Control of Posture and Balance Flashcards
What is the interaction btw research and clinical practice?
What is feedforward vs feedback control of posture?
Feedback control: automatic responses triggered by stimuli
Feedforward control: prior experience and current condition determine movt strategy
balance control schema
what systems does balance emerge from/interact with?
Define: orientation vs equilibrium
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)
Define: base of support
Base of Support (BoS)
Area contained within the perimeter of contact between the support surface and the body
Define: com/cog and where it is
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
Define centre of pressure
- 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
when does com=cop?
only when object is absolutely stationary
com - 3d, cop = 2d
what is bigger cop or cog?
ØDynamic range of CoP must be greater than CoG for safety reasons
describe body sway for normal adults with eyes open vs closed
- Sways confined to ap direction w eyes closed bc ankles are more able to move that direction
define: limit of stability
Largest possible sway without losing control or changing stance configurations
Changes depending on various factors like task, individual characteristics, base of support etc.
what is the general goal of postural control/balance and what abilities are required to accomplish this goal?
goal: Control the CoG relative to the BoS for any perturbation and during any task
Requires the ability to:
- Detect changes in CoG (sensory processes)
- Move CoG (motor processes)
- Perceive LoS (sensorimotor integration)
what 3 strategies are used in stance postural control?
Sensory
Sensorimotor
Attentional (cognitive)
- with goal to minimize loss of balance due to displacement of body CoG following internal or external perturbations
What is proactive vs reactive control?
proactive = anticipatory: Internal perturbations due to body movements: voluntary vs involuntary
reactive = triggered: External perturbations due to changes in the environment: expected vs unexpected
describe current thoughts on movement strategies - are they reflexive or voluntary? name 3 movement strategies
- 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
what is an in-place strategy?
one in which feet stay in place
describe the ankle strategy
describe hip strategy
what is used more, ankle or hip strategy?
- 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
describe steping strategy
- 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
describe the role of the sensory systems wrt postural control
- 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
describe specifically the role of vision on postural control
describe specifically the rold of the somatosensory system on postural control
what is the most heavily weighted sensation under average tasks and environmental conditions?
proprioception
describe specifically the vestibular system wrt postural control
note:
- 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)
what sensory system provides the only non-ambiguous reference for postural orientation during stance on earth?
the vestibular system
what sensory system detects acceleration and which detects velocity?
acceleration = vestibular, velocity = visual
selection of sensory strategies within the indivisual depend on what?
explain the results of the sway experiment (using the 3 sensory cues)
explain the results of the sway experiment (using the 3 sensory cues) - comparing older adults to younger
- Why do we see that as people are older, increased risk of fall?
describe the functional reach test
- instructing the patient to reach as far as they can without taking a step
- forward, back, left and right measured
describe the berg balance scale
describe the BEST-test - what 6 things it measures
I.Biomechanical Constraints
II.Stability Limits / Verticality
III.Anticipatory Postural Adjustments
IV.Postural Responses
V.Sensory Orientation
VI.Stability in Gait
describe the mini-best test - what is the cutoff score for identifying falling risk
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).
what are the limitations to functional balance tests and measures?
- 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
what is the task-oriented approach to retrain postural control?
- Resolve, reduce or prevent impairments important to balance
- Develop & train effective task-specific strategies (sensory, motor & cognitive)
- Retrain functional tasks with varying postural control demands & under changing environmental contexts
describe how to address task 1. of the task-oriented approach(Resolve, reduce or prevent impairments important to balance (intervention at the Impairment Level))
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)
describe the clinical decision-making tree to illustrate the treatment planning process in balance rehabilitation.
describe how to address task 2. of the task-oriented approach (2.Develop & train effective task-specific strategies)
Work on exercises/activities to improve: Movement strategies, Sensory strategies, & Cognitive strategies
describe movement strategies (task 2)
describe sensory strategies (task 2)
describe cognative strategies (task 2)
describe some dual and singal task conditions
describe step 3 of the task-oriented approach to retrain postural control (Retrain functional tasks with varying postural control demands & under changing environmental contexts)
