Balance And Posture 23

Question 0

Def static and dynamic equilibrium?

Ex. Of each.

Answer 0

Static: body at rest (motionless) ex. Standing
Dynamic: applied and internal forces acting on the body are balanced (no acceleration) ex. Walking

Question 1

Def. Postural orientation

Answer 1

Relative positioning of the body segments with respect to each other and the environment

Question 2

What is balance?

Answer 2

Maintain postural equilibrium by:

• controlling COM
• within BOS
• using our COP

Question 3

Def. Centre of pressure COP?

Answer 3

Single point distribution of pressure of weight bearing segments in contact with the ground
- usually get but can include others

Question 4

Def. Centre of mass?

Dependent on?

Answer 4

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

Question 5

Def. Centre of gravity COG ?

Answer 5

Projection of COM on the ground

Question 6

Def. Base of support?

Answer 6

Area enclosing the contacts with the support surfaces

Question 7

The bigger the base of support?

Answer 7

The more stability

Ex. Elderly use Kane to increase BOS

Question 8

Maintenance of Balance dependent on?

3

Answer 8

Size of BOS (bipedal vs quadrupedal stance)
Position of COG (must lie within BOS)
Height of the COM (lowering improves stability)

Question 9

What is COM-COP relationship?

Answer 9

COP controls location of the COM
- sheep-sheep dog relation
COP goes beyond COM to corral it in other direction

Question 10

Domains of balance

Body must overcome what three domains of balance to maintain balance?

Answer 10

Antigravity postural equilibrium
Internal perturbations
External perturbations

Question 11

How is antigravity posture domain of balance maintained?

Answer 11

Postural control largely the summation of simple reflexes
Spinal reflexes - no sensory information

Ex. Decelerate cats can maintain posture without brain info

Question 12

What are the two balance models?

Antigravity postural equilibrium

Answer 12

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

Question 13

Counteracting/ overcoming internal perturbations?

Where do internal perturbations come from

Answer 13

Result from voluntary limb movements OR movement of the base of support itself
- overcome by: Feedforward mechanisms - anticipatory postural adjustments (APA)

Question 14

Anticipatory postural adjustments (APA) are used during?

Answer 14

Internal perturbations

Question 15

Legs firing prior to the planned contraction of biceps is an example of:

Answer 15

Anticipatory postural adjustment

- Feedforward control

Question 16

Example of APAs used in step initiation?

Answer 16

COP first moves to swing foot to shift COM over to the stance foot

Question 17

Role of an APA?

Do APAs exist in space?

Answer 17

Maintain balance by making sure COM remains in our BOS

- no, no gravity for COM to exist, no APAs required

Question 18

Def. External perturbations?

• how do we overcome this?
• examples?

Answer 18

Unexpected force acts on the body OR support surface is moved

• controlled by: feedback actions - automatic postural response (APR)
• ex. Standing on a bus

Question 19

What are APRs ?

What do they use to generate a response?

Answer 19

Rapid, involuntary muscle response (reflexive)
- use sensory information to generate appropriate response

Must be adaptable - perturbations rarely the same

Question 20

Inverted pendulum model and open/closed loop model refer to what domain of balance?

Answer 20

Antigravity postural equilibrium

- not yet well understand, lots of contradicting info

Question 21

APAs and APRs are use for what?

Answer 21

APA for counteracting internal perturbations

APR for withstanding external perturbations

Question 22

Motor responses (APRs) refer to what?

Answer 22

Postural strategies: different response to maintain balance at different levels of perturbations

Muscle synergies: pattern of muscle activation, too fast to be voluntary

Question 23

What types of postural strategies are used?

What are their response?

Answer 23

Ankle, hip and step

• depend on the size of the perturbation
• use automatic postural response (APR motor response)

Question 24

Postural boundaries depend on?

What affects these boundaries?

Answer 24

“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

Question 25

Def. Muscle synergies

Answer 25

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

Question 26

Ankle synergy is used in what postural strategy?
What is muscle synergy order?
What is the result?

Answer 26

Ankle strategy
Either anterior of posterior
Distal to proximal activation
Results in ankle torque production

Question 27

Hip synergy is used in what postural strategy?
What is muscle synergy order?
What is the result?

Answer 27

Hip strategy
Anterior or posterior sway
Poximal to distal muscle activation
Rapid increase in shear force at the ground

Question 28

How do we determine muscle synergy/postural strategy to use?

Answer 28

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

Question 29

Postural responses adapt to context:

Different responses used for voluntary and unexpected perturbations are?

Answer 29

Voluntary - anticipatory postural adjustment (Feedforward)

Unexpected - automatic postural response (feedback)