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Human-Computer Interaction in Office and School Environments IE 327 Class #17.

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Presentation on theme: "Human-Computer Interaction in Office and School Environments IE 327 Class #17."— Presentation transcript:

1 Human-Computer Interaction in Office and School Environments IE 327 Class #17

2 Outline Brief review of cumulative trauma disorders (CTDs) Ergonomics and computer workstations in office environments Focus on children and computers in school environments

3 FRONT thoracic outlet syndrome (N) rotator cuff tendinitis (T) bicipital tendinitis (T) radial tunnel syndrome (N) medial epicondylitis (T) posterior/anterior interosseous syndrome (N) hypothenar hammer syndrome (V) De Quervain’s syndrome (T) digital neuritis (bowler’s thumb) (N) trigger finger (stenosing tenosynovitis) (T) focal dystonia (writer’s cramp) (M) Dupuytren’s contracture (T) hypothenar hammer syndrome (V) carpal tunnel syndrome (N) flexor tendinitis (T) flexor tenosynovitis (T) cubital canal syndrome (N) lateral epicondylitis (tennis elbow) (T) Disorders (by type): T = Tendon M = Muscle N = Nerve V = Vascular J = Joint Musculoskeletal disorders which may be work related (WRMSDs) (cumulative trauma disorders, repetitive strain injuries)

4 Carpal Tunnel Syndrome

5 History of WRMSDs #1 1713 – first described by Ramazzini as a risk for butchers 1855 – “scriveners’ palsy” (writers’ cramp) in England due to overuse of quill

6 History of WRMSDs #2 1960s – Japanese keypunch operators (faster, still injuries) 1970s – also in Europe, Australia, US, in electric typewriters and PCs 1981 – NIOSH office study 1990s – Major effort by OSHA- NIOSH in reducing WRMSDs Why not typewriters?

7 Extent of Problem 15% prevalence – 1988 National Health Interview Survey of the US population 63% of which in hand and wrist 14% prevalence – in 1995 resurvey 17% prevalence for those 50-59 24% prevalence for those 60-65

8 Highest Rates ( BLS, per 200,000 hrs ) Industry (SIC)19932001 Meat packing15.07.1 Poultry processing6.73.2 Auto assembly5.66.9 Banking, insurance-0.6 Communications-0.4 All private (average)0.300.24

9 Upper Limb WRMSDs as % Claims by Job (NSC, 1997) Job Class % of Total Claims Computer programming27.3 Meat packing22.2 Clerical, office13.9 Newspaper publishing9.0

10

11 Key Factors in Office Ergonomics Seated posture Visual display terminal Keyboard Mouse and other input devices Notebooks and hand-held PCs Rest breaks Psychosocial factors

12 Posture - Office Environment ■ Some standing – copying, PC station ■ But sitting is most common posture

13 Seated Posture - Problems Pelvis rotates backward Spine flattens Lordosis → kyphosis Disc pressure increases 75% Lordosis Kyphosis

14 Seated Posture - Remedy Maintain lordosis ↓ disk pressure Use lumbar pad (↓ 8% per 1 cm) Tilt backrest (↓ 13% per 10°) Use armrests (↓ pressure 16%) (Andersson, Örtengren, 1974)

15 Seated Posture – Optimum? Standard posture:  90° hip angle  90° elbow angle Keyboard at elbow rest height Is the basis for many design guidelines 90°

16 Seated Posture – Optimum? Grandjean (1983) survey:  Only 10% sit so  Keyboards are higher  Most lean back at 104°  Desire to ↑ back angle  Led to forward-sloping or saddle chairs (Mandal, 1981; Congleton, 1985) 126°

17 Seated Posture – Key factor ■ Avoid postural rigidity – sit/stand chair ■ Alternate postures and tasks

18 Key Factors in Office Ergonomics Seated posture Visual display terminal Keyboard Mouse and other input devices Notebooks and hand-held PCs Rest breaks Psychosocial factors

19 Visual Display Terminal Height of VDT screen  Line of sight of -15° (-9°,-45°) below horizontal  Larger angles ↓ occular exposure (‘dry eyes’) Preferred screen distance  Average of 59 cm  Intermediate resting focus -15° 59

20 Preferred Settings and Design Recommendations for a Computer Workstation Workstation Feature Brown (1980) Grandjean (1983,1984) AIHA Guide (1983) BSR/HFES 100 (2002)Design Feature Keyboard Height (cm)748047-7356-72Elbow rest height Screen height (cm)9910991-13067-84 est.Seated eye height Screen angle10°5°±10°±20°Small, avoid glare Screen distance (cm)5976->40Resting focus Seat height (cm)504836-5338-56 est.Popliteal height Type of StudyLab-100Field-681% F–99% M5% F–95% M

21 Keyboard – Basic features Slope: 0-15° (typewriter ~ 30°) Key size:  1.2 x 1.2 cm  2 cm separation Key resistance:  max 0.15 kg  tactile feedback But most exert 4 – 7 times larger force than necessary 30° 10°

22 Keyboard – Keying Forces 4 – 7 times larger than necessary (Armstrong, Foulke, 1994) force ratio = max min 6 – 20% MVC (Martin, Armstrong, 1996) main problem! min max

23 Keyboard – CTS Impairment CTS impaired exerted twice (10x min) the force as non impaired (Lowe, Freivalds, 1999) Due to sensor and motor nerve impairment Vicious cycle - aggravates the problem

24 Keyboard – Split, angled 40° ulnar deviation, 13% ↑ CT pressure 76° forearm pronation, muscular fatigue 50° wrist extension, CT pressures = 2x injury threshold Negative slope keyboard Maltron keyboard 40° 50° 76°

25 Keyboard - Layout QWERTY – Sholes (1878)  Like printer’s type case?  To prevent key jamming? Dvorak (1936) alternative  Most keys on home row  Most frequent keys→ strongest fingers  5% faster? (US Navy) Not worth retraining millions of typists

26 Keyboard – Chord type One character requires simultaneous activation of two keys 50% faster (Seibel, 1964) One-handed use Small, portable Special functions:  mail sorting  court stenotyping

27 Keyboard – Numeric pads Unfortunately two alternatives Telephone is 5% faster, with 50% less errors (Deininger, 1960; Conrad and Hull, 1968) BSR/HFES 100 recommends either Worst situation = causes confusion

28 Key Factors in Office Ergonomics Seated posture Visual display terminal Keyboard Mouse and other input devices Notebooks and hand-held PCs Rest breaks Psychosocial factors

29 Mouse and Other Input Devices

30 Clear speed-accuracy tradeoff Touch screen, light pen: fast but inaccurate Cursor keys, joystick: unacceptable Mouse ranks high in all categories (trackball is a close second) Thus the ubiquitous mouse, but problems!

31 Mouse - Problems 60° ulnar deviation – too far out 45° lateral shoulder rotation – too far out 50° wrist extension – too high Overgripping, 2.8 x min force CT pressures at injury level (30 mm Hg) 50°

32 Mouse – Remedies, Alternatives Use of drag-lock feature Upright handle redesign  power grip  thumb activation  23%↑ force capability  ↓ pain intensity (Aarås and Ro, 1999) Renaissance Mouse

33 Mouse - Alternatives Trackball (Burgess-Limerick, 1999)  ↓ ulnar deviation  ↑ wrist extension Touchpad (Akamatsu, MacKenzie, 2002)  22% ↓force  19% slower Trackpoint (Batra, Dykstra, 1998)  ↑ forearm loading  ↓ performance

34 Key Factors in Office Ergonomics Seated posture Visual display terminal Keyboard Mouse and other input devices Notebooks and hand-held PCs Rest breaks Psychosocial factors

35 Notebooks and Hand-held PCs 34% of US 2000 PC market (Sommerich, 2000) (Now over 50%) Reduced size and weight Smaller keys and screen Lack of mouse (unless added) ↓ keying speed (Yoshitake, 1995) ↑ neck flexion, ↑ shoulder flexion Worse with hand-held PCs

36 Rest Breaks Provides relief for frequent motions Also relief for color adaptation and ocular accommodation Short rest pauses (1-5 min) (Graf, 1960) Active rather than passive Irregular, spontaneous intervals At least every hour Perhaps even micropauses Use them!!

37 Psychosocial Factors Work environment factors  High workload (lack of rest?)  Monotonous work (counterintuitive?)  Low job control Individual factors  Gender – females at ↑ risk  Age – older workers at ↑ risk  Pain sensitivity – chronic pain-spasm reflex As ergonomists, little knowledge or control

38 Ergonomics Guidelines for Computer Use by School Children Back supported by chair Feet firmly on floor Chair seat not pressing into back of knees Head erect or slightly forward Elbow angles < 90° Upper arms close to body Wrist neutral (straight with forearm 90° GOOD

39 Adjustment of Chair Height If chair is too low:  Head tilted up  Shoulder abduction  Elbows < 90°  Wrist flexion  Mouse use is difficult BAD

40 Chair Distance from Keyboard If the chair is too far from the keyboard, Either: Back not supported Or: Arm abducted Elbow extended BAD

41 Keyboard and Wrist Angle Normal – Ulnar deviationSplit – Neutral wrist BAD GOOD

42 Change Postures Alternate posture may be OK for some time Best Posture OK BEST

43 CONCLUSIONS – What can we do to prevent WRMSDs in the office environment? 50% psychosocial – difficult to change 50% job-related/physical – can change  frequency:  give and use rest breaks  limit to 8-hour days (no 12-hr)  limit pace - no incentives/keystroke counts  tradeoff with productivity!  force: use minimum (redesign/training)  posture: keep neutral (redesign/training)

44 Writers’ Cramp – Why? Problems with quills:  Overgripping of thin shaft  Co-contractions of forearm flexors and extensors  Focal dystonia (treat with lidocaine) For the digitally challenged:  Oversized pens  Large (13.6mm) flared grip area  ↓ flexor pollicis EMG (Udo,Otani, 2000) Dr. Grip

45 QUESTIONS?


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