A. Posture and Balance

    - postural control: controlling the body's position in space for dual purpose of stability and orientation.

    - postural stability: ability to maintain the position of the body within specific boundaries - stability limits.

    - if move outside those limits control of balance is lost - resulting in a recovery step or a fall.

    - to maintain posture the central nervous system must be able to perform two basic tasks:

        1) take in and integrate sensory information from a variety of sources to allow an assessment
        of the position and motion of the body in space.

        2) generate sufficient and coordinated forces in the relevant muscles of the legs and trunk so that
        body position does not move outside stability limits.

    - young children need good postural control before they can produce coordinated movements of the limbs.

    - good posture/balance provides a foundation upon which more advances locomotor and manipulative
      skills can be built.

    - if the trunk and head are unstable then reaching movements will be flailing and uncoordinated.

    - if artificially stabilize head by holding it then a young infant will be able to perform motor behaviors normally only
      observed in older infants.

    - an immature posture system constrains the emergence of more complex motor behavior.

B. Posture and Motor Milestones

    - Motor milestones: predictable sequence of progressively more complex motor behaviors associated with improvements
                               in postural and balance control.

    - 2 months: lifting head off support surface - requires sufficient neck and arm strength and ability to sense and integrate
                      information concerning head orientation.

    - 6-7 months: upright sitting - need sufficient neck and truck muscle strength.

    - 8-10 months: creeping - need further increases in trunk muscle strength.

    - 9-10 months: supported standing - need an increase in leg strength and balance control since now only using 2
                            points of contact with the ground.

    - 12-13 months: unsupported standing - need further increases in trunk and leg strength and ability to maintain
                              balance with legs and trunk only (no hands).

    - 14-18 months: walking - increases in leg strength and coordination and dynamic balance control.

    - progression can be thought to occur in a "spiraling hierarchy": alternating advancement and regression.

    - when making initial attempts at a new motor skill there may actually be some regression to more immature
       but safer more confident postures.

    - as new skill develops child becomes more confident and subsequently progresses - old immature patterns
       are replaced with newer more complex behaviors.

C. Theories of Postural Development

    1) Reflex/heirarchy theory: emergence of postural control is dependent on the appearance and subsequent integration
    of various reflexes.
        - reflexes form the foundation for posture

    2) Systems theory: posture control arises from a complex interaction of development of muskuloskeletal and neural systems.
        - reflexes make a contribution but not necessarily the main one.

D. Reflex/heirarchy Theory

    - attitudinal reflexes: asymmetric tonic neck reflex, symmetric tonic neck reflex, and tonic labyrinthine reflex contribute to
       persistent change in body posture resulting from a change in head position.

    - righting reflexes: keep head oriented properly in space and body oriented properly with respect to head and ground.

    - three righting reflexes orient head in space: optical righting reaction, labyrinthine righting reaction, and
      body-on-head righting reaction.

    - two righting reflexes keep body oriented with respect to head and ground: neck-on-body righting reaction,
      and body-on-body righting reaction.

    - balance control emerges in association with a sequentially organized series of equilibrium reactions.

    - three categories of balance reactions: titling reactions, postural fixation reactions, and parachute or protective responses.

    - not clear whether reflex theory is correct because there are many examples of the development of mature motor
       behaviors in the absence of supposed foundational reflex.

    - assumes sensory information is integrated and used to influence motor response.

    - also assumes that there is a central representation of correct balance/posture.

    - progression towards mature posture starts at development of head control, then independent sitting, then
      independent stance, refinement of independent stance, and finally development of anticipatory postural actions.

    1) head control: ability to control neck muscles emerges at around 2 months of age.

    - infants at this age respond to postural perturbations and keep their head properly oriented.

    - sensory contributions: make use of visual cues from birth to keep head straight.

    2) independent sitting: need control and strength in both neck and trunk - requires coordination between 2 body segments.

    - spontaneous sway controlled sufficiently to remain upright.

    - as develop get increased occurrence of coordinated patterns of muscle activity in response to postural perturbations.

    - sensory contributions: visual illusion of postural perturbation causes a loss of sitting balance in infants with little
       sitting experience.

    - the ability to compensate for this improves with age - more sitting experience means less reliance on vision.

    3) independent stance: require significant reductions in stability limits and coordination between legs, trunk and head.

    - leg strength is sufficient to support own weight by 6 months of age - since standing does not emerge for at least
       another 6 months then other factors must be limiting its appearance.

    - most likely related to limitations in coordination between body segments.

    - as infant gets older start to see appropriate patterns of muscular activity during postural adjustments.

    - at a given age level exposure to more postural perturbations will lead to more coordinated patterns of muscular
      activity but not to decreases in response latency - perhaps related to myelination process.

    - visual illusion of postural sway induces a loss of balance in early standers - this is compensated for as infant gains
       more experience at standing.

    - with repeated exposure to visual illusion there is little adaptation as occurs in older adults.

    4) refinement of independent stance: relative amount of sway during quiet stance is greater in children than adults.

    - amount of sway decreases as children age from 2 to 14 years.

    - responses to postural perturbations become quicker and more consistent as children get older.

    - except during years 4 to 6 when there appears to be a regression related to a period of disproportionate growth
       with respect to critical changes in body form.

    - if remove vision during postural perturbations in 2 and 3 year olds there is a reduction in the onset of the
       compensatory response - implies that children rely on shorter latency somatosensory inputs under these conditions.

    - when both visual and somatosensory cues are removed children under 7 years can not compensate for postural
       perturbations based solely on the remaining vestibular signals.

     5) anticipatory postural adjustments: when make a reaching movement have to generate anticipatory postural adjustments
      in advance of arm movement.

    - first start to see trunk muscle activation in association with arm movements at 9 months.

    - becomes consistent in the standing posture by 12 to 15 months.

    - by 4 to 6 years observe essentially the same pattern as that seen in adults.