Movement Science Week 8 - Transcripts

Postural Control

• Postural control is the ability to maintain balance and control the body's orientation in space.
• Balance results from the interaction of the individual, the task, and the environment.
• Three types of balance control are: steady state, reactive, and proactive.
• Steady state balance: Maintaining a stable position with minimal effort, often referred to as static balance.
• Reactive balance control: Responding to unexpected disturbances to regain stability.
• Proactive balance control: Anticipating and preparing for potential disturbances.

Components of Postural Control

• Musculoskeletal Components: Joints, spine, muscles, range of motion, flexibility, muscle properties.
• Neuromuscular Components: Motor processes, muscle synergies, sensory systems and strategies.
• Sensory Systems: Vision, vestibular system, proprioception.
• Cognitive Processes: Anticipatory mechanisms, adaptive mechanisms.

Concepts in Postural Control

• Center of mass (COM): The point at the center of the body's total mass, usually around the belly button.
• Center of gravity (COG): The point at which an object can be perfectly balanced, it changes depending on the individual's actions.
• Base of support (BOS): The area of the body in contact with the supporting surface.
• Postural stability: The ability to control the COM in relation to the BOS.
• Stability limits: The points at which a person needs to adjust their base of support to maintain stability.
• Center of pressure (COP): The distribution of force applied to the supporting surface, it moves around the COM to maintain balance.

Steady State Balance

• Optimal alignment: Requires minimal muscle effort to maintain a position.
• Muscle tone: Background muscle activity in a quiet stance, it contributes to steady-state balance.
• Three factors contributing to muscle tone: Muscle stiffness, background muscle tone, and postural tone.
• Postural tone: Active muscle activation against gravity to counteract its force.
• Strategies for steady-state balance: Ankle strategy and hip strategy.
• Ankle strategy: Movement centered around the ankle joint, both the leg and trunk move in phase.
• Hip strategy: More movement at the hip, leg and trunk move out of phase.

Sensory Systems in Steady State Balance

• Vision: Provides information about position, motion, and orientation, it can be misinterpreted (e.g., moving car next to you).
• Somatosensory system: Provides information about position and motion relative to the supporting surface.
• Vestibular system: Provides information about head position and movement relative to gravity.
• Sensory re-weighting: The central nervous system modifies the importance of each sense based on environmental conditions.

Reactive Balance Control

• Reactive balance control: Recovering stability after an unexpected disturbance.
• Muscle synergies: Coupling of muscle groups to simplify control.
• Strategies: Fixed support (ankle & hip), change in support (stepping, reaching).
• Ankle strategy: Used for small disturbances, requires good ankle mobility and strength.
• Hip strategy: Used for larger disturbances, involves larger muscle activation and coordination.

Muscle Activation in Reactive Balance Control

• Forward sway: Gastrocnemius, hamstrings, paraspinal muscles are activated to slow down and reverse forward motion.
• Backward sway: Tibialis anterior, quadriceps, abdominal muscles are activated to prevent falling backward.
• Reactive balance control is crucial for navigating challenging environments and avoiding falls.

Hip Strategy

• The hip strategy uses large, quick movements at the hip joints with antiphase rotations at the ankle
• This strategy is used when the support surface is not firm or is small
• Larger activation of the quadriceps and abdominal muscles happen during forward sway
• Larger activation of the hamstrings and paraspinal muscles happen during backward sway

Change in Support Balance Reactions

• Changes in balance reactions include both stepping and reaching to grasp
• These are completed in half the time it takes to perform a similar voluntary movement
• The direction, amplitude, and speed of the compensatory change in support are programmed in response to unpredictable body movements
• These changes are used in a reactive environment

Step Strategy

• The step strategy realigns the base of support under the center of mass
• It is used when there is room to step

Reach and Grasp Strategy

• The reach and grasp strategy extends the base of support by using the arms
• It is used when there is something to reach for

Medial-Lateral Stability

• The primary motion for medial-lateral instability is lateral movement at the pelvis
• Abduction of one leg and abduction of the other leg are used to help recover stability
• The hip joint is primarily used to recover stability because the ankle and knee have very little medial to lateral movement

Response to Multi-Directional Instability

• The rectus femoris and the tensor fascia lata are most active in response to lateral perturbations
• Other muscles of the leg and trunk are active in response to diagonal perturbations

Balance in Seated Position

• Muscle activation is similar to that of stance
• Muscle responses are fast and coordinated with synergistic muscle activity
• Antagonist muscles have very little activity

Seated Balance in the Anterior-Posterior Direction

• There is a lot of trunk muscle activity if the feet are dangling
• If the legs are on the ground, there is more leg muscle activity

Seated Balance with Multi-Directional Perturbations

• Muscle activity is based on the direction of instability

Postural Muscle Synergies

• Postural muscle synergies are not fixed stereotypical reactions
• They are changed and finely tuned in response to task and environmental demands

Adaptation

• Individuals without any nerve pathology can shift and blend postural movement strategies
• As the velocity of platform movement increases, the hip strategy is added to the ankle strategy
• There is a shift to change in support strategies at some point

Efficiency

• The amplitude of muscle activity can be reduced in response to repeated perturbations at the same velocity

Anticipation

• Anticipation is used to change the amplitude of postural adjustments to perturbations
• The amplitude of the muscle response is related to expectations regarding the size of the loss of balance

Clinical Application of Balance

• Practice should include predictable and unpredictable perturbations in varying sizes
• Perturbations in variable directions should be included to avoid postural response habituation

Sensory Information and Reactive Balance

• Visual information is gathered to determine the environment
• Somatosensory information helps control body sway and provides information about changes in the support surface
• Vestibular information helps with recovery of postural control

Proactive Balance Control

• Proactive or anticipatory balance control is adapted to different tasks and environments
• The central nervous system uses anticipatory processes for controlling movements

Preparatory Phase

• Postural muscles are activated in advance of the prime mover muscles to compensate before the planned movement
• There is anticipatory postural control activity prior to lifting the right leg

Compensatory Phase

• Postural muscles are activated after the prime movers in a feedback manner to help stabilize the body

Anticipatory Postural Muscle Activity in Sitting

• The activity decreases as support to the body increases, so there are fewer anticipatory perturbations
• Activity increases with increased task load

Cognitive Systems and Balance Control

• Most daily activities involve doing more than one task at a time
• Postural control occurs automatically without much conscious effort
• Attentional resources are required for postural control
• Dual-task interference occurs when two tasks compete for available attentional resources
• The attentional requirements for postural control vary

Attentional Demands

• Postural control in young adults performing a balance task is very attentionally demanding
• The attentional demands increase as the sensory inputs for postural control are decreased
• Standing with your eyes closed, being in a dim environment, or being on foam or an uneven surface increase attentional demands

Secondary Tasks and Balance

• Focusing on a visual target can reduce sway
• Postural control can be enhanced during the performance of a secondary task

Dual-Task Conditions and Balance

• It depends whether maintaining balance takes precedence over other tasks
• Postural control is prioritized when there is a greater threat to stability
• Once a postural response is initiated, reaction time processing to other tasks becomes faster

Clinical Application of Cognitive Systems and Balance

• Balance should be assessed under single and dual-task conditions
• Treatment should strive to improve postural stability in both conditions

Aging and System Changes

• There is heterogeneity in the aging process
• Older adults of the same chronological age can have very different physical function
• Factors contributing to health and longevity are diverse

Continuum of Function Among Older Adults

• Physically elite older adults engage in competitive sports
• Physically fit older adults engage in sports, games, and hobbies and can perform moderate physical work
• Physically independent older adults are active and can perform BADLs and IADLs
• Physically frail older adults may be independent in BADLs but dependent in IADLs and may require more assistance
• Physically dependent and disabled older adults may be dependent in BADLs and IADLs and may require full-time assistance or institutional care

Age-Related Changes in the Neuromuscular System

• Strength declines with age
• Lower extremity muscle strength may be reduced by 40% from ages 30 to 80
• Strength gains have been shown in some individuals
• Muscle strength reduction is more severe in older residents in nursing homes with a history of falls
• Endurance decreases with age but is more preserved than strength
• Muscle cells die and are replaced with connective tissue and fat tissue
• There is a preferential loss of muscle fiber types with aging
• There is an age-related loss of both type one and type two muscle fibers
• The number of motor units declines with age
• Changes in skeletal muscle affect the capacity of the muscles
• Maximum isometric force decreases
• Muscles fatigue more quickly
• The rate of tension development is slower
• Concentric contractions are more affected by age than eccentric contractions
• Rapid contractions are more affected than slow contractions

Age-Related Changes in Sensory Systems

• There is a decrease in somatosensation
• Reduced somatosensation is associated with peripheral neuropathy
• Decreased sensory function is associated with a decline in gait speed
• Poor vision has also been shown to be associated with poor walking
• Vestibular function declines with age

Age-Related Changes in Cognitive Control

• Sensory and motor aspects of performance require more cognitive control
• Attentional demands tend to increase with stability challenges
• Executive attentional function is essential for successful dual-task performance in older adults

Fear of Falling

• Older adults who have experienced falls have fear of falling
• Fear contributes to changes in walking patterns
• Older adults who avoid activities because of fear of falling tend to walk at a slower pace and have higher levels of anxiety and depression
• Slowed walking velocity may be a strategy to ensure safe gait

Falls

• A fall is unintended contact with a supporting surface or the inability to recover stability independently
• Falls are a function of the individual, task, and environment
• Unintentional injuries from falls are the seventh leading cause of death in the elderly
• Both extrinsic and intrinsic factors can contribute to falls

Extrinsic Factors

• Environment
• Clutter
• Surfaces

Intrinsic Factors

• Musculoskeletal changes
• Physiological changes
• Psychosocial changes including fear of falling

Aging and Postural Changes

• Functional stability limits decline with aging
• Healthy older adults have more problems with their balance than younger adults
• Older adults have greater variability in reactive postural responses than young adults

Age-Related Changes in the Coordination of Muscle Synergies

• Problems affect the coordination of the muscle response synergies
• These problems fall into three categories:
  • Sequencing problems
  • Problems with the timely activation
  • Problems adapting postural activity to changing task and environmental demands
  • Changes in reactive balance have also shown a less ankle-dominated response and more hip-dominated response

Unstable Older Adults

• Bending at the knees and using the arms as a strategy is used by older adults to maintain balance
• Strategies may include reach and grasp or bending at the knees

ICF Model

• The ICF model is a framework used to assess the impact of health conditions on individuals
• It considers body functions, structures, activities, participation, and environmental factors
• The model is universal, neutral, and applies to all individuals regardless of their health status
• Body functions refer to physiological functions of the body's systems (e.g., sensation, balance, vision, cognition)
• Body structures are anatomical parts of the body (e.g., organs, limbs, eyes, nerves)
• Impairments refer to problems with body functions or structures (e.g., numbness, paralysis, weakness)
• Activities are tasks performed by individuals (e.g., walking, reaching)
• Activity limitations are difficulties in executing tasks (e.g., inability to walk without a cane)
• Participation involves engagement in life situations (e.g., employment, education, sports)
• Participation limitations denote problems in life situations (e.g., stigma, fear)
• Environmental factors encompass physical, social, and attitudinal aspects
• Personal factors include unique individual characteristics (e.g., injury history, pain, mobility)

Mobility

• Mobility is a domain within the ICF framework focusing on changing and maintaining body positions, moving and handling objects, and using transportation
• Walking involves distance covered, negotiating surfaces (slopes, uneven surfaces), and overcoming obstacles
• The gait pattern is considered a body function, influenced by environmental factors (terrain) and personal factors (age, sex, self-efficacy)
• Adapting gait to environmental demands is crucial for functional mobility
• Upper extremity function (reaching, grasping, manipulating) is vital in self-care and domestic life

Technology for Movement Analysis

• Motion capture technology captures movement using reflective markers placed on the body
• It provides information on joint angles, center of mass, stability, and sway limits
• Surface Electromyography (EMG) measures muscle activity through electrodes placed on the skin
• EMG data reveals muscle identity, timing and intensity of contractions, and antagonistic or synergistic muscle activity
• Force plates measure forces exerted on the ground, providing insights into postural stability, explosive force, power, and reaction force
• Pressure-sensitive walkways measure temporal and spatial parameters of walking, identifying gait abnormalities
• Accelerometers measure acceleration, quantifying gait characteristics
• Inertial Measurement Units (IMUs) report specific gravity and angular rates, equipped with gyroscopes and accelerometers
• Wearable technologies, such as smartwatches, track walking speed, step length, double support time, walking asymmetry, and stair speed

Types of Postural Control

• Steady-state balance involves controlling the center of mass relative to the base of support in predictable and non-changing conditions (e.g., sitting, standing, walking at a constant speed)
• Reactive balance allows for balance recovery following unexpected disturbances or perturbations (e.g., tripping, being bumped)
• Proactive (anticipatory) balance activates muscles for balance in advance of potential disruptions (e.g., stepping onto a step, lifting a heavy object)
• Most tasks require a combination of steady-state, reactive, and proactive balance
• Motor systems, including the frontal cortex, motor cortex, brainstem, and spinal networks, coordinate muscle synergies to maintain stability and balance

Test your knowledge on postural control mechanisms and their importance in maintaining stability. This quiz covers various components such as feedforward control, sensory systems, and the functions of the center of mass and center of gravity. Perfect for students studying human movement or kinesiology.