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Psy 552 Ergonomics & Biomechanics

Psy 552 Ergonomics & Biomechanics. Lecture 18. Pushing & Pulling. 17-20% of overexertion injuries result from pushing or pulling activities. The exertion does not adequately convey the hazards of falling. Optimal handle height depends on criterion: Posture – Abdominal pressure:

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Psy 552 Ergonomics & Biomechanics

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  1. Psy 552 Ergonomics & Biomechanics Lecture 18

  2. Pushing & Pulling • 17-20% of overexertion injuries result from pushing or pulling activities. • The exertion does not adequately convey the hazards of falling. • Optimal handle height depends on criterion: • Posture – Abdominal pressure: • Biomechanical strength:

  3. Pushing & Pulling (cont) • Hand force changes as a function of: • Feet position • One or two-handed pulls/pushes • The vertical component of the push • In all cases, create a push/pull task that • … • … • …

  4. Floor Friction • Friction is important, but: • … • … • … • …

  5. Asymmetric handling • Very limited literature • Asymmetric handling increases: • … • …

  6. Sitting • Advantages: • … • … • … • … • The study focuses on the shape of the spine.

  7. Spine shape • Lordosis • Kyphosis Image fromhttp://www.spineuniverse.com/displayarticle.php/article1286.html

  8. Sitting factors • The chair • The task • Sitting habits • The ideal posture will vary according to these factors

  9. Sitting defined • Anterior… • Middle… • Posterior…

  10. Evaluating seated work • There is no one accepted metric • Common measures include • … • … • … • … • …

  11. Sitting & low back pain • Equivocal data • Some research shows a relationship between low-back pain and prolonged sitting. Others do not. • Drivers who sit longer than 3.5 hours/day have a 3x increase in risk of disc herniation. • Increased postural changes reduce fatigue and decrease absenteeism due to sickness. • CDC recommends 15 min break per hour for VDT operators.

  12. Sitting geometry • X-rays can be used to measure the lumbar angle. • In unsupported chair (no back) the angle decreased an average of 38 degrees causing a flattening of the spine. • With a lumbar support, the total back angle increased as a function of placement.

  13. Disc pressure • Disc pressure is 35% less for standing than it is for sitting without support. • When sitting, the lowest disc pressure occurs when the back is straight. • Disc pressure changes with increases in the trunk moment

  14. Disc pressure and back supports • Disc pressure decreased • as seat back angle increased from 90 to 110 degrees • When a lumbar support was used • When arm rests were used – expect for increased back angles.

  15. Muscular Activity • Using EMG, activity decreases when • … • ... • … • … • Activity with increase when the chair is too low or too high

  16. Balans Chair

  17. Shoulders and sitting • Work surface height affect abduction and flexion of the arms. • Abduction should be … • Flexion should be …

  18. Legs and sitting • Leg support can reduce load on the ischial tuberosities and thighs • Feet should be firmly place on floor or foot rest. • Pressure at the popliteal fold can cause swelling

  19. Legs and sitting (cont) • Seat too low • … • … • … • … • Seat too high • … • …

  20. Chair characteristics • Adjustable • Dimensions to consider • Seat height, … • Back rest height, …

  21. Chair characteristics (cont) • Arm rest length, …

  22. Work surface • Consideration should be provided to: • … • … • … • …

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