1. Psy 552 Ergonomics & Biomechanics Lecture 19

2. Your workstation chair  Seat height:  Seat depth:  Seat width:  Backrest:  Seat back angle:  Lumbar support:  Lumbar support width:  Distance between arm rests:

3. Non MMH Tasks  Pose considerable risk of MSDs.  Should avoid (from text): Highly repetitive arm movements Sustained static postures Minimize should flexion and abduction Reduce or eliminate forceful or heavy peak exertions Require frequent rest breaks.

4. Work station guidelines  The upper limb itself exerts forces on the shoulder joint. Guideline  “The hand should not have to reach frequently or be held above the shoulder height for sustained periods.” Potential outcome if violated:  Shoulder muscle fatigue, shoulder tendonitis, bicep tendonitis – in older workers

5. Work station guidelines (cont.)  Guidelines Short duty cycles <20 sec of work and 40 sec of rest with light loads <.4 kg with arms below shoulder level are acceptable as long as the work is not performed over long periods. High velocity movements should be closely evaluated to determine potential injuries.

6. Work station guidelines (cont.)  Guidelines Avoid holding of loads when the upper arm is flexed and the elbow is extended. Use padded supports for the elbow and forearm to reduce loads at the shoulders. Use tool balancers to support frequently used tools to reduce moments at the elbow and shoulder.

7. Work station guidelines (cont.)  Guidelines Provide adjustable fixtures to place the work in the optimal position for the worker’s task. When forearm rotation is required, flex the elbow.  Optimal workstation design with respect to upper limb movement is complex. Mock-ups can provide insight into the design process.

8. Work station guidelines (cont.)  Head and neck Guidelines  Work stations should be designed to avoid significant neck flexion > 30 degrees.  Adding arm support can reduce the muscular activity around the neck.  Tilting the work surface can reduce neck flexion.  Position computer monitors to minimize neck flexion.  Design work to produce an upright head position.  Provide for frequent breaks.

9. Work station guidelines (cont.)  Torso When the torso is flexed 30 degrees, 50% of the maximum moments are produced. Endurance for stooped postures decrease significantly when postures require > 30% of isometric strength.  Guidelines The majority of men and women can maintain a 20 degree stooped posture during the work day. Provide adjustable work surface heights to prevent stooping and maintain a vertical position.