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
Orthopaedic Joint Injury
Vestibular
Dysfunction
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