Posture

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Posture
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Biomechanics

• our muscles and bones operate as a series of
  lever systems, that is they include an
  operational force supplied by the muscle, a
  fulcrum which is the joint between bones and a
  force to be overcome the work to be performed.

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Biomechanics
d
dr
F
Fr
1st class lever to enable balance (no
movement) F ? d Fr ? dr
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Balance

• Balance is achieved when the centre of gravity
  is vertically aligned with the base of support.
  Stability is dependent upon the size of the base
  of support and the height of the centre of
  gravity.

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Standing

• Highly efficient
• Balance is dynamic rather than static
• Energy expenditure is low

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Spinal curves

• One C shaped curve at birth
• Two reverse curves in cervical and lumbar regions
• Curves return to C with age

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Lying

• Lying prone results in marked lordosis
• Lying supine, curves will depend on support
• Disc pressure much higher when lying sideways

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Sitting

• Support the weight of the trunk
• Relax muscles
• Maintain lordosis
• Reduce intra-discal pressure

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Squatting

• Full flexion of the knees
• May affect circulation
• Said to aid emptying of the bowels

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Squatting
Squatting - said to aid in the emptying of the
bowels
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Working posture

• In general, a varied working posture is better
  than a fixed working posture, but a working
  posture that is static and relaxed is better than
  one which is static and tense.

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Awkward postures movements

• Bending the back forwards or sideways more than
  20 degrees
• Twisting the back more than 20 degrees
• Backward bending of the back more than 5 degrees
• Bending the head forwards or sideways more than
  20 degrees
• Twisting the neck more than 20 degrees
• Bending the head backwards more than 5 degrees

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Awkward postures movements

• Working with one or both hands above shoulder
  height
• Reaching forwards or sideways more than 30 cm
  from the body
• Reaching behind the body
• Squatting, kneeling, crawling, lying, semi-lying
  or jumping
• Standing with most of the bodys weight on one leg

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Awkward postures movements

• Twisting, turning, grabbing, picking or wringing
  actions with the fingers, hands or arms
• Working with the fingers close together or wide
  apart
• Very fast movements
• Excessive bending of the wrist

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Excessive bending of the wrist
15 degrees
15 degrees
Where the fingers and hands are not applying high
forces And the fingers are fairly straight (e.g.
typing)
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Excessive bending of the wrist
35 degrees
15 degrees
Where the fingers are bent or applying higher
forces (e.g. gripping)
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Excessive bending of the wrist
15 degrees
20 degrees
Where the wrist is bent to the side
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Case study 1
Is this a good posture? How could you tell?
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Case Study 2
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Case Study 3
Surveying in Tank Farms requires many awkward
postures
Us Dept. of Energy, Hanford
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Case Study 4
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Case Study 5
He used to be a motor mechanic