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IE 552 Mechanics of Musculoskeletal System Dr. Andris Freivalds Class #35

IE 552 Mechanics of Musculoskeletal System Dr. Andris Freivalds Class #35. Gross Posture Analysis – OWAS. Owaco Working Posture Analysis System (OWAS, Karhu, 1977) Developed at the Finnish Institute of Occupational Health in 1970s For use in steel industry

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IE 552 Mechanics of Musculoskeletal System Dr. Andris Freivalds Class #35

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  1. IE 552 Mechanics of Musculoskeletal System Dr. Andris Freivalds Class #35 IE 552

  2. Gross Posture Analysis – OWAS • Owaco Working Posture Analysis System (OWAS, Karhu, 1977) • Developed at the Finnish Institute of Occupational Health in 1970s • For use in steel industry • Evaluation of posture at regular intervals • Four categories: back, upper limbs, lower limbs, force (<10, <20, >20 kg) IE 552

  3. 2151 = bent back, both arms below shoulders, kneeling, <10 kg load IE 552

  4. Gross Posture Analysis – OWAS • Next produce frequency distributions of OWAS postures • Rate into four level of action categories • Test-retest correlations high, r = 0.97 • Quick but simple means of categorizing gross postures IE 552

  5. Gross Posture Analysis - RULA • Rapid upper limb assessment (RULA) • Developed at the Univ. of Nottingham (McActamney and Corlett, 1993) • Upper limb postures from Group A + Table A yield anupper limb score • Trunk/leg postures from Group B + Table B yield a trunk score • Both scores combined into grand score • Determines risk or action level IE 552

  6. RULA – Group A IE 552

  7. RULA – Table A IE 552

  8. RULA • These scores are adjusted upwards: +1 if mainly static posture (>1 min) or . repeated > 4/min +1 if 2-10 kg intermittent loads +2 if 2-10 kg static or repeated loads +3 if >10 kg static or repeated loads IE 552

  9. RULA – Group B IE 552

  10. RULA – Table B IE 552

  11. RULA – Grand Score Table IE 552

  12. RULA • If RULA grand score: 1 or 2 – acceptable conditions 3 or 4 – change may be needed 5 or 6 – change required soon 7 or 8 – change required immediately • Good correlation with discomfort • Probably best for postural evaluations • Example – t-shirt turning, 12/min IE 552

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  14. IE 552 RULA A = 4 + 1 (Freq > 4/min)

  15. +1 due to static posture IE 552

  16. Grand score = 4, Borderline risk IE 552

  17. IE 552

  18. Quantitative Upper Limb WRMSD Risk Assessment – Strain Index 1 • Strain Index (SI, Moore and Garg, 1995) • Rate 6 task variables (Table 1): • intensity of exertion • duration of exertion • efforts per minute • wrist posture • speed of work • duration of task IE 552

  19. Strain Index Rating Criteria – Table 1 IE 552

  20. Strain Index Multipliers - Table 2 IE 552

  21. Strain Index - 2 • Convert SI ratings to multipliers (Table 2) • Multiply for final SI score • Scores > 5 considered hazardous • Good validation • identified 24/25 risky/non-risky jobs • sensitivity = 0.86 • specificity = 0.79 IE 552

  22. Strain Index - 2 • Example using Strain Index • Consider task with: • 20% MVC exertions • over 60% of a cycle • with 12 efforts per minute • with 18˚ ulnar deviations • at 95% of normal pace • for a full 8-hr shift IE 552

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  24. Quantitative Upper Limb WRMSD Risk Assessment • The example job is hazardous (13.5>5) • Overall, SI improvement over RULA • Considers more than basic postures • Considers upper extremities • Considers effort, intensity, pace • Greater quantitative detail • Next step → data driven risk models IE 552

  25. Data Driven Upper Limb WRMSD Risk Assessment – PSU CTD Risk Index • Developed at Penn State University • From 13 years of Center for CTD work • Wrist postures fed directly to model • From touch glove system (using force sensitive resistors and Data Glove) • Industrial WRSMD data tunes model • Final score - predicted incidence rate • Details - Seth, Weston, Freivalds (1999) IE 552

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  27. PSU CTD Risk Index - 2 • Validation on 24 jobs with 288 workers • Regression of predicted vs. actual IR • Significant (p < 0.001) correlation, r2 = 0.52 • By 5th trial, analysis time down to 12 min. • Test/retest reliability was up to r2=0.99 • 2nd validation on 91 meatpackers, r2 = 0.75 IE 552

  28. PSU CTD Risk Index r2 = 0.52 IE 552

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  30. PSU CTD Risk Index - 3 • Also a paper and pencil version • Quicker, simpler to use for industry • No direct angle of force measurements • Workers estimate force, analyst - angles • Validated with PC version • On 12 sewing jobs • Significant (p < 0.001) correlation of scores with r2 = 0.66 • Action level = 1.0 (similar to NIOSH Lifting) IE 552

  31. Task Force (%T) vsPerceived Force (%P) IE 552

  32. IE 552

  33. PSU CTD Risk Index – P/P 1 IE 552

  34. PSU CTD Risk Index – P/P 2 IE 552

  35. PSU CTD Risk Index – P/P 3 IE 552

  36. Videoclip Analyses • Study videoclips • Analyze using: • Strain Index • PSU CTD Risk Index – paper • PSU CTD Risk Index – PC • Compare, discuss IE 552

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  44. Summary IE 552

  45. OCRA and HAL • OCRA exposure index – complicated • HAL – TLV for hand activity level IE 552

  46. Comparison of Various Tools IE 552

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