Transcript Psy 552 Ergonomics & Biomechanics

Psy 552 Ergonomics &
Biomechanics
Lecture 19
Your workstation chair
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Seat height:
Seat depth:
Seat width:
Backrest:
Seat back angle:
Lumbar support:
Lumbar support width:
Distance between arm
rests:
Non MMH Tasks
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Pose considerable risk of MSDs.
Should avoid (from text):
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Highly repetitive arm movements
Sustained static postures
Minimize should flexion and abduction
Reduce or eliminate forceful or heavy peak
exertions
Require frequent rest breaks.
Work station guidelines
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The upper limb itself exerts forces on the
shoulder joint.
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Guideline
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“The hand should not have to reach frequently or be
held above the shoulder height for sustained periods.”
Potential outcome if violated:
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Shoulder muscle fatigue, shoulder tendonitis, bicep
tendonitis – in older workers
Work station guidelines (cont.)
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Guidelines
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Short duty cycles <20 sec of work and 40 sec of
rest with light loads < .4 kg with arms below
shoulder level are acceptable as long as the work
is not performed over long periods.
High velocity movements should be closely
evaluated to determine potential injuries.
Work station guidelines (cont.)
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Guidelines
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Avoid holding of loads when the upper arm is
flexed and the elbow is extended.
Use padded supports for the elbow and forearm to
reduce loads at the shoulders.
Use tool balancers to support frequently used
tools to reduce moments at the elbow and
shoulder.
Work station guidelines (cont.)
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Guidelines
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Provide adjustable fixtures to place the work in
the optimal position for the worker’s task.
When forearm rotation is required, flex the elbow.
Optimal workstation design with respect to
upper limb movement is complex. Mock-ups
can provide insight into the design process.
Work station guidelines (cont.)
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Head and neck
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Guidelines
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Work stations should be designed to avoid significant
neck flexion > 30 degrees.
Adding arm support can reduce the muscular activity
around the neck.
Tilting the work surface can reduce neck flexion.
Position computer monitors to minimize neck flexion.
Design work to produce an upright head position.
Provide for frequent breaks.
Work station guidelines (cont.)
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Torso
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When the torso is flexed 30 degrees, 50% of the
maximum moments are produced.
Endurance for stooped postures decrease significantly
when postures require > 30% of isometric strength.
Guidelines
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The majority of men and women can maintain a 20 degree
stooped posture during the work day.
Provide adjustable work surface heights to prevent
stooping and maintain a vertical position.