Balance and Postural Control

Postural control

balance, equilibrium

Volition, feed forward control

from experience

Feedback control

happens in the moment or afterwards

Dynamic equilibrium

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You are ambulating with your patient who is using a rolling walker and you are providing CG. The BOS would be described as:

• the pt’s feet

• The pt’s hands on the walker

• the PT’s hands on the patient

• A & B

• All of the above

All of the above - anything in contact with the patient that is giving input

Limits of stability is defined as:

• ability to control the COM over the BOS

• The force applied to the supporting surface

• Active resistance to external forces acting on the body

• Maximum angle from vertical that can be tolerated without a change in BOS

Maximum angle from vertical that can be tolerated without a change in BOS

Movement systems: Balance Diagnosis

• steady state postural control

• anticipatory postural control

• reactive postural control

Steady state postural control

• ability to control the location of the body’s center of mass within the area defined by the BOS under predictable conditions

• staying till; person can be seated or standing

Anticipatory postural control

• ability to generate postural adjustments prior to the onset of and during voluntary movement

• feedforward control

• marching in place, walking

Reactive postural control

• ab ility to utilize sensory input during amovement to ensure successful maintenance of postural control

• the need for a response is unanticipated but may be generated externally or secondarily to an internally generated movement

• feedback control

• tripping, some type of perturbation

Systems: Underlying determinants (subcomponents)

• postural movement strategies

• sensory processing

• perception of verticality

• multi-tasking (cognitive function)

• balance confidence

Postural movement strategies

• musculoskeletal: ROM, flexibility, strength, endurance, alignment

• movement strategies, coordination, tone

Sensory processing

• sensory system: integrity and processing

Perception of verticality

• internal representation of alignment with gravity

• what is upright

Multi-tasking (cognitive function)

• executive function

Balance confidence

fear of falling, activity avoidance

Sitting task analysis check list

• did the pt understand the instructions

• is pt able to maintain position for 30 sec?

• are body segments aligned in all 3 planes?

• is the body aligned with gravity (verticality)?

• is there appropriate postural control? excessive postural sway?

• symptom provocation: pain, fatigue, anxiety, fearfulness, lightheadedness/dizziness?

• does the performance change w/ repetition?

• any task modifications? progression/regression

Steady state: stance - requires 2 action

• maintaining support against gravity (antigravity muscles)

• maintaining balance

Steady state: stance - maintaining support against gravity

• keeping COM at same height

• alignment, strength, and postural tone

Steady state: stance - maintaining balance

• control trajectory of COM in horizontal plane

• postural sway - majority happens from ankles

During quiet stance, which muscles are not active to control sway?

• abdominal and erector spinae

• gastroc and anterior tib

• hamstrings and quadriceps

• glute med and TFL

hamstrings and quadriceps - knees are locked out, not much activity

Muscles utilized during quiet stance

• erector spinae

• abdominals

• gluteus medius

• tensor fascia latae

• tibialis anterior

• gastrox/soleus

Postural movement strategies: Musculoskeletal system (biomechanical constraints)

• PROM/muscle flexibility

• Strength

• Biomechanical alignment

Biomechanical alignment

relationship of body segments to one another

• kyphosis, scoliosis

• leg length discrepancy

What diagnosis may present with alignment issues?

elderly, cerebral palsy, stroke (one-sided weakness), Parkinson’s (weight shifted posterior)

Postural movement strategies: Movement strategies

Controlled by brainstem tracts: reticulospinal and vestibulospinal

• medial tracts for posture/balance

• anticipatory

• reactive (automatic)

Movement strategies - Anticipatory

• feed forward control

• stabilize the body before making a movement

• predict disturbance; “best guess”

• responses influenced by prior experience

Movement strategies - reactive (automatic)

• feedback control

• stimulated by sensory events following loss of balance

• automatic rapid responses

• refined by practice and learning

What are some movement strategies that maintain postural stability?

• hip/ankle strategies - feet are planted

• stepping: change in BOS

• reaching: controlling balance with arms

Muscle Strategies

• synergies

• mostly controlled by brainstem and neural loops

Synergies

functional coupling of groups of muscle which act together as a unit

Muscle strategies - fixed base of support

• in place

• ankle strategy

• hip strategy

Movement strategies - changing base of support

• stepping response

When do we elicit an ankle strategy vs a hip strategy vs a stepping strategy?

• ankle - quiet standing

• hip - larger amplitude LOB

• stepping - large amplitude LOB, you have to move

Motor strategies during perturbed stance: ankle

• used when sway is slow and small and the COM is well within limit of stability (LOS)

Motor strategies during perturbed stance: ankle - surface

surface is firm, wide, and longer than the person’s foot length

Motor strategies during perturbed stance: ankle - muscle contraction

muscle contraction from distal to proximal, will vary based on the direction of perturbation

Motor strategies during perturbed stance: ankle - head movement

head mvmt is small and in phase with the hips - same direction

Motor strategies during perturbed stance: ankle - detection

detected by ankle proprioceptors

Ankle strategies - posterior movement of support surface

• Ankle PF, knee flex, trunk ext

• same as being pushed forward

Ankle strategies - anterior movement of support surface

• ankle DF, knee ext, abdominals

• same as being pushed backwards

Are we born with strategies?

no, strategies are learned

Motor strategies during perturbed stance - Hip strategy

• perturbation is large and fast OR the surface is unstable or shorter than the length of the person’s feet

  • ex: kevin standing on edge of desk

Motor strategies during perturbed stance - hip - muscle contraction

muscle contraction will be proximal to distal and will vary based on direction of the perturbation

Motor strategies during perturbed stance - hip - head mvmt

head mvmt will be large and out of phase with the hips - moving different directions

Motor strategies during perturbed stance - hip - trunk

upper trunk will rotate one direction and lower trunk will move in the opposite direction

Motor strategies during perturbed stance - hip - detection

detected through vestibular system

The hip strategy is _______ than the ankle strategy, and is often used during _____ or when there is ______

faster and more efficient; larger perturbations; ankle weakness

Hip strategies: muscel activation - body sway forward

• early muscles: paraspinals

• next muscles: glute max → hamstrings

Hip strategies: muscle activation - body sways backwards

• early muscles: abdominals

• next muscels:

Hip strategies provide primary control for _______

mediolateral stability

• hip abd/add are recruited

Motor strategies during perturbed stance - stepping

• a step in any direction utilized to prevent a fall when the perturbation displaced the COM beyond the LOS

• perturbation is large and fast and other strategies fail to keep the COM over the BOS

• new LOS must be created after a step is taken

• aka change in support strategy

Motor strategies during perturbed stance - stepping - detection

detected by vestibular system