Seated Work and Workplace Design Flashcards
Main contact points
Seat is the main support
Through the ischial tuberositites and the soft tissue
Secondary contact points
Feet to floor/chair
Back to backrest
Arms to armrest
Advantages of siting posture
Stability for tasks requiring fine motor movement or conc vision
Less energy than standing
Reduces stress on LE
Reduce hydrostatic pressure on legs
Seated posture reflects
the task, chair, individual
Seated postures - based on
Center of mass location relative to the ischial tuberosities
Seated posture - Affects
% TBW transferred to different supported surfaces
Affects/reflects lumbar spine position
The more ant tilt you have
the more lordosis you have
The more post tilt of the pelvis
the lordosis will disappear and may end up with some kyphosis
Posture selected reflects
Individual seating habits Task demands Height and inclination of chair seat Position, shape, inclination of backrest Presence of other types of support
Sitting relaxed (no sacrum support) CoM Feet support Lumbar spine Disk pressure EMG
CoM directly above IT
Feet support about 25% of TBW –> lumbar spine is straight or in slight kyphosis
Disk pressure higher than standing, same EMG activity
Sitting erect (no sacrum support) CoM Lumbar spine Disk pressure EMG
CoM directly above IT Achieved by rotated pelvis ant Lumbar spine is in slight lordosis Disk pressure lower than relaxed sitting Same EMG activity
Sitting leaning forward CoM How to achieve this position Disk pressure EMG
CoM in front of IT
Tilt pelvis forward or leave pelvis and induce kyphosis of the spine
Both cases - disk pressure higher than standing
EMG activity inc
Sitting leaning back CoM Feet support Disk pressure EMG
CoM behind IT
Feet support less than 25% of TBW
Backward rotation of pelvis and kyphotic lumbar spine
Disk pressure same as relaxed sitting, higher than standing
EMG activity lower
Disk force reflects
posture and supported load
Reduction of force - achieved by
arm support, sitting straight, and unsupported feet
Greater force found in
ant leaning, which was reduced by straight back
Posterior leaning force is similar to
relaxed sitting force
Office desk and disc force - disc force reflects
Posture, supported load, task, environment
Office desk and disc force - lower force was found when
writing and when depressing a foot pedal
Office desk and disc force - higher force was found when
typing and when lifting a weight
Backrest inclination - the more you have
the less activity of the erector spinae
Lumbar support vs backrest inclination - which has biggest difference
Use of lumbar support more important than backrest inclination
To reduce disc pressure when seated
Use lumbar support
Increase backrest inclination
Writing at desk
Dec noted compared with other tasks
Arms supported by the desk
Typing and lifting a phone
Inc pressure
Larger external load moments
Stability requirements
Leaning forward unsupported does what to disc pressure
inc
Posture fixity
maintaining the same posture for a period of time
We want to reduce this
10-15 minute breaks for every 2 hours seated
Seat angle and erector spinae
No differences
a good chair
functionally adapts to the occupant and the task
Comfort frequently defined as
the absense of discomfort
Determining comfort based on
Observe body posture and movement
Observe task performance
Direct subjective ratings of general comfort
Foot support - High sitting
Affects circulation
Pressure applied close on thighs close to the knees
Leg swelling –> pressure on sciatic nerve
Should not feel the edges of the chair
Foot support - high sitting - semi seated position
eases transition to standing but increased lower extremity stress
Seat height affects buttocks pressure - low seat height =
too small contact area
Seat height affects buttocks pressure - high seat
stresses on the legs inc which may cause swelling
Clinical aspects of seated posture
Avoid postural rigidity
Workers must be altered to problems occurring from long lasting low level muscular efforts
Workstation Goal
Function, comfort, user friendliness, minimizing spinal disc forces
Workstation - lumbar support
Use backrest that has lumbar support allowing for spinal curvature similar to standing
Workplace - leg positions
movement of pelvis caused by different positioning of knees and hips
Workplace - seat design
tilted seats, contoured or cushioned support to ideally position pelvis, use of armrest, adjustibility, seat width, height and depth
Workplace - desk design
bottom height, top height, inclination of surface, work suface size, surface friction
