Postural Balance Flashcards
What is balance?
Ability to maintain gravity line of body within base of support with minimal postural sway
What is sway?
Movement of CoM in the transverse plane, even when standing still
How does human body behave in the quiet stance?
Acts as a inverted pendulum
What are the 3 main categories of determinant factors for postural control?
Subject
Environmental Context
Task
What are the expended determinant factors for postural control?
Adaptive mechanism Anticipatory mechanisms Sensory strategies Individual sensory systems Neuromuscular synergies Musculoskeletal components Internal representations
What are the 3 sensory input systems involved in postural control?
Visual System
Vestibular System
Somatosensory System
What are the pathways in postural control?
Visual, Vestibular & Somatosensory > CNS integration in (brain) > motor command and CNS integration in (body) > body carries out movements > constraints information carried back to 3 sensory systems
How is sway measured?
COM: Motion capture system
CoP: Force platform
What is the difference between CoM and CoP in measuring postural sway?
CoM excursion is gold standard truly represents,
CoP is measure of activity of motor system in moving CoP > neuromuscular response to CoM displacement (not true record of body sway)
What happens during quiet standing and body is acting like an inverted pendulum?
If Wg > Rp, body will have clockwise angular acceleration (forward sway)
Subject will increase CoP to correct it (plantarflexion activation)
Now Rp > Wg, backward sway
Decreasing of CoP > decrease plantarflexion activation
COP range > CoM range
What are the parameters measured in postural sway measurement?
Time domain: Excursion, range, speed, standard deviation, root mean square, 95 CI eclipse area
Nonlinear: Fractal dimension, entropy
Frequency: Fourier analysis
What is the protocol for a postural sway test?
Barefoot
Standing in the upright position as still as possible
Upper limbs relaxed at the side of the body
Natural support area: approximately 3-5 cm between the heels and 20-25 cm
between the toes (variation: single-leg & tandem stances)
Duration: 20 to 30 seconds each trial (variation: up to 60s)
3 to 5 trials eyes open (EO condition); 3 to 5 trials eyes close (EC condition)
Data collected at 50Hz (variation: 100 to 200Hz)
In a one leg stance test, how is the dominant leg determined?
Ball kick test
Step up test
Balance recovery test
At least 2/3 of 3 tests
What are automatic postural responses?
Reactive movements to maintain one’s balance after perturbation
What are 3 strategies of maintaining balance?
Ankle, hip, stepping
When is ankle strategy used? How is it used?
Quiet stance or secondary to small perturbations
Normal support surface
Muscle activity (distal to proximal) initiated at ankle, radiating to thigh and abdominal muscles > producing torque in ankle
When is hip strategy used?
Moderate perturbation OR support surface narrow relative to base of support, OR direct perturbation to pelvis
Ankle strat not effective because support surface too small
Muscles activated proximal to distal direction
When is stepping strategy used?
When lower limb and torso cannot maintain CoM within base of support
Step increases base of support or realigns it
Describe the mixed strategy of maintaining balance (automatic postural responses)
Sensory information measured by Multi Sensory Signals (3 sensory inputs) > sent to CNS process > Estimated body kinematics > appropriate control plans selected > motor commands produced as joint torques
Describe the control mechanism: anterior posterior (ankle muscle control)
Difference between COP and COM is proportional to horizontal acceleration of COM
Describe the control mechanism: medial-lateral (load/unload mechanism)
COPc (ankle mech) and COPv (load mech) are independent of each other
What are the conditions that increase body sway?
Aging, neurological diseases (parkinsons) fatigue Muscle-skeletal conditions (osteoperosis) Dementia diseases (alzeihmer's disease) Poor physical fitness Poor vision
What did systematic review and meta analysis of Balance training reveal?
There’s a dose-response relationship.
BT > effective means to improve steady state and proactive balance
Duration: 11-12 weeks
Training frequency: 3x/week
Duration: 10-15 min / session
Amt of exercises: 4ex / session, 2 sets / exercise, 20-40s /exercise
What are the findings in terms of balance training to unlearned balance task?
Balance training is task specific
Slackline training intervention > flamingo and slackline balance task pre and post training > flamingo & slackline standing time increased significantly
BUT effect size 3x larger in slackline & body balance improvement pre v post only in slackline task
