Postural Control - Dynamic Systems Theory - Fall 2024 PDF

Postural Control Dynamic Systems Theory Perspective DPT 542 Functional Neuroscience Fall 2024  What do you know? List three things you have learned about balance or postural control (regulation)  Learning Objectives Define Postural control in the c...

Postural Control Dynamic Systems Theory Perspective DPT 542 Functional Neuroscience Fall 2024  What do you know? List three things you have learned about balance or postural control (regulation)  Learning Objectives Define Postural control in the context of task-oriented movement. Identify the motor and sensory strategies associated with postural control Describe the adaptability of these strategies to change in individual, task and/or environmental constraints Relate information of motor and sensory strategies to clinical practice  Introduction Copyright © 2017 Wolters Kluwer All Rights Reserved 4  Defining Postural Control Dual Purposes: 1. Stability: Controlling center of mass (COM) over the base of support (BOS) Center of Gravity (COG) vertical projection of COM Center of Pressure (COP) measurement: center of distribution of total forces applied to a support surface 2. Postural Orientation: Ability to maintain appropriate relationships between body segments and between the body and the environment Vertical orientation is required for most functional tasks Multiple sensory systems are required to maintain vertical orientation Orientation and Equilibrium CoM are NOT the same Postural orientation with respect to the external world sometimes requires giving up on the goal of postural equilibrium. Therapists need to evaluate postural orientation and postural equilibrium.  COM is the Key Element in Postural Control COM is not a physical element, but a virtual point in space that depends on the position of all the body segments. – Variability in control of COM CNS must have sensory systems that will detect changes in COM – CNS must have established thresholds of acceptable COM variability during postural control tasks. CNS must recruit the various elements in the system (muscles around each joint) with appropriate force and timing – Dependent on the configuration of the segments within the task and their relationship to the environment  Biomechanical Analysis Patla, Ishac and Winter, 2002 How does CNS solve the mechanical problem? Is the system an inverted pendulum?  Measurement of Postural Stability Force plate Distance and variability of Center of Pressure (COP) positional changes Changes in COP in quiet standing Also sway amplitude with body sensors Defining Systems of Postural Control  Neural Components of Postural Control Action systems: Motor processes: neuromuscular synergies Perceptual system: Sensory processes: Integration and organization of sensory information Cognitive System: High level Process: cognitive influences – Attention, motivation and intention – Adaptive postural control  Shumway Cook &Woollcott Normal Control Mechanisms Motor control of Steady State balance Motor control during Perturbations: Reactive Balance Perceptual System of Postural Control: (Sensory organization) Motor control of Anticipatory Postural Control or Balance Cognitive systems in postural control  Control of Steady State Balance or Postural Control Small amounts of postural sway Several factors: – Body alignment Maintaining a desired Minimize effect of gravity upright posture – Muscle tone Prevent body collapsing in response to gravity Intrinsic muscle stiffness Muscle tone in all muscles Postural tone in extensor muscles when upright  Steady-State Balance Steady State Movement Strategies Stability limits: point at which a person will change configuration of his or her BOS to achieve stability Not fixed boundaries Affected by perceptual and cognitive factors Ideal alignment minimizes muscular effort (Figure 7.6) Base of Support (BOS)  Movement Strategies for Steady State and Reactive balance. Inverted Pendulum – Ankle strategies: Primary movement (oscillations) around ankle with legs and trunk moving in phase Low Frequency (1hz)  Movement strategies to externally generated destabilization (perturbations) Reactive Balance Feedback Control Figure 7.8 – Ankle Strategy – Hip Strategy – Stepping Strategy  Anterior-Posterior Stability for Reactive Balance Ankle strategy Hip strategy Pattern when Pattern when 1. When unstable 1. When relatively 2. Need to move COM stable more rapidly 2. When COM does 3. More likely if not need to move impairments in distal quickly motor or vestibular 3. little or not sensory impairments. impairment How do you test for Reactive balance?  Other Planes of movement need to be controlled Mediolateral Multidirectional control – Unloading and loading of each legs – EMG turning curves – Control of hip abductors (Gluteus Medius and TFL)and hip adductors – Proximal to distal control Reactive Control Strategies are Adaptive Horak, Henry, Shumway-Cook, 1997 Reactive Control Strategies Adapt with Practice  Physiological significance of synergies? Def. – a functional coupling of groups of muscles constraining them so that they act as a unit. Multiple muscles in each synergy Muscles can be in different synergies Muscles have fixed weighting in a synergy Synergy produces specific direction of force Synergies combine and add (Ting et al 2005)  Importance to the Clinician Patients need to keep postural equilibrium Steady State and Reactive of Postural Control – Use common control mechanisms – May interchange when training individuals? Multiple synergies are needed – It is important not to limit training to the activation on one type of synergy – Individuals need to continuously modulate strategies to adapt to changes in task and types of destabilization forces  Musculoskeletal Constraints in Postural Control Abnormalities of alignment Crouched Posture in CP  Perceptual Systems in Postural Control Sensory Organization During steady state balance – Visual Position and movement of head in relationship to surrounding objects – Exocentric motion vs egocentric motion – Vestibular Position and movement of head in relationship to gravity and inertial forces – Somatosensory Position of body in relationship to supporting surfaces  Vestibular Vestibular Balance Balance Visual Somato- Somato- sensory Visual sensory Dana-Dos Santos et al 2022: Long-term effects of mTBIs includes a higher dependency on visual inputs to control vertical posture Six Sensory Conditions of Sensory Organization Figure 7.15  Control Changes as different Sensory Systems are Available Sensory Organization How is this measured? Amount of sway Test (SOT) Figure 7.16 CNS Adapts the way it uses sensory Information Task and environmental demands Reweighting with age and sensory impairment Adaptation with learning new tasks  Loss of a Single Sense Compensatory strategy depends on – What systems remain to detect position of the body in space – Availability of environmental cues – Ability to select appropriate information and interpret it Individuals can compensate for somatosensory loss if vision and vestibular information is present – But if in unlit environment and temporary somatosensory loss (e.g. foot fell asleep while napping) – postural dysfunction is more likely Example: Sensory loss of Single sensation  Loss of Sensory Redundancy and Selection Loss of multiple sensory inputs Giving greater weight to one leads to significant loss of sensory system postural control – Unable to shift to another system – Studied in normal adults Not selecting the appropriate Take away somatosensory cues & sensory system vision → falls may result – Seen in stroke, Traumatic Brain – Studied in those with stroke Injury, CP, Down syndrome and Take away somatosensory cues and vision →postural control is significantly children with developmental reduced coordination disorder (DCD)  Clinical Importance Organizing and selecting appropriate sensory inputs is important to maintain stability – Task and environment contexts Clinical approaches to improving balance need to address sensory organization; not just movement strategies  Anticipatory Postural Control Pre programming of posture prior to voluntary movement – Preparatory postural movement (or postural motor activation) more than 50 msec in a advance of the primary mover. – precede self initiated arm, leg or trunk movement to minimize instability Predictive Control or Proactive Control Central Set – Ability of the nervous system to prepare the motor system for upcoming sensory changes and sensory system for up coming motor changes Automatic Postural Adjustments (APAs) – context specific Example of Anticipatory Postural adjustment Leonard, 1999  Example of an Anticipatory postural control experiment: ▪ Subject instructed to pull handle as soon as he hears a tone ▪ Prior to volitional activation of biceps, this subject stabilizes body by activating calf mm. ▪ Prevents crashing into wall when he pulls on the handle  APA Flexibility during Arm Reaching Task Constraints Self-paced vs Reaction Bilateral vs. Unilateral UE Relate this to the Task oriented model of motor control Postural Control Environmental Individual Constraints Constraints Age Additional Load Fatigue Target location  Anticipatory Control Problems Postural synergies in advance of volitional movement not seen or reduced in. – Stroke – CP Constraints with in the individual – Traumatic Brain Injury (TBI) Effect APAs – Down syndrome – Parkinson disease – Cerebellar disorders  Clinical Importance Information about changing anticipatory postural control can be applied to the clinical environment. Clinicians can manipulate to improve anticipatory control – Task demands Slower or faster movements Goal of the task – Environment demands Adding a load Height of surface – Degree of practice can effect timing of APA  Cognitive System in Postural Control Attention requirements of postural control – Varies based on complexity of motor task Dual Task: – Competition of attentional resources – Loss of control when attention demand exceeds attentional capability – Difficulty on the postural system is dependent on complexity of the secondary task. Visual task Motor task Cognitive Task  Clinical Importance For young adults, postural control has low attentional demand For individuals with neurological deficits, clinicians need to distinguish between postural control vs. attentional processes To ensure capability to control balance in new situations and during multiple tasks, practice of postural tasks with increasing attentional demand is required Distribution of CNS Control  Summary Postural System has two important functions; Stability and Orientation Postural Control (Neural) Mechanism include steady state, reactive, anticipatory motor synergies, sensory integration and cognitive strategies. Postural control behavior is task specific and adaptable Attentional resources (cognition) required to maintain balance depend on the complexity of the task and/or the amount of impairment of the individual.