Postural Control

Introduction

• Presenter: Lisa Brown PT, DPT, NCS

Objectives

• Define Components of Postural Control:

  • Understand interactions within functional movement.

• Describe and Differentiate Components of Postural Control:

  • Steady State Control

  • Anticipatory Control

  • Reactive Control

• Review Impact of Factors:

  • Motor control

  • Sensory inputs

  • Interaction and cognition on postural control.

• Define and Apply Appropriate Outcome Assessments.

Review of Definitions

• Postural Control:

  • Control of the body’s position in space for stability and orientation.

• Balance:

  • State of equilibrium.

• Postural Orientation:

  • Ability to maintain appropriate body position (biomechanical alignment) relative to the environment and task.

• Limits of Stability:

  • Ability to control the center of mass (COM) in relation to the base of support (BOS).

• Center of Mass (COM):

  • Central point of the total body mass.

• Center of Gravity:

  • Vertical projection of the COM.

• Base of Support (BOS):

  • Area of the body in contact with the support surface.

Postural Components

Postural Alignment

• Definition:

  • Vertical line of gravity in relation to body segments, gravity, and the surface, allowing the body to maintain equilibrium with minimal energy expenditure.

Postural Tone

• Definition:

  • Antigravity muscle activation resisting gravity, influenced by somatosensory inputs, vestibular, and visual inputs.

Movement Strategies

• Postural Sway:

  • Adjustments governed by movement strategies around the ankle and hip joints to keep the COM within the BOS.

• Goal: Maintain individual COM within the boundaries of the BOS.

The Role of Balance in Various Activities

• Balance in the ICF Context:

  • Relevant for stroke patients and includes:

  • Sensation

  • Visual inputs

  • Vestibular inputs

  • Motor skills

  • Cognition

• Applications:

  • Balance required in varied situations:

  • Sitting, standing, walking, using stairs, transfers, reaching, etc.

  • Impact on self-care, recreation, vocation, etc.

System Framework for Postural Control

Individual Systems

• Motor Systems:

  • Muscle properties, joint range of motion (ROM), biomechanical relationships among body segments.

• Neural Systems:

  • Motor processes and sensory inputs (visual, somatosensory, vestibular) needed for body orientation relative to the environment.

• Cognition:

  • Cognitive resources and strategies needed to map sensations to actions for anticipatory and reactive processes.

Functional Task Postural Control

• Steady State Control:

  • Control of COM within BOS under predictable, unchanging conditions (e.g., sitting, standing, walking at constant velocity, stairs), mainly using feedforward control.

• Reactive Control:

  • Ability to regain a stable position after unexpected perturbations, requiring quick feedback motor activation to recover COM/BOS to avoid falls (e.g., tripping).

• Anticipatory Control:

  • Proactively activating muscles in legs and trunk before destabilizing movements (e.g., stepping over obstacles); uses mainly feedforward control.

Environmental Constraints

• Considerations include:

  • Support surface

  • Visual references

  • Auditory inputs

  • Cognitive load

Sensory Inputs for Postural Control

Visual Inputs

• Vertical Reference:

  • Position and movement of the head relative to the environment.

• Types of Vision:

  • Focal Vision (explicit vision):

  • Localizing features consciously in the environment.

  • Visual acuity < 20/50 can impair postural control.

  • Ambient Vision (implicit vision):

  • Uses the overall visual field, guiding movements nonconsciously.

  • Important for gaze stabilization.

Vestibular Inputs

• Functions:

  • Perception of body orientation relative to gravity and surfaces.

  • Stabilization of head and gaze for clear visual images during head movements.

  • Acts as a gravitational sensor and controls COM adjustments.

Somatosensory Inputs

• Role:

  • Provide positional and motion information regarding body parts relative to the support surface and each other.

  • Essential for responding to surface perturbations to organize appropriate postural strategies, including sensory cues from hands and fingers.

Sensory Integration and Reweighting

Sensory Interaction

• Definition:

  • Ability to process sensory inputs for accurate motor output in postural control.

Sensory Reweighting

• Definition:

  • Adjusts reliance on sensory contributions for postural control based on task demands, input integrity, and environmental conditions.

• Examples:

  • Increased reliance on visual inputs when learning a new task; increased reliance on somatosensory inputs as tasks become more automatic.

Cognitive Factors in Postural Control

Attentional Resources

• Definition:

  • Information processing resources required for task completion; complexity affects resource demand.

Dual Tasking

• Single Task Condition:

  • Performing one task alone to measure baseline performance.

• Dual Task Condition:

  • Performing two tasks simultaneously that have separate identifiable goals.

• Dual Task Interference:

  • When dual tasks decrease performance in one or both tasks.

Examples of Dual Task Conditions

• Walking while turning head.

• Standing with eyes closed.

• Walking on sandy beach at night.

• Reading text on a phone while walking.

• Standing reciting a poem from memory.

• Typing while conversing.

Functional Task Considerations in Postural Control

• Key Elements:

  • Document tasks such as seated, standing, walking, lifting.

  • Assess if upper extremity (UE) or external support is needed.

  • Observe postural alignment and weight distribution.

  • Evaluate postural sway and limits of stability.

  • Conduct qualitative description of steady state, anticipatory, reactive functional assessments.