Lecture 14 Flashcards
Center of Gravity
refers to vertical projection of COM to the ground
located about the level of S2
approx 55% of person’s height
men = higher, wider shoulders
women = lower, wider pelvis
Base of support
perimeter of the contact area between the body and its support surface
Balance is greatest when
body’s COV is maintained over its BOS
Limits of stability
the sway boundaries in which postural equilibrium is maintained without a change in the BOS
Anteroposterior sway limit
12” from post to anterior
Lateral sway limit
16” from side to side
Balance
not particular position, but it is a space.
determined by size of support base, limitations of joint range, muscle strength, sensory info
Balance is made up of
cognitive processing
biomechanical constraints
movement strategies
sensory strategies
orientation in space
control of dynamics
Postural control
complex motor skill derived from the interaction of multiple sensorimotor processes
Strategies for balance control
ankle
hip
stepping
suspension
Ankle strategy
used when displacements of COG are small
displaces COG by creating rotation about ankle joint
used on firm surfaces
muscle contractions begin distal, progress to proximal
Hip strategy
rapid hip flexion or extension to move the COG within BOS
used when ankle motion is impaired or ankle cannot compensate
surface is narrow or compliant
surface doesn’t allow ankle torque
muscles are activated proximal to distal
Stepping strategy
if displacement is large enough, a forward, backward, or lateral step is used to regain postural control
people at risk of falling have a preferential use of stepping
Suspension Strategy
rapid lowering of body by flexing knees
results in hip and ankle flexion
COG is lowered to maintain balance
Environment/Contextual Factors w/balance
Environment, can be open or closed
support surfaces (lighting, gravity)
task characteristics
musculoskeletal system contributions to postural control
joint ROM
joint integrity
muscle strength, power, endurance
flexibility
if any are impaired, it will be difficult to modify COG and put it back over BOS
Nervous system contributions to balance
sensory = visual, vestibular, somatosensory
sensorimotor = link to motor sensations
motor strategies = planning, programming, executing
Visual system
provides info regarding the position of the head relative to the environment
orientation of the head to maintain level gaze
direction and speed of head movements
Vestibular system
provides info regarding orientation of the head with respect to gravity and inertia
receptors in ears responds to movements
cannot differentiate between nodding head and bending forward
Somatosensory system
provides info about position and motion of the body and body parts relative to each other and the support surface
free nerve endings, mechanoreceptors, joint receptors, golgi tendon organs, muscle spindles
How the body combines all its systems
Somatosensory = 70%
Vision = 10%
Vestibular = 20%
increased use of vision and vestibular when on unstable surface
Push and release test
on a scale of 0 to 4, used on parkinson patients. Tests balance non-vestibular.
Balance Error Scoring System
Double leg stance
single leg stance
tandem stance
you change the surface, from firm to foam surfaces
count the number of errors in each trial to obtain a score
