1-17 Postural Control

8/11/2019 1-17 Postural Control

1/48

PTP 512Neuroscience in Physical Therapy

Postural Control

Reading Assignment

Shumway-Cook: pp. 161-162, 164-193

Min H. Huang, PT, PhD, NCS


2/48

Objectives

Define postural control and distinguish betweenpostural orientation and stability

Describe the concepts of dynamic stability limits

Describe postural control processes, including

the contribution of the motor action componentand the role of sensory functions

Compare and contrast feedback vs. feedforwardpostural control

Discuss the attentional demands of posturalcontrol and its impact on stability during multi-tasks


3/48

INTRODUCTION


4/48

Postural Control Defined

Postural Control

Controlling body

position in space for

StabilityOrientation

Postural Orientation

Ability to maintain an

appropriate relationshipbetween body segments

and between the body

and the environment


5/48

Base of Support (BOS)

BOS is the area of the body in contact with the

support surface


6/48

Gait: Chasing COG

Walking is a state of constant falling

During gait, the COG

falls anterior to the

BOS and the personmust step forward to

re-establish the COG

within the BOS to

avoid falling


7/48

Center of Pressure (COP)

COP is the centerof thedistribution of total forcesapplied to the support surface

COP represents the averagelocation of these forces butNOTthe forces! It is a point ona 2-D plane!

CNS activates muscles tochange the location of COP,which in turns shifts the

location of COG Biodex Balance System


8/48

Systems for Postural Control

Horak et al., 2009


9/48

Postural Stability = Balance

Balance is the ability to keepthe vertical projection of the

center of mass (COM), within

the limits of base of supportCOM is a point in 3-

dimensional space, usually

around L2 in standing

COG is the vertical projection

of the COM on a 2-dimensional

plane, usually the ground


10/48

Horak et al., 1989

McCollum & Leen, 1989

Stability Limits

Stability limits refer to theboundarieswithin which the

body can maintain stability

without changing thebase ofsupport.

Previous concepts of stability

limits only consider the area of

the feet utilized to maintain

balance rather static concept


11/48

Current Concepts of

Dynamic Stability Limits

Stability limits result from the interactionbetween the velocity and position of COM.

Stability limits are the boundaries of the

combined COM velocity and positionpossible withoutthe needs to change thebase of support

Other factors, such as muscle strength, range ofmotion, fears of falls, perceived stability, andvarious aspects of the environment (e.g. lighting,icy vs. dry) also affect the stability limits.


12/48

COM displacement-velocity trajectory. Subjectsstood on a platform that moved unexpectedly.

Left: Stepping response. COP velocity exceed thevelocity threshold.

Right: Non-stepping response. COM did not crossthe stability boundary.

Triangle symbol indicates the initial quiet standingposition.

Pai 2000


13/48

Current Concepts of

Dynamic Stability Limits: Try this.

Lean forward as far as possible and then

1. Throw your arms up as fastas possible

2. Throw your arms up as slowlyas possible

Which condition do you feel more stable?

Stand in your neural upright position

1. Lean backward as fastand as faras possible

2. Lean backward as slowlyand asfar aspossible

Which condition do you feel more stable? Which

condition are you able to lean further backward?


14/48

Modes of Postural Control:

Feedback vs. Feedforward Processes

Slip on the ice or trip over your catvs.

Any voluntary movements

Kandel, 1991


15/48

Mode of Postural Control

Feedback control (Compensatory or reactivepostural responses)

Sensory feedback from unexpectedexternal perturbations triggerspostural

responses

Feedforward control (Anticipatory posturalcontrol)

Postural responses are made prior tovoluntary movement that is potentiallydestabilizing in order to maintain stabilityduring the movement


16/48

ACTION SYSTEMS INPOSTURAL CONTROL


17/48

Quite Stance Postural Control

Body alignment: idealalignment requires the leastamount of energy

Postural Tone: activity in

antigravity postural musclesincreases to counteract thegravity

Samemuscle synergies usedduring perturbed stance alsoplay a role in maintainingquiet stance.


18/48

Postural Control during Perturbed

Stance

Earlier studies of

postural control used a

platform that moves in

the anteroposteriordirection. Subjects

were asked to keep

their feet in place.

These studies

found..

Moving Platform Studies


19/48

Movement Strategies to Recover

Anteroposterior Stability

Ankle Hip Stepping


20/48

Ankle Strategy

Distal to proximalmuscle activation

pattern

Body sways at

ankles with hips and

knees in relatively

extended positions

Utilized in responseto small

perturbations on

firm surface


21/48


22/48

Stepping or Reaching

Strategy

When subjects were not asked tokeep feet in place, they more

frequently step or reach, instead of

utilizing ankle or hip strategies to

restore balance (McIlroy & Maki, 1993)

Stepping or reaching are natural

responses, not the last resort to

restore balance!

Older adults more frequently step

than young adults (Mille, 2003)Horak, 2009
http://bestest.us/samples.htmlhttp://bestest.us/samples.html


23/48


24/48


Multidirectional Stability

There is a continuum response patterns that

control stability in the 360-degree of possible

perturbation directions

Shumway-Cook, 2007


25/48


Multidirectional Stability

Complex postural response patterns in 360-degree cannot be explained by simple ankleor hip strategies.

Current concepts: Synergies are flexible. each muscle

belongs to more than one synergy

Within each synergy, each muscle has aunique or fixed weighting factor thatrepresents the level of activation of thatmuscle within the synergy


26/48

Each synergy activates a specific set of muscles in a

fixed amount. Different combinations of synergies

are activated based on continuous sensory

feedback to adjust postural stability.

Ting, 2005
http://jn.physiology.org/content/93/1/609.full.pdfhttp://jn.physiology.org/content/93/1/609.full.pdf


27/48

Clinical Implications of Movement

Strategies for Postural Control

Both quiet stance and recovery of stability in

response to perturbations use common

postural synergies.

Training in one context, e.g. quite stance,

may transfer to improve stability in the other

context, e.g. recovery of perturbed stance

Do notlimit training to the activation of aspecific synergy, e.g. ankle or hip strategy


28/48

Adaptation is the ability to modify response

according to the task demands

With repeated perturbations, movement

strategies change (within 5-15 trials!)

Several studies in normal adults found

reduced sway with repeated exposure to

platform movements

Adapting Strategies


29/48

ANTICIPATORY POSTURALCONTROL


30/48

Anticipatory Postural Adjustments

(APAs)

Work with a partner. Stand with your arm

outstretched, at about waist height, palm up.

Place a heavy book on your outstretch palm.1. Have your partner remove the book

2. Lift the book using your opposite arm

Are the responses different between 1 vs. 2and why?


31/48


(APAs)

In A, Gastroc was

activated prior to

biceps.

In B, subject wassupport at the

shoulders so the

arm movement did

not disturb posture.

Thus, APAs were

not needed.

Cordo & Nashner, 1982


32/48


(APAs)

Postural muscles are activated prior to the

prime movers that produce movement

Same postural synergies utilized during quiet

stance and postural perturbations are alsoutilized in APAs.

In Cordo and Nashners study (1982), A & B had

different Central Set, which refers to the stateor readiness of the nervous system that is

determined by the context of a task


33/48

Clinical Implications

APAs increase with movement magnitudesand speed. APAs more frequently presentwith faster movements and heavier loads

Practicecan affect the timing of APAs, e.g.

dancers activate APAs much earlier in a leg-lifting task than untrained individuals

APAs are reduced when a support is

given

Your patients will never improvebalance if they practice balance tasks whileholding on to // bars!


34/48

Neural Systems Controlling

Postural Orientation and Stability

Spinal Cord

Spinal cats canactivate extensor

muscles to supportbody but theirpostural stability ispoor

Postural stability isNOT organized at thespinal cord level

Brainstem

Regulation ofpostural tone

Integration ofsensory information

Contribute toanticipatorypostural control forvoluntarymovements

N l S C lli P l


35/48

Basal ganglia-cortical loop controls posturalset, i.e. the ability to modify the postural

muscle activation patternsto changes in the

task or environmental conditions

Neural Systems Controlling Postural

Orientation and Stability

Patient withParkinsonsDisease


36/48

Neural Systems Controlling Postural

Orientation and Stability

Cerebellar-cortical loop controls the

adaptation of postural muscle activation

amplitudes, i.e. scaling, in response to

changes in task and environmental conditions Patients with damage to cerebellum were

unable to modify postural muscle activation

amplitudes even after repetitive perturbationsof the support surface (Horak and Diener, 1994).


37/48

PERCEPTUAL SYSTEMS INPOSTURAL CONTROL


38/48

Sensory Contributions to Balance

CNS processes information from sensory

receptors throughout the body to determine

the bodys position in space

Vision (especially peripheral vision)

Somatosensation (proprioception,

cutaneous, joint receptors)

Vestibular system Each sense provides a different frame of

reference, i.e. map


39/48

Sensory Weighting Hypothesis

Postural control system is able to reweight

sensory inputs in order to optimize stability in

altered sensory environments.

The gain of a sensory input will depend onits accuracy as a reference for body motion.

Try this. Stand on one leg with eyes open vs.

closed. Which sense(s) may be weightedwhen you close your eyes?


40/48

Visual Contributions

Moving Room

Experiment

Lee and Aronson, 1974

sway in youngchildren and old

adults with room

oscillation (may be

due to reduced

somatosensation)

Vision may not be

reliable

Self motion vs.

object motion?


41/48

Somatosensory contributions typicallydominatepostural control in response to

transient or fast surface perturbations (in

this type of situation, visual and vestibularinputs do not help)

Lightly touching a stablesurface reduces

sway significantly. The somatosensory

inputs from the touch, rather than the

contact force through touching a surface(Jeka, 1994; Lackner, 1999)

Somatosensory Contributions


42/48

Typically vestibular system contributes less

than somatosensory system

For example, CNS cannot tell whether it is

just head bending forward or the whole bodyis leaning forward

Vestibular system provides a frame of

reference relative to the gravity

Vestibular Contributions


43/48

Testing Adaptation of Postural toChanging Sensory Conditions:

Sensory Organization Test (SOT)


44/48

Adults and children over age 7 easilymaintain balance on all conditions

Least sway on conditions 1, 2, & 3 where thesupport service is providing accurate sensoryinformation

Greatest sway on conditions 5 & 6 becauseonly one set of sensory inputs (vestibular) are

accurate and availableVisual cues are more important when the

balance task becomes more challenging

SOT Normal Results


45/48

Cognitive Contributions to Balance

Dual-task paradigms

performance in either task because of

limited capacity in information processing

to handle both tasks simultaneously

Different postural and secondary tasks

affect postural control differently

Older or balance-impaired individualsincrease postural sway with difficulty of

secondary cognitive tasks


46/48

Cognitive Contributions to Balance

As the difficulty for maintaining stability

, there is in attention resources required

by the postural control system

What type of secondary cognitive task willaffect balance is still unclear

Executive function may be the most

important cognitive function required tomaintain normal balance under dual-task

paradigms

T ti E ti F ti d i


47/48

Testing Executive Function during

Walking: Walking Trail Making Test (W-

TMT)

Wright, 2011

B l i i d ld d lt ith d i


48/48

MDD: Majordepressivedisorder

ND: Non-depressed

Balance-impaired older adults with depression

required time to step accurately under

cognitively challenging conditions that require

executive function.

*

Wright, 2011

1-17 Postural Control

Documents

Transcript of 1-17 Postural Control