Balance & Posture

Question 0

What is balance?

Answer 0

The ability to maintain postural equilibrium by controlling our centre of mass, within our BOS with our CoP

Question 1

What is posture?
Postural
Postural equilibrium

Answer 1

⭐️Postural orientation - relative position of body segments with respect to each other and the environment
⭐️Equilibrium:
Static:motionless
Dynamic: external or internal force applied

Question 2

Centre of pressure

Answer 2

The single point distribution of weight bearing segments in contact with the ground
➡️other things such as a cane can be touching the ground

Question 3

Centre of mass

Answer 3

The point at which the whole body or individual segment mass is equally balanced
➡️completely dependent on tissue properties and postural orientation
Balance point=COM=axis of rotation
⭐️centre of gravity:the projection of the COM on the floor

Question 4

Base of support

Answer 4

The area enclosed by the contacts with the support surface

➡️the size of BoS can determine stability, I.e larger -more stable

Question 5

Maintenance of balance is dependent on: (3)

Answer 5

1⃣the size of the BOS. Bipedal versus quadrapelegal
2⃣the position of the COG , COM must lie within BOS
3⃣the height of the COM above the ground (the lower, the more stable)

Question 6

Sheep -sheep dog

Answer 6

Cop-sheep dog, com-sheep
⭐️our COP controls the location of our COM⭐️
➡️by allocating increased pressures within our BOS we can manipulate the position of our COG

Question 7

3 domains of balance

Answer 7

In order to maintain balance, the body must overcome the three following domains of balance
1⃣antigravity postural equilibrium
2⃣internal perturbations
3⃣external perturbations

Question 8

Antigravity postural equilibrium

Answer 8

⭐️maintaining an antigravity posture, resisting the force of gravity
Steady state postural control, largely the summation of simple reflexes
Spinalized cats…still able to maintain posture

Question 9

Internal perturbation

Answer 9

➡️come from voluntary limb movements, of movements of BOS itself.
How to overcome ?
FEEDFORWARD actions
⭐️anticipatory postural adjustments (APAs)

Question 10

External perturbation

Answer 10

When unexpected forces act upon the body, or when the support surface is moved. (Standing on a bus-person initially loses balance)
➡️how to overcome ?
⭐️Feedback actions
⭐️automatic postural responses (APRs)

Question 11

Anticipatory postural adjustments

Answer 11

Prior to pulling on a handle ,there is muscle activation in lower limbs (postural)
➡️FEEDFORWARD control
➡️postural response is appropriate for the load to be lifted, the speed of the limb movement and the duration
➡️no APAs in response to perturbation (unexpected)

Question 12

Automatic postural responses (APRs)

Answer 12

⭐️extremely rapid and involuntary muscle responses (reflexive) and are activated to bring the person back into a balanced state
➡️use sensory information to help generate appropriate responses
➡️must be adaptable-perturbations are rarely the same

Question 13

Motor responses (APRs) 
2

Answer 13

1⃣postural strategies

2⃣muscle synergies

Question 14

Postural strategies (3)
(Horak & Nasher)

Answer 14

1⃣ankle (distal to proximal muscle activation)
2⃣hip (proximal to distal muscle activation)
3⃣stepping
⭐️different strategies used depend on the perceived stability of the individual…also affected by the relative position of COP within the BOS
➡️what might change perception of boundaries?? Sensory feedback
⭐️Age has also been shown to play a role

Question 15

Muscular synergies

Answer 15

Synergy=acting together
Pattern of activation of muscles, too fast to be voluntary, occurring around the M2 latency (80-100ms after a disturbance)
Must respond appropriately to the perturbation…if it is small end up outside BOS