week 13- 1 Flashcards
biomechanical factors to increase stability
- increase the area of the base of support
- increased distance from the line of COG
- decrease of COM over base of support
during quiet standing
maintain antigravity posture
during unexpected perturbation
reactive balance
during voluntary self-initiated movement
anticipatory postural control
reactive balance
- postural control system come into play in response to a destabilizing external force or perturbation
-utilizes feedback mechanism where the central nervous system responds to info received during and after a movements and attempt to restore stability
muscle synergy
particular muscles work together (in synergy) to achieve the task; in the case of reactive balance, it occurs without voluntary control
- muscles involved in the synergy depend on the requirement of the task
ankle strategy
involves distal to the proximal sequence of muscles activation
- rotate about ankle only- body stays straight
hip strategy
involves proximal to distal activation
- rotate about hip only - legs and torso stay straight
suspensory strategy
crouch down- mostly observed on young children (reflective)
step strategy
take a step because move outside the limits of stability
reactive balance context dependent
- small balance perturbations usually result in the use of an ankle strategy
- as perturbation gets larger, there is a switch to hip strategy and finally stepping strategy
if the support surface is changed to a narrow beam
use hip strategy at a smaller perturbation magnitude
aging associated with
reduced muscle strength and sensory function
-increased postural sway
—– particularly in fallers
response to perturbation are slower with _____ muscle activity
greater
hypermetria
condition of the dysfunction in which voluntary muscular movements tend to result in the movement of bodily parts (as the arm and hand) beyond the intended goal
sensory contribution to postural control
effective postural control requires more than the ability to generate and apply forces and activate appropriate musculature
to know when and how to apply forces or to activate appropriate muscles
the
CNS must have an accurate picture of where the body is in space and what forces are acting on it
3 primary sources of peripheral input (to detect body position and movement relative to space and the environment
- visual system
- vestibular system
- somatosensory/ proprioception
The contribution of each sensory system is typically assessed by
- removing or altering/ distorting the sensory information available
- using patients population where it is absent or distorted
Typically assess the involvement in different settings/contexts. Two common methods
(1) Quiet standing (COM or COP)
(2) External perturbations – Re-active
vision
- no visual input postural sway increases between 30-40%
Physical Perturbation
With eyes closed COM displacement is greater following linear translation of support surface beneath feet
Visual Perturbation
Linear vection. E.g., Sitting in a car, car next to you starts to move, and you perceive that your car is actually moving
moving room
optic flow important
moving line creates the illusion that person is moving forward shift COM backwards
is vision involved in quiet standing
yes
how do we know
Remove vision, greater sway, as indicated by greater movement of the COP/COM
Alter optic flow to give the illusion that a person is swaying in one direction, they
will move the COM in the opposite direction
