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: …