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IE 327 Introduction to Work Design Dr. Andris Freivalds Class #5

IE 327 Introduction to Work Design Dr. Andris Freivalds Class #5. MOTOR UNIT RECRUITMENT. Use small muscles for precision Use large muscles for power Power vs. pinch grip!!. CONTROL OF MOVEMENTS #1. Pivot on elbow Curved motions Use both hands Begin and end motion simultaneously

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IE 327 Introduction to Work Design Dr. Andris Freivalds Class #5

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  1. IE 327 Introduction toWork Design Dr. Andris Freivalds Class #5 IE 327

  2. MOTOR UNIT RECRUITMENT • Use small muscles for precision • Use large muscles for power • Power vs. pinch grip!! IE 327

  3. CONTROL OF MOVEMENTS #1 • Pivot on elbow • Curved motions • Use both hands • Begin and end motion simultaneously • Move simultaneously to and from body • Use natural rhythms • Whole body = 17/min • Whole arm = 35/min • Forearm = 60/min IE 327

  4. CONTROL OF MOVEMENTS #2 • Use lowest classification of movement • Decrease difficulty of task • ↓ distance • ↑ target width IE 327

  5. MINIMIZE EYE MOTION(Within normal line of sight) IE 327

  6. KEY POINTS: • Design work according to human capabilities and limitations • For manipulative tasks: • Dynamic motion rather than static holds • Strength requirements < 15% max • Avoid extreme ranges of motion • Small muscles for speed and precision • Large muscles for strength IE 327

  7. MANUAL WORK GUIDELINES • ATP = immediate energy source • Aerobic metabolism → 38 ATP • Anaerobic metabolism → 2 ATP + lactic acid! • E (kcal/min) = 4.9 x oxygen consumption • Limit = ⅓ Emax ≈ ⅓ x 16 = 5.33 kcal/min IE 327

  8. ENERGY COST OF WORK IE 327

  9. HEART RATE • HR easier, proportional to energy expenditure • RA = (∆HR/40 – 1) x 100 • ∆HR = working HR – resting HR = 110 – 70 = 40 • RA = (40/40 -1) x 100 = 0 - NO rest needed • RA = (60/40 -1) x 100 = 50% (1 rest for 2 work) IE 327

  10. HEART RATE RECOVERY • Brouha guidelines • Measure HR at: • 0.5→1 min (HR1) • 2.5→3 min (HR2) • Acceptable work if: • HR1 < 110/min • HR2 - HR1 ≥ 20/min • Avoid heart rate creep • Short, frequent work/rest cycles IE 327

  11. SUBJECTIVE RATING OF PERCEIVED EXERTION • Borg’s rating • Psychophysical • Cheap • Easy • HR/10 IE 327

  12. LOW BACK COMPRESSIVE FORCES • Manual materials handling (MMH) • MMH injuries = 31% occupational injuries • Low back = 71% of MMH • 25% of Workers Comp costs • Average case = $60,000 IE 327

  13. LOW BACK ANATOMY • 25 vertebrae (bones) • Protect spinal cord • S-shaped (good) • Shock absorption • Alternating with discs • Natural cushion • But problem area IE 327

  14. DISC DEGENERATION • Normal state • Narrowing, pinched nerve • Herniated disc, extrusion of gel onto nerve root IE 327

  15. BACK AS LEVER SYSTEM • Teeter-totter with disk as fulcrum • Static equilibrium analysis with ∑M = 0 IE 327

  16. USE CHART OR UM3D MODEL IE 327

  17. DISC FAILURE LEVELS IE 327

  18. GUIDELINES FOR LIFTING • Plan the lift • Find best lifting technique: • Stoop (not as good) • Squat (best) • Get secure grip • Pull load close in • Alternate tasks: lifting vs. sitting IE 327

  19. BACK BELTS • Weightlifter use belts • Abdominal pressure reflex, ↓Fcomp 15% • Workers lift lighter loads, ↓ gain • Twisting, misaligns discs, ↓ gain • Atrophy of abdominal muscles • ‘Superman’ effect • Coronary ‘incidents’, ↑ blood pressure • Not recommended without training IE 327

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