Postural Control

Question 1

postural control

Answer 1

the controlling of the body’s position in space

Question 2

3 goals of postural control

Answer 2

1. to support the body against gravity
2. to maintain the centre of mass aligned and balanced your base
3. to stabilise parts of the body while moving other parts

Question 3

base of support (BOS)

Answer 3

the area defined by the points of contact b/w the body and environment

Question 4

centre of mass of body (COM)

Answer 4

a point in space where there is equal amounts of body mass on all sides

the location of the COM changes w/ movement (at S2 in standing)

the COM does not need to be located on the body

Question 5

limits of stability (LOS)

Answer 5

the perimeter of the BOS beyond which we cannot maintain balance, how far the body’s COM can be moved over the BOS

Question 6

Postural sway

Answer 6

• small movements of the body mass which occur when unsupported (standing, sitting)
• it is normal to have some postural sway
• you can use the trunk motion to measure postural sway

Question 7

muscles controlling anterior/posterior sway

Answer 7

gastrocs/soleus

and

tibialis anterior

Question 8

how come there is more postural sway when standing on 1 leg vs. 2 legs?

Answer 8

because base of support is reduced

Question 9

adding a finger for support in 1-legged standing decreases postural sway why?

Answer 9

• increases base of support
• increases proprioception

Question 10

to retrain standing balance you need to remove base of support(s) from….

Answer 10

upper extremities

Question 11

postural sway - aging

Answer 11

the amount of sway is increased in the elderly and is related to fall risk

Question 12

postural sway - clinical populations

Answer 12

the amount of sway is increased in some pathological conditions (cerebellar disease, stroke) and is related to fall risk

Question 13

anticipatory postural adjustments= proactive postural control

Answer 13

• we used to think that balance was maintained by feedback control
• today we know that feedback systems are too slow, and anticipatory postural control is enabled by feedforward control

Question 14

feedback control

Answer 14

signals for sensors are compared w/ the desired position/movement; the difference or error signal, is used to adjust the movement

Question 15

feedforward control

Answer 15

predicts the disturbances and produces actions to maintain stability using prior experience to make a “best guess” action

Question 16

anticipatory postural control

Answer 16

pre-setting sensory and motor systems in expectation of postural demands; anticipatory postural control is based on previous experience and learning

feedforward control as you move making your best guess as to what will be required based on past experience

Question 17

examples of anticipatory postural control

Answer 17

• arm raise while standing
• opening/pulling on a door
• rising on toe
• stepping over an obstacle

Question 18

how is center of mass being moved during raising arms in flexion?

Answer 18

• centre of mass moves forward when lifting arms into flexion forward
• compensation occurs by moving centre of pressure backwards (example: plantarflexion by gastrocs planting toes into ground)
  -> abdominal muscles, and erector spinae act as stabilizers too

Question 19

reactive postural control

Answer 19

• postural responses
• definition: responses to an unanticipated external perturbation= feedback control
• movement strategies: used to recover from a brief displacement of the supporting surface; they used moving force platforms and found 3 movement strategies in normal subjects

Question 20

postural responses are triggered by 3 types of sensory inputs

Answer 20

1. somatosensory system
   - muscle proprioceptors: muscle spindles (sense length); golgi tendon (sense force and length)
   - joint receptors
   - cutaneous receptors (skin)
2. vestibular receptors that sense sway through head motion
3. visual input that detect motion in the visual field

Question 21

all 3 inputs (proprioceptive, visual, vestibular) influence “quiet” standing balance:

Answer 21

• proprioceptors respond the fastest
• vestibular responses most important w/ eyes closed and the head rotates
• the body is slow to respond to visual cues

Question 22

slower reflexes…

Answer 22

contribute to falls

Question 23

reactive movement strategies

Answer 23

1. ankle strategy
2. hip strategy
3. stepping strategy

Question 24

falls (unsuccessful reactive control)

Answer 24

• 1 in 3 persons over the age of 65 and 1 in 2 persons over 80 experience a fall
• in elderly population, serious injuries occur in approximately 1/4 of these falls
• by 2030, seniors could represent from 21.4% to 23.4$ of the total Canadian population
• the prevention of falls should be a problem which clinicians address
• the incidence of falls is even higher in many neurological disorders; e.g. individuals w/ Parkinson’s disease or stroke have a high frequency of falls and hip fracture

Question 25

clinical assessment of balance done via...

Answer 25

1. berg balance scale (a score less than 46 is considered at risk for falls; has a high ceiling effect; inter-rater (between different physiotherapists) is low, intra-rater reliability (same physio and patient but on different occasions) is better) - not sufficient for those w/ concussions, athletes w/ a lower limb injury, adults w/ impaired balance but not quite as elderly 2. functional reach test (how far can a subject reach forwards w/o taking a step and keeping feet flat on floor-> score less than 6 or 7 inches indicates limited functional balance) 3. activities-specific balance confidence scale (ABC) 4. Community Balance and Mobility Scale (used in place of Berg balance scale for higher functioning individuals)

Question 26

fear of falling and balance confidence

Answer 26

- may develop fear due to a fall or near fall - fear of falling may restrict participation in everyday activities - enhancing confidence may need to be treated as much as the actual balance function