Lecture 7 Flashcards
Posture
1
Q
Postural control
A
controlling the body’s position in space for dual purposes of stability and orientation
Postural control is essential to independence in functional tasks and impairment is common in both neurologic and musculoskeletal injuries
Must consider task and environment when defining, as stability and orientation demands may change
2
Q
Postural orientation
A
the ability to maintain an appropriate relationship between the body segments and between the body abd tge ebviroment for a task
3
Q
“Posture”
A
Used to describe both the biomechanical alignment of the body and the orientation of the body to the environment
4
Q
postural stability
A
The ability to control the center of mass (COM) in relationship to the base of support (BOS)
5
Q
base of support
A
Area of body that is in contact with the support surface
6
Q
Center of mass
A
A point that is at the center of the total body mass, just anterior to S2 vertebra
7
Q
center of gravity
A
Vertical projection of the COM
8
Q
Center of pressure
A
Center of the distribution of the total force applied to the supporting surface
9
Q
Systems framework
Individual
A
Complex interaction of musculoskeletal and neural systems
Musculoskeletal components include:
* Joint ROM, spinal flexibility, muscle properties and biomechanical relationships among body segments
Neural components include:
* Motor processes
* Sensory processes
* Cognitive resources
10
Q
Neural Components
Motor processes
A
Include organizing muscles throughout the body into muscles synergies
11
Q
Neural components
Sensory processes
A
include detection of individual sensory signals and their integration and organizatio to prodcue limb abd obdy orientation and motion in space or with respects to the enviorment
alows us to detect the surface the body is on,
12
Q
Neural Components
Cognitive resources and stratigies
A
Essential for mapping sensation to action and ensuring anticipatory and adaptive aspects of postural control
**Does not mean conscious control
Includes attention, motivation, intent, learning, retention
if they dont attendt to what they are learnign they dont learn as well
13
Q
Influence of Task and environment
what are the difference of these tasks.
A
- Sitting on a bench reading
- Standing while scrolling through your phone
- Walking
- Ice skating
14
Q
Task Constraints
A
- Three types of balance control:
Steady State
Reactive balance
Proactive or anticipatory balance - Functional tasks often require all three aspects at some point or another
15
Q
Steady-State Balance (SSB)
A
Ability to control the COM relative to the BOS in fairly predictable and non changing conditions
Ex: Sitting, standing quietly, and walking at constant velocity
not much challange to maintain this
16
Q
Reactive Balance (RB)
A
- Ability to recover a stable position following an unexpected perturbation
- Relies on Feedback mechanisms
Corrective postural control strategies that occur in response to detected sensory errors after an external perturbation
mini best has a portion of this. (important) This is what we need to assess.
17
Q
Proactive/Anticipatory Balance
A
- Ability to activate muscles in the legs and trunk for balance control in advance of potentially destabilizing voluntary movements
Ex: Lifting heavy object, stepping up onto a curb
When delayed, performance of these tasks can lead to loss of balance and falls
- Relies on feedforward mechanisms
- Anticipatory postural adjustments (APA) executed in anticipation of a voluntary movement that is potentially destabilizing in order to maintain stability during movement (plan to help with the destabilizing)
Older adults have issues to adapt their anticiparoty balance doesnt work well with MSK system.
18
Q
What are these tasks? (steady state/ reative/ proactive balance)
1. swinging a golf club
2. sitting and studying
3. Slipping on ice
4. stepping onto and walking on moveing sidewalk
A
- Proactive Balance
- Steady-state balance
- Reactive Balance
- Steady state Balance (walking on it) Proactive (Stepping onto the moveing)
19
Q
Environmental Constraints
A
- Conditions impact the way the sensory, motor, and cognitive systems are organized to control balance
- Support surfaces: Firm, soft, moving
- Sensory Context: Differences in visual and surface conditions
- Cognitive Load: Multi-tasking demands, distractions, noise
20
Q
Steady State Balance SSB
Motor Systems
A
- Body alignment can minimize the effect of gravitational forces, which tend to pull us off center
- Muscle tone keeps the body from collapsing in response to the pull of gravity because:
- Intrinsic stiffness of the muscles themselves
- Background muscle tone, which exists normally in all muscles because of neural contributions
- Postural tone is the activation of antigravity muscles during quiet stance
21
Q
Steady State Balance
Alignment
A
- Activation of spinal mm. to maintain alignment is critical factor in minimizing postural sway during upright stance and sitting.
- Ideal alignment allows the body to maintain equilibrium with reduced energy expenditure; fatigue of paravertebral mm. may result in dramatic changes in postural control
Working less, muscles in synergies.
22
Q
Steady state Balance
Muscle Tone
A
- Defined as the force with which a muscle resists being lengthened;
Also, long-lasting and fatigue-resistant muscle activity that is sensitive to head positions - Controlled by somatic descending brainstem pathways, monoaminergic descending systems, and limbic system
Some question of how stretch reflexes may assist in feedback Postural sway does play a role in maintaining a flow of dynamic sensory inputs to the CNS Suggested that the increase in muscle spindle sensitivity is an adaptive strategy enabling an increase in sensory-related postural information to the CNS
sensory feed back that helps to s3end infor to keep us upright
23
Q
Steady State Balance
Postural Tone
A
- Sensory inputs from multiple systems are critical to maintain postural tone
Dorsal (sensory) roots of the spinal cord - somatosensory input
Plantar cutaneous inputs - Increase extensor mm activation (foot on the ground) - Cervical inputs - Changes in head orientation can influence the distribution of tone in the trunk and limbs (tonic neck reflexes)
- Visual and vestibular system inputs - Change in head orientation (vestibulocollic and vestibulospinal reflexes)
24
Q
Steady state balance
Postural tone - research says??
A
- Appropriate activation of abdominal and other trunk muscles is important for efficient postural control, including postural compensation for respiration-induced movement of the body
- Postural control involves active sensory processing with a constant mapping of perception to action
* Allows calculation regarding where the body is in space, predict where it is going and what actions will be necessary to control this movement
25
# steady state
Movement Strategies - Stability Limits
* The point at which a person will change the configuration of their BOS to achieve stability
* Affected by perceptual and cognitive factors (i.e. fear of falling)
* Movement strategies are needed even when standing or sitting quietly
26
# steady state balance
Stability Limits
* Determines if will require a step or reach for support to regain stability
* Are not fixed; must consider interaction of position and velocity of the COM at any given moment
27
# steady state balance
Movement Strategies - Modes of Control
* During quiet stance, body behaves like a multilink pendulum (trunk and legs)
Ankle strategy - move in phase (LOWER sway frequency)
Hip strategy - move out of phase (HIGHER sway frequency)
Both always present and used when task and environment demand
* Newer research is showing that quiet standing is multidimensional, involving coordination of many joints (not just ankle and hips)
Lower body control depends on reweighting sensory feedback
Upper body control depends on musculoskeletal mechanisms
Trunk control occurs in segmental zones
28
# Steady-state balnce
Seated postural control
* During unsupported quiet sitting, kyphotic posture “normal” in typically developing individuals
In a person with neurologic dysfunction, interpreted as poor seated postural control
* Research (Saavedra et al 2012) has demonstrated that the trunk can be controlled in segmental zones (4)
Indicates the coordination is complex
29
# Steady state balance
Clinical applications
* Measure ability to sit or stand independently
Berg Balance Scale, Rhomberg, etc.
* Observe orientation/alignment of trunk and body segments
Anterioposterior and mediolateral alignment
* Measure the stability (ability to maintain COM within the BOS)
Force plate, wearable sensors
30
# Reactive balance
Movement strategies - recovery stability
* Specific movement patterns used to recover stability following displacement of COM are selected by the CNS based on a number of factors:
Characteristics of the perturbation
Biomechanical constraints
Environmental conditions
* Muscle synergies - Muscle patterns that underlie movement strategies for balance
* Reactive Balance strategies:
Ankle
Hip
Stepping
Reach and Grasp
31
# Reactive balance
Anteroposterior stability - fixed support
Ankle
* Ankle - Restores COM to a position of stability through body movement centered primarily about the ankle joints
FIRM surface (more likely on this)
Forward sway - Begins 90-100 ms after perturbation at gastroc, 110-130 ms at hamstring, then paraspinals
Backward sway - Begin ant tibialis, quadriceps and abdominal mm
## Footnote
forward backward sway
32
# Reactive Balance
Anteroposterior stability - fixed support
Hip
* Hip - Controls motion of the COM by producing large and rapid motion at the hip joints with antiphase rotations of the ankles; larger faster perturbations
COMPLIANT or smaller surface
Forward sway - Muscle activation begins 90-100 ms after perturbation in abdominal mm, followed by quadriceps
Backward sway - Muscle activation begins 90-100 ms in paraspinals followed by hamstring
33
# Reactive balance
Anteroposterior stability - change in support
* Rapidly moving the limbs to change the BOS (step or reach)
- Stepping Strategy - Realigns BOS under falling COM
- Reach-to-Grasp - Extends BOS using arms
May occur even when COM is well within BOS Why??
* Balance reaction - Initiated and completed in half the time as voluntary
* Missing or reduced APAs - Increased lateral instability which requires counterforce of swing limb
## Footnote
resiteasted walking with band does this naturally. Needs to be enviormental changes
34
# Reactive Balance
Mediolateral and Multidirectional stability
* Requires activation of forces at different joints and in different directions to recover stability
* Control occurs primarily at hip and trunk vs. ankle, with primary motion at pelvis (ADD + ABD of opposing limbs)
* Rectus femoris + TFL = most active with lateral perturbations
* Remaining LE mm and trunk = most active in diagonal perturbations
35
# Reactive Balance
RB in sitting
* Recovery of stability in sitting is similar to stance and can elicit reach-to-grasp response
AP perturbation:
Without LE support = Recover using trunk
With LE support = Recover using LE
* Multidirectional perturbations in the seated position result in compensatory muscle responses similar to stance
Tonic activity (trunk) support and stabilize the head and trunk in quiet sitting (SSB)
Phasic responses are tuned to the direction of instability
Rapid response, faster than voluntary
Temporal and spatial coordination of muscle synergists, little from agonists
36
# Reactive Balance
Clinical Applications of reactive balance?
Assessing
Recovery
and Retraining??
* Assessing
Gentle pushes to displace COM, observe response
Nudge test - part of the Performance-Oriented Mobility Assessment (POMA), or Segmental Assessment of Trunk Control (SATCo) - reactive balance using nudges
Seated Postural and Reaching Control (SP&R-co) - hold and release technique
* Recovery
Postural synergies are not fixed, refined and tuned in response to demands = adaptation
Allow/encourage use of anticipation to assist in refining response
* Retrain balance without relying on a single synergy (ankle vs. hip, etc)
Create conditions where strategies can be continuously modulated
## Footnote
anticipatory postural assists.
37
# Proactive (anticipatory) balance (PB)
PB and APAs
* PB is the CNS anticipating movement and force demands and forming a representation of what perception or action subsystems are needed to accomplish the task; pretunes the systems
* Depends on anticipatory postural activity (APA)
* Adapted to changing tasks and environmental contexts, refined with practice
* For LE activities such as standing on one leg - weight is shifted to the opposite limb prior to lifting
For rapid arm movement:
* Preparatory phase of activating postural (trunk and leg) mm 50 ms in advance of prime mover mm to compensate for destabilizing effects
* Compensatory phase - postural mm are activated again after prime movers in a feedback manner, allowing for improved stabilization
38
# Proactive (anticipatory) balance (PB)
PB in sitting
* Organization of APA is dependent on the position of the person and the resulting postural demands
* Reaching in sitting - Hamstring APA absent, delayed in lumbar extensors which is a reversal of the order of recruitment (cranial to caudal)
* Anticipatory postural muscle activity decreased as support of the body increased
* Activity increased when task load increased
* Early phase to prepare the “postural set” before APAs in some tasks (e.g. when sitting on unstable surface)
39
# Proactive (anticipatory) balance (PB)
Postural set
= increased muscle tone readied for reaction; increased EMG activity of distal mm to prepare the postural configuration in sitting before performing a pushing task with hands; are not part of the APAs
40
# Proactive (anticipatory) balance (PB)
Clinical Application of Proactive Balance
Assess through observation
* Single leg stance (BBS, 4 stage balance scale, etc)
* Lifting (relatively) heavy object
* Sitting and standing reaction, solid and unstable surfaces
41
# Sensory Inputs
Sensory and perceptual systems in postural control
* CNS requires an accurate picture of where the body is in space and whether it is stationary or in motion to understand when and how to apply restoring forces
* Specific combination depends on the three main factors
* Which sense is most important for postural control?
It Depends!!!
42
# Sensory Inputs
Visual Contributions
Information regarding position and motion of head, reference for verticality
SSB - Visual inputs do actively contribute to steady-state balance control
* Vision not necessary for postural control and actually may be misinterpreted
* Object motion vs self-motion (exo vs. egocentric motion)
RB - Important when change-in-support strategies are used to recover stability
* Provides input of the environment
* Information regarding environment is gathered as soon as a person enters an environment
* Response is quite slow using visual input, close to 200 ms to activate
## Footnote
Peripheral stimulus is more important for controlling posture
Car next to you moves, brain senses car is rolling
43
# Sensory Inputs
Somatosensory Contributions
* Provides the CNS with position and motion information about the body with reference to supporting surfaces
* Provides relationship of body segments to each other
* Not appropriate to utilize reference to vertical when standing on surface that is not horizontal (i.e. ramp)
44
# Sensory Input
SSB
Inputs from all over body contribute to balance during quiet stance
* Reduced afferent input from LE showed increased COP motion
* Use of fingertip support can greatly reduce sway - orientation cue
* Very useful to older adults, B vestibular dysfunction, Down syndrome, MSK injuries
## Footnote
orient to verticle
45
# Sensory Input
RB
These inputs are preferentially relied upon by CNS
* Especially useful with support surface perturbations
* Response to perturbation within 80-100 ms
* Significantly slows with neuropathy
46
# Sesnory Input
Vestibular Contributions
SSB - Provides CNS with information about the position and movement of the head with respect to gravity and inertial forces
* Cannot be utilized alone; eg. head nod = bending over forward
*
RB - Contribution is much smaller than somatosensory inputs esp with surface perturbations
* Standing on tilting board, utilize vision and vestibular inputs more to avoid retropulsive LOB
* 4 deg/s = physiological postural sway
* Consistent LOB with B vestibular deficits at this velocity
* Overall, all three sensory inputs play a role in the recovery of stability following unexpected perturbation
47
# Sensory Input
Sensory Integration
SSB - When all three senses are present, they each contribute to postural control
Sensory reweighting - When one sense is missing or inaccurate, the CNS is able to modify how it uses sensory info
* Dependent on task, BOS; normally automatic
* Failure to use properly leads to balance impairments and falls
* Occurs during the process of learning new motor skills, often heavily visual initially, then shifts to somatosensory inputs more
* Consideration for rehab with patient with neurologic injury
48
# Sansory Input
Sensory Reweighting
When one sense is missing or inaccurate, the CNS is able to modify how it uses sensory info.
Wider BOS – no sensory reweighting occurs, remains dependent on proprioception vs. visual or vestib
Narrowing BOS – shifts to vision or vestibular from proprioceptive
49
# Sensory Input
Clinical applications of sensory inputs
* Balance rehabilitation must include clinical strategies for assessing both the integrity of individual sensory systems and the ability to organize sensory inputs for balance control
* Include activities to improve organization of muscle activity as well as the way the sensory info is used for balance
* Include tilting boards, other equipment to challenge sensory-related balance deficits
* Compensation may be necessary if altered or loss of input from one system (i.e. B vestibular loss, neuropathy, low vision)
50
Sensory Organization Test
| Sensory reweighting
Assessing for weight shifting and what system are you using. In different conditions.
How affective is the systems working together.
## Footnote
Vestibular = 5 and 6 worst
Proprioception- 2 and 3 becasue the brain will tap into it before vestibular. Later might still look the same as 2 and 3 because there may not be much same. All might look the same.
51
Cognitive systems in postural control
* Balance control normally occurs automatically
* Dual-task interference, or “cost”
* When two tasks are performed simultaneously, the competition for available attentional resources may cause a decrease in performance on one or more tasks
* Up to 10% difference in time to perform a task with a DT cog component when compared to performing task alone is considered “normal”
52
Cognitive Systems
* Postural control in young adults is attentionally demanding
* As the demand for stability increases, there is a concomitant increase in attentional resources used by the postural control system
* Postural control is organized as part of an integrated perception and action system and can be modified to facilitate the performance of other tasks
* Postural prioritization does not occur in many balance-impaired older adults and in patients with neurologic pathology
53
Orientation and Stability
Neural Subsystems involved in balance:
* Cerebellum
* Basal ganglia
* Thalamus
* Hippocampus
* Inferior parietal cortex
* Frontal lobe
54
Spinal Contributions
* Contributes to the orientation component of postural control
* Tonic activation of extensor mm. for weight support
* Directionally specific responses to perturbations also present
* Nonfunctional without supraspinal drive
## Footnote
Extensor muscles are always active
55
Brainstem Contributions
* Brainstem nuclei are active in the regulation of postural tone and automatic postural synergies
* Regulates anticipatory postural control
* Houses circuits for automatic postural synergies and restores equilibrium following a balance threat
* Process vestibular contributions to postural control
56
Basal Ganglia and Cerebellum Contrubuiosn
Cerebellum controls the adaptation of postural responses
* With injury, patients are unable to adapt to changing perturbation amplitudes
Basal Ganglia involved in control of postural set
* Postural set - Ability to quickly change reactive balance muscle patterns in response to changing task and environmental conditions
