Week 5 Flashcards
What is Balance? (aka Postural Control, in humans)
BALANCE: “The state of an object when the resultant force acting upon
it is zero”
HUMAN BALANCE: Ability of a person not to fall …postural
equilibrium
Postural Control
Controlling the body’s position in space for stability and orientation
To maintain postural control you must keep the vertical projection of
the COM – defined as the center of gravity (COG) – within the BOS
Postural stability:
ability to control the center of mass (COM) in relationship
to the base of support (BOS)
Postural orientation:
ability to maintain an appropriate relationship between
the body segments, and between the body and the environment for a task
Definition: Center of Mass (COM)
The point through which the vector of the total body weight passes
Children have a higher COM (top heavy)
Base of Support (BOS)
The area of contact between the body and
support system (if there are 2+ points of
contact then it is the area between them)
Changes with Activity
Postural Control is Context Specific
Posture demands
change based on tasks
in different
environments
Orientation in Space
Alignment of head/trunk to gravity, surface, or visual environment
Biomechanical Constraints
Range of motion
Available muscle force & length
In infants, the ratio of fat to muscle
varies; may have low force production
capabilities
Degrees of freedom
Size & quality of BOS (feet)
Rapidly changing body size & shape (in
infants)
Sensory Strategies
Vision – How is the body positioned relative to the environment
Vestibular – How is our head positioned. Is there
movement?
Somatosensory (Proprioception) - How are our limbs
positioned in relation to each other & the body
Visual Motion:
World moving
or self moving
Vestibular/ Inner Ear:
Linear acceleration or
head tilt
Surface Proprioception:
Surface tilt or body sway
Surface/Environment Dependent
stable surface:
somatosensory = 70%
vestibular = 20%
vision = 10%
unstable surface:
somatosensory = 10%
vestibular = 60%
vision = 30%
Age Dependent
Infants: Vision
* Age 4-5: Vestibular and visual > proprioceptive
- After age 5: Vestibular and proprioceptive
- Age 7-10: Resembles adult responses
- Older adults: increased dependence on Vision
Stability limits
Vary according to task/individual/environment
Must consider both position AND velocity of COM relative to stability limits
What do we do to counter a shift in equilibrium?
Compensatory
(reactive) Postural
Control
Anticipatory
(proactive) Postural
Control
Movement Strategies – Compensatory Postural Adjustments (CPA)
Involuntary movement/increased muscle activity AFTER
a disturbance
fixed-support strategies:
- ankle
- hip
change-in-support strategies:
- step
- reach-to-grasp
Movement Strategies – Compensatory Postural Adjustments (CPA)
DEVELOPMENT:
Pre-sitting (as early as 1 month) infants show reactive muscle
responses to perturbations; timing variable
In standing, infants show postural response synergies from 2 to 18
months
From 4-6 years, reactive postural control more variable (growth
spurt)
7-10 years – reactive postural control is like adults
Movement Strategies – Anticipatory Postural Adjustments (APA)
Increased muscle activity PRIOR TO voluntary movement in anticipation
of a predicted disturbance
Dependent on prior experiences and are task dependent
Seen in the first year of life in sitting and reaching tasks
Other factors that impact it: emotions and position dependence
Cognitive Processing
Attentional demands impact postural control especially when the system is stressed
Cognitive task performance decreases when postural task difficulty increases
Postural task performance decreases when engaged in a cognitive task (but not
always…)
Key Components of Postural Control
biomechanical constraints
stability limits/verticality
anticipatory postural adjustments
postural responses
sensory orientations
stability in gait
Biomechanical Constraints
Strength
Range of Motion
Limited degrees of freedom
Strength =
Must be maintained to control joint movements smoothly
Necessary for reactions to loss of balance/perturbations
Range of Motion =
Helps to maintain ability to control COM
Improves ability to utilize available force of a muscle in a lengthened position
Limited degrees of freedom due to restrictions in movement (such as
bracing) =
Affects balance
Can lead to learned movement patterns
Reactive Postural Responses
Automatic, not voluntary:
- Cannot be completely suppressed
- Onset times are faster than cued/voluntary movement
Amenable to REHABILITATION:
- Clinical assessment
- Modifiable with experience/balance training
APAs are changes in the activity of postural muscles and associated
shifts in the ____
center of pressure (COP; point of application of ground reaction forces) prior to the initiation of action
ICF Domain – Body Function
Romberg/Sharpened Romberg Test
ICF Domain – Activity
Modified Clinical Test of Sensory Interaction on Balance (modified
CTSIB)
Mini/BriefBESTest
