upright balance

who might have balance dysfunction

• persons with neurologic conditions

• persons w/ musckuloskeltal conditions

• all age groups and activity levels

why define and understand balance?

• those with balance deficits are at risk for falls, reinjuries, and new injuries

• PTs have a role in improving balance dysfunction as well as prevention of and remediation of balance-related injuries

what impacts sensory control

biomechnaincal aspects and infromation processing on task constraint and environmanrytal context

postural control (balance)

control of the body’s position in space for the puposes of orientation and stability

postural orientation

relationship between 1) body segments and 2) body and environment

postural stability/equilibrium

control of center of mass (CoM) relative to base of support (BOS); active resistance to external forces on body (static or dynamic)

CoM

point at teh center of the total body mass

• how does it differ from CoG

BoS

area of the body that is in contact with the support surface

CoG

vertical projection of the CoM

CoP

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

two primary mechanism

feedforward control (anticaptory or proactive mechanisms

feedback control (reactive mechanisms)

feedforward control

postural responses are made prior to voluntary movement that is percieved as destabilizing in order to maintain stability

feedback control

sensory feedback from unexpected perturbations triggers postural reponses

what is balance

a continuum

static stancw

• not truly quiet nor static

  • contributors: biomechanical alignment, muscle tone (eg intrinsic muscle stiffnes, postural tone)

• typycally only ankel and hip strategies

  • context dependent (could involve stepping)

automatic postural responses APRS

responses to unexpected perturbations

• reactive mechanism (feedback control)

• not a reflex (ie depends on equilibrium requirements specific to task, not simply changes in muscle length, longer latencies)

• muscle synergies: spatial and temporal characteristics

  • ex: ankle, hip, step strategies

ankle strategies

• distal to proximal muscle activation

• body sways at ankle with hips and knees in relatively extended positions

• occurs on firmer surfaces and/or with small pertubations

• employed first in anteroposterior pertubations

hip strategies

• proximal muscles activated first

• large, rapid motion at hips

• occurs when standing w/ narrow BOS/narrow surface, on compliant surface, and/or with large, fast perturbations

• employed first with mediolateral perturbations

what are APRs dependent on?

biomechanical constraintsstrat

strategies to recover multidirectional stability

• basic ankle or hip stratigeis insuffiecnt

• muscle synergies (updated concept)

  • modular, functional groups

  • flexible, each muscle belongs to more than one synergy

• within each synergy, each muscle has a unique weighting factor that represents the level of activation of that muscle

• modulated by continuous feedback; combinations of synergies based on context of situation

• there are common muscle synergies across standing and walking

• fixed patterns of co-activation at any given time point

anticpatoru postrual adjustments

• use prior knolwedge of task, enviorment, and individual constriants to stabilize and orient body for voluntary movement

• proactive mechanism (feedforward control)

• postural set or central set (previously used terms)

balance relies on

1. somatosensetion

2. vision

3. vestibular

   • needs to be integrated

   • the predominat system engaeged in static standing is somatosensation

   • used in teh development of a body schema

body schema

a central representation of body and its environment

updated with experience as wella. schanges in body and enviornment

somatosensation

• prioreceptive

• cutaneous

• joint receptors

• large diameter, fast somatosensory fibers

  • essential for reactive balance respnses (APRS)

  • otherwose delayed response latencies

  • group 1a more likely invovlved that group II in production of reactive balance due to speed of conduction

visiosn

• greater role in proactive responses thatn reaftive due to slower neural conduction

• postural orientation

• difficulty perceiving differences between object and self-motion

vestiu=lar

• engaged most with unstable surfaces and head movements

• information about head position and motion relative to gravity and inertial forces

• not critical to APR timing; impacts magnitude

rewieghting sensory ingo

• not just sensory processing within individual sensory system, but an interaction between them

• accomodate changes in environment an task goals

• adapt to loss of (or inaccurate) sensory input

sway referencing

manipulating or reweighing sensory input

• measured through 6 conditions

• alters visual and somatosensory

cogntive process or load can impact how well one maintains balace

• dual-task capacity (motor or cognitive secondary tasks)

• fear executive function

• motivation

• self-efficacy

is thera a balance control center?

no, or control system,don’t fully understand

• thught to have contributions:

  • spinal cord

  • brainstem

  • cerebellum

  • basal ganglia

  • cerebral cortex

spinal cord on balance

• ground reaction forces orientation present through diinished

• tonically active extensor muscle for antigravity support for postural orientation

• no lateral stability

• spmatosensory contributions to postual control

brianstem and cerebellum

important for integrating sensory inputs

• brainstem and vestibulocerebellum: vestibular and visioal inputs

• spinocerebellum: rapid conduction proprecptive and cutaneeous inputs

• vestibular nuclei and reticular formation: slow conductiong somatosensory fibers

• cerebrocerbellum: visual planitn

brain stem

M/L vestibulospinal tracts and reticulospinal tracts may carry signals for APRs

basal ganglia

adaptation to sudden task changes

cerebral cortex

• somatosensiry cortex: recieves somatosensory input

• temporoparietal cortex: sensory integration, body vertically

• supplementary motor area: anticipatory strategies

• motor cortex: execution