Balance Flashcards
What is balance?
Maintaining the centre of mass above the base of support
If the centre of mass moves outside of the base of support then what happens?
a fall of compensatory step will occur
Explain the Inverted Pendulum model of human Standing
During normal stance, most motion occurs at the ankle joint. Torque is provided by continuously active calf muscles which can be represented as a point mass, tending to fall forwards with active torque stabilisation
Define sway
Centre of mass over the centre of pressure where the centre of pressure is actively oscillating forwards and back to maintain the centre of mass within the limits of stability
Why do we sway? and where do these imperfections in this process arise from?
Standing is a sensorimotor control process.
Imperfections from:
- Sensory estimation - an imperfect process with sensor noise
- Motor output - imperfect process
- External/internal perturbations eg breathing or the wind
What are the 5 bits of information that help keep us upright?
- Vision - for slow & low freq control of sway
- Proprioception
- Touch
- Vestibular apparatus - for fast & high freq control eg spinning around
- Efference copy of motor command and prediction
What part of visual information, when removed, increases sway?
- Reducing visual acuity
2. Blocking parts of the visual field
Where to objects need to be to be more useful for controlling sway and why?
Closer objects
because they have greater image displacement on the retina
Distant visual information is effectively useless and it produces no retinal motion
Define Motion Parallax
Objects appear to move relative to each other depending upon focus point
What is visual vection?
A false sense of motion induced by a moving scene
Such as watching a train start to move next to you and you think it is your own train.
The brain interprets forwards scene motion as backward body motion which produces what?
A compensatory forward response
What happens to the sway response when the subjects predict it?
virtually no sway response when compared to an experimenter unexpectedly triggering scene motion
when testing the balance system with resistance to waist pull to determine stiffness… what do the changes in stiffness represent?
Changes in muscle reflexes to see how much balance alteration has occurred.
balance reflexes can also be tuned by intention…
Eg trying to stand still
The stiffness of the ankle is too low to permit passive standing without active modulation of EMG. What are the limiting factors in stiffness?
Tendon and soft tissue of the foot
