Work postures and workplace design

Ergonomics

Work posture and design of a workplace

Loisa Sessman, Halmstad University

Work posture

• Work postures often causes static workload– Amplitude, time and frequency– External load– Gravity

• Work postures affect:– Mobility– Power– Energy consumption– Circulatory stress– Coordination


Work posture

• Injuries– Muscle injuries: about 1 week healing– Skeletal injuries: about 5-6 weeks healing– Joints: Injuries will usually be permanent


Work posture and load on the back

• Body position– Sitting– Standing– Rotations– Flexion of the trunk

• Manual Material Handling (MMH)– Heavy lifting

• Vibrations of the whole body– For example; motor vehicles



• The function of the spine– Protects the spinal cord and nerves– Controls movements and loads

• Discs– Shock absorbing– Distribute pressure– Allows movement



• Flexion of the trunk– Increased pressure on the spinal discs– Increased muscle activity (erector spinae)– Increased load on the lumbar spine– Increased risk of back pain



• Lateral flexion of the trunk– Increased muscle activity on the opposite side of the movement

• Rotation of the trunk– Increased disc pressure

• Extension of the trunk– Extreme position (should always be avoided)– Increased stress on the joints



• Standing– Advantages: range, mobility and strength– Disadvantages: Energy-intensive, increased stress on the lower extremities

• Sitting– Advantages: stability, increased precision, less stress on the lower extremities– Disadvantages: increased disc pressure, increased risk of low back pain (LPB),

increased stress and fatigue of the neck


Design of a workplace

• Recommendations for standing work– Vary sitting with standing if possible, take pauses that allows sitting– Upright position, avoid flexion of neck and trunk– Use shock absorbing carpet, slip-resistant surface and level for stable foot

positions. – Plenty of space to allow movements– Adjustable work height depending on work– Upper arms should be located close to the trunk



• Recommendations for sedentary work– The angle between the seat and backrest shall be 100-120 degrees– Upright sitting position, avoid flexion of the neck and trunk– Backrest that follows the curvature of the spine– Chair that allows variation when sitting– Adjustable desk that allows standing work– Optimal seat height is closed to the knee height– Appropriate work height– Rather too low work height than too high work height– Suitable seat (not too large and deep than necessary)



• Working height– High working level – raised shoulder and arm– Low working level – leaning forward, postural stress

• Recommendations– Precision and force 50-100 mm below elbow height– Delicate manipulative tasks 50-100 mm above elbow height – Heavy 100-250 mm below elbow height– Lifting and handling, between knuckle height and elbow height– Hand-operated controls, between elbow height and shoulder height


Workspace design

• Vision and the posture of the head and neck– Relaxed line of sight, 15°– Recommended sight, 0-30 °– Minimum sight distance 500 mm


MMH & back problems

• Manual Materials Handling (MMH)– Transportation (carry, pushing, pulling, lifting)– The use of hand-held machines and tools

• Heavy lifting increases the risk of LBP but also for musculoskeletal disorders in arm and shoulder.


MMH & back problems

• Factors to be aware of:– The weight of the load and its horizontal distance from the body– The vertical positions of the hands– To lift symmetrically– Grip– Repetitive lifting– Stress


MMH & back problems

• Recommendations for MMH and lifting– Use mechanical lifting devices if possible– Good grip– Plenty of space– Work with the burden close to the body– Avoid lifting from the floor or above shoulder height– Reduce the weight and the size of the burden if possible– Allow adequate recovery


MMH & back problems

• Recommendations for MMH and pushing/pulling– Using two hands are better than one hand– Push at waist level– Pull in knee height– Flat surface, minimize friction

• Recommendations for MMH and carrying longer distances– Avoid static work– Carrying on the back if possible– Use large muscle groups– Use mechanical devices for distance longer than 10 m


Vibrations & back problems

• Body vibrations– Affects workers on moving machinery or in a vehicle, such as forestry

machinery, buses and ships.– Increased risk of injuries in muscles, joints, back and neck– Not verified how much vibration that is harmful


Conclusion

• Recommendations for design of a workplace– Create opportunities to vary the posture– Place to most important objects in the closest range– Place the most often used objects within closest reach– Place the items in the order they are used– Place the panel and its controls in a similar way– Use structure to avoid confusion– Make sure that the largest users have enough with space– Make sure that the smallest users will reach– Adjustable equipment– Avoid static load


Work postures and workplace design

Health & Medicine

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