Psy 552 Ergonomics & Biomechanics

1. Psy 552 Ergonomics & Biomechanics Lecture 19

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

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.