Postural Control Across the Lifespan

• This lecture discusses postural control and balance across the lifespan, focusing on both development in children and changes associated with aging.

Learning objectives

• Relate systems theory and postural regulation knowledge to both children and older adults.
• Anticipate changes in postural control during development when assessing balance.
• Anticipate changes in postural control associated with aging when assessing balance.

Key References

• Shumway & Woollacott Motor Control, specifically chapters 8-10.

Defining Postural Control

• Postural control has two main purposes: stability and orientation
• Stability involves controlling the center of mass (COM) over the base of support (BOS).
• Measuring the center of pressure (COP) helps determine distribution of total forces applied to a supporting surface.
• Postural orientation is the capability to maintain appropriate relationships between body segments, and between the body and the environment.
• Vertical orientation is needed for most functional tasks.
• Multiple sensory systems are needed for vertical orientation.

Systems of Postural Control

• Venn diagrams are used to represent the interaction of different systems in postural control, include the task, individual, and environment.

Neural Components of Postural Control

• Action systems involve motor processes and neuromuscular synergies.
• Perceptual systems incorporate sensory processes including the integration and organization of sensory information.
• Cognitive system functions as a high-level process including cognitive influences, attention, motivation, intention and adaptive postural control.

Normal Control Mechanisms

• Steady state balance is a key aspect of motor control.
• Reactive balance involves motor control during perturbations.
• Sensory organization is part of the perceptual system of postural control.
• Anticipatory postural control/balance is another key motor control aspect.
• Cognitive systems impact postural control.

International Classification of Functioning (ICF)

• A health condition (disease or disorder) can lead to impairments in body structures and functions, which then causes limitations in activities and restrictions in participation.
• Balance control deficits are impairments that effect steady-state, anticipatory, and reactive balance
• Mobility limitations include inability to maintain stability and orientation during postural tasks such as sitting, standing, transfers, and walking.
• Manipulation limitations include stability during reaching and grasping.
• Participation restrictions may include inability to perform self-care, take part in home-related activities, or community and social activities.

Postural Control and Development

• The simultaneous development of postural, locomotor, and manipulative systems is essential for skills to emerge and be refined.
• An immature postural system can limit the emergence of other behaviors.
• Observations support system-based theory for postural control.

Systems Theory

• Postural control is a complex interaction between neural and musculoskeletal systems.
• Motor coordination strategies, individual sensory systems, and sensory strategies for organizing all contribute to postural control.
• Cognitive resources and strategies also help shape postural control.

Motor Milestones and Postural Control

• Functional skills needing postural control: sitting, standing, walking unsupported, reaching forward, and moving from sitting to standing.

Emerging Head Control

• Steady state control is not present at birth.
• Reactive control includes directionally specific postural responses in neck muscles by 1 month.

Sensory Contributions to Head Control

• Vision calibrates vestibular and proprioceptive systems.
• Vestibular inputs facilitate postural control, gaze stabilization, homeostatic regulation, and spatial memory.
• Somatosensory inputs calibrated by information contribute to head control.

Independent Sitting

• Infants control spontaneous sway sufficiently to remain upright.
• Independent sitting usually occurs between 6 to 8 months of age.
• Trunk and head postural development is a dynamic skill.
• The general sequence in postural development goes from no control to initiating upright sitting, partial control with large range of body sway, and finally reaching functional control with minimal sway.

Reactive Balance in Sitting

• Response synergies during sitting develop during months prior to independent sitting.
• Newly sitting infants depend heavily on visual inputs which decreases with experience.

Independent Stance

• Infants must learn to balance within reduced stability limits, and to control additional degrees of freedom to stand independently.
• Before independent stance emerges, sensorimotor representations are recalibrated and the ability to support weight against gravity begins.

Postural Responses in Standing

• Adaptive ability related to hip use for balance is not mastered in infants when walking emerges.
• Hip-dominated responses present in new walkers with 3-6 months of walking experience.

Sensory Weighting

• The visual system elicits organized postural responses in new standing infants earlier than the somatosensory system.

Sensory Weighting in Standing

• The Sensory Organization Test measures the stability ratio.
• Perfect stability is measured as 100%.
• Sensory weighting varies according to age being a=6-7 years, b=8-10 years, c=10-12 years, d=12-14 years, and e=20 years.

Experience in Standing

• Sensory information to control posture is used by performatory postural sway.
• The sensorimotor workspace for posture control is investigated and explored by exploratory postural sway.

Refinement of Postural Control in Children

• Children have shorter stature and are closer to the ground than adults.
• Children are top heavy, move at a faster rate during imbalance, and are better at steady-state postural control compared to adults.
• Compensatory postural responses are more variable and slower for those who are 15 months old compared to adults.
• Postural response in those who are 7-10 years of age are like those in adults.
• Adaptability and control are also better in children at a quiet stance.
• Skill development needs postural and voluntary control.
• The ability to adapt sensory information about body position /movement to task and environmental conditions in children is important.

Cognitive Strategies

• Postural control requires attentional resources.
• Additional resources are needed with increasing postural task complexity.
• Younger children have attentional resources taxed by postural demands.
• In dual-task situations, this affects both postural and cognitive performance.
• Automaticity of postural control increases requiring less attention as the person ages.
• Decreased attentional demands during development are associated with changes in body morphology, muscular response synergies, and refinement of these things.
• Refinements in the sensory and motor aspects of postural control include decreased sway velocity, reduced oscillatory sway, and a control shift from visual to somatosensory for balance by 3 years of age.

Postural Control with Aging

• Genetic Factors influence aging, contributing 20% towards longevity and influence efficiency of DNA repair.
• Lifestyle and environment also influence aging, health-related behaviors like lifestyle, diet, exercise, stress, and self-efficacy make up 80% to longevity.
• Primary aging factors are genetics and limited control, secondary/experiential factors are nutrition, stress, exercise, and pathologies that affect mind and body.

Heterogeneity in Aging

• Assuming physical capabilities diminish as an older adult is unwise
• Physically independent adults are those who are independent in basic activities of daily living (BADLs) and instrumental activities of daily living (IADLs)
• Adults who are physically frail are independent in BADLs but depend on many IADLs.

Falls in Older Adults

• Instability/balance deficits is an indicator of falling.
• Falls involve older adults falling to the ground, and unintended contact with supporting surfaces. Further falls involve the individual being unable to recover stability independently.
• Unintentional injuries are the seventh leading cause of death in the elderly.
• Risk factors can be both intrinsic (physiological, musculoskeletal, psychosocial) and extrinsic (environmental).
• Interacting during specific tasks in certain environments also causes falls.

Falls Risk Factors

• Fall risk factors include muscle weakness, history of falls, gait and/or balance deficits, use of assistive devices, visual deficits, arthritis, depression, cognitive impairment, age over 80, and impaired ADLs.
• Environmental fall risk factors include stairs, throw rugs, slippery surfaces, and poor lighting.
• Fall risk is significantly increased for those who are hospitalized and/or live in residential facilities for 1-6 months after discharge.

Age-Related Changes

• Muscle strength declines with age.
• The capacity of a muscle to contract decreases with age during continuous sub-maximal levels.
• Skeletal muscle changes affect functional capacity.
• Decreased ROM and spinal flexibility may lead to flexed/stooped posture.
• The neuromuscular system is affected by balance control.

Older Adults

• Older adults during assessment need to be evaluated for primary neuromuscular and secondary musculoskeletal contributions to instability.

Steady-State Balance

• Balance indicators during quiet stance are determined by spontaneous sway.
• Functional stability limits decrease with age.
• Quiet stance reflects the capacity of adults to balance during changing steady-state conditions.

Cognitive Decline

• Postural sway, falls, and cognitive status were studied with older adults.

Reactive Balance

• Problems affecting coordination of muscle response synergies include sequencing, timely activation of postural responses, adapting postural activity to changing task/environmental demands.
• Stable/unstable older adults use less ankle-dominated responses and more hip-dominated responses.
• Unstable older adults use alternative strategies such as bending at the knee and/or using arms when balancing.
• Recovery involves a stepping response to both aging & falling risk.
• Recovering also involves side-step sequences.
• Falls and aging can be attributed to slowed initiation and execution of reach-and-grasp movements.

Reactive Balance Control/Motor System

• Examine motor system changes that effect reactive balance control.
• Includes muscle weakness, impaired timing/organization of synergistic muscles, and limitations to adapting movements as the task/environment changes.

Anticipatory Postural Control

• Postural adjustments are proactive in stabilizing body before making voluntary movement.
• The inability to stabilize the body in association with voluntary movements is a major contributor to falls in older adults.

Individual Sensory Systems

• Reduction of tactile sensitivity, vestibular system, and age-related changes in the visual system all affect the functional skills needed to maintain postural control.
• Loss of more than one sense (multisensory deficit) is important for balance and mobility function.
• Reducing availability of two senses affects postural steadiness.

Sensory Systems to Assess

• Sensory organization and adaptation should be examined during postural control.
• The ability to maintain stability during changing conditions should also be tested.

Cognitive Issues and Aging

• Stability challenged? Examine postural control.
• Challenging conditions? Consider dual task.
• Attentional demands increase in older adults.
• Recovery? Assess higher attentional needs during balance for older adults.

Dual Tasks and Demential

• Jehu, Langston, Sams, Young, Hamrick, Zhu, and Dong impacted balance.
• Dual-tasks and disease severity also impacted posture, gait and functional mobility.
• People with dementia in residential care facilities also impacted balance.

Steady state studies - Dual tasks - Balance control

• In one study, dual task sway in
  • Older non-fallers involved firm surface and no task with sentence completion
  • Older fallers involved firm surface or no cognitive task and sentence completion

Reactive Balance Studies

• Single tasks with balance-impaired older adults were studied

Balance and Confidence - Fear

• Measuring is essential
• Includes falling and balance
• Falls from activity in older adults were also examined.