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Balance-assessment-7.ppt
1. DR.MOHAMMAD SHAFIQUE ASGHAR
A U . D , ( U S A ) .
A M E R I C A N B O A R D O F A U D I O L O G Y ,
( B O A R D C E R T I F I E D A U D I O L O G I S T ) .
M . S C A U D I O L O G I C A L M E D I C I N E , ( U K ) .
M C P S ( E N T ) , M , B . B , S ( P B ) .
Balance Assessment
3. Introduction.
In mid 80’s after work done by Horak, Henry and
Shumway-Cook) the stress changed from ear to
Equilibrium.
Different tests were evolved to test the balance
function and recovery of astronauts after descent.
4. Introduction. (cont)..
CTSIB (clinical test for sensory integration of Balance)
CDP (Computerized Dynamic Posturography)
These tests were evolved to differentiate between ,
vest, visual, and central lesions.
Generally:
Vest lesions = 66%
Visual and CNS = 33%
5. Postural control system
1. Neural and musculoskeletal components, involved
in maintaining orientation in the environment.
2. Functions
a) Resist gravity
b) Background muscle tone
6. Postural equilibrium:
Condition in which all the forces acting on the body
are balanced such that the COG is controlled relative
to BOS.
7. Balance
An individuals ability to maintain their COG over
their BOS in a given sensory environment.
Skill the CNS learns to accomplish using multiple
interacting system, including passive
biomechanical elements, all available sensory
systems and muscles, and many different parts of
the brain. Equilibrium control is quite proactive ,
adaptive and centrally based upon prior experience
and intension. (Horak, Henry, and Shumway-
Cook).
8. Center of gravity
During erect standing with the arms at the side and
folded at the waist COG is located in the area of
lower abdomen.
In a normal person standing erect COG is placed
accurately above the center of base of support.
9. Base of support
The area contained within the perimeter of contact
between surface and the two feet.
10. Limits of stability
This is a two dimensional quantity defining the
maximum possible COG sway angle as a function of
sway direction from the center position.
11. System Model of Equilibrium.
A systemic approach to functional
balance/postural control involving
multiple interacting sensory and motor
components.
13. B: Central sensory organization
1. Process by which sensory information is correlated
and synthesized.
2. Normal sensory organization is necessary for
maintenance of balance.
3. During sensory conflict situation the brain must
quickly sensory inputs providing accurate
orientation information and ignore the misleading
information..
15. D: Central Motor response.
1. Postural strategies or synergies that;
a) Minimize sway,
b) Maintain the body’s COG within BOS
c) Control movement of COM over the BOS.
2. Reactive / Compensatory
3. Proactive / Predictive
4. CNS organized patterns of muscle activity that are
flexible, adaptable
16. D: Central motor responses (cont)…
5. Strategies are limited by internal/external
constraints
6. Responsive to learning and intention
7. Reflexes
a) Short latency (40-59 msec)
b) Stereotyped reflexes regulate muscle force in response to
external stimulus.
17. D: Central motor responses (cont)…
8. Automatic postural responses.
a) Reactivity/Compensatory
b) Elicited by external stimulus
c) Response matched to stimulus
d) Rapid short latency (70-180 msec).
e) Ankle strategy (fixed support).
f) Hip strategy (fixed support)
g) Stepping or compensatory Grasp strategies
(change in support).
18. D: Central motor responses (cont)…
9. Anticipatory postural responses.
a) Similar to automatic, but preparatory in nature
b) Proactive / Predictive responses.
c) Elicited by an expectation of disturbance of COG.
d) Onset of postural muscle activation in advance of
movement.
19. D: Central motor responses (cont)…
10. Volitional postural movements.
a) Movement patterns under volitional control.
b) Self-initiated or elicited by external stimulus.
c) No fixed relationship between stimulus and movement
pattern
d) Slower (180-250 msec).
21. Balance disorders can be due to…
1. The position of COG relative to the BOS is not
sensed accurately. ( Sensory function loss)
2. The automatic movements required to bring the
COG to a balanced position are timely or
effectively coordinated. ( Motor function loss)
23. Visual system.
Vision measures the orientation of eyes and head in
relation surrounding objects.
Vision plays a significant role in balance, especially
when the support surface is unstable.
24. Somatosensory system
Somatosensory input provides information on the
orientation of body parts relative to one another
and to support surface.
Somatosensory input is provided by:
Tactile, deep pressure , joint receptors and
muscle proprioceptors.
Somatosensory input from the contact forces and
motion between the feet and support surface is the
dominant sensory input to balance under normal
(fixed support) conditions.
25. Vestibular system
It does not provide input in relation to external
objects.
It measures gravitational linear and angular
acceleration of the head in relation to inertial space.
26. Vestibular system (cont)…
When functionally useful somatosensory and
visual inputs are available vestibular inputs plays
plays a minor role in controlling COG. This is
because somatosensory and visual inputs are more
sensitive to body sway than the vestibular system.
Vestibular input becomes more important in cases
of misleading visual or somatosensory inputs.
27. Utilization of sense of Balance
Sense Reference Conditions favoring
the Use
Conditions
disrupting Use
Somatosen
sory
Support surface Fixed support surface Irregular or moving
support
Visual Surrounding
objects
Fixed visible
surrounds
Moving
surrounds/darkness
Vestibular Gravity and
inertial space
Irregular or moving
support and moving
surrounds or darkness
Unusual motion
environment.
28. Motor control of Balance
There are principle joint systems involved
between the BOS and COG
1. Ankle
2. Knee
3. And hip
29. Anatomy of physiology of Movements
Generally the motion about a joint is controlled
by the combined action of at least one pair of
muscles working in opposition.
Many leg muscles act on two different joints.
31. Properties of three Movement systems
Movement systems
Property Reflex Automatic Voluntary
Mediating Pathways Spinal cord Brainstem and
subcortical
Brainstem and
cortical
Mode of activation External
stimulus
External
stimulus
Self generated or
external stimulus
Response properties Localized to
point of
stimulus
and highly
stereotyped
Coordinated
among leg and
trunk muscles,
and stereotyped
but adaptable
Limitless variety
32. Properties of Movement systems (cont)…
Movement systems
Property Reflex Automatic Voluntary
Role in posture
control
Regulate
muscle
forces
Coordinate
movements
across joints
Generate
purposeful
behaviors
Response times Fixed at
40 msec
Fixed at 100
msec
Varies with
difficulty,
150+ msec
33. Coordination of postural movements into
strategies.
When a persons balance is disturbed by an
external perturbation, one or combination of
three different strategies can be used to
coordinate movement of COG back to balanced
position
34. Strategies used are….
1. Ankle strategy
2. Hip strategy
3. Stepping strategy.
A step or stumbling reaction is the only movement
strategy effective in preventing a fall when the
perturbation displaces the COG beyond the LOS
perimeter.
35. Strategies (cont)…
In case the COG remains within the LOS, two
strategies (Ankle and Hip) or combination of both
is used to move the COG while maintaining the
initial placement of the feet on the support surface.
A step or stumbling reaction is the only movement
strategy effective in preventing a fall when the
perturbation displaces the COG beyond the LOS
perimeter.
36. Ankle strategy
The ankle strategy shifts the COG while
maintaining the placement of the feet by
rotating the body as an approximate rigid mass
about the ankle
Latency of the response is 90-100 msec.
37. Hip strategy
The movements are centered at hip joint.
The COG shifts in the direction opposite to the hip
because of the inertia of the trunk (moving in one
direction), generating an opposite horizontal (shear)
reaction force against the support surface.
Latency f the response is 85-95 msec.
38. Appropriate use of Postural movement strategies.
The relative effectiveness of ankle, hip and
stepping strategies in repositioning the COG over
BOS depends upon:
i. Configuration of BOS
ii. Cog alignment in relation to LOS
iii. And speed of postural movement.
39. Ankle strategy
Most effective in executing in relatively slow COG
movements, when the BOS is firm.
And COG is well within the LOS. It also helps in
maintaining static posture with COG offset from
center.
40. Ankle strategy: Limitations
The amplitude and speed of the ankle
movements are biomechanically limited by the
torque that can be exerted about the ankle
before the feet lift off from the support surface.
41. Hip strategy
Hip strategy is effective when COG is positioned near
the LOS perimeter.
And when LOS boundaries are contracted by
narrowed BOS.
Hip strategy rely on the horizontal shear force. And
so is not limited by the ankle torque.
42. Hip strategy: Limitations
They can not produce larger shifts in COG.
Because hip strategy rely on inertial reaction forces ,
they can not be used to maintain balance effectively
with the COG offset from the center.
43. Stepping strategy
When COG is displayed beyond the LOS , a step or
stumbling reaction is the only movement strategy
effective in preventing a fall.
44. Stepping Strategy: Limitations
Stepping strategy has fewer biomechanical
limitations, it is inefficient, disruptive and usually
inappropriate, when simpler ankle and hip
movements are effective.
45. Selecting a Postural strategy
It depends upon the persons past experience
and not the conscious decision.
46. Coordination of Head and Body Movements
During standing position the movement of the
head relative to trunk has a minor effect as mass of
the head is substantially smaller than the trunk.
But during motion of head during postural sway is
important , because they have strong influence on
two of the two of the three principle senses of
balance: Vision and vestibular system.
48. Coordination of Head and Body Movements
These can be classified into.
1. Trunk fixed
2. Gravity fixed
3. Combination of both.
49. Trunk fixed strategy
The head and trunk move as a unit.
Thus the strategy fixes the movements of the head
relative to the trunk.
50. Gravity fixed
This strategy rotates the head in opposite to the
trunk so that the head remains level relative to the
gravitational vertical.
51. Interaction between
Sensory & Motor Components of Balance
The pattern of ankle, knee, hip and head
movements strongly influence the visual and
vestibular inputs to balance.
52. In Normal Individuals
Movements of the head and body are coordinated
when a hip strategy is used, during in place
standing and when running jumping and hopping.
During these movements head is approximately
stabilized relative to gravitational vertical.
The motions of the head and body are coordinated
at automatic level of control.
53. In Vestibular disorder Patients
Patients with bilateral loss of vestibular system
inputs avoid hip movements under all conditions
even though they have no motor defects that impair
their hip movement control
These patients also tend to fix the position of the
head relative to the trunk.
54. Patients with Somatosensory inputs
Patients deprived of somatosensory input from the
feet by transient ischemia prefer hip strategy under
all support surface conditions even though the
sensory loss does not impair their ability to execute
ankle movements.
55. Interaction between
Sensory & Motor Components of Balance
During complex movements the COG position is
more difficult to determine from vestibular and
visual input.
This process is simplified by the stabilizing the
position of the head relative to the gravity.
56. Conclusion
Balance is a multi-component and highly adaptable
control process.
When the balance of a healthy individual is
challenged:
The sensory inputs determine the COG position and the
pattern of movement correcting the perturbation
It depends upon the task conditions and the persons
immediate past experience.
