MC 5 (standing posture and control of postural sway)

Question 1

Define equilibrium

Answer 1

when the sum of forces and moments acting on the system is zero
- any forces are equal and opposite and acting along the same line

Question 2

Define stability

Answer 2

resilience to change in response to a perturbation

Question 3

“the tendency of the system to return to equilibrium when perturbed” is what?

Answer 3

stability

Question 4

An inverted pendulum model has ….. stability?

Answer 4

low (unstable)

Question 5

Define Base of Support (BoS)

Answer 5

the area of the support surface defined by straight lines drawn between the points of ground-object contact

Question 6

What is an object’s Centre of Pressure (CoP)?

Answer 6

the point where the resultant ground reaction force is applied

Question 7

Must the CoP always fall within the BoS?

Answer 7

Yes,

under static conditions the CoP will fall directly beneath the centre of mass

Question 8

Give an example of when…

a) a leant chair is on equilibrium, yet not stable
b) a leant chair is not in equilibrium, nor is it stable

Answer 8

a) object weight and CoP act along the same vertical line.

b) the forces (W and GRF) are equal but acting along different lines (moments are different)

Question 9

The human body is an example of what kind of pendulum?

Answer 9

inverted compound pendulum.

series of jointed segments that are able to rotate relative to one another

Question 10

Why is muscular effort required during quiet upright standing posture?

Answer 10

to maintain body configuration and avoid collapse

Question 11

Define the two types of perturbed stance

Answer 11

1) environmental perturbed stance: perturbations from the environment
2) action perturbed stance: perturbations from performaning movements that can disturb upright posture.

Question 12

What body receptors sense changes to posture?

Answer 12

visual
vestibular
somatosensory

Question 13

Is quiet stance really as quiet as she says she is?

Answer 13

nah mate,

there’s some crazy sway present bro

Question 14

What types of sway are present during quiet stance?

Answer 14

anterior-posterior

lateral

Question 15

What equipment can be used in the lab to assess sway?

Answer 15

pressure mat

Question 16

When the ankle strategy of balance be employed?

Answer 16

during quiet stance for ant-post sway

Question 17

When the hip strategy of balance be employed?

Answer 17

during perturbed stance as it is fast acting for larger movements and involves adjustment at multiple joints.

Question 18

What do sway factors influence?

Answer 18

the type and amount of sway present during quiet stance

Question 19

List 5 sway factors

Answer 19

1) physical characteristics (e.g. age, fatigue)
2) body posture (e.g. feet position)
3) support surface (e.g. hardness)
4) availability of sensory feedback (e.g. visual, proprioceptive)
5) psychological factors (e.g. cognitive interference in a dual task)

Question 20

When visual feedback is removed, what is the impact on stability during quiet stance?

Answer 20

stability suffers
average CoP displacement increases
- Tresilian (2012)

Question 21

What other feedback methods can be introduced to improve stability if vision is removed?

Answer 21

cutaneous vibrations / light touch of a rigid support object.
- Tresilian (2012)

Question 22

What 3 balance strategies can be employed during perturbed stance?

Answer 22

• stereotyped activation patterns (e.g. distal to proximal)
• muscle synergies (neural networks that make actions more effective)
• anticipatory postural adjustments

Question 23

When may anticipatory voluntary movements be employed as a balance strategy?

Answer 23

> when making a voluntary movement

> when perturbation is known and expected

Question 24

What information is provided by a force plate?

Answer 24

> GRF in all 3 planes of motion

> centre of pressure

Question 25

What information is provided by a pressure mat?

Answer 25

force / area

Question 26

What are the pros (+) and cons (x) of a force plate?

Answer 26

+ gives GRF values in multiple planes

x doesn’t give pressure distribution, just CoP

Question 27

What are the pros (+) and cons (x) of a pressure mat?

Answer 27

+ able to observe pressure distribution
x only measures vertical GRF
x only samples up to 300 Hz and therefore can’t be used for high impact movements

Question 28

How can the results of a force plate be reported?

Answer 28

graphically

ant-post and med-lateral CoP can be shown and combined to give actual CoP

Question 29

What influence does removing vision and/or adding a cognitive or physical task (standing on one leg) do to the sway pattern?

Answer 29

the variability in patterns increases.
greater magnitude of forces

the area of the circle/box circumscribing the sway pattern increases.