- Welcome, everyone, to Wednesday Nite at The Lab, I'm Tom Zinnen, I work here at the UW-Madison Biotech Center, I also work for UW Extension- Cooperative Extension and on behalf of those folks and our other co-organizers, Wisconsin Public Television, the Wisconsin Alumni Association and the UW-Madison Science Alliance, thanks again to coming to Wednesday Nite at the Lab.  We do this every Wednesday night, 50 times a year.  Tonight, it's my pleasure to introduce to you Professor Kreg Gruben.  He's in the department of Biomedical Engineering here at UW-Madison.  He was born in Rochelle, Illinois, which is just down the road from where I grew up in Dixon, Illinois.  Kreg went to Rochelle Township High School, go Hubs,  they were in the North Central Illinois Conference, the NCIC, back in the day.  Then he went to the University of Illinois to study agricultural engineering, then went on to Johns-Hopkins to get his PHD in biomedical engineering, that's a transition that a lot of people make, from agricultural engineering to biomedical engineering.   He did a post-doc with IBM helping to develop laparoscopic surgery in soft tissues and then he came here and again made another transition, starting to work on the mechanics of lower limbs.   Tonight, we get to hear about an issue that's a pretty big deal for those of us who either had a stroke or who have family members who have had a stroke, and that is helping people to learn to walk again after a stroke.  And I think this is one of the pretty good examples to start off the new year with an excellent example of the Wisconsin idea at work. 

 So tonight we get to hear about Walking and Strokes: A Delicate Balance.  Please join me in welcoming Kreg Gruben to Wednesday Nite at the Lab.  (applause)  - Thanks, Tom, it's a pleasure to be here and thanks to you all for coming out this evening.  I'm gonna give you an overview of research that I've been working on.  I've been here about 21 years on campus and as Tom mentioned, had a few transitions in my life and when I came here, I hadn't studied walking, I hadn't studied human lower limb function and so I came at it with quite a different viewpoint, I think, than a lot of people had looked at it before.  And I think you'll see that as we go through the slides.   We're gonna focus quite a bit on just walking, what it is and what we've learned about it, but then try to relate it to what goes wrong after a stroke and then bring it back to trying to figure out what we can do about it.  So, imagine for a second that if every time you took a step you actually had to think about it.   Because there's a lot of complex control of all your leg muscles that has to take place for you to remain upright and take the next step.  But for most of us it really seems pretty easy. 

 And the question is, why? So by the end of today you'll have a lot better idea why we think that's the case.  So an overview of the quick journey we're gonna take here: we'll talk a little bit about walking, how we learn to walk, where walking can lead us as it starts to get difficult in older age.  We're gonna have to touch a bit on mechanics here because it's forces and torques and motions of the body that are important to understand a little bit.  Then we're gonna break down walking into some different components that we've discovered and then use another technique of looking at bicycling, recumbent bicycling, as a way to probe some of those mechanics.  And then we're gonna look at what, specifically, goes wrong after a stroke and how the human body and our adaptive nervous system responds to that deficit.  And then we're gonna wrap up with a quick overview of the new device that we're building that attempts to take all that knowledge and apply it to trying to fix walking again after people have had a stroke that hopefully will bring us back here to healthy walking.  Lot of benefits to walking efficiently, safely, provides independent living ability, has important fitness components,  important socially.  We learn it when we're really young, about one year old.  It's probably one of the most complex things we learn to do at a really young age.   But then it does slowly decline with age for many of us. 

 But there are a lot of other difficulties with walking that happen throughout our lifespan of various causes.  In fact, about 22 million Americans have trouble walking, defined as not being able to walk comfortably for three blocks.  So that's a lot of people that really need us to better understand walking because it puts them at increased risk of falling and of course severe injury can result.   So, a solution to these problems really requires that we advance our understanding of walking.   So, we're first gonna talk about what are some of the, how it is we do walk.   We can get an insight into that first by thinking about how did we learn to walk in the first place? What goes wrong after some neurological disorder or aging? And then what have we learned from, say, trying to build artificial devices that can walk on two legs like humans? So the walking robots that have been developed.  And the answer is, from those robots we've essentially learned to get a really good handle on the basic physics of moving around on two legs and how to control the joints in order to move the body in the right way, but it turns out there's a lot of solutions to the problem and it's pretty unlikely that the robotic solutions are being implemented in the same way humans are actually accomplishing walking.  And so if they're not, then we've still got something to learn if we really wanna try to fix it after something goes wrong with a human.  So a little bit of physics about what walking is and some of the simple requirements.  We simply wanna move our body from point A to point B. 

 We're not gonna talk about going up and down stairs or up and down hills, or speeding up or slowing down or turning corners, but we're just gonna talk about walking straight ahead at a constant speed for now.  And of course, we don't have wheels under us so we need to step, so we have to move our legs one at a time and, most importantly, we've gotta stay upright, okay? We've gotta keep our feet down there and our head up here.  And we're gonna simplify the view for now and just look at people from the side.  So a sagittal plane view.   And there are essentially, in that plane, three parameters that we need to control.  We need to control out vertical motion, our horizontal motion and our rotational motion of the body as a whole.  Now, the body's a bunch of linkages that moves in complex ways but we're gonna talk here about the motion of the body as a whole.   Moving, controlling the motion, horizontally and vertically is pretty easy.   The difficult part, and the way it's controlled is we have gravity as a force acting down but we've got the force of the ground acting up on our feet.  As long as those sum to zero, we're good. 

 And horizontally, we've got some horizontal forces from the ground acting on us.  As long as over a gait cycle those sum to zero, so we've got some pushing us forward, some pushing us back, as long as that sums to zero, we're gonna stay at a constant speed, we're doing pretty good.  The challenge is to try to control the rotational motion of the body.  What we need to have happen, you know, we've got a lot of arms and legs swinging back and forth, so a lot of rotation of the individual segments, so we want the whole body to not undergo too much rotational motion because if we do, we're gonna fall over.   And if we take a look at falls, when they happen, most of the time it's because the rotational motion has somehow broken down and we end up tipping over rather than falling down as would be the case if, say, the vertical force wasn't controlled appropriately.   So, how do we control rotational motion of an object? We know that we have to step so there's this limb rotation going on but the posture that we need requires that the average angular motion and rotational motion of the whole body is zero.  So how do we control rotational motion? So if we look at the person over there, we see, we know we've got gravity acting down on them, but we've got this other force from the ground acting on the feet.  And the characteristics of that force that effect how it rotates are due to torque.  So, you probably remember that back from physics at some point.  Torque is essentially calculated by looking at how big the force is and multiplying it by the moment arm. 

 So the moment arm is that little red double vector up there by the center mass over to the line.  So the force can cause the whole body to rotate if that force has a moment arm.  So in other words, it misses that center mass.  And from that, you can see that it's only this force from the ground acting on our feet that can actually cause rotation, or therefore stop rotation or keep us from rotating.  Therefore, it's the important thing that's necessary to pay attention to if we wanna figure out how people stay upright.   So if the force is in front of the center mass, as it's drawn here for example, that will generate a torque which will pitch us over backwards, okay? We could do that for a very short period of time, but we can't do it for a very long period of time because we'd end up on our back.  So, we wanna stay upright, so ideally, then, we'd want no torque about the center mass which would require us to redirect that force and make it go right through the center mass.   So, we're gonna focus in on this force between the ground and the foot or the foot on the ground because it's the thing that keeps our body upright.  Now how do we produce that force? Well, first let's think about the components of the force.  So a force is a vector. 

 It has magnitude and direction and it has location.   Those three components are due to different aspects of the muscles that we use to produce the force by pushing our foot against the ground.  So the muscles spanning the hip, knee and ankle are the most important.  If we ramp up the overall activity of all those muscles, we essentially push harder.  So that makes our force magnitude go up.  If we change the ratio of the amount of muscles we're using at the hip versus the knee, that's gonna effect the direction of that force.  As you saw earlier, I could make it change direction, make it go through the center mass or not, that's due to this hip/knee ratio of activation.   And then ankle muscles are primarily responsible for locating the force under our foot.  As you know, if you push down with your toes, you can get the force to go under your toes or you can rock back on your heels, so your ankle muscles essentially control that aspect of the force.  So we've got this magnitude, direction and location. 

  So, we're gonna focus in, then, on relative muscle activities because of their role in controlling particularly the force direction and the force location because those are the two that have a direct effect on this torque, this rotational motion and we're not so concerned about the magnitude of the force because most people don't have trouble with generating enough force to keep from falling straight down, unless you faint.  But, if you're, so, the magnitude of the force is generally controlled pretty well, it's the angle of the force, it's direction and it's location in space, that are the key factors that effect whether it's gonna generate this torque that's gonna tip us over or maybe stop a fall and keep us upright.   Okay, so basic walking has these three requirements, the vertical part of this force on the ground has to equal gravity, the horizontal part has to average zero and the torque about the center mass has to average zero.  So, how can we accomplish that? We know that when we take steps, we're gonna be moving our foot away from, in front, or then behind, our center mass and so we're gonna be changing the location of that force.  So that's gonna effect the torque and effect our angular motion.  And so possible solutions are, if you think just broadly, what could we do with that force that we now know has to move it's location front to back under our body as we move? It's kinda helpful here to maybe think about walking on a treadmill because we're gonna be thinking about the force and how it behaves relative to the center of mass.  So if you're walking on a treadmill, your body pretty much stays in one place and your feet move under you as opposed to walking over ground where your body's moving and your feet stay stationary, momentarily, as you move forward.  So kind of envision it as being on a treadmill, that center mass is staying roughly in one spot and the feet are moving relative to it.   So, what we could do is we could direct the force vertically through the whole gait cycle and that would satisfy, we could oppose gravity, it would make sure our horizontal forces sum to zero, cause there are none, and that's essentially what you have to do when the lakes do freeze up out here and you wanna walk on them is you need to make that force vertical cause you don't have access to the friction forces to generate the horizontal forces.  And you can do it, but you end up walking differently, take smaller steps and things like that. 

 And one of the reasons that you take smaller steps is because if you took as long of steps as you did when you had friction there, you'd have to use a lot bigger joint torque, so you have to use a lot more muscle activation in order to keep that force directed vertically when you take a long step out front and back.  And so we generally like to minimize the amount of effort that we put in with our muscles, we're generally lazy and so we take smaller steps in order to be able to still walk, not use as much muscle activity but keep the force vertical and not fall down on the ice.  So that's one solution that satisfies those three requirements up above.  It satisfies the rotational, the torque requirement because for a while, the forces out in front of the center mass and it's gonna generate a torque tipping us one way but a little while later it's gonna be generating a torque in the other direction so those can balance out.  And we might pitch back and forth a bit more than normal, but we would be able to stay upright.   Now another way to do it, and this is what essentially was assumed up until about 2010 that this is what people did, but we'll see later it's not, and that is to direct the force exactly through the center mass all the time, as you saw, I adjusted that force to go right through the center mass.  We certainly have the muscle capability to do that, we could direct this force right through our center of mass all the time.  We would not pitch back and forth, then, it would keep us upright very nicely and it would require less muscle effort, especially relative to a vertical force.  But the question is, we could also do a wide variety of other things.  We could have some random pattern of force direction as long as it meets those three requirements up at the top, we can be very creative with our walking. 

 And in fact, we're capable of that.  But what we're gonna be looking into is what is human's preference for walking and coordinating the muscles to generate this force? So, in the face of a wide range of solutions that could keep us upright and keep us walking, what do humans do? So, there is a walking pattern of the force that's very distinct across people that we found in our lab here and another lab has documented it from Germany and it's essentially represented by the schematic over there on the right.  So this is not a three-legged person, but this is three phases in the gait cycle.  So you see the leg going forward and then back.  So imagine there's a time component there.  So, initially you put your foot down on your heel, you get a force that acts in a particular direction, and then a little while later it's under the middle of your foot, when your foot's underneath your body, and then your foot's back behind your body when you're ready to push off, generating a force more with your toe.  But what we're really interested in was the direction of that force and where does it pass relative to the center mass? So the data actually looks like this down at the bottom, actual, the extensions of the forces that we measure as people are walking.  And you can see that they very closely, not exactly, but very closely intersect at a point and that point is clearly not at the center mass, but it's clearly much higher, and it roughly is in the vicinity of the shoulder joint.  Now, it varies due to various properties that we're continuing to study, but it's generally in some region above the center mass and around the shoulder.  We call that point the divergent point, just to recognize that it's a point that essentially the forces all, in a sense, emanate from. 

 Imagine here we're talking about the forces of the ground on the foot but there's also the force of the foot on the ground, which is pointed in the opposite direction of that, sort of diverging from that point up around the shoulder.   So, why would humans do this, because it's clearly not directed at the center mass and it's not directed vertically the whole time.  Well, it turns out that there's a fairly easy explanation.  If you think about the torque that these forces generate, they have a very nice property and it can be illustrated simply by looking at a block that you'd set on a table.   So if you sit a block on the table and you look at the support force that has to hold it up and you tip it a little bit to the right.  When you tip it to the right, the location of the force is gonna move over to the right and it's gonna have some particular direction.  Now if you don't tip it too far and you let go, it's gonna rock back toward upright.  And when it does that, it's gonna have some support force that is not passing through the center mass because if it did, then the block wouldn't rotate.  It has to pass to the right of the center mass to get that torque to get it to rotate back toward upright.  Tip it the other way, it does the same thing. 

 Let it sit in the middle, and the force goes up.  If you put those three forces together you'll see a pattern of forces that keep that block upright that intersect at a point that's above center of mass.  So this also happens in lots of things that stay upright on their own.  Things like ships floating in water, it's called a metacentric point, in that case.  But it also happens to be the way that humans direct their force.  A difference, however, is that in this block it has no brain and it's simply mechanics playing out.  But humans, we have the capability to adjust the muscle activation in our hip, knee and ankle to direct that force however we want to.  But for some reason it emerges to come out in this nice pattern which has the property of making us act like a dumb block, which pushes it back to upright.  So we're essentially a blockhead, I guess.  It pushes us back toward upright without us having to change our control. 

 Now, certainly we had to have some control to get the forces to do what we see they're doing on the right, but we don't have to modify that control.  If we tip forward a little bit, the force then will automatically be out in front of us and have a direction which is gonna tip us back toward upright.  So that's a really nice feature because it enhances upright posture.  Now, it's gonna have a side effect that slightly pitches us forward and back, okay? So we're gonna have a little bit of a pitching motion as we walk, but we're able to tolerate that pretty well.   And the location of this divergent point is variable.  We've been able to get people to move it higher or lower depending on the cognitive task we give them.  So if we give them a challenging math problem, or even counting backwards by threes, we can get them to move that divergent point, does anybody have a guess which direction it would move if we asked you to count backwards by threes?  It shifts up.  Because what that does is it then makes the forces essentially spread apart a little bit and they're now, if you remember that moment arm thing, they're now passing farther from that center of mass and that gives 'em a bigger torque and pushes them back toward upright more.  Now we're hypothesizing that that's a protective mechanism because when you're focusing on a math problem, you don't have as much attention to put toward the feedback that you need in order to stay upright, if you had a disturbance bigger than what could be accommodated for with this approach.  'Kay?  So this is a really important component of how we are hypothesizing that we walk around because it reduces our computational demand for staying upright while walking and it allows us to essentially walk and talk at the same time. 

 And in fact as we age, there's a tendency as our walking deteriorates if we're asked a question to actually slow down our walking or actually stop in order to answer the question.  So there's a cognitive interplay there that we think this may be an important part of that this sort of mechanics helps us free up cognitive resources so that we can continue to think about harder things while carrying out this complex task of walking.   But, there's a lot more under the surface.  That was just observing what the force does during walking.  This part we're gonna go through kind of quickly, but it gives us a few more tidbits at a little bit deeper level.   While walking, we notice that the location of the force changes.  We said that because our foot's out in front and then our foot goes to behind our body and so that location is changing.  But that's not the only reason the force is changing under our bodies, changing it's location under our body.  It's also changing because we have this habit of landing on our heels and pushing off with our toes.  So that also shifts the force relative to our body and we do it in synchrony with placing our leg in front and moving it behind so that the two essentially act in opposite directions. 

 We put our leg out in front but we land with our heel, so the location of the force is back farther than it would be if we landed on our toes, say.  And then when our leg goes behind us, moves the location over in that direction, we then are up on our toe, which actually shortens the distance that the force location actually shifts.  So we have these two competing mechanisms going on at once and they both can effect the direction of the force, so this rotational effect of keeping us upright.  And so we wanted to separate them.  And so to do that, we could assemble a computer model of a human, we have mass segments all linked together and we can control the way they interact, and if we do that to simulate what a human does, and then change one factor, we're just gonna change what's going on at the ankle joint, in order to shift that location of the force back and forth underneath your foot.  So, you know, going heel to toe by changing your ankle muscles.  When we do that, we see that the force changes direction as well, as you can see there.  And the forces intersect at a point.  But now the point is not located up by the shoulder region, it's located down around the knee.  And another interesting piece of this is that that particular pattern of forces intersecting at a point, they intersect at a point exactly, okay? It's not an approximate like the other behavior but it's an exact intersection point, and essentially accommodates or tells us what the effect of ankle muscles is on this direction of force. 

  So this is a nice, clean little piece of something that's going on while we're walking that we can then use to essentially subtract off of the behavior that we observed on the left.  And so it's essentially like saying, "Well, what if we walked only on the ball of our foot "or only on our heel "and didn't have this heel to toe motion?" Cause we're gonna take care of that with that middle panel.  So if we do that, we're gonna subtract off those mechanics from the ankle muscles and see what's left.  And it turns out, something very interesting.  It turns out that if we were to walk only on the ball of our foot, the forces would now be directed at a point that intersects at a pretty close intersection point that's located about at our center of mass.   Well that's a really handy thing, type of behavior, to have because as we pointed out earlier, a force that goes right through our center mass doesn't generate a torque and won't tip us over.  So if we're walking along and we need to, say, jump over something, we would like to, once we launch into the air, we're committed in whatever rotational motion we have, we're gonna continue to have that rotational motion until we land.  So we'd like it to be no rotation so that we land on our feet again, and the way to ensure that is to make sure that whatever force we use to push off of the ground with is going right through our center of mass.  And lo and behold, it turns out that that's the control that we're using while we're walking so that it's automatically there and handy if we need to jump.  But it would be a lousy controller to use all the time by itself, as you may be able to discover if you just walk on your toes around and try closing your eyes and you'll notice you feel pretty tipsy pretty quickly and the reason is that you're not getting this passive stabilization mechanism, you're getting the force to go right through your center of mass all the time, which is great for keeping you from tipping, but what happens when little disturbances come along? Your controller is not going to be perfect and so you're going to accumulate a little bit of air and you're gonna start to tip over. 

 That controller on the right then won't do anything for you, it's just gonna let you keep tipping over.  You'll have to change it, so you'll have to intervene with feedback, change your control and come up with a response that will then correct that tipping.  So you could use it for walking, but you'd have to have feedback active all the time, which would require much more cognitive resources.  If you, though, couple that behavior on the right with a habit of landing on your heel and pushing off with your toe, you then change the force direction in precisely the right way that ends up with the forces doing what we see on the left, which is intersecting at a point above the center of mass which gives us the nice stability properties that we get with a block sitting on the floor without a brain.  So we now have something that lets us jump and something that lets us walk without having to think too much about it, all together in one package.   So, just to summarize quickly, we've gone through a bunch of stuff and I just kind of wanted to get your mind wrapped around it.  So there's a hip/knee muscle coordination that directs the force from the ball of the foot to our center of mass that we use during walking that enables us to jump without inducing some additional rotational motion.  We have an ankle muscle coordination that gives us this heel to toe foot rollover and it alters the force in just the right way that gives us this divergent point, which then gives us an emergent behavior that allows us to stay upright with less computational cost and there's this possibility of adjusting the height of the divergent point which would require more energy but gives us more stability, so there's a trade off there that we may be able to use and, another thing is that the mechanics of this work out really nicely if we want to speed up or slow down.  So if you go to speed up or slow down, you're gonna induce some forces which are gonna tend to tip you over but you'd like to not tip over when you speed up and slow down so you've gotta do some careful adjustments of things and it turns out that that middle panel in the last one is also tuned to provide an appropriate adjustment to keep you upright while speeding up and slowing down without having to do any additional control on top of it.  So that's another nice piece. 

  So what could go wrong? Well there's a lot of pieces to this and understanding which piece might get disturbed in a particular deficit is a challenge  which we need to address by isolating some of these controllers that we've laid out the pieces for.  So notice that if something did go wrong with some of these mechanisms, it would lead to us falling over because we have to be precisely tuned.  If you just take something and you try to balance it on your finger, you know that the instant you don't do just the right force on that, it tips right over.  So, we know that if a person has some deficit  that's gonna lead to them starting to fall over, usually the brain is still active enough to realize this is a really bad thing and I have to do something about it now and you're gonna compensate.  And the compensations should be appropriately tuned to whatever the deficit was.  But the problem is that once we have a person who has some deficit and then has all these compensations layered on top and we see them walking, it's really hard to tease out which part is which.   So we need some means to isolate these different mechanisms.  And this, in my view, has been a reason that's kind of been a roadblock for a lot of walking research is that we haven't had a tool like this.  What we need is a task that allows us to investigate the coordination that the person will use for leg muscles, but not be too constrained so that they have to do just what's required for balance.  So we need to give them a task that takes care of the balance need in another way and we did it by giving them a seat. 

 That seat could be a bicycle seat, it could be sitting in a chair, it could be a special recumbent bicycle like this, but something so that the forces generated by the leg aren't responsible for balancing the person any longer.  So then whatever controller the person is most practiced with can emerge.  And we can measure that by putting force sensors underneath the feet in the pedals and just measure the forces that people generate, which essentially gives us then a window into what coordination they're using at hip, knee and ankle muscles all together.  And it's the net output of all those, we're not looking at what any individual muscle is doing because in terms of the physics of staying upright while walking, you really need to look at the final common output of all those muscles.  Looking at just individual ones or as many as you can measure isn't a complete picture.  So, we focused in on measuring that and we see that we are able to, by removing this balance, then observe an underlying controller.  So what does it look like? In intact individuals, we are interested in measuring the direction of the force for reasons that have been evident with what we've talked about before in walking, across a bunch of limb postures because clearly we're going to be moving our legs through space.  As we're walking, our joint angles are changing, we need to understand how humans coordinate the muscles while the legs move in different postures.  We do that by robotically controlling where the pedals move or stay stationary, both cases have been investigated, so that there's nothing about the task that's effected by the force.  So they can generate whatever force output they want to. 

 We're interested in trying to get a window into what their preferred coordination is, that we then suspect might be what they'd use during walking because during walking, a very specific control needs to be used.  During a seated task, they can use any that they want to.  All we're asking them to do is generate some force.  Just push in the most comfortable manner.  When they do that, we see a force that looks like this.  We see another force that looks like this.  And across the space of limb postures, we see that the forces tend to be directed at their center of mass.  Now, note that we're also constraining the force to be at the ball of their foot by putting them on a bicycle-type pedal.   And we then notice that, and so that they're going through the center of mass, and we notice that that control, then, resembles that that we saw for walking due to the hip/knee controller that is a force that went through the center of mass across limb postures.  So we think that this validates the ability to use this balance-free task in order to probe walking strategies. 

 So we then took that and applied it to a population that has trouble walking.  So we looked at individuals that have had a stroke and we ask, "What is the directional force "that they would generate if we put them "in a task like this?" Sometimes the pedal was stationary, sometimes it was moving.   We did two studies: one with individuals that were chronic, so they had their stroke more than six months earlier so they were fairly stable in their recovery, and also we looked at individuals who had had a stroke yesterday.  So once they were medically stable and they were still in their hospital bed, had not walked, we went into the hospital room and put a pedal under their feet and just asked them to push and we measured the force.  In all cases, and across all patients, we saw that the forces were not like that, but the forces were directed like that.  So their angle anterior to the center of mass.  On average about 10 degrees, so not a lot of change.  And the amount of rotation of the force in front of their center mass seemed to vary somewhat with the severity of their stroke.   I need to do more quantification of that, but it was a surprise that in all cases the forces rotated in that particular direction and not, none of them were directed behind the center of mass.   Clearly by not being directed at the center of mass, that would cause a problem if you were to try to walk. 

 It would tend to tip you over.  It would tip you over backwards and you would not be able to walk.   So what we have is stroke causing a specific miscoordination of hip/knee muscles that gives you a final outcome of falling over backwards.  But, the brain is still intact enough to say, "Falling is not an option, I have to do something about it." And there are many options.  There are many other ways to keep from falling over and those ways could involve, well, grab onto a handrail, grab onto a walker, a cane, something like that.  Or avoid using that leg.  Now remember, in a stroke, it effects one side of the body.  So the problem we've defined is happening in one leg and the other leg is closer to normal.   So we could avoid using that leg.  When you're standing, that's not too hard to do, you just kind of lean towards your good side and don't put so much weight on your other side and then it doesn't matter so much that it's actually directing force in a bad direction, it's not gonna have as much of an effect in tipping you over. 

 That doesn't work for walking, though.  You need to put weight on each leg individually in order to take steps.  And so there are other ways that you could intervene and you could compensate by essentially flexing your hip on that side.  And that essentially, as is illustrated in the picture over there, rotates the force so that it can now intersect the center of mass again and again, be able to be stable and not tip us over backwards.  You could also not rely on muscles to keep your leg from collapsing.  And you could do that by essentially hyper-extending your knee, locking your knee, and if you can do it far enough, a few degrees so it stays stable, then the force would then be redirected up through your center mass, or approximately through your hip joint, which is closer to your center of mass and so provides some stability.  So these would all lead to further deviations because they're an interference of the normal way we walk and it's very interesting that you can hypothesize these initial ones that I've shown you as well as further walking deviations that would be mechanically consistent with being able to keep you upright while having this underlying deficit and compare all of those potential behaviors with what we see after stroke and they line up one to one.  So it's likely, we think, that what's happening in someone who has had a stroke is that a major part of the deficit of the walking disorder is that there's this one underlying deficit that has manifested itself in a bunch of compensations.   So, what does therapy do? Well current therapy essentially sees all these deviations of walking but can't see the underlying deficit and so attempts to fix it by removing them.  But since they are the thing that keeps us from falling over, it's been a very frustrating endeavor. 

  And it's been difficult because of this mix, that stroke walking is this mix of some underlying deficit and all these compensations.  So when we look at rehabilitation, we first need to identify the deficit, that's the base level deficit, and we have found force misdirection which seems to be consistent with the behaviors that are observed.   It's also interesting that it predicts the failure of current therapies.  So, some therapies that have been gaining popularity in the past 10 or more years are the lower picture on the right is body weight supported treadmill training where a harness is put on the patient and the idea is that if you give them a little bit of body support, so you pull up on them with a harness, some fraction of their body weight, they then don't have to push as hard with their leg muscles and they're able to practice walking.  And then gradually reduce the support and be able to return to walking.  Now the interesting thing is that the force, when you provide that body weight support, and you look at the way their limbs move during walking, the limbs start moving closer to normal almost right away, indicating that there's still a residual capacity to do normal walking that's somehow being elicited by this intervention.  Well, that makes complete sense if you think about why, we explained on the last slide, that they actually have all these odd behaviors after walking, it's because the force control that they now have is tipping them over backwards.  So if I put you in a harness that's now not gonna let you tip over backwards, you're gonna be much more comfortable to be able to push on the ground with the force that even though it has a bad direction, it can't tip you over now, so you're going to be confident in putting your weight on that leg and be able to walk closer to normal.  The therapeutic community embraced this technology because it looked like walking was improving.  But it turned out through many multiple, multi-site clinical trials, that once you take the harness off, the walking was not significantly improved. 

 And when the people went back to the behaviors that they had had before.  And that makes complete sense if you look at it from the perspective that we have here.  And then another approach has been to use robotic devices which guide the leg through a normal motion during walking.  Again, the theory here is that the motion of the leg during walking has been somehow disrupted and that if we could help the person by guiding the leg through the right motion pattern that they would somehow learn to do that motion pattern.  But that hasn't worked out so well either, and has not shown additional benefit beyond just traditional walking over ground type of therapy.   So, what about a new approach?  We first have to be able to measure the underlying deficit and so that's gonna, we can borrow some of the knowledge that was gained from body weight supported treadmill training and realize that if we put the right kind of harness on our person we can probably get them to generate the force output that shows  that they have this misdirection.  We can then use that as feedback, in multiple forms, in order to try and get them to retrain, particularly the hip and knee muscle coordination, to direct the force in the right direction.  And if we're able to accomplish that, then they should be able to walk because we've now gotten them to generate the force that will keep them from tipping over backwards, which was the underlying deficit caused in the first place.  So, if we target that underlying deficit, that's where we can really hopefully make a difference.  So this is a little bit more detail about what our, we call it KIINCE, this is our device. 

 It's a Kinetic Immersive Interfaces for Neuromuscular Coordination Enhancement.  So it kind of wraps into it a bunch of the stuff that we've been talking about here.  And here's how it kind of works: so your brain sends some signals down to your muscles to coordinate them in a certain way.  After a stroke, those have been messed up in a certain way.  We need to measure that, so we put you in a harness so you can't tip over, we put four sensors in the plates that you're standing on, those plates are robotically controlled so they can move back and forth however we program them to.  The plates will measure that coordination, measure the force, and therefore be able to infer what the coordination is that you're using.  Those plates will only move if you then improve, take steps toward improving that coordination that we see has a deficit and then we'll also give game-like interfaces, both visually and the motion of the plates, in order to encourage that learning of a new coordination strategy which will then hopefully get your brain to send the better signals down to your muscles and create the feedback loop that can improve learning.  So at present, we have built this device, we're testing it in our lab, we have two more devices that are almost finished that we'll be putting out in clinics to gain more interactions with a larger patient base.  In order to gather the data that we need to prove out the theories that I've just described.  So we're at a critical junction where we have a lot of theory, we have devices built and we're ready to test it out. 

 So we're looking for subjects and interested in collaborators who can help guide us in the clinical direction.   And with that I'd like to acknowledge the team that's been a part of this and the funding sources that have provided the support to get us to this point.   And I thank you for your attention, and would open it up for questions.  (applause)