Ergonomics/Human Factors “ Occupational Biomechanics”

1. Ergonomics/Human Factors“Occupational Biomechanics” Hardianto Iridiastadi, Ph.D.

2. Motivation • Epidemiological support (1984) • 23 people with musculoskeletal impairments in the US • Musculoskeletal problems rank second; cost $65 billion/yr • Problems rank second in physician visit, third in hospitalizations, and third in surgical procedures • Low back pain (LBP) is one of the most common problems, and is associated with substantial amounts of morbidity, disability, and economic loss

3. Motivation • Class • LBP statistics • How it occured • Implications • Other problems? • See also CTS clip

4. Definition • What is biomechanics? • Mechanical behavior during work • Follow laws of physics • Interdisciplinary science • Physics, biology, engineering • Behavioral science • Occupational biomechanics • Study physical interactions of workers and their tools, machines, materials • To enhance performance and minimize MSDs

5. Muscle Testing • Why? • Understand strength (force or moments) • Compare with job requirements • Measurements • Isometric (Static) • Dynamic

6. Work-related Musculoskeletal Disorders (WMSDs) • What it is • Physical problems, symptoms, issues, etc. • Associated with work • Risk factors • Deviated postures; Static postures • Repetitive; Forceful tasks • Contact stress; Vibration • Temperature (cold)

7. WMSDs • What are they? Injuries that affect the soft tissues of the body (muscles, tendons, nerves, ligaments) that develop gradually over time. • Other terms • Cumulative trauma disorders (CTDs) • Repetitive strain injuries (RSIs) • Repeated trauma disorders (RTDs)

8. Costs Associated with WMSDs • 705,800 cases of work days lost in 1995. Mean job absence per case is 20 days. (Bureau of Labor, 1995) • $13-$20B in annual costs in lost days and compensation (NIOSH, 1996) • $7.4B in worker’s compensation costs alone (CTD News, 1996).

9. Costs Associated with WMSDs • A recent NIOSH study estimated 22% of all VDT workers had some type of WMSD problem. • Underestimated • Difficulty in diagnosis these types of injuries • Seen as normal aches and pain • Some states say they aren’t compensable injuries (can’t prove the work did it)

10. Types of WMSDs • tendon disorders • nerve disorders

11. Types of WMSDs neurovascular disorders • Tendinitis is inflammation of the tendon causing pain when the tendon is placed under tension. • Stenosing tendinitis is inflammation of both the tendon and the synovial tissue that has caused a dramatic increase in the friction between the tendon and the tendon sheath.

12. Back WMSDs • Abnormal Conditions • Degenerative disc disease • Herniated disc • Ligament sprain • Muscle strain • Contributing Factors • Prolonged static load on the upper torso musculature • Awkward posture: extensive trunk flexion or extension • Lifting of objects from the floor

13. Back WMSDs • Prevention and Control • Proper lifting techniques • Stretching exercises

14. Shoulder WMSDs • Abnormal Conditions • Shoulder Tendonitis • Contributing Factors • Prolonged flexion/abduction of the shoulders • Frequent reaching above the shoulders • Tasks which pull shoulders back and down • Prolonged load on the shoulders • Repetitive throwing of heavy loads

15. Shoulder WMSDs • Prevention and Control • Increase recovery time where force requirements are high • Reduce awkward shoulder postures using fixtures, clamps, etc. • Reduce frequent reaching above the shoulders • Reduce loads on the shoulders

16. Tendon Disorders • Rotator Cuff Injuries – Tendinitis at the head of the humerus. From Putz-Anderson, V. (1988). Cumulative Trauma Disorders: A Manual for Musculoskeletal Diseases of the Upper Limbs. London, UK: Taylor & Francis., Fig. 6

17. Finger WMSDs • Abnormal Conditions • e.g. DeQuervain’s Disease • Contributing Factors • Vibrating tools • Repetitive Ulnar deviation • Flexion of the wrist with effort • Forceful gripping

18. Finger WMSDs • Prevention and Control • Implement job rotation and/or job enlargement • Use protective materials to absorb vibrations effects

19. Wrist CTDs • Abnormal Conditions • e.g. Carpal Tunnel Syndrome • Contributing Factors • Repetitive forceful wrist extension/flexion • High speed finger movements • Ulnar deviation • Rapid wrist rotational movement

20. Wrist CTDs • Prevention and Control • Stretching exercises • Implementation of rest periods

21. Risk Factors • Occupational Factors implicated as causes of WMSDs of the hand and wrist: • Postural stress • Forceful exertions • Repetitive exertions • Sustained (static) exertions • Localized mechanical (contact) stresses • Vibration • Cold temperature

22. Wrist Posture • The wrist has three degrees-of-freedom: • Flexion - Extension • Radial deviation - Ulnar deviation • Pronation - Supination • Deviations from a neutral posture in any of these three dimensions has been associated with an increased risk of WMSDs

23. Wrist Posture Which tool shape is best?? Depends on: location, orientation, task, etc. From Putz-Anderson, V. (1988). Cumulative Trauma Disorders: A Manual for Musculoskeletal Diseases of the Upper Limbs. London, UK: Taylor & Francis., Fig. 38

24. Controls for Postural Deviations Ulnar deviation of wrist required to hold needle-nose pliers for bench assembly work Additional Benefits: improved precision (vision) From: TJ Armstrong (1986) Hand Clinics 2:553-565

25. Example Controls for Postural Deviations Ulnar deviation of wrist required to hold knife for boning turkey thighs Additional Benefits: safety, increased wrist strength in neutral posture From: TJ Armstrong (1986) Hand Clinics 2:553-565

26. Example Controls for Forceful Exertions Concern: more effort to ‘engage’ the tool? Effort required to support tool weight and keep it from twisting out of the hand

27. Controls for Postural Deviations Install gas fuel neck (2m from floor) Operator had neck strain, 8 months of lost work Installation moved to different place on assembly line

28. Controls for Postural Deviations Install brake booster After installation of engine, radiator, bumper Installation moved earlier on assembly line Use of ‘extended’ tool

29. WMSD Prevention Strategies 1. Minimize required hand forces • design for power grip • keep handle diameters > 1.5" • use tool balancing 2. Minimize postural deviations • keep hand and forearm aligned • shape the tool to match the task • change work piece orientation

30. WMSD Prevention Strategies 3. Minimize Repetition • allow for tissue recovery and circulation • rotate workers among tasks • job enlargement 4. Design Work Practices • train workers to rest (esp. hands) • stretching exercises or warm-up • allow for slow-down with gloves 5. Recognize that these strategies will likely increase productivity in the long run

31. Sample Intervention: Before • Risk factors? • Intervention? www.osha.gov/ergonomics/ergo1.html

32. Sample Intervention: After www.osha.gov/ergonomics/ergo1.html

33. D (moments) < C (strength) Are the demands excessive? Is the percentage capable too small? What is an appropriate percentage? Task Evaluation and Ergonomic Controls

34. Strategies to Improve the Task: Decrease D Forces: masses, accelerations (increase or decrease, depending on the specific task) Moment arms: Increase C Design task to avoid loading of relatively weak joints Maximize joint strength Use only strong workers Task Evaluation and Ergonomic Controls