Posture Flashcards
static posture
- body and segments are aligned and maintained in certain positions
- standing, sitting, lying, kneeling
dynamic posture
- body/segments are moving
- walking, running, jumping, throwing, lifting
base of support (BoS)
area bounded posteriorly by the tips of the heels and anteriorly by a line jointing the tips of the toes
postural control
maintenance of center of mass (CoM) over BoS to control body’s orientation in space and stabilize head with respect to vertical to orient gaze
afferent inputs for postural control
- proprioceptive
- vestibular
- visual
efferent inputs for postural control
muscular contraction
primary goal of postural control
stabilize the head
reactive (compensatory) responses
responses occur as reactions to external forces that displace the body’s CoM
proactive (anticipatory) responses
responses occur in anticipation of internally generated destabilizing forces
altered or absent inputs
- posture may be altered
- stability may be compromised
- example: decreased sensation of LEs or post-injury
alterations in ____ can compromise posture
outputs
example of altered output
inability of muscles to respond appropriately to signals from CNS due to a neuromuscular disorder
maintenance of standing posture is the result of ____ controls
dynamic
sensory perturbation
may be caused by altering visual input
mechanical perturbation
displacement causing changes in the relationship of the body’s CoM to BoS
fixed support synergies/strategies
centrally organized patterns of muscle activity that occur in response to perturbations of standing postures
ankle synergy
discrete bursts of muscle activity that occur in a distal-to-proximal pattern
hip synergy
discrete bursts of muscle activity that occur in a proximal-to-distal pattern
when would an ankle synergy be helpful for maintaining standing posture?
- minor perturbations
- small changes in terrain
when would a hip synergy be helpful for maintaining standing posture?
fast perturbation
muscles activated in ankle strategy during forward sway
- gastroc
- hamstrings
- paraspinals
muscles activated in ankle strategy during backward sway
- tib anterior
- quads
- abdominals
muscles activated in hip strategy during forward sway
- abdominals
- quads
muscles activated in hip strategy during backward sway
- paraspinals
- hamstrings
change-in-support strategies
- stepping and grasping strategies
- can move or enlarge the body’s BoS so it remains under the CoM
stepping strategies
- take a step to widen BoS
- forward, backward, or sideways
grasping strategies
using one’s hands to grab a fixed surface
what is the only strategy that is successful with a large perturbation?
change-in-support strategies (stepping and grasping)
differences between young and old individuals in stepping strategies
young people usually only take one step whereas older individuals more commonly take multiple, shorter steps
what produces internal forces?
- muscle activity
- passive tension in ligaments, tendons, and joint capsules
external forces include…
- inertia
- gravity
- ground reaction forces
equilibrium = sum of ____ and ____ forces equal to ____
- internal
- external
- zero
postural sway
constant swaying motion due to inertial and gravitational forces
ground reaction force (GRF)
- force of ground pushing back on the body in standing
- represents magnitude and direction of loading applied to one or both feet
line of gravity (LoG)
line extending from center of gravity to BoS
center of pressure (CoP)
- point of application of the GRF
- located b/w the feet in BL stance
what happens when LoG passes directly through joint axis?
no torque is created around the joint
what happens when LoG passes at a distance from the joint axis?
- external gravitation moment
- results in rotation around the joint axis unless opposed by a counterbalancing internal moment or muscle contraction
magnitude of external moment ____ as the distance between LoG and joint axis increases
increases
direction of rotation depends on the ____ of the LoG in relation to the joint axis
location
if LoG is anterior to joint axis, external moment will cause ____ motion of the ____ segment supported by that joint
- anterior
- proximal
when LoG is anterior to ankle, gravity creates a ____ moment and the ____ muscles contract to counteract this moment
- dorsiflexion (tibia moves forward)
- gastroc and soleus
more distance b/w LoG and AOR = ____ counteracting muscle contraction
stronger
LoG passes ____ to all joint axes, minimizing ____ moments
- through or very close
- external
what types of internal moments will balance external moments?
- passive capsular and ligamentous tension
- passive muscle tension
- small, continuous amount of muscle activity
large deviations in the location of LoG relative to the joint axis result in…
- excessive strain on passive structures
- increased muscular activity
long-term deviation in the location of LoG relative to the joint axis results in…
structural changes
