Control of Posture and Balance

Question 1

What is the interaction btw research and clinical practice?

Answer 1

Question 2

What is feedforward vs feedback control of posture?

Answer 2

Feedback control: automatic responses triggered by stimuli

Feedforward control: prior experience and current condition determine movt strategy

Question 3

balance control schema

Answer 3

Question 4

what systems does balance emerge from/interact with?

Answer 4

Question 5

Define: orientation vs equilibrium

Answer 5

Orientation

Appropriate alignment of body segments with respect to each other and with reference to the environment

Equilibrium

State in which all the forces acting through all the joints are balanced at the body center of mass (CoM) or center of gravity (CoG)

Question 6

Define: base of support

Answer 6

Base of Support (BoS)

Area contained within the perimeter of contact between the support surface and the body

Question 7

Define: com/cog and where it is

Answer 7

CoM/CoG

• Theoretical point in space at which the entire mass of the body is balanced and the resultant of external forces act upon located ~ 2 cm anterior to L2
• for symmetrical objects can draw a vertical and horizontal line and that = com

Question 8

Define centre of pressure

Answer 8

• Summed focal point of all downward forces in the horizontal plane
• Origin of the ground reaction force (GRF)

ØCoP reflects neuromuscular response to imbalance of CoG

ØCoP controls the CoG

ØDynamic range of CoP must be greater than CoG for safety reasons

Question 9

when does com=cop?

Answer 9

only when object is absolutely stationary

com - 3d, cop = 2d

Question 10

what is bigger cop or cog?

Answer 10

ØDynamic range of CoP must be greater than CoG for safety reasons

Question 11

describe body sway for normal adults with eyes open vs closed

Answer 11

• Sways confined to ap direction w eyes closed bc ankles are more able to move that direction

Question 12

define: limit of stability

Answer 12

Largest possible sway without losing control or changing stance configurations

Changes depending on various factors like task, individual characteristics, base of support etc.

Question 13

what is the general goal of postural control/balance and what abilities are required to accomplish this goal?

Answer 13

goal: Control the CoG relative to the BoS for any perturbation and during any task

Requires the ability to:

1. Detect changes in CoG (sensory processes)
2. Move CoG (motor processes)
3. Perceive LoS (sensorimotor integration)

Question 14

what 3 strategies are used in stance postural control?

Answer 14

Sensory

Sensorimotor

Attentional (cognitive)

• with goal to minimize loss of balance due to displacement of body CoG following internal or external perturbations

Question 15

What is proactive vs reactive control?

Answer 15

proactive = anticipatory: Internal perturbations due to body movements: voluntary vs involuntary

reactive = triggered: External perturbations due to changes in the environment: expected vs unexpected

Question 16

describe current thoughts on movement strategies - are they reflexive or voluntary? name 3 movement strategies

Answer 16

• simplified by stereotyped patterns or strategies
• selected in advance of movement and based on prior experience (influenced by central set)

automatic - but not reflex nor voluntary

• TPR typical latency 100-150 ms, too long for simple stretch reflex but too short for voluntary; directionally specific
• inter-segmental timing is crucial
  1) ankle strategy, 2) hip strayegy, 3) stepping strategy

Question 17

what is an in-place strategy?

Answer 17

one in which feet stay in place

Question 18

describe the ankle strategy

Answer 18

Question 19

describe hip strategy

Answer 19

Question 20

what is used more, ankle or hip strategy?

Answer 20

• ankle bc vestibular system is in the head and don’t want to move head too much, therefore hip strategy not used as much… ankle strategie used the most (keeps vestibular system stable)
• note ankle and hip strategies do not operate separately

Question 21

describe steping strategy

Answer 21

• Used when in-place strategies are not sufficient in balance recovery
• Involves taking a step or reaching in order to increase BoS to re-align CoG within the BoS
• Employed when CoG is displaced out of BoS or when CoG is displaced rapidly

Question 22

describe the role of the sensory systems wrt postural control

Answer 22

• Goal: to “sense” position of CoM relative to current conditions (environment, task, etc)
• CNS combines and ‘weights’ sensory information from vision, vestibular and somatosensory sources
• No one sense can give us appropriate information in all tasks and in all environments

Question 23

describe specifically the role of vision on postural control

Answer 23

Question 24

describe specifically the rold of the somatosensory system on postural control

Answer 24

Question 25

what is the most heavily weighted sensation under average tasks and environmental conditions?

Answer 25

proprioception

Question 26

describe specifically the vestibular system wrt postural control

Answer 26

note: ## Footnote * Visual, proprioceptive and vestibular sensory feedback provide redundant information about body position in space * Vestibular input provides the only absolute body orientation reference * Yet, vestibular input (unlike other senses) does not project to conscious levels * Thus, vestibular dysfunctions can only be perceived via visual and proprioceptive senses (ataxia, vertigo, blurred vision) as well as autonomic projections (nausea, vomiting)

Question 27

what sensory system provides the only non-ambiguous reference for postural orientation during stance on earth?

Answer 27

the vestibular system

Question 28

what sensory system detects acceleration and which detects velocity?

Answer 28

acceleration = vestibular, velocity = visual

Question 30

selection of sensory strategies within the indivisual depend on what?

Answer 30

Question 31

explain the results of the sway experiment (using the 3 sensory cues)

Answer 31

Question 32

explain the results of the sway experiment (using the 3 sensory cues) - comparing older adults to younger

Answer 32

Question 33

- Why do we see that as people are older, increased risk of fall?

Answer 33

Question 34

describe the functional reach test

Answer 34

- instructing the patient to reach as far as they can without taking a step - forward, back, left and right measured

Question 35

describe the berg balance scale

Answer 35

Question 36

describe the BEST-test - what 6 things it measures

Answer 36

I.Biomechanical Constraints II.Stability Limits / Verticality III.Anticipatory Postural Adjustments IV.Postural Responses V.Sensory Orientation VI.Stability in Gait

Question 37

describe the mini-best test - what is the cutoff score for identifying falling risk

Answer 37

Good psychometric properties\*: High reliability & validity Less floor & ceiling effect (compared to Berg); Good responsiveness & sensitivity to change MIC (Minimal important change) – 4 pts in MiniBEST (vs. 7 in Berg) Maybe more useful in detecting milder or subtler balance problems; sensitivity/specificity higher than Berg Scores of \<19 or 20 implies higher risk of falling. Possible cut-off score of 20/28 to identify fallers (study with Parkinson’s Disease).

Question 38

what are the limitations to functional balance tests and measures?

Answer 38

* Few measures examine all three aspects of postural control * Most tests provide little insight into quality of movement * Most tests provide no way to identify specific neuronal or musculoskeletal subsystems responsible for a decline in performance

Question 39

what is the task-oriented approach to retrain postural control?

Answer 39

1. Resolve, reduce or prevent impairments important to balance 2. Develop & train effective task-specific strategies (sensory, motor & cognitive) 3. Retrain functional tasks with varying postural control demands & under changing environmental contexts

Question 40

describe how to address task 1. of the task-oriented approach(Resolve, reduce or prevent impairments important to balance (intervention at the Impairment Level))

Answer 40

1) Work to correct impairments that can be corrected or improved (resolve or reduce) 2) Prevent worsening or the development of secondary impairments - address orientation, alinment, or posutre - address other impairments they might have such as ROM, strength, flexibility, or tone - look at compensations and adaptations (using a walking aid for example)

Question 41

describe the clinical decision-making tree to illustrate the treatment planning process in balance rehabilitation.

Answer 41

Question 42

describe how to address task 2. of the task-oriented approach (2.Develop & train effective task-specific strategies)

Answer 42

Work on exercises/activities to improve: Movement strategies, Sensory strategies, & Cognitive strategies

Question 43

describe movement strategies (task 2)

Answer 43

Question 44

describe sensory strategies (task 2)

Answer 44

Question 45

describe cognative strategies (task 2)

Answer 45

Question 46

describe some dual and singal task conditions

Answer 46

Question 47

describe step 3 of the task-oriented approach to retrain postural control (Retrain functional tasks with varying postural control demands & under changing environmental contexts)

Answer 47

Answer 140