My Class

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IE 552 Mechanics of Musculoskeletal System Dr.
Andris Freivalds Class 35
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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 (lt10, lt20, gt20 kg)

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2151 bent back, both arms below shoulders,
kneeling, lt10 kg load
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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

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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
  an upper 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

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RULA Group A
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RULA Table A
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RULA

• These scores are adjusted upwards
• 1 if mainly static posture (gt1 min) or
  . repeated gt 4/min
• 1 if 2-10 kg intermittent loads
• 2 if 2-10 kg static or repeated loads
• 3 if gt10 kg static or repeated loads

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RULA Group B
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RULA Table B
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RULA Grand Score Table
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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

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RULA A 4 1 (Freq gt 4/min)
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1 due to static posture
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Grand score 4, Borderline risk
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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

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Strain Index Rating Criteria Table 1
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Strain Index Multipliers - Table 2
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Strain Index - 2

• Convert SI ratings to multipliers (Table 2)
• Multiply for final SI score
• Scores gt 5 considered hazardous
• Good validation
• identified 24/25 risky/non-risky jobs
• sensitivity 0.86
• specificity 0.79

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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

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Quantitative Upper Limb WRMSD Risk Assessment

• The example job is hazardous (13.5gt5)
• 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

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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)

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PSU CTD Risk Index - 2

• Validation on 24 jobs with 288 workers
• Regression of predicted vs. actual IR
• Significant (p lt 0.001) correlation, r2 0.52
• By 5th trial, analysis time down to 12 min.
• Test/retest reliability was up to r20.99
• 2nd validation on 91 meatpackers, r2 0.75

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PSU CTD Risk Index
r2 0.52
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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 lt 0.001) correlation of scores
  with r2 0.66
• Action level 1.0 (similar to NIOSH Lifting)

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Task Force (T) vsPerceived Force (P)
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PSU CTD Risk Index P/P 1
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PSU CTD Risk Index P/P 2
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PSU CTD Risk Index P/P 3
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Videoclip Analyses

• Study videoclips
• Analyze using
• Strain Index
• PSU CTD Risk Index paper
• PSU CTD Risk Index PC
• Compare, discuss

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Summary
Type of WRMSD Risk Analysis Range Action Level Stitch
Strain Index 0.1-1053 5 20
CTD Risk Index P/P 0 - 4 1.0 1.46
CTD Risk Index - PC 0 300? IR? 12.8
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OCRA and HAL

• OCRA exposure index complicated
• HAL TLV for hand activity level

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Comparison of Various Tools
Tool Equip Posture Force Freq Learn Time Anal Time T/RT r Valid r
OWAS P/P Sh3 3 time Short Short 0.74-0.99 -
RULA P/P S5, El3 W3 4 2 Med Short - -
HAL P/P - 10 10 V.short V.short - -
SI P/P 5 5 5 Med Short - 86se 79sp
PSUCTD P/P 2-4 Cont Cont Short Med - r20.66
PSUCTD PC SEW5-7 Cont Cont Long Long 0.72 r20.52