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Biomechanics of Human Movement

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					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

Sensory                             Motor
              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):



1) Activates Supporting Musculature
2) 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