Balance And Posture 23 Flashcards
Def static and dynamic equilibrium?
Ex. Of each.
Static: body at rest (motionless) ex. Standing
Dynamic: applied and internal forces acting on the body are balanced (no acceleration) ex. Walking
Def. Postural orientation
Relative positioning of the body segments with respect to each other and the environment
What is balance?
Maintain postural equilibrium by:
- controlling COM
- within BOS
- using our COP
Def. Centre of pressure COP?
Single point distribution of pressure of weight bearing segments in contact with the ground
- usually get but can include others
Def. Centre of mass?
Dependent on?
Point which whole body or individual segment mass is “equally balanced”
- completely dependent on postural orientation and tissue properties
- balance point = centre of mass = axis of rotation
Def. Centre of gravity COG ?
Projection of COM on the ground
Def. Base of support?
Area enclosing the contacts with the support surfaces
The bigger the base of support?
The more stability
Ex. Elderly use Kane to increase BOS
Maintenance of Balance dependent on?
3
Size of BOS (bipedal vs quadrupedal stance)
Position of COG (must lie within BOS)
Height of the COM (lowering improves stability)
What is COM-COP relationship?
COP controls location of the COM
- sheep-sheep dog relation
COP goes beyond COM to corral it in other direction
Domains of balance
Body must overcome what three domains of balance to maintain balance?
Antigravity postural equilibrium
Internal perturbations
External perturbations
How is antigravity posture domain of balance maintained?
Postural control largely the summation of simple reflexes
Spinal reflexes - no sensory information
Ex. Decelerate cats can maintain posture without brain info
What are the two balance models?
Antigravity postural equilibrium
Inverted pendulum model - (stiffness control of posture)
- no use of sensory info, not enough processing time for rxns
Open/closed loop model
- open loop over small deviations, no sensory info
- closed loop larger windows of time, use sensory info
Counteracting/ overcoming internal perturbations?
Where do internal perturbations come from
Result from voluntary limb movements OR movement of the base of support itself
- overcome by: Feedforward mechanisms - anticipatory postural adjustments (APA)
Anticipatory postural adjustments (APA) are used during?
Internal perturbations
Legs firing prior to the planned contraction of biceps is an example of:
Anticipatory postural adjustment
- Feedforward control
Example of APAs used in step initiation?
COP first moves to swing foot to shift COM over to the stance foot
Role of an APA?
Do APAs exist in space?
Maintain balance by making sure COM remains in our BOS
- no, no gravity for COM to exist, no APAs required
Def. External perturbations?
- how do we overcome this?
- examples?
Unexpected force acts on the body OR support surface is moved
- controlled by: feedback actions - automatic postural response (APR)
- ex. Standing on a bus
What are APRs ?
What do they use to generate a response?
Rapid, involuntary muscle response (reflexive)
- use sensory information to generate appropriate response
Must be adaptable - perturbations rarely the same
Inverted pendulum model and open/closed loop model refer to what domain of balance?
Antigravity postural equilibrium
- not yet well understand, lots of contradicting info
APAs and APRs are use for what?
APA for counteracting internal perturbations
APR for withstanding external perturbations
Motor responses (APRs) refer to what?
Postural strategies: different response to maintain balance at different levels of perturbations
Muscle synergies: pattern of muscle activation, too fast to be voluntary
What types of postural strategies are used?
What are their response?
Ankle, hip and step
- depend on the size of the perturbation
- use automatic postural response (APR motor response)
Postural boundaries depend on?
What affects these boundaries?
“Perceived” boundaries of the individual
Based on the relative position of the COP within the BOS - different postural strategies will be used (ankle, hip, step)
- age plays large role
Def. Muscle synergies
Pattern of activation if muscles, too fast to be Volentary ( occurs around M2 latency ~ 80-100ms after disturbance )
- APR muscle activation occurs in particular order, work together and elicite proper magnitude
Ankle synergy is used in what postural strategy?
What is muscle synergy order?
What is the result?
Ankle strategy
Either anterior of posterior
Distal to proximal activation
Results in ankle torque production
Hip synergy is used in what postural strategy?
What is muscle synergy order?
What is the result?
Hip strategy
Anterior or posterior sway
Poximal to distal muscle activation
Rapid increase in shear force at the ground
How do we determine muscle synergy/postural strategy to use?
Proprioception relative to ground
Sensory info about our environment (spindle joint and skin receptors)
- what disturbance has happened
- what directed
Proper response evoked when sensory input is integrated correctly
Postural responses adapt to context:
Different responses used for voluntary and unexpected perturbations are?
Voluntary - anticipatory postural adjustment (Feedforward)
Unexpected - automatic postural response (feedback)
