Postural Control

1.3

Steady State Postural Control

The ability to control center of mass (COM) relative to base of support (BOS) in predictable conditions

Anticipatory (Proactive) Postural Control

The ability to activate muscles in legs and trunk for balance in advance of potentially destabilizing voluntary movements

Postural muscles kick in PRIOR to a skilled movement

Reactive Postural Control

The ability to recover a stable position following an unexpected perturbation

Adaptive Postural Control

The ability to modify sensory and motor systems in response to changing task and environmental demands; maintain postural control while moving through space

What is the standard test position for examining sitting postural control alignment?

Feet supported on ground, no trunk or UE support (if safe to do so)

What is the standard test position for examining standing postural control alignment?

No assistive device (if safe to do so), gait belt

What are the three components of postural orientation?

1. Alignment to midline

2. Verticality

3. Symmetry

Postural Stability

The ability to control the body’s position in space for the purpose of movement and balance

Limits of Stability

Maximum angle from vertical that can be tolerated without loss of balance or taking a step

Stability Limits

Boundaries within which the body can maintain stability without changing the base of support (stance)

What are some factors to consider with stability limits?

COM characteristics, environmental constraints, COM position, velocity, fear of falling, perception of safety

Muscle Recruitment Directions of Anticipatory Postural Control

Sitting: cranial to caudal recruitment

Standing: caudal to cranial recruitment

APA activation is decreased as support to the body is increased

APA activation is increased when the speed of the task or load is increased

What do the muscles that are activated during reactive strategies respond to?

The direction of instability (i.e. abdominals are most active in response to backward instability, extensors are most active in response to anterior instability)

What are three factors to consider when examining reactive balance in a patient?

1. Observing the patient during unexpected losses of balance

2. In Place responses

3. Change in BOS responses

Sensory Inputs & Integration for Postural Control

Vision

Posture/Alignment

Somatosensation

Vestibular Function

Sensory weighting/Integration

What are the 2 primary components of the somatosensory system that account for 60-70% of standing balance control?

Proprioception and cutaneous sensitivity

CTSIB (Clinical Test of Sensory Integration and Balance)

Tests a patient’s ability to maintain standing balance for 30 seconds under 6 different sensory conditions that either eliminate input or produce inaccurate visual or surface orientation inputs, to determine how sensory information is being used to maintain vertical orientation

What are the 4 modified CTSIB setups?

1. Eyes open, standing on a firm surface

2. Eyes closed, standing on a firm surface

3. Eyes open, standing on foam

4. Eyes closed, standing on foam

What are the Activities-Specific Balance Test (ABC) and Falls Efficacy Scale (FES) used to measure?

Balance confidence

Berg Balance Scale (BBS)

A comprehensive functional balance assessment tool used for any patient with a balance problem (though may not be appropriate for high functioning clients)

Good reliability (max score = 56, cut-off score = 45)

Less than 45 = prediction of moderate fall risk

Less than 36 = close to 100% fall risk

Dynamic Gait Index (DGI)

Developed for use with individuals with higher-level balance problems

Assesses an individual’s ability to modify balance while walking, in the presence of external demands

Consists of 8 items that assess gait abilities under different environmental or task conditions

Highest possible score = 24, cut-off score = 19/24 as a marker for moderate risk of falls

DGI Task Components

1. Steady state walking

2. Walking with changing speeds

3. Walking with head turns both horizontally and vertically

4. Walking while stepping over and around obstacles

5. Pivoting while walking

6. Stair climbing

Functional Gait Assessment (FGA)

Assesses postural stability during various walking tasks (modified DGI) with improved reliability to decrease the ceiling effect of the DGI

10-item test with 7 of the 8 original DGI components

Highest score = 30, cut-off score = 22/30 as classifying fall risk in older adults and predicting unexplained falls in community-dwelling older adults

Hi-Level Mobility Tool (HiMAT)

Appropriate for assessing people with high-level balance and mobility problems

Requires a minimal mobility level of independent ambulation > 20m without gait aids or orthoses

Highest score = 54

Mini BESTest

Shortened version of the BESTest to assess balance impairments across six contexts of postural control (mechanical constraints, limits of stability, anticipatory postural adjustments, postural response to induced loss of balance, sensory orientation, gait)

MDC = 3.5, MCID = 4/28 points

Falls Efficacy Scale (FES)

Measures balance confidence

Consists of 10 ADL items that assess the individual’s fear of falling while completing those ADLs

Higher scores = greater confidence in maintaining balance

Activity Specific Balance Confidence Scale (ABC Scale)

16-item questionnaire rating confidence performing a variety of in-home and community-based functional activities, which includes 16 ADL items

Score of 0 = no confidence, score of 100 = complete confidence

Higher scores = greater balance confidence

Scores < 67% in community-dwelling elders = risk for falling

What are the 3 motor strategies for reactive postural control?

1. Ankle

2. Hip

3. Stepping (change in BOS)

Orientation

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

Stability

Ability to control the COM in relationship to the BOS

Center of Mass (COM)

Point at the center of total body mass

Center of Gravity (COG)

Vertical projection of COM

Base of Support (BOS)

Area of the body in contact with a support surface (ground, chair, etc)

Center of Pressure (COP)

Center of the distribution of total force applied to the supporting surface

What are the three elements of postural reactions?

1. Righting reactions

2. Equilibrium reactions

3. Protective reactions

Righting Reactions

Support positioning of the head vertically in space, alignment of the head and trunk, and alignment of the trunk and limbs

Head Righting vs Body Righting

Head Righting: aligns the eyes with the horizon and the head with the trunk

Body Righting: contributes to movement around the body axis (necessary to assume anti-gravity positions)

Equilibrium Reactions

Provide balance when the center of gravity is disturbed

More mature responses to regain balance than righting reactions

What happens to the head and trunk during equilibrium reactions?

They counter-rotate away from the direction of the displacement

Protective Reactions

Required to prevent injury if the equilibrium reactions are unable to restore balance in a timely manner

Emerge first to the front, then to the side, then backwards

What is the order of positional development of protective reactions?

Prone > quadruped > sitting > standing

What are the three ways in which tasks are classified in motor control?

1. Body action

2. Organization

3. UE manipulation

Body Action (Task Classification)

Stability vs mobility task (is the BOS still or in motion)

Organization (Task Classification)

Does the movement have a recognizable beginning and end?

Tasks are characterized as being:

1. Discrete

2. Continuous

3. Serial

UE Manipulation (Task Classification)

Is UE interaction with an object present or absent? (ranges from none to complex interaction)

Open Task vs Closed Task

Open Task: variability and flexible, changing environment, greater difficulty to plan movement, increased demand on information processing-systems

Closed Task: fixed, habitual patterns, minimal variation, lower demand on information processing-systems

Note: not the same as open vs closed-chain activities

Regulatory vs Non-Regulatory Features (Environmental Constraints)

Regulatory: shape of the movement itself (e.g. weight, size, shape of the object, type of walking surface)

Non-regulatory: affect performance (e.g. background noise, distractions)

Open vs Closed Predictability (Environmental Considerations)

Closed Predictable: the environment is stable and predictable (safe, know what will happen)

Open Unpredictable: the environment is variable and unpredictable (wild, don’t know what’s going on)

Self vs Externally Paced (Environmental Considerations)

Example of self-pacing: climbing stairs, walking down a quiet hall

Example of external pacing: stepping onto an escalator, walking down a crowded hall

What three things affect static stability?

1. Postural alignment

2. Muscle tone

3. Postural muscle tone

True or False: All skilled movements have both postural and voluntary movement components.

True

Preparatory Phase (feedforward) of Anticipatory Postural Control

Postural muscles are activated >50ms in advance of prime movers to compensate for destabilizing effects

Compensatory Phase (feedback) of Anticipatory Postural Control

Postural muscles are activated again after primary movers to further stabilize the body

Central Set

The state of the nervous system that is influenced or determined by the context of a task

Enables the CNS to optimize postural responses under new task conditions

True or False: Practice affects the timing of anticipatory postural adjustments.

True

In which types of postural control can we observe adaptive postural control?

All (steady state, anticipatory, reactive)

Which sensory system from the CNS do healthy adults rely on most for maintaining postural control?

Somatosensory system information

Pusher Syndrome

An abnormal perception of verticality (seen by post-stroke patients)

Leaning and active pushing toward the involved (hemiplegic) side in all positions with no attempt to compensate for the imbalance, and resistance to any attempt at passive correction toward the ipsilesional side (midline)

Associated with slower recovery

Impaired Dual-Task Ability

Difficulties with maintaining balance and doing a simultaneous task (e.g. counting backwards, telling a story, etc)