Biomechanics of Human Movement Biomechanics of Balance

Biomechanics of Human MovementBiomechanics of Human Movement

Biomechanics of Balance Biomechanics of Balance

Biomechanics of BalanceBiomechanics of Balance TopicsTopics

Applications Relating to Biomechanics of BalanceApplications Relating to Biomechanics of Balance Determinants of StabilityDeterminants of Stability Factors Influencing StabilityFactors Influencing Stability Role of Sensory Input in BalanceRole of Sensory Input in Balance CNS Strategies for the Maintenance of BalanceCNS Strategies for the Maintenance of Balance Enhancing BalanceEnhancing Balance Assessment of BalanceAssessment of Balance

Biomechanics of BalanceBiomechanics of Balance

ApplicationsApplications

Incidence of FallsIncidence of Falls

Biomechanics of BalanceBiomechanics of BalanceIncidence of FallsIncidence 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



Incidence of FallsIncidence of Falls Economic Impact of FallsEconomic Impact of Falls

Falls…..Economic ImpactFalls…..Economic Impact

16.4 Billion Dollars annually

Average cost per fall - $9400

48% of cost paid by Medicare



Incidence of FallsIncidence of Falls Economic Impact of FallsEconomic Impact of Falls Influence of Pathology and Injury on BalanceInfluence of Pathology and Injury on Balance

Falls…..Influence of Pathology on Falls…..Influence of Pathology on BalanceBalance

Stroke

Alzheimer’s Disease

Head Injury

Parkinson’s Disease

Vestibular Dysfunction

Degenerative Joint Disease

Orthopaedic Joint Injury

Muscle Atrophy

Diminished Balance



Incidence of FallsIncidence of Falls Economic Impact of FallsEconomic Impact of Falls Influence of Pathology and Injury on BalanceInfluence of Pathology and Injury on Balance Relationship between balance and posture – Relationship between balance and posture –

implicationsimplications

Balance – Influence on PostureBalance – Influence on Posture



Incidence of FallsIncidence of Falls Economic Impact of FallsEconomic Impact of Falls Influence of Pathology and Injury on BalanceInfluence of Pathology and Injury on Balance Relationship between balance and posture – Relationship between balance and posture –

implications implications Sport ConsiderationsSport Considerations

– PerformancePerformance

– Injury PreventionInjury Prevention


Sport ConsiderationsSport Considerations

Performance

Injury Prevention


What Causes Instability?What Causes Instability?

Destabilizing “External “Torques Act on Segments Destabilizing “External “Torques Act on Segments • Gravity Gravity

• Distribution and Position of MassDistribution and Position of Mass

• InertiaInertia

• External ForcesExternal Forces


What Produces Stability?What Produces Stability?

Stabilizing “Internal Torques” Act on Stabilizing “Internal Torques” Act on SegmentsSegments

• Muscle ForcesMuscle Forces• Ligament forcesLigament forces• Distribution and Position of MassDistribution and Position of Mass• External ForcesExternal Forces


StabilityStability

Internal (Stabilizing) Torques = External (Destabilizing) Torques

Stability is Maintained as long as the:

Biomechanics of BalanceBiomechanics of BalanceFactors Influencing StabilityFactors 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

BiomechanicsBiomechanicsCenter of GravityCenter of Gravity

Definition – The point around which Definition – The point around which the mass of the body is equally the mass of the body is equally

distributeddistributed

BiomechanicsBiomechanicsCenter of Gravity – Factors InfluencingCenter of Gravity – Factors Influencing

MassMass Location of Mass – position of the body Location of Mass – position of the body

segmentssegments Added (external) massAdded (external) mass


Control of BalanceControl of Balance

Sensory

CNS

Motor

Biomechanics of BalanceBiomechanics of BalanceSensory Input 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


SomatosensorySomatosensory

Muscle SpindlesMuscle Spindles Joint ReceptorsJoint Receptors Tendon OrgansTendon Organs MechanoreceptorsMechanoreceptors

Biomechanics of BalanceBiomechanics of BalanceVestibular System - The Inner Ear

Head Linear AccelerationHead Linear Acceleration Head Rotation (angular accelerations)Head Rotation (angular accelerations) Head PositionHead Position

The Vestibular System provides information about:


Sensory Input and ControlSensory Input and Control

1) Activates Supporting Musculature

2) Activates Muscle synergies to produce correction

Sensory Input activates reflexes that (in order):


CNS and ControlCNS 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


The Ankle StrategyThe Ankle Strategy

Minimal Instability – the “Ankle Strategy”

Simple ResponseRotation at the ankleInverted Pendulum


The Hip StrategyThe Hip Strategy

Greater Instability – the “Hip Strategy”

More complexIncreased translation of massAdjustment at Hip


The Stepping StrategyThe Stepping Strategy

Maximum Instability – the “Stepping Strategy”

Most complex Multiple segments involved Slowest


Muscle Response to InstabilityMuscle 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 BalanceBiomechanics of BalanceCan Balance Be Improved????Can Balance Be Improved????

YES !!

Sensory Input

CNS Processing

Muscle Output

Cognitive Factors

All capable of Degradation…or…Improvement (sometimes)

Biomechanics of BalanceBiomechanics of BalanceCan Balance Be Improved????Can Balance Be Improved????

Assistive Devices

Evaluating BalanceEvaluating Balance

Force Plate

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Biomechanics of Human Movement Biomechanics of Balance