Normal Postural Control

Define postural control

involves controlling body's position in space for:

- postural orientation

- postural stability

- postural control = dynamic balance

Postural orientation

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

- think: orient thyself in space

- ex: bent posture = slouched - not suited for movement

Postural stability

ability to control COM in relationship to BOS

- think: orient myself within my cone of stability

- COM usually L1 of vertebral body

- body will instinctively do something to prevent a fall

COM vs COP

- COM: point at center of TOTAL body mass

- COP: center of distribution of total support force applied to supporting surface (ground rxn force acting on body)

- COP MOVES continuously arounf COM to keep it within BOS

center of gravity (COG)

vertical projection of COM

BOS

area of body in contact w/ support surface

COM and COP together gives a better insight into___

stability than either COP or COM alone

postural demands

change based on different tasks and environments

- each indiv solves postural demands with unique movement ability

- ex: task: maintain sitting posture; indiv: constraints on strength; environ: chair on wheels

how do stability requirements vary with tasks?

COG can be projected within or outside BOS (walking)

- all tasks req postural control

- stability and orientaton demands change with overy task

- task and environ influence porientation and stability demands of task (sitting vs walking)

Balance/postural control emerges from the

- indiv

- postural task

- environment

(venn diagram)

Types of postural tasks

- steady state

- proactive

- reactive

Postural task (constraints): steady state balance

ability to control COM relative to BOS in fairly predictable and nonchanging conditions.

- Sitting, standing quietly, and walking at a constant velocity

- maintaining your position

- mod plantigrade

Postural task (constraints): Reactive balance

ability to recover a stable position following unexpected perturbation by an external force

- older pt have poor rxn

- inability to rapidly generate and apply appropriate corrective muscle forces to recover balance = fall

reactive balance - mechanism (movement strategy)

feedback - postural control that occurs in response to sensory feedback (visual, vestibular, or somatosensory) from an external perturbation

anticipatory balance: mechanism (movement strategy)

feedforward = anticipatory postural adjustments made in anticipation of a voluntary movement that is destabilizing to maintain stability during mvmt

Postural task (constraints): anticipatory balance

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

- Ex: lifting heavy object from the ground or stepping onto curb

- assuming posutre in state of readiness

- delayed in Parkinson's

Movement strategies come ____ concious movement in postural control

before

Individual Systems for Postural Control

- motor

- sensory

- cognitive

Individual systems: motor (4)

- joint ROM

- spinal flexibility

- muscle properties

- biomech relationships among linked body segments

Individual systems: cognitive

- unconcious, not effected by environment

- basis of adaptive and anticipatory effects

- modifying sensory and motor systems in response to changing task and environ

- dual taksing, attention

- aging effects this

Individual systems: sensory

individual sensory systems

- visual, vestibular, and somatosensory systems

- process of sensory organization

- ex: neuropathy and sensory feild deficits

Types of environmental constraints (3)

- support surface

- sensory context

- cognitive load

Environmental constraint: supporting surface

- Thick foam, carpet, grass vs solid floor

- Pebbles, stone walkways

Environmental constraint: Sensory context

way sensory information is used for balance control

- how we are getting info trom the environment

- Dim, laser, disco lights

- Loudness, roller coasters (vestibular)

- Bay bridge: shadows in peripheral vision that causes distraction

- Foreground and background

Environmental constraint: Cognitive load

environment increases mental load (crowds)

- pt is hard of hearing --> may focus on hearing instead of balance

- multi-tasking --> affects cog systems used for balance

Individual Systems for Postural Control require 7 things:

- Musckuloskeletal components

- internal representations

- adaptive mechanisms

- anticipatory mechanisms

- sensory strategies

- individual sensory systems

- neuro-muscular synergies

internal representation

how the indiv has an idea of the environment

adaptive mechanisms

with pathology or habit

sensory strategies

- using railing while walking down stairs (hapatic touch)

- looking down while walking

- parkinson's: rhythmic auditory for stepping

Indiv systems: higher level planning (2)

- frontal cortex

- motor corext

Indiv systems: Coordination (2)

- brainstem

- spinal networks coordinating muscle response synergies

Indiv systems: force generation (2)

- motor neurons

- muscles

Indiv systems: Sensory/perceptual processes (3)

- visual

- vestibular

- somatosensory

Motor control of quiet stance (3)

- alignment

- muscle tone

- postural tone

Quiet stance: Alignment

like stacking blocks

- vertical line between mastoids, front of SH, hip, just infront knee, and infront of ankle (posture assessment)

- minimizes effects of gravity

- tonic muscle activity

- body maintained with least amount of energy expenditure

Quiet stance: Muscle tone

intrinsic stiffness

- there is no muscle tone in a relaxed state (dead weight)

- tone is attributed to low-level conciousness of recycling cross bridges (stiffness, being awake)

- tone = state of readiness

Quiet stance: Postural tone

activation of anti-grav muscles to counteract force of gravity

- Back ect, abdominals, glute med, neck ext, PF, DF, iliopsoas

- lesion in dorsal roots = dec postural tone

- somatosensory inputs to neck influence trunk and limbs - tonic neck reflex

Antero-posterior stability (3) strategies

- ankle

- hip

- stepping

- most sway occurs in AP direction

AP strategies occur in which direction?

distal --> proximal

- Ankle strategy: distal

- Hip strategy: intermediate

- Stepping strategy: proximal

Alternate strategies:

- Reach-and-grasp

- Parachute response

- Suspensory strategy

Ankle strategy

- postural sway control from the ankles and feet

- head and hips move in same direction at same time as a unit

- response to small, slow, midline displacement

- surface broad and stable enough to allow pressure against it - nonmoving surface

Ankle strategy with FORWARD sway (plate moving back)

Order of muscle activation:

1. gastrocnemius

2. hamstrings

3. paraspinals

think: MA in direction of plate

Ankle strategy with BACKWARD sway (plate moving forward)

Order of MA:

1. anterior tibialis

2. quadriceps

3. abdominals

- ant muscles activated

ankle - distal to proximal MA for both directions

Hip strategy

- Postural sway control from hip, pelvis, trunk

- Head and hips travel in opposite directions (Counterbalance)

- Used when movement is large, fast, nearing limit of stability

- Surface is too narrow or unstable to allow counter pressure

- NO ANKLE STRAT

Hip strategy with FORWARD sway (plate moving back)

Order of MA (but kinda at same time)

1. abdominals muscles

2. quadriceps

Think: MA in direction of sway

Hip strategy with BACKWARD sway

MA

1. Paraspinals

2. hamstrings

Stepping strategy

used when Ankle and Hip fails

- attempt to re-establish new BOS with active limb when COG has exceeded original BOS

Suspensory strategy

Lowering the COG toward BOS

- Used when a combination of mobility and stability is required

- used when Ankle and Hip fails

Reach-and-Grasp (RG) strategy

Complex: multi-limb coordination

- takes loss of balance & environmental factors (available/NA) into account

- used when Ankle and Hip fails

How much time does it take to perform the RG compared to a similar voluntary movement?

takes half the time (is 2x faster)

- No pre-planning. Timing, direction, amplitude, speed are spontaneous (most likely pre-programed)

Parachute response

protective responses that body from injury during a fall

- in response to a tilting surface

- used when Ankle and Hip fails

Medio-lateral strategy

- Abduction-Adduction at the hip

- Muscle patterns in proximal-to-distal direction

- NO ANKLE

Multi-directional strategies

- No unique muscle activation pattern for each direction

- No clear synergy organization

- Complex CNS process modulated by continuous feedback signals that are context specific

strategies adapt to the environment by...

modifying behavior in response to new tasks

- ex: firm surface vs foam; narrow beam vs firm surface

--> narrow beam = hip strat

Newer concepts of postural control strategies: strategy order

Ankle>hip>step in this order

- step strategy doesnt have to be last

- based on BOS and speed (new research)

- pertubation too fast --> step

Newer concepts of postural control strategies: order with increasing speed

Ankle>hip>step in this order with increasing speed

- Strategies dont need to change with speed

- Based on critical point (new research) - 1st increased muscle work at lower strategy till critical point.

Newer concepts of postural control strategies: clinical applications

train for all strategies, in all environments, for all postural demands

- Individual factors determine use of postural control

strategies

proactive balance control

Anticipatory postural muscle activity seen before voluntary arm and leg movement

phases

- prepatory balance

- Compensatory balance

Proactive/anticipatory control: Prepatory phase

50 ms before voluntary movement

- Compensate for destabilizing forces

- activating core muscles, taking wide base, etc

Proactive/anticipatory control: Compensatory phase

Reactivation after voluntary movement

- Stabilize body with feedback

Sensory Systems in postural control (3)

postural control is not just the ability to generate and apply forces to control body position

- sensory

- vestibular

- vision

Visual system

Provide info on postion and motion of head with respect to surrounding objects

- not always accurate source of orientation info about self motion

Sensory system

kinesthetic and proprioceptive, skin sensation, DTR, joint capsule (position and motion about body with refrence to supporting surface)

- includes haptic touch

- Cruising, using hand for sensation to balance)

- Light touch dec sway that happens

Vestibular system

- used in steady state and postion of head with movement

- cannot work alone to provide how body is moving in space

EXAMPLE

- Moving room closer to baby --> child sways back to keep same distance from TV (anterior muscles activated)

- Sensory field changed (no perturbation)

- Labyrinthine reflex

sensory organization test (SOT)

objectively identifies abnormalities in the patient's use of the three sensory systems that contribute to postural control: somatosensory, visual and vestibular

SOT: Condition 1 (Stable surface, EO)

- Accurate: Vest, Vision, Somato

- Inaccurate: NA

SOT: Condition 2 (Stable Surface, EC)

- Accurate: Vest, Somato

- Inaccurate: Vision

SOT: Condition 3 (Stable Surface, Unstable Vision)

- Accurate: Vest, Somato

- Inaccurate: Vision

SOT: Condition 4 (Untable Surface, EO)

- Accurate: Vest, Vision

- Inaccurate: Somato

SOT: Condition 5 (Untable Surface, EC)

- Accurate: Vest

- Inaccurate: Vision, Somato

SOT: Condition 6 (Untable Surface, Unstable Vision)

- Accurate: Vest

- Inaccurate: Vision, Somato

SOT: which condition is the most difficult?

situation 6