Postural Control

Controlling posture is accomplished by cooperation of sensory, motor, and muscular systems. Senses that contribute to postural control are vision (perhaps most powerful sensory system -- helps regulate posture as feedback correction and selecting anticipatory postural strategies), somatosensory (engages postural activity in relation to body postion), and vestibular (head control and serves as a reference to gravity while preventing drifting of the trunk during complicated postural control tasks) senses. The motor system part of postural control develops through a series of reactive postural adjustments including sitting then standing, and then anticipatory postural adjustments including movement in sitting then movement in standing. Changes in the muscular system follow typical growth patterns, and allow for increased control and therefore more advanced postural skills as children age and grow. For example the body of a 1 month old does not have the musculature or femoral head alignment to allow for walking, however by around 12 months they do.

There is a lot of variance in the sequence of development in postural control motor responses. This is a reflection of the neuromuscular responses developing before the child is able to determine which response is the most appropriate for task. Methods of analyzing movement throughout development are high variable and do not differentiate between levels of development.

Typical Development of Postural Control: Sensory System

Components
Age
Skills/Behavior
Vision
4 to 6 days old to 2 months
Activation of neck muscles following visual stimuli from looming visual stimulation in supported sitting

5 to 13 months
Scaling of postural responses to visual stimulation from moving room

5 months
Postural response to looming visual stimulation in stance

13 to 17 months and <7 months walking experience
Apt to fall in looming moving room

2 to 10 years
Decreased falls and reaction to eyes closed conditions in moving room, movable platform, SOT*
Somatosensory
  • >6 months
Can control head and sitting balance using somatosensory input

4 to 6 years
Beginning ability to use somatosensory input form sensory conflict in standing during SOT

4 to 10 years
Ability to re-weight within visual and somatosensory stimuli of various amplitudes by 4 years age; ability to re-weight between visual and somatosensory input by 10 years

7 to 10 years
Adult-like ability to use somatosensory input to balance during sensory conflicts during SOT
Vestibular
7 to 10 years
Adult-like ability to use vestibular input to balance during sensory conflict during SOT

12 to 16 years
Adult-like ability to balance during sensory conflict SOT
*SOT = Sensory Organization Test

If children develop without visual sensory information they do not learn to minimize their postural sway as efficiently as sighted children. Pretchl suggest the visual system acts as a calibrator for the proprioceptive and vestibular systems. The availability of vision produces more variable responses to anterior-posterior (AP) displacements. Without vision infants produce a more consistent vestibular and somatosensory driven response to AP displacements.

Typical Development of Postural Control: Motor System

Components
Age
Skills/Behavior
Reactive Postural Adjustments (RPA)


Sitting
3-5 months
Single postural muscle groups activated or antagonist activated rather than RPA sequence

5-6 months
Directionally specific motor coordination patterns; co-contractions; poor adaptation to task specific conditions

7-10 months
Decreased timing variability or directional specific motor coordination patterns

9 months to 3 years
Invariant use of directional specific motor coordination patterns; some co-contraction; adaptation to task specific conditions with modulation of pelvic muscles

>3 years
Variability in directionally specific motor coordination patterns
Standing
7 to 8 months
Infants that pull to stand begin to engage ankle strategies for balance

10 to 12 months
Adult-like RPA; distal to proximal motor coordination patterns

12 to 16 months
More consistent directionally specific motor coordination patterns

3 months walking experience
Compensatory stepping balance responses occur

4 to 6 years
Increased variability of motor coordination patterns occur,

7 to 10 years
Adult-like use of directionally specific motor coordination patterns

Anticipatory Postural Adjustments (APA)


Movement in Sitting



6 to 8 months
APA in trunk muscles before lifting the arm in sitting
Can adapt to different sitting positions and velocities of reaching movement

12 to 15 months
Consistent APA, particularly in neck muscles

2 to 11 years
APA variable and incomplete by age 11 years when compared to adults
Movement in Standing



10 to 17 months
APA activity is gastrocnemius muscles (to counteract the reach and pull movements with arms) in 10-13 month-old infants
More consistent and temporarily specific APAs in 16-17 month-olds

3 to 5 years
APA response variable, with immature as well as adult-like activity
Anterior shifts in COP are present before raising an arm while standing but these are less well coordinated

4 to 6 years
APAs recorded in the following tasks, lever pull
Voluntary drop weight, raise arm
APA may shift from a supporting function to movement to a compensatory function of postural stability

6 to 8 years
More continuous, systematic and harmonious APA during a reaching movement
APA show greater variability of muscle coordination patterns than 9-12 year-olds

9 to 10 years
Some children exhibit insufficient APA before movement into digitigrade stance
APA shown only when postural control disturbances reached “perilous” limits
APA less variable during stand and reach
Modulation of APA in weighted and unweighted wrist reach task

12 years
APA with forward leg raising similar to adults and both affected by segmental acceleration (slow verses fast movement) and sensory context (eyes open versus closed)

Movement during gait initiation



1 to 17 months walking experience
Inexperienced walkers use gait initiation APAs involving lateral rather than posterior COP shifts and use both the upper and lower body to make the shifts

1 to 2.5 years
Variable APA in reaction to a perturbation (holding the limb back) during gait initiation
APA (posterior COP shift) present, but not coordinated with the velocity of the step forward

4 to 6 years
Adult-like APA patterns of anterior tibialis activity and posterior COP shifts during gait initiation
APA (decrease in latency and increase in amplitude of muscles for push-off) in reaction to a perturbation (holding the limb back) during gait initiation
With 4 to 5 years walking experience, postural control motor coordination patterns move distally with ability to control gravitational forces with leg muscles during gait

6 to 8 years
APA (posterior COP shift) present and coordinated with the velocity of the step forward

Atypical Postural Control Patterns


Children with other developmental delays also often exhibit irregular development of postural control strategies as is seen in children with Down syndrome and cerebral palsy.

Down Syndrome: Children with Down syndrome reach their milestones such as grasping, rolling, standing, walking, etc. later than normal children do. Investigators question whether or not the motor progression of kids with Down syndrome is just delayed or if there is actually a difference in the physical structure of their muscles, tendons, ligaments or CNS that creates that delay. Children with Down syndrome often continue to rely on visual information when their neurotypical peers have begun using somatosensory and vestibular cues. These children can produce correct neuromuscular patterns in response to perturbations, but their compensatory muscle firing is initiated later than other children.

Cerebral Palsy: CP is associated with disordered muscle activation in response to sitting perturbations. Children with CP demonstrate more variable anticipatory postural adjustments, indicating that they have difficulty choosing the appropriate response. When sensory information input is conflicting, they have difficulty initiating motor responses. Children with CP initiate muscles in a reverse sequence firing proximal to distal musculature rather than distal to proximal. These children were also found to use less core activation when perturbed while standing. Additionally children with CP demonstrate slowed frequency in swaying which may be linked to rotational control and overall postural stability. Poor ankle control has also been suggested as a factor in decreased stability in such individuals. Therapist may use external cues to help reduce sway in children with CP. (Campbell, pg104)

Developmental Coordination Disorder and Strategies used by Kids with Atypical Postural Control
Children with DCD demonstrate inappropriate and ineffective neuromuscular strategies, both in muscular activation and in sequencing. They tend to have problems using vestibular input and reacting when the sensory information input is conflicting.

Their ineffective neuromuscular strategies are particularly evident in their use of atypical postural control strategies, including when their balance is challenged. An increased level of muscle co-contraction has also been described, in which children with DCD demonstrated a much less effective method of muscular organization than their peers, which did not improve with age. Children with movement difficulties tend to “fix” or stabilize their joints during task performance. The deliberate stabilization of their joints in this way leads to lack of fluency in their movement and contributes to their stiff, awkward, and clumsy appearance; it also increases the time it takes them to adapt to changes in their movement environment. Fixing can be thought of as a strategy to control the multiple degrees of freedom of joints and muscles for efficient functioning. Children with DCD who “fix” their joints during task performance are more likely to fatigue and to demonstrate inconsistency in task performance. (Campbell, p. 503)

The following video demonstrates an infant struggling with typical development of postural control and his PT working on postural stabilization on therapy ball.


References

1. Campbell, S., Vander Linden, D., & Palisano, R. (2006). Physical Therapy for Children (3rd Ed.). P 95- 106. St. Louis: Saunders Elsevier.