Balance and posture

Centre of mass, base of support and three sources of information: vision, vestibule and proprioception.

The outline, topic by topic

Each topic is weighted the way the exam weighs it.

Balance: what is it?
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The ability to keep the centre of mass projected within the base of support.
It can be static or dynamic: in walking, the projection leaves the base and each step catches it.
A wrestler wants to resist a push. What should they do?
- Widen the stance and bend the legs
- Bring the feet together, legs straight
- Stand on tiptoe
- Straighten up to stand taller
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Widen the stance and bend the legs
A wider base and a lower centre of mass keep its projection further from the edge: a stronger push is needed to move it out.
Base of support: what is it?
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The area bounded by the contact points with the ground.
Spreading the feet enlarges it.
Why does a gymnast feel dizzy after fast spins?
- The otoliths come loose from their membrane
- The fluid in the semicircular canals is still moving
- Blood pools in the legs during the spins
- The neck muscle spindles tire
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The fluid in the semicircular canals is still moving
At the stop, the endolymph carries on and bends the cupula: the vestibule reports a spin, in the opposite direction, that no longer exists.