can be a potentially a a local increase in the procity of the bone. So how bone repairs this micropack is it sends some cells in to kind of burrow it out and then cells behind that come in and replace it with new bone. So there's this period in that um in between those two where there could be this temporary increase in paracity and that potentially lead to increased load on the remaining bone tissue that's left over and if we continue this cycle that could potentially lead us to a bad situation. The other way that stress fractures could potentially occur is if in response to this if if this targeted repair response just isn't enough. So if our accumulation of micro damage is just overwhelming that repair response, we have micro damage that isn't repaired.

[00:06:42]And if we continue this repetitive loading, that'll again lead us into this paradigm of stress fracture. So both of these two kind of pathways are still debated in literature. We don't exactly know what's going on, but know that with repetitive loading, there's some sort of response that can lead to the susceptible nature of going to stress fracture.

[00:07:00]All right, so in our lab, we like to try and quantify stress fractures as fatigue phenomenon. So what does that mean?

[00:07:06]Well, if we go back to our example of the paper, essentially we can track the magnitude of load that we're applying to that tissue. So in this case, bone, we can also track how many cycles that bone lasts until it fails. So this is some data from particular I tested of bone where on the y axis we have the strain that we're loading that bone at and on the x-axis we have the number of cycles of that samples lasting. So what's important to see here is that this is a very um it's a highly nonlinear relationship. So the x-axis here is in a logarithmic scale which basically means that um small changes in the y axis lead to big changes in the x axis. I'll just show a quick example of that. So if we load our bone at about 6,000 micro strain, it's going to last about 1,000 cycles. If you reduce that strain to about 4,800, so not even half that magnitude of the initial load, it lasts 10,000 cycles. So not even a 50% reduction in the loading magnitude leads to a tfold increase in the number of cycles that that bone can last until it fails. So essentially what this summarizes is small changes to the magnitude of load that we're applying to the bone that might even seem insignificant can result in large increases in the number of cycles that bone can last until it fails. So it's important to try and find ways that we can potentially reduce that load on the bone even if they're small.

[00:08:23]So in my master's degree I kind of looked at something similar to this metatarsal strains and minimless footwear and I was looking at how much strain that bone was under. So in the graph here, we're looking at the peak strain on the metaphors. We have all five of the metaphors here and the yellow um the yellow curves or the yellow dots are the middle shoe and the blue dots are the traditional shoe. So our minimalist shoe here has very little cushioning. It's very flexible. It's designed to mimic barefoot running. And our control shoe in this study is just a normal running shoe with no kind of balance control, just a regular cushion.

[00:08:54]You can see here for peak strength for all five edited parcels, there's significant increase in strength in the middle of the shoe compared to that traditional shoe. And what was driving that? Well, if we look specifically at the inputs into our model that we're using to calculate strength, we have the angle of the metatarsal and the force applied to that metatarsal. So if we specifically kind of zero in on metatarsils two and three here we can see that in the control shoe or regular shoe the angle was significantly higher than in the minimless shoe. So essentially to kind of say that colloquial colloquially the metaphor was seemed flatter in that minimless shoe at the time of peak strength. So that was causing this increase in strength paired with a change in force magnitude. So if we now look at the peak force magnitude applied to the bone uh in the controls shoe it was about 784 for the second metatarsal that went significantly higher to 793 and the third metal went from 283 to 296 also see so we had two kind of things happening here in this this minimalist shoe we had the bone sitting flatter so or different orientation and increased load applied to it and those kind of pair together to create this perfect storm for increased strain on the bone.

[00:10:05]So in that minimal issue, there's a few things going on. There's changes in cushioning, changes in longitudinal bending stiffness. So it's hard to say exactly what was causing those the the results we saw. Um so it's important to kind of look at different ways that we can systematically evaluate this. So I was particularly interested in longitudinal stiffness. So what is that?

[00:10:23]Well, longitudinal stiffness is the shoe's resistance to flexion along the longitudinal axis. So if we look at a minimalist shoe here, it's really easy to curl it up. You can almost roll it into a ball. And so that has very little longitude. If we look at a more traditional running shoe here with a lot more cushioning and a lot more material on it, it's a lot harder to flex that shoe. So, we would say that has a high longitudinal stiffness.

[00:10:46]We look at um super shoes or advanced footware technology. They're specifically designed to have a higher longitudinal stiffness than normal footwear. And that's because they have this uh carbon fiber plate that kind of runs through the middle of the midsole.

[00:10:59]Um, and that's that it's designed to as a skipping element essentially. So, it's designed to increase the shoes resistance to flexion um for the purpose of allowing someone to run potentially faster.

[00:11:15]So, longitude bending stiffness has been investigated with respect to planter loading um in some modeling studies and there's some very interesting findings on the effect that this has. So if we look um at this study here, essentially what they did was they finite element modeled to the pler pressure in a bunch of different conditions. So in the far left condition here, this is the shoe with no stiffening element in it. So no carbon fiber plate. You can see this is the kind of planter pressure distribution again where red is high and blue is low. So under the metatarsal heads here, you can see some high pressure happening.

[00:11:47]The next three are all with the carbon fiber plate that was modeled inside the finite elder bottle. And the carbon fiber plate as we go to the right is getting thicker and thicker. So you can already see compared to the no carbon carbon fiber plate condition the first thinnest carbon fiber plate condition already has a reduction in that peak strain stress happening under the metaral heads. And as that plate gets thicker in the model those peak stresses get even lower.

[00:12:11]So although this is just a modeling study it's very interesting to see that this could be a potential effect of increasing the longitudinal stute.

[00:12:18]Second study um they also took it one step further and then they modeled metatarsal stresses in different situations with a carbon fiber plate and they showed that the increasing the carbon fiber plate thickness decrease those metatarsal stresses. This is cool but it's not actual experimental data.

[00:12:34]So it's kind of still important to see what happens in the real world with these situations. So with that being said, the purpose of this research was to examine the influence that shoe longitudinal bending stiffness had on metatarsal strains. And I hypothesized that aligned with some of the background that I just presented, metarsal strains would increase in shoes with a lower longitudinal bend stiffness due to a potentially less dorsif flex or flatter metal orientation and it increased apply load to the metal.

[00:13:02]So, in order to tackle this, I took a pretty common shoe in the AFT world, an Nike Vapide 3, and had men's size 10 and women's size eight. And I had two conditions of this. The first condition with the intact plate was basically didn't touch the shoe at all. It was just kind of the stock shoe. In the cut plate condition, I made six medial lateral cuts through the the forefoot of the shoe. So, you can see all the cuts here. They went all the way up and through the carbon fiber plate. So this is this was an attempt to try and systematically lower the longitudinal betting stiffness of the shoe while keeping as much other stuff constant as possible.

[00:13:41]So we had some subjects come in and do some trigonal running for us. We had 16 people total. Eight of them were females, eight of them were males. Uh the inclusion criteria was pretty standard. They ran they were they were all recreational runners who ran at least 10 kilometers per week. Had no prior history of foot injury or no lower leg injuries from the previous six months. and they were able to run at five minute per kilometer pace.

[00:14:01]This is just a quick video of one of the people people that we had in. They ran at 5 minutes per kilometer for 5 minutes in each of those two shoe conditions during which we captured motion capture and fire pressure data.

[00:14:14]All right. So once we had that pressure motion capture data, we wanted to put into a muscular scal model of the metatarscils so that we could estimate exactly the loads that were happening on them. So I'll take you through that quick. This is a second metattorsal bone here and the second felangi bone. And essentially what we can do in this model is split them into two different rigid segments. So the metatarsal is now this segment here and it is anchored at the base and then our flanges just kind of floating off. So if we know the force acting on the metatarsal the the toe and we get that from the finer pressure data.

[00:14:46]We can model two different um forces acting from the musculature that crosses under the metatarsal fangial joint. One is the long um we call it the long tendons and the long force of the long muscles and the other one is the short tendons or short muscles.

[00:15:02]If we know the distance from that toe force to the metatarsal head and we also know the distance between the uh plant musculature that goes under the joint there and the metatarsal head, we can solve that system of equations and come up with an estimate for the force acting on the metatarsal head due to that plan musculature.

[00:15:19]We can combine that force with the metatarsal directly measured metatarsal head force that comes from the planer pressure data as well. And if we know the angle alpha that that metatarsal is at. So the orientation of the metatarsal we can convert those two forces into a sheer component acting on the metatarsal head and ax component acting on the metatarsal head.

[00:15:41]So this all really relies on a good estimate for that metattorsal orientation alpha.

[00:15:47]So what we've done in the past for this is a combination of two things. We take a nonweightbearing neutral metatarsal orientation which we get from a clinical CT scan. So the person will go into a normal CT scanner lying down with their foot kind of flat and we'll take a scan of their foot and call that the neutral orientation and we'll add that with what we get for motion capture. So we have a rear foot angle that we get on a motion capture. If we add that neutral orientation with the rear foot angle, we can come up with this dynamic estimate of the metatarsal orientation.

[00:16:19]So, we know how important that is. Um, and we know we're not exactly sure what the foot's doing inside the shoe. So, what we wanted to do is actually incorporate a potential correction factor for that angle alpha for the metatarsal orientation. And we um thought there would be a good idea of trying to use weight bearing tomography to do this. So in weight bearing communive tomography um you're actually able to have the person standing inside the CT scanner and grab images that way rather than having them be prone and it gives us this ability to potentially get these different weight bearing postures that we can use to correct our data. So we had participants come in for a second session in this weight bearing CT scanner. You can see the setup here. We had scanner itself for the people in stand and then we had motion capture cameras set up all around it so that we could do the the same kind of motion capture that we were doing in the first session.

[00:17:05]Um, and then we had people stand in a bunch of different postures. So, we had them stand in the non-weight bearing posture to mimic what would happen in the clinical CT setting. We had them stand in a full weightbearing flat posture. So, all the weight was on their right foot and their left foot was just kind of in the air. We had them stand at a 50% peak dorsif flexion posture and that was estimated from the running session. So, we took half their peak dorsif flexion from that running session, made them stand in it in this session and then peak dorsif flexion also from that running session. And we did this for both shoes. So from this we came up with some data that we could use to potentially correct that metatarsal orientation. So on the y- axis here we have our motion capture estimated angle and then our x-axis here we had our directly measured angle of the metatarsals from that weight bearing CT.

[00:17:51]Each of these is a different data point um from each one of those scans all the participants. And we can essentially come up with these two curves that we can use to correct the data. One curve is for the cut plate, one curve is for the intact plate condition. Um, so yeah, that's kind of what we use to correct that data there.

[00:18:08]All right, so now we know we have estimates of the force acting on the metatarsal heads. We have hopefully a pretty good estimate of the orientation of the metatarsal inside the shoe. Now we can make a finite element model of that to come up with the actual strains acting on the metatarscils. So we did this using 10 node tetrahedral quadratic elements with a maximum edge length of 3 mm. We use linear elastic material properties that we applied to all the the box with all the elements within our model there. Uh last sorry a young mod was 20.7 gap pascal and poson ratio of.3 and there's just some numbers there of the number of nodes and elements for the second and third meta for the females and males. So second meta had about 12,000 nodes 6,6500 elements and the third metal was slightly smaller.

[00:18:53]with us.

[00:18:56]We also had to figure out the boundary conditions for the model. So essentially we constrained the base of the metatarsal similar to the muscular scal model that I just explained that was constrained in all three dimensions and then we applied the axial forces that we calculated to the metatarsal head. So here we tried to identify kind of the articulating surface of the metatarsal head and distribute those axial sheer forces across that articulating surface.

[00:19:20]Once we run the model, we use it to extract those strain data from it. So what we chose to do is extract the 99th percentile strains from our distribution here. So this is a big distribution of different strains across the entire bone from 30% of stance to 80% of stance. So 0% of stance being heel strike, 100% of stance being co-op. We're kind of grabbing that late middle stance phase because that's how we know metatarsal strengths are generally the highest. And we were grabbing them from the diaphosis region. So just the the skinniest part of the bone there because that's generally where the highest strains occur and that's where we normally see metatarsal stress factors happen.

[00:19:56]So this is kind of just a standard time series plot for what the strain would look like the 99th percentile strain. So again we're solving finite and element models at every 5% of stance all the way from 30 to 80%. So each one of these is it own little finite element model that got solved and that's the 99th percentile string value there. So all we're taking for the analysis that we're going to do is just the peak value. So the value of that one that comes and that's what we're analyzing.

[00:20:22]All right. So some results um I wanted to make sure that the cuts that I made in the shoe were actually doing something. So uh I measured the longitude of medications for the two shoe conditions and I was also curious to see what that effect might have on just the compressive stiffness. So I just did some direct compressive measurements as well. So the intact plate condition um for the men's and women's shoes is about 0.5 Newton meters per degree. Uh and then the cut plate condition is about half that. So 0.28 0.25 for the men's and women's shoes respectively. Um so definitely had an effect putting that carbon fiber plate into the longitudinal stiffness.

[00:20:59]Interesting to see though that it didn't have much of an effect on the actual just linear compressive or the actual compressive stiffness on the shoe uh in the forefoot. So in the intact leg condition it was about 64 newtons per millimeter of stiffness if you just squish the foroot and it went up to about 66 uh newtons per millimeter in the cutler condition. So slightly stiffer but not a huge change there.

[00:21:21]All right. So now as we get into some of the results for the peak 99% compressor strain uh in the second and third metal here um you'll see plots for both the cut plate and the intact plate condition.

[00:21:33]And for the second and third metal unfortunately we didn't see any effect of longitudinal benic surface on peak strain. So no significant change there.

[00:21:42]Uh it was good to see that the third metatarsal strains were slightly lower than the second metatarsal strains.

[00:21:46]That's kind of what we'd expect but no change due to the the plate condition.

[00:21:53]We did however see significant increases in axial force. So the force that was applied to the metatarsal head in the axial direction in the second metatarsal. We didn't see any change in the third metal but there was a trend for an increase and we also saw a significant increase in sheer force acting on that metatal head and the second metatarsal. So for both these two cases the cup condition had significantly higher shear and axial force applied to that second metatarsal head. Uh same news for the third metal here there's a trend for an increase but not significant. So this is kind of confusing. We saw no change in strain but we saw this increase in extra force applied to the metarsal head. We also saw that the time point of peak strain occurred later in that lower longitudinal bending stissue the cut. So this is a representative subject here just looking at the time series data of the strains there. Um and the peak strain here occurs significantly later in the peak strain the intact plate shoe and we just kind of plot that in box plot form. We can see that for both the second and third metatarsal that time point of peak strain occurs later um in that plate shape. So if the strains are there's something happening there with the timing and there's something happening there with the force that's just not translating to a change in the actual strain metric.

[00:23:05]So what we wanted to do is actually split it one step further into the female group and the male group to see if there's a change happening because of sex. And we actually did see something cool. We saw a significant increase in that peak uh 99th percentile strain in females in the cup ratio and we saw no change in that group.

[00:23:23]So where was this where was this change coming from? Well uh there's those two kind of inputs that we can look at into the final model. There's the metatarsal orientation and then there's the magnitude of force that we're applying.

[00:23:36]So in terms of the orientation of metatarscils there's no significant change between the two. So the cut plate condition metatarsal angle for the second metatarsal is about 45° at peak strength and for the intact plate condition is about 43° not significantly different but there was significantly increased forces applied to that metatarsal head in the cut condition. So the axial force went from 293 newtons on average to 341 newtons and that sheer force also significantly increased from 161 newtons to 157 newton.

[00:24:11]Uh this is also reflected in the finer pressure. Um so if we look at a representative subject here this is the planter pressure at the time point of peak strain. So this is just kind of a heat map of of the pressure under their foot. Red is high, blue is low. You can see that intact plate condition here slightly less red compared to the cup condition where it gets a little the area kind of grows and the magnitude also gets a little bit higher too. So that's probably what's driving those increase forces.

[00:24:39]We also looked at some of the spatial temporal differences between these two just to see if that was an a factor as well and we did see some significant ch or a trend for significant changes here.

[00:24:49]So intact plate versus cut plate stance time it uh decreased slightly from 234 milliseconds down to 227 milliseconds if you value that was 0.1 and the stride time consequently increased to reflect that. So the intact was only 652 and that went up to 659.

[00:25:06]So slight spatial type was actually all right so we saw this cool change in strain happening at the second and third personal females. But what does that mean practically? What we can do is actually take that fatigue life data that I talked about before and we can use that to show what uh the effect or factor of a change constraint has on the number of cycles together. And what we can actually see is that that 200 micro strain increase that we see when we go from the intact plate to the cut plate condition in the second parcel actually corresponds to a 1.7fold reduction in the number of cycles to failure. So 1700% reduction in numbers of cy number of cycles of failure from that 200 micro strain increase that we see. Same thing for the third visor. Although the strain increase that we observed from the intact plate to the cup plate shoe was slightly smaller. So it's only 160 micro strain and that corresponded to about a 1,600% reduction in the number of cycles of failure event.

[00:26:06]So the conclusions from this work were that this reduced longitudinal bending stiffness shoe was associated with significant increases in metatarsal strain in the female running population which represented about a 16 to 1700% reduction in number cycles that those metatarsils could withstand before fatigue failure. So when we look at this and frame this in terms of metatarsal stress fracture risk, this research potentially shows the benefits of using AFT shoes at least for metatarsal stress fracture reduction in female runners.

[00:26:36]that I'd like to thank Dr. Markerson, Dr. Stansky for help with the way CT and Dr. Brett Edwards and his lab mates for their uh great help with this project.

[00:26:46]So, thank you for questions. You know, who would like to start us off?

[00:27:00]>> Thanks, Colleen. Uh, I'm curious about how you choose your sensors like from the insole to match with the like the bones were.

[00:27:12]>> Yeah.

[00:27:13]>> How do you do that?

[00:27:14]>> I was just kind of grabbing go back to that sliver.

[00:27:28]I was basically just grabbing all the cells within the general region of each metal head and each toe um and applying that pressure to the metatarsal head. So it could be slightly larger than what's the actual metal is experiencing but it's generally within the the region um kind of each test that's the first metal and then we kind of work our way across and segment out each try to juggle discreetly um yeah there's no like amazing way other than that that I've seen to do it other than like discreetly just mapping into different zones. Um, so we might be slightly missing it eventually. We're getting too big of a region, but that's kind of the the limitation of just working with those pressure sensors with those discrete cells that they >> and other question for like your female participants.

[00:28:16]>> You had like one pretty big outlier of the strain. I think do you know if it was driven by a change in force, a change in angle, both?

[00:28:27]>> I'm not sure it was driving that specific person. I would suspect is probably a force thing and not a orientation thing. No. Yeah, if I had to guess. Yeah.

[00:28:37]>> Thanks.

[00:28:38]>> Yeah.

[00:28:44]>> Were your participants running? Um I think you mentioned this in your methods, but were they running at different speeds that were based on each participant?

[00:28:52]>> They all ran at 3 m 3.3 meters per second. So five minutes per kilometer.

[00:28:57]And have you seen anything that has to do with the speed like an effective speed? Did we find that?

[00:29:05]>> I couldn't analy because they're all the same. They're all the same speed.

[00:29:08]>> Oh, I'm so sorry.

[00:29:11]>> Answered my question.

[00:29:12]>> And for some reason heard they were all running at the >> No, they're all Yes.

[00:29:17]>> Yeah. Can you just talk to your rescue?

[00:29:25]>> Yeah, I don't know if there'd be an effective speed. I mean, at some point, you do have to be kind of engaging, like if you're running fast, you're probably getting more flexion out of the shoe, so it might be able to kind of amplify the results that we're seeing, I think. So, you'd be kind of engaging the plate or the non plate more. So, that might Yeah, I suspected probably be kind of a a higher speed thing. And that's kind of what Patrick saw too in his research when he split it into the faster emails that he was collecting versus the slower emails. He saw an effect and he grouped it all together, he didn't see. So yeah, >> I think even going back to the fact the force is really as we go up with speed.

[00:30:00]So probably >> Yeah, >> but I don't know. Yeah, within the change between the cut and no cut would be >> Yeah. What?

[00:30:15]>> Very nice talk. Nice to listen to um I like the applicability at the end there.

[00:30:22]Um I want to make sure I understand it.

[00:30:25]Let's assume my feet are perfectly symmetrical.

[00:30:30]>> And I run every day with your cut shoe on the right foot and my uncut shoe on the left. You're telling me if I get a stress fracture in my right foot, cut you, I can run 17 times more the total distance up to that point until I get a stress fracture in my left foot.

[00:30:51]>> 1.7 and that's >> 1700%. I'm going to make the number bigger so it looks cooler.

[00:31:01]Well, you're not going to see an effect that because you're a male, but if you're a female, you might >> Yes.

[00:31:07]>> Um, but that I mean that it's it's nice to kind of be able to quantify it in terms of number of cycles of failure, but we also, you know, need to account for a lot of biological processes that are happening and stuff, too. So it's definitely >> I wouldn't stand behind 1.7 with my life, but it's it's interesting to kind of frame it that way to see like the small change has a huge effects.

[00:31:31]>> Follow up on stuff.

[00:31:33]>> When did you do this?

[00:31:35]>> When did I collect this data?

[00:31:36]>> When did you cut your shoes? I There was another study that cut the vapor.

[00:31:42]>> Yeah.

[00:31:43]>> And what did they find?

[00:31:45]>> They were looking They weren't looking at strains or anything. They were looking at like expired vass, >> right? And I think they found no change.

[00:31:54]Yeah.

[00:31:54]>> So they're showing us more of the cushioning.

[00:31:57]>> I always think you should cut it vocals >> like not just towards but also >> Yeah.

[00:32:04]>> There's other stuff. It's not just pure.

[00:32:09]>> If we want to get into like the running economy side of things, I think there's kind of changed my mind on the effect of the plate. I think the effect of the plate is to engage more of that super efficient bone because if you have this stiff plate underneath, right, like your small metal that the plates is going to affect way more. I think that's kind of what they were showing too. It's dry. So >> I have one more question. So um you gave two stiffness values for the material.

[00:32:41]Yes.

[00:32:43]Can you explain what one was a push down and just 10? Yeah. And one was just for for degree.

[00:32:51]>> Yes. So one was a one was a flexion test and one was just a straight compression test.

[00:32:57]>> Yeah.

[00:32:59]I assume there's a difference between the shooters. Are we using the wrong test?

[00:33:04]>> No, there is difference. You're right.

[00:33:12]Yeah.

[00:33:12]>> So this longitudinal night sickness test is you climb the front of the shoe and then it flexes the heel, right? So it's just flexing along that the long axis of the shoe. So that would be showing changes because of the cut plate. This 4 foot compressive stiffness, I just put the shoe flat in the instrument on the material assessing machine and compressed it >> and you kind of have >> like shoe or where the foroot sits in between. We push down.

[00:33:36]>> That's No, no, no. This is just the shoe sitting exactly like this. I have a a piston pushing down flow.

[00:33:41]>> Thank you. Okay.

[00:33:42]>> So, I just wanted to see like are these notches that I'm cutting out, are they affecting how stiff the shoe is this way, >> like when we compress it vertically?

[00:33:51]>> Because if that changes, well, then we're creating a completely different system, right? That that could be driving some changes, but we weren't like that change is pretty small.

[00:34:00]>> So, we're showing it's probably mostly either the the longitudinal status and not the compressive st. >> Got it. Thank you.

[00:34:08]I have a question. Along those uh the leader lateral cuts, >> you made the cuts and they're obviously like a certain distance of guard.

[00:34:17]>> Do you think the alignment of the person's head of the metatarsals with those cut versus not on those cuts would play a role in your results?

[00:34:28]>> I think it could, but I think there's also like if you look at where that plate is positioned in this part of the shoe is pretty far down. So there's a lot of foam between the metatarsal head and the actual plate itself. So it could, but it's also think of it.

[00:34:43]There's probably a huge low pass filter between what the metatarsal is experiencing and where the actual plate is. So it it could, but it probably pretty minor, I would think. But yeah, it could be factor like where that slit actually ends up being. Yeah, potentially.

[00:35:00]One of the figures added to bones. Um it also talked about the magnitude there but it als >> I quickly because I saw the same thing I was like oh maybe that's a something that's cool. I quickly calculated like all the the number of elements with a string greater than whatever 95% I think and it was pretty there was no syn between the two. So I think that might just look like it might not actually like be for the for the high high so yeah mean so why between >> yeah it's a great question could speculating I think it could have something to do with anatomy like are the females the plate is essentially the same plate in both shoes, I'm pretty sure, or like same thickness. So, does it functionally feel stiffer for females? So, that when the cut plate gets cut, maybe it's a greater perception of reduction compared to the males who are able to kind of flex the the plate more and the intact plate condition and then the the cut condition isn't as big of a change for them. That could be something. There was a trend for the males to have an increase in strength. So, maybe it'll come out too with more participants. I don't know.

[00:36:28]But um yeah, that's kind of what I was thinking. It's it's potentially towards like an anatomical like females have smaller toes compared to males. So maybe they're just able to engage the plate less. So um when they get that cupplay condition, it's a bigger change. I don't know.

[00:36:49]>> So what about the uh initially I think you gave some statistics that females also are times more. to you to be injured and made that muscles compared to >> that wasn't specifically stress that was just stress fractures and yeah it was all over stress fractures yeah >> because the quality of the bone is eh >> I don't I think there's a lot of factors going into that change but I think bone quality is one of them for sure yeah yeah bone quality bone morphometry there's a lot going into it Um, okay. I'll go with people first. Um, Matt, Brent, and then Torian.

[00:37:32]>> Thanks for the talk. Um, I really like the way that you investigated like the the angle and then like correct it for that.

[00:37:40]>> If you were to brief the study and you did like a fluoroscopy, how close do you think you would alter and essentially like estimating that?

[00:37:52]I mean, the corrections that we were getting were actually unfortunately and frustratingly pretty minor. I was like, I'm going to change the field. Uh, but they were pretty small. So, I think we'd probably be pretty close to the fluoroscopy.

[00:38:05]Um, at least in this actual thing. I've done a walking study tracking the first metatarsal with dual fllororoscopy and there's some subtle things that we've missed like there's some toe flexion down into the so there's actually a tiny bit of actual planter function that occurs right at the beginning of the stance that we wouldn't capture with this might be slight changes but grossly I would say it's pretty >> you showed a slide that I haven't seen Um it's this idea that for the women the just the planer pressure data for the women.

[00:38:49]Okay. So the women had sorry yeah in in the the forces were higher underneath the metatarsal head in the cut at any time.

[00:39:00]And that makes sense to me, but only from the standpoint that I would have thought what the plate is doing >> is better distributing the load. So what I would have expected to see is a greater area of red in the intact plate.

[00:39:17]>> Sorry, >> greater area of loading in the intact plate, but a lower peak. What you said is that not only does the magnitude of the pressure increase, meaning there's the red gets higher, you also said that the area is higher.

[00:39:35]>> I didn't I didn't test that, so maybe I'm just speaking on that one.

[00:39:38]>> Well, I'm looking at believing you.

[00:39:41]>> That's one person. Let's not go crazy.

[00:39:43]>> Okay. Because otherwise, I don't really know how you would explain that finding.

[00:39:52]>> Yeah. other than a change in like the compressive stiffness potentially that but that I mean it was slightly stiffer.

[00:39:59]So maybe that's that's the function of that. I don't know.

[00:40:04]That is that is kind of weird though.

[00:40:05]You're right.

[00:40:09]I mean I'm assuming that the the ground reaction force is really changing between different conditions. So you have more force and more area >> it should be >> the greater for I I just sorry more pressure and more area then so I just >> I'll look into that area and see what the actual is >> um kind of follow up on that uh do you ever look at it just depending so how much sensors be pressure just pipe mandate.

[00:40:47]>> I did test that after you told me to test it and it looked it's pretty minor like there's there's not a lot of artifact just from the flection going on.

[00:40:54]>> Okay. I was going to say that could be part of it because I know our system >> definitely artifacts >> from pending and then applying a load load shape increase the pressure reading >> right >> yeah terms politics regarding >> you said the advantage of the plate is the same for >> I think it's similar like because the the launch then he said this was almost identical between the two I'm inclined to think that the blade is probably the same >> so they didn't get further with that you would assume that for every shoe >> I think so I don't think the scaling plate thickness would choose size I doubt that's happening >> so what kind of things do you think that would >> yeah so like the effect stiffness of that shoe could potentially be different depending on it's it's a function of shoe size. It's also a function of like where the load is being applied. So longer shoes should have a functionally less stiff longitudinal stiffness I guess than a short shoe >> but not the way you calculated in Newton meters per degree.

[00:42:14]>> No. And I'm >> and so I don't know what way you should be calculating it how >> a person actually loads it >> like Tony's calculation that he presented Dr. Art was showing kind of pulling off on the toe. Mine is >> having the shoe flat on these two plates and one the heel plate kind of moves up and down. And I don't know if that's accounting for exactly where the force is being applied to the shoe. So yours is because it's doing meters for degree.

[00:42:43]It's giving you a torque. Yes. So, >> but yeah, I don't know. I think I think we refined a little bit.

[00:42:51]>> You were lining the shoes up at roughly the same location.

[00:42:55]>> Yeah. The the point of rotation is always the metatarsal joint.

[00:42:59]>> Yeah.

[00:43:01]Yeah.

[00:43:05]>> But for a given Yeah. You would think for a given thickness, you get a longer moment arm, that shoe's going to get less stiff.

[00:43:15]in terms of applied load.

[00:43:18]>> Yeah.

[00:43:19]>> But it's going to take the same torque to change it.

[00:43:22]>> Yes. Y >> All right. Yeah. So that's the issue with reporting it as Newton meters per degree. But other questions for Yes. So do you know um like what type of shoes your subjects usually use?

[00:43:44]>> I would say not in general it's mostly just traditional like normal non-plated program.

[00:43:50]>> So are they more >> like nonplated? So like the low stiffness condition was what they cut the regular conditions.

[00:44:00]>> Uh yes something similar >> like they are adapted to run in the cut plate. That's why I don't see >> I because the orientation that >> I think they were given I mean the five minute of climatization that they had I think was plenty enough to kind of adapt to the shoe and we saw we saw pretty standard changes that a lot of other research has shown like the mentors felangial joint flexion goes down significantly and that's what we saw. Um, so in that sense, I don't think them being like conditioned to a aft shoe would really change much. Um, yeah.

[00:44:40]So I don't think that would really much of a factor there. Um, yeah, I I I can't see a really big thing. If we just got them to put the shoes on right away and go for like 30 seconds, maybe we wouldn't see them kind of like settling into kind of their, you know, their normal run.

[00:44:59]Yeah, after five minutes they're pretty adjusted.

[00:45:04]>> Thank you.

[00:45:06]>> Hey, >> um so this injury with AFTs all started with this study of N equals 5 >> where the language around the treatments they might create stress fractures. It was no big deal.

[00:45:25]But yeah, >> stress fractur >> stress fractures.

[00:45:29]>> I would argue that you and your colleagues over the last few years have showed at least in these kinds of studies that that's not the case. If anything, it's low.

[00:45:42]>> Yes.

[00:45:42]>> Do you how much do you believe in vaccinating that it reduces the likely?

[00:45:51]I mean it I think it's potentially there like the modeling study showed the study shows it. So in terms of metaphors >> I think it's potentially a kind of benefit of what I would say.

[00:46:03]>> Yeah.

[00:46:04]>> But um and and the reason I asked and I asked this question maybe a year ago.

[00:46:08]>> Yeah.

[00:46:09]>> Is that people have been running in these shoes now for what >> seven years?

[00:46:13]>> Since 2018 I think was the first question. But do we have any data about stress fractures?

[00:46:21]>> There is some data that's starting to come out. We have the data.

[00:46:25]>> Uh it's changing. It was a conference proceedings that was back in October. So I don't know the whole thing, but it's the location.

[00:46:34]I'm not sure if the incidence of stress fraction change, but it looks like the location is shipping more approximately.

[00:46:43]So away from the foot into the into the femur. Stressoral stress fractures last who did that >> uh I don't remember who Aoyaki is the name of the person they presented at Sports Medicine Australia October.

[00:47:08]>> Yeah.

[00:47:10]>> Yeah.

[00:47:12]But there's starting to get Yeah. Yeah.

[00:47:19]>> Yeah. I'll ask a question I had.

[00:47:21]>> Okay.

[00:47:21]>> Um hypothetical.

[00:47:23]>> So let's say you have a shoe that has the same bending stiffness as a plated shoe but doesn't have a plate in it um through other factors. So let's say the foam is thick enough or whatever is going on that the thickness is the same in bedding.

[00:47:40]>> Sure. Would you say that we still need a plate in there to be able to reduce those metatarsal strains or is it just the bending stiffness doesn't matter regardless of how it's come from?

[00:47:54]>> Um I think it's probably just the bending stiffness itself. I don't know if it's necessarily the plate that's doing all the work because again like that plate is free for down the shoe. So there's a lot of foam. There's like 90% of the foam is on top of the plate and there's about 10% of the foam below the plate.

[00:48:09]So yeah, I don't know.

[00:48:15]I I don't know what methods you have to go to to get the shoe of that same stiffness without a plate, but if you >> have one right now.

[00:48:21]>> Oh, there you go.

[00:48:22]>> Yeah.

[00:48:24]Like even curious like hypothetically if you were to think of like running energetic results would you think that >> since you have the same bending stiffness you have the same like kind of energy return do you have also the same energy cost >> eventually but then then you're going to get to like the properties too right like is the identical that so that's that's a whole another but yeah >> good luck Is it compressive or dark side?

[00:49:00]>> This was we're looking compressive.

[00:49:02]>> But did you look at the side of them?

[00:49:05]Because I know that bone is more sensitive.

[00:49:07]>> Yeah, most of the stress fractures we see.

[00:49:10]>> Yeah, most of the stress almost all the stress fractures on the metatarsils occur in the compressive side. That's pretty consistent with the tibia too occurs in the compressive side of the tibia and the femur. So we looking at compressor notes, >> but you can skip it.

[00:49:27]Y just looking dorsal surface compressive.

[00:49:35]>> All right. Well, any last questions for both?

[00:49:39]>> No. uh let's say not related.

[00:49:45]So in your uh graph regarding that special difference.

[00:49:57]So what the happening there and also for example for golf club for golfing the oral frequency of the ch is tailored to the uh >> speed.

[00:50:17]>> Yeah. So is there any effect something like that stiffness to speak?

[00:50:29]>> I don't know of study that have looked at it. I'm assuming there is um there are there's some research looking at like your metatarsal fangial u strength I guess like how hard you can plant or flex your toe basically and there's correlations of that with the stiff like how stiff the shoe can be for you to get an energetic benefit and if the shoe's too stiff compared to your natural kind of metatarsal strength then you're not really going to get a benefit. So in that sense I I think there could be also like a speed effect too how fast you're running and engaging the shooter basically versus yeah how much benefit you're getting out of it. So in terms of stance time um I don't know I'm not sure exactly why there was a decrease in the cup shoe versus the intact play shoe. Maybe they're just able to kind of get on their toes faster and take off sooner.

[00:51:31]That would be my speculation.

[00:51:38]>> All right, that if there are no more questions for Colin, let's thank him for his talk.