W4 - Balance Flashcards
What is balance?
How movement is controlled
* “the ability to regulate or direct the mechanisms essential to movement”
* “regulation or maintenance of a function or action”
* e.g.: to be able to throw a ball, you need to be able to balance your body in order to do it
* Never stood still, always some type of motor control of the CNS
What is human balance?
- Human balance is 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 insufficiencies
- Not an equilibrium, humans not stable from a passive sense (need for active movement to keep still)
What are some common reflexes for a human to keep their balance?
- Ankle strategy - movement only at ankles
- Hip strategy - e.g.: gymnast has more movement about the hips when on a balancing beam
- Stepping
- Arm swing
Vision, vestibular system, somatosensory proprioception - tells us that our weight is shifting(becoming unbalanced)
What structure in the ear allows us to maintain our balance?
- Vestibular system informs CNS on the position & motion of the head in space
- Vestibular system is less obvious in controlling posture
What type of acceleration does the utricle and sacculus detect?
Linear acceleration of the ear approx. 90 degrees from each other
How do the semi-circular canals detect acceleration?
Liquid moves through the semi-circular canals
3 as we live in a 3D world to control our movement
13-14ms reflexes in the eye (fastest reflex in the body)
Vestibular ocular reflex - is moving your head trying to read something in front of you - 30-40 ms reflex
–> causes scades which is when you move your head quickly and eyes get moved quickly to catch up
- Nerve fibres are a sensor
- As the gelatinous material moves through ampulla, causes hairs to move to the side = tells us if we accelerate in our head
In what proportion do:
* proprioception
* vestibular
* vision
Contribute to balance
- 70%
- 20%
- 10% (peripheral mainly in balance)
What is meant by:
- Visual perturbations
- Sensory conflict
Visual perturbations - when an object gets bigger, causes the person to move backwards. The body believes you are moving forwards
Sensory conflict - Viscosity of the liquid changes in the semi-circular canals which causes us to feel sick
How is postural sway measured?
AP - Anteroposterior
ML - Mediolateral
- Body sways around a migrating point (not fixed) (Oie et al., 2002Maurer et al., 2006Duarte and Zatsiorsky, 1999)
What is meant by stability?
The tendency of the body to keep/return to equilibrium state after a perturbation
○ Stability can be active OR passive
○ Passively unstable (tiny knock and we will fall over)
what are the 4 factors that passive stability depend on?
- Weight (mass of object) - less likely to move
- Area of the base - wider base of support allows for more stability
- Horizontal distance of the CoG to the pivot point
- Height of the CoG above the base (CoM and CoG is the same thing in this case) - taller/higher CoG makes them less stable
When the CoM is outside the base of support, the object will fall over
What is meant by an equilibrium?
Equilibrium = the sum of all the forces acting on the object is zero
Describe how human stability is maintained
What are some problems when evaluating stability?
- Humans are not very stable
- Inverted pendulum (small movements to maintain the person’s balance)
○ Problems:
○ Joint stiffness is not well defined
○ Joint stiffness estimations are lower than an inverted pendulum representation of the body
○ Muscle fibres can change direction, from that in an observation of joint motion
Explain humans as a dynamically stable system
- Humans need to use to muscular forces (joint torques) - control forwards & backwards movement creating torque
- State of active/dynamic equilibrium
- CoG must remain within the base of support
What is a perturbation?
Explain some ways in which we can counter perturbations
Perturbations: nudges/movement
Perturbations create torque, which changes our COP, controlled by muscles to resist perturbations
Unexpected Perturbations;
- Elasticity - when a force is applied it creates a torque to try and counter the movement
- Stretch reflexes - e.g.: a knee tap
- Pre-programmed actions - could cause a startle reflex, inbuilt reactions that are voluntary
