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Gait and GRFs
35 Plays2 months ago
In this episode, Dr. Michael Powers examines gait through the lens of functional tasks throughout the gait cycle and the impact of ground reaction forces on kinetic demands during ambulation. After this episode, you will understand the WHY of what we observe during gait analysis, including why patients ALWAYS lean toward the area of weakness and/or pain when they are walking!
All music courtesy of Free Music Archive and used via attribution 4.0 international license.
- Intro and Outro: Stylin' by JMHBM
- Transitional: Our Reality by Ketsa
Contact: neuropowerhour@drmichaelpowers.com
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Transcript
Introduction to NeuroPowerHour
00:00:10
Speaker
Welcome to the NeuroPowerHour. I'm your host and neurological navigator, Dr. Michael Powers, physical therapist, board certified in neurologic physical therapy and clinical electrophysiology.
00:00:21
Speaker
Let's get started.
Understanding Gait: An Overview
00:00:23
Speaker
Today I'll be talking about gait. This is obviously a topic that's much too large for any one single podcast. so we're going to break it down into a few stages, really given a 30,000 foot view and thinking about the functions of GATE. We will talk a little bit about the phases of GATE, but I want to orient us to what are we trying to accomplish?
00:00:43
Speaker
When we're walking, if we have a keen sense of ground reaction forces, the actual functional tasks of gait, then we can stack those together and make more sense of the phases of gait. Because, well, let's be honest, ambulation and gait is really the bread and butter of physical therapy practice. I'm not going to be talking at length about gait deviations in this podcast.
00:01:07
Speaker
I want us to get comfortable with what's happening when the foot hits the ground, how our ground reaction force is impacting gait, and again, what are the functional tasks of gait.
Ground Reaction Forces and Gait Dynamics
00:01:17
Speaker
So that's the big picture overview. We're going to spend time on ground reaction forces, functional aspects of gait, probably two main categories here in today's episode.
00:01:28
Speaker
Ground reaction forces. Let's start there. And the goal is not to put you to sleep or to have you digging back through your physics books. But if you understand what's happening with ground reaction forces, you can piece together what's happening when the foot hits the ground without having to memorize the tables upon tables that you'll find in your textbooks. I'm not dogging or knocking tables. Looking at tables is fine. But if you can get a good understanding of how the ground reaction force acts to pull on various joints, you can then understand why your body is kicking in with the muscles it is at various points in time to prevent you essentially from falling. So what is the ground reaction force? It's a force exerted by the ground on a body in contact with it. It's typically measured via force plates. And because of Newton's third law, which says there's an equal and opposite force, the ground reaction force, we can think of it as essentially the same vector as the gravity line.
00:02:33
Speaker
Think about your center of mass. And if we imagine all our mass is kind of located that point, center mass is synonymous with center gravity, we can imagine a line extending down from that point. And that's going to be the same as the ground reaction force line. So I just, for me personally, I have an easier sense of imagining that center of gravity line coming down. But the actual ground reaction force is the force exerted from the ground coming up. The long and the short of it is, though, whichever direction you imagine this this arrow pointing up or an arrow pointing down, it's the line that we're concerned about or that we want to focus on.
00:03:11
Speaker
And as that line passes in front or behind a joint or medial or lateral to a joint, it's essentially pulling on that side of the joint. So let's start by maybe thinking about the ankle that's in contact with the ground. And if our ground reaction force is passing anterior to the ankle,
00:03:31
Speaker
imagine that line coming in front of the ankle. Imagine it's almost like a tug of war rope or imagine it's a line with a weight attached to it. It is going to be pulling on that tibia. It's going to be pulling into dorsiflexion. It's creating what's called a dorsiflexor moment. In order for us not to collapse or in order for that tibia not to keep going into extended dorsiflexion,
00:03:57
Speaker
we are going to need to kick in with our plantar flexor muscles to counteract that ground reaction force.
Quadriceps in Gait and Therapy
00:04:05
Speaker
In a nutshell, that's how we're using the ground reaction force to figure out what's happening at various stages or phases of the gait cycle.
00:04:15
Speaker
When we start out in what's called loading response, and I'll cover this in more detail um as we go into the functional aspects of gait and the phases of the gait cycle, but as we think about loading response, and that's right after our foot has contacted the ground, our foot has gone flat, we're shock absorbing, we have a very large impact ground reaction force moment at the knee that's pulling us into knee flexion. So our ground reaction force line or our gravity line is posterior to the knee.
00:04:51
Speaker
and we imagine that tug of war line we or yeah that tug of war rope or that line with a weight on it, it's pulling down behind the knee. It's trying to get that knee to buckle and go into flexion This is why as we're walking and we absorb weight during that loading response, we need very strong quadriceps muscles. We need knee extensors to counteract what's happening, that knee flexor moment.
00:05:19
Speaker
This is why for those of us in clinical practice, there's many clinical prediction rules, or if you look at, let me go into spinal cord injury, One of the big predictors after spinal cord injury as to whether someone will walk again is going to be that recovery of knee extensor strength.
00:05:37
Speaker
It's also why when we look at fitting someone with orthotics and we use the Rancho's Roadmap to figure out does someone need a knee brace or a KFO, a brace that involves the knee and the ankle, versus merely an AFO, an ankle brace,
00:05:53
Speaker
That three plus out of five knee extensor strength is so critical because if we don't have that strength as we're absorbing weight during that initial part of the gait cycle, our knee is going to
Forces Impacting Gait Stability
00:06:05
Speaker
buckle. And this is all due to the ground reaction force.
00:06:09
Speaker
Typically, in most cases, we're looking at that ground reaction force in the sagittal plane. So at the hip, we're looking at, okay, are we being pulled into hip flexion or extension? At the knee, we're looking at flexion extension. And at the ankle, we're looking at dorsiflexion, plantar flexion. plant reflexion I do want to point out, and i'm I'm keeping gait on purpose a little more simplified, so looking mostly in the sagittal plane, and there's much more than what we're discussing here. i do want to point out, though, in the frontal plane, think about when you're standing on one leg, you also want your hips to be relatively level. You don't want that hip drop. Some of you may have heard about Trendelenburg gait, where you get a hip drop in single limb stance, that has to do with side-to-side stability or that hip abductor stability.
00:06:58
Speaker
And so that is what's happening with the ground reaction force in a frontal plane. Just wanted to put that out there because most of what we talk about is in the sagittal plane, but we don't want to neglect that, yes, in single limb stance, we're going to also be looking at what's happening in the frontal plane as well.
00:07:17
Speaker
Most of what we're looking at then with the ground reaction force is in the sagittal plane, but I didn't want to neglect a brief mention of the ground reaction force as it relates to being in the frontal plane and the hip abductor strength.
00:07:33
Speaker
We're going to come back to the ground reaction force towards the end of the podcast. I want to next segue over into functional tasks in gait, talk a little bit about the phases of the gait cycle.
00:07:45
Speaker
At the conclusion, though, of the podcast, we're going to come back, talk about the ground reaction force and how we can use these to predict gait deviations and stance.
Functional Tasks of Gait Explained
00:08:01
Speaker
Let's talk about now functional tasks in gate. And I find this kind of 30,000 foot view or the functional tasks gate to be in many ways more helpful than merely memorizing phases of the gate cycle. I'm not knocking faces the gait cycle. We will review those here.
00:08:20
Speaker
But I think they don't tell the story of what's actually happening. And the more time I've spent neuro, the more time I've spent as ah as a PT, the more I've realized the ability to tell a cohesive story. Obviously, that's backed by the evidence and solid anatomy. But the more you can tell a story of what's happening, the more things make sense clinically.
00:08:41
Speaker
And easier it is to remember as, again, opposed to memorizing tables or disparate information that doesn't make sense. For gait, then, we're going to talk about three main functional tasks that we're trying to achieve, keeping in mind that we're going to use one leg as our reference leg. So gait cycle is going to include the heel strike of the one leg, or let's use our right leg as a reference heel strike of the right leg.
00:09:07
Speaker
all the way through stance, pre-swing, right before or right towards when that right foot hits the ground again. So we're talking about that as our gait cycle. We're going to use our right leg as a reference, imagining we're looking at someone in the sagittal plane going through one full revolution here.
00:09:27
Speaker
in In the gait cycle, that right leg is going to have three jobs, and they're going to have distinct muscle requirements, so distinct kinetic requirements, and distinct kinematic or range of motion requirements. And you may hear some people also call gait almost a pendulum-like activity. There's kind of a rising and falling, both in height of the person in general, and also what the limb, the reference limb, is doing. It's going from long to short,
00:09:55
Speaker
depending on which phase of gait we're in. The three main functional jobs of our reference leg are going to be weight acceptance, single limb support, and swing limb advancement.
00:10:08
Speaker
For each of these, I will mention phases of the gait cycle, but I want you to think about Okay, my job, if I'm the right leg going through the gait cycle, I have three jobs.
00:10:22
Speaker
First, as I'm getting ready to put that heel on the ground, and then I'm accepting weight, this is going to be our weight acceptance. So if we're talking about phases of the gait cycle, this is going to be your initial contact,
00:10:37
Speaker
in your loading response. Initial contact and loading response are your weight acceptance. That initial contact in most textbooks and references is just a moment in time. It's the heel hitting the ground and boom, immediately we go into loading response where the foot goes flat and there's a pretty big or a very big knee flexor ground reaction force. So we need to kick in heavily with our knee extensors.
00:11:03
Speaker
If we're, again, looking at kind of more of a 30,000 foot view, the goal or the the functional task of weight acceptance is shock absorption and, for lack of a better term, braking. Think of an airplane coming in for a landing.
00:11:20
Speaker
That's what we're doing. Our leg is coming in for a landing. We need to slow some of that momentum down. that we just had from swing phase. We need a shock absorb. We need to stick the landing.
00:11:32
Speaker
Muscular requirements throughout are primarily going to be eccentric. These are lengthening contractions, breaking contractions, slowing down contractions during this weight acceptance phase.
Muscle Activity in Weight Acceptance
00:11:46
Speaker
Let's talk then, let's move from the ankle up. You'll get various descriptors or advice from people. How do you analyze gait? How do you look at gait? I tend to look at it holistically, but I can make that shortcut because I've been doing this for so long. I've heard other instructors recommend start at the ankle and work your way up. And I think that's very reasonable. So i'm going to adhere to that during this discussion.
00:12:09
Speaker
As we go from initial contact to loading response, so as our heel hits the ground and then we go into foot flat, that ground reaction force is going to move from behind the ankle to in front of it. So we're...
00:12:27
Speaker
Going from a initially, as we're getting our foot on the ground, there's there's a strong plantar flexor moment. The foot wants to slap down. And many of you may have seen this, that if someone's weak in the dorsiflexors, you get that foot slap. So initially, during that loading response, we're going to kick in with our dorsiflexors. But then as we continue to load the ankle, that ground reaction force line moves in front of the ankle. We're going to start kicking in. with our plantar flexors actually to prevent the tibia from moving too far forward. Again, key thing not to get too far in the weeds is these are going to be eccentric muscle contractions. At the knee, heavy, heavy eccentric quadriceps activity, heavy knee extensor activity. At the hip, the ground reaction force is in front of the hip. So we're going to need to kick in with our hip extensors.
00:13:21
Speaker
We're going to call attention to knee extensors and hip extensors At the end of the podcast, when we talk more about a few gait deviations relative to the ground reaction force. So to recap, weight acceptance is comprised of the gait phases or the phases of the gait cycle of initial contact,
00:13:41
Speaker
And loading response. Initial contact, that heel's hitting the ground. It's a moment in time. We're not even really going to talk about muscle requirements because we're going right into loading response. So think of the airplane landing. Those wheels touch initially, but that loading response is all the wheels are on the ground and we're starting to hit the brakes. That's our loading response.
00:14:01
Speaker
Loading response is going to have heavy muscular demands that are eccentric in nature. So we're slowing down, we're braking, and we're stabilizing. At this point in time, as we've moved into loading response, I do want to call attention to what's happening to the other leg. Where the right leg, I mentioned that's our reference leg, our job is we're stabilizing. On the other side, the left leg is moving into preparation for swing phase. So once we've gotten into loading response and we're getting stable,
00:14:34
Speaker
Once we're stable, that opposite leg is going to start swinging, and now the functional task of gait becomes single limb support. So we've moved from accepting weight into single limb support.
Single Limb Support Phase
00:14:48
Speaker
This single limb support, if we're talking about traditional phases of the gait cycle, is going to consist of mid-stance, and terminal stance. In this part, in this functional task of single limb support, the main job here is going to be stability. We want to be stable because we only have one foot in contact with the ground. So we want to provide a stable base for that opposite leg to swing through. Functionally, we're trying to get as tall as we can. That stance leg needs to be big because we need to clear up room
00:15:23
Speaker
for the other leg to swing through. Hopefully that makes sense. So we're looking at from a kinematic perspective, from a range of motion perspective, we're going to get close to full knee extension. We're going to get close to neutral at the hip. We want to be as tall as we can be.
00:15:42
Speaker
Muscle requirements, the ground reaction force is now moving through pretty much the center of the hip and the knee during that mid stance. So not a whole lot of muscle requirements needed in the sagittal plane.
00:15:57
Speaker
Big muscle requirements in the frontal plane in terms of hip abduction hip abduction to keep the pelvis level. So mid stance is relatively stable front to back at the hip and the knee.
00:16:11
Speaker
has some big muscle requirements at the hip side to side in terms of hip abduction. At the ankle, and I apologize, I went backwards. I went hip to ankle instead of ankle to hip, but it made sense in terms of mid stance. At the ankle, that ground reaction force is pretty far in front of the ankle. We've got a pretty big dorsiflexor moment. So our plantar flexors are going to kick in to prevent the tibia from going forward on the ankle too far. So I've mentioned this as a stability portion, primarily through mid stance. At the ankle, we have some continued eccentric plantar flexion motion to prevent uncontrolled progression of the tibia.
00:16:53
Speaker
on the fixed ankle. Terminal stance, now as we move, so think mid stance, the leg is almost completely straight, our right leg, we're almost straight up and down. Terminal stance now, our body has moved in front of our right leg, we're moving into heel off,
00:17:10
Speaker
on the right leg and our left leg is getting ready for a landing. Our left leg is getting ready for initial contact. So terminal stance, our heel is starting to come up.
00:17:22
Speaker
We're getting ready to enter swing phase of this leg and the other leg, the opposite side is getting ready to come down. What's happening here in terms of muscle activity at the ankle, let me go back. I promise we go ankle up. Let me hold to that. At the ankle, we're still firing with our plantar flexors, our ground reaction forces in front of the ankle. But what's happening, the contraction type is changing. So we've slowed down the tibia from going to too far, but now we're getting the heel coming up.
00:17:52
Speaker
And we're going to want some power to help push that leg forward. So we remain firing with our plantar flexors, but we're moving into concentric. We're talking gastroxoleus, posterior tib, anything that's plantar flexor is going to start firing to help give us that push off that's needed to enter swing phase.
00:18:14
Speaker
Muscle activity at the knee in terminal stance, not a whole lot going on. Some starting perhaps of some flexor activity, getting ready to bend the knee. And that's going to be concentric. And there's going to be a little bit starting of maybe hip flexor activity at the hip. But not a ton. The biggest muscular requirements in terminal stance are going to be at the plantar flexors, getting ready for that push.
00:18:43
Speaker
That concludes single limb support. As we've gotten to heel off, now we're going into the functional task of swing limb advancement.
Pre-swing and Swing Limb Advancement
00:18:51
Speaker
For this functional task, I've included pre-swing in this model, the pre-swing phase of gait.
00:18:58
Speaker
Some people may disagree with that because pre-swing, technically the foot is still in contact with the ground, and some people may consider that part of single limb support. But because in pre-swing,
00:19:10
Speaker
The job is the swinging. i'm going to include it into swing limb advancement. Phases of the gait cycle then for swing limb advancement are going to be pre-swing, initial swing, mid-swing, terminal swing.
00:19:22
Speaker
So let's talk about what's happening now in the pre-swing phases. So pre-swing, it starts with the initial contact of the other side. So as soon as the left leg has contacted the ground, our job as the right leg, we're now in pre-swing. Pre-swing is going to end when we actually get that toe off the ground. We've got now our heel is up, our knee is bent, the other leg has contacted the ground, and we are ready to launch. So think about that airplane analogy. We're on the runway. You can feel kind of that booting up or that roar of the engine as we're getting ready to accelerate. Essentially, we want some power because we're going to now lift off in terms of what that leg is doing.
00:20:10
Speaker
What's happening during pre-swing? At the ankle, we're going to have strong plantar flexor activity. This is going to peter out relatively quickly because as we move through swing, we need to make the leg shorter and we're going to need to dorsiflex. So what I'd like you to consider is in that pre-swing, plantar flexors are firing, give us that push, and then we're going to switch very quickly to dorsiflexor. So big plantar flexor activity.
00:20:38
Speaker
At the hip and the knee, some flexor activity at the hip, and you may get a little rectus activity at the knee, really trying to just help out that hip flexor. The plantar flexors are driving the motion early on, giving us that big thrust. They're going to turn over that thrust to the hip flexors, though, later on in swing.
00:21:00
Speaker
Pre-swing now, we've move we're moving from pre-swing to initial swing. So initial swing is starting with the foot lifting up and it ends when our swinging foot is opposite the stance foot. So it's essentially ending right about mid stance of the other leg.
00:21:19
Speaker
Again, using that airplane analogy, pre-swing, we fired with the plantar flexors, that's giving us the initial thrust. Now we're into initial swing. Plantar flexors are turning off. Instead, the dorsiflexors are turning on. In this initial swing, what's critical is that our leg becomes shorter.
00:21:39
Speaker
We don't want to trip our toe. We don't want to catch our toes. We don't want to trip on anything. So we need this leg to very quickly get short. Because of that, the plantar flexors turn off. We don't want a longer leg by having those toes dangling down. We need a shorter leg. Our dorsiflexors are going to kick in At the knee, we're going to get some hamstring activity. We want the knee bent, right? We need that leg shorter. So we're going to get some hamstring activity to shorten the shorten the limb, bend the knee. But biggest activity in terms of driving the leg forward now is going to become is going to be coming from the hip flexor. So a lot of hip flexor muscle activity during initial swing.
00:22:19
Speaker
What's a little bit confusing to me in terms of phases, the gait cycle is initial swing is kind of lined up when the other leg is in mid stance. It would be easier if they were both lined up at what's called mid, but it's not. Initial swing is lined up with the other leg in mid stance.
00:22:35
Speaker
Mid swing is actually when the other leg is more in terminal stance. So mid swing, now the swinging leg is in front of the stance leg. It ends, the cycle ends when the tibia is pretty much vertical. So we're still accelerating and we haven't started turning on the brakes yet. That's mid swing. Here, we're making sure that we've cleared through the the scariest part, which is getting that leg cleared.
00:23:03
Speaker
We've now cleared the leg and we need to start preparing for when where we wanna place the foot to land. We're going from the shortest that our swing leg was to it's starting to lengthen a little bit. What we'll find then, let's talk through muscle requirements throughout,
00:23:21
Speaker
We're continuing to fire our dorsiflexors because we want to still make sure our toes have cleared and we want that good heel strike. So our dorsiflexors are going to still be firing. Maybe a little bit of knee flexor activity just to kind of stabilize the knee as the leg is coming forward. You can imagine momentum. would just let the knee, if we didn't check extension, the knee would just kind of kick out or go forward. So a little bit of knee flexor activity to control the knee.
00:23:50
Speaker
At the hip, we've got that strong hip flexor activity that's now starting to convert over to hip extensors as we get towards the end of mid-swing. We're starting to enter the okay, we need to start braking now. We need to start slowing down.
00:24:08
Speaker
As we move into terminal swing, this is the part from when the tibia was vertical until the foot strikes the floor. So until we get to that initial contact. Here, what we're really trying to do is slow down.
00:24:25
Speaker
and get ready to absorb the weight because now we're going back at the Segate cycle. We're going back to initial contact and loading response. So we need to get ready. Here, let's work from the ankle up.
00:24:38
Speaker
We're going to have our dorsiflexor activities continuing. And we've got the toe cleared. So we're getting a heel strike toes, not flat. And we know there's going to be a big plantar flexor moment coming up. So the dorsiflexors are ready. The brakes are ready. We're going to slow that ankle down because once we accept weight, we're going slowly lower the the foot down to the ground. We don't want that foot slap.
00:25:01
Speaker
At the knee, you can probably imagine what's going to happen. We've gone from the knee flexor activity being strong towards the knee extensors are starting to fire. The brakes are getting ready.
00:25:12
Speaker
We said that in loading response, we need that strong knee extensor um activity to counteract the flexor ground reaction force. So we're going from flexion to knee extension strengthening, or kneeat not strengthening, knee extensor contraction. The quadriceps are going to fire. The brakes are getting ready for the landing.
00:25:33
Speaker
At the hip, hip extensors. We know we're going to have a hip flexor moment when we land, so the hip extensors are coming online, getting ready to brake. That takes us through the functional task of swing limb advancement.
00:25:47
Speaker
What we have is we move from pre-swing to initial swing to mid-swing to terminal swing. What we had, if we think of the airplane on the runway, we had the plantar flexors doing most of the work in pre-swing, really getting that acceleration ready. That's our push-off.
00:26:06
Speaker
Then as we moved into more of mid swing, those plantar flexors, I'm sorry, initial swing, those plantar flexors turned off went to dorsiflexors. we're going to stay dorsiflexing throughout the rest of swing phase, right? We want that leg to be shorter.
00:26:21
Speaker
We want to clear the toe. So at the ankle, strong plantar flexors initially, then over to dorsiflexors. the if we think of the gait cycle as an airplane, the plantar flexor started out the takeoff and then handed off the energy pretty much to the hip. The hip flexors are going to pull us most of the way through. The knee is going to have a little knee flexor activity to both bend the knee, but to stabilize the knee as we're getting ready to land. And right before we land, when we go into terminal swing,
00:26:53
Speaker
Most of the muscles that are active are getting ready to serve their breaking purposes or the eccentric purposes. So we've got strong dorsiflexor activity, strong knee extensor activity, and strong hip extensor activity.
00:27:08
Speaker
To recap then, we did cover phases of the gait cycle, but I hope that this was helpful to look at What's functionally happening? During gate, we're trying to do different things at different phases of the gate cycle. So our functional tasks are weight acceptance.
00:27:26
Speaker
This includes initial contact and loading response. Most of our muscular activity in this phase is going to be eccentric to make sure we're not collapsing from the ground reaction force that's acting on our joints as we're contacting the ground.
00:27:42
Speaker
Then as the ah as we move through... and our body starts moving forward, we move into single limb support, which is mid stance and terminal stance.
00:27:54
Speaker
During this phase, the main job is stability because we only have one leg in contact with the floor. The other leg is in swing phase. We have muscular activity that's going to be primarily isometric. There may be little variations in this, but from a sagittal plane perspective,
00:28:12
Speaker
not as much muscular requirement in this phase. In the frontal plane, we're going to have a lot of hip abductor strength requirements to maintain a level pelvis as the other leg is lifted up for swing.
00:28:26
Speaker
Then when we move into the functional tasks of swing limb advancement, we've got pre-swing, initial swing, mid-swing, terminal swing. We've got essentially concentric contractions throughout. And these will then shift towards more of an eccentric contraction in terminal swing as we get ready for initial contact and loading response.
Predicting Gait Deviations with Forces
00:28:57
Speaker
Now that we've talked about the functional tasks of gait and the ground reaction forces, let's conclude with a little discussion of how ground reaction forces can assist during your gait analysis and talk a little bit about common gait deviations and how those come to be from responses to the ground reaction force.
00:29:17
Speaker
We mentioned that the ground reaction force, we can think of that as a tug of war rope or a line with a weight attached to it that's trying to pull a joint in a certain direction. Again, it's not doing it out of any malice. This is just gravity. And this is where the external force is being applied to our body.
00:29:36
Speaker
And our job, especially in single limb stance or loading response, is to counteract that external torque or that external force with an internal t torque or force that our body produces.
00:29:50
Speaker
One of the main areas of muscular requirements going to be that loading response where we need very strong quadriceps to prevent our knee from buckling. In loading response,
00:30:04
Speaker
that ground reaction force is behind the knee. Our our body is kind of behind that leg that's contacting the ground. That's why the line of gravity and the ground reaction force is behind the knee.
00:30:17
Speaker
It's going to want that. It's trying to make that knee buckle, essentially. If we do not have adequate knee extensor strength to counteract that, There's a couple strategies we can use, and you will see these in clinical practice. One would be to lean our trunk forward during loading response.
00:30:37
Speaker
Imagine your center of mass located around that navel area, maybe a little bit distal to that. If we lean forward, we're shifting that center mass anteriorly.
00:30:49
Speaker
We're moving that ground reaction force from behind the knee, to in front of the knee. If I lean forward and move that ground reaction force in front of the knee, externally now I have an extensor moment. Gravity's trying to pull my knee into extension.
00:31:08
Speaker
So if I don't have quad strength, I can lean my trunk forward change, I've moved the ground reaction force from behind my knee to in front of my knee, the knee is very stable in an extended position, and my knee will not buckle.
00:31:23
Speaker
So this is a compensation that you may see someone with weak quadriceps will lean the trunk forward. And what they've essentially done is they've moved that ground reaction force from behind the knee to in front of the knee.
00:31:36
Speaker
The other deviation you'll see for weak quadriceps would be A knee hyperextension, again, the knee is very stable in extension, so you may see, and it looks pretty rough when you see it looks pretty violent, is that you'll see the knee snap backwards into hyperextension. Same kind of premise, rather than leaning the trunk all the way forward, it's a little more subtle, but it's moving that ground reaction force in front of the knee.
00:32:00
Speaker
Two main ones that you'll see at the hip One would be around the similar time as that loading response of what we talked about at the knee. We might see extensor weakness during loading response, but here the trunk lean will be backward. So if we think about loading response at the hip, we talked about during that initial loading response as we're accepting weight, the ground reaction force is in front of the hip. but It creates a hip extensor moment, we're trying to counteract the flexor pull with our hip extensors.
00:32:35
Speaker
So if someone's got weak glutes, you'll see a posterior or a backward lean as they're accepting weight on that leg. Same premise as what we talked about at the knee, they're moving that ground reaction force from in front of the joint to behind the joint.
00:32:52
Speaker
And the hip is actually very stable in extension. So if I lean back and kind of hang out there, I'm going to be very stable. There's the wide ligaments in front of the hip.
00:33:03
Speaker
I'm not going to buckle. So weak hip extensors, you may see a lean back. The person's not strutting. They're not having any kind of a fancy walk. That's weak glutes, and they're doing it to move the ground reaction force or the center of mass, the the gravity vector line behind the
Compensations for Hip Abductor Weakness
00:33:21
Speaker
joint. In the frontal plane, someone that has weak abductors, we've talked about a Trendelenburg gait.
00:33:27
Speaker
If someone has weak hip abductors, if my right hip abductors are weak and I lift my left leg up, you might see the pelvis drop. You'll see that the left side kind of comes down a little bit because I don't have strength to maintain a level pelvis.
00:33:43
Speaker
That's Trendelenburg. The other option you might see is the trunk leaning over the right side. So now we're in the frontal plane. The center of mass is around the the belly button. So it is creating relative to the hip joint. It's creating an adductor moment, right? It's trying to pull us towards the center, right?
00:34:05
Speaker
And if I lean my trunk laterally, I've moved my center of mass from the center, kind of a double double center there, but I've moved my center of mass from medial to the hip joint.
00:34:20
Speaker
I'm now trying to move it lateral to the hip joint, and I'm creating an artificial or an external hip abduction moment. When you see that lateral trunk lean, you can assume the person is trying to move that ground reaction force across the hip going from adductor external moment to an abductor external moment.
00:34:42
Speaker
We talked about then some common deviations, some trunk leans that you might see. And these are all strategies for someone to move the ground reaction force from one having ah one muscular requirement towards another, so ah compensating for weakness. The other thing you'll find that people may also do this and issues or if they're having pain because they're trying to change the lever arm or the mechanical arm for the painful area, and they're trying to reduce the muscular requirements or the force
Observational Gait Analysis Recap
00:35:15
Speaker
requirements. The general rule of thumb, and I have not found an exception to this yet,
00:35:20
Speaker
If the leg is the foot's in contact with the ground, your patient will always lean their body towards the area of pain and or weakness. Let me say that again. So with the foot on the ground, your patient will always lean their body towards the area that is either weak and or painful.
00:35:44
Speaker
So if we think of a forward trunk lean, what they're doing is they're leaning towards the weak quadriceps muscle. They do a backwards t trunk lean. They're leaning towards the weak hip extensors. They are essentially moving that ground reaction force across the joint to be aligned with the area that's weak.
00:36:05
Speaker
Also, if if an area is painful, you'll see the same thing because they're trying to shorten the lever arm or the force requirements needed if a joint or an area is painful.
00:36:17
Speaker
To summarize, today we've looked a gait in under an hour, which is a lot. But I wanted to have us look at functionally what's happening because you can drive yourself crazy going into the various gait tables. I am a big fan of observational gait analysis. We can look at what's happening in the minutiae. But I think if you understand what's happening from a big picture perspective and the physics involved, it allows you to tell a much cleaner and a better story, which helps with generating hypotheses. And I think it makes observational gait analysis a little bit easier.
00:36:53
Speaker
We started out talking about ground reaction forces. Again, that's the force that the ground is putting upon the body that's in contact with it. Think of that as the same as our gravity vector line. So as you're looking at people walking or moving, consider where that center of mass or that center of gravity is.
00:37:12
Speaker
That's the same as the ground reaction force line. And as we're moving or as we're walking, we are constantly responding to these external forces produced by the ground reaction force with internal forces and torques. And this really predicts and tells us what muscles we see active throughout the gait cycle during periods that were in contact with the ground.
00:37:36
Speaker
In terms gait function or the functions of gait, I propose that we look at it in three distinct buckets or categories. Weight acceptance. These are going to be primarily eccentric muscle contractions. The job is to accept the weight to kind of slow down from swing phase, brace ourselves, stick the landing.
00:37:57
Speaker
Then we've got single limb support. Our job here is to be stable, to have that stance leg be long so that we're stable as the swing limb advances and we've provided enough space for that swing limb to advance, that other side swing limb. Then during swing limb advancement, our job is to generate concentric force to propel the leg forward, also to get that leg shorter. We don't want to stub our toes. We don't want to catch on anything. So those concentric contractions, these are shortening contractions, remember, and that's what we need. We need that limb shorter.
00:38:32
Speaker
Then as we end up right towards terminal stance, we're moving towards eccentric contractions because we're getting ready to break and go back into weight acceptance. Thank you.
00:38:43
Speaker
Finally, we concluded with talking about ground reaction forces and how these can predict some of the gate deviations you'll see. Those trunk leans that you may see by patients are all an attempt to move the ground reaction force across the joint and to change the external torque requirements.
00:39:01
Speaker
Thank you for listening to the NeuroPowerHour. I'm your host, Dr. Michael Powers, and I hope to catch you next episode to continue learning.