Week 5

Question 1

What is Balance? (aka Postural Control, in humans)

Answer 1

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

Question 2

Postural Control

Answer 2

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

Question 3

Postural stability:

Answer 3

ability to control the center of mass (COM) in relationship
to the base of support (BOS)

Question 4

Postural orientation:

Answer 4

ability to maintain an appropriate relationship between
the body segments, and between the body and the environment for a task

Question 5

Definition: Center of Mass (COM)

Answer 5

The point through which the vector of the total body weight passes

Children have a higher COM (top heavy)

Question 6

Base of Support (BOS)

Answer 6

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

Question 7

Postural Control is Context Specific

Answer 7

Posture demands
change based on tasks
in different
environments

Question 8

Orientation in Space

Answer 8

Alignment of head/trunk to gravity, surface, or visual environment

Question 9

Biomechanical Constraints

Answer 9

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)

Question 10

Sensory Strategies

Answer 10

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

Question 11

Visual Motion:

Answer 11

World moving
or self moving

Question 12

Vestibular/ Inner Ear:

Answer 12

Linear acceleration or
head tilt

Question 13

Surface Proprioception:

Answer 13

Surface tilt or body sway

Question 14

Surface/Environment Dependent

Answer 14

stable surface:
somatosensory = 70%
vestibular = 20%
vision = 10%

unstable surface:
somatosensory = 10%
vestibular = 60%
vision = 30%

Question 15

Age Dependent

Answer 15

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

Question 16

Stability limits

Answer 16

Vary according to task/individual/environment

Must consider both position AND velocity of COM relative to stability limits

Question 17

What do we do to counter a shift in equilibrium?

Answer 17

Compensatory
(reactive) Postural
Control

Anticipatory
(proactive) Postural
Control

Question 18

Movement Strategies – Compensatory Postural Adjustments (CPA)

Answer 18

Involuntary movement/increased muscle activity AFTER
a disturbance

fixed-support strategies:
- ankle
- hip

change-in-support strategies:
- step
- reach-to-grasp

Question 19

Movement Strategies – Compensatory Postural Adjustments (CPA)
DEVELOPMENT:

Answer 19

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

Question 20

Movement Strategies – Anticipatory Postural Adjustments (APA)

Answer 20

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

Question 21

Cognitive Processing

Answer 21

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…)

Question 22

Key Components of Postural Control

Answer 22

biomechanical constraints

stability limits/verticality

anticipatory postural adjustments

postural responses

sensory orientations

stability in gait

Question 23

Biomechanical Constraints

Answer 23

Strength
Range of Motion
Limited degrees of freedom

Question 24

Strength =

Answer 24

Must be maintained to control joint movements smoothly

Necessary for reactions to loss of balance/perturbations

Question 25

Range of Motion =

Answer 25

Helps to maintain ability to control COM

Improves ability to utilize available force of a muscle in a lengthened position

Question 26

Limited degrees of freedom due to restrictions in movement (such as
bracing) =

Answer 26

Affects balance

Can lead to learned movement patterns

Question 27

Reactive Postural Responses

Answer 27

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

Question 28

APAs are changes in the activity of postural muscles and associated
shifts in the ____

Answer 28

center of pressure (COP; point of application of ground reaction forces) prior to the initiation of action

Question 29

ICF Domain – Body Function

Answer 29

Romberg/Sharpened Romberg Test

Question 30

ICF Domain – Activity

Answer 30

Modified Clinical Test of Sensory Interaction on Balance (modified
CTSIB)

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