Biomechanics of Human Movement Biomechanics of Balance

Biomechanics of Balance Topics Applications Relating to Biomechanics of Balance Determinants of Stability Factors Influencing Stability Role of Sensory Input in Balance CNS Strategies for the Maintenance of Balance Enhancing Balance Assessment of Balance

Biomechanics of Balance Applications Incidence of Falls

Biomechanics of Balance Incidence of Falls 1.8 million falls among elderly result in medical treatment 1/3 of all Community-dwelling adults experience at least one fall yearly Sixth leading cause of death in over 65 age group

Biomechanics of Balance Applications Incidence of Falls Economic Impact of Falls

Falls…..Economic Impact 16.4 Billion Dollars annually Average cost per fall - $9400 48% of cost paid by Medicare

Biomechanics of Balance Applications Incidence of Falls Economic Impact of Falls Influence of Pathology and Injury on Balance

Falls…..Influence of Pathology on Balance Head Injury Stroke Vestibular Dysfunction Orthopaedic Joint Injury Parkinson’s Disease Alzheimer’s Disease Degenerative Joint Disease Muscle Atrophy Diminished Balance

Biomechanics of Balance Applications Incidence of Falls Economic Impact of Falls Influence of Pathology and Injury on Balance Relationship between balance and posture – implications

Balance – Influence on Posture

Biomechanics of Balance Applications Incidence of Falls Economic Impact of Falls Influence of Pathology and Injury on Balance Relationship between balance and posture – implications Sport Considerations Performance Injury Prevention

Biomechanics of Balance Sport Considerations Performance Injury Prevention

Biomechanics of Balance What Causes Instability? Destabilizing “External “Torques Act on Segments  Gravity Distribution and Position of Mass Inertia External Forces

Biomechanics of Balance What Produces Stability? Stabilizing “Internal Torques” Act on Segments Muscle Forces Ligament forces Distribution and Position of Mass External Forces

Biomechanics of Balance Stability Stability is Maintained as long as the: Internal (Stabilizing) Torques = External (Destabilizing) Torques

Biomechanics of Balance Factors Influencing Stability In Practical Terms: Sensory Factors Motor Factors Biomechanical Factors – Size of the base of support Height of the COG above the base of support Mass

Biomechanics Center of Gravity Definition – The point around which the mass of the body is equally distributed

Biomechanics Center of Gravity – Factors Influencing Mass Location of Mass – position of the body segments Added (external) mass

Biomechanics of Balance Control of Balance CNS Motor Sensory

Biomechanics of Balance Sensory Input Purpose: To provide the CNS with information about the direction and magnitude of De-Stabilizing Torques To monitor the effects of Internal Stabilizing Torques Components: Vision Somatosensory Vestibular

Biomechanics of Balance Somatosensory Muscle Spindles Joint Receptors Tendon Organs Mechanoreceptors

Biomechanics of Balance Vestibular System - The Inner Ear The Vestibular System provides information about: Head Linear Acceleration Head Rotation (angular accelerations) Head Position

Biomechanics of Balance Sensory Input and Control Sensory Input activates reflexes that (in order): Activates Supporting Musculature Activates Muscle synergies to produce correction

Biomechanics of Balance CNS and Control The CNS Implements “Strategies” that are intended to be selectively applied to various levels of instability Quiet Stance – maintained by postural alignment, associated joint stiffness and muscle tone

Biomechanics of Balance The Ankle Strategy Minimal Instability – the “Ankle Strategy” Simple Response Rotation at the ankle Inverted Pendulum

Biomechanics of Balance The Hip Strategy Greater Instability – the “Hip Strategy” More complex Increased translation of mass Adjustment at Hip

Biomechanics of Balance The Stepping Strategy Maximum Instability – the “Stepping Strategy” Most complex Multiple segments involved Slowest

Biomechanics of Balance Muscle Response to Instability Muscle Response to Instability Results in a Distal to Proximal Activation Pattern Gastroc/Soleus – 90 – 100 msec Hamstrings – 120- 130 msec Psoas – 130 – 140 msec

Biomechanics of Balance Can Balance Be Improved???? YES !! Sensory Input CNS Processing Muscle Output Cognitive Factors All capable of Degradation…or…Improvement (sometimes)

Biomechanics of Balance Can Balance Be Improved???? Assistive Devices

Evaluating Balance Force Plate