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5.4 Biomechanics: Seating
Biomechanics of Sitting
Seated work and chair design
lumbar spine while standing erect is curved forward
thoracic spine is curved backward
Backrest inclination level -
the angle between the backrest and the seat surface should be between 110 degrees and 120 degrees.
Body weight is transferred to the following when sitting:
Chairs should distribute weight as far as possible
Lower back pain
Primary mechanism of low back pain is localized muscle fatigue due to prolonged static muscle contractions
Provides both a seat back that inclines backwards and has a lumbar support that is cirical to prevent excessive low back disc pressures.
Major ergonomics issues:
Seat back Lumbar support (5 cm)
Seat back Inclination angle (110 degrees)
Seat back Height
Seat pan Tilt angle
Seat Pan height Adjustment
Chair Design and Back Pain
Task and workplace layout greatly affect torso postures and low back stresses
Myoelectric activity (EMG) decreases when back rest inclination increases
Amerian National Standards Institute (ANSI)
on avg, people spend 1/3 of their lives in a chair.
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