Balance Flashcards
COM
the point that represents the average position of the body’s total mass; balancing point of the body
COM in quiet standing is where
20 mm anterior to L2
10 cm lower than navel
Is COM fixed?
NO! it moves depending on your position
Can COM be outside of the body
YES
Why do we care about COM
Researchers think that with gait in particular the brain is concerned about where the COM is in space relative to the support surface
Vertical projection of the COM is what
COG
BOS
Area of the body that is in contact with the support surface
Defined as the area within an outline of all ground contact points
LOS
The greatest distance in any direction a person can lean away from a midline vertical position without falling, stepping, or reaching for support
The range over which individuals can transfer their COG within the BOS
LOS - implies what
movement
Looking at how far they can move or lean within their BOS
balance is often interchanges with
equilibrium
Balance is the ability to
control the COM relative to the BOS or within the LOS
Balance is a process whereby
the body;s equilibrium is controlled for a given purpose
Functionally significant components of balance
1 maintenance of posture
2 post adjustments in anticipation of and during a self initiated movement (proactive, feedforward)
3 postural adjustments made in response to an external disturbance (reactive control)
3 components of the postural control system
Sensory
Integration
Execution
3 components of the postural control system - Sensory involves what
Sensory detection of body movements
Visual, Vestibular, Somatosensory inputs
3 components of the postural control system - Integration includes what
Integration of sensorimotor information within the CNS
3 components of the postural control system - Execution includes what
Execution of musculoskeletal responses
synergies
Synergies
functional coupling of muscles that work as a unit
Sensory input for reactive and anticipatory control includes what
Vision
Somatosensory
Vestibular
Sensory input for reactive and anticipatory control - Vision provides info about what
position and motion of the head with respect to surrounding objects
Sensory input for reactive and anticipatory control - Vision is a reference for
verticality
Sensory input for reactive and anticipatory control - Vision gives what type of information
anticipatory feedforward information
Sensory input for reactive and anticipatory control - Somatosensory provides info about what
position/motion of body with reference to support surface
Relationship of body segments to one another
Sensory input for reactive and anticipatory control - Vestibular provides info dealing with
gravitational, linear, and angular acceleration of the head with respect to inertial space
What is the problem with single leg balance
Bad when you stand directly in front of your patient because you are blocking their visual cues
Reactive postural control - happens when
when there are perturbations
Reactive postural control - what is happening
Feedback systems provide sensory inputs to initiate corrective responses to maintain/recover balance
Proactice/Anticipatory Postural Control happens when
before voluntary movement (in anticipation of it)
Proactice/Anticipatory Postural Control - what is happening
Feedforward - counteract internally generated destabilizing forces pretune or ready the system for upcoming movement
A lot of problems with standing and walking are due to what
loss of APAs
Reactive control - ankle strategy - muscle activity is __ to __ ms after perturbation in __
80 to 100ms after perturbation in gastroc/tib
Reactive control - ankle strategy - muscle activity is ___, ___, ____
Gastroc/tib
Hamstrings/quads 20-30 sec later
Paraspinals/abdominals
Reactive control with the ankle strategy is ___ to ___
distal to proximal
When we use the ankle strategy the perturbation is __ and the surface is ___
Perturbation is small
Surface is firm
Muscle synergy response adapts according to
stability needs
Ankle strategy - when the force plate translates backwards (inducing a forward sway) what does the person do
compensates with a backward sway
extensors are contracting
gastroc, hams, paraspinals
Ankle strategy - when the force plate translates forwards (inducing a backward sway) what does the person do
compensates with a forward sway
flexors are contracting
tib, quads, abdominals
Reactvie control - hip strategy - muscle activity is __ to ___ ms after perturbation to what
90-100ms after perturbation in abdominals/paraspinals
Reactive control - hip strategy - muscle activity is ___, ___, ___
Abdominals/paraspinals
Quads/hamstrings
Reactive control - hip strategy - is __ to __
proximal to distal
Reactive control - hip strategy is for what type of perturbations and what support surface
larger/faster perturbation
support surface is compliant or smaller
Reactive control - stepping strategies - involves a change in what
change in support strategy - movement of the limbs to make a new contact with the support surface
Reactive control - stepping strategies - realigns what ___ within ___ by using what
COM within BOS by using rapid steps in the direction of the displacing force
Reactive control - stepping strategies is typically recruited in response to what type of perturbations
fast, large perturbations where the ankle and hip strategies are not adequate
Stepping strategies can also be what (in the UE)
Reaching strategies
Reactive control - stepping strategies are NOT always a last resort - who is common to use it first and why
people with balance deficits because it is the bigger thing to go for that they know is the safest
Can we train compensatory stepping?
YES
Takes a lot of repetition
Who would step training be beneficial for
step training can be beneficial for older adults but additional multidirectional training may be necessary to facilitate generalization of postural stepping responses for any direction of a slip or trip
Do we use ankle.hip strategies as discrete synergies
NO! They blend together
Study showed that as velocity of the translation increased there was a blend - the ankles turned on and then the hips were added, but the ankle strategy was still on
Anticipatory postural control is what
activating postural muscles in advance of a skilled movement
Anticipatory postural control is feed___
FEEDFORWARD
Study with pulling on fixed handle - what did they do
They cued the subjects with what percent of their max force that they wanted them to pull the handle with
Study with pulling on fixed handle - what did they find
As the pulling force requested increased, the postural component increased in amplitude as well
Study with pulling on fixed handle - the larger the pulling force, what happened with ankle strategy
The larger and earlier the ankle force came on
Study with pulling on fixed handle - what happened when they were cued to pull with 95% of max force
the gastroc came on in anticipation of (before the voluntary movement) to stabilize the body
Study with pulling on fixed handle - What was the order of the muscle activation
gastroc and hams before the onset of when the person pulled the handle, and the biceps came on as they pulled the handle
Study with pulling on fixed handle - what happened when the person was given a brace
the system knew that they were not going to fall forward, so the APA did not even turn on - you only see the activation of the biceps at the time of pull
Study with pulling on fixed handle - clinical implications of the study
Even if you are just touching your patient, there is a change in the system to reduce sway - so you cannot say that someone has normal balance when you test them if you have even a single finger on them
Spinocerebellum is important for what
adapting postural responses based on experience
With a spinocerebellum deficit - the participants could
use immediate sensory input but not experience to adjust automatic postural responses
What happened with study that involved healthy and non healthy spinocerebellum participants
Healthy - learned and adapted through experience to adjust their responses
Deficit - did not change with exposure - they always had a large activation
In the study where the platform was translated backwards in healthy controls and those with ant lobe of cerebellum damage - what were the findings
Control - small gastroc activation
Deficit - Large gastroc and tib firing - coactivation - overall response where system isn’t sure how to respond so just gives larger response than necessary
Postural responses are
task specific
we can adapt them as needed
What were the findings of the study that went from stand to sit in healthy controls compared to individuals with PD
Control - standing show typical ankle strategy as going to sit - gastroc - ham - PSP and then when they sat only the PSP stayed firing because we do not need LE firing with sitting - task specific
PD - A lot of co contraction with standing and sitting - LE stayed activated with sitting - so they show postural inflexibility - they employ the same strategy with standing and sitting
Cbm and BG are important in adaptation of posture! They are not necessary for…
triggering or constructing the basic postural pattern - but they play a role in adapting the response to a change in the condition
Gait initiation - feedforward anticipatory - in those with PD
they showed a longer APA duration overall with a lower peak (dec amplitude of it)