MC 5 (standing posture and control of postural sway) Flashcards
Define equilibrium
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
Define stability
resilience to change in response to a perturbation
“the tendency of the system to return to equilibrium when perturbed” is what?
stability
An inverted pendulum model has ….. stability?
low (unstable)
Define Base of Support (BoS)
the area of the support surface defined by straight lines drawn between the points of ground-object contact
What is an object’s Centre of Pressure (CoP)?
the point where the resultant ground reaction force is applied
Must the CoP always fall within the BoS?
Yes,
under static conditions the CoP will fall directly beneath the centre of mass
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
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)
The human body is an example of what kind of pendulum?
inverted compound pendulum.
series of jointed segments that are able to rotate relative to one another
Why is muscular effort required during quiet upright standing posture?
to maintain body configuration and avoid collapse
Define the two types of perturbed stance
1) environmental perturbed stance: perturbations from the environment
2) action perturbed stance: perturbations from performaning movements that can disturb upright posture.
What body receptors sense changes to posture?
visual
vestibular
somatosensory
Is quiet stance really as quiet as she says she is?
nah mate,
there’s some crazy sway present bro
What types of sway are present during quiet stance?
anterior-posterior
lateral
What equipment can be used in the lab to assess sway?
pressure mat
When the ankle strategy of balance be employed?
during quiet stance for ant-post sway
When the hip strategy of balance be employed?
during perturbed stance as it is fast acting for larger movements and involves adjustment at multiple joints.
What do sway factors influence?
the type and amount of sway present during quiet stance
List 5 sway factors
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)
When visual feedback is removed, what is the impact on stability during quiet stance?
stability suffers
average CoP displacement increases
- Tresilian (2012)
What other feedback methods can be introduced to improve stability if vision is removed?
cutaneous vibrations / light touch of a rigid support object.
- Tresilian (2012)
What 3 balance strategies can be employed during perturbed stance?
- stereotyped activation patterns (e.g. distal to proximal)
- muscle synergies (neural networks that make actions more effective)
- anticipatory postural adjustments
When may anticipatory voluntary movements be employed as a balance strategy?
> when making a voluntary movement
> when perturbation is known and expected
What information is provided by a force plate?
> GRF in all 3 planes of motion
> centre of pressure
What information is provided by a pressure mat?
force / area
What are the pros (+) and cons (x) of a force plate?
+ gives GRF values in multiple planes
x doesn’t give pressure distribution, just CoP
What are the pros (+) and cons (x) of a pressure mat?
+ 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
How can the results of a force plate be reported?
graphically
ant-post and med-lateral CoP can be shown and combined to give actual CoP
What influence does removing vision and/or adding a cognitive or physical task (standing on one leg) do to the sway pattern?
the variability in patterns increases.
greater magnitude of forces
the area of the circle/box circumscribing the sway pattern increases.
