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Balance
21 Plays1 month ago
In this episode, Dr. Michael Powers outlines key considerations for assessing and treating balance. He discusses the importance of considering contributions to balance from the individual, the environment, and the balance task including differences between various dimensions of balance. He differentiates normal age-related changes from balance dysfunction, and encourages clinicians to NOT accept balance dysfunction as part of the normal aging process. Your ability to effectively assess and treat balance will be enhanced after listening to this episode!
Show References
- Motor Control, 6th edition
- Changes in Sensory Organization Test Scores with Age
- Motor Unit Number Estimates in Masters Runners: Use it or Lose it?
- Muscle Changes in Aging
- Heavy Strength Training in Older Adults
- Resistance Training for Older Adults: Position Statement From the National Strength and Conditioning Association
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
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Transcript
Introduction to NeuroPowerHour
00:00:05
Speaker
I'm
00:00:10
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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
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Let's get started.
Task-Oriented Approach to Balance
00:00:22
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Today I'll be talking about balance and we'll be focusing in on multiple different domains of balance with the overriding or overarching concept that we're approaching balance from a task-oriented perspective.
00:00:35
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Within Neural World, the task-oriented approach really looks at movement or the task or the motor skill as being the intersection of what the individual brings, what the task is or the task goals, and what the environment brings. And we're going to look at balance the same way from a systems perspective, talking about all the contributors that go into keeping your balance. I think a lot of times it's easy to consider balance as, well, we just don't want to fall, or I'll hear students or novice clinicians say, this patient needs to work on balance without maybe considering all the different aspects and systems that go into balance. And I think this is important because if we have a better understanding of the systems and the processes involved in balance, this will help not only our assessment, but absolutely also help our treatment interventions.
Customizing Balance Interventions
00:01:29
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I was recently at Lab Immersion and I made the analogy to students that we can conceptualize balance interventions almost like a recipe where once we understand the various sensory systems involved, the domains of balance, are we talking about anticipatory or reactive balance, et cetera, we can then in our interventions adjust the recipe. So rather than saying, well, I'm treating balance, we can say, well, maybe I need to dial up or dial down certain sensory contributions, or maybe I need to emphasize anticipatory balance or reactive balance.
00:02:03
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A good understanding then of the systems involved in balance is really going to help in terms of your interventions and your outcomes.
Postural Control Dimensions
00:02:12
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Today, then, we'll be talking about the task-oriented approach to balance, what's happening at the individual, the task, the environment level.
00:02:19
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I want to talk about the dimensions of postural control. Postural control is another synonym for balance. The dimensions of postural control being steady state, anticipatory, and reactive.
00:02:32
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And then we'll close by talking about age-related changes in balance. I think it's important to know what we can expect physiologically, what's kind of normal aging, how that impacts balance, but also areas of age-related changes are amenable to treatment or how we can positively impact age-related changes in balance.
00:02:53
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Before we get going, let's define some key terms so we're making sure that we're consistent with what we're talking about. The two biggest terms that I want you to have a handle on that I think come up repeatedly are going to be center of mass and base of support.
00:03:08
Speaker
Center of mass is the point at the center of the total body mass. So if we imagine an individual standing, You can imagine a point at which all of the mass, all of the center mass is synonymous with center of gravity, essentially, where all of their mass lives.
00:03:26
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And in a standing position, an anatomical position, center mass can be conceptualized as being just below the navel or just below the belly button. I like vivid pictures and analogies. So I imagine when I'm thinking about center mass, I imagine an orange that's sitting right below the belly button.
00:03:44
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That is the person's center mass. Base of support is then the area of the body in contact with the support surface. In a standing position, an anatomical position, without using an assistive device, the base of support then would be the two feet that are in contact with the floor.
00:04:04
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We can see then a key aspect of balance is going to be keeping that center of mass, within that base of support. So in a standing position, feet or shoulder width apart, we need to keep that bright orange, orange, or we can picture it as a mandarin, a tangerine. I'm going to use an orange. We're going to picture that orange being located within that base of support.
00:04:29
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The other key definition I want to mention is stability limits. That's the point at which a person will change the configuration of the base of support to maintain stability. And stability limits come into play when you think about functional reach tests or other tests where a person is really approaching their limits of stability.
00:04:48
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In terms of posture definitions, and let's add a couple more definitions. So we talked center mass. We talked about base of support and stability limits. Let's talk about some definitions that have the term posture in them.
00:05:02
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Postural control, that is ah synonymous with balance. So postural control is controlling the body's position in space. And there's two main goals here. We want stability and we want orientation. So imagine kind of a big umbrella Postural control, that's our big umbrella of balance.
00:05:22
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Now within that, we're going to need to be oriented in the right direction. Our body parts need to be oriented between our body and the environment. So this is postural
Understanding Postural Control
00:05:33
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orientation. our ability to maintain the relationship between our body segments and between the body and the environment for a task.
00:05:41
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And in certain activities, that may mean staying completely upright. But imagine so a soccer player going for a header. Posture orientation means we've jumped and we're oriented almost horizontally, but that's appropriate for the task and the environment.
00:05:56
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Postural stability is another subset of postural control, and here is where we want to control the center of mass in relationship to the base of support.
00:06:07
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Hopefully you can see that in some instances, depending on the task and the environment, we may sacrifice postural stability because we want better postural orientation for the task.
00:06:18
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Most times, I think clinically in most clinical environments as it relates to neuro, we're probably emphasizing postural stability, the ability to control the center of mass in relationship to the base of support.
00:06:32
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But I want to make sure we talked about both. So to recap, our big umbrella term, postural control, that's a synonym for balance. So if I say balance, I'm meaning postural control. And postural control includes postural stability. Can we keep our center mass within the base of support?
00:06:49
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And postural orientation, have we aligned our body segments and our body relative to the environment and the task? Now, if we think about maintaining balance, really what's happening is we're taking in information to figure out where we are to then drive decision-making in terms of what we need to
Sensory and Motor Integration in Balance
00:07:09
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do. So one way to conceptualize the ability to maintain balance is can we take in sensory cues, environmental cues? can we Do we have the receptors and the sensory systems and the perceptual ability to figure out, can we answer the question, where am I?
00:07:27
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And then once that information's come in, do we have the capacity to generate the appropriate motor responses to figure out and answer the question, what am I going to do?
00:07:39
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Big picture level then, when we think about patients who have difficulty maintaining balance, we can start to wonder, are they able to answer the question, where am i And or are they able to answer the question and develop a plan for what am I going to do?
00:07:56
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Thinking back then to what I previously mentioned about the systems framework, we can imagine that balance is the key task. This is what someone is trying to accomplish. We'll say postural control, so trying to maintain balance. This is going to be the interaction between what the individual is bringing to the task, what the actual postural task is. Are we trying to maintain steady state balance? Is this an anticipatory balance task? Is it reactive balance?
00:08:24
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And what's happening in the environment? What's the support surface? Is this an open or closed environment? Keep in mind that we can separate these individual areas out to think about them as variables, but they don't act in isolation. They're going to exert some influence on each other.
00:08:42
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If we break this down further, thinking about what's happening at the environment, we can think about support surfaces, sensory context, what sensory cues are being provided, and what cognitive load is being added to the task.
00:08:59
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At the individual level, we can think about what is the individual bringing in terms of sensory, motor, and cognitive systems. And I'm going to break down each of these in a little bit more detail.
00:09:12
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At the individual level, sensory, motor, or cognitive, these are things that you're probably assessing. These are going to show up on your examination. You may identify some impairments that might make you think a person may have some challenges with balance.
00:09:26
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In terms of postural tasks, we're really talking about domains of balance. Is the goal to maintain a steady state position? Is there an anticipatory balance component or a reactive balance component? And again, I'll break this down further as we progress through today's podcast.
00:09:45
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Let's start then by talking about environmental considerations. So within this task-oriented approach, I mentioned we've got the task, what the individual is bringing, what the
Environmental Influence on Balance
00:09:55
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environment is bringing. So we're going to start with the environment.
00:09:58
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Here we want to think about support surfaces. Are we talking about walking on carpet? Are we talking about walking on linoleum? Are we on foam? Are we on grass?
00:10:09
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So changing the support surfaces is absolutely going to impact the organization of muscles and forces needed for balance, and it may also impact what sensory cues are coming in from the environment.
00:10:24
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Think about also in terms of environmental cues, if someone's walking barefoot versus with shoes on, what sensory information is coming in? The environment then will provide sensory cues that we will pick up via our primarily via vision, vestibular, and somatosensory systems. These are our three main sensory systems involved in balance. So when we think about the environment, we're thinking about support surfaces, and we're thinking about what messages is the environment sending in in terms of sensory cues.
00:10:59
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A final consideration for the environment is how is the environment affecting potential cognitive load? If we need to really concentrate on what we're doing to maintain our balance, then a noisy environment with a lot of distractions might impact our patient's balance.
00:11:18
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So considering what the person is bringing in from a cognitive perspective, but also considering the cognitive demands of the task, we can then look at the environment and think, is this then open environment where there's a lot of possible distractions, a lot of things going on? Or is this a closed environment? Maybe the person is working on balance. There's no other people around. There's no distractions. And that can really impact how the person is able to maintain balance.
00:11:49
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Moving on to individual factors. So we talked about environmental considerations. Let's talk about individual considerations. And here we're talking primarily cognitive, sensory, and motor.
Influence of Attention on Balance
00:12:01
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In terms of cognition, there's multiple aspects of cognition and cognition we can have a whole separate podcast on. But what I really want to hone in on is the person's ability to pay attention, the person's perhaps need to pay attention. So if someone is performing a task or is needs to have good postural control, and it's a task they've done many times before, they're in automatic stage or expert level, then they may not need to pay a lot of attention. But someone relearning a task or learning a task for the first time is going to need to pay a lot of attention. And the ability to pay attention could depend on, again, the task, the age of the person, and the underlying balance capacities.
00:12:43
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Here, a key concept that comes up repeatedly is what's known as a dual task condition. Dual tasking means that While we're working on one task, let's say that we're practicing standing on one leg, we've introduced either a cognitive or a motor task to be completed at the same time. So very commonly with walking tasks, dual tasking would be counting backwards from three.
00:13:08
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looking for changes in gait speed, with the thought being that as more of the brain is occupied with the second task, we can't pay as much attention to the first task. And that really hones in or gives us an idea of how much cognitive resource is needed to maintain balance.
00:13:26
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So to to recap a little bit, for cognition, think about how much attention needs to be paid to the task, whether the task changes under dual task conditions. And this will give you some cues of how might you want to set up the environment for the balance assessment and or balance treatment, because you want to match the cognitive demands with what the person is able to do.
00:13:49
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Now, if you're thinking of treatment progression, you may want to ramp up cognitive demands. If you're thinking about treatment regression, you back them down. So it's not a one size fits all, but you're learning about different aspects of this balanced recipe. So if you understand cognitive impact on performance, what is the individual bringing and what is the environment asking, you can match those up to make those equal or to make them harder or easier, depending on if you're trying to progress or regress a treatment.
Primary Sensory Systems in Balance
00:14:18
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Sensory systems used in balance. This is what the patient is bringing in. So there are sensory systems. You would be assessing this in your clinical exam. The three primary sensory systems involved in balance are going to be vision, somatosensation, and vestibular system.
00:14:35
Speaker
We'll talk a little bit more about these when we get into the domains of balance because certain systems are more involved with certain tasks of balance. One key thing, though, I think here that seems to hold true across most balance tasks is that the vestibular system generally hangs out a little bit more in the background and serves as more of an absolute reference for calibration with vision and somatosensation.
00:15:01
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Under most conditions, vision and or somatosensation are going to take the lead. And then vestibular kicks in if there's some kind of a disagreement, if there's maybe some kind of an error, vestibular kind of comes into play.
00:15:16
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And also if there's a lot of angular acceleration of the head and or a lot of movement, vestibular may be more involved. So three primary sensory systems involved in balance are going to be vision, somatosensation, and vestibular system.
00:15:31
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Good news is with the sensory systems is that even if we have challenges in one or more systems, we can use a process or tap into what's known as sensory reweighting.
00:15:42
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When all three senses are present, they're going to contribute to postural control. But if we take away or minimize the input of a system, the other systems will ramp up in terms of how they're perceived by the central nervous system. So I should mention,
00:15:57
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It's a central nervous system adjustment. The central nervous system will modify how it uses sensory information when incoming information from one, let's say, vision, a vision is decreased. Central nervous system will work to increase how it waits incoming vestibular and somatosensation information.
00:16:19
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Some of you may be familiar with the modified CAT-SIB, the standing on firm surfaces, eyes open, eyes closed, standing on foam, eyes open, eyes closed. And this tests the various sensory systems in static balance.
00:16:32
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Good news is that sensory reweighting means that we can actually train the central nervous system to increase how it's using sensory input properly. So we have patients with peripheral neuropathy, or maybe we have patients with peripheral vestibular dysfunction. We have inroads we can make to actually work on balance and changing how the central nervous system weights this incoming sensory information.
00:17:05
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Let's now move to talking about the domains or the dimensions of postural control.
Anticipatory vs. Reactive Balance
00:17:11
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Talked about, there's three main ones we want to think about. Anticipatory, steady state, and reactive. Each one has different demands from a sensory perspective. Each one is going to have different motor outputs.
00:17:26
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So it's very helpful to think about when we're assessing balance and or treating balance to start considering, well, is this task or is this balance more of a steady state? Is it more anticipatory? Is it more reactive?
00:17:40
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Along with that, depending on which task of balance we're talking about, we can think about the feedback control that's needed. So there's two main types. We have feedback control.
00:17:52
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and feed forward. Feedback means we're processing information and then we're generating a motor output. Primarily when we talk about feedback, we're thinking about reactive balance.
00:18:07
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Reactive balance is involved when there's some kind of a sensory error and then we adjust a motor response to keep our balance, specifically thought of after a perturbation or after a nudge or a push.
00:18:20
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Feed forward is self-directed postural adjustments in anticipation of some voluntary movement. So as we're reaching, maybe we're stepping over a box, we're changing our center of mass, we're potentially experiencing destabilizing movements, but we're generating these internally, so we plan ahead, and that's a different type of feedback control. So feedback and feed forward involved in balance.
00:18:50
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When we talk about the dimensions or the domains of balance, let's start with steady state balance. So imagine standing still in one place, no big voluntary movements.
00:19:01
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So there's no anticipatory balance component, just standing still. So your balance test that involves standing still, eyes open, standing still, eyes closed, standing with a narrow base of support. These are all steady state balance.
00:19:16
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Our ability to maintain balance here is going to be influenced by body alignment, general posture, by muscle tone, which includes both intrinsic muscle stiffness and normal muscle tone from neural contribution. So when we think about muscle tone, someone with a neurologic condition, maybe that's experiencing hypertonicity, hypotonicity, spasticity, changes in that muscle tone can absolutely impact steady state balance.
00:19:46
Speaker
Also postural tone, so normal postural tone, which is going to be influenced by the somatosensory system, cutaneous afferent input, and somewhat by the visual and vestibular system. So we see all three sensory systems involved.
00:20:02
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Generally speaking, steady state balance is going to be primarily driven by the somatosensory system. That one's going to be in the driver's seat, but we do have visual and vestibular system input.
00:20:14
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And we know that's the case because you've probably observed and or experienced if you're standing still with eyes open and then close your eyes, you're going have probably more of that postural sway. You're going to sway a little bit more.
00:20:27
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What about anticipatory balance? Anticipatory balance may also be called proactive balance. These are the adjustments you make in preparation of destabilizing voluntary movement. Here we're going to rely on feed forward.
00:20:42
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The motor response here is not necessarily predictable. It's going to be varied to meet the task demands. And the key take home point here is for anticipatory balance, we rely on experience.
00:20:55
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In order to plan ahead for movements that may throw us off balance, we draw upon prior experiences to execute our plan. This is why in pediatrics, you'll see that protective balance reactions develop sooner than the ability to maintain your balance regularly.
00:21:15
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in sitting or in various positions while reaching. So reactive develops sooner than anticipatory because anticipatory relies on experience and we're pulling from that experience to then adjust our motor outputs.
00:21:29
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Reactive balance then is a response to unexpected perturbation. Clinically, we see this primarily with either nudge tests, maybe we're doing parts of the mini best test where we have a patient lean into us and see what their response is. Our bodies detect a sensory error.
00:21:45
Speaker
Something's not right. So in that balance question, where am i We get an alarm saying, I'm not where I'm supposed to be. And then to answer that motor question, what do I need to do?
00:21:57
Speaker
There are multiple strategies that are appropriate depending on the size of perturbation and the surface we're standing on. For reactive balance, the primary driver is going to be somatosensation.
00:22:11
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However, in cases where maybe an object's coming at you real fast, think of the movie Dodgeball, trying to dodge a ball or a wrench, depending on what's thrown at you, then the primary sensory system would be visual.
00:22:21
Speaker
So think for reactive balance, usually it's somatosensation, but if it's an object coming at you, it could be the visual system that's driving the motor response. In reactive balance, we're trying to answer the question, where am I? Or that question leads us to realize I'm not where I should be to maintain my balance. So let's imagine that we're standing and someone pushes us from behind.
00:22:45
Speaker
There are stereotypical responses that are considered normal depending on the context. And these increase in amount of motor response needed, and these increase in terms of size of perturbation. You may also find, however, that patients with balance difficulties, especially in reactive balance strategies, may not be ah able to generate the appropriate low-level response. They jump to a higher-level response, and that increases their fall risk and their challenges with reactive balance.
00:23:18
Speaker
Let's start at the ankle. And essentially, we can conceptualize this as we start at the ankle and move up and move bigger. So a small perturbation, a small nudge, and or we're standing on a big surface. So let's say we're standing at the in the grocery store. Someone gently pushes us from behind.
00:23:36
Speaker
We're going to have what's called an ankle response. Muscles around our ankle are going to kick in We're going to essentially move around the ankle to keep our balance. So our body wants to be efficient, use the smallest response it can. Ankle response is appropriate for small but fast perturbations and being on a large surface.
00:23:59
Speaker
I don't want to get too far into the weeds here. It's a good discussion of thinking about, well, which ankles, sorry, which muscles at the ankle are kicking in. It is pretty interesting, though, and I'll just make a brief mention here for an ankle response, the muscles opposite the direction that you're being pushed in are going to kick in.
00:24:18
Speaker
And when we move on to the hip response, it'll be on the same side. So I'll refer you to some references in the show notes. It is worthwhile to think about, okay, which side of the joint is active, but we could get pulled into the weeds here. So don't want to don't want to hang out there too long. Key point is normal response for a small but fast perturbation, surface is big, is going to be an ankle response.
00:24:41
Speaker
Now, let's imagine instead you're standing on maybe a platform at the pool, kind of that square. I'm thinking of a square that's on the side of the pool, not a diving board, but one of those platforms.
00:24:54
Speaker
And if you get bumped there, so it's a small surface, or if you're back in the grocery store, but someone, one of your friends pushes you, they think they're being funny. And I don't know. I don't think they are because they didn't warn you they're doing it, but they push you and it's a little bit harder.
00:25:08
Speaker
So small surface or a harder push, you're going to have a hip response. You're going to bend at the waist. You can try this out if you're standing on a box and have someone give you a push. You're going to see that you bend at the waist instead of having an ankle response. That would be normal.
00:25:25
Speaker
Progressing further then, our next two responses are going to be a stepping response and or a change in support. So maybe you need to take a step or you widen your stance.
00:25:37
Speaker
And then finally, we have a reach and grasp. So reaching with your upper extremities is the final response. Stepping response and reach and grasp are used if ankle and hip strategies either fail or there's occasions where they're appropriate for the task. So if you're standing on a bus and you're not holding on to anything and the bus suddenly accelerates, you're probably going to both step and reach for upper extremity support. And that would be appropriate for the task.
00:26:07
Speaker
If, however, someone gives you a gentle nudge at the supermarket, again, you're standing in line, it's an accident, someone gently nudges you, and you have to take a big step or you have to reach out for support, that would warrant further investigation.
00:26:20
Speaker
How we can use this clinically then is there's various ways to assess, well, what motor strategy is my patient using and do I need to work on this in order to improve their reactive balance? Let's go back and talk a little bit more about sensory strategies for each of the dimensions of balance. I mentioned it briefly, but I think it warrants a little bit further conversation.
00:26:45
Speaker
We know then that at the individual level, the individual is bringing in cognition, sensory, and motor. Let's hone in on sensory as it relates to these three dimensions of balance.
00:26:57
Speaker
For steady state balance, somatosensory information from all body parts is the key driver of maintaining steady state balance. Visual input contributes, but isn't necessary. So the vision is going to help. It improves the ability to feel balanced. We'll see increased sway in steady state balance if the eyes are closed. But somatosensory is driving the car when we're talking about steady state balance.
00:27:26
Speaker
Vestibular system is helpful, but not effective in isolation. And again, we'll see if someone has vestibular issues, they will have some challenges maintaining steady state balance. But it's going to be somatosensation that's the primary driver for steady state.
00:27:40
Speaker
For anticipatory balance, the visual system is going to be the primary driver. Obviously, we need some somatosensation to know where we're at, but somatosensation really provides us more feedback, back whereas the visual system provides us more feedforward. And since anticipatory balance is a feedforward activity, visual system is going to be primarily involved.
00:28:05
Speaker
Same as with steady state, vestibular system will contribute a bit, but isn't the primary driver. For reactive balance, the somatosensory system is going to play the biggest role in most situations. We think about being perturbed, not, hey, I'm perturbed, but being bumped, having a nudge. So with perturbations, it's the somatosensory system that's going to kick in and help us maintain our balance.
00:28:31
Speaker
The visual system will play a bigger role if there's a change in support strategy needed. So maybe if we're stepping and stepping and reaching, vision kicks in. Or if someone throws an item quickly at us, visual system will kick in.
00:28:44
Speaker
The vestibular system will become more involved if the support surface moves vertically. and or the eyes are closed. So we see this commonality with the vestibular system being involved kind of on the periphery or having context-specific increased involvement. But in most cases, vision and somatosensation are going to be the prime drivers, with vision being most involved in anticipatory balance and generally speaking somatosensation most involved in steady state and reactive balance.
Impact of Aging on Balance
00:29:25
Speaker
Let's close in by talking about age-related changes with balance, starting out by talking about age-related changes in some of the sensory systems and age-related changes in muscle strength, because this will help us get an idea of what's considered normal versus what is malleable or changeable.
00:29:44
Speaker
And I have two kind of key points here. One is I think a lot of times, as we see impaired balance in the elderly, as we see impaired balance in patients who have had neurologic conditions or dysfunction, I think it's unfortunately kind of easy to think, well, this is part of the normal aging process.
00:30:02
Speaker
And I'd really like to push back on that because some of the physiology that we see is normal age-related changes, but decreased function or decreased ability in the task of balance should not be immediately thought of as normal age-related changes. We'll see that there's a lot we can do to either counteract normal physiologic age-related changes and or adapt to those.
00:30:28
Speaker
So I think that's important to keep in mind that we can push that back, especially as it relates we'll see with muscle strength or the ability to generate force. So we don't want to throw our hands up and say, well, this person's old, because we could even ask, well, what does it mean to be old? We'll talk about the definition, the textbook definition for geriatric. But I think as we see more emphasis and interest in health span, in wellness,
00:30:55
Speaker
I think that consideration of aging is going to be changing over the next, it's already changing now, but over the next five, 10 years or so, I think we're going to see significant changes in how physical therapists think about age-related changes in sensory systems, motor systems, and balance.
00:31:13
Speaker
In terms of aging, generally speaking, the factors contributing to aging are thought to be 20% due to intrinsic factors, such as DNA, genetics, and about 80% are extrinsic. So things that are not set in stone, things such as diet, exercise, self-efficacy.
00:31:34
Speaker
That's a pretty big distinction to make. So we've got theoretically 20% of our aging component is hardwired and up to 80% of that would be modifiable via diet, exercise, and self-efficacy.
00:31:48
Speaker
We know then that our three main sensory systems involved in balance are vision, somatosensation, and the vestibular system. So let's talk about what are normal age-related changes to each of these systems. Because if we think that there's a decline in the function of these sensory systems, we may then expect some challenges or difficulties with balance.
00:32:12
Speaker
Starting out with vision, some normal age-related changes include decline in visual acuity. You might see as people get older, they need to put on their readers. They lose that ability to see things that are close up.
00:32:25
Speaker
That's pretty much normal across the board. And if you kind of chuckle when you see people putting on their readers, I've got news for you. It's coming for you. This is something that really no one is able to get away from. This is a normal age-related change, the loss in visual acuity.
00:32:41
Speaker
Other normal age-related changes include less light is transmitted to the retina, loss of visual field, some impaired depth perception, and you'll notice some increased postural sway when standing with eyes closed. and we're going to talk a little bit about that later as to whether that's an abnormal finding, whether that finding a alone causes you to be more concerned about risk of falls.
00:33:06
Speaker
Somatosensory changes with age, you're going to have decreased vibratory thresholds, decreased tactile sensitivity, and a decrease in the number of sensory receptors.
00:33:17
Speaker
As someone who's been involved with electrodiagnostic testing, I can tell you that the norms for nerve conduction velocity as we get older We expect that those nerve conduction velocity values drop, so we have slowed nerve conduction velocity, some prolonged latencies.
00:33:35
Speaker
takes a little bit longer time for those sensory signals to travel. We will also find an increased incidence of peripheral neuropathy. doesn't mean that everyone gets peripheral neuropathy as they get older. It just means that we're seeing higher proportions of individuals with peripheral neuropathy with increased age.
00:33:55
Speaker
oh boy, the vestibular system. And I said, oh boy, because now that I've gotten older, I don't love going on swings. My daughter will say, hey dad, come play with me. Let's go on the swing. And something as simple as the swing, my stomach doesn't love that anymore. My head doesn't love that motion.
00:34:12
Speaker
And there's probably some pretty good reasons because of vestibular changes with age. I'll still go on the swing, I'll suck it up and do it, but again, I don't love it. I don't love the carnival rides anymore that are very spinny, and I used to love those as a kid.
00:34:27
Speaker
So what happens to the vestibular system with age? We lose about 40% of our vestibular hair and nerve cells by the age of 70, and there's a 3% loss of vestibular nuclei cells each decade from 40 to 90 years of age. So we're losing key functional components of the vestibular system.
00:34:48
Speaker
How this impacts balance is the vestibular system serves kind of as the absolute reference for calibration with the visual system and the somatosensation system. So if we've got a decline in vestibular system functioning, we have less ability to resolve sensory conflict and we have less stability when sensory information is reduced.
00:35:11
Speaker
An analogy I thought of being ah a child or a product of the 80s, thinking about maybe you've got two kids playing in the other room, you've got vision and somatic sensation, and maybe they're arguing, they're fighting. The vestibular system is the parent over in the other room.
00:35:26
Speaker
And if the kids get too rowdy or there's some conflict, the parent's going to chime in hey, knock it down, you know don't fight, and come in and resolve the conflict, essentially. But as that vestibular system, as we lose some function with age, the ability of that parent to come in when there's conflict between vision and somatosensation goes down. So maybe that conflict is allowed to persist longer. Maybe there's some actual damage or some errors. And I don't know if that analogy is helpful. It made sense to me. But that's what we're looking at with the vestibular system is really coming in when there's sensory conflict and or coming in
00:36:04
Speaker
If one of the kids can't do the chores, the parent's going to take over and do that. And that ability is reduced with age. Which brings me back to the point of sensory reweighting. We mentioned that earlier.
00:36:17
Speaker
So good news is we can train the central nervous system to modify how it uses that sensory information when a certain sensory system is providing maybe lower information or incorrect information. So think about your testing that you can do on firm surfaces, foam surfaces, eyes open, eyes closed.
00:36:39
Speaker
we can train the nervous system to dial up other sensory systems as needed and in context-specific ways, and this can go a long way to improving postural control.
00:36:51
Speaker
What about motor system changes with age?
Muscle Mass and Resistance Training
00:36:55
Speaker
There's a lot of doom and gloom, about loss of muscle with age, but there's also a lot, I think, of untapped access to counteracting this and actually staying in a very good position as we get older. So first, let's talk about the doom and gloom and then talk about what the evidence says in terms of counteracting some age-related changes.
00:37:15
Speaker
Muscle mass declines about 3% to 8% per decade after age 30, with strength loss declining about 10% per decade after 30. But resistance training leads to adaptive strength gains similar to those seen in younger populations. So my question is, what's true age-related responses versus how much is disuse, i don't want to say atrophy, but disuse loss of strength?
00:37:40
Speaker
And the evidence will suggest that resistance training is going to lead to strength gains similar to those seen in younger populations. There's good evidence that those individuals involved in running, so masters runners, runners 65 and up, and I apologize, I should have mentioned earlier,
00:37:57
Speaker
Textbook definition for elderly or geriatric is 65 and up. We just have that as a number. Doesn't mean that anyone 65 and up feels old, but that's what we'll use as our qualifier. So master's runners, those 65 and up that are engaged in prolonged periods of training have similar number of motor units as younger controls versus those that aren't training elderly 65 and up don't have the same number of motor units.
00:38:26
Speaker
Other consideration is the rate of force development is probably just as, if not more important in maintaining balance. So how quickly can you generate force, not just your general strength, can actually improve in older adults,
00:38:42
Speaker
following heavy strength training. There's some evidence to suggest that we're really under training the older adults, the elderly population. We think we want to, and I'm using air quotes here, be safe. Let's not do heavy weights.
00:38:57
Speaker
Heavy weight training is actually very safe and we may be under training individuals and losing weight. some ability to improve strength, muscle mass, motor units, but also this rate of force development, because we've got data that says this can improve, not only does it not get worse, it can improve with heavy strength training. So I want you to think about that, because in the next little bit, we're going to talk about especially reactive balance, and the ability to generate force. And I think
00:39:27
Speaker
keeping our patients strong and counteracting this loss of strength, loss of rate of force development is a key to improving balance. We talked about then sensory changes with age, some muscle strength changes with age. Let's talk then about how age-related changes may show up across steady state, anticipatory, and reactive balance.
Postural Sway in the Elderly
00:39:51
Speaker
In steady state balance, we're going to see increased sway as people get older. There's more difficulty minimizing this so-called spontaneous sway. So we're just going to see older adults sway more than younger adults.
00:40:03
Speaker
Really an unanswered question here, though, is that increased sway, is that predictive of falls? Does that mean that there's balanced dysfunction? And it doesn't necessarily seem to be the case, but That increased sway means someone's at a higher risk of a fall or has more balance problems. So instead, it's recommended that looking at functional stability limits is probably a better measure of balance dysfunction as it relates to steady state balance.
00:40:35
Speaker
And I recognize when we talk about functional stability limits, technically we're doing both steady state and anticipatory balance. We are having someone reach, that's anticipatory, but we're theoretically also asking them to hold a position.
00:40:49
Speaker
So here, think about a functional reach test, whether it's sitting and or standing. that that can be a good indicator of balance issues along steady state balance. And we do see that these functional stability limits significantly decrease with age, both in sitting and in standing.
00:41:09
Speaker
Anticipatory balance changes, we see impairments as individuals get older. Those impairments seem to be more pronounced in people in their 70s and eighty s And what we see then is in the elderly population, a difficulty in switching between recruiting what are known as prime muscles. So the big muscles involved with movement and the more tonic postural muscles. There's almost some confusion in more elderly population. where both of these muscles get recruited almost at the same time. So maybe a loss of ability to really be task specific in terms of which muscles are being recruited.
00:41:52
Speaker
What about reactive balance changes with age? So the young and the elderly tend to respond similarly to perturbations with responses first happening in the stretched ankle and then radiating upward to the thigh. And we remember we talked about ankle response first, then a hip response, then step, then reach and grab. So the order of response is similar between the young and the elderly.
00:42:17
Speaker
The biggest difference that's noted in the literature is the latency, so time from stimulus to response of muscle activity. So younger population just respond quicker.
00:42:31
Speaker
That makes sense. We previously talked that nerve conduction velocity slow with age, so possibly the sensory signal of where am I is slower in the older adult and the motor response, that ability of nerves to get down to the muscle to respond so that they can answer the question, what do I need to do is slower as well. So we get some latency in terms of how quick the muscles kick in after a perturbation.
00:42:58
Speaker
couple other differences we might see includes more frequent hip strategy and co-activation of antagonist muscles in the elderly. So similar to what I talked to with anticipatory balance, where maybe more challenges discriminating or having nuanced recruitment of prime and postural muscles, here we see that with reactive balance challenges, older adults might skip the ankle, go right to the hip,
00:43:23
Speaker
but they also may just recruit everything that they can, and that would be an error in response. You really want one side of the ankle or one side of the hip to kick in If you're recruiting everything and it makes sense, you're just throwing everything at the wall, you may then not be able to maintain your balance because you're really trying to pull back across the joint, and if you recruit both sides of the joint, you may not have pulled back far enough to maintain your balance.
00:43:50
Speaker
So reactive balance changes. The biggest one is increased latency in the older adults, but also maybe more frequent hip strategies and coactivation of antagonist muscles.
00:44:03
Speaker
couple other things we see in reactive balance in the elderly, there's going to be an increased risk of falls in elders who take more than one step After an initial step response, this is on the many best tests. They're stepping strategies specifically, and it's deemed abnormal if more than one step is taken. And this ties into because that does show an increased risk of falls.
00:44:25
Speaker
Also, if someone needs to follow a forward or backward step reaction with a lateral step, there's going to be an increased risk of falls. And that makes intuitive sense. If I'm being pushed forward and I need to take a forward step, that's normal. But if I'm not able to maintain my center of mass within that base of support, and now I have to step laterally, that's telling me I have challenges keeping that center am mass within the base of support. Not only that, but that need to take a lateral step means I need a bigger support surface. It's going to take longer. I'm going to be at an increased risk of falls.
00:45:01
Speaker
Also, if you're doing lateral stepping and the legs hit each other, that's going to be a bigger risk of falls in the elderly. Elderly that need to use arm movements despite instructions not to, and that makes sense. That's a reach and grab strategy.
00:45:15
Speaker
And if that's not needed for the amount of perturbation, That's essentially telling you that the person's exhausted all their other strategies and they're going all the way to level five, let's say, instead of responding at a level two. So their homeostasis window, their ability to adapt is pretty much non-existent. They're at a big risk of falls.
00:45:35
Speaker
And then if they do need a reach and grasp response, if they're slow, so slow initiation and execution, they're going have a higher risk of falls there. To summarize then what we've covered, postural control or balance involves the coordinated activity across multiple systems.
Comprehensive Balance Systems
00:45:52
Speaker
And we can really think of balance lying at the intersection of the balance task. And here, think about are we trying to do steady state, anticipatory, or reactive. The individual and the individuals bringing cognition, sensory systems, motor systems into it, and the environment. The environment's bringing support surfaces, sensory cues, and overall cognitive demands.
00:46:16
Speaker
As we're working with patients, whether it's assessing balance, treating balance, we can then manipulate, and I say manipulate because we can then impact or change many of these variables across the balance task, the individual, and the environment.
00:46:33
Speaker
The main sensory systems involved in balance are vision, somatosensory, and vestibular. Keep in mind these systems experience changes with age, but we can weight the inputs within the CNS. The central nervous system is trainable, and we can absolutely work on improving muscle strength and motor outputs to help with maintaining balance.
00:46:54
Speaker
Thanks for listening to the NeuroPowerHour. I'm your host, Dr. Michael Powers, and I hope to catch you next time to continue learning. Thank you.