Exam 3 Hk 253

Systems approach

Motor behavior emerges from the interaction of neural, biomechanical, sensory, and environmental systems rather than a strict CNS hierarchy.

reflex-hierarchial model

Theory that motor control develops through suppression of primitive reflexes by higher CNS centers.

Systems (distributed control) model

Theory that posture and movement emerge from interactions among multiple systems, not CNS levels alone.

Bernstein’s contribution

Introduced systems theory and the concept of motor synergies.

postural control

Ability to maintain the body’s center of mass (COM) within the base of support (BOS).

Cephalocaudal development

Postural control develops from head to trunk to legs.

Independent sitting onset

Around 7–8 months

pull to stand

around 9-10 months

cruising

around 10-11 months, holding onto furniture

Independent walking onset

Average ~12 months (normal range 9–17 months).

Delayed walking

Walking onset ≥18 months may indicate developmental delay.

Early walking strategy

Prioritizes stability over mobility.

Center of mass (COM)

Weighted average location of total body mass.

Base of support (BOS)

Area of body in contact with the support surface.

Postural stability

COM is maintained within the BOS.

Center of pressure (COP)

Point location of the ground reaction force vector.

Force plate

Tool used to measure COP movement and postural sway.

Stability cone

Range of COM positions from which balance can be recovered without stepping.

Limits of stability

Outer boundaries of the stability cone.

Ankle strategy

Balance corrections made mainly at the ankle; body behaves like an inverted pendulum.

Hip strategy

Balance corrections made primarily at the hip.

Suspensory strategy

Flexion at ankles, knees, and hips to lower COM.

Strategy selection depends on

Body morphology, task demands, and environmental conditions.

Muscle synergy

Group of muscles activated together as a functional unit.

Infant sitting muscle synergies

Become more organized with age and experience.

Early postural responses in infants

Appear first in neck muscles, then trunk, then legs.

Direction-specific responses

Postural muscle activation matches the direction of sway.

Practice effect

Postural synergies improve through experience at each new skill level.

8-month-old standing response

Often no postural responses observed.

10-month-old standing response

Inconsistent distal muscle activation.

14-month-old standing response

Adult-like distal-to-proximal muscle activation.

Immature postural responses

Longer duration, larger amplitude, more co-contraction.

Antagonist coactivation

Simultaneous agonist and antagonist activation to stiffen joints.

4–6 year transition period

Increased variability and delayed responses in postural control.

7–10 years

Postural responses become adult-like.

Adult-like sensory integration

Achieved around 7 years of age.

Primary sensory systems for balance

Somatosensory, visual, and vestibular.

Adult sensory reliance

Primarily somatosensory under normal conditions.

Visual dominance in infants

Young children rely more on vision than adults.

Cause of visual dominance

Poorly calibrated proprioceptive information early in development.

Purpose of SOT (sensory organization Test)

Assesses ability to maintain balance under altered sensory conditions.

SOT Rule 1

Solid surface is always more stable than foam.

SOT rule 2

Accurate vision > no vision > inaccurate vision.

Vestibular-only condition

Most difficult for children <7 and older adults.

4–6 year-olds

Unable to efficiently resolve sensory conflicts.

Children under 7 years

Struggle when only vestibular input is available.

Older adults

Lose balance more often when sensory redundancy is reduced.

Anticipatory postural control

Feedforward planning to stabilize posture before voluntary movement.

External vs internal threats

External = imposed perturbations; Internal = self-generated movements.

APC muscle sequence

Postural stabilizers fire before prime movers.

APC development onset

Begins around 4 months of age.

Double support

Period during walking when both feet are on the ground.

Early gait pattern

Wide base, short steps, high guard arm posture.

Step length

Distance between opposite foot contacts.

Stride length

Distance between successive contacts of the same foot.

Step width

Medial–lateral distance between feet.

Wide BOS (base of support)

Increases stability

High guard arm position

Enhances balance control.

infant falls

~31 falls/hour (non-injury).

toddler falls

~17 falls/hour (non-injury).

older adults

Exhibit increased sway and delayed muscle responses.

latency increase

Older adults show small but significant delays in muscle onset.

Temporal disruption

Altered sequencing of postural muscle activation.

Reversal of muscle sequences

Proximal muscles activate before distal ones.

Sensory redundancy loss

Leads to instability in older adults.

Vestibular-only reliance

Causes significant balance loss in older adults.

Dual-task interference

Cognitive load worsens postural control in aging.

strength decline

~40% decrease between ages 30–80.

Critical muscle group

Ankle dorsiflexors (tibialis anterior).

Fall risk correlation

Weak ankle dorsiflexors strongly linked to falls.

Similarity between children and older adults

Increased co-contraction and sensory dependence.

Coactivation purpose

Joint stiffening to reduce degrees of freedom.

Systems model advantage

Explains development and aging without invoking CNS hierarchy regression.