Postural Control & Balance

Postural Control

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

Postural Orientation

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

Postural Stability

ability to control center of mass in relationship to the base of support

Static Balance

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

Dynamic Balance

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

• happens when you walk or run

Base of support

• area of the body in contact with the support surface

• wide BOS = increased stability

• narrow/small BOS = decreased stability

Center of Mass

• the point at the center of the total body mass (anterior to L2 when standing)

• Higher COM = less stability

• Lower COM = more stability

  • think snowboarding and how the lower your center of mass is the more stable you are

Center of Gravity

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

Center of Pressure

• average “location” of the ground reaction force vector

• for static equilibrium COP must be directly under COM

• but standing is never truly static (COM and COP are continually in motion and rarely aligned)

If COM goes well beyond the COP…

then BOS must be changed to ensure that COP and COM are close (establish a new base of support)

Stability limits

• refer to the boundaries within which the body can maintain stability without changing the base of support

• maximum angle from vertical before a loss of balance or repositioning BOS

Dynamic Stability Limits

• stability limits from the interaction between the position and velocity of COM

• boundaries of the combined COM velocity and position possible without the need to change base of support

steady state tasks

• ability to control COM relative to BOS in fairly predictable conditions

• low demand

Reactive Tasks 

• require ability to recover a stable position following an unexpected perturbation

• feedback mechanism

Proactive tasks

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

• require anticipatory/feedforward control

Feedback Control (compensatory or reactive)

sensory feedback from unexpected external perturbations triggers postural responses

Feedforward Control

postural responses are made prior to a voluntary movement that is potentially destabilizing to maintain stability during the movement 

Environment Plays a Crucial Role

• changes in support surface

  • walking on smooth, firm, flat vs uneven/irregular surface

• changes in sensory and cognitive contexts

  • walking and talking; walking in dark vs walking in light

Sensory Systems

• vision

• somatosensory 

• vestibular

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

What contributes to the high risk in older adults for falling?

• system changes with age

  • vision decreases with age

  • vestibular decreases with age

  • somatosensory little to no change

• MSK changes

  • muscle strength decreases

  • bone strength decreases

  • changes in motion/flexibility

• cognition: slowed with aging/decreased with disease