Dept. of Biomedical, Industrial, & Human Factors Engineering 1 Workstation Design Sitting at Work Improves well-being, efficiency, reduces fatigue Standing is poor physiologically (static work) ¾ of worker in industrial countries are sedentary Advantages Take weight off legs Increase stability of upper body posture Reduce energy consumption Reduces demands on circulatory system Disadvantages Slackening of abdominal muscles Spine curvature impedes digestion and breathing Stresses spine and back muscles, increases disc pressure

Dept. of Biomedical, Industrial, & Human Factors Engineering 2 Seat design Comfortable chair Seat pan tilt  24º Backrest tilt º to seat pan Lumbar pad mm with apex between 3 rd and 5 th lumbar vertebrae Office chairs General recommendation: high back-rest with back contour – better to support weight of trunk Specific features Adaptable to traditional and computer work Accommodate forward and reclined seating Adjustable angle backrest Backrest height  500 mm from seat surface Backrest should have well formed lumbar pad from L3 to sacrum Seat pan: mm across, mm deep, cavity in seat, lightpad, non- slip, permeable material Footrests Adjustable height, swivel, rounded front edge, 5 arm base, user-friendly controls

Dept. of Biomedical, Industrial, & Human Factors Engineering 3 Seat design Promote lumbar support (a) Standing(b) Sitting Minimize disc pressure Discs between vertebrae and spine can be damaged due to excessive pressure Unsupported seating (i.e., no backrest) increased pressure Minimize static loading of back muscles Slumping will reduce but causes other problems Reduce postural fixity Sitting in one position Reduces blood flow to discs Chair design can allow user to rock and reduce problems Inward arch Hip Outward arch Hip rotates ~60 

Dept. of Biomedical, Industrial, & Human Factors Engineering 4 Computer workstations VDT operator tied to workstation Attention on screen Hands on keyboard Problems: Constrained posture Repetitive activities Poor photometric display characteristics Inadequate lighting Discomforts Visual strain Physical discomfort in back, neck/shoulder, forearm, wrist, hand Reported problems highest among data-entry and full- time typists

Dept. of Biomedical, Industrial, & Human Factors Engineering 5 Computer workstations Workstation characteristics linked to discomforts Keyboard height Nor forearm/wrist support Key tops too high above table Wrist deviation (keyboard design) Head inclination (visual field placement) Insufficient leg room Should provide adjustability Keyboard height Screen height, distance, inclination Document holder inclination

Dept. of Biomedical, Industrial, & Human Factors Engineering 6 Preferred VDT Workstation Settings Grandjean et al. (1983) N=68: 48 females, 20 males 45 conversational computer work, 17 data entry, 6 word procesing Desk If keyboard: 80 mm desk – mm 30 mm desk mm Overall: mm height Screen: 75 % users positioned between mm Depends more on individual preference than anthropometry Posture Trunk inclination: degrees Only 10 % upright Preferred slightly open elbows

Dept. of Biomedical, Industrial, & Human Factors Engineering 7 Preferred con’t Posture Arm/wrist support 80% used if available 50% used desk if unavailable Discomfort Was reduced by implmenting adjustable workstation with preferred settings Neck, shoulder, back reduced Effects of adjustable workstation enhanced by good chairs

Dept. of Biomedical, Industrial, & Human Factors Engineering 8 Guidelines Furniture as flexible as possible Keyboard height mm Screen center height mm fro floor Screen inclination from horizontal 105 degrees Screen distance to table edge mm If not adjustable, not for continuous use Adjustable controls should be easy to use Provide ample knee and foot space Promote easy body movement but minimize excessive motions

Dept. of Biomedical, Industrial, & Human Factors Engineering 9 Keyboard Design Traditional design with 4 parallel rows of keys Unnatural posture of wrists and hands Mechanical required more force Modern keyboard activity More keys Less force Greater keying speed More users Physical discomfort, tendinitis, tenosynovitis, CTS Flat keyboard assist resting of forearm and wrist on desk Minimal height Split keyboards: 2 pairs with 30 degree opening and downward tilt 0-90 degrees Less pain fatigue Less electrical activity with degree tilt downward and split Large forearm/wrist support New technologies – voice recognition

Dept. of Biomedical, Industrial, & Human Factors Engineering 10 Carpal Tunnel Syndrome Affected area