Biomechanics of Sitting
Seated work and chair design
  • Lordosis - lumbar spine while standing erect is curved forward
  • Kyphosis - 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
  • Seat
  • Floor
  • Armrest
  • Backrest
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:
Chair Design:
  • Seat back Lumbar support (5 cm)
  • Seat back Inclination angle (110 degrees)
  • Seat back Height
  • Seat pan Tilt angle
  • Seat Pan height Adjustment
  • Armrest 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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