Week 6 Flashcards
Define static and dynamic posture.
static - not moving posture
dynamic - moving posture
Define base of support and center of gravity/center of mass.
BoS - area bounded posteriorly by tips of heels and anteriorly by tips of toes
CoG - point where mass of body is centered
What systems play a role in postural control?
Afferent
- proprioceptive
- vestibular
- visual
Efferent
- muscular contraction
What are reactive responses?
- compensatory
- occur as reactions to external forces that displace the body’s CoM
What are proactive responses?
- anticipatory
- occur in anticipation of internally generated destabilizing forces
What may happen to posture when an individual has altered or absent inputs? What are some examples of altered or absent inputs?
altered posture and stability is compromised
ex: decreased sensation of the lower extremities or post injury
What may happen to posture when an individual has altered or absent outputs? What are some examples of altered or absent outputs?
- compromise posture
ex: inability of muscles to respond appropriately to signals from CNS due to a neuromuscular disorder
What are sensory perturbations?
perturbations that may be caused by altering visual input
What are mechanical perturbations?
displacement causing changes in the relationship of the body’s CoM to BoS
ex: leaning forward to the point you have to step forward to catch yourself
What are fixed support synergies/strategies?
Centrally organized patterns of muscle activity that occur in response to perturbations of standing postures
What are ankle strategies?
Discrete bursts of muscle activity that occur in a distal-to-proximal pattern
What are hip strategies?
Discrete bursts of muscle activity that occur in a proximal-to-distal pattern
What are change-in-support strategies?
movement to counteract large perturbations
- stepping strategies
- grasping strategies
What are stepping strategies?
forward, backward, or sidewise steps to increase BoS after large perturbation
What are grasping strategies?
using one’s hands to grab a fixed surface after a large perturbation
What are internal forces vs external forces?
Internal forces - produced by muscle activity and passive tension in ligaments, tendons, and joint capsules
External forces - inertia, gravity, and ground reaction forces
Define ground reaction force
force of the ground pushing back on the body in standing
Define Line of Gravity
Line extending from center of gravity to the base of support
Define Center of Pressure
- Point of application of the GRFV – ground reaction force
- Located between the feet in bilateral stance
Describe the relationship of the position of the LOG and a joint axis
LoG THROUGH a joint = no torque
LoG at a DISTANCE = external gravitational moment
What impacts the magnitude and direction of the external moment?
Magnitude of the external moment increases as the distance between the LoG and joint axis increases
Direction depends on the location of the LoG in relation to the joint axis
Describe the alignment associated with ideal standing posture from a side view
- through external auditory meatus
- midway through the shoulder
- slightly posterior to hip
- slightly anterior to knee
- slightly anterior to lateral malleolus
Describe the alignment associated with ideal standing posture from a posterior view
Midline
- Head
- Spine
- Feet evenly spaced
Shoulder and scapula
- Scapulae lie flat on the thorax
- Approximately between T2 and T7
- Approximately 4 inches apart
- Shoulder ipsilateral to handedness is often lower – dominant hand shoulder is typically lower
Describe the alignment associated with ideal standing posture from an anterior view
Alignment of Knees
- Patellae face directly forward
- Slight physiological valgus
Alignment of Ankles
- Neutral- neither supinated or pronated
Alignment of Feet
- Heels separated by about 3 inches
- Out-toeing 8° - 10°
