The effects of task duration on psychophysically-determined maximum acceptable weights and forces

Area of Science:

• Occupational Health and Safety
• Ergonomics
• Human Factors Engineering

Background:

• Manual handling tasks are prevalent in industrial settings.
• Assessing safe workload limits is crucial for preventing injuries.
• Previous research has explored various methods for determining acceptable manual handling limits.

Purpose of the Study:

• To investigate maximum acceptable weights and forces for continuous manual handling tasks over four hours.
• To evaluate the suitability of the psychophysical methodology for determining these limits.
• To assess the impact of task frequency (≤4.3 min-1) on acceptable workloads.

Main Methods:

• A psychophysical approach was used with 22 industrial workers (12 female, 10 male).
• Subjects performed 18 manual handling tasks (lifting, lowering, pushing, pulling, carrying) at slow frequencies.
• Participants selected self-perceived sustainable workloads for an 8-hour day; physiological measures were also recorded.

Main Results:

• Weights selected after 40 minutes were not significantly different from those selected after four hours.
• Average oxygen consumption for faster tasks was 28% VO2 max, aligning with 8-hour physiological guidelines.
• Maximum acceptable weights for combined lifting, carrying, and lowering tasks were dictated by the lifting and lowering components.

Conclusions:

• The psychophysical methodology is appropriate for determining maximum acceptable weights in manual handling tasks at frequencies of 4.3 min-1 or slower.
• For combined manual handling tasks, the overall maximum acceptable weight is limited by the component with the lowest acceptable weight.
• Findings provide valuable data for establishing safer manual handling guidelines in industrial environments.