3) Postural Control

why care about postural control

essential for balance

provides a background for fine and skilled movements

PTs treat people with ___________ more than any other profession

balance disorders

postural control defintion

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

postural orientation

posture

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

postural stability

(balance) ability to control the center of mass in relationship to the base of support

COM does not necessarily stay within the

BOS

static balance

the ability to maintain the COG within BOS while standing or sitting still

dynamic balance

maintaining upright position while COG and BOS are moving, and the COG is moving outside of the BOS

functional balance

the ability to perform daily movement tasks requiring balance

may involve both static and dynamic balance

stability and orientation vary with

the task

postural orientation affects

postural stability

postural orientation is altered to

regain postural stability

postural orientation and stability is influenced by

biomechanical variables :

- base of support

- center of gravity

- center of pressure

- stability limits

base of support (BOS) definition

the area of the body in contact with the support surface

wide BOS

increase stability

narrow BOS

decrease stability

center of mass (COM)

the point at the center of the total body mass, it is a point in 3D space

center of gravity (COG)

the vertical projection of COM in a 2D plane, usually on the ground

are COG and COM interchangeable?

yes

higher COM

decrease stability

lower COM

increase stability

as COM shifts upward

the object becomes more "top heavy"

stability increases when

COG is within BOS

stability decreases when

COG is outside the BOS

center of pressure (COP)

the center of total forces applied to the support surface

where is the average location of the COP

the "location" of the ground reaction force vector

for static equilibrium COP must be

directly under the COM (perfectly aligned)

but standing is never truly static --

COP and COM are continually in motion and rarely aligned

muscle activate to

align COP and COG

if COM is anterior to the ankle the

plantar flexors act to move the COP anteriorly

if COM goes well beyond the COP, then

BOS must be changed to ensure that COP and COM are close

stability limits refer to the

boundaries within which the body can maintain stability without changing the BOS

stability limits results from

the interaction between the position and velocity of COM

stability limits are the boundaries of the

Combined COM velocity and position possible without the need to change the BOS

testing performance at different speeds may

provide a better indication of balance abilities

(the dancing man video)

the goal of the postural control system

postural orientation and stability

postural orientation and stability is accomplished by

controlling the COM/COP through active muscle control

controlling/adjusting the BOS if needed

postural control depends on the task

steady state tasks

reactive tasks

proactive tasks

steady state tasks

ability to control COM relative to BOS in fairly predictable conditions

reactive tasks

require ability to recover a stable position follow an unexpected perturbation

proactive tasks

ability to activate muscles for control of COM in advance of potentially destabilizing voluntary movement

requires anticipatory/feedforward control

feedback control

(compensatory or reactive) - sensory feedback from unexpected external perturbations triggers postural responses

feedforward control

(Anticipatory) - Postural responses are made prior to voluntary movement that is potentially destabilizing to maintain stability during the movement

feedback control response depends on

amount of perturbation

surface properties

speed of perturbation

pathology and pain

Environment plays a crucial role in balance

changes in the support surface (uneven/irregular surface)

changes in sensory and cognitive contexts (walking and talking)

sensory systems

vision, somatosensory and vestibular systems interact for success

why do we test balance?

- to determine risk of falling

- to determine what areas of postural control are affected and which areas are remediable to change

- to quantify deficits to justify the need for therapeutic intervention and to measure changes

which populations have a higher risk of falling

older population

physically or neurologically compromised children and adults

sensory system changes with age

- vision decreases with age

- vestibular decreases with age

- somatosensory: little to no change

MSK system changes with age

muscle strength decreases with age

bone strength decreases with age

changes in motion/flexibility with age

cognition/cognitive strategies

slowed with aging/decreased with disease

how do we determine fall risk

- balance performance measure assess balance, not fall risk

- cut-off scores are generally determined retrospectively

- prospective studies focus only on how physical function contributes to falls

usual vs best performance

what is different in the clinc compared to the patients "real world"

- internal and external environment

- encouragement and curs

- control vs lack of control

dual task

there is an interplay between postural control limitations and environmental and task limitations

cognitive load

counting backwa5d by 8 by 67

physical load

carryong a full cup of coffee over a white carpet

interventions to improve balance

- include a variety of interventions based on the balance problem and its contributors

- important to develop a hypothesis about the cause of the balance deficit so intervention can be directed to the causes

interventions may address structure/function impairments

motion

force

energy

control

interventions may address activity/task-specific movement

sitting or standing

single or dual tasks

simple or complex

static or dynamic

in closed or open environment

principles of balance training

enhancing individual capacity - force, motion, energy

improving task performance

Practice the task

optimally challenge

changing the environment

cognitive load

sensory challenge

speed