balance+posture and locomotion Flashcards
1
Q
what is quiet standing/balance?
A
- keeping COM within base of support
- is COM moves outside BOS = fall/compensatory step
2
Q
what does quiet standing involve?
A
- inverted pendulum model- most motion in ankles
- torque provided by active calf muscle
- falls forward with active torque stabilisation
3
Q
centre of mass v pressure
A
- COP oscillates forward and backward to maintain COM stability
- COM moves less and slower than COP
4
Q
why do we sway?
A
- sensory estimation
- motor output
- external and internal perturbations
5
Q
what info keeps us upright?
A
- sensory info
- touch
- vision
- proprioception
- vestibular apparatus
- efferent copt of motor command and prediction
6
Q
what sensory inputs are used at what times?
A
- vision most sensitive at low frequencies (standing without movement)
- vestibular otoliths - higher frequencies (standing on uneven floors)
- canals - higher frequencies - rapid head turns
7
Q
how does sway increase?
A
- blocking parts of visual field increases sway
- peripheral vision just as important as foveal
- close objects useful at controlling sway as greater image displacement on retina
- distant is useless as no retinal motion
8
Q
what does motion parallax mean?
A
- objects appear to move relative to each other depending on focus point and during small motion due to sway
- largest sway reduction when foreground + background scenery present together and furthest apart
9
Q
what happens when visual point is perturbed?
A
- visual section
- false sense of motion induced by a moving scene
- train
- subject sways in direction of visual movement
- brain interprets forward scene motion as backward body motion
- compensatory forward response
10
Q
what is the visual perturbation response?
A
- initial sway in direction of visual field
- corrective sway after 2-3s in opposite direction conflicting sensory channels
- responds best to slow low frequency
- habituates quickly
11
Q
testing balance system
A
- when body topples forward, activity generated in torque around ankles to resist
- resistance to waist pull measured to determine stiffness and changes in stiffness represent changes in muscle reflexes
12
Q
what is the motor output for standing
A
- continuous calf muscle contractions prevent falling forwards
- passive ankle stiffness as part to play
- stiffness too low = can’t permit passive standing and stiffness won’t be changed by intention or sensation
- ankle needs to constantly produce little movements to produce enough ankle torque to not move forwards
13
Q
what is the swing stance pattern
A
- flexors ac time during swing
- extensors during stance
alternating pattern
14
Q
ground reaction forces during walking
A
- large vehicle force on heel-strike
- decelerating shear force
- pushy-off includes accelerating shear force accompanied by secondary vertical force
15
Q
ground reaction forces during running
A
- heel strike = injury
