postural control

postural control

controlling the body’s position in space for the dual purposes of stability and orientation

required by all tasks

postural orientation

the ability to maintain an appropriate relationship btwn the body segments and btwn the body and environment for a task

includes biomechanical alignment of body segments relative to environment to accomplish a task

postural stability

ability to control COM in relationship to BOS

COM

a point at the center of total body mass

COG

vertical projection of COM

BOS

area of body in contact w/ support surface

COP (center of pressure)

center of distribution of the total force applied to the supporting surface

moves continuously around COM to keep COM w/in support base

orientation and stability demands of a task

influenced by task and environment

requirements vary according to ^

individual contraints/factors for postural control

postural control system

neural components

postural control results from complex interaction among many systems taht control both orientation & stability

task constraints

balance control

feedback control

feed-forward control

most fxl tasks require all 3 aspects of balance control at some point

environmental constraints

support surfaces

sensory context

cognitive load

steady-state (not static) balance

body alignment can minimize effect of gravitational forces

muscle tone keeps body from collapsing in response to pull of gravity

postural tone

increase activity in antigravity postural muscles when we stand upright

muscles tonically active during steady state balance/quiet stance

static postural control is actually dynamic

limits of stability

not fixed boundaries

best understood by looking at position and velocity of COM relative to BOS

affected by perceptual and cognitive factors

ankle and hip strategies

reactive balance control

motor patterns at ankle, hip; step, reach to grasp strategies

fixed support vs change in support

anteroposterior stability

ankle strategy, hip strategy, change in support strategies

medioalteral and multidirectional stability

alignment of body segments & muscles require activation of forces at different joints and in different directions to recover stability

ankle strategy—minimally involved

hip and trunk, change in support strategies

refining and tuning muscle synergies

stereotyped reactions

in response to changing demands in task and environment=adaptation

very quick response

reactive balance control in sitting

recovery of stability in seated position controlled similarly to that in stance

individual muscles change relative activation depending on direction of instability

why do corrective strategies occur proximal→distal?

energy conservation

it’s easier to fix balance closer to sensory input

go back and watch the panopto for this one i actually dont know why he siad proximal to distal

proactive/anticipatory balance control

CNS uses anticipatory processes in controlling action

critical to LE activities

posture anticipates voluntary movement

sensory inputs for steady state balance

vision, vestibular, somatosensory

visual inputs for steady-state balance

position and motion of head with respect to surrounding objects

reference for verticality

self-motion

somatosensory contributions for steady-state balance

provide CNS w/ position & motion info about body w/ reference to supporting surfaces

report info about relationship of body segments to one another

somatosensory info integrated for steady-state balance

vestibular inputs for steady state balance

provides CNS info about position and movement of head w/ respect to gravity & inertial forces

sensory integration

reweighting

stability in variety of environments

sensory triad

visual info gathered

somatosensory inputs

cnotribution of vestibular system smaller than somatosensory

all 3 systems play a role in recovering stability after an unexpected perturbation

sensory inputs for proactive balance

visual inputs typically most critical, depending on individual and task

cognitive systems in postural control

attentional resources

dual-task interference

dual task interference in postural control

attentional demands vary as function of sensory context

performance of secondary task not always detrimental to posture

important to assess balance under both single and dual task conditions

spinal contributions to postural orientation and stability

tonic activation of extensor muscles for weight support

directionally specific responses to perturbations present at spinal cord level

brainstem contributions to postural orientation and stability

regulation of postural tone and automatic postural synergies

basal ganglia and cerebellar contributions to postural orientation and stability

cerebellum: controls adaptation of postural responses

basal ganglia: control of postural set

fall statistics

5th leading cause of death in elderly

¾ of deaths from falls occur in ppl 65+

1/3 of ppl 65+ fall each yr

RFs for falls

muscle weakness

fall hx

gait deficits

balance deficits

AD use

visual deficits

arthritis

impaired ADLs

depression

cognitive impairment

80+ y/o

presence of stairs

throw rugs

slippery surfaces

poor lighting

4+ meds

and many others

age related changes to postural control

MSK

ROM

somatosensory

vision

vestibular

progressive supranuclear palsy

BG pathology related/similar to PD

lack brainstem involvement, limiting postural control

mainly struggle with backwards postural responses

falls in ppl w/ neuro pathology

prevalence varies by diagnosis and setting

associated w/ mobility, occuring during walking, transfers, stair climbing

impaired balance found to be most consistent RF for indiv who have neuro path who fall

alignment

relationship of body segments to one another as well as to position of body w/ reference to gravity and BOS

determiens constellation of movement strategies effective in controlling posture

infl how muscles recruited and coord for recovery of stability

examination: verticality, symmetry

postural sway

assessing stability during quiet stance

pathology in cerebellum—directionally specific incr postural sway

postural sway in PD and levodopa replacement therapy

keep in mind effects of medication state when seeing pt

fxl stability limits

determined by biomechanics of body, postural control abilities, environmental factors

exam: COP excursion during voluntary leaning (reduced in MS and PD)

limits of stability: reactive balance

sequencing problems

problems w timely activation of postural responses

problems adapting postural activity to changing task and environmental demands

impaired in-place strategies: sequencing problems, co-activation, delayed onset of postural responses, problems modifying postural strategies (postural adaption), impaired central set

sequencing

co-activation

problems modifying postural strategies

sway (see picture)

delayed onset of postural responses

reaction time

most common across different populations

impaired central set

similar recruitment pattern regardless of task being performed

anticipatory postural control

loss of anticipatory processes that activate postural adjustments in advance of potentially destabilizing voluntary movements

dependent on previous experience & learning

activating muscles before stabilized→destabilization in anticipated motion

sensory problems affecting steady-state balance

detect position of body in space, accurate orientation cues in environment, sensory weighting

disrupt ability to adapt sensory inputs to changes in task and environmental demands

disrupt development of accurate internal models and perceptions of body

somatosensory inputs from LEs in reactive balance

trigger centrally organized postural synergies

provide direct sensory feedback

loss of somatosensory inputs can result in

profound changes in motor adaptation

earlier activation of anticipatory postural adjustments as a compensatory strategy

perceptual problems affecting postural control

perceptions of verticality: subjective visual vertical, haptic or kinesthetic vertical, subjective postural vertical

balance and falls self-efficacy

confidence/fear

avoidance

major factor predicting participation in community mobility

activity & participation are limited not only by person’s actual balance abilities but also by perceived balance abilities

impaired postural stability and dual-task interference

attentional capacity

neurologic pathology produces deficits in executive attention

neuro pathology deficits in executive attention (dual task)

infl allocation of attention under dual task conditions impairing balance

maintaining stability requires more attentional resources

may contribute to instability under dual task conditions