Control of Posture

Question 1

What is postural control, postural orientation, postural stability?

Answer 1

Control: involves controlling body’s position in space
Orientation: ability to maintain appropriate relationships between body segments and between body and the environment for successful task completion
Stability: ability to control the COM in relationship to the base of support

Question 2

What are the terms for postural control?

Answer 2

Center of control (COM): point at the center of total body mass
Center of pressure (COP): center of distribution of total force applied to the supporting surface
Relationship between COM and COP provides better insight into stability than either of them alone

Question 3

When is postural stability attained?

Answer 3

When COM is over the BOS. The COG is the vertical projection of the COM

Question 4

What are reasons that cause the COM to change in relationship to the BOS?

Answer 4

Voluntary: leaning forward, reaching out to pick something up
External perturbation: pushed in a crowded hall
Structural and develop slowly or suddenly: leg cast, BKA amputation, age related development

Question 5

How is postural control related to the task, environment, individual?

Answer 5

Specific orientation and stability requirements vary according to the task and environment.
Strategies used to accomplish postural control must adapt to varying task and environmental demands.
Postural control emerges from an interaction of the individual with a task and the environment.

Question 6

What are the defining systems for postural control?

Answer 6

Musculoskeletal components

Neural components

Question 7

What are characteristics and strategies of stance postural control?

Answer 7

Stability limits change according to the task and individual characteristics.
Position and velocity of COM influence stance.
Strategies: sensory, sensorimotor, attentional

Question 8

What are the action systems in postural control?

Answer 8

Higher level planning (frontal cortex, motor cortex)
Coordination (brainstem, spinal networks coordinating muscle response synergies)
Generation (motor neurons and muscles)

Question 9

What is motor control during quiet stance?

Answer 9

Alignment
Muscle tone
Postural tone

Question 10

What are movement strategies during perturbed stance?

Answer 10

Controlling forward and backward sway
Feedback control
Feedforward (anticipatory) control

Question 11

What are strategies to regain anteroposterior stability?

Answer 11

Ankle strategy
Hip strategy
Stepping strategy

Question 12

What is ankle strategy for forward and backward sway?

Answer 12

Forward: gastrocs fire to slow movement, hamstrings fire, then paraspinals to keep hip and knees extended
Backward: anterior tib fires to slow movement, quads fire later, then abs

Question 13

What is hip strategy for forward and backward sway?

Answer 13

Forward: abs fire to produce trunk flexion, then quads fire, then paraspinals
Backward: paraspinals fire to produce trunk extension, then hamstrings fire, then abs fire much later

Question 14

What is stepping strategy?

Answer 14

BOS is changed in this strategy unlike the ankle and hip where the subject moves the COM and keeps the BOS the same.
However, people may step even when COM is not outside the BOS

Question 15

T/F: the 3 postural strategies are discrete

Answer 15

False: they are on a continuum

Question 16

What is mediolateral stability?

Answer 16

Alternative strategy. Hard for ankle and knee to help with this. Muscle patterns organized in a proximal to distal direction starting with the head

Question 17

T/F: patients with brain pathology due to disease or trauma can lose their muscle synergy flexibility

Answer 17

True

Question 18

What are sense contributing to postural control?

Answer 18

Visual: not essential, may give us wrong info
Somatosensory: proprioceptive, cutaneous, joint receptors; there are times when this input is not helpful
Vestibular: by itself it cannot provide a true picture of how body is moving in space

Question 19

What are the central integration strategies (combining and adapting senses for postural control)?

Answer 19

Sensory strategies during quiet stance: healthy young adults use vision, somatosensory, vestibular
Sensory strategies during perturbed stance: vision not critical, somatosensory inputs most important, vestibular plays minor role

Question 20

Adapting senses when learning a new task: As the task is learned…?

Answer 20

A decrease in the relative importance of visual inputs for postural control
An increase in reliance on somatosensory inputs

Question 21

T/F: it is thought that our patients who are recovering from brain pathology rely more on vision on the early stages of recovery?

Answer 21

True