W3 - Balance Flashcards
Define Human balance:
- the active control of the physical shape of the limbs to provide varying degrees of passive stability and muscular actions to provide compensating active stability for passive inefficiencies
- Balance is considered to be a simple skill, but is actually quite complex underneath
- Humans are passively unstable, so there is a need for active control to maintain balance
What is meant by posture?
includes the body orientation e.g.: vertical posture, maintained over a certain period of time & resistance to external perturbations[local stability] –> such conditions effecting posture include Parkinson’s disease, impairing balance and body equilibrium
Provide 3 examples of postural control:
- A figure skater maintaining a beautiful arm configuration while sliding over the skating rink (arm orientation maintained
respect to the body but not with respect to the environment) - A musician playing the violin, moving the body and the violin (hand posture may be maintained with
respect to the violin, not necessarily to the body or the external space) - Holding the handles while riding a bicycle (posture is maintained with respect to a part of the bicycle, not the whole bicycle, e.g., during sharp turns, not the body, and not the environment).
What are the 2 views on postural sway (Nikolai Bernstein, 1896-1967)?
- A consequence of noise in the neuromotor system, a sign of imperfection in the human body(kept low by good neural control & to avoid losing balance. The necessary background component for any voluntary motor action
- A purposeful design of the neurophysiological system for postural control e.g.: Parkinson’s patients may loose balance due to little perturbations. Meaning healthy people have higher sway but more control
What are the reasons for postural sway?
- Passive instability
- Muscle errors
- Sensory errors
- Feedback delays - delays from neuron control between sensory and muscle systems
- Control strategies
What is the posture-movement paradox(Von Holst & Mittelstaedt, 1950)?
How does this relate to a postural equilibrium?
- a number of posture-stabilizing mechanisms generating forces against external perturbations applied during steady-state motor tasks at very short time delays (under 100 ms), shortest simple reaction time
- caused quick postural corrections, but not voluntary movements
- Where posture is a spatial characteristic e.g.: muscle length, joint angle, stabillised –> maintained by synergies
- similar to the equilibrium hypothesis, assuming that equilibrium states of the body in environment is controlled by muscle correction reflexes
What is stability?
goes hand-in-hand with sway
* The tendency of a body to remain or return to its initial position following the application of a force
* Stability can be passive or dynamic
* Maintain CoM within base of support
Provide examples of:
- stable equilibrium (triangle)
- unstable equilibrium (hammer)
- neutral equilibrium (circle)
- Stable - force has to rise(humans) e.g.: a triangle
- Unstable - energy e.g.: gravity keeps getting lower. Perturbations cause imbalance(humans) e.g.: Pendulum
- Neutral - energy does not change, it just keeps going does not fall e.g.: sphere
What are the factors that determine passive stability?
What makes things stable/unstable
* weight - harder to perturb it as has increased weight
* area of the base
* horizontal distance of the CoG to pivot point - CoM has to go further to reach pivot point
* height of the CoG above the base - does have to be tipped as far when higher up
- CoP is the vertical resultant forces acting on the body from the supporting surface
What is passive instability?
In standing, humans are passively unstable, based on:
– Small base of support
– High CoG above the base
– Like balancing a pencil
—> Resistance to current state, thought of in a passive state
Human standing is dynamically stable
– Needs active muscle contractions
Describe muscle errors:
Muscles cannot produce a perfectly consistent force:
– Variation / error
– Underestimate and overestimate force causes sway
Muscles produce force between attachments:
– Across multiple joints: variation between muscle forces
– In multiple planes / axes: needs to be counteracted by
Other muscles
what are sensory errors?
Our sensory system is not perfect
There are many different sensory organs:
– Vision 10%
– Vestibular apparatus 20%
– Somatosensory proprioception 70%
This leads to sensory conflict from different systems having different inputs
Some require movement to work, not an absolute state
Describe and draw the sensory threshold effect:
(Clark et al., 1995)
(Fitzpatrick & McCloskey, 1994)
Slow movements can only detect position sense, and only detect movement sense if moved enough along position sense
- Vestibular system is not used for quiet stance as does not detect small movements/perturbations
When can feedback delays occur?
Draw the graph by (Blenkinsop, Pain & Hiley, 2006)
INPUT –> delay –> PROCESS –> delay –> OUTPUT ¬v
¬> FEEDBACK DELAY <———–
What is sensory delay?
- Sensory delay is the amount of time it takes the sensory threshold to be reached, fast movement is smaller delay
- the delay of signals coming into the brain that cause muscle contraction etc
