Posture
Why is posture important?
 ability of an individual to maintain and adjust his or her overall
body position so the extremities can be utilized to perform gross
and fine motor tasks.
 Proximal stability for distal mobility
Static Posture
 Body and its segments are aligned and maintained in a position
 Eg. Standing, sitting, lying
Dynamic Posture
 The body and/or its segments are moving
 Eg. Walking, running, jumping, throwing, and lifting
Postural Control
 A person’s ability to maintain stability of the body and body
segments in response to forces that threaten to disturb the body’s
structural equilibrium
 Static – maintenance of a stability against gravity
 Dynamic – maintenance of stability during movements of the body
or body segments and/or changes in the supporting surface.
However, even static postural control is NOT completely static. WHY?
Sway – analyze center of pressure with force plate to see this.
Sagittal plane – 120
Frontal plane - 160
What does postural control (balance) require?
 Intact CNS that can integrate and process a variety of inputs and
then respond to these inputs
 Inputs
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Vision
Vestibular
Proprioception – muscle and joint receptors
Sensation – tactile and pressure
 Output from CNS
1. Instructions to certain muscles to fire
What happens when one or more of these inputs are impaired?
1. postural control is altered/reduced
2. body compensates by depending on the other intact inputs
Examples of altered/impaired inputs
Astronauts in weightless – What is altered?
1. proprioception
2. tactile
3. vestibular
Can a sprained ankle alter one’s postural control?
Why?
 Altered kinesthesia secondary to stretching of ligaments and joint
capsule
Postural control or balance has most recently been studied via perturbation
studies.
These studies have helped identify three different strategies/patterns for
maintaining postural control.
1. Ankle
2. Hip
3. Stepping
The strategy used depends on:
1. magnitude/intensity of the perturbation
2. limitations in other strategies (ROM, ligamentous strategies, etc.
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Ankle strategy
 posterior perturbation of surface results in activation of anterior
musculature
 dorsiflexors, hip flexors, abdominals, neck flexors
Hip strategy
 20:
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


limitation in ankle motion
excessive velocity of perturbation
excessive displacement
standing on unstable surface where ankle strategy is
ineffective
 posterior perturbation of surface results in a forward sway &
activation of anterior musculature:
 hip flexor and abdominal musculature
Stepping strategy
 20:
 excessive displacement or velocity
 ineffective ankle and/or hip strategies
 posterior perturbation  forward step
 to prevent falling when limits of stability have been exceeded 
line of gravity falls outside the base of support
Forces that affect postural control or equilibrium:  same as gait
 External
1. gravity
2. ground reaction forces
3. inertia
 Internal
1. muscle activity
2. passive tension of ligaments, tendons, capsules, etc.
Relationship of Line of Gravity and Postural Control
COG anterior to S2
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Static Optimal Posture
Ankle – just anterior to lateral malleolus  dorsiflexion moment  soleus
activity
Knee – just anterior to anterior to knee  extension moment  passive
structures (posterior capsule & ligaments)
Hip – through the greater trochanter (slightly posterior to hip joint) 
extension moment passive structures (iliofemoral, pubofemoral,
ischiofemoral)
L/S – LOG passes thru body of L5 which is anterior to the other lumbar
vertebrae  extension moment  resisted by the anterior longitudinal
ligament
Head – LOG thru external auditory meatus  falls anterior to AOR 
flexion moment  ligamentum nuchae, tectorial membrane, neck extensors
What happens if there are deviations from this normal posture?
 effectively  the moment arm/torque being applied to a joint thus
requiring more torque/force to counteract this  torque
Where is this additional force/torque coming from?
1. muscular activity
2.  stress on passive structures
Deviations from Optimal Posture
What is the concern with deviations from optimal posture?
1.  energy expenditure 20 to  muscular activity
2.  stress on supporting structures  injury
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Lateral View
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Forward head posture
Excessive anterior tilt
Sway-back posture
Flat-back posture
Military posture
Flexed knee posture
Genu recurvatum
Anterior/Posterior view
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Scoliosis – primary vs. compensatory curves
Genu valgum – “knock knees”
Genu varum – “bow-legged”
Pes planus
Pes cavus
Hallux valgus
Toe clawing – active vs. passive
Hammer toe – extension of MTP and DIP w/ flexion of PIP
Proposed sequence of events for adolescent idiopathic scoliosis:
1. failure in the supporting and/or control systems
2. lateral flexion moment
3. deviation of the vertebrae w/ rotation
4. compression of the vertebral body (concave-side)
5. inhibition of growth of vertebral body (concave-side)
6. wedging of vertebra
7. head out of line w/ sacrum
8. compensatory curve
9. adaptive shortening of muscle (concave –side)
10.stretching of muscles and passive structures (convex-side)
What factors affect postural control?
1. Age
2. Pregnancy
3. Lifestyle / occupation
Relationship of Posture to RSIs (Repetitive Strain Injuries)
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