Steven Fischer - the 11th annual Human Factors IUW 2010

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  • Slide Purpose: To illustrate the continued influence of overexertion injuries in the workplace – more than 1 in 4 lost time claims in Ontario is related to overexertion.
  • Slide Purpose: To illustrate the how an overexertion injury can occur at a maximal or sub-maximal threshold.
  • Slide Purpose: To illustrate the how an overexertion injury can occur at a maximal or sub-maximal threshold.
  • Slide Purpose: To discuss the importance of having some predictive ability to understand what can be done in order to determine what should be done.
    Currently three methods have been published to enable designers / ergonomists to predict hand force capability or at least the influence of certain hand forces (3DSSPP)
  • Slide Purpose: To highlight the current interface for the 3DHFPM – focusing on the required inputs and the resultant output capacity
  • Slide Purpose: To highlight the key model output features and to elaborate on the potential impact this information could have for a decision maker.
  • Slide Purpose: To thank my PhD funding sources
  • With a 9 minute talk and 6 minutes for questions I may have an opportunity to respond to questions by presenting some of the evaluation data.
  • Slide Purpose: To highlight the predictive capacity of the model using a subset of three participants
  • Slide Purpose: To highlight the predictive capacity of the model using a subset of three participants
  • Slide Purpose: To demonstrate the difference in COP calculated top-down versus bottom-up using a force plate
  • Steven Fischer - the 11th annual Human Factors IUW 2010

    1. 1. The Three-Dimensional Hand Force Prediction Model (3DHFPM): A method for predicting maximal and sub-maximal exposure thresholds in the workplace Steven L Fischer, Clark R Dickerson and Richard P Wells University of Waterloo, Canada
    2. 2.  Overexertion occurs when the load, whether lifted, carried, pushed, pulled or otherwise handled, exceeds the limits of the human joint system doing the work1 . Overexertion – It is a problem 1 Wisha-training.lni.wa.gov/training/presentations/Overexertion.ppt 2 Workplace Safety and Insurance Board, Ontario, Canada - 2008 1 in 4 lost time claims are related to overexertion2 .
    3. 3. Overexertion – Why it is a problem Exceed a maximum capacity threshold limit3 Exceed a sub-maximal capacity threshold limit3 Threshold Limit Threshold Limit 3 McGill, 1997
    4. 4. Overexertion – How we avoid it Measure empirically or predict using 3DSSPP ™ 4 Measure empirically or use Liberty Mutual Tables™ 5 Threshold Limit Threshold Limit 4 Chaffin, 1997 5 Snook and Ciriello, 1991
    5. 5. A thought experiment  Balance, friction and joint strength can all act to limit exertion capacity6,7 .  Can we predict the limiter?  Can we predict the exertion capacity at that limit? ? ? ? ? 6 Grieve, 1983 7 Kerk et al., 1998
    6. 6. Overexertion – Better tools? Predict the limiting factor Predict the maximum capable exertion Predict the psycho- physically acceptable exertion
    7. 7. The 3DHFPM – A schematic
    8. 8. The 3DHFPM – How it works  Inverse static linked segment model  Joint moments  Normal force  Center of pressure location (COP) msegment g +z +y +x Fzprox Fyprox Fxprox Fzdist Fydist Fxdist Mdist (Mxdist, Mydist, Mzdist) Mprox rdist rprox
    9. 9. The 3DHFPM – How it works  Probabilistic estimation of limiting factors
    10. 10. The 3DHFPM – The user interface
    11. 11. The 3DHFPM – What it provides 4 = right side balance – 25 = torso twisting strength
    12. 12. The 3DHFPM – Is it adequate? SWFP = shoulder width foot placement FFP = free foot placement
    13. 13. The 3DHFPM – A schematic
    14. 14. The 3DHFPM – How it works  Realization of psychophysical forces %100*% MVF PAF PAF =
    15. 15. The 3DHFPM – Is it still adequate? Maximum CapacitySub-maximal Capacity Pull Down
    16. 16. The 3DHFPM – A schematic
    17. 17. Potential for impact Ergonomic assessment 3DHFPM Improved ability to match demands to capacity
    18. 18. Acknowledgments Natural Sciences and Engineering Research Council (NSERC) of Canada Ontario Graduate Scholarship CRE-MSD
    19. 19. Thank you for listening
    20. 20. Additional Slides for Open Discussion Period
    21. 21. Comparison of theoretical limiter to predicted limited
    22. 22. Comparisonbetweenmeasuredandpredictedmaximum handforcecapability
    23. 23. Comparison of theoretical limiter to revised predicted limiter
    24. 24. Comparisonbetweenmeasuredandtherevisedpredicted maximumhandforcecapability
    25. 25. Impact of COP calculation X = projection of the COM O = COP calculated using 3DHFPM O = COP calculated from force place Medial push Pull COPx typically overestimated by 4% relative to force plate COP COPy typically overestimated by 5% relative to force plate COP

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