Lecture 19: Age-related changes to balance and gait Flashcards
Age-Related slowing exists for:
- reaction time
2. movement rime
reaction time becomes ___ to initiate
slower
movement time has a ___ duration
prolonged (longer execution times)
the greater the complexity of the movement, the more likely ____ increases in older vs younger adults
reaction time increases
Musculoskeletal/Biomechanical constraints
- strength (force production) at ankles, hips, trunks, UE
- ROM (kinematic degrees of freedom) at neck, trunk, knees, ankles
stability limitations
the boundary of the base of support within which the center of mass sways
-combining strength, ROM, foot size, and structure to maintain the CM within the BOS
___ stability limits are reported to be decreased in older adults
functional
Romberg =
feet together
Sharpened Romberg EO =
tandem stnace
Standing one-leg test results
age 60-69 mean: 27s
age 70-79 mean: 17.2s
age 80-89 mean: 8.5s
Younger adult postural sway
more up and down (A/P) direction compared to older adult
Non-faller vs faller postural sway
- general increased sway with BoS configuration and age
- Notice ML COP amplitude in adults who fall compared AP amplitude
- Older adults who fall sway disproportionately in the ML direction compared to their same age counter-parts who don’t have a history of falls that sway in a more AP direction & younger-adults
Older adults tend to stand more ___
asymmetrical
older adults exhibited a statistically significant increase in asymmetry under an ___ condition
eyes-closed
- the difference is also significantly greater than that observed in younger-adults
- how functional is this? ; probably not a lot
Postural sway summary (older adults)
- increased amounts of postural sway are linked to increase risk of falling
- increased sway in ML direction may be special to increased risk of falling, poorer performance on balance scales and age-related disease
postural control implies an ability to maintain:
balance during:
- voluntary movements (proactive) and
- in response to an external perturbation (reactive)
A movement before movement
Well in advance
“get stable before movement”
-example: going to gran a railing before climbing stairs (widens base of support, dont need to activate all muscles needed)
Anticipatory postural adjustments (APAs)
-anticipate voluntary movement
-precede voluntary movement
- a couple of milliseconds
Examples:
-arm
-trunk bend; posterior muscles of the leg & back fire before the anterior deltoid when it comes to reaching
-step
autonomic postural responses
corrective postural response or protective postural response
What is needed to initiate a voluntary step?
- an APA is needed
Step initiation in older adults
- increased reaction time
- greater difference (increaase) in weight transfer time in older vs younger adults
- directional differences
- greater weight transfer time poses a greater challenge to rapid stepping than reaction time alone
Over-simplified view of the hierarchy of postural responses
corrective vs protective change is BOS strategy
corrective: not changing BOS
Protective: BOS changes
Older adults step more than younger adults
-older adults (fallers) step at lower perturbation and take multiple steps
Pardoxically, older adults very step very fast
liftoff times in OA are as fast (nonfallers) or faster (fallers) than YA following external mechanical perturbation
what makes older adults step faster?
-theres no APA when you get pulled off balance
how is the faster step moving differently?
-move steps higher frequency at termination because stance is not stable at termination
Older Adult fallers’ stepping responses are different
Fallers: lateral foot placement
non-fallers/young adults: medial foot placement
lateral stepping in response to lateral perturbation (younger adults)
-lateral step with direction of perturbation
lateral stepping in response to lateral perturbation (older adults)
- cross over step (B)
- medial step with contralateral (unloaded side first)
- more common in OA w/ history of falls
Lateral Stepping in Response to Perturbation (summary)
When pulled, a side-step is more common in younger adults. But a
crossover step can happen without incident. Older adults often use a
crossover step but there is an increase in limb collision during a crossover
step. This increases the likelihood of falling. Older adult fallers tend
towards a medial step with the unloaded LE first. This usually means that
multiple steps are needed to regain balance and the older adult may be
unstable at step termination.
Posterior stepping tresholds
- older adults who reported a fall had significantly reduced posterior stepping force thresholds
- at home falls (fallers) were associated with reduced posterior and lateral force thresholds
automatic postural responses (protective stepping) summary
Protective stepping is different in older adults
- initiate a protective step as fast or faster than younger adults
- take multiple steps
- more laterally-directed steps when pulled forward
- latter issues more likely to occur in older adults who have a history of falling
- cross-over or medial step (with unloaded leg) for lateral perturbations in older adults. the medial then lateral step seems to be used a lot by older persons who fall
visual changes in older adult
reduced acuity, contrast sensitivity, depth perception, dark adaptation
vestibular changes in older adult
-progressive loss of labyrinthine hair cells, vestibular ganglion cells, and nerve fibers
somato-sensation changes in older adulthood
reduced propioception, touch sensitivity, two-point discrimination, and vibration sense
fancy way to challenge balance by altering sensory orientation/use
sway-referencing
-forcing the vestibular system to be tested
Postural sway by “sensory” condition
Effectors (neuromusculoskeletal machinery) age associated changes
- unlikely that typical-age related changes in the effector system will immobilize a person
- Effector changes: strength decline, tissue property of tendons and ligaments, mass distribution, body posture due to skeletal changes, muscle properties like fatigability
-effector changes may influence distance traveled, time it takes to travel, and types of terrains that can be traveled
safe walking speed is
1.2 m/s
walking speed you need to get across a busy street safely
1.2-1.4 m/s
older adults have ___ gait speed
decreased
older adults tend to have ___ stride lengths and ___ time in double limb supprt
- shorter stride lengths
- increased time in double-leg support
kinematics and kinetics of older adult (gait)
- generally less ROM at pelvis, hip, knee ankle
*2. PF less power (PF push off problem)
*3. Less hip extension is particularly common
- later part of stance phase –> less push off –> reduced propulsive power –>
slower gait
comfortable gait speed 60-69
1.24m/s
comfortable gait speed 70-79
1.25m/s
comfortable gait speed 80-89
0.82 m/s
comfortable gait speed 90-101
0.71m/s
older adults have more ___ head movement (less rhythmical) especially over irregular terrain
more variable head movement
Stride width tends to be __ in older adults
- greater
- variability is also greater
- too much or too litle step-wish variability is associated with falls; association doesn’t exist for older adults who walked <1 m/s
stride to stride variability may be due to
choosing a more cautious gait
- slower walking is associated with greater variability anyway (regardless of age)
- age associated changes in variability may be accounted for by loss of strength or ROM. Thus, the problem may be due to a loss of something rather than simply due to aging
stability during self-imposed (internal) perturbations: head turning while walking
older adults may limit isolated movmeent of the head suggesting a modified motor pattern for head turning
older adults require __ to regain balance during perturbed walking, yet:
more steps
-older adults are capable of reactively adapting their gait to improve their stability following repeated gait perturbations (similar to Younger adults)
which is more critical for balance recovery during walking: rate of torque development or available strength
rate of torque production; however, magnitude and rate of development of muscle activity in older adults is lower than younger adults
Selecting an avoidance strategy
- is well preserved
- younger adults transition from going over to going around
- older adults more variable, and given the choice, tend to go around instead of over
older adults have greater difficulty modulating step length to an environmental cue when the cue is given within one step duration ahead
may be harder to shorten step than lengthen step for older adults
Dual task increases ___
obstacle contact
