wk 4 - postural control Flashcards
posture / postural control definitions
Relative position of the body (or parts of the body) with respect to a reference frame
Maintaining the position of the body (or parts of the body) with respect to the environment (e.g. influence of gravity)- postural adjustments
what is centre of mass
another term for centre of gravity.
the line of action of the weight of an object passes through a centre of gravity of the object.
there is an equal amount of mass
-above and below it
-in front and behind
-to the left and right
what is centre of pressure and what is it’s relation to GRF
also known as the base of support.
if the centre of mass (gravity), remains within the centre of pressure (base support) then you maintain stability. if outside, then body will be unstable/fall
it is the point on the ground which a single resultant force appears to act (GRF)
what is moment of inertia
resistance to angular acceleration.
what is ground reaction force determined by
the ground produces a reaction force equal and opposite
determined by newtons third law
what is a joint moment
when a force is applied some distance away from a joint or fulcrum, it will tend to rotate the joint around its axis, there are internal and external joint moments
what occurs in the foot if the COP is 5cm anterior to the ankle joint. how does the foot maintain balance?
the foot would tend to dorsiflex under the influence of GRF (internal joint moment)
there must be an oppposite and equal moment produced by tension in the achilles tendon (external joint moment)
the two forces (GRF and achilles tendon) act like an inverted see-saw
what GRF and external moments occur during single leg stance in the frontal plane
GRF passes lateral to ankle (outside), medial to knee and medial to hip
therefore the external moments are
ankle - eversion is occuring: resisted actively by ankle invertors
knee- varus: passively resisted by lateral knee structures
hip- adduction: resisted actively by abductors
neurophysiology and postural control, what structures help the unstable body maintain balance? (5)
postural control involves the whole nervous system
-CNS (cerebellum, basal ganglia, cortex)
-Sensory system (proprioceptive, cutaneous information from feet, visual, vestibular)
-spinal neuronal networks (central pattern generators)
-efferent (motor) neurons
-effectors (muscles)
what does the CNS (cerebellum) do for postural control
- processes information from cerebral motor cortex, proprioceptrs and visual/equilibrium pathways
- provides instructions to cerebral motor cortex and subcortical motor centres
- resulting in smooth skeletal muscle movements
what can cerebellar lesions cause as motor features
loss of coordination and movement
increased sway of trunk
tremor
wide based gait
inability to make postural adjustments
what does the basal ganglia do for postural control
function not completely understood but important role in
1. motor control
2. learned movement patterns
3. role in initiating and terminating movements
what does the cerebral cortex do for postural control
- Neurons within the cortex transform sensory
stimuli into a motor “plan”
preprogramming the movement pattern here
how does the sensory system help with postural control
vestibular system- system of the brain and inner ear provides signals related to the orientation of the head with respect to gravity.
visual- One of the most reliable sources of postural control information for the brain.
* Vertical posture depends strongly on visual input
proprioception- percieves location, movement and action of the body through constant monitoring of joint position, muscle length and tension
cutaneous receptors- skin sensory receptors that detect pain, pressure, temp
receptor types of proprioceptors
– Pacinian corpuscles (joint capsule, ligament)
– Ruffini’s corpuscles (joint capsule)
– Muscle spindles (sensitive to muscle length)
– Golgi tendon organs (responsive to muscle tension
measurements of postural sway (4)
trajectory of centre of pressure can be measured to indicted postural sway
COP displacement (mm)
mean velocity- the speed of the adjustments
path length- the COP line measured out
and 95% confidence ellipse- 95% of the COP is within this area
postural synergy is what?
pattern of muscle co-activation that is used by the nervous system to maintain standing balance as anticipation or response to a disturbance
what is postural adjustment?
central nervous system uses anticipatory and compensatory postural adjustments to maintain equilibrium while standing when displacements of the centre of mass and pressure occur
types of postural adjustments
anticipatory- see the disruption coming, occurs before the movement starts
compensatory- reacting to an unexpected disruption
postural adjustments (lines of defence) against unexpected disturbances 4
- Tissue elasticity (muscle and tendon)
- Stretch reflex (30-50 ms)
- Pre-programmed reactions/responses (kick in at 70 ms)- ankle/hip synergistic strategies
- Voluntary actions (150 ms)
types of postural adjustment strategies 4
ankle strategy
hip
step strategy
reach to grasp strategy
ankle strategy, what is it
an example of postural synergy during stance in order to maintain upright balance. ankle strategy is typically adopted by a young healthy person when the support surface is slowly changing.
it involves joints in a distal to proximal order. activates ankle muscles followed by leg, thigh than trunk muscles to fight changes to centre of mass.
eg, body sways backwards, muscles on the front of the ankle contract to pull the com forward
hip strategy, what is it
involves joints proximal to distal, seen in older adults in situations where a young person would use ankle strategy to maintain balance when a support surface is slowly changing.
a loss of balance going backwards results in the hips quickly extending and creating a back bending movement to bring the centre of mass forward
change in support strategies
if ankle and hip strategy cannot change their centre of mass for the change of surface then
1. a step strategy, step towards falling COM
2. reach to grasp strategy- extending the base of support by grasping an external object for stability
what are the 3 psychometric properties of a measurement
- reliability- take a measurement on separate conditions and produce the same
- validity- the test is measuring what you intend to measure
- responsiveness to change-
a) minimal detectable change in a score that represents a true change beyond measurement error
b) minimal clinically important different score that reflects meaningful change perceived by a patient
what are examples of walking and balance tests (8)
Functional ambulation classification
* Timed up and go (TUG)
* 2-minute or 6-minute walk test
* Dynamic gait index
* Functional gait assessment
* Four square step test (FSST)
* Modified Gait Abnormality Rating Scale (GARS-M)
* Berg Balance Scale (BBS)
timed up and go test- what is it and what is the cut off time for community dwelling adults
sitting and timed for their up and go back to original start position.
cut off for community-dwelling adults is greater than 13.5 seconds.
2 min or 6 min walk test what is it
6min- test functional exercise capacity
2min- similar but allows to test in adults with cardiorespiratory dysfunction who cannot perform the more rigorous 6 min test
