Lecture 15: Age Related Changes

Why is postural development important?

Because the immature postural system is the hypothesized limiting factor for the emergence of other skilled behavior

""Motor milestones" reflect ________

Development of postural control

T/F: Development of skilled behavior follows a distinct linear pattern

False!

Time frames are just guesses, they are not definite (lots of variability)
Also, it is possible that as they progress to other skills, they may regress previously attained skills (temporarily)

What is the "motor milestone" at ~1 month?

Lifting head

What is the "motor milestones" at 4-7 months?

• Sitting with support (then)

• Sitting independently

What is the "motor milestone" at 8-10 months?

• Crawling

• Creeping

What is crawling?

Baby moves on hands and stomach ("army crawl")

What is creeping?

Baby moves on hands and feet ("up on all for limbs")

What is the "motor milestone" at 9-10 months?

Pulling to stand

What is the "motor milestone" at 12-13 months?

Independent stance

What is the motor milestone at 14-18 months?

Walking

Define "systems theory"

The idea that each body system (MSK, neuro, etc.) requires varying times to mature and they do not all line up with when they are fully functional

Head control evolves with increased ________ and ________ of the head and neck

Neural control, Strength

What does head control trigger the calibration of?

• Visual, propriceptive, and vestibular inputs

• It allows them to recognize where the head is in space

In early development, babies depend on ________ info for locomotion

Visual

What are the three balance requirements necessary for independent sitting?

• Steady State Balance

• Reactive Balance Control

• Proactive Balance Control

What is steady-state balance  (for independent sitting)?

When infant can control spontaneous sway and degrees of freedom

What is reactive balance control (for independent sitting)?

Unexpected balance disturbance triggers EMG activity to correct posture

When does reactive balance control "develop" in relation to steady state balance?

• Reactive balance control may be available in a limited capacity earlier than steady state balance control

  • Could be available as earlier as one month

What is proactive balance control?

Make adjustments prior to movement; balance plans are incorporating into descending motor plan

When does proactive balance control emerge?

Emerges after reactive control

Support surface perturbations are primarily detected by ________

Somatosensory inputs

Discuss the stability demands for independent stance (12-13 months).

Increased static stability demands compared to static sitting (d/t greater DOF)

How does reaching trajectory relate to postural development?

As postural control improves, reaching trajectory is more accurate

Task formation is dependent upon ________ and ________ postural sway

Exploratory, Performatory

What is exploratory sway?

• Child explores and tests limits of base of support

• "If I do this what happens"

• Use sway to determine their BOS

What is performatory sway?

• Child now knows their base of support

• Going to use postural sawy to keep COM within BOS

What is reactive balance control for independent stance?

Gradual development of segmental synergistic balance reactions (APRs)

What sensory input is preferred in independent stance?

• Initially, there is reliance on visual input

• Eventually this changes to a somatosensory preference

What type of sensory input is preferred in early infancy with sitting? Why?

• Somatosensory

• During sitting, somatosensory is preferred because a large portion of their body is contacting the supporting surface

  • For example -- consider a child long-sitting

Perturbation responses emerge at ________, but are consistent and effective activation is achieved at ________

3-6 months, 7-10 years

How does steady state balance change with postural control refinement?

Gradual decrease in sway amplitude and frequency with maturation

How does reactive balance control change with postural control refinement?

• Compensatory responses (APRs) are inconsistent and delayed in younger children ages 1-3

• Therefore, as we age these become more consistent and less delayed

When is mature reactive balance control usually demonstrated? 

7-10 years

How does proactive balance control change with postural control refinement?

• Evidence of postural muscle activation prior to upper extremity task at 10 months 

• Consistent responses occur by 13 months 

• Adaptations to varying demands emerge at 15 months 

• Adequate anticipatory postural adjustment developed by 4-6 years

Discuss sensory organization in relation to postural control refinement.

• Until 7-8 years old, we have decreased ability to adapt to sensory reliance under variable conditions 

• Difficulty with re-prioritizing with specific situations

Reflexive reaching behaviors may help with the development of ________

Hand-eye coordination

Reaching behaviors may evolve from ________

Maturation of reflexive function

How do head and arm movements change with maturation?

• They become uncoupled as infant matures

• Now, if you move head to the right, they can decide if they want to move their arms or not

Reflexes become intergrated during ________ into complex hierarchy of movement

Neural maturation

T/F: There is evidence of reflexive reaching behavior in utero

True

Skill develops from a combination of ________ and ________

Genetic predisposition, Environmental experience
There is a reflexive nature to reaching before we have environmental context

Emergence of reaching is constrained by ________

Postural contral mechanisms

What occurs during early development of reach to grasp?

• Maturation from reflexively-driven reaching behaviors to volitional motor control (ATNR → volitional)

• Synergistic muscle activation patterns → Skilled upper extremity dissociation

  • Transitioning from everything flexing extending to "can do anything they want with each jt." also known as fractionating movement

What occurs during childhood development of reach to grasp?

• Refinement of kinematic trajectory and interlimb coordination and grip aperature

• Essentially, trajectory and pre-shaping becomes more accurate (d/t greate coordination)

How does hand orientation develop in manipulation?

• Transition from reflexive grasping patterns at birth to precision grip at 10 months

• Example

  • Initially, babies have "fist" behavior; place something in hand → reflexively grasp

  • As babies mature, this becomes more precise (rather than reflexive)

Ultrasound techniques highlight ________ in utero

Embryonic locomotor rhythms
Esentially, pre-natal limb activation is see in-utero

How does infant stepping change from newborns with maturation?

• Initially, stepping behavior can be elicited in newboarns in unweighted, sensory-triggered conditions

  • Reflexive Flexion/Extension of Limbs (CPGs)

• However, these stepping patterns disappear at approx 2-3 months before re-appearing at age 10 months (when they are starting to want to walk, etc.)

What is this development of infant stepping attributed to?

• Attributed to comination of neural and non-neural maturation

  • Integration of hierarchical stepping reflex

  • Altered strength demands

What neural maturation needs to occur for a child to take a voluntary step?

Communication between the cotex, midbrain locomotor region (MLR), basal ganglia, cerebellum, and CPGs needs to improve/mature

What is a rate-limiting factor for volitional ambulation?

• Inadequate postural control mechanisms

• Strength inadequacies

When do rudimentary CPG function and sensory contributions become available for volitional ambulation?

5-6 months

What is the developmental sequence of volitional ambulation?

• Transition from immature stepping patterns to adult-like kinematics 

• Synchronous activation with agonist / antagonist co-contraction → reciprocal activation

  • Babies walk "stiff-legged" to minimize DOF (easier to control)

    • "Locking the limb out" = agonist/antagonist co-contraction

  • As we develop, we start to let go of this, making our stepping more consistent with adult pattern

    • "One leg flexes, other extends'"

What sensory contributions are relevant to volitional ambulation?

• Reliance of visual information during walking development 

• As we develop, somatosensation and vestibular information becomes more utilized

There is evidence to support the emergence of walking associated with ________ maturation

Otolith (vestibular)

As we age and become older (geriatric), what physiological musculoskeletal changes occur?

• Loss of Type I and II Fibers

• Decreased # of Motor Units

• Adipose infiltration of muscle

  • Leads to changes in body composition and metabolism

As we get older (geriatric), how much does MVC decline?

MVC declines as much as 40% between 30-80 y/o

At what age do we have peak MVIC?

• Peak at 30 y/o

• Start to lose strength quickly after 30

How does range of motion change as we age (geriatric)?

Decreased spinal and ankle joint mobility (lose ROM and become more rigid)

As we age (geriatric), our tactile sensitivity ________

Decreases

As we age (geriatric), our vibratory threshold ________

Increases
A stronger vibration is required for it to fire

How does our vision change as we age (geriatric)?

• Increased visual threshold

  • More light for rods and cones to activate

• Decreased visual acuity

  • Reading glasses for bluriness, etc.

• Decreased visual contrast

  • Can't see depth / divisions

• Decreased accomodation 

  • Changes in ability to alter thickness/convexity of lens

What senses are impacted by a loss of hair cells?

• Hearing/Auditory

• Vestibular

There is a _______ loss of hair cells by age 70

40%

How does steady state control change as we age (geriatric)?

• Increased size (excursion) and frequency of sway

• Demonstrate similar characteristics as babies

How does anticipatory control change as we age (geriatric)?

• Decreased response onset for postural muscle groups

• Essentially, postural muscles activate at the same time as reaching is initiated (which, we want postural mm. to active first for reaching task)

What changes are seen in reactive control as we age (geriatric)?

• Sensory dysfunction

• Activation timing deficits

• Impaired adaptation

Considering reactive control, what specific changes are seen in sequencing with aging (geriatric)?

• Pre-emptive proximal muscle activity

  • Proximal muscles being activated first then distal muscles (should be opp)

• Related to the basal ganglia not picking the right APR strategy 
  

Considering reactive control, what specific changes are seen in activation timing with aging (geriatric)?

• Delayed muscle activation

• Takes longer to activation an APR

Considering reactive control, what specific changes are seen in adaptation with aging (geriatric)?

• Decreased accuracy of response amplitude to variable pertrubations

• With different types of perturbations ("shove" vs "light tap"), have a hard time changing the magnitude of response for the perturbation

• Due to cerebellum not setting appropriate gain on APR

How does sensory (re)organization change as we age (geriatric)?

• Reduced ability to alternatively weigh orientation differences

• "Weighing either vision, somatosensation, vestibular for certain controls"

• Older (and younger/babies) struggle with this and become too reliant on one system over another (e.g., vision)

As we age (geriatric), the latency of APRS ________

Increases

As we age (geriatric), our movement time ________

Increases
(aka -- movement velocity decreases)

As we age (geriatric), a ________ reduction in movement velocity is observed

30-90%

Why does movement time change as we age (geriatric)?

• Related to changes in

  • Visual detection (cannot see as well)

  • Central processing speed (decreases)

  • Altered motor systems (strength deficits)

  • Arousal/Cognitive sub-system

As we age (geriatric), our coordination ________

Decreases/worsens

Why does coordination change as we age (geriatric)?

• Over reliance on feedback processes 

  • Was observed since there was prolonged deceleration phase during reach

• (therefore looks more uncoordinated)

As we age (geriatric), grip force activation becomes ________

Excessive

What causes the inaccuracy of grip force as we age (geriatric)?

• Related to decreased tactile sensitivity

• As we become older, we cannot feel things / object characteristics as well

• To compensate for this, we squeeze the object harder to hopefully compensate (so we do not drop it)

What locomotive temporal changes are seen with aging (geriatric)?

• Decreased

  • Velocity

    • (combination of ↓ step length + cadence = ↓ velocity)

  • Step / Stride Length

  • Cadence (not stepping as much)

• Increased 

  • Stride Width (inc BOS; compensation for postural instability)

  • Stance Phase

  • Double Limb Support (more time with both limbs on ground)

What locomotive kinematic changes are seen with aging (geriatric)?

• Decreased 

  • Vertical COG displacement

    • Our vertical displacement ↑ with velocity, so may be d/t ↓ in gait speed

    • Also may be d/t lack of stability

  • Arm Swing / Trunk Rotation

    • Due to ↓ flexibility

  • Lower Extremity Flexion

  • Heel Strike

• Increased 

  • Intra-individiual variability

What locomotive kinetic changes occur as we age (geriatric)?

• Decreased

  • Plantarflexor power

  • Quadriceps force generation

• Increased coactivation

• Redistribution of joint torque/power
  

How does obstacle navigation change with aging (geriatric)?

• Earlier initiation of step adjustments (because they need more time to make adjustments)

• Shorter step length

  • As they get closer to object, step length gets shorter and shorter to help ensure they are in right position to clear object

• Slower speed

• Decreased obstacle clearance (more likely to trip/fall)

How does precision stepping change with aging (geriatric)?

• Decreased step accuracy

• Increased step adjustment time

How does dual tasking change with aging (geriatric)?

• Increased gait variability (step-to-step)

• Decreased speed

• Decreased cadence

• Impaired cognitive performance (to focus on gait)