Sitting provides stability for tasks requiring visual and motor skills while being less energy consuming than standing. It places less stress on the lower extremities and lessens pressure on lower extremity circulation. When sitting, the main body weight is transferred to the seat, with some weight transferred to the floor, backrest, and armrests. Sitting erect with support for the sacrum decreases the compressive force on the lumbar discs compared to sitting in other positions such as relaxed without sacrum support, leaning forward, or leaning back. Proper desk and elbow height can also minimize shoulder muscle activity and stress on the body.

2. Muhammad Arslan Yasin

3. Sitting

4. Weight Transfer:
• Main body weight transferred to seat. Some
transferred to floor, backrest, and armrests.
Advantages:
• provides stability to tasks involving visual
and motor control
• less energy consuming than standing
• places less stress on lower extremity
joints
• lessens pressure on lower extremity
circulation

5. Lower Back:
Lumbar Disc Forces

6. Cervical
Vertebrae
(C1 to C7)
Thoracic
Vertebrae
(T1 to T12)
Lumbar
Vertebrae
(L1 to L5)
Sacrum
(S1 to S5)
[Hall, 1999]

7. STANDING
SITTING
RELAXED
(no sacrum
support)
SITTING
ERECT
(sacrum
support)
SITTING
(leaning
forward)
SITTING
(leaning
back)
[Chaffin et al., 1999]

8. Chair and Disc Force
Disc
Force
[Andersson et al., 1974a]

9. Disc
Force
[Andersson et al., 1974b]
Office Desk and Disc Force

11. Lower Back
Muscle Activity

12. Erector Spinae Muscle
• extends down the back
• involved in lateral
(sideways) flexion of back &
extension activities, e.g.
maintaining back posture in
any “sitting” position
• the greater the EMG
(electromyography) muscle
activity, the greater the
compressive force on discs

13. Ideal desk and elbow height
minimize shoulder EMG
muscle activity (i.e. deltoids,
trapezii, dorsal)
[Engdahl, 1978]
Shoulders

15. Higher seating
changes the pelvic
angle towards a
more vertical
posture, decreasing
the compressive
force on discs. But,
stresses on the legs
increase, which
may cause swelling.
Legs

27. LYING

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Reference
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